Supermassive black holes can sometimes break a star apart and eat it, releasing a huge burst of energy as they do so. This process, called a Tidal Disruption Event (TDE), was thought to be pretty rare but new observations, published in Nature Astronomy, suggest that this might not be the case.
Astronomers from the University of Sheffield have discovered that in colliding galaxies, TDEs are 100 times more frequent than expected. The new survey looked at a tiny sample of 15 galaxy mergers that are in a starburst phase, producing new stars 100 times faster than our Milky Way.
“Each of these 15 galaxies is undergoing a ‘cosmic collision’ with a neighboring galaxy,” Dr James Mullaney, Lecturer in Astronomy and co-author of the study, said in a statement. “Our surprising findings show that the rate of TDEs dramatically increases when galaxies collide. This is likely due to the fact that the collisions lead to large numbers of stars being formed close to the central supermassive black holes in the two galaxies as they merge together.”
The team looked at these galaxies in 2005 and again in 2015, and discovered that one of them, F01004-2237, looked significantly different. Looking up this object in the Catalina Sky Survey, the team discovered it had a particularly strong emission in 2010, consistent with a TDE.
This is the first time that a TDE has been observed in a starburst galaxy. And given the small size of the sample, either the researchers have been extremely lucky in finding this one particular case, or the rate of TDE for these galaxies must be higher than expected. According to previous studies, there should be a TDE per galaxy every 10,000 to 100,000 years.
These results expand our understanding of galaxy mergers and galaxy evolution, and while it doesn’t have practical applications right now, it might come in handy when our galaxy collides with Andromeda.
“Based on our results for F01004-2237, we expect that TDE events will become common in our own Milky Way galaxy when it eventually merges with the neighboring Andromeda galaxy in about 5 billion years,” lead author Professor Clive Tadhunter added. “Looking towards the center of the Milky Way at the time of the merger we’d see a flare approximately every 10 to 100 years. The flares would be visible to the naked eye and appear much brighter than any other star or planet in the night sky.”
F01004-2237 is located 1.7 billion light-years from Earth and tells us that there’s a lot more that we need to understand about galaxies smashing into each other.