Juan A. Fernández-Ontiveros of the Istituto Nazionale di Astrofisica (INAF) in Rome and Teo Muñoz-Darias of the Instituto de Astrofisica de Canarias (IAC) in Canarias have written an article in which they describe the different states of activity of a large sample of supermassive black holes in galaxies’ centers. The behavior of their nearest “relations,” stellar-mass black holes in X-ray binaries, was used to classify them. The study was just published in the journal Monthly Notices of the Royal Astronomical Society (MNRAS).
Black holes can have masses ranging from a few times the mass of the sun to billions of millions of solar masses. For decades, scientists have been trying to figure out how to interpret their activity cycles from a global viewpoint. A stellar black hole (also known as a stellar-mass black hole) is a black hole generated when a star collapses due to gravity. They have masses ranging from a few tens of solar masses to many hundreds of solar masses.
The stellar mass variety is found in binary systems with a companion star from which they suck out the gas required to sustain their activity, whereas the supermassive variety is found in the galactic nuclei and feeds on the gas, dust, and stars that fall into the galactic nucleus’ gravitational well.
Only the most massive stars have the ability to become black holes; only the most massive stars achieve this desired status. Stars with at least 2 to 3 times the mass of our Sun produce the smallest stellar-mass black holes. After silicon, the star’s core is just a piece of iron, at which time nuclear fusion can’t produce any more energy.
The greatest mass that a neutron star can have (without turning into a black hole) remains unknown. The TOV limit, which was established in 1939, was set at 0.7 solar masses. A separate estimate from 1996 put the highest mass in the 1.5 to 3 solar mass range.
The study demonstrates the presence of accretion states in supermassive black holes, with properties very similar to those we know from stellar-mass black holes, where the systems in the ‘soft’ state harbor a bright disc, and those in the ‘hard’ state show intense radio emission while the disc is very weak.
Juan A. Fernández-Ontiveros
Black holes with a stellar-mass develop quickly. They go through several stages or phases during their activity cycles, which generally span a few months or years. Changes in the features of their accretion discs (where hot gas gathers before going into the black hole), winds, and material jets describe them.
There are two main states, the first of which is dominated by the accretion disc, and the second of which is dominated by the jet. The ‘soft’ state is marked by the disc’s thermal emission, whereas the ‘hard’ state is marked by the disc cooling down and the emission at radio frequencies being highly strong.
Because they are significantly more massive than their stellar mass counterparts, supermassive black holes grow much more slowly. As a result, demonstrating the presence of states and transitory events in these would need millions of years of observation, because the changes over a human lifetime would be too minor to observe.
Furthermore, galaxies’ nuclei are densely populated places, and light absorption by hydrogen and dust conceals and hides the radiation from the accretion disc around the core black hole.
Fernández-Ontiveros and Muoz-Darias used a sample of 167 active galaxies in their work to accurately identify the potential accretion states of supermassive black holes. The accretion disc’s emission is not directly detectable, but the center region’s gas absorbs and processes the radiation in the form of spectral lines. It is feasible to test the presence of the disc in these objects by looking for oxygen and neon lines in the mid-infrared.
“The study demonstrates the presence of accretion states in supermassive black holes, with properties very similar to those we know from stellar-mass black holes, where the systems in the ‘soft’ state harbor a bright disc, and those in the ‘hard’ state show intense radio emission while the disc is very weak,” explains Juan A. Fernández-Ontiveros, an INAF researcher who was trained at the IAC.
“This work opens a new window to understand the behavior of material (gas) when it falls into black holes with a wide range of masses, and helps a more precise understanding of the activity cycles of the supermassive black holes which are in the centers of most galaxies,” adds Teo Muñoz-Darias, a researcher at the IAC.
In the most fundamental sense, the star’s outer shell implodes because there is no interior pressure to maintain it. Those falling outer layers rebound off the star’s core, detonating it as a supernova for stars somewhat more massive than the Sun.
Other than procedures involving a single star, such as black hole mergers, black holes may be discovered in the mass gap. Nothing, however, can stop the crushing collapse of the most enormous stars. When such stars die, they will collapse into stellar-mass black holes.
