Integral locates origin of high-energy emission from Crab Nebula

Thanks to data from ESA’s Integral gamma-ray observatory, scientists have been able to locate where particles in the vicinity of the rotating neutron-star in the Crab Nebula are accelerated to immense energies.

The discovery, resulting from more than 600 individual observations of the nebula, put in place another piece of the puzzle in understanding how neutron stars work.
Rotating neutron-stars, or pulsars, are known to accelerate particles to enormous energies, typically one hundred times more than the most powerful accelerators on Earth, but scientists are still uncertain exactly how these systems work and where the particles are accelerated.

A step forward in this understanding is now accomplished thanks to a team of researchers from the UK and Italy, led by Professor Tony Dean of the University of Southampton, who studied high-energy polarised light emitted by the Crab Nebula – one of the most dramatic sights in deep space.

The Crab Nebula is the result of a supernova explosion which was seen from Earth on 4 July 1054. The explosion left behind a pulsar with a nebula of radiating particles around it. The pulsar contains the mass of the Sun squeezed into a volume of about 10 km radius, rotating very fast – about 30 times a second – thereby generating very powerful magnetic fields and accelerating particles. A highly collimated jet, aligned with the spin axis of the pulsar and a bright radiating ‘donut’ structure (or torus) around the pulsar itself, are also seen.

So, the Crab is known to accelerate electrons - and possibly other particles - to extremely high speed, and so produces high energy radiation. But where exactly are these particles accelerated?

Looking into the heart of the pulsar with Integral’s spectrometer (SPI), the researchers made a detailed study to assess the polarization – or the alignment - of the waves of high-energy radiation originating from the Crab.


They saw that this polarised radiation is highly aligned with the rotation axis of the pulsar. So they concluded that a significant portion of the electrons generating the high-energy radiation must originate from a highly-organised structure located very close to the pulsar, very likely directly from the jets themselves. The discovery allows the researchers to discard other theories that locate the origin of this radiation further away from the pulsar.

Professor Tony Dean of the University’s School of Physics and Astronomy commented that the discovery of such alignment – also matching with the polarisation observed in the visible band - is truly remarkable. “The findings have clear implications on many aspects of high energy accelerators such as the Crab,” he added.

"The detection of polarised radiation in space is very complicated and rare, as it requires dedicated instrumentation and an in-depth analysis of very complex data”, said Chris Winkler, Integral Project Scientist at ESA. “Integral’s ability to detect polarised gamma-radiation and, as a consequence, to obtain important results like this one, confirms it once more as a world-class observatory.”
Notes for editors:

The results are published in the 29 August issue of the scientific journal Science, in a paper titled ‘Polarized gamma-ray emission from the Crab’, by: A. J. Dean, D.J. Clark, V.A.McBride, A.J.Bird, A.B.Hill and S.E.Shaw (University of Southampton’s School of Physics and Astronomy); J.B. Stephen and L. Bassani (INAF-IASF, Bologna); and A. Bazzano and P. Ubertini (INAF-IASF, Roma).

How does my galaxy grow?

Assembling the Most Massive Galaxies in the Universe

Astronomers have caught multiple massive galaxies in the act of merging about 4 billion years ago. This discovery, made possible by combining the power of the best ground- and space-based telescopes, uniquely supports the favoured theory of how galaxies form.

How do galaxies form? The most widely accepted answer to this fundamental question is the model of 'hierarchical formation', a step-wise process in which small galaxies merge to build larger ones. One can think of the galaxies forming in a similar way to how streams merge to form rivers, and how these rivers, in turn, merge to form an even larger river. This theoretical model predicts that massive galaxies grow through many merging events in their lifetime. But when did their cosmological growth spurts finish? When did the most massive galaxies get most of their mass?

To answer these questions, astronomers study massive galaxies in clusters, the cosmological equivalent of cities filled with galaxies. "Whether the brightest galaxies in clusters grew substantially in the last few billion years is intensely debated. Our observations show that in this time, these galaxies have increased their mass by 50%," says Kim-Vy Tran from the University of Zürich, Switzerland, who led the research.

The astronomers made use of a large ensemble of telescopes and instruments, including ESO's Very Large Telescope (VLT) and the Hubble Space Telescope, to study in great detail galaxies located 4 billion light-years away. These galaxies lie in an extraordinary system made of four galaxy groups that will assemble into a cluster.

In particular, the team took images with VIMOS and spectra with FORS2, both instruments on the VLT. From these and other observations, the astronomers could identify a total of 198 galaxies belonging to these four groups.

The brightest galaxies in each group contain between 100 and 1000 billion of stars, a property that makes them comparable to the most massive galaxies belonging to clusters.

"Most surprising is that in three of the four groups, the brightest galaxy also has a bright companion galaxy. These galaxy pairs are merging systems," says Tran.

The brightest galaxy in each group can be ordered in a time sequence that shows how luminous galaxies continue to grow by merging until recently, that is, in the last 5 billion years. It appears that due to the most recent episode of this 'galactic cannibalism', the brightest galaxies became at least 50% more massive.

This discovery provides unique and powerful validation of hierarchical formation as manifested in both galaxy and cluster assembly.

"The stars in these galaxies are already old and so we must conclude that the recent merging did not produce a new generation of stars," concludes Tran. "Most of the stars in these galaxies were born at least 7 billion years ago."

The team is composed of Kim-Vy H. Tran (Institute for Theoretical Physics, University of Zürich, Switzerland), John Moustakas (New York University, USA), Anthony H. Gonzalez and Stefan J. Kautsch (University of Florida, Gainesville, USA), and Lei Bai and Dennis Zaritsky (Steward Observatory, University of Arizona, USA). The results presented here are published in the Astrophysical Journal Letters: "The Late Stellar Assembly Of Massive Cluster Galaxies Via Major Merging", by Tran et al.

Science Contact:

Kim-Vy Tran
Institute for Theoretical Physics
University of Zürich, Switzerland
Phone: +41 44 635 5820
E-mail: vy (at) physik.unizh.ch

Generations of Stars Pose for Family Portrait

Credit: NASA/JPL-Caltech/
L. Allen & X. Koenig (Harvard-Smithsonian CfA)

A new image from NASA's Spitzer Space Telescope tells a tale of life and death amidst a rich family history. The striking infrared picture shows a colorful cosmic cloud, called W5, studded with multiple generations of blazing stars.

It also provides dramatic new evidence that massive stars - through their brute winds and radiation - can trigger the birth of stellar newborns.

"Triggered star formation continues to be very hard to prove," said Xavier Koenig of the Harvard Smithsonian Center for Astrophysics in Cambridge, Mass. "But our preliminary analysis shows that the phenomenon can explain the multiple generations of stars seen in the W5 region." Koenig is lead author of a paper about the findings in the December 1, 2008, issue of the Astrophysical Journal.

The image, which can be seen at http://www.nasa.gov/mission_pages/spitzer/multimedia/20080722.html, is being unveiled today at 12:30 p.m. Pacific Time at the Griffith Observatory, Los Angeles, as part of Spitzer's five-year anniversary celebration. Spitzer launched on August 25, 2003, from Cape Canaveral Air Force Station, Fla.

The most massive stars in the universe form out of thick clouds of gas and dust. The stars are so massive, ranging from 15 to about 60 times the mass of our sun, that some of their material slides off in the form of winds. The scorching-hot stars also blaze with intense radiation. Over time, both the wind and radiation blast away surrounding cloud material, carving out expanding cavities.

Astronomers have long suspected that the carving of these cavities causes gas to compress into successive generations of new stars. As the cavities grow, it is believed that more and more stars arise along the cavities' expanding rims. The result is a radial "family tree" of stars, with the oldest in the middle of the cavity, and younger and younger stars farther out.

Evidence for this theory can be seen easily in pictures of many star-forming regions, such as W5, Orion and Carina. For example, in the new Spitzer picture of W5, the most massive stars (some of the blue dots) are at the center of two hollow cavities, and younger stars (pink or white) are embedded in the elephant-trunk-like pillars as well as beyond the cavity rim. However, it is possible that the younger stars just happen to be near the edge of the cavities and were not triggered by the massive stars.

Koenig and his colleagues set out to test the triggered star-formation theory by studying the ages of the stars in the W5 region. They used Spitzer's infrared vision to peer through the dusty clouds and get a better look at the stars' various stages of evolution. They found that stars within the W5 cavities are older than stars at the rims, and even older than stars farther out past the rim. This ladder-like separation of ages provides some of the best evidence yet that massive stars do, in fact, give rise to younger generations.

"Our first look at this region suggests we are looking at one or two generations of stars that were triggered by the massive stars," said co-author Lori Allen of the Harvard-Smithsonian Center for Astrophysics. "We plan to follow up with even more detailed measurements of the stars' ages to see if there is a distinct time gap between the stars just inside and outside the rim."

Millions of years from now, the massive stars in W5 will die in tremendous explosions. When they do, they will destroy some of the young nearby stars - the same stars they might have triggered into being.

W5 spans an area of sky equivalent to four full moons and is about 6,500 light-years away in the constellation Cassiopeia. The Spitzer picture was taken over a period of 24 hours. The color red shows heated dust that pervades the region's cavities. Green highlights the dense clouds, and white knotty areas are where the youngest of stars are forming. The blue dots are older stars in the star-forming cloud, as well as unrelated stars behind and in front of the cloud.

Other authors include Robert Gutermuth, now at Smith College in Northampton, Mass.; Chris Brunt of the University of Exeter, England; James Muzerolle of the University of Arizona, Tucson; and Joseph Hora of Harvard-Smithsonian Center for Astrophysics.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology, also in Pasadena. Caltech manages JPL for NASA.

Whitney Clavin 818-354-4673/818-648-9734
Jet Propulsion Laboratory, Pasadena, Calif.

The Matter of the Bullet Cluster

Composite 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.

Explanation: The matter in galaxy cluster 1E 0657-56, fondly known as the "bullet cluster", is shown in this composite image. A mere 3.4 billion light-years away, the bullet cluster's individual galaxies are seen in the optical image data, but their total mass adds up to far less than the mass of the cluster's two clouds of hot x-ray emitting gas shown in red. Representing even more mass than the optical galaxies and x-ray gas combined, the blue hues show the distribution of dark matter in the cluster. Otherwise invisible to telescopic views, the dark matter was mapped by observations of gravitational lensing of background galaxies. In a text book example of a shock front, the bullet-shaped cloud of gas at the right was distorted during the titanic collision between two galaxy clusters that created the larger bullet cluster itself. But the dark matter present has not interacted with the cluster gas except by gravity. The clear separation of dark matter and gas clouds is considered direct evidence that dark matter exists.

Astronomy Picture of the Day

The winding Milky Way

A theoretical model of a galaxy like the Milky Way, showing trails of stars torn from disrupted satellite galaxies that have merged with the central galaxy. The region shown is about 1 million light-years on a side; the Sun is just 25,000 light-years from the center of the galaxy and would appear close to the center of this picture. Credit: K. Johnston/J. Bullock

A new map reveals a complicated outer halo in our galaxy.
Provided by Sloan Digital Sky Survey

The halo of stars that envelops the Milky Way is like a river delta crisscrossed by stellar streams large and small, according to new data from the Sloan Digital Sky Survey (SDSS-II). While the largest rivers of this delta have been mapped out over the last decade, analysis of the new SDSS-II map shows that smaller streams can be found throughout the stellar halo, says Kevin Schlaufman, a graduate student at the University of California at Santa Cruz.

Schlaufman reported his results Saturday at an international symposium in Chicago, titled "The Sloan Digital Sky Survey: Asteroids to Cosmology." Over the last 3 years, Schlaufmann explains, the SEGUE survey of SDSS-II has measured the motions of nearly a quarter million stars in selected areas of the sky. A careful search for groups of stars at the same velocity turned up 14 distinct structures, 11 of them previously unknown.

"Even with SEGUE, we are still only mapping a small fraction of the galaxy," says Schlaufman, "so 14 streams in our data implies a huge number when we extrapolate to the rest of the Milky Way." If each velocity structure were a separate stream, Schlaufman explains, there would be close to 1,000 in the inner 75,000 light-years of the galaxy. However, these structures could arise from a smaller number of streams that are seen many times in different places.

"A jumble of pasta" is the way Columbia University researcher Kathryn Johnston described her theoretical models of the Milky Way's stellar halo. In a review talk at the symposium, Johnston explained how dwarf galaxies that pass close to the Milky Way can be stretched by gravitational tides into spaghetti-like strands, which wind around the galaxy as stars trace out the same orbital paths at different rates.

"In the center of the galaxy, these stellar strands crowd together and you just see a smooth mix of stars," says Johnston. "But as you look further away you can start to pick out individual strands, as well as features more akin to pasta shells that come from dwarfs that were on more elongated orbits. By looking at faint features, Kevin may be finding some of the 'angel hair' that came from smaller dwarfs, or ones that were destroyed longer ago."

Heidi Newberg of Rensselaer Polytechnic Institute and her thesis student Nathan Cole have been trying to follow some of the larger strands as they weave across the sky. "It's a big challenge to piece things together," says Cole, "because the stream from one dwarf galaxy can wrap around the Milky Way and pass through streams of stars ripped from other dwarf galaxies."

Toward the constellation Virgo, where SDSS images revealed an excess of stars covering a huge area of sky, Newberg finds that there are at least two superposed structures, and possibly three or more. The SEGUE velocity measurements can separate systems that overlap in sky maps, Newberg explained in her symposium talk. "Part of what we see toward Virgo is a tidal arm of the Sagittarius dwarf galaxy, whose main body lies on the opposite side of the Milky Way, but we don't know the origin of the other structures. There really aren't enough pasta varieties to describe all the structures we find."

In addition to stellar streams, astronomers searching the SDSS data have found 14 surviving dwarf companions of the Milky Way, including two new discoveries announced Saturday at the symposium by Gerard Gilmore of Cambridge University. These satellite galaxies are orbiting within the halo of invisible dark matter whose gravity holds the Milky Way itself together. Most of them are much fainter than the ten satellites known prior to the SDSS.

Because even the SDSS can only detect these ultra-faint dwarfs if they are relatively nearby, there could be several hundred more of them further out in the Milky Way's dark halo, according to independent analyses by graduate students Sergey Koposov, of the Max Planck Institute for Astronomy in Heidelberg, Germany, and Eric Tollerud, of the University of California at Irvine. "Even so," says Koposov, "we expect that the number of dark matter clumps is much larger than that, so something must prevent the smaller clumps from gathering gas and forming stars."

The SDSS dwarfs have far fewer stars than the previously known satellites, notes Gilmore, but they have similar spatial extents, and the stars within them move at similar speeds. "I think the internal dynamics of these tiny galaxies may be hard to explain with our conventional ideas about dark matter," says Gilmore.

"The SDSS has taught us a huge amount about the Milky Way and its neighbors," says Johnston, who is pleased to see some of the predictions of her models confirmed by the new data. "But we're still just beginning to map the galaxy in a comprehensive way, and there's a trove of discoveries out there for the next generation of surveys, including the two new Milky Way surveys that will be carried out in SDSS-III."

Astronomy.com

See you again in 22,000 years

This image shows the orbit of the newly discovered solar system object SQ372 (blue), in comparison to the orbits of Neptune, Pluto, and Sedna (white, green, red). The location of the Sun is marked by the yellow dot at the center. The inset panel shows an expanded view, including the orbits of Uranus, Saturn, and Jupiter inside the orbit of Neptune. Even on this expanded scale, the size of Earth's orbit would be barely distinguishable from the central dot.
Credit: N. Kaib

Astronomers find an unusual new denizen of the solar system. Provided by the Sloan Digital Sky Survey

A "minor planet" with the prosaic name 2006 SQ372 is just over 2 billion miles from Earth, a bit closer than the planet Neptune. But this lump of ice and rock is beginning the return leg of a 22,500-year journey that will take it to a distance of 150 billion miles, nearly 1,600 times the distance from the Earth to the Sun, according to a team of researchers from the Sloan Digital Sky Survey (SDSS-II).

The discovery of this remarkable object was reported August 18 in Chicago, at an international symposium titled "The Sloan Digital Sky Survey: Asteroids to Cosmology." A paper describing the discovery technique and the properties of 2006 SQ372 is being prepared for submission to the Astrophysical Journal.

The orbital paths of the major planets are nearly circular, but the orbit of 2006 SQ372 is an ellipse that is 4 times longer than it is wide, says University of Washington astronomer Andrew Becker, who led the discovery team. The only known object with a comparable orbit is Sedna — a distant, Pluto-like dwarf planet discovered in 2003 — but 2006 SQ372's orbit takes it more than 1.5 times further from the Sun, and its orbital period is nearly twice as long.

The new object is much smaller than Sedna, Becker says, probably 30-60 miles across instead of nearly 1,000. "It's basically a comet, but it never gets close enough to the Sun to develop a long, bright tail of evaporated gas and dust."

Becker's team found 2006 SQ372 by applying a specialized computer searching algorithm to data taken for a completely different purpose: finding supernovae explosions billions of light-years away to measure the expansion of the universe. The SDSS-II supernovae survey scanned the same long stripe of sky, an area 1,000 times larger than the Full Moon, every clear night in the fall of 2005, 2006, and 2007.

"If you can find things that explode, you can also find things that move, but you need different tools to look for them," says team member Lynne Jones, also of the University of Washington. The only objects close enough to change position noticeably from one night to the next are in our own solar system, Jones explains.

SQ372 was first discovered in a series of images taken between September 27 and October 21, 2006. Team member Andrew Puckett, of the University of Alaska Anchorage, then searched the supernovae survey's fall 2005 observations to find earlier detections, thus securing the discovery. Subsequent SDSS detections of SQ372 have been found in data from the 2006 and 2007 observing seasons.

University of Washington graduate student Nathan Kaib, another member of the discovery team, has been running computer simulations to try to understand out how 2006 SQ372 might have acquired its unusual orbit. "It could have formed, like Pluto, in the belt of icy debris beyond Neptune, then been kicked to large distance by a gravitational encounter with Neptune or Uranus," says Kaib. "However, we think it is more probable that SQ372 comes from the inner edge of the Oort Cloud."

In 1950, Kaib explains, the Dutch astronomer Jan Oort hypothesized that most comets come from a distant reservoir of icy, asteroid-like bodies, which were ejected from the inner solar system by gravitational kicks from the giant planets as the planets themselves were forming 4.5 billion years ago. Most objects in the Oort Cloud orbit the Sun at distances of several trillion miles, but the gravity of passing stars can alter their orbits, flinging some into interstellar space and deflecting others to the inner solar system where they "light up" as comets.

Even at its most distant turning point, 2006 SQ372 will be 10 times closer to the Sun than the supposed main body of the Oort Cloud, says Kaib. "The existence of an 'inner' Oort Cloud has been theoretically predicted for many years, but SQ372 and perhaps Sedna are the first objects we have found that seem to originate there. It's exciting that we are beginning to verify these predictions."

Becker notes that 2006 SQ372 was bright enough to find with the SDSS only because it is near its closest approach to the Sun, and that the SDSS-II supernovae survey observed less than one percent of the sky. "There are bound to be many more objects like this waiting to be discovered by the next generation of surveys, which will search to fainter levels and cover more area," says Becker. "In a decade, we should know a lot more about this population than we do now."

"One of our goals," says Kaib, "is to understand the origin of comets, which are among the most spectacular celestial events. But the deeper goal is to look back into the early history of our solar system and piece together what was happening when the planets formed."

Astronomy.com

Hubble Sees Magnetic Monster in Erupting Galaxy

Credit: NASA, ESA, and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration

Credit: NASA, ESA,
and the Hubble Heritage (STScI/AURA)-ESA
/Hubble Collaboration

NASA's Hubble Space Telescope has found an answer to a long-standing puzzle by resolving giant but delicate filaments shaped by a strong magnetic field around the active galaxy NGC 1275. It is the most striking example of the influence of the immense tentacles of extragalactic magnetic fields, say researchers.

One of the closest giant elliptical galaxies, NGC 1275 hosts a supermassive black hole. Energetic activity of gas swirling near the black hole blows bubbles of material into the surrounding galaxy cluster. Long gaseous filaments stretch out beyond the galaxy, into the multimillion-degree, X-ray–emitting gas that fills the cluster.

These filaments are the only visible-light manifestation of the intricate relationship between the central black hole and the surrounding cluster gas. They provide important clues about how giant black holes affect their surrounding environment.

Exploiting Hubble's view, a team of astronomers led by Andy Fabian from the University of Cambridge, UK, have for the first time resolved individual threads of gas that make up the filaments. The amount of gas contained in a typical thread is around one million times the mass of our own Sun. They are only 200 light-years wide, are often very straight, and extend for up to 20,000 light-years. The filaments are formed when cold gas from the core of the galaxy is dragged out in the wake of the rising bubbles blown by the black hole.

It has been a challenge for astronomers to understand how the delicate structures withstood the hostile, high-energy environment of the galaxy cluster for over 100 million years. They should have heated up, dispersed, and evaporated by now, or collapsed under their own gravity to form stars.

A new study published in the August 21 Nature magazine proposes that magnetic fields hold the charged gas in place and resist the forces that would distort the filaments. This skeletal structure is strong enough to resist gravitational collapse.

"We can see that the magnetic fields are crucial for these complex filaments – both for their survival and for their integrity," said Fabian.

Similar networks of filaments are found around other more remote central cluster galaxies. However, they cannot be observed with comparable resolution to the view of NGC 1275. The team will apply the understanding of NGC 1275 to interpret observations of these more distant galaxies.

The authors of the science paper are: A.C. Fabian, R.M. Johnstone, and J.S. Sanders (University of Cambridge, UK), C.J. Conselice (University of Nottingham, UK), C.S. Crawford (University of Cambridge, UK), and J.S. Gallagher III and E. Zweibel (University of Wisconsin, Madison).

The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency (ESA) and is managed by NASA's Goddard Space Flight Center (GSFC) in Greenbelt, Md. The Space Telescope Science Institute (STScI) conducts Hubble science operations. The institute is operated for NASA by the Association of Universities for Research in Astronomy, Inc., Washington, D.C.

CONTACT

Ray Villard
Space Telescope Science Institute, Baltimore,
Md. 410-338-4514
villard@stsci.edu

Lars Lindberg Christensen
Hubble/ESA, Garching,
Germany 011-49-89-3200-6306 011-49-173-3872-621 (cell)
lars@eso.org

A.C. Fabian Institute of Astronomy,
University of Cambridge,
UK 011-44-1223-3375-09
acf@ast.cam.ac.uk

M87 - A Nearby Galaxy Metropolis

Credit: X-ray: NASA/CXC/CfA/W. Forman et al.; Radio: NRAO/AUI/NSF/W. Cotton; Optical: NASA/ESA/Hubble Heritage Team (STScI/AURA), and R. Gendler

This image is a composite of visible (or optical), radio, and X-ray data of the giant elliptical galaxy, M87. M87 lies at a distance of 60 million light years and is the largest galaxy in the Virgo cluster of galaxies. Bright jets moving at close to the speed of light are seen at all wavelengths coming from the massive black hole at the center of the galaxy. It has also been identified with the strong radio source, Virgo A, and is a powerful source of X-rays as it resides near the center of a hot, X-ray emitting cloud that extends over much of the Virgo cluster. The extended radio emission consists of plumes of fast-moving gas from the jets rising into the X-ray emitting cluster medium.

Credit: NASA/CXC/CfA/W. Forman et al.

In X-rays, M87 also reveals evidence for a series of outbursts from the central supermassive black hole. The loops and bubbles in the hot, X-ray emitting gas are relics of small outbursts from close to the black hole. Other interesting features in M87 are narrow filaments of X-ray emission, which may be due to hot gas trapped by magnetic fields. One of these filaments is over 100,000 light years long, and extends below and to the right of the center of M87 in almost a straight line.

The optical data of M87 were obtained with Hubble's Advanced Camera for Surveys in visible and infrared filters (data courtesy of P. Cote, Herzberg Institute of Astrophysics, and E. Baltz, Stanford University). Wide-field optical data of the center of the Virgo Cluster were also provided by R. Gendler (Copyright Robert Gendler 2006). The X-ray data were acquired from the Chandra X-ray Observatory's Advanced CCD Imaging Spectrometer (ACIS), and were provided by W. Forman (Harvard-Smithsonian Center for Astrophysics) et al. The radio data were obtained by W. Cotton and also archive processing using the National Radio Astronomy Observatory's Very Large Array (NRAO/VLA) near Socorro, New Mexico.

Chandra X-Ray Observatory Center

Schoolteacher discovers 'cosmic ghost'

About this image: "Hanny's Voorwerp" is the green blob of gas (center) and is believed to be a "light echo" from the bright, stormy center of a distant galaxy that has now gone dim.
Credit:Dan Smith/Peter Herbert/Matt Jarvis/the ING

Galaxyzoo.org team members believe the gaseous object is the "light echo" of a quasar.
Provided by the University of Oxford

A Dutch schoolteacher has discovered a mysterious and unique astronomical object through the Galaxy Zoo project, which enables members of the public to take part in astronomy research on-line.

Hanny van Arkel, a primary schoolteacher from the Netherlands, came across the image of a strange gaseous object with a hole in the center that has been described as a "cosmic ghost" while using the galaxyzoo.org web site to classify images of galaxies.

She posted about the image — which quickly became known as Hanny's "Voorwerp" after the Dutch word for "object" — on the Galaxy Zoo forum and the astronomers who run the site began to investigate. They soon realized the potential significance of what they think is a new class of astronomical object and will now use the Hubble Space Telescope to get a closer look at "Hanny's Voorwerp."

"At first we thought it was a distant galaxy," said Dr. Chris Lintott of Oxford University, a galaxyzoo.org team member, "but we realized there were no stars in it so that it must be a cloud of gas." What was particularly puzzling to astronomers was that the gas was so hot — more than 18,000° Fahrenheit (10,000° Celsius) — when there were no stars in the vicinity to heat it up.

"We now think that what we're looking at is light from a quasar — the bright, stormy center of a distant galaxy powered by a supermassive black hole," said Dr. Lintott. "The quasar itself is no longer visible to us, but its light continues to travel through space and the Voorwerp is a massive 'light echo' produced as this light strikes the gas."

The black hole at the center of the galaxy, IC 2497, is now "turned off" — which is why the quasar has gone dim — but around 100,000 years ago the quasar was bright enough to have been visible from Earth through a small, inexpensive telescope.

Dr. Lintott added: "From the point of view of the Voorwerp, the galaxy looks as bright as it would have done before the black hole turned off — it's this light echo that has been 'frozen in time' for us to observe. It's rather like examining the scene of a crime where, although we can't see them, we know the culprit must be lurking somewhere nearby in the shadows."

Hanny van Arkel, a Dutch primary schoolteacher,
discovered a mysterious new astronomical object while on galaxyzoo.org.
Credit: Edd Edmondson

"IC 2497 is so close that if the quasar was still shining today, on a good night you could probably see it with a small telescope," said galaxyzoo.org team member Kevin Schawinski of the Yale University who recently moved there from Oxford University. "The nearest active quasar, called 3C 273, is 1.7 billion light-years further away."

Smaller light echoes have been noted around supernovae before but never anything of the scale and shape of the Voorwerp. As yet nobody has a sensible explanation for the hole that runs through its center.

"It's amazing to think that this object has been sitting in the archives for decades and that amateur volunteers can help by spotting things like this on-line," said van Arkel. "It was a fantastic present to find out on my 25th birthday that we will get observational time on the Hubble Space Telescope to follow-up this discovery."

"This discovery really shows how citizen science has come of age in the Internet world," commented Professor Bill Keel of the University of Alabama, a galaxyzoo.org team member. "Hanny's attentiveness alerted us not only to a peculiar object, but to a window into the cosmic past, which might have eluded us for a long time otherwise. Trying to understand the processes operating here has proven to be a fascinating challenge, involving a whole range of astrophysical techniques and instruments around the world and beyond. This has also been some of the most rewarding astronomy I've done in years!"

Dr. Dan Smith of Liverpool John Moores University and Peter Herbert of the University of Hertfordshire were observing using the Isaac Newton Group of telescopes in La Palma, Spain, when word of the discovery filtered through. "When we got the news about Hanny's Voorwerp we were intrigued to find out what it was, and, fortunately, we were able to slew the telescopes round and get some great images and spectra to study it," said Dr Smith. "It was only later that we heard the story about how it had been discovered; it's inspirational that Hanny picked out this object from Galaxy Zoo in her spare time and nobody had ever seen anything like it before.'

During the last year, 50 million classifications of galaxies have been submitted on one million objects at www.galaxyzoo.org by more than 150,000 armchair astronomers from all over the world.

The next stage of Galaxy Zoo will ask volunteers for more detailed classifications, making it easier to identify more unusual objects such as Hanny's Voorwerp.

Astronomy.com

Hubble Unveils Colorful and Turbulent Star-Birth Region on 100,000th Orbit Milestone

Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)

In commemoration of NASA's Hubble Space Telescope completing its 100,000th orbit in its 18th year of exploration and discovery, scientists at the Space Telescope Science Institute in Baltimore, Md., have aimed Hubble to take a snapshot of a dazzling region of celestial birth and renewal.

Hubble peered into a small portion of the nebula near the star cluster NGC 2074 (upper, left). The region is a firestorm of raw stellar creation, perhaps triggered by a nearby supernova explosion. It lies about 170,000 light-years away near the Tarantula nebula, one of the most active star-forming regions in our Local Group of galaxies.

The three-dimensional-looking image reveals dramatic ridges and valleys of dust, serpent-head "pillars of creation," and gaseous filaments glowing fiercely under torrential ultraviolet radiation. The region is on the edge of a dark molecular cloud that is an incubator for the birth of new stars.

The high-energy radiation blazing out from clusters of hot young stars already born in NGC 2074 is sculpting the wall of the nebula by slowly eroding it away. Another young cluster may be hidden beneath a circle of brilliant blue gas at center, bottom.

In this approximately 100-light-year-wide fantasy-like landscape, dark towers of dust rise above a glowing wall of gases on the surface of the molecular cloud. The seahorse-shaped pillar at lower, right is approximately 20 light-years long, roughly four times the distance between our Sun and the nearest star, Alpha Centauri.

The region is in the Large Magellanic Cloud (LMC), a satellite of our Milky Way galaxy. It is a fascinating laboratory for observing star-formation regions and their evolution. Dwarf galaxies like the LMC are considered to be the primitive building blocks of larger galaxies.

This representative color image was taken on August 10, 2008, with Hubble's Wide Field Planetary Camera 2. Red shows emission from sulfur atoms, green from glowing hydrogen, and blue from glowing oxygen.

For additional information, contact:

Ray Villard / Cheryl Gundy / Donna Weaver

Space Telescope Science Institute, Baltimore, Md.

410-338-4514 / 410-338-4707 / 410-338-4493

villard@stsci.edu / gundy@stsci.edu / dweaver@stsci.edu

Mario Livio

Space Telescope Science Institute, Baltimore, Md.

410-338-4439

mlivio@stsci.edu

Spitzer Notices Star Birth Spike in Galaxies Moving to Cosmic Cities

About this image: A Hubble Space Telescope snapshot of galaxy cluster MS1054 is featured in the center, while individual galaxies spotted by the Spitzer Space Telescope are highlighted along the side. Wisps of blue show infrared emission from star formation.

Hubble Image - Dr. John Blakeslee (Washington State University)
Spitzer Images - NASA/JPL-Caltech/A. Saintonge (University of Zurich)

New evidence from NASA's Spitzer Space Telescope reveals that most galaxies undergo a huge stellar baby boom when they first enter a "cosmic city", or galaxy cluster. And the more distant the galaxy cluster, the greater the star formation rate.

"The infrared Spitzer observations let us peek at otherwise hidden, powerful star formation harbored in some of these cluster galaxies," says Dr. Amelie Saintonge, of the Institute for Theoretical Physics, University of Zurich, in Switzerland. "By looking at both nearby and distant galaxy clusters, we can look back in time and observe an increase in the fraction of galaxies undergoing these intense star-forming events."

Sanitonge and Dr. Kim-Vy Tran, also of the University of Zurich, studied a total of 1,300 galaxies in eight clusters spread across 7 billion light-years. The galaxies were observed by Spitzer's Multiband Imaging Photometer (MIPS), and archived for the astronomical community to use.
Moving to the City

Across the Universe, galaxies reside in communities big and small. Like big cities on Earth, there are densely populated galactic communities called galaxy clusters. Thousands of galaxies live within the limits of a cluster, which are connected by a web of dusty "highways" called filaments. Sprinkled along each filament are smaller galactic communities, or the celestial suburbs. Over time, astronomers suspect that all galactic suburbanites will be gravitationally pulled into the cluster, traveling there by way of the filaments.

Scientists believe that when a galactic suburbanite first falls into a cluster, the galaxy slams into the cluster's hot gas, producing shockwaves that trigger dusty gas clouds in the galaxy to collapse. Like raindrops, stars will form in these condensing cosmic clouds.

In their baby years, these stars are optically invisible - shrouded by the dust cloud that condensed to form them. Eventually, the stars will develop powerful winds, strong enough to blow away surrounding dust. Until then, only Spitzer's dust-piercing infrared eyes can glimpse the infant stars.

According to Saintonge, Spitzer is the first telescope able to produce sensitive images of galaxies located 7 billion light-years away in the mid-infrared, at 24 microns. At this wavelength, astronomers can see most of the dust-obscured star formation in a distant galaxy.

Previously the Infrared Space Observatory mission hinted that as much as 90 percent of star formation in cluster galaxies is hidden at optical wavelengths. However, Spitzer is the only telescope that allows astronomers to observe very distant clusters and confirm that the effect is increasing with distance - meaning, the farther away the cluster is, the more galaxies it has that are forming stars in very dusty environments.

Although scientists are currently unsure about the physical mechanisms that induce the exuberant star formation in these galaxies, they believe that the more distant galaxies form more stars because of the epoch they are located in. Light needs time to travel, so humans never see cosmic objects as they currently are, only as they were in the distant past. For example, the light from an object that is located 7 billion light-years away needs to travel for 7 billion years to reach our eyes.

Approximately 7 billion years ago, when the universe was only half the age it is now, galaxy clusters across the Universe were actively accreting galaxies. The gas clouds in these infalling galaxies were shocked and began condensing to form stars.

"There has been growing observational evidence that the increase in star formation with look back time is driven by cluster assembly and galaxy infall, the Spitzer observations not only confirm this scenario, but also show that the effect is even stronger than previously thought," says Saintonge. "By unveiling star formation events hidden at optical wavelengths, Spitzer finally lets us see more than the tip of this dusty iceberg."

A copy of this paper is posted at: http://arxiv.org/abs/0806.2157

Written by Linda Vu, Spitzer Science Center

Globular Clusters Tell Tale of Star Formation in Nearby Galaxy Metropolis

Credit: NASA, ESA, and E. Peng (Peking University, Beijing)

Globular star clusters, dense bunches of hundreds of thousands of stars, have some of the oldest surviving stars in the universe. A new study of globular clusters outside our Milky Way Galaxy has found evidence that these hardy pioneers are more likely to form in dense areas, where star birth occurs at a rapid rate, instead of uniformly from galaxy to galaxy.

Astronomers used NASA's Hubble Space Telescope to identify over 11,000 globular clusters in the Virgo cluster of galaxies. Most are older than 5 billion years. The sharp vision of Hubble's Advanced Camera for Surveys resolved the star clusters in 100 galaxies of various sizes, shapes, and brightnesses, even in faint, dwarf galaxies. Comprised of over 2,000 galaxies, the Virgo cluster is the nearest large galaxy cluster to Earth, located about 54 million light-years away.

Astronomers have long known that the giant elliptical galaxy at the cluster's center, M87, hosts a larger-than-predicted population of globular star clusters. The origin of so many globulars has been a long-standing mystery.

"Our study shows that the efficiency of star cluster formation depends on the environment," said Patrick Cote of the Herzberg Institute of Astrophysics in Victoria, British Columbia. "Dwarf galaxies closest to Virgo's crowded center contained more globular clusters than those farther away."

The team found a bounty of globular clusters in most dwarf galaxies within 3 million light-years of the cluster's center, where the giant elliptical galaxy M87 resides. The number of globulars in these dwarfs ranged from a few dozen to several dozen, but these numbers were surprisingly high for the low masses of the galaxies they inhabited. By contrast, dwarfs in the outskirts of the cluster had fewer globulars. Many of M87's star clusters may have been snatched from smaller galaxies that ventured too close to it.

"We found few or no globular clusters in galaxies within 130,000 light-years from M87, suggesting the giant galaxy stripped the smaller ones of their star clusters," explained Eric Peng of Peking University in Beijing, China, and lead author of the Hubble study. "These smaller galaxies are contributing to the buildup of M87."

Hubble's "eye" is so sharp that it was able to pick out the fuzzy globular clusters from stars in our galaxy and from faraway galaxies in the background. "It's hard to distinguish globular clusters from stars and galaxies using ground-based telescopes," Peng said.

"With Hubble we were able to identify and study about 90 percent of the globular clusters in all our observed fields. This was crucial for dwarf galaxies that have only a handful of star clusters."

Evidence of M87's galactic cannibalism comes from an analysis of the globular clusters' composition. "In M87 there are three times as many globulars deficient in heavy elements, such as iron, than globulars rich in those elements," Peng said. "This suggests that many of these 'metal-poor' star clusters may have been stolen from nearby dwarf galaxies, which also contain globulars deficient in heavy elements."

Studying globular star clusters is critical to understanding the early, intense star-forming episodes that mark galaxy formation. They are known to reside in all but the faintest of galaxies.

"Star formation near the core of Virgo is very intense and occurs in a small volume over a short amount of time," Peng noted. "It may be more rapid and more efficient than star formation in the outskirts. The high star-formation rate may be driven by the gravitational collapse of dark matter, an invisible form of matter, which is denser and collapses sooner near the cluster's center. M87 sits at the center of a large concentration of dark matter, and all of these globulars near the center probably formed early in the history of the Virgo cluster."

The fewer number of globular clusters in dwarf galaxies farther away from the center may be due to the masses of the star clusters that formed, Peng said. "Star formation farther away from the central region was not as robust, which may have produced only less massive star clusters that dissipated over time," he explained.

The results appeared July 1 in The Astrophysical Journal.

CONTACT
Donna Weaver/Ray Villard
Space Telescope Science Institute, Baltimore, Md.
410-338-4493 / 410-338-4514
dweaver@stsci.edu / villard@stsci.edu

Eric Peng
Peking University, Beijing, China
011-86-10-6275-8629
peng@bac.pku.edu.cn

Astronomers Simulate the First Stars Formed After the Big Bang

Artist concept of the first stars.
Credit: Harvard Smithsonian CfA

What were the first stars like that formed shortly after the Big Bang? We don't know much about the conditions of the early universe 13 billion years ago, but a new computer simulation provides the most detailed picture yet of the first stars and how they came into existence. The composition of the early universe was quite different from that of today, said Dr. Naoki Yoshida, Nagoya University in Nagoya, Japan and Dr. Lars Hernquist at the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA. An article that will be published to the August 1 journal Science describes their findings from the computer model that simulates the early days of the universe, the "cosmic dark ages," where the physics governing the universe were somewhat simpler. The astronomers believe small, simple protostars formed, which eventually became massive, but short-lived stars.

According to their simulations, gravity acted on minute density variations in matter, gases, and the mysterious "dark matter" of the universe after the Big Bang in order to form the early stages of a star called a protostar. With a mass of just one percent of our Sun, Dr. Yoshida's simulation also shows that the protostar would likely evolve into a massive star capable of synthesizing heavy elements, not just in later generations of stars, but soon after the Big Bang. These stars would have been up to one hundred times as massive as our Sun and would have burned for no more than one million years. "This general picture of star formation, and the ability to compare how stellar objects form in different time periods and regions of the universe, will eventually allow investigation in the origins of life and planets," said Hernquist.

"The abundance of elements in the Universe has increased as stars have accumulated," he says, "and the formation and destruction of stars continues to spread these elements further across the Universe. So when you think about it, all of the elements in our bodies originally formed from nuclear reactions in the centers of stars, long ago."

The goal of their research is to be able to figure out how the primordial stars formed, as well as predicting the mass and properties of the first stars of the universe. The researchers hope to eventually extend this simulation to the point of nuclear reaction initiation – when a stellar object becomes a true star. But that's the point where the physics becomes much more complicated, and the researchers say they'll need more computational resources to simulate that process.

Original news source: Harvard Smithsonian Center for Astrophysics
Universe Today

A Midsummer Night's Dream: NGC 4618 and NGC 4625

NGC 4625/18
Credit: Winder / Hager

"Night's swift dragons cut the clouds full fast, And yonder shines…" Another galactic pair? Discovered by Friedrich Wilhelm Herschel in 1787, this particular galactic pairing known as Arp 23 find its home in Canes Venetici, and the duo most certainly has a colorful history. The smaller of the pair - NGC 4625 is a distorted dwarf galaxy formally classified as Sm, a structure which resembles spiral galaxies - especially the Magellanic clouds. So what does a single arm galaxy have to say for itself?

It's been theorized that asymmetrical structure could be the result of a gravitational interaction with NGC 4618 - its larger, interactive member in this picture. Yes, asymmetric structure isn't new when it comes to interacting galaxies, but the rub is only some of the neutral hydrogen gas outside the optical disc of NGC 4618. What does that mean? Quite probably that the single arm shape of the galaxy isn't a product of the interaction - but natural to the galaxy's own, unique properties.

In reading studies done by 2004 by Bush (et al) , "Asymmetry is a common trait in spiral galaxies and is particularly frequent among Magellanic spirals. To explore how morphological and kinematic asymmetry are affected by companion galaxies, we analyze neutral hydrogen observations of the interacting Magellanic spirals NGC 4618 and NGC 4625. The analysis of the H I distribution reveals that about 10% of the total H I mass of NGC 4618 resides in a looping tidal structure that appears to wrap all the way around the galaxy. Through calculations based on derived H I profiles, we show that NGC 4618 and NGC 4625 are no more asymmetric than the noninteracting Magellanic spirals analyzed recently by Wilcots & Prescott. We also derive rotation curves for the approaching and receding sides of each galaxy. By fitting the mean curves with an isothermal halo model, we calculate dynamical masses of 4.7×109 and 9.8×109 Msolar out to 6.7 kpc for NGC 4618 and NGC 4625, respectively. While the rotation curves had systematically higher velocities on the receding side of each galaxy, the effect was no more pronounced than in studies of noninteracting spirals. The degree of interaction-driven asymmetry in both galaxies is indistinguishable from the intrinsic degree of asymmetry of lopsided galaxies."

In 1985, A. V. Filippenko discovered something unusual in the spectrum of NGC 4618: "The object is almost certainly a supernova in an advanced stage, although its spectrum does not conform to published supernova spectra. Based on the present brightness and on the distance modulus of NGC 4618, it is estimated that the object reached maximum about 160 days ago and has faded by 5 to 6 mag, if it was initially a normal Type I or Type II supernova. It is noteworthy that Minkowski (1939, Ap.J. 89, 156) observed the [O I] 630.0/636.4-nm doublet to be strong after 184 days past maximum in the spectrum of the Type I supernova 1937C in IC 4182. The feature was not present in the spectrum of SN 1972E in NGC 5253 some 400 days after maximum (Kirshner and Oke 1975, Ap.J. 200, 574). Prediscovery data on the brightness of the object and future observations of the evolution of its spectrum would be of great interest."

Later that year: "Optical spectra of a bright stellar object near the nucleus of the spiral galaxy NGC 4618 reveal strong, very broad emission lines similar to those in quasars but having the wrong relative wavelengths. Although lines of hydrogen and helium are absent, the most prominent features can be attributed to neutral atoms of oxygen, sodium, and magnesium at the redshift of NGC 4618. The object is almost certainly a supernova whose highly unusual spectrum may be indicative of a fundamentally new subclass." By 1986 the studies had broadened and; "The spectrum of SN 1985f does not resemble any previously published spectra of supernovae, and it is postulated that its progenitor was a massive Wolf-Rayet star that expelled its outer atmosphere of H and He prior to supernova explosion."

However, the real beauty to this picture is what appears to be sparkling star forming regions. According to the studies done by the Elmegreens; "It is suggested that prominent star forming regions occur near the peripheries of barred Magellanic spirals and irregulars because the galaxies experience gas dynamics similar to that in the inner barred regions of massive barred spirals." But… Is the interaction between the two what's causing these exterior star forming regions? Science doesn't seem to think so. Says Zaritsky; "The stellar disks of many spiral galaxies are twice as large as generally thought (and) the phenomenon of low-level star formation well outside the apparent optical edges of disks is common and long lasting."

This is further backed up by studies done by Gil de Paz (et al). "Recent far-UV (FUV) and near-UV (NUV) observations of the nearby galaxy NGC 4625 made by the Galaxy Evolution Explorer (GALEX) show the presence of an extended UV disk reaching to 4 times the optical radius of the galaxy. The UV-to-optical colors suggest that the bulk of the stars in the disk of NGC 4625 are currently being formed, providing a unique opportunity to study today the physics of star formation under conditions similar to those when the normal disks of spiral galaxies like the Milky Way first formed. In the case of NGC 4625, the star formation in the extended disk is likely to be triggered by interaction with NGC 4618 and possibly also with the newly discovered galaxy NGC 4625A."

Yet, star formation isn't all that's going on here. NGC 4618 and NGC 4625 have also been studied for spin as well, and there's a strong possibility that tidal interaction can affect it. According to studies done by Helou. "Clues to the origin of spin in galaxies are also direct clues to the mechanism of galaxy formation. The evidence so far is clearly against a simple picture where primeval turbulence is the source of spin. But the data are consistent with, and suggestive of, the hypothesis that spins were acquired via tidal torquing; a detailed discussion is given, treating separately the possibility that the effect is primordial and the possibility that it is a result of evolution. Enough data are now becoming available that specific calculations are required to sharpen the predictions for the statistical behavior of spins, especially in binaries."

Is there still more to this pair than meets the eye? Certainly. This pair has also been studied for Seyfert nuclei - a brilliant, compact core region which can take a variety of forms, perhaps carrying clues to how the central engine is fed or triggered. Studies show that Seyfert nuclei may happen more frequently among interacting spirals - but more so those that only interact strongly, rather than with extreme tidal distortion. The fascinating work was originally done by Bill Keel and his findings backed up by later studies. It is also very possible this phenomenon simply occurs as a natural process, and the spectral features of Wolf-Rayet stars have also been detected as well. So many different factors can come into play!

No matter what happens in this unusual "inside out" forming pair - be it a detection of a black hole or just a long duration gamma ray burst - they make for fascinating study and a truly beautiful image. "If we shadows have offended, Think but this, and all is mended, That you have but slumber'd here While these visions did appear. And this weak and idle theme, No more yielding, but a dream, Gentles, do not reprehend; If you pardon, we will mend."
The light for this awesome image was gathered over a period of about 7.5 hours by AORAIA member Martin Winder and then processed by member Dr. Dietmar Hager. We thank both of them for the exclusive look at this beautiful galaxy duo.

Universe Today

Astronomers Find New Evidence for Dark Energy

Dark Energy's stretching effect.
Credit: U of Hawaii

A team of astronomers has found what they say is the clearest detection to date of dark energy in the universe. Scientists at the University of Hawaii compared an existing database of galaxies with a map of the cosmic microwave background radiation (CMB), and were able to detect dark energy's effect on vast cosmic structures such as superclusters of galaxies, where there is a high concentration of galaxies, and supervoids, areas in space with a small number of galaxies. “We were able to image dark energy in action, as it stretches huge supervoids and superclusters of galaxies,” said Dr. István Szapudi said, from U of Hawaii's Institute for Astronomy.

The discovery in 1998 that the universe was actually speeding up in its expansion was a surprise to astronomers. Dark energy refers to the fact that something must fill the vast reaches of mostly empty space in the Universe in order to be able to make space accelerate in its expansion. Dark energy works against the tendency of gravity to pull galaxies together and so causes the universe’s expansion to speed up.But the nature of dark energy and why it exists is one of the biggest puzzles of modern science.

The team from the University of Hawaii made the discovery by measuring the subtle imprints that superclusters and supervoids leave in microwaves that pass through them. Superclusters and supervoids are the largest structures in the universe.

“When a microwave enters a supercluster, it gains some gravitational energy, and therefore vibrates slightly faster,” explained Szapudi. “Later, as it leaves the supercluster, it should lose exactly the same amount of energy. But if dark energy causes the universe to stretch out at a faster rate, the supercluster flattens out in the half-billion years it takes the microwave to cross it. Thus, the wave gets to keep some of the energy it gained as it entered the supercluster.”

“Dark energy sort of gives microwaves a memory of where they’ve been recently,” postdoctoral scientist Mark Neyrinck said.

Comparing superclusters (red circles) and supervoids (blue circles) with the CMB.

Credit: U of Hawaii

When the team compared galaxies against the CMB, they found that the microwaves were a bit stronger if they had passed through a supercluster, and a bit weaker if they had passed through a supervoid.

“With this method, for the first time we can actually see what supervoids and superclusters do to microwaves passing through them,” said graduate student Benjamin Granett.

The signal is difficult to detect, since ripples in the primordial CMB are larger than the imprints of individual superclusters and supervoids. To extract a signal, the team averaged together patches of the CMB map around the 50 largest supervoids and the 50 largest superclusters that they detected in extremely bright galaxies drawn from the Sloan Digital Sky Survey, a project that mapped the distribution of galaxies over a quarter of the sky.

The astronomers say there is only a one in 200,000 chance that the evidence they detected would occur by chance.

Original News Source: U of Hawaii press release
Universe Today