Stockholm university

Fast flickering black hole caught in breakout

In the latest issue of the journal Nature, astronomers from Stockholm University participate in a study of an optical transient displaying fast flickering of light. A small black hole in a distant galaxy could lie behind the phenomenon.

Supernovae – exploding stars - are well known transients that suddenly appear on the night sky and then shine on for a few weeks.  Current supernova survey telescopes find thousands of these each year, but also start to find different and faster optical transients. The Zwicky Transient Facility at Palomar in California discovered the object named AT2022tsd in September last year (2022), and it was soon clear that it was not an ordinary supernova.

Illustration av svart hål mot bakgrunden av vintergatan
Artist impression of flickering black hole AT2022tsd. Credit: Robert Hurt, Caltech/IPAC

- It was initially brighter and faded faster than do supernovae, explains lead-author Professor Anna Ho from Cornell University. It shone not only in optical light but was also visible in radio-waves and X-rays.

Then came the surprise. 100 days after the outbreak short flares of light were serendipitously discovered from the same position on the sky. Months of episodic and energetic flaring followed from this distant (4.4 billion light years) object, where each flare lasted only some few minutes and kept on for at most some hours..

- We used 15 different telescopes to catch 14 episodes of flaring, describes Steve Schulze from Stockholm University, one of the co-investigators in this study. This included the ZTF camera we originally used to find the object, as well as the Nordic Optical Telescope on La Palma.

This penomenon has never been seen before, perhaps in part since no one has really looked for it. One of the interpretations forwarded in the Nature article is a compact object, maybe a small black hole, that is fed at intermittent intervals.  More of these objects will likely be discovered, now when the astronomers know what to search for.

The paper Minutes-duration optical flares with supernova luminosities  is published in the journal Nature (online November 15 2023) and is led by Anna Ho from Cornell University in the US.
From Stockholm university participated post-doc Steve Schulze from the Department of Physics and postdocs Conor Omand and Priscila Pessi from the Department of Astronomy as well as Professor Jesper Sollerman from the same department.

Read the Nature paper here