NASA’s TESS Satellite Spots Star Being Ripped Apart by Black Hole
NASA’s Transiting Exoplanet Survey Satellite (TESS) is orbiting the Earth to search for alien worlds, but it spotted something much different recently. NASA says TESS observed a rare phenomenon known as a “tidal disruption event.” As TESS watched from a safe distance, a star spiraled toward a black hole before being torn to shreds.
TESS is a followup to the dearly departed Kepler Space Telescope. Whereas Kepler focused on small parts of the sky out to great distances, TESS aims to search for exoplanets across the entire sky out to a distance of about 300 light years. It uses the same transit method as Kepler for spotting exoplanets: when a planet passes in front of its host star, there’s a small dip in brightness. TESS watches for changes in brightness, and that’s how it spotted the tidal disruption event.
The data from TESS shows a distant object getting brighter over the course of several days in January 2019. A tidal disruption event like this occurs when a star passes too close to a black hole. It becomes trapped in the black hole’s gravity and spirals in toward the event horizon. In the process, the extreme gravity breaks the star apart into an elongated stream of gas. Some of the matter escapes into space, but most of it forms an accretion disk around the black hole and is eventually consumed.
TESS saw the first hint of the event now known as ASASSN-19bt on January 21st, 2019. It took place about 375 million light years away in a galaxy called 2MASX J07001137-6602251. The black hole is believed to be 6 million times as massive as the sun. Luckily, the break-up of the star was quite bright, and it happened in the satellite’s continuous viewing zone above the south pole.
TESS only transmits data to Earth every two weeks, and it needs to be processed at NASA’s Ames Research Center before anyone can evaluate it. So, no one knew TESS had seen ASASSN-19bt until March. The All-Sky Automated Survey for Supernovae (ASAS-SN) is a network of robotic telescopes designed to detect events like ASASSN-19bt. However, ASAS-SN didn’t see the event until a week after TESS. Astronomers were able to gather data from ASASSN-19bt with the ASAS-SN array as usual before they knew anything about TESS’s observation.
Having the data from TESS allows scientists to track how ASASSN-19bt behaved when it was still too dim for other instruments to see. The smooth increase in brightness detected by TESS also confirms this was a tidal disruption event and not another high-energy outbursts like a supernova. The TESS observational campaign is still ongoing, so there’s still time to spot some more tidal disruption events. We’re hoping for exoplanets, too.