Fifth in series, Big Bang V: Puberty deals with some early and yet somewhat enigmatic events like supernovae, black holes, pulsars, quasars and similar. I do not get into details how they happened as this is something still highly debated. This is by far longest post I made so far, but it is worth reading as it gives overview of some earliest structure we see today. We believe these may (or most of them) happened before galaxies appeared. We believe these events/structures appeared just before 13.2 billion light years ago (as that is the oldest galacy we see at the moment). If you missed, preivous articles on this subject were:
In latest of previous posts, first starlight, we saw creation of first stars and how first light got ignited. We also suspect those were really bug stars and as such their lifetime was somewhat short. As we have seen, big stars end up in explosions (supernova) and depending on mass left behind may produce even a black hole. As with anything first, there is certain level of uncertainty and currently our research is resolving this puzzle on daily basis. If you read last article you might have noticed that gas fillaments caused first stars to be born, but this might have happened on large scale so question here is: what came first - galaxies or black holes? Did we have already galaxy structures in place before first black holes got created? Did the black holes come first, helping to build galaxies by pulling material towards them, or did they arise in the centre of already formed galaxies? In it interesting question and for long time this question hasn't been addressed. According to latest data it turns out black holes came first.
Earlier studies had revealed an intriguing link between the masses of black holes and the central "bulges" of stars and gas in galaxies. Generally, the black hole's mass was seen to be about 1000th that of the mass of the surrounding galactic bulge. This indicated an interactive relationship between the black hole and the bulge. What was not clear was whether one grew before the other, or whether they grew together. New radio telescope observations reaching back almost to the birth of the first galaxies may now have answered that question.
Radio waves received from these galaxies and travelling at the speed of light were emitted only about a billion years after the Big Bang which started the universe. These young distant galaxies had much larger black holes in relation to their bulge mass than older and closer galaxies. The implication is that the black holes started growing first. The next challenge is to work out how the black hole and the bulge affect each other's growth. To understand how the universe got to be the way it is today, we must understand how the first stars and galaxies were formed when the universe was young. The bottom line is that the final mass of a black hole is not primordial; it is determined during the galaxy formation process. Supermassive black holes (SMBHs) with masses 106-109.5 solar masses reside in the centers of most galaxies, including Milky Way.
Astronomers plumb the depths of the universe, and probe its history, by measuring how much the light from an object has been stretched by the expansion of space. This is called the redshift value or "z". In general, the greater the observed "z" value for a galaxy, the more distant it is in time and space as observed from our own Milky Way. Before Hubble was launched, astronomers could only see galaxies out to a z of approximately 1, corresponding to halfway across the universe. The original Hubble Deep Field taken in 1995 leapfrogged to z=4, or roughly 90 percent of the way back to the beginning of time. The Advanced Camera for Surveys (ACS) produced the Hubble Ultra Deep Field of 2004, pushing back the limit to z~6. Hubble's first infrared camera, the Near Infrared Camera and Multi-Object Spectrometer, reached out to z=7. The WFC3 first took us back to z~8, and has now plausibly penetrated for the first time to z=10. The very first stars may have formed between z of 30 and 15. Observations of quasars with redshifts z > 6 imply that SMBHs must have already existed at such high redshifts. Stellar explosions can produce black holes with masses up to 10-15 Sun masses, but there is no mechanism by means of which such small objects could grow to become SMBHs, except if dark matter has a sufficient self-interaction to facilitate a rapid transfer of angular momentum and kinetic energy (see this paper for more detailed discussion). The early formation of SMBHs, which is necessary to account for high-redshift quasars, implies that SMBHs may have preceded star formation. As seen before, masses of SMBHs exhibit a remarkable correlation with the bulge masses of their host galaxies. The bulge mass is 1000 times larger than the black hole mass, and the proportionality holds over some four orders of magnitude.
Investigating this black hole-galaxy mass correlation at different distances, and thus at different times in cosmic history, allows astronomers to study galaxy and black hole evolution in action. For galaxies further away than 5 billion light-years (corresponding to a redshift of z > 0.5), studies of black hole center and galaxy relationship face considerable difficulties. The typical objects of study are so-called active galaxies, and there are well-established methods to estimate the mass of such a galaxy's central black hole. It is the galaxy's mass itself that is the challenge: At such distances, standard methods of estimating a galaxy's mass become exceedingly uncertain or fail altogether. Max Planck Institute for Astronomy succeeded in directly "weighing" both a galaxy and its central black hole at such a great distance using a sophisticated and novel method. The galaxy, known to astronomers by the number J090543.56+043347.3 (which encodes the galaxy's position in the sky) has a distance of 8.8 billion light-years from Earth (redshift z = 1.3). Using this information, the researchers reconstructed the galaxy's dynamical mass. The star shape indicates the position of the galaxy's active nucleus; the surrounding contour lines indicate brightness levels or light emitted by the nucleus. Dark blue pixels indicate gas moving towards us at a speed of 250 km/s, dark red pixels gas moving away from us at 350 km/s. The key idea is the following: A galaxy's stars and gas clouds orbit the galactic centre; for instance, our Sun orbits the centre of the Milky Way galaxy once every 250 million years. The stars' different orbital speeds are a direct function of the galaxy's mass distribution. Determine orbital speeds and you can determine the galaxy's total mass.
Now that we know black holes might have appeared before, we need to get to the point of creating one. Cosmologists believe that the lightest chemical elements - hydrogen and helium - were created shortly after the Big Bang, together with some lithium, while almost all other elements were formed later in stars. Supernova explosions spread the stellar material into the interstellar medium, making it richer in metals. New stars form from this enriched medium so they have higher amounts of metals in their composition than the older stars. Therefore, the proportion of metals in a star tells us how old it is. Sometimes, we get some mysteries along the way too. Last year a faint star in the constellation of Leo, called SDSS J102915+172927, has been found to have the lowest amount of elements heavier than helium (what astronomers call "metals") of all stars yet studied. It has a mass smaller than that of the Sun and is probably more than 13 billion years old. A widely accepted theory predicts that stars like this, with low mass and extremely low quantities of metals, shouldn't exist because the clouds of material from which they formed could never have condensed. But there it is. Also very surprising was the lack of lithium in SDSS J102915+172927. Such an old star should have a composition similar to that of the Universe shortly after the Big Bang, with a few more metals in it. But researchers found that the proportion of lithium in the star was at least fifty times less than expected in the material produced by the Big Bang. Below is the pcicture of the star.
And while there are few more candidates to match this story, we will mostly focus on main line of the story. And that means we start with star ending its life in supernova creating seed for new generations. Supernovas - stars in the process of exploding - open a window onto the history of the elements of Earth's periodic table as well as the history of the universe. There are two possible routes to a supernova: either a massive star may run out of fuel, ceasing to generate fusion energy in its core, and collapsing inward under the force of its own gravity to form a neutron star or a black hole; or a white dwarf star may accumulate (accrete) material from a companion star until it reaches a critical mass and undergoes a thermonuclear explosion. In either case, the resulting supernova explosion expels much or all of the stellar material with velocities as much as 10% the speed of light.
All of those heavier than oxygen were formed in nuclear reactions that occurred during these explosions. Supernovae are classified into one of two primary types. White dwarfs which gain matter via accretion have their cores collapse once they approach the Chandrasekhar limit of 1.38 solar masses, thus yielding a Type Ia supernova (used as standard candle). Accretion of matter can be accomplished by a variety of means including via a close binary star companion or a merger with another white dwarf. In contrast, type Ib and Ic involve large stars which have exhausted their available fuel and collapse due to gravity. Type II supernovae involve much more massive stars (at least nine solar masses) where the nuclear fusion follows a steady path from lighter to progressively heavier elements (such as hydrogen to helium which is then converted to carbon etc) and until nuclear fusion is no longer possible at the core due to the iron and nickel that has been accumulated, thus leading to a huge core collapse and an ensuing stellar explosion. Spectroscopy has also played a key role in identifying the type of supernova one observes and, in fact, now forms the basis for their classification. More specifically, type Ia supernovae are characterized without any hydrogen emission lines in their spectra and in contrast to type II which exhibit strong hydrogen emission lines. Furthermore, type I are further subdivided on the basis of the presence of a silicon line (615nm, type Ia), a helium line (type Ib) or neither one (type Ic) in their spectra.
An exploding star known as a Type Ia supernova plays a key role in our understanding of the universe. Studies of Type Ia supernovae led to the discovery of dark energy. Yet the cause of this variety of exploding star remains elusive. All evidence points to a white dwarf that feeds off its companions star, gaining mass, growing unstable, and ultimately detonating. But does that white dwarf draw material from a Sun-like star, an evolved red giant star, or from a second white dwarf? Or is something more exotic going on? Clues can be collected by searching for "cosmic crumbs" left over from the white dwarf's last meal. There are two different models for how Type Ia supernovae are created from this type of binary system. In the so-called double-degenerate (or DD) model, the orbit between two white dwarf stars shrinks until the lighter star's path is disrupted and it moves close enough for some of its matter to be absorbed into the primary white dwarf and initiate an explosion. In the so-called single-degenerate (or SD) model, the white dwarf slowly accretes mass from a different, non-white dwarf type of star, until it reaches an ignition point. There are three potential methods for the transfer of mass and--depending on which one is used--the second star is likely to be a red giant, a helium star, or a so-called subgiant or main-sequence star.
In two comprehensive studies of SN 2011fe - the closest Type Ia supernova in the past two decades - there is new evidence that indicates that the white dwarf progenitor was a particularly picky eater, leading scientists to conclude that the companion star was not likely to be a Sun-like star or an evolved giant. This supernova occurred in the Pinwheel galaxy, which is located in the "Big Dipper" within the Ursa Major constellation. Early detection gave astronomers the extraordinary opportunity to observe the evolution of the brightness and spectra of the energy emitted from the explosion over time. Based on these data, researchers were able to approximate how big the star was and when it exploded, in addition to details about the companion star in the system. Researchers examined SN 2011fe with a suite of instruments in wavelengths ranging from X-rays to radio. They saw no sign of stellar material recently devoured by the white dwarf. Instead, the explosion occurred in a remarkably clean environment. Additional studies using NASA's Swift satellite, which examined a large number of more distant Type Ia supernovae, appear to rule out giant stars as companions for the white-dwarf progenitors. Taken together, these studies suggest that Type Ia supernovae likely originate from a more exotic scenario, possibly the explosive merger of two white dwarfs. Observations of the early stages of the supernova presented by Lawrence Berkeley Laboratory showed direct evidence that the primary star was a type of white dwarf called a carbon-oxygen white dwarf. Below images from Swift's Ultraviolet/Optical Telescope (UVOT) show the nearby spiral galaxy M101 before and after the appearance of SN 2011fe (circled, right), which was discovered on Aug. 24, 2011. At a distance of 21 million light-years, it was the nearest Type Ia supernova since 1986. Left: View constructed from images taken in March and April 2007. Right: The supernova was so bright that most UVOT exposures were short, so this view includes imagery from August through November 2011 to better show the galaxy.
These explosions, which can outshine their galaxy for weeks, release large and consistent amounts of energy at visible wavelengths. These qualities make them among the most valuable tools for measuring distance in the universe. Because astronomers know the intrinsic brightness of Type Ia supernovae, how bright they appear directly reveals how far away they are. Thanks to unprecedented X-ray and ultraviolet data from Swift, we have a clearer picture of what's required to blow up these stars. The studies suggest the companion to the white dwarf is either a smaller, younger star similar to our sun or another white dwarf. For more details, click here. Very sensitive and early radio and X-ray observations, presented in a separate paper in The Astrophysical Journal, show no evidence of interaction with surrounding material. Combining this data with an analysis of historical images, we can rule out luminous red giants and the vast majority of helium stars for the second star in the binary system before the explosion. These clues mean that the secondary star was either another white dwarf, as in the DD model, or a subgiant or main-sequence star, as created by one of the three SD model methods. Analysis of the matter ejected by the supernova's explosion suggests that the second star is less likely to be another white dwarf. Thus, the solution to the mystery of SN2011fe's origin was thought to be probably a primary white dwarf accreting matter from a neighboring subgiant or main-sequence star. Many possible explanations have been suggested, and all but one of these requires that a companion star near to the exploding white dwarf be left behind after the explosion. So, a possible way to distinguish between the various progenitor models is to look deep in the center of an old supernova remnant to find (or not find) the ex-companion star.
The star system that produces the Type Ia thermonuclear supernova was previously determined to be a closely orbiting pair of white dwarf stars that spiraled inward for an explosive collision. Finally, LSU Professor of Physics & Astronomy Bradley Schaefer and graduate student Ashley Pagnotta used images from the Hubble Space Telescope of a supernova remnant named SNR 0509-67.5 to illustrate the lack of any possible surviving companion star to the exploding white dwarf, allowing the rejection of all possible classes of progenitors except for the close pair of white dwarfs. Any such result naturally requires extensive data processing and analysis as well as detailed theory calculations before it can be considered finalized. When finished, the central region of SNR 0509-67.5 was found to be starless to a very deep limit (visual magnitude 26.9). The faintest possible ex-companion star for all models (except the double degenerate) is a factor of 50 times brighter than the observed limit, and this makes for the rejection of all explanations except for the pair of white dwarf stars.
University of Pittsburgh took it a step further this year. There were obvious reasons to suspect that Type Ia supernovae come from the merging of a double white dwarf, but biggest question was whether there were enough double white dwarfs out there to produce the number of supernovae that we see. Because white dwarfs are extremely small and faint, there is no hope of seeing them in distant galaxies. Therefore, researchers turned to the only place where they could be seen: the part of the Milky Way Galaxy within about a thousand light years of the sun. To find the star's companion, the team needed two spectra to measure the velocity between the two. However, SDSS only took one spectrum of most objects. The team decided to make use of a little-known feature in the SDSS spectra to separate each one into three or more subspectra. Although the reprocessing of the data was challenging, the team was able to compile a list of more than 4000 white dwarfs within a year, each of which had two or more high-quality subspectra. They found 15 double white dwarfs in the local neighborhood and then used computer simulations to calculate the rate at which double white dwarfs would merge. Then, they compared the number of merging white dwarfs here to the number of Type Ia supernovae seen in distant galaxies that resemble the Milky Way. The result was that, on average, one double white dwarf merger event occurs in the Milky Way about once a century.
Image above shows mosaic which shows 99 of the nearly 4000 white dwarfs examined. Of the four thousand, they found fifteen double white dwarfs. That number is remarkably close to the rate of Type Ia supernovae we observe in galaxies like our own. This suggests that the merger of a double white dwarf system is a plausible explanation for Type Ia supernovae.
While I spent some time on Ia, that doesn't mean others are to neglect. Recetly one IIb type made headlines too - Cassiopeia A. Using very long observations of Cassiopeia A (or Cas A), a team of scientists has mapped the distribution elements in the supernova remnant in unprecedented detail. Now, check following picture first.
An artist's illustration on the left shows a simplified picture of the inner layers of the star that formed Cas A just before it exploded, with the predominant concentrations of different elements represented by different colors: iron in the core (blue), overlaid by sulfur and silicon (green), then magnesium, neon and oxygen (red). The image from NASA's Chandra X-ray Observatory on the right uses the same color scheme to show the distribution of iron, sulfur and magnesium in the supernova remnant. The data show that the distributions of sulfur and silicon are similar, as are the distributions of magnesium and neon. Oxygen, which according to theoretical models is the most abundant element in the remnant, is difficult to detect because the X-ray emission characteristic of oxygen ions is strongly absorbed by gas in along the line of sight to Cas A, and because almost all the oxygen ions have had all their electrons stripped away. A comparison of the illustration and the Chandra element map shows clearly that most of the iron, which according to theoretical models of the pre-supernova was originally on the inside of the star, is now located near the outer edges of the remnant. Surprisingly, there is no evidence from X-ray (Chandra) or infrared (Spitzer Space Telescope) observations for iron near the center of the remnant, where it was formed. Also, much of the silicon and sulfur, as well as the magnesium, is now found toward the outer edges of the still-expanding debris. The distribution of the elements indicates that a strong instability in the explosion process somehow turned the star inside out. That's pretty much cool, isn't it?
The most ancient explosions, far enough away that their light is reaching us only now, can be difficult to spot. Last year researchers has uncovered a record-breaking number of supernovas in the Subaru Deep Field, a patch of sky the size of a full moon. Supernovas are nature's "element factories". During these explosions, elements are both formed and flung into interstellar space, where they serve as raw materials for new generations of stars and planets. Closer to home, these elements are the atoms that form the ground we stand on, our bodies, and the iron in the blood that flows through our veins. By tracking the frequency and types of supernova explosions back through cosmic time, astronomers can reconstruct the universe's history of element creation.
In 2011, only fourteen days after the explosion of a star in the M51 galaxy, coordinated telescopes around Europe have taken a photograph of the cosmic explosion in great detail - equivalent to seeing a golf ball on the surface of the moon. This is the earliest high resolution image of a supernova explosion. From this photograph, we can define the expansion velocity of the shock wave created in the explosion. With this precision, we can look for the previous star on the earlier galaxy photographs, as well as weigh up better our future observations.
The most recent observation of supernova comes from M95 galaxy and it is called SN 2012aw. On March 16th, 2012, news broke of possible supernova. Soon, this has been confirmed. M95 is about 35-40 million light years away, and is part of a small group of a couple of dozen galaxies called the Leo I group. This supernova is type II supernova. Exploding star is sitting right on a spiral arm as seen on picture below. I also attached video giving some more details.
Neutron stars are extremely dense ball of matter only a few kilometers across, the collapsed remnants of the cores of stars that went supernova. By dense, we mean dense: imagine taking a mountain and crushing down in size to where it could fit in your hand. Or think of it this way: a cubic centimeter (roughly the size of a sugar cube or dice) of neutron star material would have about the same mass as all the cars in the US combined. Dense means dense! Simply check picture below; the size of a neutron star compared to Manhattan while neutron star packs more mass than the sun into a sphere just 10 to 15 miles wide.
By being so dense gravity of a neutron star is nearly beyond comprehension. If you let something drop from a height onto the star’s surface, that material will be moving at a large fraction of the speed of light upon impact. The energy release is monumental; a marshmallow traveling at that speed would explode like a nuclear weapon. There could be exotic kinds of particles or states of matter, such as quark matter, in the centers of neutron stars, but it’s impossible to create them in the lab. The only way to find out is to understand neutron stars. The warping of space-time by the neutron star's powerful gravity, an effect of Einstein's general theory of relativity, shifts the neutron star's iron line to longer wavelengths. We see these asymmetric lines from many black holes, but this is the confirmation that neutron stars can produce them as well. It shows that the way neutron stars accrete matter is not very different from that of black holes, and it gives us a new tool to probe Einstein’s theory too. Another study saw gas whipping around just outside the neutron star's surface, and since the inner part of the disk obviously can't orbit any closer than the neutron star's surface, these measurements give us a maximum size of the neutron star's diameter. The neutron stars can be no larger than 29 to 33 km across, results that agree with other types of measurements.
In general, compact stars of less than 1.38 solar masses (Chandrasekhar limit) are white dwarfs, and above 2 to 3 solar masses (Tolman-Oppenheimer-Volkoff limit), a quark star might be created; however, this is uncertain. Gravitational collapse will usually occur on any compact star between 10 and 25 solar masses and produce a black hole. Current understanding of the structure of neutron stars is defined by existing mathematical models. The inner structure might be derived by analyzing observed frequency spectra of stellar oscillations. On the basis of current models, the matter at the surface of a neutron star is composed of ordinary atomic nuclei crushed into a solid lattice with a sea of electrons flowing through the gaps between them. It is possible that the nuclei at the surface are iron, due to iron's high binding energy per nucleon. It is also possible that heavy element cores, such as iron, simply sink beneath the surface, leaving only light nuclei like helium and hydrogen cores. If the surface temperature exceeds 106 kelvin (as in the case of a young pulsar), the surface should be fluid instead of the solid phase observed in cooler neutron stars (temperature <106 kelvins). The "atmosphere" of the star is hypothesized to be at most several micrometers thick, and its dynamic is fully controlled by the star's magnetic field. Below the atmosphere one encounters a solid "crust". This crust is extremely hard and very smooth (with maximum surface irregularities of ~5 mm), because of the extreme gravitational field. Proceeding inward, one encounters nuclei with ever increasing numbers of neutrons; such nuclei would decay quickly on Earth, but are kept stable by tremendous pressures. Proceeding deeper, one comes to a point called neutron drip where neutrons leak out of nuclei and become free neutrons. In this region, there are nuclei, free electrons, and free neutrons. The nuclei become smaller and smaller until the core is reached, by definition the point where they disappear altogether. The composition of the superdense matter in the core remains uncertain. One model describes the core as superfluid neutron-degenerate matter (mostly neutrons, with some protons and electrons). More exotic forms of matter are possible, including degenerate strange matter (containing strange quarks in addition to up and down quarks), matter containing high-energy pions and kaons in addition to neutrons, or ultra-dense quark-degenerate matter.
A neutron star is the closest thing to a black hole that astronomers can observe directly, crushing half a million times more mass than Earth into a sphere no larger than a city. In October 2010, a neutron star near the center of our galaxy erupted with hundreds of X-ray bursts that were powered by a barrage of thermonuclear explosions on the star's surface. NASA's Rossi X-ray Timing Explorer (RXTE) captured the month-long fusillade in extreme detail. Using this data, an international team of astronomers has been able to bridge a long-standing gap between theory and observation. At low rates of accretion, this system displays the familiar X-ray pattern of fuel build-up and explosion: a strong spike of emission followed by a long lull as the fuel layer reforms. At higher accretion rates, where a greater volume of gas is falling onto the star, the character of the pattern changes: the emission spikes are smaller and occur more often. But at the highest rates, the strong spikes disappeared and the pattern transformed into gentle waves of emission. This as a sign of marginally stable nuclear fusion, where the reactions take place evenly throughout the fuel layer, just as theory predicted. Obviously there is an impact of rotatition too. Above makes sense with model where rotation is not so fast. Faster rotation would introduce friction between the neutron star's surface and its fuel layers, and this frictional heat may be sufficient to alter the rate of nuclear burning in all other bursting neutron stars previously studied.
Pulsars were discovered in 1967 and that discovery earned the Nobel Prize in 1974. A pulsar (portmanteau of pulsating star) is a highly magnetized, rotating neutron star that emits a beam of electromagnetic radiation. This radiation can only be observed when the beam of emission is pointing towards the Earth, much the way a lighthouse can only be seen when the light is pointed in the direction of an observer, and is responsible for the pulsed appearance of emission. Neutron stars are very dense, and have short, regular rotational periods. They appear to pulse because the magnetic axis is not aligned with the axis of rotation, so the pole comes in and out of view as the neutron star rotates. This produces a very precise interval, between pulses that range from roughly milliseconds to seconds for an individual pulsar. The precise periods of pulsars makes them useful tools. Observations of a pulsar in a binary neutron star system were used to indirectly confirm the existence of gravitational radiation.
Pulsars are among the most exotic celestial bodies known. They have diameters of about 20 kilometres, but at the same time roughly the mass of our sun. A sugar-cube sized piece of its ultra-compact matter on Earth would weigh hundreds of millions of tons. A sub-class of them, known as millisecond pulsars, spin up to several hundred times per second around their own axes. Millisecond pulsars are strongly magnetized, old neutron stars in binary systems which have been spun up to high rotational frequencies by accumulating mass and angular momentum from a companion star. Today we know of about 200 such pulsars with spin periods between 1.4 to 10 milliseconds. These are located in both the Galactic Disk and in Globular Clusters. Previous studies reached the paradoxical conclusion that some millisecond pulsars are older than the universe itself. Through numerical calculations on the base of stellar evolution and accretion torques, astrophysicist Thomas Tauris demonstrated that millisecond pulsars lose about half of their rotational energy in the so-called Roche-lobe decoupling phase. This phase describes the termination of the mass transfer in the binary system. Hence, radio-emitting millisecond pulsars should spin slightly slower than their progenitors, X-ray emitting millisecond pulsars which are still accreting material from their donor star. This is exactly what the observational data seem to suggest. Furthermore, these new findings help explain why some millisecond pulsars appear to have characteristic ages exceeding the age of the Universe and perhaps why no sub-millisecond radio pulsars exist. The key feature of the new results is that it has now been demonstrated how the spinning pulsar is able to break out of its so-called equilibrium spin. At this epoch the mass-transfer rate decreases which causes the magnetospheric radius of the pulsar to expand and thereby expel the collapsing matter like a propeller. This causes the pulsar to lose additional rotational energy and thus slow down its spin rate.
Discover blog pointed out recently to nice article by BBC. On Earth, GPS gives us a highly accurate way of determining position. This works because GPS satellites provide a set of clocks, the relative timings of the signals from which can be translated into positions. Out in deep space, of course, our clocks are unfortunately useless for this purpose, and the best we currently can do is by comparing the timing of signals as they are measured back on Earth by different detectors with limited accuracy. The further away a spacecraft is, the worse this method is. Werner Becker (Max-Planck Institute for Extraterrestrial Physics) realized universe comes equipped with its own set of exquisite clocks – pulsars – the timing of which can, in principle, be used to guide spacecraft in a similar way to how GPS is used here on Earth. A significant obstacle to making this work today is that detecting signals from the pulsars requires X-ray detectors that are compact enough to be easily carried on spacecraft. However, it turns out the relevant technology is also needed by the next generation of X-ray telescopes, and should be ready in twenty years or so. Researching pays off.
The Crab pulsar is a rapidly spinning neutron star, the collapsed core of a massive star that exploded in a spectacular supernova in the year 1054, leaving behind the brilliant Crab Nebula, with the pulsar at its heart. It is one of the most intensively studied objects in the sky. Rotating about 30 times a second, the pulsar has an intense, co-rotating magnetic field from which it emits beams of radiation. The beams sweep around like a lighthouse beacon because they are not aligned with the star's rotation axis. So although the beams are steady, they are detected on Earth as rapid pulses of radiation. Scientists have long agreed on a general picture of what causes pulsar emission. Electromagnetic forces created by the star's rapidly rotating magnetic field accelerate charged particles to near the speed of light, producing radiation over a broad spectrum. But the details remain a mystery. After many years of observations and results from the Crab, we thought we had an understanding of how it worked, and the models predicted an exponential decay of the emission spectrum above around 10 GeV. So it came as a real surprise when we found pulsed gamma-ray emission at energies above 100 GeV.
Then month ago this value got 4x higher. This was now confirmed by the two MAGIC (Major Atmospheric Gamma-Ray Imaging Cherenkov) Telescopes on the Canary island of La Palma. They observed the pulsar in the area of very high energy gamma radiation from 25 up to 400 gigaelectronvolts (GeV), a region that was previously difficult to access with high energy instruments - 50 to 100 times higher than theorists thought possible. These latest observations are difficult for astrophysicists to explain. There must be processes behind this that are as yet unknown. A few years ago, the MAGIC telescopes detected gamma rays of energy ≥ 25 GeV from the Crab Pulsar. This was very unexpected since the available EGRET satellite data were showing that the spectrum ceases at much lower energies. However, at the very high energies MAGIC demonstrated to have few orders of magnitudes higher sensitivity compared to the satellite missions. At the time, scientists concluded that the radiation must have been produced at least 60 kilometres above the surface of the neutron star. This is because the high-energy gamma rays are so effectively shielded by the star's magnetic field that a source very close to the star could not be detected. As a consequence that measurement ruled out one of the main theories on high energy gamma-ray emission from the Crab pulsar. The recent measurements by MAGIC, together with those of the orbiting Fermi satellite at much lower energies, provide an uninterrupted spectrum of the pulses from 0.1 GeV to 400 GeV. These clear observational results create major difficulties for most of the existing pulsar theories that predict significantly lower limits for highest energy emission. A new theoretical model developed by MAGIC team associate explains the phenomenon with a cascade-like process which produces secondary particles that are able to overcome the barrier of the pulsar's magnetosphere. Another possible explanation links the puzzling emission to the similarly enigmatic physics of the pulsar wind - a current of electrons, positrons and electromagnetic radiation which ultimately develops into the Crab Nebula. However, even though the above models are able to provide explanations for the extremely high energy and the shortness of the pulses, further refinements are necessary for achieving a good agreement with observations. Astrophysicists hope that future observations will improve the statistical precision of the data and help solving the mystery. This could shed new light on pulsars and on the Crab Nebula itself, as one of the most studied objects in our Milky Way.
Johan Hansson and Anna Ponga at Lulea University of Technology in Sweden pointed out there is another way for magnetic fields to form, other than the movement of charged particles. This other process is by the alignment of the magnetic fields of the body's components, which is how ferromagnets form. Their suggestion is that when a neutron star forms, the neutron magnetic moments become aligned because this is the lowest energy configuration of the nuclear forces between them. When this alignment takes place, a powerful magnetic field effectively becomes frozen in place. This makes neutron stars giant permanent magnets (Hansson and Ponga call them neutromagnets). A neutromagnet would be hugely stable, just like a permanent ferromagnet. The field would be likely to align with the star's original field, which although much weaker, acts as a seed when the field forms. Significantly, this needn't be in the same direction as the axis of spin. What's more, since neutron stars all have about the same mass (sort of), Hansson and Ponga can calculate the maximum strength of the fields they ought to generate. This number turns out to be about 1012 Tesla's, exactly the value that's observed in the highest strength fields around neutron stars. That immediately solves several of the outstanding puzzles about pulsars in a remarkably simple way. The theory is testable too - it predicts that neutron stars cannot have magnetic fields greater than 1012 Tesla, so the discovery of a neutron star with a stronger field would immediately scupper it. This idea also raises some questions of its own; the Pauli exclusion principle would, at first sight, seem to exclude the possibility of neutrons being aligned in this way. But Hansson and Ponga point to laboratory experiments which suggest that nuclear spins can become ordered, like ferromagnets. One should remember that the nuclear physics at these extreme circumstances and densities is not known a priori, so several unexpected properties (such as "neutromagnetism") might apply. Keep in mind this idea is speculative, but is surely contains elegance and explanatory power that makes it worth pursuing in significantly more detail.
One of the most studied objects in the sky, the Crab Nebula is powered by a pulsar. This composite image of the Crab Nebula uses data from the Chandra X-ray Observatory (x-ray image in blue), Hubble Space Telescope (optical image in red and yellow), and Spitzer Space Telescope (infrared image in purple).
At this point you should ask yourself, what is nebula? A nebula is an interstellar cloud of dust, hydrogen, helium and other ionized gases. Originally, nebula was a general name for any extended astronomical object, including galaxies beyond the Milky Way. Nebulae are often star-forming regions, such as in the Eagle Nebula. This nebula is depicted in one of NASA's most famous images, the "Pillars of Creation".
In these regions the formations of gas, dust, and other materials "clump" together to form larger masses, which attract further matter, and eventually will become massive enough to form stars. The remaining materials are then believed to form planets, and other planetary system objects.
Deep in the heart of the southern Milky Way lies a stellar nursery called the Carina Nebula. It is about 7500 light-years from Earth in the constellation of Carina. This cloud of glowing gas and dust is one of the closest incubators of very massive stars to Earth and includes several of the brightest and heaviest stars known. One of them, the mysterious and highly unstable star Eta Carinae, was the second brightest star in the entire night sky for several years in the 1840s and is likely to explode as a supernova in the near future, by astronomical standards. The Carina Nebula is a perfect laboratory for astronomers studying the violent births and early lives of stars. Using VLT hundreds of individual images have been combined to create this picture, which is the most detailed infrared mosaic of the nebula ever taken and one of the most dramatic images ever created by the VLT. It shows not just the brilliant massive stars, but hundreds of thousands of much fainter stars that were previously invisible.
Nebulae come in all sorts of shapes. Below is a SH2-284, a star forming nebula. The image is false color, but each hue represents a different part of the infrared spectrum. Blue and teal is mostly coming from stars, while red and yellow is dust. Green comes from a very specific kind of material called a polycyclic aromatic hydrocarbons - long-chain carbon molecules which are essentially soot. PAHs are made in various ways, but are abundant where stars are being born, and that’s what we’re seeing here. There’s a cluster of young stars in the center of this cloud, and they’re so hot they’re eating out the inside of the cloud, creating that cavity you can see. Like so many of these structures, the clock is ticking: many of those stars will explode, and when they do they’ll tear the cloud apart - this rainbow cloud only has a few million years left before it’s extinct.
Researchers using NASA's Stratospheric Observatory for Infrared Astronomy (SOFIA) have captured an infrared image of the last exhalations of a dying sun-like star. It is named M2-9 (planetary nebula Minkowski 2-9). The SOFIA images provide our most complete picture of the outflowing material on its way to being recycled into the next generation of stars and planets. Objects such as M2-9 (see picture below) are called planetary nebulae due to a mistake made by early astronomers, who discovered these objects while sweeping the sky with small telescopes. Many of these nebulae have the color, shape and size of Uranus and Neptune, so they were dubbed planetary nebulae. The name persists despite the fact that these nebulae are now known to be distant clouds of material, far beyond our solar system, which are shed by stars about the size of our sun undergoing upheavals during their final life stages.
Nebulae can be big. Really big really big. Take for example these two: Orion nebula and Drangonfish one. Orion Nebula is one of the biggest, most active star forming regions in the Milky Way galaxy. It has enough gas to form thousands of stars like the Sun, and it’s one of the brightest and closest such gas clouds in the sky. The stars in the nebula are about 1 million years old. The nebula’s diameter is 14 light-years across. If you look on the Intenet, you will find some amazing picture of it. Enjoy the view.
And now dragonfish. The beast! It’s something like 450 light years across! Compare that to the Orion Nebula’s 14 light year width and you get the picture. It’s also incredibly massive: it may have a total mass exceeding 100000 times the Sun’s mass, and may contain millions of stars. Even from other galaxies, it must be one of the most obvious features in the Milky Way. Yet, ironically, it’s very difficult to see at all from Earth. It’s located over 30000 light years away, on the other side of the galaxy. There’s a vast amount of interstellar material (like dust) between us and it, absorbing its light, so in optical light it’s essentially invisible, but infrared light can pierce that fog, and the image above was taken using NASA’s Spitzer Space Telescope, designed to look in the infrared.
Astronomers used a different infrared telescope to look at the individual stars in the nebula, and found that it has an incredible 400+ O-type stars, the most massive stars that can exist. These stars are young, hot, massive, and blast out ultraviolet light. That’s what’s making this huge gas cloud glow, and in fact the cloud is expanding under the influence of the terrible flood of radiation. Those stars will eventually explode in the next million years or so, one after another, blasting out radiation and material that will dwarf even what they’re putting out right now. That will eventually tear through the nebula, ramming it, causing parts of it to collapse and form new stars, and other parts to dissipate entirely.
On Christmas 2010, the light from a gamma-ray burst reached Earth and was detected by NASA’s orbiting Swift satellite - GRB 101225A. It lasted a staggering half hour, when most GRBs are over within seconds, or a few minutes at most. Follow up observations came pouring in from telescopes on and above the Earth, and the next weird thing was found: the fading glow from the burst seemed to be coming from good old-fashioned heat: some type of material heated to unbelievable temperatures. Usually, the afterglow is dominated by other forces like rapidly moving super-intense magnetic fields that accelerate gigatons of subatomic particles to huge speeds, but in this case it looked like a regular-old explosion. So what could have caused this burst? Normally, GRBs are the birth cries of black holes. When a giant star explodes, or two tiny but ultra-dense neutrons stars merge, they can form a black hole and send vast amounts of gamma rays (super high-energy light) sleeting out into the Universe. In this case, though, something different happened, and two ideas of what was behind it are emerging, but both involve neutron stars. According to first one, a comet or other large chunk of material was orbiting a neutron star. It got too close, broke apart, and fell on the surface. As each piece hit it released far more energy than all the nukes on Earth combined - by a factor of millions - sending out huge amounts of light into space. That explains both the flash of the GRB detected last year and the fact that the afterglow was in the form of heat; the vast energy of the repeated slamming impacts of the comet chunks would've heated the material (and the neutron star) to millions of degrees. Another approach is that neutron star was orbiting another star. Eventually neutron star stripped off material from swallowing star and eventually it would get its core too. Mind-numbingly powerful gravity would’ve squeezed that stuff as it fell on the neutron star, and the gravity became so intense not even the neutron star-stuff could resist: the neutron star itself collapsed into a black hole, releasing a flash of energy focused into two tightly-focused beams that lasted for a few seconds, equal to the Sun’s total lifetime of energy release. This wave of energy slammed into the material previously ejected from the normal star, heating it and causing the long afterglow seen last year. Following video, made by NASA, reflects both scenarios:
This brings us to black holes - ultimate mystery of the Universe. I did touch subject of black holes already when talking about Holographic Universe. Basics of the black holes can be found there, but I will go through necessary bits here too. A black hole is a concentration of mass great enough that the force of gravity prevents anything from escaping it except through quantum tunnelling behaviour (known as Hawking Radiation). The gravitational field is so strong that the escape velocity near it exceeds the speed of light. This implies that nothing, not even light, can escape its gravity. This makes this object invisible to the rest of the universe, hence the word "black". Around a black hole there is a mathematically defined surface called an event horizon that marks the point of no return. Quantum mechanics predicts that black holes emit radiation like a black body with a finite temperature. This temperature is inversely proportional to the mass of the black hole, making it difficult to observe this radiation for black holes of stellar mass or greater.
Near a black hole, just outside the event horizon, there's some incredible stuff going on. First off, the matter. Every black hole has a flat disc of matter orbiting it at an incredibly high speed. Due to forces like friction and gravitational tides, the matter gets ripped apart into individual molecules, atoms, and subatomic particles, and eventually spirals in towards the center. So we wind up with - somewhat close to the event horizon - a bunch of small, fast-moving, and charged particles.
In the early days of the universe, a mere 700 to 800 million years after the Big Bang, most things were small. The first stars and galaxies were just beginning to form and grow in isolated parts of the universe. According to astrophysical theory, black holes found during this era also should be small in proportion with the galaxies in which they reside. Supermassive black holes are the largest black holes, with masses billions of times larger than that of the sun. Typical black holes have masses only up to 30 times larger than the sun's. Astrophysicists have determined that supermassive black holes can form when two galaxies collide and their two black holes merge into one. These galaxy collisions happened in the later years of the universe, but not in the early days. In the first few millions of years after the Big Bang, galaxies were too few and too far apart to merge. Recent observations from the Sloan Digital Sky Survey (SDSS) have shown that this isn't the case - enormous supermassive black holes existed as early as 700 million years after the Big Bang. Computer simulations, completed using supercomputers at the National Institute for Computational Sciences and the Pittsburgh Supercomputing Center and viewed using GigaPan Time Machine technology, show that thin streams of cold gas flow uncontrolled into the center of the first black holes, causing them to grow faster than anything else in the universe. Btw, GigaPan Time Machine technology is really cool stuff; this technology allows the researchers to view their simulation as if it was a movie. You can easily pan across the simulated universe as it forms, and zoom in to events that look interesting, allowing to see greater detail than what could be seen using a telescope. Picture below shows the projected gas density over the whole volume ('unwrapped' into 2D) in the large scale (background) image. The two images on top show two zoom-in of increasing factor of 10, of the regions where the most massive black hole - the first quasars - is formed. The black hole is at the center of the image and is being fed by cold gas streams.
As researchers zoomed in to the creation of the first supermassive black holes, they saw something unexpected. Normally, when cold gas flows toward a black hole it collides with other gas in the surrounding galaxy. This causes the cold gas to heat up and then cool back down before it enters the black hole. This process, called shock heating, would stop black holes in the early universe from growing fast enough to reach the masses we see. Instead, researchers saw in their simulation thin streams of cold dense gas flowing along the filaments that give structure to the universe and straight into the center of the black holes at breakneck speed, making for cold, fast food for the black holes. This uncontrolled consumption caused the black holes to grow exponentially faster than the galaxies in which they reside. This results could also shed light on how the first galaxies formed, giving more clues to how the universe came to be.
By pointing Chandra at a patch of sky for more than six weeks, astronomers obtained what is known as the Chandra Deep Field South (CDFS). When combined with very deep optical and infrared images from NASA's Hubble Space Telescope, the new Chandra data allowed astronomers to search for black holes in 200 distant galaxies, from when the universe was between about 800 million to 950 million years old. The observations found that between 30 and 100 percent of the distant galaxies contain growing supermassive black holes. Extrapolating these results from the small observed field to the full sky, there are at least 30 million supermassive black holes in the early universe. This is a factor of 10000 larger than the estimated number of quasars in the early universe. Because these black holes are nearly all enshrouded in thick clouds of gas and dust, optical telescopes frequently cannot detect them. However, the high energies of X-ray light can penetrate these veils, allowing the black holes inside to be studied.
Although evidence for parallel growth of black holes and galaxies has been established at closer distances, the new Chandra results show that this connection starts earlier than previously thought, perhaps right from the origin of both. Most astronomers think in the present-day universe, black holes and galaxies are somehow symbiotic in how they grow. It has been suggested that early black holes would play an important role in clearing away the cosmic "fog" of neutral, or uncharged, hydrogen that pervaded the early universe when temperatures cooled down after the Big Bang. However, the Chandra study shows that blankets of dust and gas stop ultraviolet radiation generated by the black holes from traveling outwards to perform this "reionization." Therefore, stars and not growing black holes are likely to have cleared this fog at cosmic dawn.
Early times and black holes are indeed puzzle. The farrest black hole we found is coming from galaxy called J1120+0641 and light we see coming from the galaxy center is only 740 million years after the Big Bang, when the universe was only 1/18th of its current age. Using the IRAM array of millimetre-wave telescopes in the French Alps, a team of European astronomers from Germany, the UK and France have discovered a large reservoir of gas and dust that includes significant quantities of carbon in a galaxy that surrounds the most distant supermassive black hole known. This is quite unexpected, as the chemical element carbon is created via nuclear fusion of helium in the centres of massive stars and ejected into the galaxy when these stars end their lives in dramatic supernova explosions. The presence of so much carbon confirms that massive star formation must have occurred in the short period between the Big Bang and the time we are observing the galaxy. From the emission from the dust, researchers were able to show that the galaxy is still forming stars at a rate that is 100 times higher than in our Milky Way. The astronomers are excited about the fact that this source is also visible from the southern hemisphere where the Atacama Large Millimeter/submillimeter Array (ALMA), which will be the world's most advanced sub-millimetre / millimetre telescope array, is currently under construction in Chile. Observations with ALMA will enable a detailed study of the structure of this galaxy, including the way the gas and dust moves within it.
Image above shows the bright emission from carbon and dust in a galaxy surrounding the most distant supermassive black hole known. At a distance corresponding to 740 Million years after the Big Bang, the carbon line, which is emitted by the galaxy at infrared wavelengths (that are unobservable from the ground), is redshifted, because of the expansion of the Universe, to millimetre wavelengths where it can be observed using facilities such as the IRAM Plateau de Bure Interferometer.
But ok, what about "normal" black holes? Although exotic by everyday standards, black holes are everywhere. The lowest-mass black holes are formed when very massive stars reach the end of their lives, ejecting most of their material into space in a supernova explosion and leaving behind a compact core that collapses into a black hole. There are thought to be millions of these low-mass black holes distributed throughout every galaxy. Despite their ubiquity, they can be hard to detect as they do not emit light so are normally seen through their action on the objects around them, for example by dragging in material that then heats up in the process and emits X-rays. But despite this, the overwhelming majority of black holes have remained undetected. In recent years, researchers have made some progress in finding ordinary black holes in binary systems, by looking for the X-ray emission produced when they suck in material from their companion stars. So far these objects have been relatively close by, either in our own Milky Way Galaxy or in nearby galaxies in Local Group. Researchers used the orbiting Chandra X-ray observatory to make six 100000 second long exposures of Centaurus A, detecting an object with 50000 times the X-ray brightness of our Sun. A month later, it had dimmed by more than a factor of 10 and then later by a factor of more than 100, so became undetectable. This behaviour is characteristic of a low mass black hole in a binary system during the final stages of an outburst and is typical of similar black holes in the Milky Way. It implies that the team made the first detection of a normal black hole so far away (12 million light years away), for the first time opening up the opportunity to characterise the black hole population of other galaxies.
The yellow arrow in the picture above identifies the position of the black hole transient inside Centaurus A. The location of the object is coincident with gigantic dust lanes that obscure visible and X-ray light from large regions of Centaurus A. Other interesting X-ray features include the central active nucleus, a powerful jet and a large lobe that covers most of the lower-right of the image. There is also a lot of hot gas. In the image, red indicates low energy, green represents medium energy, and blue represents high energy light.
There are two ways to grow a supermassive black hole: with gas clouds and with stars. Sometimes there's gas and sometimes there is not. We know that from observations of other galaxies. But there are always stars. A new study led by a University of Utah astrophysicist found a new explanation for the growth of supermassive black holes in the center of most galaxies: they repeatedly capture and swallow single stars from pairs of stars that wander too close. So, while gas did initial kick, it was stars that continued feeding process. A binary pair of stars orbiting each other is essentially a single object much bigger than the size of the individual stars, so it is going to interact with the black hole more efficiently. The binary doesn't have to get nearly as close for one of the stars to get ripped away and captured. But to prove the theory will require more powerful telescopes to find three key signs: large numbers of small stars captured near supermassive black holes, more observations of stars being "shredded" by gravity from black holes, and large numbers of "hypervelocity stars" that are flung from galaxies at more than 1.5 million kmh when their binary partners are captured. Astrophysicists long have debated how supermassive black holes grew during the 14 billion years since the universe began in a great expansion of matter and energy named the Big Bang. One side believes black holes grow larger mainly by sucking in vast amounts of gas; the other side says they grow primarily by capturing and sucking in stars. The new theory about binary stars - a pair of stars that orbit each other - arose from earlier research to explain hypervelocity stars, which have been observed leaving our Milky Way galaxy at speeds ranging from 1.5 million to 2.9 million kmh, compared with the roughly 560000 kmh speed of most stars.
Picture above is artist’s conception of a supermassive black hole (lower left) with its tremendous gravity capturing one star (bluish, center) from a pair of binary stars, while hurling the second star (yellowish, upper right) away at a hypervelocity of more than 1 million mph. The grayish blobs are other stars captured in a cluster near the black hole. They appear distorted because the black hole’s gravity curves spacetime and thus bends the starlight. The hypervelocity stars we see come from binary stars that stray close to the galaxy's massive black hole. The hole peels off one binary partner, while the other partner - the hypervelocity star - gets flung out in a gravitational slingshot. The calculations show how the model's rate of binary capture and consumption can explain how the Milky Way's supermassive black hole has at least doubled to quadrupled in mass during the past 5 billion to 10 billion years. When the researchers considered the number of stars near the Milky Way's center, their speed and the odds they will encounter the supermassive black hole, they estimated that one binary star will be torn apart every 1,000 years by the hole's gravity. During the last 10 billion years, that would mean the Milky Way's supermassive black hole ate 10 million solar masses - more than enough to account for the hole's actual size of 4 million solar masses. Confirmation of the theory must await more powerful orbiting and ground-based telescopes. Future observations should address this model for good.
Black hole, like all star-type objects, has a magnetic field. Unlike the Earth, which has a magnetic field of about 0.6 Gauss at the surface, or the Sun, which can reach a field strength of up to 4,000 Gauss on a Sunspot, a black hole can have magnetic fields in excess of 1000000000000 Gauss. Go figure! One of the basic law of physics is that, if you hold your right hand in an "L" shape (fingers together, thumb out), and point your fingers in the direction of the magnetic field and thumb in the direction the particle is moving, your palm "pushes" the particle perpendicular to both directions. This causes black holes to suck these particles up and down, perpendicular to the disk, and shoot them out at ultra-high speeds in two jets. Scientists study jets to learn more about the extreme environments around black holes. Much has been learned about the material feeding black holes, called accretion disks, and the jets themselves, through studies using X-rays, gamma rays and radio waves. But key measurements of the brightest part of the jets, located at their bases, have been difficult despite decades of work.
In 2011, theoretical physicist and black hole guru Kip Thorne, unveiled what he considers a new way to visualize how black holes stretch and bend the fabric of space-time. The approach relies on imaginary lines of force called tendex and vortex lines - roughly the gravitational equivalents of the electromagnetic field lines that dictate the arrangement of iron filings around a magnet. Tendex lines radiate from all objects with mass; they describe how gravity compresses or extends space-time. Vortex lines surround rotating objects and depict how space-time becomes twisted, like water swirling down a drain.
You most likely have heard of Stephen Hawking. Hawking is important for many things; he triggered holographic principle for example which came from his comments about information and black holes. He also established something we call today Hawkings's radiation. Hawking radiation is black body radiation that is predicted to be emitted by black holes, due to quantum effects near the event horizon. Hawking's work followed his visit to Moscow in 1973 where Soviet scientists Yakov Zeldovich and Alexei Starobinsky showed him that according to the quantum mechanical uncertainty principle, rotating black holes should create and emit particles. Hawking radiation reduces the mass and the energy of the black hole and is therefore also known as black hole evaporation. Because of this, black holes that lose more mass than they gain through other means are expected to shrink and ultimately vanish. In June 2008, NASA launched the GLAST satellite, which will search for the terminal gamma-ray flashes expected from evaporating primordial black holes. In September 2010, a signal which is closely related to black hole Hawking radiation was claimed to have been observed in a laboratory experiment involving optical light pulses, however the results remain unverified and debatable. In the event that speculative large extra dimension theories are correct, CERN's Large Hadron Collider may be able to create micro black holes and observe their evaporation (micro black holes are predicted to be larger net emitters of radiation than larger black holes and should shrink and dissipate faster). In 2010, a team of Italian scientists has fired a laser beam into a hunk of glass to create what they believe is an optical analogue of the Hawking radiation that many physicists expect is emitted by black holes. It remains under debate if they are correct or not (click here to see why).
Speaking of Hawking and black holes, he is known to make bets on things he believe. In 1974 he made one close to this subject. Back then he bet that Cygnus X-1 did not contain a black hole. Using several telescopes, both ground-based and in orbit, the scientists unravelled longstanding mysteries about the object called Cygnus X-1, a famous binary-star system discovered to be strongly emitting X-rays nearly a half-century ago. The system consists of a black hole and a companion star from which the black hole is drawing material. The scientists' efforts yielded the most accurate measurements ever of the black hole's mass and spin rate. Though Cygnus X-1 has been studied intensely since its discovery, previous attempts to measure its mass and spin suffered from lack of a precise measurement of its distance from Earth. This has changed now. We now know that Cygnus X-1 is one of the most massive stellar black holes in the Milky Way - 15 times more massive than our Sun and is spinning more than 800 times per second.
Picture above: On the left, an optical image from the Digitized Sky Survey shows Cygnus X-1, outlined in a red box. Cygnus X-1 is located near large active regions of star formation in the Milky Way, as seen in this image that spans some 700 light years across. An artist's illustration on the right depicts what astronomers think is happening within the Cygnus X-1 system. Cygnus X-1 is a so-called stellar-mass black hole, a class of black holes that comes from the collapse of a massive star. The black hole pulls material from a massive, blue companion star toward it. This material forms a disk (shown in red and orange) that rotates around the black hole before falling into it or being redirected away from the black hole in the form of powerful jets.
A black hole’s outer boundary, known as the event horizon, is a point of no return. Once trapped inside, nothing - not even light - can escape. At the center is a core, known as a singularity, that is infinitely small and dense, an affront to all known laws of physics. Since no energy, and hence no information, can ever leave that dark place, it seems quixotic to try peering inside. As with Las Vegas, what happens in a black hole stays in a black hole. But one man, Andrew Hamilton, wishes to challenge that. A black hole, Hamilton realized, could be thought of as a kind of Big Bang in reverse. Instead of exploding outward from an infinitesimally small point, spewing matter and energy and space to create the cosmos, a black hole pulls everything inward toward a single, dense point. Whether in a black hole or in the Big Bang, the ultimate point - the singularity - is where everything started and where it all might end.
Hamilton took the known attributes of black holes and plugged them into a basic computer graphics program. All it involved was applying Einstein’s relativity equations, which describe how light rays would bend as they approach a black hole. Hamilton’s first, simple movies were broad and cartoonish, but they served their purpose: showing how different kinds of black holes might look as you approached them from the outside and then ventured in. In one animation, the observer flew by a star system and plunged across a black hole’s event horizon, represented by a spherical red grid. Another movie offered a glimpse of an alternate universe, shown in pink, before the observer met his end at the singularity. In a third, the event horizon split in two as the observer entered the interior - a bizarre effect (later validated by Hamilton) that initially convinced some critics that these simulations must be flawed (below are two animated gifs, but animation might require browser refresh to work).
In 2001 Denver Museum of Nature and Science were building a new planetarium with a state-of-the-art digital projection system, and they needed help developing eye-popping shows. Hamilton spent his time developing visualization software far more powerful than the off-the-shelf program he had been using. His final software package had more than 100000 lines of code and it attracted attention. In 2002 he was invited to collaborate on a Nova documentary about black holes. That is when Hamilton had to face the painful truth that all his visualizations to date had been based on calculations done by others. In Einstein’s geometric conception of gravity, a massive body like the sun dents the fabric of space-time, much as a large person deforms the surface of a trampoline. Earth follows the curved shape of the warped space around the sun, which is why it moves in a circular orbit; this description has been experimentally verified to high precision. Ten linked equations (Einstein’s field equations) describe precisely how space-time is curved for any given distribution of matter and energy, even for something as extreme as a black hole. Relativity is confusing enough for conventional objects; it is far stranger for a black hole because such an object does not merely dent space-time - it creates a discontinuity, a bottomless pit in the middle of an otherwise smooth fabric.
Hamilton tried to make the problem more manageable by looking at black holes from a different perspective. He proposed a new analogy to describe what happens when something, or someone, approaches a black hole’s event horizon, likening it to a waterfall crashing into an abyss. A fish can swim near the edge and safely slip away - unless it gets too close, in which case it will be dragged over the precipice no matter how hard it resists. Similarly, any object or even any kind of energy is swept across the event horizon by a “waterfall” of space that is constantly cascading into the black hole. If a flashlight sailed over the edge of that metaphorical waterfall, not only the flashlight but also its light beam would be pulled in. Hamilton describes a black hole as a place where space is falling faster than light (no object can move through space faster than light, but there is no restriction on how quickly space itself can move).
The more Hamilton worked with his computer models, the more he realized just how strange the interior of a black hole is. A charged black hole actually has a secondary boundary - an inner horizon - inside the main event horizon that defines the hole’s outer limit. Physics legend Roger Penrose had been the first person to show that something bizarre must happen at that inner horizon, because all the matter and energy falling into a black hole piles up there. The inner horizon may be the most energetic and violently unstable place in the universe. Building on the groundbreaking work of physicists Eric Poisson and Werner Israel, Hamilton describes the conditions at the inner horizon as an "inflationary instability". It is inflationary because everything - mass, energy, pressure - keeps growing exponentially. And it is unstable because, according to Hamilton’s calculations, the surface - the inner horizon - cannot sustain itself and must ultimately collapse. Continuing his quest for realism, Hamilton considered the case of a black hole that rotates (as every known object in the universe, and perhaps the universe itself does too) and plugged it into his computer models. When a particle falls into a black hole and approaches the inner horizon, it is diverted into one of two narrowly focused, laserlike beams. If the particle enters in the direction opposite that of the black hole’s rotation, it will join an "ingoing beam" that has positive energy and moves forward in time. But here is the real brainteaser: If the particle enters in the same direction as the black hole's spin, it joins an "outgoing beam" that has negative energy and moves backward in time. Trying to make physical sense of these abstract conceptual insights, Hamilton discovered that the inner horizon acts as an astonishingly powerful particle accelerator, shooting the ingoing and outgoing beams past each other at nearly the speed of light. A person moving with the outgoing beam (if such a thing were possible) would think he was moving away from the black hole when he was, from an outsider's perspective, actually being pulled toward its center-the same place that someone traveling with the ingoing beam would inevitably go. Even though both parties are moving toward the center, the extreme curvature of space-time would cause them to feel like they were falling in different directions. This particle accelerator has another peculiar attribute: Once started, it never stops. The faster the streams move, the more energy there is; the more energy there is, the more gravity there is, and the faster the particles accelerate.
It is then not far fetched idea where black hole’s inner accelerator could spawn entire new universes. According to some cosmological models, our universe began as a blip of extreme energy within some other, preexisting universe (brane world collision), which then bubbled off to create a whole reality of its own. Something like this could occur inside a black hole, with a baby universe forming as a tiny bubble at the inner horizon. For a moment this infant would be connected to its "mother" by a kind of umbilical cord, a minuscule wormhole. Then the baby universe would break off to pursue a destiny completely removed from ours. That means if there’s anywhere in our universe where baby universes are being created, it’s likely happening inside black holes. And this inflationary zone near the inner horizon is where the process may occur. Needless to say, not everyone agrees with this, but when it comes to probing the inside of a black hole, theory is the only available tool. And it is reliable up to a certain point. If interested in visual work by Andrew Hamilton, click here.
A quasi-stellar radio source (quasar) is a very energetic and distant active galactic nucleus. Quasars are extremely luminous and were first identified as being high redshift sources of electromagnetic energy, including radio waves and visible light, that were point-like, similar to stars, rather than extended sources similar to galaxies. While the nature of these objects was controversial until as recently as the early 1980s, there is now a scientific consensus that a quasar is a compact region in the center of a massive galaxy surrounding its central supermassive black hole. Its size is 10-10000 times the Schwarzschild radius of the black hole. Quasars are among the brightest objects in the universe, far outshining the total starlight of their host galaxies. The output of light is equivalent to one trillion suns. Quasar host galaxies are hard or even impossible to see if the central quasar far outshines the galaxy. Therefore, it is difficult to estimate the mass of a host galaxy based on the collective brightness of its stars. However, gravitational lensing candidates are invaluable for estimating the mass of a quasar's host galaxy because the amount of distortion in the lens can be used to estimate a galaxy's mass. It comes as an interesting fact that light from quasars might have something in common with ordinary bulbs.
Astronomers have determined that quasars are incredibly variable, with some quasars quadrupling in brightness in the span of just a few hours. Although rarely that dramatic, variability in light output is seen in nearly all quasars, with average quasars changing in brightness by 10 to 15 percent over the course of one year. Recently, researchers at Illinois and NCSA found that this variability is related to both the mass of the black hole at the center of the quasar, and to the efficiency of the quasar at converting gravitational potential energy into light energy. Using data obtained by the Sloan Digital Sky Survey, the researchers monitored the brightness and estimated the central black hole mass of more than 2500 quasars, observed over a period of four years. They found that, for a given brightness, quasars with large black hole masses are more variable than those with low black hole masses. Quasars with more massive black holes have more gravitational energy that can potentially be extracted, which we would see in the optical as light. If two quasars have the same brightness, the one with the larger black hole mass is actually less efficient at converting this gravitational energy into light. These less-efficient quasars have more variable light output. It could be a little like flickering light bulbs - the bulbs that are the most variable are those that are currently the least efficient.
Quasars are believed to be powered by accretion of material onto supermassive black holes in the nuclei of distant galaxies, making these luminous versions of the general class of objects known as active galaxies. As stars and interstellar gas fall into the black holes, they swirl around them and then are swallowed up - but not before giving off bright light at nearly all wavelengths of the electromagnetic spectrum. No other currently known mechanism appears able to explain the vast energy output and rapid variability. In seeking to understand how, and when, galaxies such as our own formed, astronomers often turn to quasars. Because quasars are extremely bright, they can be seen at much larger distances from Earth than other galaxies, and so allow us to peer into the early history of the Universe (we are linking them against early galaxies - actually, they are being seen as early galaxies themselves by some). In 2010, discovery of two quasars in the distant Universe that apparently have no hot dust in their environments provides evidence that these systems represent the first generation of their family. Quasars are powered by supermassive black holes. One could say that what is pulsar to neutron star, that is quasar to black hole. Of course, related to quasars you might have heard of blazars too.
Quasars also provide some clues as to the end of the Big Bang's reionization. The oldest quasars (redshift ≥ 6) display a Gunn-Peterson trough and have absorption regions in front of them indicating that the intergalactic medium at that time was neutral gas. More recent quasars show no absorption region but rather their spectra contain a spiky area known as the Lyman-alpha forest. This indicates that the intergalactic medium has undergone reionization into plasma, and that neutral gas exists only in small clouds. Quasars show evidence of elements heavier than helium, indicating that galaxies underwent a massive phase of star formation, creating population III stars between the time of the Big Bang and the first observed quasars. This results contradict theory that says black holes and galaxies become more massive through gravitational mergers as the universe evolves.
While often ignored, there is also question of magnetic field role in early universe. Why is the gas found between galaxies or between the stars of the same galaxy magnetized? Recently astrophysicists have put forward the first potential explanation for this phenomenon: an initially weak magnetic field could have been amplified by turbulent motions, like those that take place within Earth and the sun, and which must have existed in the primordial universe.
Credits: US National Radio Astronomy Observatory, NASA, Wikipedia, CNRS, ESO, Max-Planck-Gesellschaft, Phil Plait, Harvard-Smithsonian Center for Astrophysics, National Science Foundation, UCSB, Nature, Louisiana State University, Space Telescope Science Institute, University of Pittsburgh, STScI, University of Nottingham, University of Arizona, ESO, WISE, Max Planck Institute for Physics, Andrew Hamilton, Discover magazine, Carnegie Mellon University, Royal Astronomical Society (RAS), University of Utah, ***** Vargas, Maritxu Poyal, Mark Trodden