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Posts Tagged ‘Galaxies

Hubble Catches a Side-on Spiral Streak

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A side-on spiral streak
This thin, glittering streak of stars is the spiral galaxy ESO 121-6, which lies in the southern constellation of Pictor (The Painter’s Easel). Viewed almost exactly side-on, the intricate structure of the swirling arms is hidden, but the full length of the galaxy can be seen — including the intense glow from the central bulge, a dense region of tightly packed young stars sitting at the center of the spiral arms.

Tendrils of dark dust can be seen across the frame, partially obscuring the bright center of the galaxy and continuing out towards the smattering of stars at its edges, where the dust lanes and shapes melt into the inky background. Numerous nearby stars and galaxies are visible as small smudges in the surrounding sky, and the brightest stars are dazzlingly prominent towards the bottom left of the image.

ESO 121-6 is a galaxy with patchy, loosely-wound arms and a relatively faint central bulge. It actually belongs to a group of galaxies, a clump of no more than 50 similar structures all loosely bound to one another by gravity. The Milky Way is also a member of a galactic group, known as the Local Group.
Read more: http://www.nasa.gov/mission_pages/hubble/science/eso121-6.html

Written by physicsgg

February 9, 2013 at 7:17 am

Posted in ASTRONOMY, ASTROPHYSICS

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Astronomers Uncover A Surprising Trend in Galaxy Evolution

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http://youtu.be/voq3Wfr5cho

A study of 544 star-forming galaxies observed by the Keck and Hubble telescopes shows that disk galaxies like our own Milky Way unexpectedly reached their current state long after much of the universe’s star formation had ceased. Over the past 8 billion years, the galaxies lose chaotic motions and spin faster as they develop into settled disk galaxies. Credit: NASA’s Goddard Space Flight Center

A comprehensive study of hundreds of galaxies observed by the Keck telescopes in Hawaii and NASA’s Hubble Space Telescope has revealed an unexpected pattern of change that extends back 8 billion years, or more than half the age of the universe.

“Astronomers thought disk galaxies in the nearby universe had settled into their present form by about 8 billion years ago, with little additional development since,” said Susan Kassin, an astronomer at NASA’s Goddard Space Flight Center in Greenbelt, Md., and the study’s lead researcher. “The trend we’ve observed instead shows the opposite, that galaxies were steadily changing over this time period.”

Today, star-forming galaxies take the form of orderly disk-shaped systems, such as the Andromeda Galaxy or the Milky Way, where rotation dominates over other internal motions. The most distant blue galaxies in the study tend to be very different, exhibiting disorganized motions in multiple directions. There is a steady shift toward greater organization to the present time as the disorganized motions dissipate and rotation speeds increase. These galaxies are gradually settling into well-behaved disks.

This plot shows the fractions of settled disk galaxies in four time spans, each about 3 billion years long. There is a steady shift toward higher percentages of settled galaxies closer to the present time. At any given time, the most massive galaxies are the most settled. More distant and less massive galaxies on average exhibit more disorganized internal motions, with gas moving in multiple directions, and slower rotation speeds. Credit: NASA’s Goddard Space Flight Center

Blue galaxies — their color indicates stars are forming within them — show less disorganized motions and ever-faster rotation speeds the closer they are observed to the present. This trend holds true for galaxies of all masses, but the most massive systems always show the highest level of organization.

Researchers say the distant blue galaxies they studied are gradually transforming into rotating disk galaxies like our own Milky Way.

“Previous studies removed galaxies that did not look like the well-ordered rotating disks now common in the universe today,” said co-author Benjamin Weiner, an astronomer at the University of Arizona in Tucson. “By neglecting them, these studies examined only those rare galaxies in the distant universe that are well-behaved and concluded that galaxies didn’t change.”

Rather than limit their sample to certain galaxy types, the researchers instead looked at all galaxies with emission lines bright enough to be used for determining internal motions. Emission lines are the discrete wavelengths of radiation characteristically emitted by the gas within a galaxy. They are revealed when a galaxy’s light is separated into its component colors. These emission lines also carry information about the galaxy’s internal motions and distance.


http://youtu.be/_Ssc1GsqHds

Simulations such as this will help astronomers better understand the new findings in galaxy evolution. It tracks the development of a single disk galaxy from shortly after the Big Bang to the present day. Colors reveal old stars (red), young stars (white and bright blue) and the distribution of gas density (pale blue); the view is 300,000 light-years across. Credit: F. Governato and T. Quinn (Univ. of Washington), A. Brooks (Univ. of Wisconsin, Madison), and J. Wadsley (McMaster Univ.). Hi-res video is on the same SVS page as the above video

The team studied a sample of 544 blue galaxies from the Deep Extragalactic Evolutionary Probe 2 (DEEP2) Redshift Survey, a project that employs Hubble and the twin 10-meter telescopes at the W. M. Keck Observatory in Hawaii. Located between 2 billion and 8 billion light-years away, the galaxies have stellar masses ranging from about 0.3 percent to 100 percent of the mass of our home galaxy.

A paper describing these findings will be published Oct. 20 in The Astrophysical Journal.

The Milky Way galaxy must have gone through the same rough-and-tumble evolution as the galaxies in the DEEP2 sample, and gradually settled into its present state as the sun and solar system were being formed.

In the past 8 billion years, the number of mergers between galaxies large and small has decreased sharply. So has the overall rate of star formation and disruptions of supernova explosions associated with star formation. Scientists speculate these factors may play a role in creating the evolutionary trend they observe.

Now that astronomers see this pattern, they can adjust computer simulations of galaxy evolution until these models are able to replicate the observed trend. This will guide scientists to the physical processes most responsible for it.

Read more: www.nasa.gov

Written by physicsgg

October 19, 2012 at 7:47 pm

Posted in ASTRONOMY, ASTROPHYSICS

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Galaxy dance of death creates starburst shockwave

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(Image: Gemini Observatory/AURA)

Meet a poor crazy mixed-up galaxy, NGC 660. It’s a lenticular galaxy, meaning it’s not a crowd-pleasing spiral or a shapeless blob elliptical, but essentially both. Visible in this image from a Gemini telescope on the mountain Mauna Kea, Hawaii, is a surrounding ring of gas, dust and stars, which is what’s confusing astronomers.

First, some bad news: in a few billion years, the Andromeda galaxy (which, on a clear night you might be able to see from your backyard without a telescope) is going to swallow the Milky Way. That’s us. It’s nothing personal, it’s just what galaxies do sometimes. Anyway, this won’t happen until long after apes have taken over the Earth.

At first, that seemed the easiest explanation for how NGC 660 formed.

However, when that happens, we usually see a collapsed core at the galaxy’s centre and sudden heightened activity of star formation, not to mention an extra supermassive black hole at the centre of the new galaxy. Also missing are the tails of ejected stars, gas and dust that get thrown out of the newly merged galaxies as a result of the violence of the event.

Brian Svoboda of the University of Arizona believes the ring came from a “tidal accretion event scenario” – in simplest terms, the gravitational dance of death of a pair of galaxies resulted in a massive shockwave.

The shockwave created gigantic blue stars, in this case 100 times the mass of our sun. They exploded, adding to the chaos, creating more and more shockwaves and turning NGC 660 into a starburst galaxy, one of the most intense star-forming environments.

“It really is the most incredibly picture I’ve seen of the galaxy,” Svoboda said. “None of the other images I’ve seen, including those from the Hubble Space Telescope, show the star-forming region with such clarity.”

To top it off, NGC 660’s host galaxy and ring rotate at velocities inconsistent with the amount of gas they contain. This points straight at the existence of huge amounts of dark matter, that invisible, elusive substance that is thought to make up the huge majority of the universe. This weird, wonderful galaxy further may offer some clues, if it feels like talking.
Joanna Carver
Read more: www.newscientist.com

Written by physicsgg

October 19, 2012 at 5:08 pm

Posted in ASTRONOMY, ASTROPHYSICS

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Video: Galaxy Formation

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Written by physicsgg

October 17, 2012 at 6:04 pm

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NASA Telescopes Spy Ultra-Distant Galaxy

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In the big image at left, the many galaxies of a massive cluster called MACS J1149+2223 dominate the scene. Gravitational lensing by the giant cluster brightened the light from the newfound galaxy, known as MACS 1149-JD, some 15 times. At upper right, a partial zoom-in shows MACS 1149-JD in more detail, and a deeper zoom appears to the lower right.. Image credit: NASA/ESA/STScI/JHU

With the combined power of NASA’s Spitzer and Hubble space telescopes, as well as a cosmic magnification effect, astronomers have spotted what could be the most distant galaxy ever seen. Light from the young galaxy captured by the orbiting observatories first shone when our 13.7-billion-year-old universe was just 500 million years old.

The far-off galaxy existed within an important era when the universe began to transit from the so-called cosmic dark ages. During this period, the universe went from a dark, starless expanse to a recognizable cosmos full of galaxies. The discovery of the faint, small galaxy opens a window onto the deepest, most remote epochs of cosmic history.

“This galaxy is the most distant object we have ever observed with high confidence,” said Wei Zheng, a principal research scientist in the department of physics and astronomy at Johns Hopkins University in Baltimore who is lead author of a new paper appearing in Nature. “Future work involving this galaxy, as well as others like it that we hope to find, will allow us to study the universe’s earliest objects and how the dark ages ended.”

Light from the primordial galaxy traveled approximately 13.2 billion light-years before reaching NASA’s telescopes. In other words, the starlight snagged by Hubble and Spitzer left the galaxy when the universe was just 3.6 percent of its present age. Technically speaking, the galaxy has a redshift, or “z,” of 9.6. The term redshift refers to how much an object’s light has shifted into longer wavelengths as a result of the expansion of the universe. Astronomers use redshift to describe cosmic distances.

Unlike previous detections of galaxy candidates in this age range, which were only glimpsed in a single color, or waveband, this newfound galaxy has been seen in five different wavebands. As part of the Cluster Lensing And Supernova Survey with Hubble Program, the Hubble Space Telescope registered the newly described, far-flung galaxy in four visible and infrared wavelength bands. Spitzer measured it in a fifth, longer-wavelength infrared band, placing the discovery on firmer ground.

Objects at these extreme distances are mostly beyond the detection sensitivity of today’s largest telescopes. To catch sight of these early, distant galaxies, astronomers rely on gravitational lensing. In this phenomenon, predicted by Albert Einstein a century ago, the gravity of foreground objects warps and magnifies the light from background objects. A massive galaxy cluster situated between our galaxy and the newfound galaxy magnified the newfound galaxy’s light, brightening the remote object some 15 times and bringing it into view.

Based on the Hubble and Spitzer observations, astronomers think the distant galaxy was less than 200 million years old when it was viewed. It also is small and compact, containing only about 1 percent of the Milky Way’s mass. According to leading cosmological theories, the first galaxies indeed should have started out tiny. They then progressively merged, eventually accumulating into the sizable galaxies of the more modern universe.

These first galaxies likely played the dominant role in the epoch of reionization, the event that signaled the demise of the universe’s dark ages. This epoch began about 400,000 years after the Big Bang when neutral hydrogen gas formed from cooling particles. The first luminous stars and their host galaxies emerged a few hundred million years later. The energy released by these earliest galaxies is thought to have caused the neutral hydrogen strewn throughout the universe to ionize, or lose an electron, a state that the gas has remained in since that time.

“In essence, during the epoch of reionization, the lights came on in the universe,” said paper co-author Leonidas Moustakas, a research scientist at NASA’s Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, Calif.

Astronomers plan to study the rise of the first stars and galaxies and the epoch of reionization with the successor to both Hubble and Spitzer, NASA’s James Webb Telescope, which is scheduled for launch in 2018. The newly described distant galaxy will likely be a prime target.
Read more: www.jpl.nasa.gov

Written by physicsgg

September 19, 2012 at 6:30 pm

Space-time ripples record black hole crashes

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Did monster black holes pull the first galaxies together, or were they born inside those galaxies? It’s a long-standing mystery. Now a new analysis of the gravitational ripples from colliding black holes could reveal the answer by helping astronomers reconstruct a crash rather than just surveying its aftermath.

Most large galaxies we see have supermassive black holes at their centres. When these galaxies collide, their black holes merge into one even more massive beast, according to theory. Observations of the final black hole yield no information about the original black holes, however.

So astronomers have been trying to look for gravitational waves. General relativity predicts that colliding black holes should emit such ripples in the fabric of space-time, including a wave called the ringdown that contains information about the final black hole’s mass and spin.

Now computer simulations led by Ioannis Kamaretsos of the University of Cardiff, UK, show that the ringdown can also tell us the masses and spins of the two original black holes (arxiv.org/abs/1207.0399).

Some theories say the gravity of nascent black holes pulled matter together to form the first galaxies, but it remains unclear if the earliest black holes were massive enough to do this. By applying the new analysis to observations of the early universe, we might be able to settle that question at last.

Although nobody has detected gravitational waves as yet, next-generation observatories may spot them within a few years.

Read more: newscientist.com

Written by physicsgg

August 19, 2012 at 10:54 pm

Posted in RELATIVITY

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Hubble Spots Rare Gravitational Arc from Distant, Hefty Galaxy Cluster

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Seeing is believing, except when you don’t believe what you see.
Astronomers using NASA’s Hubble Space Telescope have found a puzzling arc of light behind an extremely massive cluster of galaxies residing 10 billion light-years away. The galactic grouping, discovered by NASA’s Spitzer Space Telescope, was observed when the universe was roughly a quarter of its current age of 13.7 billion years. The giant arc is the stretched shape of a more distant galaxy whose light is distorted by the monster cluster’s powerful gravity, an effect called gravitational lensing.

The trouble is, the arc shouldn’t exist.

“When I first saw it, I kept staring at it, thinking it would go away,” said study leader Anthony Gonzalez of the University of Florida in Gainesville. “According to a statistical analysis, arcs should be extremely rare at that distance. At that early epoch, the expectation is that there are not enough galaxies behind the cluster bright enough to be seen, even if they were ‘lensed’ or distorted by the cluster. The other problem is that galaxy clusters become less massive the farther back in time you go. So it’s more difficult to find a cluster with enough mass to be a good lens for gravitationally bending the light from a distant galaxy.”

Galaxy clusters are collections of hundreds to thousands of galaxies bound together by gravity. They are the most massive structures in our universe. Astronomers frequently study galaxy clusters to look for faraway, magnified galaxies behind them that would otherwise be too dim to see with telescopes. Many such gravitationally lensed galaxies have been found behind galaxy clusters closer to Earth.

The surprise in this Hubble observation is spotting a galaxy lensed by an extremely distant cluster. Dubbed IDCS J1426.5+3508, the cluster is the most massive found at that epoch, weighing as much as 500 trillion suns. It is 5 to 10 times larger than other clusters found at such an early time in the universe’s history. The team spotted the cluster in a search using NASA’s Spitzer Space Telescope in combination with archival optical images taken as part of the National Optical Astronomy Observatory’s Deep Wide Field Survey at the Kitt Peak National Observatory, Tucson, Ariz. The combined images allowed them to see the cluster as a grouping of very red galaxies, indicating they are far away.

This unique system constitutes the most distant cluster known to “host” a giant gravitationally lensed arc. Finding this ancient gravitational arc may yield insight into how, during the first moments after the big bang, conditions were set up for the growth of hefty clusters in the early universe.

The arc was spotted in optical images of the cluster taken in 2010 by Hubble’s Advanced Camera for Surveys. The infrared capabilities of Hubble’s Wide Field Camera 3 (WFC3) helped provide a precise distance, confirming it to be one of the farthest clusters yet discovered.

Once the astronomers determined the cluster’s distance, they used Hubble, the Combined Array for Research in Millimeter-wave Astronomy (CARMA) radio telescope, and NASA’s Chandra X-ray Observatory to independently show that the galactic grouping is extremely massive.

CARMA helped the astronomers determine the cluster’s mass by measuring how primordial light from the big bang was affected as it passed through the extremely hot, tenuous gas that permeates the grouping. The astronomers then used the WFC3 observations to map the cluster’s mass by calculating how much cluster mass was needed to produce the gravitational arc. Chandra data, which revealed the cluster’s brightness in X-rays, was also used to measure the cluster’s mass.

“The chance of finding such a gigantic cluster so early in the universe was less than one percent in the small area we surveyed,” said team member Mark Brodwin of the University of Missouri-Kansas City. “It shares an evolutionary path with some of the most massive clusters we see today, including the Coma Cluster and the recently discovered El Gordo Cluster.”

An analysis of the arc revealed that the lensed object is a star-forming galaxy that existed 10 billion to 13 billion years ago. The team hopes to use Hubble again to obtain a more accurate distance to the lensed galaxy.

Gonzalez has considered several possible explanations for the arc.

One explanation is that distant galaxy clusters, unlike nearby clusters, have denser concentrations of galaxies at their cores, making them better magnifying glasses. However, even if the distant cores were denser, the added bulk still should not provide enough gravitational muscle to produce the giant arc seen in Gonzalez’s observations, according to a statistical analysis.

Another possibility is that the initial microscopic fluctuations in matter made right after the big bang were different from those predicted by standard cosmological simulations, and therefore produced more massive clusters than expected.

“I’m not yet convinced by any of these explanations,” Gonzalez said. “After all, we have found only one example. We really need to study more extremely massive galaxy clusters that existed between 8 billion and 10 billion years ago to see how many more gravitationally lensed objects we can find.”

The team’s results are described in three papers, which will appear in the July 10, 2012 issue of The Astrophysical Journal. Gonzalez is the first author on one of the papers; Brodwin, on another; and Adam Stanford of the University of California at Davis, on the third…

Read more: www.nasa.gov

Written by physicsgg

June 26, 2012 at 7:31 pm

Hubble Spies Edge-on Beauty

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Credit: ESA/Hubble & NASA

Visible in the constellation of Andromeda, NGC 891 is located approximately 30 million light-years away from Earth. The NASA/ESA Hubble Space Telescope turned its powerful wide field Advanced Camera for Surveys towards this spiral galaxy and took this close-up of its northern half. The galaxy’s central bulge is just out of the image on the bottom left.

The galaxy, spanning some 100,000 light-years, is seen exactly edge-on, and reveals its thick plane of dust and interstellar gas. While initially thought to look like our own Milky Way if seen from the side, more detailed surveys revealed the existence of filaments of dust and gas escaping the plane of the galaxy into the halo over hundreds of light-years. They can be clearly seen here against the bright background of the galaxy halo, expanding into space from the disk of the galaxy.

Astronomers believe these filaments to be the result of the ejection of material due to supernovae or intense stellar formation activity. By lighting up when they are born, or exploding when they die, stars cause powerful winds that can blow dust and gas over hundreds of light-years in space.

A few foreground stars from the Milky Way shine brightly in the image, while distant elliptical galaxies can be seen in the lower right of the image.

NGC 891 is part of a small group of galaxies bound together by gravity.

A version of this image was entered into the Hubble’s Hidden Treasures Image Processing Competition by contestant Nick Rose. Hidden Treasures is an initiative to invite astronomy enthusiasts to search the Hubble archive for stunning images that have never been seen by the general public.
Read more: www.nasa.gov

Written by physicsgg

May 18, 2012 at 9:29 pm