abcstarstuff:

Green Pea galaxies could help astronomers understand early universe

The rare Green Pea galaxies discovered by the general public in 2007 could help confirm astronomers’ understanding of reionization, a pivotal stage in the evolution of the early universe, say University of Michigan researchers.

Reionization occurred a few hundred million years after the Big Bang as the first stars were turning on and forming the first galaxies. During this period, the space between the galaxies changed from an opaque, neutral fog to a transparent charged plasma, as it is today. Plasma is gas that’s electrically charged.

As for how this happened, the prevailing theory holds that massive stars in the early galaxies produced an abundance of high-energy ultraviolet light that escaped into intergalactic space. There, the UV light interacted with the neutral hydrogen gas it met, blasting electrons off the hydrogen atoms and leaving behind a plasma of negatively charged electrons and positively charged hydrogen ions.

“We think this is what happened but when we looked at galaxies nearby, the high-energy radiation doesn’t appear to make it out. There’s been a push to find some galaxies that show signs of radiation escaping,” said Anne Jaskot, a doctoral student in astronomy.

Jaskot and Sally Oey, an associate professor of astronomy in the College of Literature, Science, and the Arts, have found that the Green Peas could hold that evidence. Their findings are published in the current edition of the Astrophysical Journal.

“The Green Peas are compact, highly star-forming galaxies that are very similar to the early galaxies in the universe,” Jaskot said. “Our analysis shows they may be leaking ionizing radiation.”

The researchers focused on six of the most intensely star-forming Green Pea galaxies, which are between one billion and five billion light years away. They studied their emission lines as observed by the Sloan Digital Sky Survey. Emission lines show how light interacts with matter, and in this case, they helped the astronomers understand the relationship between the stars and gas in these galaxies.

The emission lines told Jaskot and Oey how much light the galaxies absorbed. Then, to determine how much light was there to start with, they ran models to estimate, for example, how old the galaxies are and how many stars they contain. The galaxies, the researchers determined, produced more radiation than the researchers detected, so they infer that some of it must have escaped.

“An analogy might be if you have a tablecloth and you spill something on it. If you see the cloth has been stained all the way to the edges, there’s a good chance it also spilled onto the floor,” Jaskot said. “We’re looking at the gas like the tablecloth and seeing how much light it has absorbed. It has absorbed a lot of light. We’re seeing that the galaxy is saturated with it and there’s probably some extra that spilled off the edges.”

Jaskot says the Green Peas are exciting candidates to help astronomers understand a major milestone in the development of the cosmos 13 billion years ago.

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The paper is called “The Origin and Optical Depth of Ionizing Radiation in the ‘Green Pea’ Galaxies. The research is funded by the National Science Foundation.

infinity-imagined:

A Flight Through the Universe, rendered from the Sloan Digital Sky Survey.

Largest Structure in Universe Discovered

Astronomers have discovered the largest known structure in the universe, a clump of active galactic cores that stretches 4 billion light-years from end to end.

The structure is a large quasar group (LQG), a collection of extremely luminous galactic nuclei powered by supermassive central black holes. This particular group is so large that it challenges modern cosmological theory, researchers said.

“While it is difficult to fathom the scale of this LQG, we can say quite definitely it is the largest structure ever seen in the entire universe,” lead author Roger Clowes, of the University of Central Lancashire in England, said in a statement. “This is hugely exciting, not least because it runs counter to our current understanding of the scale of the universe.”

Quasars are the brightest objects in the universe. For decades, astronomers have known that they tend to assemble in huge groups, some of which are more than 600 million light-years wide.

But the record-breaking quasar group, which Clowes and his team spotted in data gathered by the Sloan Digital Sky Survey, is on another scale altogether. The newfound LQC is composed of 73 quasars and spans about 1.6 billion light-years in most directions, though it is 4 billion light-years across at its widest point.

To put that mind-boggling size into perspective, the disk of the Milky Way galaxy — home of Earth’s solar system — is about 100,000 light-years wide. And the Milky Way is separated from its nearest galactic neighbor, Andromeda, by about 2.5 million light-years.

The newly discovered LQC is so enormous, in fact, that theory predicts it shouldn’t exist, researchers said. The quasar group appears to violate a widely accepted assumption known as the cosmological principle, which holds that the universe is essentially homogeneous when viewed at a sufficiently large scale.

Calculations suggest that structures larger than about 1.2 billion light-years should not exist, researchers said.

“Our team has been looking at similar cases which add further weight to this challenge, and we will be continuing to investigate these fascinating phenomena,” Clowes said.

The new study was published today (Jan. 11) in the Monthly Notices of the Royal Astronomical Society.

image: Light from the most distant quasar yet seen reveals details about the chemistry of the early universe.
CREDIT: ESO/M. Kornmesser

The experiment is the Baryon Oscillation Spectroscopic Survey (BOSS), which is using the 2.5-meter (100-inch) Sloan Digital Sky Survey telescope.

The original Sloan survey compiled the most detailed three-dimensional map to date of a large swath of the universe. It used bundles of digital fibers to observe more than one million galaxies. The data included each galaxy’s location on the sky and its distance from Earth.

A team of astronomers used the observations of how galaxies are distributed through space to search for evidence of baryon acoustic oscillations. Observations of 46,000 luminous red galaxies, which are especially bright and red, across several billion light-years of space revealed a slight excess of galaxies that are 500 million light-years apart. This distance is like the crest in a ripple from a rock thrown into a still pond. As the universe expands, the size of these ripples should increase with it, so measuring the size of the ripples at different times will reveal how the expansion of the universe has changed.

(Source: ikenbot)

leonis2012:

Andrew Fazekas

for National Geographic News

Published August 9, 2012

A new 3-D map of the universeis the biggest ever made, providing the most detailed view of the sky yet, astronomers say.

The crown jewel of the six-yearSloan Digital Sky Survey III (SDSS III), the map was created by targeting nearly a million galaxiesup to 12 billion light-years from Earth—in part by using a spectrometer that can measure the distances to thousands of separate galaxies simultaneously.

Watch a fly-through video of the 3-D map.

sciencesoup:

A Flight Through the Universe

The Sloan Digital Sky Survey III creates detailed 3D maps of the sky by using spectroscopic data of hundreds of thousands of galaxies. The video is so breathtaking that it deserves to be watched in high definition—it shows almost 400,000 galaxies in their actual positions, as dictated by the SDSS Data Release 7, but although it seems vast, the objects are only up to 1.3 billion light years from Earth. The very recent Data Release 9, on the other hand, includes data for over half a million galaxies up to 7 billion light years away. Since the light of distant galaxies can take billions of years to reach Earth, it’s like looking at a fossil record of the distant past, and so the SDSS team is basically tracing billions of years of the Universe’s history, which will hopefully give us a better understanding of the nature of dark energy—the mysterious force that drives the Universe’s acceleration. Encouragingly, the survey’s data appears to be consistent with current models of the structure of the Universe that account for dark energy. Though the survey ends in 2014, the SDSS aims to map a quarter of the sky, and is confident that their maps will aid us, or future generations, in solving our Universe’s mysteries.

Galactic Gong - Milky Way Struck, Still Ringing After 100 Million Years

When galaxies collide, stars are thrown from orbits, spiral arms are stretched and twisted, and now scientists say galaxies ring like a bell long after the cosmic crash.

A team of astronomers from the United States and Canada say they have heard echoes of that ringing, possible evidence of a galactic encounter 100 million years ago when a small satellite galaxy or dark matter object passed through the Milky Way Galaxy; close to our position in the galaxy, as if a rock were thrown into a still pond causing the stars to bounce up and down on the waves. Their results were published in the Astrophysical Journal Letters.

“We have found evidence that our Milky Way had an encounter with a small galaxy or massive dark matter structure perhaps as recently as 100 million years ago,” said Larry Widrow, professor at Queen’s University in Canada. “We clearly observe unexpected differences in the Milky Way’s stellar distribution above and below the Galaxy’s midplane that have the appearance of a vertical wave — something that nobody has seen before.”

Astronomers took observations from about 300,000 nearby stars in the Sloan Digital Sky Survey. Stars move up and down at 20-30 kilometers per second while see-sawing around the galaxy at 220 kilometers per second. By comparison, the International Space Station putters around Earth at 7.71 kilometers per second; Voyager 1, the fastest man-made object, currently is leaving the solar system at about 17.46 kilometers per second. Widrow and colleagues at the University of Kentucky, The University of Chicago and Fermi National Accelerator Laboratory found that the positions of nearby stars is not quite as regular as previously thought. The team noticed a small but statistically significant difference in the distribution of stars above and below the midplane of the Milky Way.

“Our part of the Milky Way is ringing like a bell,” said Brian Yanny, of the Department of Energy’s Fermilab. “But we have not been able to identify the celestial object that passed through the Milky Way. It could have been one of the small satellite galaxies that move around the center of our galaxy, or an invisible structure such as a dark matter halo.”

Susan Gardner, professor of physics at the University of Kentucky added, “The perturbation need not have been a single isolated event in the past, and it may even be ongoing. Additional observations may well clarify its origin.”

Other possibilities considered for the variations were the effect of interstellar dust or simply the way the stars were selected in the survey. But as those events failed to explain fully the observations, the astronomers began to explore possible recent events in the history of the galaxy.

More than 20 visible satellite galaxies circle the Milky Way. Invisible satellites made up of dark matter, hypothetical matter that cannot be seen but is thought to make up a majority of the mass of the Universe, might also orbit our galaxy. Scientists believe that most of the mass orbiting the galaxy is in the form of dark matter. Using computer simulations to explore the effects of a small galaxy or dark matter structure passing through the disk of the Milky Way, the scientists developed a clearer picture of the see-saw effects they were seeing.

In terms of the nine-billion lifetime of the Milky Way Galaxy, the effects are short-lived. This part of the galaxy has been “ringing” for 100 million years and will continue for 100 million years more as the up-and-down motion dissipates, say the astronomers – unless we are hit again.

Image caption: The Small Magellanic Cloud is one of 20 visible satellite galaxies that orbit the Milky Way Galaxy. Astronomers report that a smaller counterpart or dark matter object passed through the Milky Way near our position about 100 million years ago.

thescienceofreality:

Predicting “Cosmic Fireworks” From Our Own Backyard

Using the largest map of the cosmos ever, astronomers have counted nearby double white dwarfs, stars thought to cause an important type of supernova

The right resource, and a lot of hard work, can really light up the sky.

Taking advantage of a little-known feature of the National Science Foundation-funded Sloan Digital Sky Survey (SDSS), a team of astronomers led by Carles Badenes of the University of Pittsburgh recently helped clarify the origins of an important type of cosmic explosion using nothing but a few thousand small, faint stars.

The SDSS already has produced the most detailed map of the universe ever created, with images of nearly 500 million stars and galaxies available to the public. The map shows the structure of the universe at the grandest scales, with long walls of galaxies snaking around near-empty voids. But in addition to these ultra-distant galaxies, the SDSS also has mapped nearby stars in the Milky Way.

Badenes is interested in both scales. He studies distant, incredibly bright stellar fireworks called Type Ia supernovae. Although rare, Type Ia supernovae are important.

Continue.

(via wildlydistorted)