The destruction of a star by a supermassive black hole observed from the beginning

Artist's concept of tidal destruction event (Image NASA's Goddard Space Flight Center)
Artist’s concept of tidal destruction event (Image NASA’s Goddard Space Flight Center)

An article published in “The Astrophysical Journal” reports the study of an event cataloged as ASASSN-19bt in which a supermassive black hole destroyed a star that came too close to it. A team of researchers led by Patrick Vallely and Tom Holoien discovered the start of the event thanks to the ASAS-SN network, obtained observations thanks to the NASA TESS space telescope, which was aimed at that area, and conducted follow-up observations using NASA’s Swift and ESA’s XMM-Newton space telescopes and the network of ground-based Las Cumbres Observatories.

The TESS space telescope, launched on April 18, 2018, was designed to search for exoplanets but sometimes its continuous observation of an area of ​​space can lead to the discovery of other objects and other phenomena. On January 29, 2019 the network of the ASAS-SN (All-Sky Automated Survey for Supernovae) international collaboration identified the first traces of an tidal destruction event, the technical description of what happens when a star approaches a supermassive black hole’s event horizon and gets destroyed. By a stroke of luck, TESS was already observing that area and the data collected indicate that, thanks to its sensitivity, on January 21 it already identified the beginning of the event that was cataloged as ASASSN-19bt.

The supermassive black hole that caused that destruction has a mass estimated at six million times the Sun’s and is at the center of the galaxy 2MASX J07001137-6602251, about 375 million light years away from Earth. When the star was torn to pieces, part of its gas was projected outwards while another part was brought closer to the black hole, which warmed it while swallowing it, generating electromagnetic emissions that peaked on March 4, 2019. This is a rare event and so far only a few dozen have been discovered but thanks to the information gathered by TESS the event ASASSN-19bt was observed from the beginning.

Patrick Vallely of Ohio State University, among the entities that run the ASAS-SN network, stated that the early TESS data allow to see light very close to the black hole, much closer than we’ve been able to see so far. Those data allowed to recognize a tidal destruction event recognizing it from other explosive events such as supernovae, the main objective of the ASAS-SN network.

The quick discovery of the ASASSN-19bt event allowed researchers to obtain observations in other electromagnetic wavelengths as well detecting utraviolet emissions with NASA’s Swift Observatory and X-rays with Swift and ESA’s XMM-Newton space telescope.

The ultraviolet emissions made it possible to assess the temperature in the area of ​​the event, which had a significant drop from 40,000 to 20,000° Celsius (from 71,500 to 35,500° Fahrenheit) in a matter of days. That’s a very sudden and surprising drop, never seen before in a tidal destruction event. The X-ray emissions were relatively low while ultraviolet emissions were high, which are typical of these events but their causes are still not well understood.

The data from the event ASASSN-19bt could help clarify what happens during a tidal destruction event. To get such an amount of data it takes a bit of luck, in this case with the TESS space telescope already observing the area where it happened. However, it’s also important to be able to coordinate the observations of various telescopes to make the most of a stroke of luck and of systems such as the ASAS-SN network.

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