Representation of the timeline of the universe over 13.7 billion years, and the expansion in the universe that followed. Credit: NASA/WMAP Science Team.
Remnants of the first stars have helped astronomers get closer to unlocking the “dark ages” of the cosmos. A team of researchers from the University of Cambridge and California Institute of Technology are using light emitted from massive black holes called quasars to “light up” gases released by the early stars, which exploded billions of years ago. As a result, they have found what they refer to as the missing link in the evolution of the chemical universe.
The first stars are believed to hold the key to one of the mysteries of the early cosmos: how it evolved from being predominantly filled with hydrogen and helium to a universe rich in heavier elements, such as oxygen, carbon and iron.
However, although telescopes can detect light reaching Earth from billions of light-years away, enabling astronomers to look back in time over almost all of the 13.7-billion-year history of the universe, one observational frontier remains: the so-called “dark ages.” This period, lasting half a billion years after the Big Bang, ended when the first stars were born and is inaccessible to telescopes because the clouds of gas that filled the universe were not transparent to visible and infrared light.
“We have effectively been able to peer into the dark ages using the light emitted from a quasar in a distant galaxy billions of years ago. The light provides a backdrop against which any gas cloud in its path can be measured,” said Professor Max Pettini at Cambridge’s Institute of Astronomy (IoA), who led the research with PhD student Ryan Cooke.
Taking precision measurements using the world’s largest telescopes in Hawaii and Chile, the researchers have used Quasar Absorption Line Spectroscopy to identify gas clouds called ‘damped Lyman alpha systems’ (DLAs). Among the thousands of DLAs known, the team have succeeded in finding a rare cloud released from a star very early in the history of the universe.
“As judged by its composition, the gas is a remnant of a star that exploded as much as 13 billion years ago,” Pettini explained. “It provides the first analysis of the interior of one of the universe’s earliest stars.”
The results provide experimental observations of a time that has so far been possible to model only with computers simulations, and will help astronomers to fill gaps in understanding how the chemical universe evolved.
“We discovered tiny amounts of elements present in the cloud in proportions that are very different from their relative proportions in normal stars today. Most significantly, the ratio of carbon to iron is 35 times greater than measured in the Sun,” Pettini said. “The composition enables us to infer that the gas was released by a star 25 times more massive than the Sun and originally consisting of only hydrogen and helium. In effect this is a fossil record that provides us with a missing link back to the early universe.”
The study was published in Monthly Notices of the Royal Astronomical Society by Ryan Cooke, Max Pettini and Regina Jorgenson at the IoA, together with Charles Steidel and Gwen Rudie at the California Institute of Technology in Pasadena.
Anyhow, this prompted me to look up different ways in which apparent superluminal motion might be generated, partly to reassure myself that the bottom hadn’t fallen out of relativity physics and partly to see if these things could be adequately explained in plain English. Here goes…
1) Cause and effect illusions
The faster than light pulsar story is essentially about hypothetical light booms – which are a bit like a sonic booms, where it’s not the sonic boom, but the sound source, that exceeds the speed of sound – so that individual sound pulses merge to form a single shock wave moving at the speed of sound.
Now, whether anything like this really happens with light from pulsars remains a point of debate, but one of the model’s proponents has demonstrated the effect in a laboratory – see this Scientific American blog post.
What you do is to arrange a line of light bulbs which are independently triggered. It’s easy enough to make them fire off in sequence – first 1, then 2, then 3 etc – and you can keep reducing the time delay between each one firing until you have a situation where bulb 2 fires off after bulb 1 in less time than light would need to travel the distance between bulbs 1 and 2. It’s just a trick really – there is no causal connection between the bulbs firing – but it looks as though a sequence of actions (first 1, then 2, then 3 etc) moved faster than light across the row of bulbs. This illusion is an example of apparent superluminal motion.
There are a range of possible scenarios as to why a superluminal Mexican wave of synchrotron radiation might emanate from different point sources around a rapidly rotating neutron star within an intense magnetic field. As long as the emanations from these point sources are not causally connected, this outcome does not violate relativity physics.
2) Making light faster than light
You can produce an apparent superluminal motion of light itself by manipulating its wavelength. If we consider a photon as a wave packet, that wave packet can be stretched linearly so that the leading edge of the wave arrives at its destination faster, since it is pushed ahead of the remainder of the wave – meaning that it travels faster than light.
However, the physical nature of ‘the leading edge of a wave packet’ is not clear. The whole wave packet is equivalent to one photon – and the leading edge of the stretched out wave packet cannot carry any significant information. Indeed, by being stretched out and attenuated, it may become indistinguishable from background noise.
Also this trick requires the light to be moving through a refractive medium, not a vacuum. If you are keen on the technical details, you can make phase velocity or group velocity faster than c (the speed of light in a vacuum) – but not signal velocity. In any case, since information (or the photon as a complete unit) is not moving faster than light, relativity physics is not violated.
3) Getting a kick out of gain media
You can mimic more dramatic superluminal motion through a gain medium where the leading edge of a light pulse stimulates the emission of a new pulse at the far end of the gain medium – as though a light pulse hits one end of a Newton’s Cradle and new pulse is projected out from the other end. If you want to see a laboratory set-up, try here. Although light appears to jump the gap superluminally, in fact it’s a new light pulse emerging at the other end – and still just moving at standard light speed.
Light faster than light. Left: Stretching the waveform of light can make the leading edge of the wave seem to move faster than light. Right: Gain media can act like a Newton's Cradle, making light seem to jump the gap superluminally.
4) The relativistic jet illusion
If an active galaxy, like M87, is pushing out a jet of superheated plasma moving at close to the speed of light – and the jet is roughly aligned with your line of sight from Earth – you can be fooled into thinking its contents are moving faster than light.
If that jet is 5,000 light years long, it should take at least 5,000 years for anything in it to cross that distance of 5,000 light years. A photon emitted by a particle of jet material at point A near the start of the jet really will take 5,000 years to reach you. But meanwhile, the particle of jet material continues moving towards you nearly as fast as that photon. So when the particle emits another photon at point B, a point near the tip of the jet – that second photon will reach your eye in much less than 5,000 years after the first photon, from point A. This will give you the impression that the particle crossed 5,000 light years from points A to B in much less than 5,000 years. But it is just an optical illusion – relativity physics remains unsullied.
5) Unknowable superluminal motion
It is entirely possible that objects beyond the horizon of the observable universe are moving away from our position faster than the speed of light – as a consequence of the universe’s cumulative expansion, which makes distant galaxies appear to move away faster than close galaxies. But since light from hypothetical objects beyond the observable horizon will never reach Earth, their existence is unknowable by direct observation from Earth – and does not represent a violation of relativity physics.
And lastly, not so much unknowable as theoretical is the notion of early cosmic inflation, which also involves an expansion of space-time rather than movement within space-time – so no violation there either.
Other stuff…
I’m not sure that the above is an exhaustive list and I have deliberately left out other theoretical proposals such as quantum entanglement and the Alcubierre warp drive. Either of these, if real, would arguably violate relativity physics – so perhaps need to be considered with a higher level of skepticism.
The signatures of a bubble collision at various stages in our analysis pipeline. A collision (top left) induces a temperature modulation in the CMB temperature map (top right). The "blob" associated with the collision is identi ed by a large needlet response (bottom left), and the presence of an edge is determined by a large response from the edge detection algorithm (bottom right). (Feeny, et al.)
In the realm of far out ideas in science, the notion of a multiverse is one of the stranger ones. Astronomers and physicists have considered the possibility that our universe may be one of many. The implications of this are somewhat more fuzzy. Nothing in physics prevents the possibilities of outside universes, but neither has it helped to constrain them, leaving scientists free to talk of branes and bubbles. Many of these ideas have been considered untestable, but a paper uploaded to arXiv last month considers the effects of two universes colliding and searches for fingerprints of such a collision of our own universe. Surprisingly, the team reports that they may have detected not one, but four collisional imprints.
The foamy cosmic web – at this scale we run out of superlatives to describe the large scale structure of the universe.
[/caption]
The so-called End of Greatness is where you give up trying to find more superlatives to describe large scale objects in the universe. Currently the Sloan Great Wall – a roughly organised collection of galactic superclusters partitioning one great void from another great void – is about where most cosmologists draw the line.
Beyond the End of Greatness, it’s best just to consider the universe as a holistic entity – and at this scale we consider it isotropic and homogenous, which we need to do to make our current cosmology math work. But at the very edge of greatness, we find the cosmic web.
The cosmic web is not a thing we can directly observe since its 3d structure is derived from red shift data to indicate the relative distance of galaxies, as well as their apparent position in the sky. When you pull all this together, the resulting 3d structure seems like a complex web of galactic cluster filaments interconnecting at supercluster nodes and interspersed by huge voids. These voids are bubble-like – so that we talk about structures like the Sloan Great Wall, as being the outer surface of such a bubble. And we also talk about the whole cosmic web being ‘foamy’.
It is speculated that the great voids or bubbles, around which the cosmic web seems to be organised, formed out of tiny dips in the primordial energy density (which can be seen in the cosmic microwave background), although a convincing correlation remains to be demonstrated.
The two degree field (2df) galaxy redshift survey – which used an instrument with a field of view of two degrees, although the survey covered 1500 square degrees of sky in two directions. The wedge shape results from the 3d nature of the data - where there are more galaxies the farther out you look, within one region of the sky. The foamy bubbles of the cosmic web are visible. Credit: The Australian Astronomical Observatory.
As is well recorded, the Andromeda Galaxy is probably on a collision course with the Milky Way and they may collide in about 4.5 billion years. So, not every galaxy in the universe is rushing away from every other galaxy in the universe – it’s just a general tendency. Each galaxy has its own proper motion in space-time, which it is likely to continue to follow despite the underlying expansion of the universe.
It may be that much of the growing separation between galaxies is a result of expansion of the void bubbles, rather than equal expansion everywhere. It’s as though once gravity loses its grip between distant structures – expansion (or dark energy, if you like) takes over and that gap begins to expand unchecked – while elsewhere, clusters and superclusters of galaxies still manage to hold together. This scenario remains consistent with Edwin Hubble’s finding that the large majority of galaxies are rushing away from us, even if they are not all equally rushing away from each other.
van de Weygaert et al are investigating the cosmic web from the perspective of topology – a branch of geometry which looks at spatial properties which are preserved in objects undergoing deformation. This approach seems ideal to model the evolving large scale structure of an expanding universe.
The paper below represents an early step in this work, but shows that a cosmic web structure can be loosely modelled by assuming that all data points (i.e. galaxies) move outwards from the central point of the void they lie most proximal to. This rule creates alpha shapes, which are generalised surfaces that can be built over data points – and the outcome is a mathematically modelled foamy-looking cosmic web.
WMAP data of the Cosmic Microwave Background. Credit: NASA
[/caption]
Have scientists seen evidence of time before the Big Bang, and perhaps a verification of the idea of the cyclical universe? One of the great physicists of our time, Roger Penrose from the University of Oxford, has published a new paper saying that the circular patterns seen in the WMAP mission data on the Cosmic Microwave Background suggest that space and time perhaps did not originate at the Big Bang but that our universe continually cycles through a series of “aeons,” and we have an eternal, cyclical cosmos. His paper also refutes the idea of inflation, a widely accepted theory of a period of very rapid expansion immediately following the Big Bang.
Penrose says that inflation cannot account for the very low entropy state in which the universe was thought to have been created. He and his co-author do not believe that space and time came into existence at the moment of the Big Bang, but instead, that event was just one in a series of many. Each “Big Bang” marked the start of a new aeon, and our universe is just one of many in a cyclical Universe, starting a new universe in place of the one before.
Penrose’s co-author, Vahe Gurzadyan of the Yerevan Physics Institute in Armenia, analyzed seven years’ worth of microwave data from WMAP, as well as data from the BOOMERanG balloon experiment in Antarctica. Penrose and Gurzadyan say they have identified regions in the microwave sky where there are concentric circles showing the radiation’s temperature is markedly smaller than elsewhere.
These circles allow us to “see through” the Big Bang into the aeon that would have existed beforehand. The circles were created when black holes “encountered” or collided with a previous aeon.
“Black-hole encounters, within bound galactic clusters in that previous aeon, would have the observable effect, in our CMB sky,” the duo write in their paper, “of families of concentric circles over which the temperature variance is anomalously low.”
And these circles don’t jive with the idea of inflation, because inflation proposes that the distribution of temperature variations across the sky should be Gaussian, or random, rather than having discernable structures within it.
Penrose’s new theory even projects how the distant future might emerge, where things will again be similar to the beginnings of the Universe at the Big Bang where the Universe was smooth, as opposed to the current jagged form. This continuity of shape, he maintains, will allow a transition from the end of the current aeon, when the universe will have expanded to become infinitely large, to the start of the next, when it once again becomes infinitesimally small and explodes outwards from the next big bang.
Penrose and Gurzadyan say that the entropy at the transition stage will be very low, because black holes, which destroy all information that they suck in, evaporate as the universe expands and in so doing remove entropy from the universe.
“These observational predictions of (Conformal cyclic cosmology) CCC would not be easily explained within standard inflationary cosmology,” they write in their paper.
Ancient woodcarving of where heaven and earth meet. Credit: Heikenwaelder Hugo at Wikimedia Commons.
Cosmology is a fairly young science, one which attempts to reconstruct the history of our Universe from billions of years ago. Looking back so far in time is extremely difficult, and adding to the complexity is that many of the pillars upon which the theories of cosmology rest have only been conceived within the last 20 years or so. That hasn’t given scientists and theorists much time to fully flesh out and comprehend the situation, and cosmologist Michael Turner says either some important new physics will have to be discovered or we’re going to find a fatal flaw in our prevailing view of the Universe.
So, what will it take to push cosmology over the edge, where it goes fully from theory to science, and we have at least a grasp of cosmological understanding? I had the chance to ask that question to Turner at last week’s National Association of Science Writers conference. Turner, who coined the term “dark energy,” is the Director of the Kavli Institute for Cosmological Physics at the University of Chicago. Here are his top four wishes for discoveries in cosmology:
Wish # 1: Figure out the nature of dark matter.
“I think we’re very close to solving this dark matter problem and I think its going to be stunning when it sinks in to everyone that most of the stuff in the Universe is made of something other than what we are,” Turner said.
Dark matter holds universe together, according to cosmologists. But since it does not emit electromagnetic radiation and we can’t see it, how do we know it is there? “It is needed to hold galaxies together, it is needed to hold clusters together, it is that simple,” Turner said. “There is not enough gravity in all the stars put together to hold clusters together.”
Turner has likened dark matter to an outdoor tree decorated with Christmas lights. From far away, all that can be seen are the lights, but it is the unseen tree that holds the lights where they are and gives them their shape. More poetically Turner said, “The universe is a web of dark matter that is decorated by stars.”
Turner made a bold prediction: “The 2010 is the decade of dark matter – we are going to finish this thing off.”
Dark matter in the Bullet Cluster. Otherwise invisible to telescopic views, the dark matter was mapped by observations of gravitational lensing of background galaxies. Credit: X-ray: NASA/CXC/CfA/ M.Markevitch et al.; Lensing Map: NASA/STScI; ESO WFI; Magellan/U.Arizona/ D.Clowe et al. Optical: NASA/STScI; Magellan/U.Arizona/D.Clowe et al.;
Wish # 2. Figure out the nature of dark energy.
“Dark energy may be most profound problem in cosmology today, and I’ve been wandering around for 10 years saying this,” Turner said. “If dark matter holds the Universe together, dark energy controls its destiny.”
Dark energy likely makes up 66% of the cosmos, and it’s existence has only been theorized since 1998 when astronomers realized that contrary to the prevailing notion that the expansion of the universe should be slowing down, it is actually moving faster as time goes on.
What is the current theoretical understanding of dark energy? “We don’t have a clue,” said Turner. “But let me go out here on a limb with dark energy, and say we may find it is not vacuum energy. Vacuum energy is mathematical equivalent to Einstein’s cosmological constant, and I hope we’ll figure out it is something weirder than the energy of nothing. That doesn’t solve the problem, but it would be a gift to my younger colleagues, because science is all about big questions and they need clues and something big they can sink their teeth into.”
Yes, dark energy is a big problem, but for theorists it’s a big opportunity. However, Turner has some doubts. “Dark energy is one of the big questions that will occupy the next decade, and I don’t know if we’ll be able to solve it,” he said.
Michael Turner at the 2010 National Association of Science Writers conference at Yale University. Image: Nancy Atkinson
Wish # 3: Confirming inflation with the discovery of B-Mode polarization.
Our current best theory about the earliest moments of the universe is called inflation, where during a tiny fraction of a second after the Big Bang, the Universe appears to have expanded exponentially. In particular, high precision measurements of the so-called B-modes (evidence of gravity waves) of the polarization of the cosmic microwave background radiation would be evidence of the gravitational radiation produced by inflation, and they will also show whether the energy scale of inflation predicted by the simplest models is correct.
“That is the smoking gun for inflation.” said Turner. “It explains where all the structure came from – that quantum mechanical fluctuations at the subatomic scale were blown up by this enormous expansion. That is an amazing idea, and in one equation we could figure out exactly when inflation took place. You’ll notice in all our talk of inflation no one ever tells you when it took place, because we don’t know. But those B-modes would tell us.”
Wish #4. Make the mulitiverse go away.
If there was inflation, that means there is also very likely a multitude of Universes out there.
Turner called the concept of the multiverse the 800 lb gorilla in the room.
“The dilemma is, we have evidence that inflation took place and the equations of inflation say that if it took place once, it took place twice and it’s sort of like the mouse and the cookie – if it took place twice it could have taken place an infinite number of times,” he said.
The multiverse hypothesizes multiple universes or parallel universes comprise everthing that is, not just our one “local” universe. “If there is a mulitverse structure, and if you marry this with string theory you end up with a picture of a Universe where there might be different local laws of physics and the different sub-universes might be incredibly different from each other – differences in space and time, some don’t have stable particles, many don’t have life, and so on. This is an incredibly bold idea and may even be the most important idea since Copernicus.”
But, Turner asked, how do you test it? “And if you can’t test it, therefore you can’t call it science,” he said. “So I call it the mulitiverse headache – you have this incredibly important idea, but is it science?”
“That’s where we are in cosmology,” he said. “We are the blind cosmologists feeling the Universe and each piece of data describes something. There are still big questions to be answered, and what we’re doing in cosmology is trying to put it all together, and we might actually, in the next 10-15 years put it all together. That is absolutely amazing; the universe is very big and our abilities are very primitive. But look what we’ve done so far.”
Slide from Turner's presentation showing the Universe as an elephant. Image: Nancy Atkinson
Allan Sandage. Credit: Carnegie Institution for Science.
[/caption]
Cosmologist Allan R. Sandage, who helped define the fields of observational cosmology and extragalactic astronomy, died November 13, 2010, at his home in San Gabriel, California, of pancreatic cancer. He was Edwin Hubble’s former observing assistant and one of the most prominent astronomers of the last century. Sandage was 84. Below is his biography from the Carnegie Institution for Science:
Allan Sandage became a Carnegie staff member in 1952 after serving as the observing assistant in observational cosmology to Edwin Hubble on both Mount Wilson and Palomar from 1950 to 1953, and Walter Baade’s PhD student in stellar evolution starting in 1949. Upon the death of Hubble in 1953, Sandage became responsible for developing the cosmology program using the 60- and 100-inch telescopes on Mount Wilson and with the newly commissioned Palomar 200-inch reflector. The programs centered on the recalibration of Hubble’s extragalactic distance scale and combining discoveries in stellar evolution with observational cosmology. Much of his research in the past 50 years has been directed toward these goals.
Early discoveries at Palomar showed that Hubble’s distances to galaxies were progressively incorrect, starting with Baade’s finding in 1950 that Hubble’s measured distance to the Andromeda Nebula, M31, was too small by a factor of about two. Sandage, first alone and later with G.A. Tammann professor of astronomy at the University of Basel, have carried the corrections progressively outward. This work indicates that by the time we reach the nearest cluster of galaxies in Virgo, the correction to Hubble’s scale is close to a factor of 10. Since 1988, Sandage and Tammann have led a consortium using the Hubble Space Telescope to determine distances to parent galaxies that have produced type Ia supernovae, shown earlier to be one of the best standard candles in luminosity known. From the results of the calibrations, Sandage, Tammann, and Abijit Saha of the Kitt Peak National Optical Observatory have determined at this writing (2005) the value of the Hubble constant to be 60 km s -1 Mpc -1.
Sandage’s other early research in observational stellar evolution led to a method developed in 1952 with Martin Schwarzschild of age-dating the stars from the luminosity turn-off from the main sequence of evolving stars in the Hertzsprung-Russell diagram. This method, improved over the years from theoretical calculations of stellar structure by many astronomers, remains the principal method of age dating. Sandage recently returned to problems related to the absolute magnitudes of RR Lyrae variable stars in globular clusters, important to the age dating of these most ancient of objects in the Galaxy.
The image shows the first area of sky viewed as part of the Herschel-ATLAS survey. The five inset show enlarged views of the five distant galaxies whose images are being gravitationally lensed by foreground galaxies (unseen by Herschel). The distant galaxies are not only very bright, but also very red in colour in this image, showing that they are brighter at the longer wavelengths measured by the SPIRE instrument. Image credits: ESA/SPIRE/Herschel-ATLAS/SJ Maddox (top); ESA/NASA/JPL-Caltech/Keck/SMA (bottom).
[/caption]
One of the predictions of Einstein’s predictions from general relativity was that gravity could distort space itself and potentially, act as a lens. This was spectacularly confirmed in 1919 when, during a solar eclipse, Arthur Eddington observed stars near the Sun were distorted from their predicted positions. In 1979, this effect was discovered at much further distances when astronomers found it to distort the image of a distant quasar, making one appear as two. Several other such cases have been discovered since then, but these instances of gravitational lensing have proven difficult to find. Searches for them have had a low success rate in which less than 10% of candidates are confirmed as gravitational lenses. But a new method using data from Herschel may help astronomers discover many more of these rare occurrences.
The Herschel telescope is one of the many space telescopes currently in use and explores the portion of the spectrum from the far infrared to the submillimeter regime. A portion of its mission is to produce a large survey of the sky resulting in the Herschel ATLAS project which will take deep images of over 550 square degrees of the sky.
While Herschel explores this portion of the electromagnetic spectrum in far greater detail than its predecessors, in many ways, there’s not much to see. Stars emit only very faintly in this range. The most promising targets are warm gas and dust which are better emitters, but also far more diffuse. But it’s this combination of facts that will allow Herschel to potentially discover new lenses with improved efficiency.
The reason is that, although galaxies lack strong emission in this regime in the modern universe, ancient galaxies gave off far more since during the first 4 billion years. During that time, many galaxies were dominated by dust being warmed by star formation. Yet due to their distance, they too should be faint… Unless a gravitational lens gets in the way. Thus, the majority of small, point-like sources in the ALTAS collection are likely to be lensed galaxies. As Dr Mattia Negrello, of the Open University and lead researcher of the study explains, “The big breakthrough is that we have discovered that many of the brightest sources are being magnified by lenses, which means that we no longer have to rely on the rather inefficient methods of finding lenses which are used at visible and radio wavelengths.”
These panels show a zoom of one of the lenses, with high resolution images from Keck (optical light, blue) and the submillimeter Array (sub-millimetre light, red). Image credits: ESA/NASA/JPL-Caltech/Keck/SMA
Already, this new technique has turned up at least five strong candidates. A paper, to be published in the current issue of Science discusses them. Each of them received followup observations from the Z-Spec spectrometer on the California Institute of Technology Submillimeter Observatory. The furthest of these these objects, labeled as ID81, showed a prominent IR spectral line had a redshift of 3.04, putting it at a distance of 11.5 billion lightyears. Additionally, each system showed the spectral profile of the foreground galaxy, demonstrating that the combined light received was indeed two galaxies and the bright component was a gravitational lens.
This method of using gravitational lenses will allow the Herschel team to probe distant galaxies in detail never before achieved. As with all telescopes, longer wavelengths of observations result in less resolution which means that, even if one of the distant systems were to be broken into distinct portions, Herschel would be unable to resolve them. But the fact that we can see them at all means their spectral signatures of the galaxies as a whole can still be studied. Additionally, as Professor Steve Eales from Cardiff University and the other leader of the survey noted: “We can also use this technique to study the lenses themselves.” This potential to explore the mass of the nearby galaxies may help astronomers to understand and constrain the enigmatic Dark Matter that makes up ~80% of the mass in our universe.
Dr Loretta Dunne of Nottingham University and joint-leader of the Herschel-ATLAS survey adds, “What we’ve seen so far is just the tip of the iceberg. Wide area surveys are essential for finding these rare events and since Herschel has only covered one thirtieth of the entire Herschel-ATLAS area so far, we expect to discover hundreds of lenses once we have all the data. Once found, we can probe the early Universe on the same physical scales as we can in galaxies next door.”
The AMS-02 will be mounted on the outside of the International Space Station's S3 Truss element. Image Credit: NASA
[/caption]
The Principal Investigator (P.I.) for the Alpha Magnetic Spectrometer-2 (AMS-02) experiment, Professor Samuel Ting, says that the experiment is already accruing data as it awaits its February 2011 launch date. Scheduled to fly aboard the final flight of the space shuttle Endeavour, STS-134, AMS-02 will search through cosmic rays for exotic particles, antimatter and dark matter. The experiment will be mounted to the outside of the International Space Station (ISS) and will require no spacewalks to attach. Continue reading “ISS Particle Detector Ready to Unveil Wonders of the Universe”
An infrared/optical representative-color image of a massive galaxy cluster located 7 billion light-years from Earth. Credit: Infrared Image: NASA/JPL-Caltech/M. Brodwin (Harvard-Smithsonian CfA) Optical Image: CTIO Blanco 4-m telescope/J. Mohr (LMU Munich)
[/caption]
Looking back to when our Universe was about half the age it is now, astronomers have discovered the most massive galaxy cluster yet seen at so great a distance. The researchers say that if we could see it as it appears today, it would be one of the most massive galaxy clusters in the universe. The cluster, modestly named SPT-CL J0546-5345, weighs in at around 800 trillion Suns, and holds hundreds of galaxies. “This galaxy cluster wins the heavyweight title,”said Mark Brodwin, from the Harvard-Smithsonian Center for Astrophysics. “This cluster is full of ‘old’ galaxies, meaning that it had to come together very early in the universe’s history – within the first two billion years.”
Using the new South Pole Telescope, Brodwin and his colleagues are searching for giant galaxy clusters using the Sunyaev-Zel’dovich effect – a small distortion of the cosmic microwave background, a pervasive all-sky glow left over from the Big Bang. Such distortions are created as background radiation passes through a large galaxy cluster.
They found the heavyweight cluster in some of their first observations with the new telescope.
Located in the southern constellation Pictor (the Painter), the cluster has a redshift of z=1.07, putting it at a distance of about 7 billion light-years, meaning we see it as it appeared 7 billion years ago, when the universe was half as old as now and our solar system didn’t exist yet.
Even at that young age, the cluster was almost as massive as the nearby Coma cluster. Since then, it should have grown about four times larger.
This optical image of the newfound galaxy cluster highlights how faint and reddened these galaxies are due to their great distance. Credit: CTIO Blanco 4-m telescope/J. Mohr (LMU Munich)
Galaxy clusters like this can be used to study how dark matter and dark energy influenced the growth of cosmic structures. Long ago, the universe was smaller and more compact, so gravity had a greater influence. It was easier for galaxy clusters to grow, especially in areas that already were denser than their surroundings.
“You could say that the rich get richer, and the dense get denser,” quipped Harvard astronomer Robert Kirshner, commenting on the study.
As the universe expanded at an accelerating rate due to dark energy, it grew more diffuse. Dark energy now dominates over the pull of gravity and chokes off the formation of new galaxy clusters.
The main goal of the SPT survey is to find a large sample of massive galaxy clusters in order to measure the equation of state of the dark energy, which characterizes cosmic inflation and the accelerated expansion of the universe. Additional goals include understanding the evolution of hot gas within galaxy clusters, studying the evolution of massive galaxies in clusters, and identifying distant, gravitationally lensed, rapidly star-forming galaxies.
The team expects to find many more giant galaxy clusters lurking in the distance once the South Pole Telescope survey is completed.
Follow-up observations on the cluster were done using the Infrared Array Camera on the Spitzer Space Telescope and the Magellan telescopes in Chile. A paper announcing the discovery has been published in the Astrophysical Journal.
