Astronomers have spotted what appears to be a star being torn up and devoured by a black hole just over 1 billion light years away. A star being ripped apart is a rare event 鈥� we鈥檝e only seen it happen around 20 times 鈥� but it might be happening in a distant galaxy right now, as we watch.
In the centre of every large galaxy lies a supermassive black hole with a mass up to billions of times larger than that of the sun. If a star gets too close to one of these black holes, the pull of gravity will be much stronger on the near side of the star than the far side, so it will be stretched and elongated until it rips in what鈥檚 called a tidal disruption event (TDE).
The black hole then swallows up bits of the shredded star. These pieces release enough energy in the process to remain bright for months or even years. But black holes don鈥檛 get these meals often.
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鈥淭he density of stars in galaxies is greatest at the centre, but even so, the frequency with which stars buzz very close to that central black hole is very low,鈥� says at Johns Hopkins University in Baltimore, Maryland. 鈥淚n a typical galaxy it might occur once every ten thousand years at most.鈥�
A team of astronomers led by at the University of Hawaii in Honolulu,聽think that they may have spotted the aftermath of this process. They reported four sets of telescope observations that led to these suspicions , a website where astronomers post observations of short-lived cosmic phenomena.
Sudden burst
At first glance, a star being devoured can look similar to a supernova, because both produce relatively sudden, bright bursts of light in the sky. So, when researchers spot a potential TDE, the first thing they do is take as much data as possible to try to tell the difference.
There are a few factors that make researchers think this particular signal might be a tidal disruption. It seems to be in the centre of its galaxy, a requirement for a TDE but not for a supernova. And its light is very blue, meaning it鈥檚 extremely hot, while supernovae tend to cool down over time as they expand. It also shows no sign of the heavy elements that absorb some of a supernova鈥檚 light.
Shappee says that there isn鈥檛 enough data yet to confirm that this is a TDE and not a supernova, though. His group and others are continuing to observe it. The event is just reaching its peak brightness, so there鈥檚 plenty of time to keep looking for clues, says at the University of Maryland in聽College Park, a member of one of those groups.
鈥淭here are rare kinds of supernovae that produce signals similar to this one early on, so we cannot rule out that kind of supernova just yet,鈥� says van Velzen.
Read more: Black holes that shred stars burp out cosmic rays and neutrinos
