The accretion disks around these systems, and around SMBHs in general, are made up of infalling dust, gas, stars, and inevitably planets and other solar system debris. Astronomers can actually, to a certain extent, determine when an SMBH is about to consume one of these chunkier objects. The gravitational force across the diameter of a star or other extended object can be dramatically different, and these differences in pull can actually pull the object apart. These are called tidal disruption events (TDE), and they often release massive bursts of energy, including X-rays, which can push bubbles into the surrounding interstellar medium. Often isn’t the same as always, however, and theorists have had a chore in sorting what exactly is going on. 

According to researcher Tiara Huang: In classical theory, the TDE flare is powered by an accretion disk, producing x-rays from the inner region where hot gas spirals into the black hole. But for most TDEs, we don’t see x-rays—they mostly shine in the ultraviolet and optical wavelengths—so it was suggested that, instead of a disk, we’re seeing emissions from the collision of stellar debris streams. 

This theory wasn’t a great match to observations, however, and theorists continued to struggle with this problem. In 2018, a new model postulated that we don’t see the X-rays because they are being blocked by material. This paper, by Enrico Ramirez-Ruiz and Jane Dai, made specific predictions of what should be seen to confirm this idea, and in follow-up observations to a 2018 TDE, they saw exactly what they predicted: emission from hydrogen gas with a double peak showing it is in a spinning disk. 

These new results are now published in a paper lead by Huang and appearing in The Astrophysical Journal.

According to Ramirez-Ruiz: This is the first solid confirmation that accretion disks form in these events, even when we don’t see x-rays. The region close to the black hole is obscured by an optically thick wind, so we don’t see the x-ray emissions, but we do see optical light from an extended elliptical disk.

What is interesting about this story is that we had the basic science right all along – those X-rays were getting released during the TDE. What we failed to account for was the environment. Our universe is nothing if not more complex than we like to give it credit for and to understand our reality, we had to make things messier, adding dust and gas and outflows that can obscure the clean physics that we’re most interested in. 

More Information

University of California Santa Cruz article 

“Prompt Accretion Disk Formation in an X-Ray Faint Tidal Disruption Event,” Tiara Hung et al., to appear in The Astrophysical Journal (Preprint on arxiv.org)