Supermassive black holes at the centers of galaxies can rapidly swallow matter while simultaneously ejecting narrow beams of plasma - jets accelerated to almost the speed of light. This raises a physical puzzle: rapid accretion should create a cold, flat disk that is thought to hinder the formation of powerful jets.
An international team led by Hirofumi Noda of Tohoku University and Kazuhiro Hada of Nagoya City University has found evidence supporting a solution to this puzzle. The scientists combined observations from the XRISM X-ray telescope (the X-ray Imaging and Spectroscopy Mission) with data from international networks of radio telescopes and millimeter-wave telescopes. The results were published in The Astrophysical Journal Letters.
The researchers studied the galaxy 3C 120 in the constellation Taurus. At its center is a supermassive black hole that rapidly accretes matter and launches a powerful jet. XRISM detected iron emission from the disk around the black hole. The shape of this line is distorted by the effects of Einstein's general theory of relativity, which made it possible to determine how close to the black hole the disk extends.
It turned out that the cold, relatively flat disk ends at a distance of about 20 black hole radii. Beyond that it transitions into a hot flow of plasma heated to hundreds of millions of degrees. At the same time, radio and millimeter observations using the Global Millimeter VLBI Array, the Very Long Baseline Array and the East Asian VLBI Network traced the narrowing jet back to its origins - inside this hot flow, near the black hole.
According to the authors, such a hot environment allows magnetic fields to accumulate around the black hole. These fields are thought to extract part of the black hole's rotational energy and channel it into a powerful jet. The observations show that 3C 120 meets the conditions for this mechanism to operate. This provides new insight into how rapidly accreting supermassive black holes can produce relativistic jets.
The work also offers a new way to study the immediate surroundings of supermassive black holes. The team continues coordinated observations of a more massive black hole using XRISM and global radio telescopes, comparing the results with theoretical models and computer simulations.
"Our next goal is to build a more complete picture of how matter, magnetic fields and black hole rotation interact in these extreme conditions," Noda was quoted as saying by the press service. "Understanding this process may also help us better understand how supermassive black holes influence the evolution of galaxies and the large-scale structure of the Universe."
It is important to note: this concerns observations of a single object, and the researchers' conclusions concern the conditions under which the proposed mechanism can work, rather than a proven universal law for all black holes.