Artist’s impression of an inner accretion flow and a jet from a supermassive black hole when it is actively feeding, for example, from a star that it recently tore apart. Image: ESO/L. Calçada
The flickering light emitted by astrophysical accretion disks can reveal the mass of the supermassive black holeA black hole is a place in space where the pull of gravity is so strong not even light can escape it. Astronomers classify black holes into three categories by size: miniature, stellar, and supermassive black holes. Miniature black holes could have a mass smaller than our Sun and supermassive black holes could have a mass equivalent to billions of our Sun.”>black hole (SMBH) at their center, according to a new study. The findings provide a novel method for characterizing the masses of SMBHs using optical observations and help to constrain the poorly understood processes that occur within accretion disks.
Accretion disks – made of gas, dust and plasmaPlasma is one of the four fundamental states of matter, along with solid, liquid, and gas. It is an ionized gas consisting of positive ions and free electrons. It was first described by chemist Irving Langmuir in the 1920s.”>plasma – surround the SMBHs located at the centers of active galaxies. As material from the accretion disk falls toward the black hole, it heats up, emitting an enormous amount of radiation, including ultraviolet and optical light.
Although these disks are much smaller than their host galaxy – roughly the size of the Solar System – they can often out-shine the entire rest of the galaxy. However, accretion disks flicker for unknown reasons, causing their luminosity to fluctuate over a wide range of time scales.
Colin Burke and colleagues report that a characteristic time scale measured from the optical variability of accretion disks is correlated with the masses of the SMBHs they surround. The authors measured the optical variability of 67 well-observed active galaxies to determine the time scale on which the fluctuations became noticeably smaller, known as the “damping” time scale (usually several hundred days). They find that this damping time scale is related to SMBH mass over the entire range of SMBH masses observed in active galaxies and may even extend to smaller accretion discs around other objects.
“One of the most interesting aspects of the study of Burke et al. is that it extends its findings to much less massive objects, such as white dwarfA white dwarf star is the remnant of star that has exhausted its nuclear fuel, but it lacks the mass to become a neutron star. A typical white dwarf is only slightly bigger than Earth, yet it is 200,000 times as dense.”>white dwarf stars, which emit radiation through a similar accretion disk mechanism and can be regarded as miniature accreting SMBHs,” write Paulina Lira and Patricia Arevalo in a related Perspective.
For more on this discovery, read Mysterious Flickering Decoded: Supermassive Black Hole Size Revealed by Its Feeding Pattern.
Reference: “A characteristic optical variability timescale in astrophysical accretion disks” by Colin J. Burke, Yue Shen, Omer Blaes, Charles F. Gammie, Keith Horne, Yan-Fei Jiang, Xin Liu, Ian M. McHardy, Christopher W. Morgan, Simone Scaringi and Qian Yang, 12 August 2021, Science.
DOI: 10.1126/science.abg9933
Source: SciTechDaily
