Alumnus Leads Discovery of Star-Shredding Black Hole

A Department of Energy Computational Science Graduate Fellowship (DOE CSGF) alumnus led the observation of a rare astronomical phenomenon – a black hole destroying a star – and its progress.

Thomas Holoien, a fellow from 2014-2017 and now a fellow at the Carnegie Observatories in Pasadena, California, is part of ASAS-SN, the All-Sky Automated Survey for SuperNovae at Ohio State University, where he earned his doctoral degree. Using small telescopes based around the world, ASAS-SN automatically images the entire sky about once every three days. Holoien and his colleagues use these pictures to find supernovae – exploding stars – and other transient objects. Computer algorithms Holoien helped develop sift the data, comparing images to identify changes that merit further observation.

Holoien was at the Las Campanas Observatory in Chile on January 29, 2019, when he received an alert that the ASAS-SN telescope in South Africa had spotted the event, designated ASASSN-19bt, a NASA release says. He quickly pointed two Las Campanas scopes at the object and requested follow-up observations from other facilities.

The object was a tidal disruption event (TDE), in which a star moves too close to a black hole. The star deforms into a stream of gas, with the tail extending into space while the rest wraps around the black hole as a debris disk.

The ASAS-SN telescopes were concentrating on a section of the sky that also was closely watched by NASA’s TESS, the Transiting Exoplanet Survey Satellite, which hunts for planets orbiting stars elsewhere in our galaxy. TESS had spotted the brightening object on January 21, but had not yet downloaded the data to Earth. It provided more detailed observations when NASA made the information available in March. The space agency’s Swift satellite, which can observe objects at X-ray wavelengths, added additional data.

For the first time, Holoien said, the TESS data let astronomers see exactly when the TDE began to get brighter. “Because we discovered the tidal disruption quickly with the ground-based ASAS-SN, we were able to trigger multiwavelength follow-up observations in the first few days. The early data will be incredibly helpful for modeling the physics of these outbursts.”

The team’s results were published in the September issue of The Astrophysical Journal. Holoien explained the discovery for San Francisco television station KGO in this video. The DOE CSGF does not endorse any product appearing in advertisements before the video.