Astronomers have gathered the most direct evidence yet of a supermassive black hole shredding a star that wandered too close. Using ground- and space-based telescopes, a team of astronomers, led by Suvi Gezari of the Johns Hopkins University in Baltimore, identified the victim as a star rich in helium gas. The star resides in a galaxy 2.7 billion light-years away. NASA's Galaxy Evolution Explorer, a space-based observatory, and the Pan-STARRS1 telescope on the summit of Haleakala in Hawaii were among the first to help identify the stellar remains.
Gezari says, "When the star is ripped apart by the gravitational forces of the black hole, some part of the star's remains falls into the black hole while the rest is ejected at high speeds. We are seeing the glow from the stellar gas falling into the black hole over time. We're also witnessing the spectral signature of the ejected gas, which we find to be mostly helium. It is like we are gathering evidence from a crime scene. Because there is very little hydrogen and mostly helium in the gas, we detect from the carnage that the slaughtered star had to have been the helium-rich core of a stripped star."
The astronomers believe the star's hydrogen-filled envelope surrounding the core was lifted off a long time ago by the same black hole. After consuming most of its hydrogen fuel, it probably ballooned in size, becoming a red giant. Astronomers think the bloated star was looping around the black hole in a highly elliptical orbit. On one of its close approaches, the star was stripped of its puffed-up atmosphere by the black hole's powerful gravity. The stellar remains continued its journey around the center, until it ventured even closer to the black hole to face its ultimate demise.
Astronomers observed a flare in ultraviolet and optical light from the gas falling into the black hole and glowing helium from the stars' helium-rich gas expelled from the system. The astronomers created this animation that shows the star being shredded by the gravity of the supermassive black hole. The blue dot pinpoints the black hole's location. The elapsed time corresponds to the amount of time it takes for the Sun-like star to be ripped apart by the black hole. Take a look:
The team's results were published here in the journal Nature.
Image: NASA, S. Gezari (The Johns Hopkins University), and J. Guillochon (University of California, Santa Cruz)