How Much Light Has The Universe Created Since the Big Bang?

The universe, most cosmologists tell us, began with a bang. At some point, the lights turned on. How much light has the universe produced since it was born, 13.8 billion years ago?

It seems a difficult answer at first glance. Turn on a light bulb, turn it off and the photons appear to vanish. In space, however, we can track them down. Every light particle ever radiated by galaxies and stars is still travelling, which is why we can peer so far back in time with our telescopes.

A new paper in the Astrophysical Journal explores the nature of this extragalactic background light, or EBL. Measuring the EBL, the team states, “is as fundamental to cosmology as measuring the heat radiation left over from the Big Bang (the cosmic microwave background) at radio wavelengths.”

Turns out that several NASA spacecraft have helped us understand the answer. They peered at the universe in every wavelength of light, ranging from long radio waves to short, energy-filled gamma rays. While their work doesn’t go back to the origin of the universe, it does give good measurements for the last five billion years or so. (About the age of the solar system, coincidentally.)

Artist's conception of how gamma rays (dashed lines) bump against photons of electromagnetic background light, producing electrons and positrons. Credit: Nina McCurdy and Joel R. Primack/UC-HiPACC; Blazar: Frame from a conceptual animation of 3C 120 created by Wolfgang Steffen/UNAM
Artist’s conception of how gamma rays (dashed lines) bump against photons of electromagnetic background light, producing electrons and positrons. Credit: Nina McCurdy and Joel R. Primack/UC-HiPACC; Blazar: Frame from a conceptual animation of 3C 120 created by Wolfgang Steffen/UNAM

It’s hard to see this faint background light against the powerful glow of stars and galaxies today, about as hard as it is to see the Milky Way from downtown Manhattan, the astronomers said.

The solution involves gamma rays and blazars, which are huge black holes in the heart of a galaxy that produce jets of material that point towards Earth. Just like a flashlight.

These blazars emit gamma rays, but not all of them reach Earth. Some, astronomers said, “strike a hapless EBL photon along the way.”

When this happens, the gamma ray and photon each zap out and produce a negatively charged electron and a positively charged positron.

More interestingly, blazars produce gamma rays at slightly different energies, which are in turn stopped by EBL photons at different energies themselves.

So, by figuring out how many gamma rays with different energies are stopped by the photons, we can see how many EBL photons are between us and the distant blazars.

Scientists have now just announced they could see how the EBL changed over time. Peering further back in the universe, as we said earlier, serves as a sort of time machine. So, the further back we see the gamma rays zap out, the better we can map out the EBL’s changes in earlier eras.

The Fermi Gamma-ray Space Telescope (formerly called GLAST).  Credit: NASA
The Fermi Gamma-ray Space Telescope (formerly called GLAST). Credit: NASA

To get technical, this is how the astronomers did it:

– Compared the gamma-ray findings of the Fermi Gamma-ray Space Telescope to the intensity of X-rays measured by several X-ray observatories, including the Chandra X-Ray Observatory, the Swift Gamma-Ray Burst Mission, the Rossi X-ray Timing Explorer, and XMM/Newton. This let astronomers figure out what the blazars’ brightnesses were at different energies.

– Comparing those measurements to those taken by special telscopes on the ground that can look at the actual “gamma-ray flux” Earth receives from those blazars. (Gamma rays are annihilated in our atmosphere and produce a shower of subatomic particles, sort of like a “sonic boom”, called Cherenkov radiation.)

The measurements we have in this paper are about as far back as we can see right now, the astronomers added.

“Five billion years ago is the maximum distance we are able to probe with our current technology,” stated the paper’s lead author, Alberto Dominguez.

“Sure, there are blazars farther away, but we are not able to detect them because the high-energy gamma rays they are emitting are too attenuated by EBL when they get to us—so weakened that our instruments are not sensitive enough to detect them.”

Source: University of California High-Performance AstroComputing Center

New Movie of a Neutron Star Looks Eerily Like the Phantom of the Opera

This incredible new movie of the Vela pulsar has the unnerving appearance of the Phantom of the Opera – wearing not only a mask, but also a steam-blowing hat like the Tin Man in “The Wizard of Oz.” What you are seeing here are observations from the Chandra X-ray Observatory, showing a fast moving jet of particles produced by a rapidly rotating neutron star. Scientists say these observations may provide new insight into the nature of some of the densest matter in the universe.

The Vela pulsar is about 1,000 light-years from Earth, about 19 km (12 miles) in diameter, and makes a complete rotation in 89 milliseconds. As the pulsar whips around, it spews out a jet of charged particles that race along the pulsar’s rotation axis at about 70 percent of the speed of light. The Chandra data used in the movie were obtained from June to September 2010, and it may suggest the pulsar may be slowly wobbling, or precessing, as it spins. The period of the precession, which is analogous to the slow wobble of a spinning top, is estimated to be about 120 days.

“We think the Vela pulsar is like a rotating garden sprinkler — except with the water blasting out at over half the speed of light,” said Martin Durant of the University of Toronto in Canada, who is the first author of the paper describing these results.

The eight images shown in the movie suggest that the pulsar may be slowly wobbling, or precessing, as it spins. If the evidence for precession of the Vela pulsar is confirmed, it would be the first time that a jet from a neutron star has been found to be wobbling, or precessing, in this way.

One possible cause of precession for a spinning neutron star is that it has become slightly distorted and is no longer a perfect sphere. This distortion might be caused by the combined action of the fast rotation and “glitches”, sudden increases of the pulsar’s rotational speed due to the interaction of the superfluid core of the neutron star with its crust.

A paper describing these results will be published in The Astrophysical Journal on January 10, 2013.

This is the second Chandra movie of the Vela pulsar. The first one, released in 2003, looks like a Halloween Jack-o-lanatern gone wrong:

This movie contains shorter, unevenly spaced observations so that the changes in the jet were less pronounced and the authors did not argue that precession was occurring. However, based on the same data, Avinash Deshpande of Arecibo Observatory in Puerto Rico and the Raman Research Institute in Bangalore, India, and the late Venkatraman Radhakrishnan, argued in a 2007 paper that the Vela pulsar might be precessing.

The Earth also precesses as it spins, with a period of about 26,000 years. In the future Polaris will no longer be the “north star” and other stars will take its place. The period of the Vela precession is much shorter and is estimated to be about 120 days.

Wide field Optical and X-ray image of the supernova remnant in the Vela Pulsar region. Credit: Anglo-Australian Observatory.
Wide field Optical and X-ray image of the supernova remnant in the Vela Pulsar region. Credit: Anglo-Australian Observatory.

The supernova that formed the Vela pulsar exploded over 10,000 years ago. This optical image from the Anglo-Australian Observatory’s UK Schmidt telescope shows the enormous apparent size of the supernova remnant formed by the explosion. The full size of the remnant is about eight degrees across, or about 16 times the angular size of the Moon. The square near the center shows the Chandra image with a larger field-of-view than used for the movie, with the Vela pulsar in the middle.

A 'Phantom of the Opera' - like mask.
A 'Phantom of the Opera' - like mask.


Source:
NASA

Combining Light to Reveal Monster Black Holes

NGC 3627 glows in the combined light of Hubble, Chandra, Spitzer and the Very Large Telescope in this image. Astronomers conducted a survey of 62 galaxies, including NGC 3627 to study monster black holes at their centers.

It’s not just pretty, it’s science. Like a starry watercolor, astronomers combining light from Earth and space-based observatories found 37 new supermassive black hole candidates lurking in nearby galaxies.

Included in that survey is NGC 3627 pictured above. Astronomers combined X-ray data from NASA’s Chandra X-ray Observatory, infrared data from the Spitzer Space Telescope, and optical data from the Hubble Space Telescope and the Very Large Telescope. The other images give the galaxy context but it’s the ghostly blue images from Chandra that show super bright in the X-ray images; X-ray light powered by material falling into a monster black hole.

Gas and dust slowly spins around the black hole creating a flattened disk, or accretion disk. As material falls inward, it heats up and releases large amounts of energy that shine brightly in the ultraviolet region of the spectrum.

NGC 3627, located about 30 million light-years from Earth, was just one of a survey of 62 nearby galaxies using archived data from Chandra and data from the Spitzer Infrared Nearby Galaxy Survey. Of those, 37 galaxies contained bright X-ray sources, indicating active black holes at their cores. Scientists believe that seven of those sources are new supermassive black hole candidates.

The paper describing the survey results was published in the April 10, 2011 issue of The Astrophysical Journal.

Combining ultraviolet and infrared observations confirm previous Chandra results that found that there may be many more galaxies powered by monster black holes than believed previously through optical surveys. Scientists say in the paper that low-levels of black hole activity previously may have been hidden by dust or washed out by the bright light of the galaxy.

Image caption: Bright X-ray sources glow a ghostly blue in this image in NGC 3627 from NASA’s Chandra X-ray Observatory. A study confirms previous Chandra results that indicate that more galaxies powered by monster black holes populate the cosmos.

Source: Chandra X-ray Observatory website

Blowing a Super-duper Celestial Bubble

Image credit: X-ray: NASA/CXC/U.Mich./S.Oey, IR: NASA/JPL, Optical: ESO/WFI/2.2-m. Zoom by John Williams/TerraZoom using Zoomify

When NASA combines images from different telescopes, they create dazzling scenes of celestial wonder and in the process we learn a few more things. Behold this wonder of combined light, known as LHA 120-N 44, or N 44 for short. Zoom into the scene using the toolbar at the bottom of the image. Click the farthest button on the right of the toolbar to see this wonder in full-screen. (Hint: press the “Esc” key to get back to work)

Continue reading “Blowing a Super-duper Celestial Bubble”

The Unusually Colossal Kepler Supernova

A composite image of Chandra X-ray data shows a rainbow of reds, yellows, green, blue and purple, from lower to higher energies. Optical data from the Digitized Sky Survey, shown in pale yellow and blue, offer a starry background for the image. Optical: DSS

An arc of hot gas that spewed from the Kepler Supernova offers tantalizing clues that the cataclysmic stellar explosion of 1604 was not only more powerful than previously thought but also farther away according to a recent study using Chandra X-ray Observatory data published in the September 1, 2012 edition of The Astrophysical Journal.

A new star appeared in the autumn skies of 1604. Although it was described by other astronomers, it was famous astronomer Johannes Kepler who thoroughly detailed the the second supernova sighting in a generation. The star shined more brilliant than Jupiter and remained visible – even during the day – over several weeks.

Look for Kepler’s Supernova at the foot of the constellation Ophiuchus, the Serpent Bearer, in visible light and you won’t see much. But the hot gas and dust glow brightly in the X-ray images from Chandra. Astronomers have long puzzled over Kepler’s Supernova. Astronomers now know the explosion that created the remnant was a Type Ia supernova. Supernovae of this class occur when a white dwarf, the white-hot dead core of a once Sun-like star, gains mass by either merging with another white dwarf or drawing gas onto its surface from a larger companion star until temperatures soar and thermonuclear processes spiral out of control resulting in a detonation that destroys the star.

Kepler’s Supernova is a bit different because the expanding debris cloud is shaped by gas and dust clouds throughout the area. Most Type Ia supernovae are symmetrical; nearly perfect expanding bubbles of material. A quick look at the Chandra image of the supernova and one notices the bright arc of material across the top edge of shockwave. In one model, a pre-supernova white dwarf and its companion were moving through a nebulous area creating a bow shock, like a boat plowing through water, in front. Another model suggests that the glowing arc is the edge of the supernova shockwave as it passes through an area of increasingly dense gas and dust. Both models push the distance of the supernova from the previously believed 13,000 light-years to more than 20,000 light-years from Earth, scientists say in the paper.

Scientists also found large amounts of iron by looking at the X-ray light from Chandra meaning that the explosion was far more powerful than an average Type Ia supernova. Astronomers have observed a similar Type Ia supernova using Chandra and an optical telescope in the Large Magellanic Cloud.

Kepler’s Supernova is the last Milky Way supernova visible to the naked eye. It was the second supernova to be observed in that generation after SN 1572 in Cassiopeia studied by the famous astronomer Tycho Brahe.

Source: http://chandra.harvard.edu

About the author: John Williams is owner of TerraZoom, a Colorado-based web development shop specializing in web mapping and online image zooms. He also writes the award-winning blog, StarryCritters, an interactive site devoted to looking at images from NASA’s Great Observatories and other sources in a different way. A former contributing editor for Final Frontier, his work has appeared in the Planetary Society Blog, Air & Space Smithsonian, Astronomy, Earth, MX Developer’s Journal, The Kansas City Star and many other newspapers and magazines. Follow John on Twitter @terrazoom.

Chandra Witnesses Big Blast from an Old Black Hole

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Astronomers keeping an eye out for a supernova explosion in the nearby galaxy M83 instead witnessed a prodigious blast of another type: a new ultraluminous X-ray source, or ULX. In what scientists are calling an “extraordinary outburst,” the ULX in M83 increased in X-ray brightness by at least 3,000 times, one of the largest changes in X-rays ever seen for this type of object.

“The flaring up of this ULX took us by surprise and was a sure sign we had discovered something new about the way black holes grow,” said Roberto Soria of Curtin University in Australia, who led the new study.

The researchers say this blast provides direct evidence for a population of old, volatile stellar black holes and gives new insight into the nature of a mysterious class of black holes that can produce as much energy in X-rays as a million suns radiate at all wavelengths.

Astrophysicist Bill Blair of Johns Hopkins University, writing in the Chandra Blog, “A Funny Thing Happened While Waiting for the Next Supernova in M83,” said this galaxy, also known as the Southern Pinwheel Galaxy, “is an amazing gift of nature. At 15 million light years away, it is actually one of the closer galaxies (only 7-8 times more distant than the Andromeda galaxy), but it appears as almost exactly face-on, giving earthlings a fantastic view of its beautiful spiral arms and active star-forming nucleus.”

M83 has generated six observed supernovas since 1923, but the last one seen was in 1983. “We are overdue for a new supernova!” Blair wrote.

So, many astronomers have been observing M83, hoping to spot a new supernova, but instead saw a dramatic jump in X-ray brightness, which according to the researchers, likely occurred because of a sudden increase in the amount of material falling into the black hole.

A ULX can give off more X-rays than most “normal” binary systems in which a companion star is in orbit around a neutron star or black hole. The super-sized X-ray emission suggests ULXs contain black holes that might be much more massive than the ones found elsewhere in our galaxy.

Composite image of spiral galaxy M83. (X-ray: NASA/CXC/Curtin University/R. Soria et al., Optical: NASA/STScI/ Middlebury College/F. Winkler et al.)

The companion stars to ULXs, when identified, are usually young, massive stars, implying their black holes are also young. The latest research, however, provides direct evidence that ULXs can contain much older black holes and some sources may have been misidentified as young ones.

The observations of M83 were made over a several year period with Chandra. No sign of the ULX was found in historical X-ray images made with Einstein Observatory in 1980, ROSAT in 1994, the European Space Agency’s XMM-Newton in 2003 and 2008, NASA’s Swift observatory in 2005, the Magellan Telescope observations in April 2009 or in a Hubble image obtained in August 2009.

But in 2011, Soria and his colleagues used optical images from the Gemini Observatory and NASA’s Hubble Space Telescope and saw a bright blue source at the position of the X-ray source.

The lack of a blue source in the earlier images indicates the black hole’s companion star is fainter, redder and has a much lower mass than most of the companions that previously have been directly linked to ULXs. The bright, blue optical emission seen in 2011 must have been caused by a dramatic accumulation of more material from the companion star.

“If the ULX only had been observed during its peak of X-ray emission in 2010, the system easily could have been mistaken for a black hole with a massive, much younger stellar companion, about 10 to 20 million years old,” said co-author Blair.

The companion to the black hole in M83 is likely a red giant star at least 500 million years old, with a mass less than four times the sun’s. Theoretical models for the evolution of stars suggest the black hole should be almost as old as its companion.

Another ULX containing a volatile, old black hole recently was discovered in the Andromeda galaxy by a team led by Amanpreet Kaur from Clemson University, published in the February 2012 issue of Astronomy and Astrophysics. Matthew Middleton and colleagues from the University of Durham reported more information in the March 2012 issue of the Monthly Notices of the Royal Astronomical Society. They used data from Chandra, XMM-Newton and HST to show the ULX is highly variable and its companion is an old, red star.

“With these two objects, it’s becoming clear there are two classes of ULX, one containing young, persistently growing black holes and the other containing old black holes that grow erratically,” said Kip Kuntz, a co-author of the new M83 paper, also of Johns Hopkins University. “We were very fortunate to observe the M83 object at just the right time to make the before and after comparison.”

A paper describing these results will appear in the May 10th issue of The Astrophysical Journal.

Sources: NASA, Chandra Blog

Supernova G350 Kicks Up Some X-Ray Dust

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Located some 14,700 light years from the Earth toward the center of our galaxy, a newly photographed supernova remnant cataloged as G350.1+0.3 is making astronomers scratch their heads. The star which created this unusual visage is suspected to have blown its top some 600 to 1,200 years ago. Although it would have been as bright as the event which created the “Crab”, chances are no one saw it due to the massive amounts of gas and dust at the Milky Way’s heart. Now NASA’s Chandra X-ray Observatory and the ESA’s XMM-Newton telescope has drawn back the curtain and we’re able to marvel at what happens when a supernova imparts a powerful X-ray “kick” to a neutron star!

Credit: X-ray: NASA/CXC/SAO/I.Lovchinsky et al, IR: NASA/JPL-Caltech
Photographic proof from Chandra and XMM-Newton are full of clues which give rise to the possibility that a compact object located in the influence of G350.1+0.3 may be the core region of a shattered star. Since it is off-centered from the X-ray emissions, it must have received a powerful blast of energy during the supernova event and has been moving along at a speed of 3 million miles per hour ever since. This information agrees with an “exceptionally high speed derived for the neutron star in Puppis A and provides new evidence that extremely powerful ‘kicks’ can be imparted to neutron stars from supernova explosions.”

As you look at the photo, you’ll notice one thing in particular… the irregular shape. The Chandra data in this image appears as gold while the infrared data from NASA’s Spitzer Space Telescope is colored light blue. According to the research team, this unusual configuration may have been caused by the stellar debris field imparting itself into the surrounding cold molecular gas.

These results appeared in the April 10, 2011 issue of The Astrophysical Journal. The scientists on this paper were Igor Lovchinsky and Patrick Slane (Harvard-Smithsonian Center for Astrophysics), Bryan Gaensler (University of Sydney, Australia), Jack Hughes (Rutgers University), Stephen Ng (McGill University), Jasmina Lazendic (Monash University Clayton, Australia), Joseph Gelfand (New York University, Abu Dhabi), and Crystal Brogan (National Radio Astronomy Observatory).

Original Story Source: NASA Chandra News Release.

Astronomers Complete the Puzzle of Black Hole Description

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Light may not be able to escape a black hole, but now enough information has escaped one black hole’s clutches that astronomers have, for the first time, been able to provide a complete description of it. A team of astronomers from the Harvard-Smithsonian Center for Astrophysics (CfA) and San Diego State University have made the most accurate measurements ever of X-ray binary system Cygnus X-1, allowing them to unravel the longstanding mysteries of its black hole and to retrace its history since its birth around six million years ago.

Cygnus X-1, which consists of a black hole that is drawing material from its massive blue companion star, was found to be emitting powerful X-rays nearly half a century ago. Since its discovery in 1964, this galactic X-ray source has been intensely scrutinized with astronomers attempting to gain information about its mass and spin. But without an accurate measurement of its distance from the Earth, which has been estimated to be between 5,800 and 7,800 light-years, we could only imagine what secrets Cygnus X-1 was harboring.

Astronomer Mark Reid of CfA led his team to garner the most accurate measurement of the distance to Cygnus X-1 with the help of the National Science Foundation’s Very Long Baseline Array (VLBA), a continent-wide radio-telescope system. The team locked down a direct trigonometric measurement of 6,070 light-years.

“Because no other information can escape a black hole, knowing its mass, spin and electrical charge gives a complete description of it,” says Reid who is a co-author of three papers on Cygnus X-1, published in the Astrophysical Journal Letters (available here, here, and here). “The charge of this black hole is nearly zero, so measuring its mass and spin make our description complete.”

Using their new precise distance measurement along with the Chandra X-ray Observatory, the Rossi X-ray Timing Explorer, the Advanced Satellite for Cosmology and Astrophysics and visible-light observations made over more than two decades, the team pieced together the “No Hair” theorem – the complete description that Reid speaks of – by revealing a hefty mass of nearly 15 solar masses and a turbo spin speed of 800 revolutions per second. “We now know that Cygnus X-1 is one of the most massive stellar black holes in the Milky Way,” says Jerry Orosz of San Diego State University, also an author of the paper with Reid and Lijun Gou of the CfA. “It’s spinning as fast as any black hole we’ve ever seen.”

As an added bonus, observations using the VLBA back in 2009 and 2010 had also measured Cygnus X-1’s movement through the galaxy leading scientists to the conclusion that it is much too slow to have been produced by the explosion of a supernova and without evidence of a large “kick” at birth, astronomers believe that it may have resulted from the dark collapse of a progenitor star with a mass greater than about 100 times the mass of the Sun that got lost in a vigorous stellar wind. “There are suggestions that this black hole could have formed without a supernova explosion and our results support those suggestions,” says Reid.

It seems that with these measurements, Professor Stephen Hawking has well and truly had to eat his own words after placing a bet with fellow astrophysicist Kip Thorne, a professor of theoretical physics at the California Institute of Technology, that Cygnus X-1 did not contain a black hole.

“For forty years, Cygnus X-1 has been the iconic example of a black hole. However, despite Hawking’s concession, I have never been completely convinced that it really does contain a black hole – until now,” says Thorne. “The data and modeling in these three papers at last provide a completely definitive description of this binary system.”

Sources: CfA

Space Telescopes Provide New Look at 2,000 Year Old Supernova

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What caused a huge explosion nearly 2,000 years ago, seen by early Chinese astronomers? Scientists have long known that a “guest star” that had mysteriously appeared in the sky and stayed for about 8 months in the year 185 was the first documented supernova. But now the combined efforts of four space observatories have provided insight into this stellar explosion and why it was so huge – and why its shattered remains — the object known as RCW 86 – is now spread out to great distances.

“This supernova remnant got really big, really fast,” said Brian Williams, an astronomer at North Carolina State University in Raleigh. “It’s two to three times bigger than we would expect for a supernova that was witnessed exploding nearly 2,000 years ago. Now, we’ve been able to finally pinpoint the cause.”

By studying new infrared observations from the Spitzer Space Telescope and data from the Wide-field Infrared Survey Explorer, and previous data from NASA’s Chandra X-ray Observatory and the European Space Agency’s XMM-Newton Observatory, astronomers were able to determine that the ancient supernova was a Type Ia supernova. And doing some “forensics” on the stellar remains, the astronomers could piece together that prior to exploding, winds from the white dwarf cleared out a huge “cavity,” a region of very low-density surrounding the system. The explosion into this cavity was able to expand much faster than it otherwise would have. The ejected material would have traveled into the cavity, unimpeded by gas and dust and spread out quickly.

This is the first time that astronomers have been able to deduce that this type of cavity was created, and scientists say the results may have significant implications for theories of white-dwarf binary systems and Type Ia supernovae.

At about 85 light-years in diameter, RCW occupies a region of the sky that is slightly larger than the full moon. It lies in the southern constellation of Circinus.

Source: JPL

Taking a Galaxy’s Temperature

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The role that supermassive black holes play in the formation of galaxies is a “hot” topic in astronomy. Using the Chandra X-Ray Observatory, an international team of astronomers have been able to create a temperature map of one galaxy, NGC 5813, which is located in the Virgo III Group of galaxies. The new map shows in unprecedented detail the history of various periods of activity of the Active Galactic Nucleus (AGN), which is associated with a supermassive black hole that resides at its center. They found that regular outbursts of the AGN maintained the temperature of the gas in the region of the galaxy, continually reheating the gas that would otherwise have cooled down.

Paper co-author Dr. Scott Randall of the Chandra Mission Planning Team at the Harvard-Smithsonian Center for Astrophysics said, “Although there are other systems that show AGN outburst shocks, this is still the only system where unambiguous shocks from multiple outbursts are seen. This allows us to directly measure the heating from shocks, and directly observe how often these shocks take place. Thus, at present NGC 5813 is *uniquely* well suited to the study of AGN heating.”

By studying images taken by the Chandra X-Ray Observatory, and combining these observations with those taken by the Giant Metrewave Radio Telescope (GMRT) and the Southern Astrophysical Research Telescope (SOAR), they were able to make out large cavities produced by periods of activity in the supermassive black hole. The researchers were able to determine that there were three pairs of large cavities, which corresponded to active outbursts of the galactic nucleus 3 million, 20 million and 90 million years ago (from our perspective here on Earth).

What makes the galaxy NGC 5813 especially suited to this study is its relative isolation from other galaxies that could influence the formation of these cavities – it is an older galaxy that is relatively undisturbed, allowing for these cavities in the gas to persist over such a long time period.

Current models of galaxy formation must take into account just how much of an influence the output of the supermassive black hole at the center of a galaxy has on the formation of stars within the galaxy, and the evolution of the shape and size of the galaxy as a whole. This process of “AGN feedback” has a dramatic influence on how the galaxy takes shape. The research by Dr. Randall, et. al shows an intimate portrait of this process.

Dr. Randall explained, “This is an important result for stellar formation and galaxy evolution. The AGN heats the gas, preventing it from cooling and forming large amounts of stars. There have been several galaxy evolution models proposed that require this kind of “AGN feedback” near the centers of galaxies to explain the observed differences in galaxies. Here we show explicitly that this kind of feedback can and does take place, at least in this system.”

A labeled image of the various shock waves and cavities formed by the activity of the AGN. Image Credit: Credit: NASA/CXC/SAO/S.Randall et al.

As you can see in the image directly above, various outbursts of the AGN create shock waves in the gas near the center of the galaxy. As these shock waves expanded and the galaxy evolved over millions of years, the heat generated by the shocks spread outwards and into the gas surrounding NGC 5813. The gas between all of the galaxies in a cluster is called the intracluster medium (ICM). The heat – which is produced by the friction of the gases at the edge of each of the shock waves – radiates outward into the surrounding gas, increasing its temperature.

The output of the jets streaming from the supermassive black hole in the center vary over a span of roughly 10 million years, and the amount of energy that each outburst puts out is rather variable – the difference between the last two largest outbursts, for example, is almost an order of magnitude.

This process is cyclical, though the details of the mechanisms involved are still a topic that isn’t completely understood.

Dr. Randall explained this process as follows:

“…the gas cools radiatively, and flows in towards the AGN. The cool gas is rapidly accreted by the black hole, dirving [sic] an energetic outburst. The outburst heats the gas (via shocks), stopping the inflow and starving the AGN. The gas is then able to cool once more, and the cycle repeats, with, in this case, a period of about 10 million years. However, the fine details of how the jet and the ICM interact are not currently well uderstood [sic], and it is not clear how well this simple model describes reality. Our goal with the upcoming deep Chandra observation is to better understand the details of this process, most likely through comparisons with detailed numerical simulations.”

Further observations of NGC 5813 in the fall of 2011 using Chandra are in the works, Dr. Randall said. The results of their analysis will be published in the Astrophysical Journal. A preprint version of the paper, “Shocks and Cavities from Multiple Outbursts in the Galaxy Group NGC 5813: A Window to AGN Feedback,” is available on Arxiv.

Sources: Chandra press release, Arxiv paper, email interview with Dr. Scott Randall