Time for another sequel in this series.  To refresh the memory, I had so far written about these topics:

Big Bang I: Dawn of time - very early Universe from Planck epoch to baryogenesis

Big Bang II: First cry of baby Universe - early Universe up to photon epoch

Big Bang III: Origins of creation - reionization phase

Big Bang IV: First starlight - first stars

Big Bang V: Puberty - early supernovae, black holes, pulsars, neutron stars, nebulas and quasars

 

With all above in place we can take next step where large scale structures have been created that today we recognize as void and galaxy clusters, fillaments, etc. Today, we know that stars cluster together to form galaxies. Galaxies also cluster together to form much larger structures. There are clusters of galaxies called Groups which contain 10's of galaxies. Our own galaxy, the Milky Way resides in such a group of about 30 galaxies, named the Local Group. Additionally there are much larger clusters of galaxies containing anywhere from 50 - 1000's of galaxies. The closest cluster to us is the Virgo cluster. The average distance between clusters is some tens of millions of light years. Groups and Clusters cluster together to form even larger clusters known as Superclusters. The Local Group belongs to the Local Supercluster, whose center is at the Virgo Cluster. In between Superclusters are enormous voids of space where there are almost no galaxies at all.

 

The largest structures discovered in the Universe are systems of voids and clusters. At this scale the Universe takes on a foamy look. The voids appear as great bubbles and galaxies lie along them in great filaments that connect Superclusters. To visualize this, check following video; initial picture covers some 2.4 billion light years (which with expansion is some 1.5% of whole observable universe) and each point of light represents one galaxy (each containing billion of stars).

 

 

 

 

Impressive, isn't it? How did these structures form? The Big Bang theory is widely considered to be a successful theory of cosmology, but the theory is incomplete. It does not account for the needed fluctuations to produce the structure we see. Most cosmologists believe that the galaxies that we observe today grew from the gravitational pull of small fluctuations in the nearly-uniform density of the early universe. These fluctuations leave an imprint in the cosmic microwave background radiation in the form of temperature fluctuations from point to point across the sky. The WMAP satellite measures these small fluctuations in the temperature of the cosmic microwave background radiation and in turn probe the early stages of structure formation. Although the "Big Bang" is often presented as if it is proven fact, there is a wealth of data, including recent revelations of the several space probes and findings in fundamental physics, which possibly tell a different story. One of the first problems are found in the Large Scale Structures in the Universe.

 

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In recent years, there have been a number of very serious challenges to the current theory of cosmic evolution and the belief the universe began just 13.7 billion years ago. The existence of these "Superclusters", "Great Walls" and "Great Attractors" could have only come to be organized and situated in their present locations and to have achieved their current size, in a universe which is at least 80 billion to 250 billion years in age. The largest superclusters, for example, the  "Coma", extend up to 100 Mpc! In 1986, Brent Tully reported detecting superclusters of galaxies 300 million light years (mly) long and 100 mly thick - stretching out about 300 mly across. At the speeds at which galaxies are supposed to be moving, it would require 80 billlion years to create such a huge complex of galaxies. In 1989, a group lead by John Huchra and Margaret J. Geller discovered "The Great Wall" - a series of galaxies, lined up and creating a "wall" of galaxies 500 million light years (mly) long, 200 mly wide, and 15 mly thick. This superstructure would have required at least 100 billion years to form. A team of the British, American, and Hungarian astronomers have reported even larger structures. As per their findings, the universe is crossed by at least 13 'Great Walls', apparent rivers of galaxies 100Mpc long in the surveyed domain of 7 billion light years. They found galaxies clustered into bands spaced about 600 million light years apart. The pattern of these clusters stretches across about one-fourth of the diameter of the universe, or about seven billion light years. This huge shell and void pattern would have required nearly 150 billion years to form, based on their speed of movement, if produced by the standard Big Bang cosmology. The "Sloan Great Wall" of galaxies, as detected by the Sloan Digital Survey, has earned the distinction of being the largest observed structure in the Universe. It is 1.36 billion light years long and 80% longer than the Great Wall discovered by Geller and Huchra. It runs roughly from the head of Hydra to the feet of Virgo. It would have taken at least 250 billion years to form. Another large-scale structure is the Newfound Blob, a collection of galaxies and enormous gas bubbles which measures about 200 million light years across.

 

Then there is the problem of gravity. "Hubble length" Universe, which consists of those galaxies and stars which can be observed by current technology, appears, therefore, to be organized as titanic walls and clusters of galaxies separated by a collection of giant bubble-like voids. The Great Walls are far too large and massive to have been formed by the mutual gravitational attraction of its member galaxies alone. Based on the cosmological principle, which is one of the cornerstones of the Big Bang model, cosmologists predicted the distribution of matter to be homogeneous throughout the universe, implying thereby that the distribution of the galaxies would be essentially uniform. There would be no large scale clusters of galaxies or great voids in space. Instead, contrary to the "Big Bang" universe, we exist in a very "lumpy" cosmos. The bottom line is, we have incomplete picture about beginning so I will focus further on what we know and what current state is.

 

Sky surveys and mappings of the various wavelength bands of electromagnetic radiation (in particular 21-cm emission) have yielded much information on the content and character of the universe's structure. The organization of structure appears to follow as a hierarchical model with organization up to the scale of superclusters and filaments. Larger than this, there seems to be no continued structure, a phenomenon which has been referred to as the End of Greatness. The names which have been given to these large scale structures are filaments, voids, walls, cluster of galaxies and great attractor (which stands for itself).

 

In physical cosmology, galaxy filaments, also called supercluster complexes or great walls, are, so far, the largest known cosmic structures in the universe. They are massive, thread-like structures with a typical length of 50 to 80 megaparsecs h-1 that form the boundaries between large voids in the universe. Filaments consist of gravitationally bound galaxies; parts where a large number of galaxies are very close to each other are called superclusters. Discoveries of structures larger than superclusters started in the 1980s. In 1987 astronomer R. Brent Tully identified what he called the Pisces-Cetus Supercluster Complex. In 1989 the CfA2 Great Wall was discovered, followed by the Sloan Great Wall in 2003. In 2006, scientists announced the discovery of three filaments aligned to form the largest structure known to humanity, composed of densely packed galaxies and enormous blobs of gas known as Lyman alpha blobs.

 

 

 

 

The movie above illustrate the formation formation of clusters and large-scale filaments in the Cold Dark Matter model with dark energy. The frames show the evolution of structures in a 43 million parsecs (or 140 million light years) box from redshift of 30 to the present epoch (z=30 to z=0). At the initial epoch (z=30), when the age of the Universe was less than 1% of its current age, distribution of matter appears to be uniform. This is because the seed fluctuations are still fairly small. As time goes on, the fluctuations grow resulting in a wealth of structures from the smallest bright clumps which have sizes and masses similar to those of galaxies to the large filaments. Notice the filament spanning the entire box from left to right and how it becomes more and more pronounced with time. Also, note that it does not change much between z=0.5 and z=0. This is because the expansion of the universe is in the stage of acceleration as the "dark energy" becomes dominant at z<1. On large scales seen here, gravity cannot compete with the dark energy-driven acceleration and the growth of structures ceases. As the contraction of large-scale structures is halted they expand with the universe and appear "frozen" in our co-moving system of coordinates.

 

 

 

 

Formation of a group of galaxies is quite similar to our Local Group in which our galaxy, the Milky Way, is approaching our biggest neighbor the Andromeda Galaxy. The region shown here is 1/10 of the box shown in the filament formation before and is equal to 4.3 megaparsec or 14 million light years. In video above, "camera" is tracking the progenitor of the group so that it is always new the center of the field of view. The formation of an object such as our Local Group proceeds hierarchically in the Cold Dark Matter models. Small-mass objects form first at z>5, they quickly grow in size and violently merge with each other, creating increasingly larger and larger system. This galactic "cannibalism" persists even to the present day epoch (z=0). Indeed, the two main objects that you can see approaching at z~0, will also merge in about one billion years into the future. Note that many of the "cannibalized" systems do not loose their identity and become satellites orbiting in the gravitational pull of larger systems. The groups like the one modeled in these simulations are very common in the Universe. In fact, up to half of all galaxies are thought to be part of groups of different sizes.

 

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The panels above show (clock-wise from the top left) regions of 36 kiloparsec, 72 kiloparsec, 144 kiloparsec, 288 kiloparsec, respectively. The young galaxy forms in a high-density peak in which several large-scale filaments of matter intersects. These filaments deliver a fresh supply of gas and dark matter to the galaxy. The acretting gas fuels very active star formation, while accreted dark matter and smaller galaxies lead to the rapid growth of the galaxy's mass. In the top panels, showing the smallest regions, you can see a young spiral disk. The disk is forming stars very actively with regions of star formation concentrated towards the densest regions near the plane of the disk (the brightest blue) and so the distribution of stars is also disk-like. Unlike gas, however, the stars can be "heated" by frequent collisions and mergers with other galaxies common at these early epochs. Therefore, the stellar disk is somewhat thicker than the gas disk. The distribution of stars in the disk is shown in the two panels (face-on and edge-on view) below. The stellar particles were color-coded according to their age, so that white-colored stars are the youngest and red are the oldest. You can see that the youngest stars concentrate towards the plane of the disk and the central regions, while the old stars have a more extended distribution and form what astronomers call a "bulge". Our Milky Way galaxy has a bulge quite similar to the bulge of red stars you see on these pictures. A team of astronomers has discovered the most distant cluster of red galaxies ever observed using FourStar, a new and powerful near-infrared camera on the 6.5m Magellan Baade Telescope. The galaxy cluster is located 10.5 billion light years away in the direction of the constellation Leo. It is made up of 30 galaxies packed closely together, forming the earliest known "galaxy city" in the universe.

 

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Remarkably, the cluster was completely missed by previous surveys, which searched this region of the sky for thousands of hours and were conducted by all the major ground- and space-based observing facilities, including the Hubble Space Telescope. Despite these intense observations, accurate distances for such faint and distant galaxies were missing until the advent of FourStar. The 3-D map revealed the conspicuous concentration of galaxies that existed when the universe was only three billion years old. This means the galaxy cluster is still young and should continue to grow into an extremely dense structure possibly containing thousands of galaxies. Studying this system will help astronomers understand how galaxies are influenced by their environment, evolve, and assemble into larger structures.

 

We can go back even for in time if you want. Last month astronomers found one cluter which is 12.7 billion light years away. Each of those circled red dots on picture below is a young galaxy, so distant that the light has been on its way here for more than 90% of the current age of the Universe. And they’re almost lost among all those other stars and galaxies in the image (though their intense red color helps). The astronomers used the massive 8.2 meter Subaru telescope to look at large swaths of the sky. They looked at the colors of the galaxies they found; distant objects would be so far away their light is significantly redshifted by the expansion of the Universe itself. Galaxies are distributed throughout space, so you expect to see them scattered across the sky as well as in redshift (distance). When looking at one part of the sky, however, they found an unusually high concentration of galaxies that were very red. Using a different camera on Subaru, they took spectra of those galaxies - breaking the light up into very fine divisions of colors, like a rainbow with hundreds of colors in it - to accurately measure the redshifts of those galaxies. The astronomers confirmed that many of the galaxies in their sample were at the same redshift (z=6). The odds of these galaxies all being at the same distance happening by chance is extremely small: only about one in a billion! So it’s pretty clear these galaxies really are physically associated with each other. That is, clustered together.

 

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In astronomy, voids are the empty spaces between filaments (the largest-scale structures in the Universe), which contain very few, or no, galaxies. They were first discovered in 1978 during a pioneering study by Stephen Gregory and Laird A. Thompson. Voids typically have a diameter of 11 to 150 megaparsecs; particularly large voids, defined by the absence of rich superclusters, are sometimes called "supervoids". Voids located in high-density environments are smaller than voids situated in low-density spaces of the universe. Voids are believed to have been formed by baryon acoustic oscillations in the Big Bang by collapses of mass followed by implosions of the compressed baryonic matter.

 

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While much remains to be discoeverd about these large scale structures, our best understanding lies within galaxies. Last year in October, an international team of astronomers used the VLT as a time machine, to look back into the early Universe and observe several of the most distant galaxies ever detected. They have been able to measure their distances accurately and find that we are seeing them as they were between 780 million and a billion years after the Big Bang. The new observations have allowed astronomers to establish a timeline for what is known as the age of reionisation for the first time. During this phase the fog of hydrogen gas in the early Universe was clearing, allowing ultraviolet light to pass unhindered for the first time. At the time the first stars and galaxies formed, the Universe was filled with electrically neutral hydrogen gas, which absorbs ultraviolet light. As the ultraviolet radiation from these early galaxies excited the gas, making it electrically charged (ionised), it gradually became transparent to ultraviolet light. This process is technically known as reionisation, as there is thought to have been a brief period within the first 100000 years after the Big Bang in which the hydrogen was also ionised.

 

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Different chemical elements glow brightly at characteristic colours. These spikes in brightness are known as emission lines. One of the strongest ultraviolet emission lines is the Lyman-alpha line, which comes from hydrogen gas. It is bright and recognisable enough to be seen even in observations of very faint and faraway galaxies. Spotting the Lyman-alpha line for five very distant galaxies allowed the team to do two key things: first, by observing how far the line had been shifted toward the red end of the spectrum, they were able to determine the galaxies' distances, and hence how soon after the Big Bang they could see them. This let them place them in order, creating a timeline which shows how the galaxies' light evolved over time. Secondly, they were able to see the extent to which the Lyman-alpha emission - which comes from glowing hydrogen within the galaxies - was reabsorbed by the neutral hydrogen fog in intergalactic space at different points in time. When the Universe was only 780 million years old this neutral hydrogen was quite abundant, filling from 10 to 50% of the Universe' volume. But only 200 million years later the amount of neutral hydrogen had dropped to a very low level, similar to what we see today. It seems that reionisation must have happened quicker than astronomers previously thought. As well as probing the rate at which the primordial fog cleared, the team's observations also hint at the likely source of the ultraviolet light which provided the energy necessary for reionisation to occur. There are several competing theories for where this light came from - two leading candidates are the Universe's first generation of stars, and the intense radiation emitted by matter as it falls towards black holes. The detailed analysis of the faint light from two of the most distant galaxies found suggests that the very first generation of stars may have contributed to the energy output observed. These would have been very young and massive stars, about five thousand times younger and one hundred times more massive than the Sun, and they may have been able to dissolve the primordial fog and make it transparent. There is no doubt that we might need more powerful telescopes to probe these galaxies, but at least we know where to look. And this is how it looks:

 

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Every object you see there is a galaxy, a collection of billions of stars. That little red dot in the middle is the light we see from that galaxy traveled for 12.9 billion years. Wow!

 

Galaxy morphological classification is a system used by astronomers to divide galaxies into groups based on their visual appearance. There are several schemes in use by which galaxies can be classified according to their morphologies, the most famous being the Hubble sequence. Hubble’s scheme divides galaxies into 3 broad classes based on their visual appearance (originally on photographic plates):

  • Elliptical galaxies have smooth, featureless light distributions and appear as ellipses in images. They are denoted by the letter E, followed by an integer representing their degree of ellipticity on the sky.
  • Spiral galaxies consist of a flattened disk, with stars forming a (usually two-armed) spiral structure, and a central concentration of stars known as the bulge, which is similar in appearance to an elliptical galaxy. They are given the symbol S. Roughly half of all spirals are also observed to have a bar-like structure, extending from the central bulge. These barred spirals are given the symbol SB.
  • Lenticular galaxies (designated S0) also consist of a bright central bulge surrounded by an extended, disk-like structure but, unlike spiral galaxies, the disks of lenticular galaxies have no visible spiral structure and are not actively forming stars in any significant quantity.

 

These broad classes can be extended to enable finer distinctions of appearance and to encompass other types of galaxy, such as irregular galaxies, which have no obvious regular structure (either disk-like or ellipsoidal). The Hubble sequence is often represented in the form of a two-pronged fork, with the ellipticals on the left (with the degree of ellipticity increasing from left to right) and the barred and unbarred spirals forming the two parallel prongs of the fork. Lenticular galaxies are placed between the ellipticals and the spirals, at the point where the two prongs meet the “handle”.

 

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It has long been known that gas-rich spiral galaxies like our Milky Way smash together to create elliptical galaxies. These big, round galaxies have very little star formation. The reddish glow of aging stars comes to dominate the complexion of elliptical galaxies, so astronomers refer to them as "red and dead". The process that drives the dramatic transformation from spiral galactic youth to elderly elliptical is the rapid loss of cool gas, the fuel from which new stars form. Supernova explosions can start the decline in star formation, and then shock waves from the supermassive black hole finish the job. Astronomers think they have identified a recently merged galaxy where this gas loss has just gotten underway. They have caught a galaxy in the act of destroying its gaseous fuel for new stars and marching toward being a red-and-dead type of galaxy. The supermassive black holes that reside in the centers of galaxies can flare up when engorged by gas during galactic mergers. As a giant black hole feeds, colossal jets of matter shoot out from it, giving rise to what is known as an active galactic nucleus. According to theory, shock waves from these jets heat up and disperse the reservoirs of cold gas in elliptical galaxies, thus preventing new stars from taking shape.

 

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Galaxy called NGC 3801 (see above), shows signs of such a process. NGC 3801 is unique in that evidence of a past merger is clearly seen, and the shock waves from the central black hole's jets have started to spread out very recently. The researchers used the Galaxy Evolution Explorer to determine the age of the galaxy's stars and decipher its evolutionary history. The ultraviolet observations show that NGC 3801's star formation has petered out over the last 100 to 500 million years, demonstrating that the galaxy has indeed begun to leave behind its youthful years. The lack of many big, new, blue stars makes NGC 3801 look yellowish and reddish in visible light, and thus middle-aged. What's causing the galaxy to age and make fewer stars? The short-lived blue stars that formed right after it merged with another galaxy have already blown up as supernovae. Data from NASA's Hubble revealed that those stellar explosions have triggered a fast outflow of heated gas from NGC 3801's central regions. That outflow has begun to banish the reserves of cold gas, and thus cut into NGC 3801's overall star making. Some star formation is still happening in NGC 3801, as shown in ultraviolet wavelengths observed by the Galaxy Evolution Explorer, and in infrared wavelengths detected by NASA's Spitzer Space Telescope. But that last flicker of youth will soon be extinguished by colossal shock waves from the black hole's jets. These blast waves are rushing outward from the galactic center at a velocity of nearly 900 kilometers per second. The waves will reach the outer portions of NGC 3801 in about 10 million years, scattering any remaining cool hydrogen gas and rendering the galaxy truly red and dead.

 

While some galaxies are rotund and others are slender disks like our spiral Milky Way, new observations from NASA's Spitzer Space Telescope show that the Sombrero galaxy is both. The galaxy, which is a round elliptical galaxy with a thin disk embedded inside, is one of the first known to exhibit characteristics of the two different types. The only way to understand all we know about this galaxy is to think of it as two galaxies, one inside the other. The Sombrero galaxy, also known as NGC 4594, is located 28 million light-years away in the constellation Virgo. From our viewpoint on Earth, we can see the thin edge of its flat disk and a central bulge of stars, making it resemble a wide-brimmed hat. Astronomers do not know whether the Sombrero's disk is shaped like a ring or a spiral, but agree it belongs to the disk class. Below is the infrared vision picture which has revealed that the Sombrero galaxy - named after its appearance in visible light to a wide-brimmed hat - is in fact two galaxies in one.

 

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Spitzer captures a different view of the galaxy than visible-light telescopes. In visible views, the galaxy appears to be immersed in a glowing halo, which scientists had thought was relatively light and small. With Spitzer's infrared vision, a different view emerges. Spitzer sees old stars through the dust and reveals the halo has the right size and mass to be a giant elliptical galaxy. While it is tempting to think the giant elliptical swallowed a spiral disk, astronomers say this is highly unlikely because that process would have destroyed the disk structure. Instead, one scenario they propose is that a giant elliptical galaxy was inundated with gas more than nine billion years ago. Early in the history of our universe, networks of gas clouds were common, and they sometimes fed growing galaxies, causing them to bulk up. The gas would have been pulled into the galaxy by gravity, falling into orbit around the center and spinning out into a flat disk. Stars would have formed from the gas in the disk. This poses all sorts of questions; how did such a large disk take shape and survive inside such a massive elliptical? How unusual is such a formation process? Centaurus A appears also to be an elliptical galaxy with a disk inside it. But its disk does not contain many stars. Astronomers speculate that Centaurus A could be at an earlier stage of evolution than the Sombrero and might eventually look similar. The findings also answer a mystery about the number of globular clusters in the Sombrero galaxy. Globular clusters are spherical nuggets of old stars. Ellipticals typically have a few thousand, while spirals contain a few hundred. The Sombrero has almost 2000, a number that makes sense now but had puzzled astronomers when they thought it was only a disk galaxy.

 

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So, galaxies essentially have three different shapes. The vast majority are flattened discs, often with spiral arms; some are ellipsoids, like rugby ball; and a few are completely irregular with no symmetry.  Earlier this year, discovery of a galaxy with an entirely different shape attracted some attention.

 

Alister Graham announced the discovery of a dwarf galaxy designated LEDA 074886 that is distinctly rectangular. The galaxy sits in a group of about 250 dwarf galaxies some 21 megaparsecs from Earth in the constellation of Eridanus.

 

It's just a nipper, with a mass some 10 billion times that of the Sun. By contrast, the Milky Way is about a thousand times heavier. The obvious question is how did it form. Graham thinks the emerald cut galaxy formed from the merger of two disc galaxies, like a couple of pancakes on top of each other. From the side, this looks rectangular. That's clearly a rare type of event but not entirely unknown.

 

Spiral galaxies are among the most beautiful objects in the Universe. Their grand, majestic nature is sweeping on a scale of hundreds of thousands of light years; their delicate arms are composed of a hundred billion stars blurred into a milky stream; and as for their cores… well, that’s a different story. Check following two spiral galaxies. On left we have NGC 4698 and on right M 77.

 

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Both are spiral galaxies and while they are not look alike in details, there is nothing wrong from outside. Apparently. The red glow dotting the arms is indicative of star formation; those are vast gas clouds glowing from the heat of young, hot stars embedded in them. So both of these galaxies look normal at a perfunctory glance, but clearly have something else going on, something not obvious that makes them special. Now, stars give off light at all wavelengths, all colors. That’s called a continuous spectrum. But a thin, hot gas (like inside the glass tubes of a neon sign) emits light at only specific colors, called emission lines. If you use a prism to break the light up from a neon sign, you see very thin lines with only a few colors represented. Gas clouds in space are the same. They emit colors at specific wavelengths, depending on what’s in the cloud. Oxygen glows green, hydrogen red, sodium yellow-orange. It’s more complicated than this, but that’s the gist of it. If you put a spectrograph - a camera that can break up light and carefully measure its component colors - on a telescope, you can determine what’s emitting the light seen, what’s in it, and even its temperature and speed. Under a spectrograph, both NGC 4698 and M77 reveal complicated emission line spectra, meaning they have lots of hot, thin gas in their cores. That in itself is interesting enough, but raises another question: what could possibly be lighting those gas clouds up on a galactic scale? And that’s where astronomers have cracked the true secret of these galaxies: they have monstrous black holes in their cores. In fact, we think all big galaxies do, including our own. But the difference here is that the ones in these two galaxies are actively feeding. Matter is falling in to these black holes, but first it’s piling up in huge disks around them. These disks get infernally hot and glow extremely brightly. This light escapes, and hits the gas clouds farther out in the galaxies… causing them to glow as well. In M77 the disk of matter is actually helping to focus a focused wind of light and matter that blasts away from the black hole, which is why it looks like there’s a spotlight emanating from the galaxy’s core. In a sense, there is. Galaxies like this are said to be active. Our Milky Way’s black hole isn’t feeding right now, so it’s quiescent. But a significant fraction of galaxies have active cores, and can be so bright they can be detected even from billions of light years away. Most galaxies seem normal enough on the surface, but for the monsters in their hearts. And in the case of at least these two island universes, it’s the fierce light from those beasts that makes them so remarkable.

 

At a distance of around 12 million light years, Centaurus A is the closest large elliptical galaxy to our own Milky Way. It has been marked as unusual since shortly after its discovery in the 19th century due to a thick lane of dust across its centre - an unusual feature for an elliptical galaxy. But it wasn't until a century later that the galaxy's true nature was revealed. Emanating from its core are two massive jets of material streaming from a massive black hole in the heart of Centaurus A. When observed by radio telescopes, the jets stretch for up to a million light years.

 

Centaurus A is the closest example of a galaxy to us with massive jets from its central black hole. Strong radio emission is caused by electrons travelling at close to the speed of light through strong magnetic fields, and is so bright that the jets are even visible in the far-infrared images from the Herschel Space Observatory. As well as the jets, the images from this infrared observatory also show a twisted disc of dust near the galaxy's centre. This odd shape is strong evidence that Centaurus A underwent a cosmic collision with another galaxy in the distant past.

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The colliding galaxy was ripped apart to form the warped disc, and the formation of young stars heats the dust to cause the infrared glow seen by Herschel. Such collisions often result in shells and rings of gas and dust, and Centaurus A is no exception. Herschel observations have now confirmed the presence of two clumps of dust that seem to be lined up with the two lobes of the jets. The apparent alignment of two clumps with the two jets now seems to be a cosmic coincidence, and it appears that the dust originated from one of the colliding galaxies. Unlike most dust Herschel sees, which is heated by nearby star formation, the dust in these clumps is being heated by old stars in Centaurus A itself, up to 50000 light years away. In x-rays the effect of the two jets of material is clearly visible. Showing the presence of extremely hot gas, the images from the XMM-Newton x-ray satellite clearly show the axis of the one of the jets. While the other jet itself is not seen in by XMM-Newton, the gas it is ploughing into is shocked and heated to very high temperatures, creating a bright x-ray glow. In the centre of the galaxy, the massive black hole is also having an effect on its immediate surroundings. The material around it glows brightly in x-rays, but there Herschel has identified an apparent deficit of dust within a few thousand light years of the black hole. This could be due to intense x-rays destroying the tiny dust grains, or due to the way the warped ring of dust is affecting star formation. Either way, Centaurus A is the ideal place to study the extreme processes that occur near super-massive black holes.

 

The connection between black holes and galaxy size is intimate one and I already discussed the in previous sequel. 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. But there is another connection which recently has been discovered. Scientists wanted to know how star formation and black hole activity are linked. The two processes increase together up to a point, but the most energetic black holes appear to turn off star formation. Supermassive black holes, weighing as much as millions of suns, are believed to reside in the hearts of all large galaxies. When gas falls upon these monsters, the material is accelerated and heated around the black hole, releasing great torrents of energy. Earlier in the history of the universe, these giant, luminous black holes, called active galactic nuclei, were often much brighter and more energetic. Star formation was also livelier back then. Studies of nearby galaxies suggest active black holes can squash star formation. The revved-up, central black holes likely heat up and disperse the galactic reservoirs of cold gas needed to create new stars. These studies have only provided "snapshots" in time, however, leaving the overall relationship of active galactic nuclei and star formation unclear, especially over the cosmic history of galaxy formation.

 

bb107.jpgTo understand how active galactic nuclei affect star formation over the history of the universe, scientists investigated a time when star formation was most vigorous, between eight and 12 billion years ago. At that epoch, galaxies were forming stars 10 times more rapidly than they are today on average. Many of these galaxies are incredibly luminous, more than 1000 times brighter than our Milky Way. For the new study, scientists used Herschel data that probed 65 galaxies at wavelengths equivalent to the thickness of several sheets of office paper, a region of the light spectrum known as the far-infrared. These wavelengths reveal the rate of star formation, because most of the energy released by developing stars heats surrounding dust, which then re-radiates starlight out in far-infrared wavelengths.

 

The researchers compared their infrared readings with X-rays streaming from the active central black holes in the survey's galaxies, measured by NASA's Chandra X-ray Observatory. At lower intensities, the black holes' brightness and star formation increased in sync. However, star formation dropped off in galaxies with the most energetic central black holes. Astronomers think inflows of gas fuel new stars and supermassive black holes. Feed a black hole too much, however, and it starts spewing radiation into the galaxy that prevents raw material from coalescing into new stars. Now that we see the relationship between active supermassive black holes and star formation, we need to know more about how this process works. Does star formation get disrupted from the beginning with the formation of the brightest galaxies of this type, or do all active black holes eventually shut off star formation, and energetic ones do this more quickly than less active ones?

 

Black holes further away from Earth than any ever found before have given astronomers a peek at how galaxies were evolving 13 billion years ago - less than a billion years after the Big Bang. Milky Way's black hole was formed at about the same time as the black holes observed in the study, and likely went through a very similar infancy. Study showed that black holes in the early universe grew in tandem with the galaxies that surround them, just as black holes at the centre of all galaxies - including our own Milky Way - do today. Observations show that extremely massive black holes already existed as early as 700 to 800 million years after the Big Bang which suggests that either they were born massive to start with, or they experienced rapid growth bursts. Chicken-and-egg problem of what was there first - the galaxy or the black hole - has been pushed all the way to the edge of the universe. One recent finding makes this a puzzle.

 

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Black holes at the centre of galaxies 'switch on' from time to time, driving material around them into outflows that can stretch for millions of light years. The flows plough through galactic gas, compressing, heating and pushing it out of the way. Much of this gas is the raw material from which stars are made, so the outflows significantly affect star formation in the galaxies that host them.

 

The astronomers used the Hubble's WFC3 (Wide Field Camera) to study the central regions of Centaurus A, catalogued as NGC 5128, a bright galaxy 13 million light years away in the direction of the southern constellation of Centaurus.

 

In visible light, a prominent belt of dust can be seen running across the galaxy and when observed at X-ray and radio wavelengths it has jets extending for up to a million light years from a central black hole. With WFC3, the scientists took a close look at the 'inner filament', a region located close to the outflow that is a source of ultraviolet and X-ray emission, as well as being bright in visible light. Using the Hubble images, the team were then able to map out the star formation history of the filament with unprecedented accuracy.  They found that the tip of the filament closest to the outflow contains young stars, the ages of which are similar to the time since the outflow 'switched on' but that there are no young stars further up the filament. This is exactly what is expected from an outflow overrunning a cloud of gas sitting in its path. The densest central parts of the cloud are compressed and collapse to form stars, while the gas on the outskirts is swept away from the tip of the filament, like a pile of autumn leaves in the wind. This enhancement of star formation by outflows would have been even more important in a younger universe, where dense clumps of gas were much more common. This study highlights the need to consider the role of 'positive' feedback from outflows in our current paradigm of galaxy formation. It adds an exciting new piece to a great puzzle - that of understanding how galaxies came to be the way they are today.

 

Studies also showed that these early black holes were shrouded in thick clouds of dust and gas from their galaxies, suggesting they were not responsible for a major event in the history of the universe that ended a period called the Dark Ages. Astronomers know particularly little about the first billion years of the 13.7 billion year old universe, when the first stars and galaxies formed. Before this study, the only black holes detected from that period were massive quasars, which are nearly fully grown with masses a billion times that of the sun. Black holes were detected in at least 30 per cent of the galaxies. Only the light with the very highest energy could be detected, suggesting that the rest was swallowed up nearby by dust. That explains why the distant black holes have been so hard to see up until now, and also answers a question that had puzzled astrophysicists for some time - whether black holes or stars ended a period in the early universe called the Dark Ages. Astrophysicists thought black holes might have existed at the time of reionization and that their light may have caused the process to occur. What we now can say is that the first black holes - yes, they were there and they were putting out lots of light, but it was completely eaten away by the gas and dust. They couldn't have reionized the universe. It must have been something else - most likely the first stars. Hubble's observations in 2012 demonstrate the progressive buildup of galaxies. They also provide further support for the hierarchical model of galaxy assembly, in which small objects accrete mass, or merge, to form bigger objects over a smooth and steady but dramatic process of collision and collection.

 

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The composite image at left (above), taken in visible and near-infrared light, reveals the location of five tiny galaxies clustered together 13.1 billion light-years away. The circles pinpoint the galaxies. The developing cluster is the most distant ever observed - the young galaxies lived just 600 million years after the universe's birth in the big bang. The five bright galaxies spotted by Hubble are about one-half to one-tenth the size of our Milky Way, yet are comparable in brightness. The galaxies are bright and massive because they are being fed large amounts of gas through mergers with other galaxies. The team's simulations show that the galaxies eventually will merge and form the brightest central galaxy in the cluster But if you think 600 million years after Bing Bang is young, what would you say about 200 million years after Big Bang?  Check following photo.

 

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The giant cluster of elliptical galaxies in the centre of this image contains so much dark matter mass that its gravitational field bends light. This means that for very distant galaxies in the background, the cluster acts as a sort of magnifying glass, bending and concentrating the distant object’s light towards Hubble. These gravitational lenses are one tool astronomers can use to extend Hubble’s vision beyond what it would normally be capable of seeing. This picture, from 2011, shows a distant galaxy that began forming stars just 200 million years after the Big Bang. This challenges theories of how soon galaxies formed and evolved in the first years of the Universe. It could even help solve the mystery of how the hydrogen fog that filled the early Universe was cleared. The distant galaxy is visible through a cluster of galaxies called Abell 383, whose powerful gravity bends the rays of light almost like a magnifying glass. The chance alignment of the galaxy, the cluster and Earth amplifies the light reaching us from this distant galaxy, allowing the astronomers to make detailed observations. Without this gravitational lens, the galaxy would have been too faint to be observed even with today's largest telescopes. After spotting the galaxy in Hubble and Spitzer images, the team carried out spectroscopic observations with the Keck-II telescope in Hawaii. By analysing spectra, the team was able to make detailed measurements of its redshift and infer information about the properties of its component stars. The galaxy's redshift is 6.027, which means we see it as it was when the Universe was around 950 million years old. This does not make it the most remote galaxy ever detected - several have been confirmed at redshifts of more than 8, and one has an estimated redshift of around 10, placing it 400 million years earlier. However the newly discovered galaxy has dramatically different features from other distant galaxies that have been observed, which generally shine brightly with only young stars. Spitzer infrared detection indicated that the galaxy was made up of surprisingly old and relatively faint stars. This tells us that the galaxy was made up of stars already nearly 750 million years old - pushing back the epoch of its formation to about 200 million years after the Big Bang, much further than anyone had expected.

 

Galaxies collide too. It is not a secret that Milky Way and Andromeda are on collision path, but it will happen in far future (far when measured in human life duration). Even then, this is not a collision like 2 trains colliding as galaxies have plenty of empty space inside so hard collisions or explosions as one would expect. But sometimes cluster of galaxies collide too. And here is the picture which shows how it looks like:

 

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Picture shows collision on a massive scale: not just two galaxies, but two clusters of galaxies slamming into each other, forming this object, called Abell 2052. The total mass of this combined cluster is almost beyond imagining: something like a quadrillion times the mass of the Sun - 1000000000000000 Suns! Note that our galaxy has about a hundred billion stars in it, so Abell 2052 is about 10000 more massive. Something that big has a lot of gravity, and that’s the key to what happened here. As the clusters approached each other prior to the collision, gas in one cluster was drawn off and headed toward the other. Once the clusters passed, the gas got whipped around by gravity, reversing direction, and essentially, well, sloshed. The analogy the astronomers used was wine in a wineglass as you swirl it; if you suddenly whip the glass a bit faster the wine will slosh up the side in a wave. What about long blue curved streamer? That’s the wave: extraordinarily hot gas (30 million degrees C!) that got sloshed around by the cluster’s gravity. The scale of it is simply epic; that streamer is over a million light years long! Again, for comparison, the Milky Way is 100000 light years across, 1/10th as big as that wave. Travis Rector is the man who takes incredible pictures - click here to see his amazing work. Meanwhile, enjoy one such collision picture of his below.

 

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Of course, only hi-tech equipment by our ground and space telescopes can catch those collisions far far away. The Hercules galaxy cluster (also known as Abell 2151) lies about 500 million light-years away in the constellation of Hercules. It is unlike other nearby galactic assemblies in many ways. As well as being rather irregular in shape, it contains a wide variety of galaxy types, particularly young, star-forming spiral galaxies, and there are no giant elliptical galaxies in sight. The new image was taken with the VST, the most recent addition to ESO's Paranal Observatory in Chile. The VST is a survey telescope equipped with OmegaCAM, a 268-megapixel camera that provides images covering very large areas on the sky. Normally only small telescopes can image large objects such as this in a single shot, but the 2.6-metre VST not only has a wide field, but can also exploit the superb conditions on Paranal to simultaneously obtain very sharp and deep images quickly. Galaxy pairs getting up close and personal and on their way to merging into single, larger galaxies can be seen all over this image. The numerous interactions, and the large number of gas-rich, star-forming spiral galaxies in the cluster, make the members of the Hercules cluster look like the young galaxies of the more distant Universe. Because of this similarity, astronomers believe that the Hercules galaxy cluster is a relatively young cluster. It is a vibrant and dynamic swarm of galaxies that will one day mature into one more similar to the older galaxy clusters that are more typical of our galactic neighbourhood.

 

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Galaxy clusters are formed when smaller groups of galaxies come together due to the pull of their gravity. As these groups get closer to each other, the cluster becomes more compact and more spherical in shape. At the same time, the galaxies themselves get closer together and many start to interact. Even if spiral galaxies are dominant in the initial groups, the galactic collisions eventually distort their spiral structure and strip off their gas and dust, quenching most star formation. For this reason, most of the galaxies in a mature cluster are elliptical or irregular in shape. One or two large elliptical galaxies, formed from the merger of smaller galaxies and permeated by old stars, usually reside at the centres of these old clusters.

 

This beautiful image shows not only the galaxies of the Hercules galaxy cluster, but also many faint and fuzzy objects in the background, which are galaxies that are much further away from us. The Hercules galaxy cluster is believed to be a collection of at least three small clusters and groups of galaxies that are currently being assembled into a larger structure. Furthermore, the cluster itself is merging with other large clusters to form a galaxy supercluster. These giant collections of clusters are some of the largest structures in the Universe. The wide field of view and image quality of OmegaCAM on the VST make it ideal for studying the outskirts of galaxy clusters where the poorly-understood interactions between clusters are taking place.

 

Galaxies like our own are believed to form over billions of years through the merging of many smaller galaxies. So it's expected that there should be many smaller dwarf galaxies buzzing around the Milky Way. However, very few of these tiny relic galaxies have been observed which has led astronomers to conclude that many of them must have very few stars or possibly may be made almost exclusively of dark matter. Scientists theorize the existence of dark matter to explain observations that suggest there is far more mass in the universe than can be seen. However, because the particles that make up dark matter do not absorb or emit light, they have so far proven impossible to detect and identify. Computer modeling suggests that the Milky Way should have about 10000 satellite dwarf galaxies, but only 30 have been observed. Scientists have long struggled to detect the dim dwarf galaxies that orbit our own galaxy. So it came as a surprise on Jan. 18 when a team of astronomers using Keck II telescope's adaptive optics has announced the discovery of a dwarf galaxy halfway across the universe.

 

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Picture above shows gravitational lens B1938+666 (supermassive elliptical galaxy) as seen in the infrared when observed with the 10-meter Keck II telescope with Adaptive Optics on Mauna Kea, Hawaii. A so-called gravitational lens is produced when space is warped by a massive foreground object, whether it is the Sun, a black hole, or an entire cluster of galaxies. The light from more-distant background objects is distorted, brightened, and magnified as it passes through this gravitationally disturbed region. In the center is a massive red galaxy 9.8 billion light-years from Earth that acts like a cosmic magnifying glass, distorting the light from an even more distant galaxy. The result is a spectacular Einstein ring image of the background galaxy. The presence of the lens helps show how galaxies evolved from 10 billion years ago to today. While nearby galaxies are fully mature and are at the tail end of their star-formation histories, distant galaxies tell us about the universe's formative years. The light from those early events is just now arriving at Earth. Very distant galaxies are not only faint but also appear small on the sky. Astronomers would like to see how star formation progressed deep within these galaxies. Such details would be beyond the reach of Hubble's vision were it not for the magnification made possible by gravity in the intervening lens region.

 

Globular star clusters have a remarkable characteristic: the typical number of stars they contain appears to be about the same throughout the Universe. This is in contrast to much younger stellar clusters, which can contain almost any number of stars, from fewer than 100 to many thousands. The team of scientists proposed that this difference can be explained by the conditions under which globular clusters formed early on in the evolution of their host galaxies. The researchers ran simulations of isolated and colliding galaxies, in which they included a model for the formation and destruction of stellar clusters. When galaxies collide, they often generate spectacular bursts of star formation (“starbursts”) and a wealth of bright, young stellar clusters of many different sizes. As a result it was always thought that the total number of star clusters increases during starbursts. But the team found the opposite result in their simulations. While the very brightest and largest clusters were indeed capable of surviving the galaxy collision due to their own gravitational attraction, the numerous smaller clusters were effectively destroyed by the rapidly changing gravitational forces that typically occur during starbursts due to the movement of gas, dust and stars. The wave of starbursts came to an end after about 2 billion years and the researchers were surprised to see that only clusters with high numbers of stars had survived. These clusters had all the characteristics that should be expected for a young population of globular clusters as they would have looked about 11 billion years ago.

 

bb91.jpgIt is ironic to see that starbursts may produce many young stellar clusters, but at the same time also destroy the majority of them. This occurs not only in galaxy collisions, but should be expected in any starburst environment. In the early Universe, starbursts were commonplace - it therefore makes perfect sense that all globular clusters have approximately the same large number of stars. Their smaller brothers and sisters that didn’t contain as many stars were doomed to be destroyed. According to the simulations, most of the star clusters were destroyed shortly after their formation, when the galactic environment was still very hostile to the young clusters. After this episode ended, the surviving globular clusters have lived quietly until the present day. The researchers have further suggestions to test their ideas - in the nearby Universe, there are several examples of galaxies that have recently undergone large bursts of star formation. It should therefore be possible to see the rapid destruction of small stellar clusters in action. If this is indeed found by new observations, it will confirm our theory for the origin of globular clusters.

 

The simulations suggest that most of a globular cluster’s traits were established when it formed. The fact that globular clusters are comparable everywhere then indicates that the environments in which they formed were very similar, regardless of the galaxy they currently reside in. In that case they can be used as fossils to shed more light on the conditions in which the first stars and galaxies were born. Two biggest globular clusters up to date are Omega Centauri (below left) and M54 (below right).

 

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Every day we learn something new about the Universe and galaxies itself. Sometimes we confirm our theories, but sometimes we find data which suggests we need to add more parameters to the story as otherwise our theories would be incomplete. For example, observations of dwarf galaxy I Zw 18 recently brought some question marks above many heads. Research led to the conclusion that this enigmatic blue compact dwarf might force astronomers to review current galaxy formation models.

 

I Zw 18 is one of the most studied dwarf galaxies, because among those that have strong star forming activity, it's one of the poorest in heavy elements. Besides, it's proximity to Earth, combined with a total exposure time of nearly 3 days, gave the researchers data with unprecedented resolution and sensitivity. Analysis of these data revealed an extended gas halo surrounding this galaxy, 16 times larger than the star component of the galaxy, and without any stars. This halo is the result of huge amounts of energy generated by the starburst this galaxy is going through. This energy heats and disturbs I Zw 18's cold gas, which ends up emitting an amount of light comparable to what's being emitted by the stellar component. This emission is designated nebular emission. This is ground-breaking work because it provides the first observational proof that, in the early Universe, young galaxies that underwent starbursts must have been surrounded by a huge halo of nebular emission. This extended nebular halo results from the cumulative energetic output from thousands of massive stars exploding as supernovae, shortly after their formation.bb92.jpg

 

So far, in distant galaxies where it's not possible to reach resolutions high enough in order to distinguish between nebular and star emission, it was assumed that the gas occupied the same region as the stars and stars were responsible for emitting most of the light. This study showed that galaxies undergoing starbursts, similar to I Zw 18, might not obey this rule. This result might lead to substantial corrections in a lot of the work being developed in cosmology and extragalactic astronomy. An example is the estimate of star mass in a galaxy, which is calculated from the galaxies total luminosity. But, as these results shows, up to 50% of that luminosity might originate in nebular, and not star, emission. Another result from this research shows that the distribution of nebular emission might be misinterpreted as a stellar disk. These galaxies, still in early stages of formation, might thus be wrongly classified as fully formed galaxies (such as spirals or ellipticals), a classification mistake that might have happened in many past studies to determine galaxy evolution in the early Universe. These results are also of importance for our understanding of galaxy formation, because the team concluded that I Zw 18 is extremely young, with most stars younger than 1 billion years. So this galaxy is currently undergoing the dominant phase of its formation, much like the ones formed shortly after the Big Bang.

 

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Stars and their planets are born when giant clouds of interstellar gas and dust collapse. You've probably seen the resulting stellar nurseries in beautiful astronomical images - colorful nebulae. Astronomers know quite a bit about these so-called molecular clouds; they consist mainly of hydrogen molecules - unusual in a cosmos where conditions are rarely right for hydrogen atoms to bond together into molecules. And if one traces the distribution of clouds in a spiral galaxy like our own Milky Way galaxy, one finds that they are lined up along the spiral arms.

 

But how do those clouds come into being? What makes matter congregate in regions a hundred or even a thousand times more dense than the surrounding interstellar gas? One candidate mechanism involves the galaxy's magnetic fields. Everyone who has seen a magnet act on iron filings in the classic classroom experiment knows that magnetic fields can be used to impose order. Some researchers have argued that something similar goes on in the case of molecular clouds: that galaxies' magnetic fields guide and direct the condensation of interstellar matter to form denser clouds and facilitate their further collapse. Some astronomer see this as the key mechanism enabling star formation. Others contend that the cloud matter's gravitational attraction and turbulent motion of gas within the cloud are so strong as to cancel any influence of an outside magnetic field. If we were to restrict attention to our own galaxy, it would be difficult to find out who is right. We would need to see our galaxy's disk from above to make the appropriate measurements; in reality, our Solar System sits within the galactic disk.

 

That is why Hua-bai Li and Thomas Henning (Max Planck Institute for Astronomy) chose a different target: the Triangulum galaxy, 3 million light-years from Earth and also known as M 33, which is oriented in just the right way - see picture above. Using a telescope known as the Submillimeter Array (SMA), which is located at Mauna Kea Observatory, they measured specific properties of radiation received from different regions of the galaxy which are correlated with the orientation of these region's magnetic fields. They found that the magnetic fields associated with the galaxy's six most massive giant molecular clouds were orderly, and well aligned with the galaxy's spiral arms. If turbulence played a more important role in these clouds than the ordering influence of the galaxy's magnetic field, the magnetic field associated with the cloud would be random and disordered. These observations are a strong indication that magnetic fields indeed play an important role when it comes to the formation of dense molecular clouds - and to setting the stage for the birth of stars and planetary systems like our own.

 

2 months ago it has been announced scientists have used a laser to create magnetic fields similar to those thought to be involved in the formation of the first galaxies. Magnetic fields exist throughout galactic and intergalactic space, what is puzzling is how they were originally created and how they became so strong. A team, led by Oxford University physicists, used a high-power laser to explode a rod of carbon, similar to pencil lead, in helium gas. The explosion was designed to mimic the cauldron of plasma - an ionized gas containing free electrons and positive ions - out of which the first galaxies formed.

 

 

The team found that within a microsecond of the explosion strong electron currents and magnetic fields formed around a shock wave. Astrophysicists took these results and scaled them through 22 orders-of-magnitude to find that their measurements matched the "magnetic seeds" predicted by theoretical studies of galaxy formation.

 

This experiment recreates what was happening in the early Universe and shows how galactic magnetic fields might have first appeared. It opens up the exciting prospect that we will be able to explore the physics of the cosmos, stretching back billions of years, in a laser laboratory here on Earth.

 

The results closely match theories which predict that tiny magnetic fields -"magnetic seeds" - precede the formation of galaxies. These fields can be amplified by turbulent motions and can strongly affect the evolution of the galactic medium from its early stages.

 

 

Composite image: the left side is a laser-produced shock wave whilst the right is a simulation of a collapsing shock wave arising during the pre-galactic phase.

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Our galaxy, as you might know, is called Milky Way. The name didn't came after chocolate, but rather its appearance as a dim "milky" glowing band arching across the night sky, in which the naked eye cannot distinguish individual stars. The Milky Way is a barred spiral galaxy 100000 - 120000 light-years in diameter containing 200-400 billion stars. The Galaxy is estimated to contain at least as many planets, 10 billion of which could be located in the habitable zone of their parent star. The rotational rate of the Galaxy is once every 15 to 50 million years. The Galaxy is also moving at a velocity of 552 to 630 km per second, depending on the relative frame of reference. It is estimated to be about 13.2 billion years old, nearly as old as the Universe.

 

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The first series of astronomical observations with GREAT (German Receiver for Astronomy at Terahertz Frequencies) on board of SOFIA (Stratospheric Observatory for Infrared Astronomy) were successfully completed in November 2011. Now, six months later, the scientific results have been published in a special issue of the European journal Astronomy & Astrophysics. As a joint project between NASA and the German Aerospace Center, SOFIA operates a 2.7-m telescope in a modified Boeing 747SP aircraft and is the world's largest ever airborne infrared observatory. SOFIA flies at altitudes as high as 13700 meters to provide access to astronomical signals at far-infrared wavelengths that would otherwise be blocked due to absorption by water vapour in the atmosphere. The SOFIA observatory and the GREAT instrument open the far-infrared skies for high-resolution spectroscopy, and GREAT pushes its technology to higher frequencies and sensitivities than ever reached before. Many of the contributed papers study the star formation process in its earliest phases, first when the protostellar molecular cloud is contracting and condensing, and then when the embryonic star is vigorously interacting with its surrounding parental molecular cloud -tearing it apart and ionizing it. The high spectral resolution capabilities of GREAT enabled scientists to resolve the velocity field of gas in the parental molecular clouds traced by the important cooling line radiation of ionized carbon in several star forming regions.

 

GREAT detected the velocity signature of infalling gas motion ("collapse") in the envelopes of three protostars, directly probing the dynamics of a forming star. Two interstellar molecular species were detected for the first time ever: OD, an isotopic substitute of hydroxyl (OH) with the hydrogen atom replaced by the heavier deuterium, and the mercapto radical SH. Observations of the ground-state transition of OH at a frequency of 2.5 Terahertz (120 microns wavelength) explored new astrochemical territories while pushing the technological frontier.

 

bb106.jpgThe remnant envelope of an evolved star, ionized by its hot stellar core, was also investigated as was the violent shock interaction of a supernova remnant and the surrounding interstellar medium. Furthermore, the circumnuclear accretion disk, ultimately feeding the black hole in the centre of the Milky Way galaxy was studied, as well as star formation in the circumnuclear region of the nearby galaxy IC342. The rich harvest of scientific results from this first observing campaign with SOFIA and the GREAT instrument gives a first glimpse of the tremendous scientific potential of this observatory and promises unique astronomical observations for years to come, particularly in the topical research areas of star formation and astrochemistry. The high resolving power of the GREAT spectrometer is designed for studies of interstellar gas and the stellar life cycle, from a protostar's early embryonic phase when still embedded in its parental cloud to an evolved star's death when the stellar envelope is ejected back into space. This stunning collection of first scientific results is reward for the many years of development work, and underlines the huge scientific potential of airborne far-infrared spectroscopy.

 

Galaxies are the birthplaces of stars, each with a dense, visible central core and a huge envelope, or halo, around it containing extremely low-density gases. Until now, most of the mass in the envelope, as much as 90 percent of all mass in a galaxy, was undetectable by any instrument on Earth. But Hubble's sensitive new Cosmic Origins Spectrograph (COS), the only one of its kind, has dramatically improved the quality of information regarding the gaseous envelope of galaxies. This huge gain in precision is one of the enormous accomplishments of the COS mission. In particular, data on the chemical composition and temperature in the gas clouds allow the astronomers to calculate a galaxy's halo mass and how the gaseous envelope regulates the galaxy's evolution. Another overall mission focus is to explore how galaxies gather mass for making stars.

 

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The illustration above shows how quasistellar object (QSO) absorption lines are used to study the vast (and effectively invisible) gaseous halos of galaxies. When the light from a distant QSO passes through the gas surrounding a foreground galaxy (schematically indicated with a red dashed circle), some of the colors of the QSO light are absorbed by the foreground material. Consequently, the Hubble Space Telescope observes that some of the colors are “missing". By studying the absorbed colors, astronomers can determine many things about the gaseous halo, such as composition, temperature, density and mass. This technique has revealed that the gaseous halos of galaxies as much larger and more massive than the distribution of stars within the galaxy. These large halos are produced by “winds” of matter rapidly moving away from the galaxies.

 

Unlike humans, galaxies learned to "go green" early in the history of the universe, continuously recycling immense volumes of hydrogen gas and heavy elements to build successive generations of stars stretching over billions of years. This ongoing recycling keeps galaxies from emptying their "fuel tanks" and therefore stretches out their star-forming epoch to over 10 billion years. However, galaxies that ignite a rapid firestorm of star birth can blow away their remaining fuel, essentially turning off further star-birth activity. This conclusion is based on a series of Hubble Space Telescope observations that flexed the special capabilities of its comparatively new COS to detect otherwise invisible mass in the halo of our Milky Way and a sample of more than 40 other galaxies. The color and shape of a galaxy is largely controlled by gas flowing through an extended halo around it. All modern simulations of galaxy formation find that they cannot explain the observed properties of galaxies without modeling the complex accretion and "feedback" processes by which galaxies acquire gas and then later expel it after processing by stars. The three studies investigated different aspects of the gas-recycling phenomenon. Results confirm a theoretical suspicion that galaxies expel and can recycle their gas, but they also present a fresh challenge to theoretical models to understand these gas flows and integrate them with the overall picture of galaxy formation.

 

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Large mass of clouds is falling through the giant corona halo of our Milky Way, fueling its ongoing star formation. These clouds of ionized hydrogen reside within 20000 light-years of the Milky Way disk and contain enough material to make 100 million suns. Some of this gas is recycled material that is continually being replenished by star formation and the explosive energy of novae and supernovae, which kicks chemically enriched gas back into the halo; the remainder is gas being accreted for the first time. The infalling gas from this vast reservoir fuels the Milky Way with the equivalent of about a solar mass per year, which is comparable to the rate at which our galaxy makes stars. At this rate the Milky Way will continue making stars for another billion years by recycling gas into the halo and back onto the galaxy. We now know where is the missing fuel for galactic star formation. The surprise was discovering how much mass in heavy elements is far outside a galaxy. Scientists measured 10 million solar masses of oxygen in a galaxy's halo, which corresponds to about 1 billion solar masses of gas - as much as in the entire interstellar medium between stars in a galaxy's disk. They also found that this gas is nearly absent from galaxies that have stopped forming stars. This is evidence that widespread outflows, rather than accretion, determine a galaxy's fate.  Because so much of the heavy elements has been ejected into the halos instead of sticking around in the galaxies, the formation of planets, life, and other things requiring heavy elements could have been delayed in such galaxies.

 

For the end, something to impress. Using the VISTA telescope in Chile and the UKIRT telescope in Hawaii, astronomers have made an incredibly detailed map of the sky in infrared. This map will help understand our own galaxy, more distant galaxies, quasars, nebulae, and much more. To understand meaining of "detailness", consider following and try not to be impressed - you will fail. The story starts with a section of the survey they made, showing the star-forming region G305, an enormous cloud of gas about 12000 light years away which is busily birthing tens of thousands of stars.

 

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In this picture we have 10000 stars!

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Picture on left is just tiny part of much bigger picture.

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And above right is again tiny part of another bigger picture.

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This again, shows how picture on left is tint part of what would be now final picture. How big it is? Very big! If you really wish to see it in real life size, click here. But be warned: it is 20000 x 2000 pixels.  And that's not much since original picture from survey is 150 billion pixels. Just stop thinking about it - it is number hard to grasp anyway. If you have modern camera, your pictures are, given that you have one of those latest modern sensors, 24MP or 36MP. This is waaay more.

 

And if you would like to see final picture as something normally watchable, but with option to zoom in just like Google Maps - no worry - this is possible. Indeed, you can click here and get original shaped image with option to zoom in and explore. There are over a billion stars in the original image. It’s one of the most comprehensive surveys of the sky ever made, and yet it still only scratches the surface. This survey only covers the part of the sky where the Milky Way galaxy itself is thickest - in the bottom image above you can see the edge-on disk of our galaxy plainly stretching across the entire shot - and that’s only a fraction of the entire sky. Think on this: there are a billion stars in that image alone, but that’s less than 1% of the total number of stars in our galaxy. As deep and broad as this amazing picture is, it’s a tiny slice of our local Universe.

 

Many of the world's leading physicists believe we are entering  a "golden age" of cosmological discoveries. Astronomers working on the WMAP mission stunned the scientific community with their announcement that the first generation stars in the universe were surprisingly born just after 200 million years of the Big Bang birth of the cosmos. The age of the universe has been steadily pushed backwards in time, from 2 billion year to 8 billion after it was determined the Earth was 4.6 billion years in age, and now the estimates are 13.75 billion years. The James Webb Space Telescope (JWST), successor to the HST with ten times the light-gathering power due to be launched in 2018, may well detect ever more distant galaxies. Likewise, the ultra-high resolution radio telescopes such as Atacama Large Millimeter Array (ALMA) in Chile which is to become fully operational by the end of 2012, will be peering still deeper into the universe, and probably pushing the hypothetical Big Bang further backward in time as ever more distant galaxies are detected.

 

 

Credits: NASA, Wikipedia, Casey Kazan, National Center for Supercomputer Applications, Andrey Kravtsov, Anatoly Klypin, Andrey Kravtsov, ESO, Phil Plait, VLT, W. M. Keck Observatory, Space Telescope Science Institute, Royal Astronomical Society, Astronomy & Astrophysics magazine, Travis Rector, Carnegie Institution, Max Planck Institute for Astronomy, arXiv, University of Oxford, University of Stuttgart, Mike Read