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montage of images shows the evolution of a white dwarf star

A montage of images shows the evolution of a white dwarf star as it is being disrupted by a massive black hole. In this scenario, the star, which is being flexed by the tidal field of the black hole, develops strong shocks on its surface (blue and green) but its remnant core survives disruption (illustrated in red color in the cutout).

A sequence of 3D snapshots is produced by Forrest Kieffer, a Georgia Tech undergraduate student, and is based on a relativistic hydrodynamic simulation carried out by Roseanne Cheng, both of whom are members of Bogdanovićʼs research group. The group is using this type of simulation to learn about the physical conditions under which tidal disruptions occur and to decode the signatures of observed tidal disruption events.

Credit: Tamara Bogdanović, Georgia Tech

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Forrest Kieffer (left), postdoctoral researcher Roseanne Cheng (right) and Tamara Bogdanovic

Group members involved in investigation of tidal disruptions of stars by black holes are an undergraduate student Forrest Kieffer (left), postdoctoral researcher Roseanne Cheng (right) and Tamara Bogdanović, (center). The group is based at the Center for Relativistic Astrophysics at the Georgia Institute of Technology in Atlanta, GA.

Credit: Tamara Bogdanović, Georgia Tech

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Black hole caught red-handed in a stellar homicide

This computer-simulated image shows gas from a star that is ripped apart by tidal forces as it falls into a black hole. Some of the gas also is being ejected at high speeds into space.

Using observations from telescopes in space and on the ground, astronomers have gathered the most direct evidence yet for this violent process: a supermassive black hole shredding a star that wandered too close. NASA's orbiting Galaxy Evolution Explorer (GALEX) and the Pan-STARRS1 telescope on the summit of Haleakala in Hawaii were used to help to identify the stellar remains. A flare in ultraviolet and optical light revealed gas falling into the black hole as well as helium-rich gas that was expelled from the system. When the star is torn apart, some of the material falls into the black hole, while the rest is ejected at high speeds. The flare and its properties provide a signature of this scenario and give unprecedented details about the stellar victim. To completely rule out the possibility of an active nucleus flaring up in the galaxy instead of a star being torn apart, the team used NASA's Chandra X-ray Observatory to study the hot gas. Chandra showed that the characteristics of the gas didn't match those from an active galactic nucleus. The galaxy where the supermassive black hole ripped apart the passing star is known as PS1-10jh and is located about 2.7 billion light years from Earth. Astronomers estimate the black hole in PS1-10jh has a mass of several million suns, which is comparable to the supermassive black hole in the Milky Way galaxy.

Credit: NASA, S. Gezari (The Johns Hopkins University), and J. Guillochon (University of California, Santa Cruz)

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