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Title: “Beads-on-a-string” Star Formation Tied to One of the Most Powerful Active Galactic Nucleus Outbursts Observed in a Cool-Core Galaxy Cluster
Authors: Osase Omoruyi et al.
First Author’s Institution: Center for Astrophysics ∣ Harvard & Smithsonian
Status: Published in ApJ
Billions of years ago, around 3.8 billion light-years away, there was a black hole outburst so explosive that we can still see remnants of it today — and it may be the most powerful event of its kind we have ever observed. The authors identified this outburst when they noticed a remarkable structure that formed from the wreckage, a 28 kiloparsec (91,000 light-year) arc of star formation that resembles beads on a string, as shown in Figure 1.
Figure 1: SDSS 1531 image from Hubble’s Wide Field Camera 3, emission in the V-band (bottom left), and near-ultraviolet (bottom right). [Omoruyi et al. 2024]
Multiwavelength studies are especially illuminating, because each wavelength range can provide unique information about the underlying physical processes in a system. The Chandra X-ray Observatory was used to observe the hot intracluster medium. Radio observations from the Low Frequency Array (LOFAR) and the Very Large Array (VLA) were used to search for activity associated with the black hole outburst. The Gemini Multi-Object Spectrograph (GMOS) observed the warm ionized gas and searched for ionization sources. Finally, the Atacama Large Millimeter/submillimeter Array (ALMA) observed the cold molecular gas from which stars form.
From these observations, the authors were able to piece together a picture of the outburst, the lasting effect it had on its environment, and specifically how it created the string of star formation. Some 200 million years before SDSS 1531 was as it appears today (in reality, billions of years ago when light travel time is accounted for), a supermassive black hole at the center of one of the large merging galaxies was actively accreting material and emitting two extremely powerful jets in opposite directions, making it an active galactic nucleus. The jets blasted hot material away, forming massive cavities. One cavity was identified by Chandra and LOFAR observations because it lacks hot X-ray emission and is filled with radio emission. The symmetric cavity created by the other jet was not observed, but the authors proposed it may have since faded away if the jet blew into a less dense region of gas, or the motion of the surrounding gas pushed the cavity away from its original location.
This active galactic nucleus was not observed, so the authors know that it has since “turned off” and is no longer active. However, the major disruption caused by the active galactic nucleus outburst and the complex dynamics of the ongoing galaxy merger are likely the cause of the “beads on a string” star formation. The GMOS and ALMA observations revealed warm ionized gas and cold molecular gas along the edge of the star formation arc. The authors believe that hot gas pushed away by the outburst’s jets eventually cooled and is now falling back on to the merging galaxies. This cold gas then began to collapse to form stars, initiated by a cooling wake, strong ram pressure forces, or tidal interactions from the galaxy merger. See Figure 2 for an overview of these findings.
Figure 2: An overview of this article’s interpretation of SDSS 1531. The light blue “avocado” shapes represent the cavities formed by the active galactic nucleus jets. The light green dots show regions of star formation along the edge of the dark blue region of cold molecular gas. [Omoruyi et al. 2024]
Original astrobite edited by Abbe Whitford.
About the author, Annelia Anderson:
I’m a 4th-year Astrophysics PhD student at the University of Alabama. My current research uses simulations to study the circumgalactic medium and inform interpretations of observations. Beyond research, I enjoy playing piano and guitar, cooking, spending time with my cat, and I hope to someday write astronomy children’s books.