Massive Gas Cloud Tumbling into Nearby Black-Hole

The supermassive black hole at the heart of the Milky Way galaxy is about to have lunch. An enormous gaseous cloud, with almost three times the mass of planet Earth, is fast approaching the black hole's event horizon, and it will be ripped, shredded and gobbled down in 2013.

"It is not going to survive the experience," Stefan Gillessen, of the Max Planck Institute for Extraterrestrial Physics in Germany, confirms in no uncertain terms.

This unique event will give astronomers a front row seat to something that's never been observed up close, before: how a black hole gulps down gas, dust and stars as it grows ever bigger. All other black holes are too far away to see first hand, while our closest one is just 27,000 light years from Earth.

"When we look at the black holes in the centres of other galaxies, we see them get bright and then fade, but we never know what is actually happening," said Eliot Quataert, a theoretical astrophysicist at University of California.

"This is an unprecedented opportunity to obtain unique observations and insight into the processes that go on as gas falls into a black hole, heats up and emits light. It's a neat window onto a black hole that's actually capturing gas as it spirals in."

Gillessen, Quataert and physicist Reinhard Genzel have been tracking the cloud since 2008, using the European Southern Observatory's Very Large Telescope in Chile. They have seen the gaseous entity speed up to a velocity of 8 million kilometres an hour, and are now starting to see its edges fray as it tumbles deeper into the black hole's gravitational whirlpool.

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This cloud is mostly helium and hydrogen, and it's particularly cold -- just 280 degrees celsius. It likely formed when plumes of gas from two nearby stars were shoved together by stellar winds, and it is now glowing under the ultraviolet radiation from surrounding hot stars.

The cloud will soon come within about 40 billion kilometres of the event horizon. That's the limit beyond which nothing, not even light, can escape from a black hole. By 2013 the team should see violent outbursts of X-rays and radio waves as the cloud gets hotter and is torn to shreds. The light emitted around the black hole could increase by a hundredfold to a thousandfold, Quataert has calculated.
The Chandra X-ray satellite has already scheduled its largest single chunk of observation time in 2012 near the Milky Way's central black hole.
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Two Behemoth Black Holes Could Swallow Billions of Suns

Astronomers have measured the two most enormous supermassive black holes found so far, vast realms of titanic gravity large enough to swallow 10 of our solar systems. The black holes are much bigger than predicted, suggesting extra-large galaxies and their black holes grow and evolve differently than smaller ones.

One of the monstrous black holes, in the center of the galaxy NGC 3842, weighs as much as 9.7 billion suns. It is about 331 million light-years away in the constellation Leo. The other one, NGC 4889, is of comparable or even greater mass, the researchers say — they’re not positive, but the numbers suggest it could be up to 21 billion solar masses. It's 336 million light-years away in the Coma galaxy cluster.

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Behemoth Black Hole This figure shows the immense size of the black hole discovered in the galaxy NGC 3842. The black hole is at its center and is surrounded by stars (shown as an artist's concept in the central figure). The black hole is seven times larger than Pluto's orbit. Our solar system (inset) would be dwarfed by it. Pete Marenfeld

The former heavyweight champ is a dwarf by comparison, tipping the scales at 6.3 billion solar masses. That black hole is at the center of the giant elliptical galaxy Messier 87.
Supermassive black holes of 10-billion-sun magnitude have been predicted based on the brightness of quasars, ultra-luminous distant objects that are largely thought to be spiraling discs surrounding the event horizons of black holes in the very early universe. But this is the first time such enormous black holes have ever been seen. They could be a missing link to the quasars, according to astronomer Michele Capellari, writing in a companion piece to the new black hole paper.




"These objects probably represent the missing dormant relics of the giant black holes that powered the brightest quasars in the early universe," she wrote.
To weigh the black holes, Nicholas McConnell and Chung-Pei Ma at the University of California-Berkeley used the Keck and Gemini observatories to measure the speed of stars moving around the black holes. The faster the stars were moving, the more gravity was needed to keep them in check, so the researchers used these velocities to calculate the black holes’ masses.
They found the black holes were much bigger than predictive math would suggest, which means astronomers still have a lot to learn about how the biggest black holes form and evolve.
“Our measurements suggest that different evolutionary processes influence the growth of the largest galaxies and their black holes,” the researchers write.
The paper will appear in the journal Nature.

Our Own Black Hole, Through Adaptive Optics: Image of the center of our galaxy from laser-guide-star adaptive optics on the Keck Telescope. If a 10 billion solar mass black hole resided at the Milky Way's center, its immense event horizon would be visible, as illustrated by the central black disk. The actual black hole at the galactic center is 2,500 times smaller, however.  Andrea Ghez, Lynette Cook

 BBC
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A Distant Black Hole Devoured A Star

Positions from Swift's XRT constrained the source to a small patch of sky that contains a faint galaxy known to be 3.9 billion light-years away. But to link the Swift event to the galaxy required observations at radio wavelengths, which showed that the galaxy's center contained a brightening radio source. Analysis of that source using the Expanded Very Large Array and Very Long Baseline Interferometry (VLBI) shows that it is still expanding at more than half the speed of light.

 Two studies appearing in the Aug. 25 issue of the journal Nature provide new insights into a cosmic accident that has been streaming X-rays toward Earth since late March. NASA's Swift satellite first alerted astronomers to intense and unusual high-energy flares from the new source in the constellation Draco.

"Incredibly, this source is still producing X-rays and may remain bright enough for Swift to observe into next year," said David Burrows, professor of astronomy at Penn State University and lead scientist for the mission's X-Ray Telescope instrument. "It behaves unlike anything we've seen before."

Astronomers soon realized the source, known as Swift J1644+57, was the result of a truly extraordinary event -- the awakening of a distant galaxy's dormant black hole as it shredded and consumed a star. The galaxy is so far away, it took the light from the event approximately 3.9 billion years to reach Earth.

Burrows' study included NASA scientists. It highlights the X- and gamma-ray observations from Swift and other detectors, including the Japan-led Monitor of All-sky X-ray Image (MAXI) instrument aboard the International Space Station.

The second study was led by Ashley Zauderer, a post-doctoral fellow at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. It examines the unprecedented outburst through observations from numerous ground-based radio observatories, including the National Radio Astronomy Observatory's Expanded Very Large Array (EVLA) near Socorro, N.M.

Most galaxies, including our own, possess a central supersized black hole weighing millions of times the sun's mass. According to the new studies, the black hole in the galaxy hosting Swift J1644+57 may be twice the mass of the four-million-solar-mass black hole in the center of the Milky Way galaxy. 

As a star falls toward a black hole, it is ripped apart by intense tides. The gas is corralled into a disk that swirls around the black hole and becomes rapidly heated to temperatures of millions of degrees. 

 The innermost gas in the disk spirals toward the black hole, where rapid motion and magnetism create dual, oppositely directed "funnels" through which some particles may escape. Jets driving matter at velocities greater than 90 percent the speed of light form along the black hole's spin axis. In the case of Swift J1644+57, one of these jets happened to point straight at Earth.

Swift's X-Ray Telescope continues to record high-energy flares from Swift J1644+57 more than three months after the source's first appearance. Astronomers believe that this behavior represents the slow depletion of gas in an accretion disk around a supermassive black hole. The first flares from the source likely coincided with the disk's creation, thought to have occurred when a star wandering too close to the black hole was torn apart. 

"The radio emission occurs when the outgoing jet slams into the interstellar environment," Zauderer explained. "By contrast, the X-rays arise much closer to the black hole, likely near the base of the jet."

Theoretical studies of tidally disrupted stars suggested they would appear as flares at optical and ultraviolet energies. The brightness and energy of a black hole's jet is greatly enhanced when viewed head-on. The phenomenon, called relativistic beaming, explains why Swift J1644+57 was seen at X-ray energies and appeared so strikingly luminous.

When first detected March 28, the flares were initially assumed to signal a gamma-ray burst, one of the nearly daily short blasts of high-energy radiation often associated with the death of a massive star and the birth of a black hole in the distant universe. But as the emission continued to brighten and flare, astronomers realized that the most plausible explanation was the tidal disruption of a sun-like star seen as beamed emission.

By March 30, EVLA observations by Zauderer's team showed a brightening radio source centered on a faint galaxy near Swift's position for the X-ray flares. These data provided the first conclusive evidence that the galaxy, the radio source and the Swift event were linked.

Images from Swift's Ultraviolet/Optical (white, purple) and X-Ray telescopes (yellow and red) were combined to make this view of Swift J1644+57. Evidence of the flares is seen only in the X-ray image, which is a 3.4-hour exposure taken on March 28, 2011. 

"Our observations show that the radio-emitting region is still expanding at more than half the speed of light," said Edo Berger, an associate professor of astrophysics at Harvard and a coauthor of the radio paper. 

"By tracking this expansion backward in time, we can confirm that the outflow formed at the same time as the Swift X-ray source." Swift, launched in November 2004, is managed by NASA's Goddard Space Flight Center in Greenbelt, Md. It is operated in collaboration with Penn State, the Los Alamos National Laboratory in N.M. and Orbital Sciences Corp., in Dulles, Va., with international collaborators in the U.K., Italy, Germany and Japan. MAXI is operated by the Japan Aerospace Exploration Agency as an external experiment attached to the Kibo module of the space station.

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