Astronomers from Queen's University Belfast have gathered the most direct evidence yet of a supermassive black hole shredding a star that wandered too close. The Queen's astronomers are part of the Pan-STARRS international team, whose discovery has been published in the journal Nature today (Wed, 2 May).
Supermassive black holes, weighing millions to billions times more than the Sun, lurk in the centers of most galaxies. These hefty monsters lie quietly until an unsuspecting 'victim', such as a star, wanders close enough to get ripped apart by their powerful gravitational clutches.
Using a slew of ground and space-based telescopes, a team of astronomers led by Suvi Gezari of The Johns Hopkins University in Baltimore, has identified the victim in this case as a star rich in helium gas. The star resides in a galaxy 2.7 billion light-years away.
The observation yields insights about the harsh environment around black holes and the types of stars swirling around them.
Speaking about the discovery Professor Stephen Smartt of Queen's Astrophysics Research Centre in the School of Maths and Physics said: "Astronomers have spotted these stellar 'murders' before, but this is the first time they can identify the victim.
"What we're seeing is a star being shredded by a monster black-hole in the centre of this distant galaxy. Our own galaxy, the Milky Way has a black hole at its centre, about a million times the mass of the sun. We can see stars whizzing around our Milky Way black hole, but they are too far away from it to be captured.
"In this case a star got too close to the black hole and was sucked right in. We're seeing the star being shredded, heated and destroyed and as it swirls around the black hole. Suvi Gezari, team leader from John Hopkins University in Baltimore, alerted us to something unusual caught by the NASA spacecraft called GALEX, and as our computers sifted through terabytes of Pan-STARRS data, we found the tell-tale signature of the event. We knew it was something weird then."
To find this one event, the team monitored hundreds of thousands of galaxies in ultraviolet light with the Galaxy Evolution Explorer (GALEX), a space-based observatory, and in visible light with the Pan-STARRS1 telescope on the summit of Haleakala, in Hawaii. Pan-STARRS, short for Panoramic Survey Telescope and Rapid Response System, scans the entire night sky for all kinds of transient phenomena, including supernovae.
The team was looking for a bright flare in ultraviolet light from the nucleus of a galaxy with a previously dormant black hole. They found one in June 2010, which was spotted with both telescopes. Both telescopes continued to monitor the flare as it reached peak brightness a month later, and then slowly began to fade over the next 12 months. The brightening event was similar to that of a supernova, but the rise to the peak was much slower, taking nearly one and a half months.
Team leader, Suvi Gezari from The Johns Hopkins University, Baltimore, Md. said: "This is the first time where we have so many pieces of evidence, and now we can put them all together to weigh the perpetrator (the black hole) and determine the identity of the unlucky star that fell victim to it. These observations also give us clues to what evidence to look for in the future to find this type of event."
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Journal
Nature