Queen's Astronomers Help Discover Black Hole Swallowing Star

Astronomers at Queen's University in Belfast have helped discover a black hole swallowing star.

They were part of an international team that solved the mystery of an extraordinarily brilliant point of light seen in a distant galaxy.

Dubbed ASASSN-15lh, the light was thought to be the brightest supernova ever seen, however new observations propose that the source was an even more extreme and very rare event, a rapidly spinning black hole ripping apart a passing star that came too close.

In 2015, the All Sky Automated Survey for SuperNovae (ASAS-SN) detected an event, named ASASSN-15lh, that was recorded as the brightest supernova ever — and categorised as a superluminous supernova, the explosion of an extremely massive star at the end of its life. It was twice as bright as the previous record holder, and at its peak was 20 times brighter than the total light output of the entire Milky Way.

The new paper published on Monday, 12 December, in Nature Astronomy is led by Giorgos Leloudas at the Weizmann Institute of Science, Israel, and the Dark Cosmology Centre, Denmark.

Professor Stephen Smartt from Queen's University's Astrophysics Research Centre is the lead and principal investigator of the project at the European Southern Observatory. The new observations led to the team proposing a new explanation for this extraordinary event.

Professor Smartt said: "This object puzzled us for months. Our international team has experts who work on the most extreme physics in the Universe and the initial explanation of a supernova just didn't seem to fit all the data comfortably. The team studied all the data carefully, kept observing, applied models and physics and considered all possible explanations. This is an excellent example of international collaboration and scientific team work, ably led by Giorgos Leloudas."

Dr Leloudas said: "We observed the source for 10 months and have concluded that the explanation is unlikely to lie with an extraordinarily bright supernova. Our results indicate that the event was probably caused by a rapidly spinning supermassive black hole as it destroyed a low-mass star."

Although the team said a supernova source is therefore very unlikely, they accept that a classical tidal disruption event would not be an adequate explanation for the event either.

Dr Leloudas concluded: "Even with all the collected data we cannot say with 100% certainty that the ASASSN-15lh event was a tidal disruption event, but it is by far the most likely explanation."

(CD)