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NASA: "X-Rays Light Up Sun-Like Coronas of Black Holes"

 

 

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A new study by astronomers at NASA, Johns Hopkins University and the Rochester Institute of Technology confirms long-held suspicions about how stellar-mass black holes produce their highest-energy light. "Our work traces the complex motions, particle interactions and turbulent magnetic fields in billion-degree gas on the threshold of a black hole, one of the most extreme physical environments in the universe," said lead researcher Jeremy Schnittman, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Md.

By analyzing a supercomputer simulation of gas flowing into a black hole, the team finds they can reproduce a range of important X-ray features long observed in active black holes.

In the the inner zone of the accretion disk of a stellar-mass black hole shown below, gas is heated to 20 million degrees Fahrenheit as it spirals toward the black hole glows in low-energy, or soft, X-rays. Just before the gas plunges to the center, its orbital motion is approaching the speed of light. X-rays up to hundreds of times more powerful ("harder") than those in the disk arise from the corona, a region of tenuous and much hotter gas around the disk. Coronal temperatures reach billions of degrees. The event horizon is the boundary where all trajectories, including those of light, must go inward. Nothing, not even light, can pass outward across the event horizon and escape the black hole.

 

 

 

Gas falling toward a black hole initially orbits around it and then accumulates into a flattened disk. The gas stored in this disk gradually spirals inward and becomes greatly compressed and heated as it nears the center. Ultimately reaching temperatures up to 20 million degrees Fahrenheit (12 million C) - some 2,000 times hotter than the sun's surface - the gas shines brightly in low-energy, or soft, X-rays.

For more than 40 years, however, observations have shown that black holes also produce considerable amounts of "hard" X-rays, light with energy tens to hundreds of times greater than soft X-rays. This higher-energy light implies the presence of correspondingly hotter gas, with temperatures reaching billions of degrees.

The new study bridges the gap between theory and observation, demonstrating that both hard and soft X-rays inevitably arise from gas spiraling toward a black hole.

Working with Julian Krolik, a professor at Johns Hopkins University in Baltimore, and Scott Noble, a research scientist at the Rochester Institute of Technology in Rochester, N.Y., Schnittman developed a process for modeling the inner region of a black hole's accretion disk, tracking the emission and movement of X-rays, and comparing the results to observations of real black holes.

Noble developed a computer simulation solving all of the equations governing the complex motion of inflowing gas and its associated magnetic fields near an accreting black hole. The rising temperature, density and speed of the infalling gas dramatically amplify magnetic fields threading through the disk, which then exert additional influence on the gas.

The result is a turbulent froth orbiting the black hole at speeds approaching the speed of light. The calculations simultaneously tracked the fluid, electrical and magnetic properties of the gas while also taking into account Einstein's theory of relativity.

Running on the Ranger supercomputer at the Texas Advanced Computing Center located at the University of Texas in Austin, Noble's simulation used 960 of Ranger's nearly 63,000 central processing units and took 27 days to complete.

Over the years, improved X-ray observations provided mounting evidence that hard X-rays originated in a hot, tenuous corona above the disk, a structure analogous to the hot corona that surrounds the sun.

"Astronomers also expected that the disk supported strong magnetic fields and hoped that these fields might bubble up out of it, creating the corona," Noble explained. "But no one knew for sure if this really happened and, if it did, whether the X-rays produced would match what we observe."

Using the data generated by Noble's simulation, Schnittman and Krolik developed tools to track how X-rays were emitted, absorbed, and scattered throughout both the accretion disk and the corona region. Combined, they demonstrate for the first time a direct connection between magnetic turbulence in the disk, the formation of a billion-degree corona, and the production of hard X-rays around an actively "feeding" black hole.

In the corona, electrons and other particles move at appreciable fractions of the speed of light. When a low-energy X-ray from the disk travels through this region, it may collide with one of the fast-moving particles. The impact greatly increases the X-ray's energy through a process known as inverse Compton scattering.

"Black holes are truly exotic, with extraordinarily high temperatures, incredibly rapid motions and gravity exhibiting the full weirdness of general relativity," Krolik said. "But our calculations show we can understand a lot about them using only standard physics principles."

The study was based on a non-rotating black hole. The researchers are extending the results to spinning black holes, where rotation pulls the inner edge of the disk further inward and conditions become even more extreme. They also plan a detailed comparison of their results to the wealth of X-ray observations now archived by NASA and other institutions.

Black holes are the densest objects known. Stellar-mass black holes form when massive stars run out of fuel and collapse, crushing up to 20 times the sun's mass into compact objects less than 75 miles (120 kilometers) wide.

The Daily Galaxy via Goddard Space Flight Center

Image credits: "Interstellar" -Paramount Pictures, Warner Bros., Legendary Pictures

Comments

"Stellar-mass black holes form when massive stars run out of fuel and collapse, crushing up to 20 times the sun's mass into compact objects less than 75 miles (120 kilometers) wide".

I think that the basic content of the paper is correct. But I do not agree the above conclusions.

Why? Do you think stellar mass black holes are not formed this way or do you think and object smaller than the Schwarzschild radius is not possible?

I meant "an object" not "and object".

I think star gives birth to its planets, planets are short-lived stars. Thus, the star and their planets should experience the same cooling process, under normal circumstances, the results should be the same, the star will eventually become a giant planet. The only difference is the length of their cooling time.

In fact, in our solar system, there is no planetary collapse, even mass between the planets vary greatly. Therefore, the sun should be the same.

From physics point of view, star / planets will naturally / gradually cool, the outer layer will gradually become solid from liquid, and will become more and more thick. In this process, the liquid core will generate outward force to support the outer solid layer, finally, the strength of the outer solid layer will be strong enough to prevent itself from collapse, just like the construction of a concrete bridge.

Because the core pressure of an object is the sum of the pressure generated by its out layers, the result of accretion / condensation will not produce an object with equal density from the utmost layer to the core, even it is a black hole. This means even the said collapse occurs, the outcome will be unlikely as described in the article.

According to the following links, you can find all my relevant comments:

https://www.google.ca/?gws_rd=ssl#q=Posted+by:+jihaiz++in+dailygalaxy

Further, I think that instead of running out of fuel and collapsing to form a black hole, more likely, disintegration / burning / accretion ( size reduction ) occur dynamically within a massive star until its mass being reduced to a normal star’s level, its core temperature begins to drop, and eventually becomes a giant planet.

Therefore, under normal circumstances, a superstar itself will not form a black hole as described in the article.

The image presented in the following article showed a massive star exploded many times at the Galaxy center, it is still a massive star (not a black hole) though, however, its size must have been very significantly reduced since its first explosion and will likely be further reduced.

http://www.dailygalaxy.com/my_weblog/2015/05/spectacular-galaxy-with-a-2400-light-year-ring-of-star-clusters-observed-devouring-a-dwarf-galaxy.html#comments

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