In a paper published in the May 2 online issue of the top scientific journal Nature, astronomers reveal the most concrete evidence to date that a supermassive black hole is consuming a nearby star that was unfortunate enough to get too close.
Unlike previous studies to observe the destruction of stars at the hands of these dark behemoths, the new investigation was also able to identify the victim. The object is a massive star rich in helium, located around 2.7 billion light-years away.
This was done by using a number of space- and ground-based telescopes. The research was led by astronomer Suvi Gezari, who holds an appointment with the Johns Hopkins University (JHU), in Baltimore, Maryland.
The expert says that supermassive black holes are usually found at the cores of large galaxies, where they simply wait for their next meal. As soon as a star strays too close to the event horizon, intense gravitational and tidal forces begin to rip it apart, eventually destroying and consuming it.
“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,” Gezari says of the new study.
“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,” the investigator adds, saying that all evidence suggests the victim was a star whose core was very rich in helium.
In order to keep an eye on other instances when such an event may be taking place in the Milky Way, Gezari and her team have recently conducted a survey of more than 100,000 stars, using the NASA
Galaxy Evolution Explorer (GALEX) satellite. The spacecraft surveys the night sky in ultraviolet wavelengths.
Data from the Haleakala, Hawaii-based Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) were also used for this research. Additional observations were conducted with the MMT (Multiple Mirror Telescope) Observatory, on Mount Hopkins in Arizona.
In June 2010, the team noticed a bright UV flare coming from a supermassive black hole at the core of a galaxy that was previously thought to be somewhat inactive. Though similar to a supernova, this signature took about 45 days to reach peak brightness, which is way too long for a stellar explosion.
“The longer the event lasted, the more excited we got, since we realized that this is either a very unusual supernova or an entirely different type of event, such as a star being ripped apart by a black hole,” Space Telescope Science Institute expert and study team member, Armin Rest, concludes.