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  • Black Hole Caught Having a Snack

    An artist's impression of the passage of a star close to a black hole, causing a a Tidal Disruption Event (image courtesy CXO/NASA).

    One of the few things we know about black holes is that it is not a good idea to get too close to one of them. Their powerful gravitational pull can rip apart anything that ventures in their vicinity. Yet, a star may have survived such a close encounter.

    Only a few such stellar disruptions have been seen before. Stars may have the misfortune to pass close to a black hole but this is not happening often. Their discovery has been left to chance and has been largely accidental. In order to catch such a rare event, astronomers need to look at a large fraction of the sky, and look often. This is what the All-Sky Automated Survey for Supernovae (ASAS-SN, pronounced "assassin") is designed to do. Its six telescopes -- four in Hawai, USA, and two in Chile, scan the sky every night, looking for variable sources and for "new" objects. On January 25, 2014, an otherwise anonymous galaxy located a "mere" 650 million light years away in Ursa Major, the constellation that contains the "Big Dipper", looked significantly brighter than usual. This object, nicknamed ASASSN-14ae, was initially thought to be a supernova, the explosion of a massive star, albeit an unsual one.

    Several telescopes were immediately used to obtain more data. PhD student Thomas Holoien of the Ohio State University led the effort and coordinated the observing campaign. Data were obtained with several telescopes, including NASA's Swift observatory and LJMU's robotic Liverpool Telescope

    The Liverpool Telescope

    As the story was unfolding, it became clear however that this was not a supernova but something entirely different: a tidal disruption event. A star got close to a black hole with a mass several million times the mass of our Sun but only had a small chunk of matter ripped off. In other words, it survived the encounter and was able to tell the tale.

    The amount of energy released during the event allowed researchers to calculate that only one thousandth of the mass of our sun -- about the mass of the planet Jupiter -- had been sucked into the black hole. David Bersier, of LJMU Astrophysics Research Institute, said: "The Liverpool Telescope is the perfect machine to follow an event like this. We need access to the telescope only ten minutes per night but we need this over a long period of time. The fact that the LT is entirely computer-controlled means that we only need to instruct a computer to take observations every night, without the need for a very lengthy stay in a remote observatory. This is perhaps a less romantic way of observing but it is a lot more efficient."

    Monitoring the whole night sky every other night, the ASAS-SN survey has a good chance of detecting more of these events, and perhaps even more exotic cosmic catastrophes that we haven't thought of yet!

    External Link: Ohio State University press release