Did you miss us? Cause we missed you! Reborn of Black Holes

Volcanoes on Earth can be dangerous; they remain dormant for years and can erupt unexpectedly. Recently, however, a similar process occurred in the universe. A black hole, located at the center of the galaxy J1007+3540, that hadn't had any activity for 100 million years, suddenly erupted. Not only that, but instead of being a smaller stellar black hole, it was a supermassive black hole.

Image of J1007+3540, with a bright inner jet, representing the reactivation of a past dormant black hole.

Copyright and credit to LOFAR, Pan-STARRS, S. Kumari et al.

Supermassive Black Hole (SMBH)

 Living at the center of most known galaxies, those black holes are millions and billions of times the mass of our sun. They can be quiet or actively feeding and violent, the latter have clouds of matter surrounding them that "feed” them, commonly called “accretion disk”. This part, due to the intense gravitational force that generates friction on the surrounding matter and gas, heats up and glows. Some of the mass on the accretion disk is channeled from the magnetic field to the poles of the SMBH. It is then emitted as jets at nearly the speed of light, becoming bright and reaching vast distances. Erupting SMBHs are also called Active Galactic Nuclei (AGN).

Galaxy J1007+3540

 The galaxy became a subject of study when astronomers observed its unusual "footprint". Such a large structure with jet activity, indicated by plasma lobes, isn't unusual; what is unusual is that there was a smaller, brighter jet within the other normal jets. That suggests that the AGN had returned to activity, as scientists compare it to a switch being turned on and off. This system, composed of two very large cosmic structures, facilitates astronomical analysis.

Analyzing jets

Scientists seek evidence of past active phases of AGNs, such as ionized gas that has traveled far from the galaxy's center. The radio images of J1007+3540 provide evidence of both the active phase, with a newborn jet, and the dormant phase, with surrounding older material from previous blasts.

Environmental effect

 It is well established that AGN jets affect the intracluster medium (the region between galaxies, filled with superheated gas), but the details of their impact remain unclear. This recent eruption, however, provided insight into that problem: the material from the jet, after interacting with the hot gas, was bent and distorted non-uniformly, with some jets compressed and others elongated.

Related links:

Scientific American: https://www.scientificamerican.com/article/back-from-the-dead-a-black-hole-is- erupting-after-a-100-million-year-hiatus/

Space.com: https://www.space.com/astronomy/black-holes/reborn-black-hole-seen-erupting-across-1- million-light-years-of-space-like-a-cosmic-volcano

LiveScience: https://www.livescience.com/space/black-holes/like-watching-a-cosmic-volcano-erupt- scientists-see-monster-black-hole-reborn-after-100-million-years