Artist’s animation of the black hole at the center of SDSS1335+0728 waking up in real time – a first for astronomers.
In December 2019, astronomers were surprised to observe a long-quiet galaxy 300 million light-years away suddenly spring to life, emitting ultraviolet, optical and infrared light into space. Far from going quiet again, by February of this year the galaxy had begun to emit X-ray light; it’s up More ▼ active. Astronomers believe it is most likely an active galactic nucleus (AGN) that gets its energy from supermassive black holes at the center of the galaxy and/or from the rotation of the black hole. That’s the conclusion of a new paper accepted for publication in the journal Astronomy and Astrophysics, though the authors acknowledge the possibility that it could also be some kind of rare tidal disturbance event (TDE).
The brightness of SDSS1335_0728 in the constellation Virgo, after decades of silence, was detected for the first time by the Zwicky Transient Facility telescope. Its supermassive black hole is estimated to be about 1 million solar masses. To better understand what might be going on, the authors reviewed archival data and combined it with data from new observations from a variety of instruments, including the X-shooter, part of the Very Large Telescope (VLT) in Chile’s Atacama Desert.
There are many reasons why a normally quiescent galaxy can suddenly brighten, including supernovae, or TDEs, in which some of the original mass of the shattered star is ejected abruptly outwards. This in turn can form an accretion disk around the black hole that emits powerful X-rays and visible light. But these events don’t last nearly five years – usually no more than a few hundred days.
So the authors concluded that the galaxy has woken up and now has an AGN. First discovered by Carl Seifert in 1943, the glow results from the cold dust and gas surrounding the black hole, which can form orbital accretion disks. Gravitational forces compress the matter in the disk and heat it to millions of degrees Kelvin, producing radiation across the electromagnetic spectrum.
Alternatively, the activity could be due to a particularly long and faint TDE—the longest and faintest ever detected, if so. Or it could be an entirely new phenomenon. So SDSS1335+0728 is a galaxy to watch. Astronomers are already preparing for follow-up observations with the VLT’s Multi Unit Spectroscopic Explorer (MUSE) and Extremely Large Telescope, among others, and perhaps even the Vera Rubin Observatory, scheduled to come online next summer. Its Large Synoptic Survey Telescope (LSST) will be able to continuously image the entire southern sky, potentially capturing even more galaxy wakes.
“Regardless of the nature of the variations, [this galaxy] provides valuable information about how black holes grow and evolve,” said co-author Paula Sanchez Saes, an astronomer at the European Southern Observatory in Germany. “We expect the tools to like it [these] will be the key to understanding [why the galaxy is brightening].”
There is also a supermassive black hole at the center of our Milky Way galaxy (Sgr A*), but not enough material has yet accreted for astronomers to detect any emitted radiation, even in the infrared. So its galactic core is considered inactive. It may have been active in the past and may reawaken in a few million (or even billion) years when the Milky Way merges with the Andromeda galaxy and their respective supermassive black holes combine. Only time will tell.
Astronomy and Astrophysics, 2024. DOI: 10.1051/0004-6361/202347957 (About DOI).
List image from ESO/M. Kornmesser
