When the bright light appeared in the sky on June 14, 2015, emanating from a distant galaxy, astronomers from around the world thought it was most likely to be one thing; a star exploding in a fiery supernova. Not only that, but the event appeared to be the brightest supernova ever recorded.
Or was it?
This isn’t the first ‘tidal disruption of a star by a black hole to be observed on Earth. This is an artist’s impression of the aftermath of a black hole tearing apart a nearby star. Material circles around the black hole like water circling a drain. Credit : NASA/Swift/Aurore Simonnet, Sonoma State University
In a recent paper published in Nature Astronomy, researchers took a closer look at the event and found that there was another possible explanation. Instead of exploding at the end of its life, the star was torn apart in an event called a Tidal Disruption Event, during which the star was yanked apart by a nearby supermassive black hole.
Supermassive black holes are the largest type of black holes known to exist, with a mass greater than one million Suns. They are often found at the center of massive galaxies, including the Milky Way.
This black hole, in this case, is estimated to be about 100 million times as massive as our own Sun. For the black hole to tear apart a star in such a way that it would create the brilliant flash seen on Earth, the black hole would have to be spinning very rapidly, something that is hard to measure from our vantage point here on Earth.
An artist’s interpretation of a star getting torn apart by a supermassive black hole (center). Credit: ESO, ESA/HUBBLE, M. Kornmesser
This new kind of star death hadn’t been directly observed before now. The spinning black hole tore apart the star scattering its remains, which began orbiting the black hole. As the pieces of the star ran into each other as they circled towards their fate, they created the bright light seen here on Earth as a strangely bright supernova.
“This is like discovering a new kind of dinosaur,” co-author of the study Andrew Howell said. “Now that we have the right tools and know what to look for, we’re going to find more and get a better sense of the population. It’s exciting to have new ways of learning about black holes and stellar death.”