The European Space Agency’s Gaia is an ambitious mission creating an unbelievably accurate map of billions of stars in the Milky Way. Now, its exceptional capabilities are also being used elsewhere. The telescope can spot short-term changes in distant galaxies and has been used to discover 480 explosions from galactic cores in just one year.
As reported in the Monthly Notices of the Royal Astronomical Society, a good number of the sudden flashes of light spotted by Gaia are tidal disruption events (TDEs). When a star gets too close to a massive black hole, the extreme gravitational field breaks it apart. The disruption heats the plasma which becomes incredibly bright, allowing our telescopes to detect it.
Another explanation for some of the events is a supermassive black hole feeding on a cloud of gas that got too close to its core. Both scenarios involve black holes. The signal appears to be consistent with the center of these galaxies and is very brief, making other explanations very unlikely.
“Such events have great value because they could allow astronomers to study for a brief period previously invisible supermassive black holes,” co-author Peter Jonker, from the Netherlands Institute for Space Research and Radboud University, said in a statement. “Especially the short-duration events could point us to the location of the so far elusive intermediate-mass black holes ripping stars apart.”
Intermediate-mass black holes are rare to find. They are much bigger than the black holes that can be created by supernovae but way smaller than the absolute monsters that reside in the cores of galaxies. Researchers have suggested that many of these black holes orbit closer to the central supermassive one. Unfortunately, due to their very nature, they don’t emit light so we can only catch a glimpse of them when they're feeding.
Fewer than 90 confirmed TDEs have been spotted so far, thanks to surveys mainly aimed at discovering supernovae. Gaia looks at every position in the sky once a month, which equates to 70 times throughout the entire mission. This is useful for measuring changes in the brightness and position of stars in the Milky Way, but it is also superb for studying transient events many millions of light-years away.
The team used the well-established Sloan Digital Sky Survey and a custom-made mathematical tool to identify the events from a galaxy catalog. This approach cannot be used as an alert system to follow up the events immediately, but it could possibly be extremely important to the long-term study of these objects.