How heavy are the supermassive black holes, which are mostly invisible in the heart of galaxies? According to a study, the flickering of the light from the disks of matter around such black holes reflects their mass. This connection offers a new way of characterizing the mysterious gravitational giants with the help of optical observations. The method could also help to better understand the poorly understood processes in accretion disks, say the astronomers.
Their gravitational force is so strong that not even light escapes them: Because of their spectacular physical features and cosmic significance, the black holes are a particular focus of astrophysics. Up to now, one inferred their masses from their effect on the environment. They come in three categories. There are stellar black holes with a mass that is up to ten times the mass of the Sun, specimens of medium mass that weigh about 100 to 100,000 times as much as our suns and then there are the absolute gravitational monsters: super-massive black holes are up to millions Billions of times more massive than the sun and typically sit in the center of galaxies.
The giants among the black holes in particular still pose many puzzles to astronomers. It is also unclear how they form and grow. In order to investigate this question it would be beneficial to be able to use another method to determine their masses. The research team led by the University of Illinois at Urbana Champaign is now showing such a possibility. The astronomers initially focused on active supermassive black holes (SMBHs) in the center of galaxies – or the disks of matter from which they “feed”. These accretion discs are about the size of our solar system and can emit strong radiation due to the processes of “eating”. Often it can even outshine the glow of the entire galaxy.
Are there characteristic patterns in the flickering?
It is known that the light of the “hole lining” flickers: Due to physical processes that are not yet fully understood, the radiation fluctuates over time scales from hours to decades. “There have already been attempts to establish a relationship between the flicker observed and the mass of SMBHs, but the results were inconclusive,” says first author Colin Burke. For their study, he and his colleagues have therefore compiled a data set of 67 active SMBHs with known masses in order to be able to analyze the variability patterns of radiation more extensively.
As the researchers report, they have now been able to identify patterns that clearly show a connection between the flickering and the mass of SMBHs: They determined a characteristic time course in the flickering that correlated closely with the known features of the respective black hole. They then expanded their investigations to include growing white dwarf stars, which can also have flickering accretion disks. These are remnants of stars from the mass of our sun. The scientists found that the same flicker-to-mass ratio is also present in these celestial bodies, although white dwarfs are millions to billions of times less massive than SMBHs.
Potential for astronomy
“These results suggest that the processes that drive flicker during accretion are universal – regardless of whether the central object is a supermassive black hole or a much lighter white dwarf,” says co-author Yue Shen. His colleague Yan-Fei Jiang from the Center for Computational Astrophysics in New York adds: “The connection between the observed light flicker and the fundamental properties of the center could help us to better understand accretion processes.”
As the scientists point out, the results could, above all, shed light on the so far hardly explored medium-sized black holes (IMBHs): “Now that the correlation is clear, we can predict what the flickering signal of the medium-sized specimens might look like,” says Burke . In this context, the scientists are now hoping for the data from the sky survey by the Legacy Survey of Space and Time (LSST) project from the end of 2023. “The evaluation of the LSST data set to search for flicker patterns that match accretive IMBHs has the potential to to discover and study this long-sought mysterious population of black holes, ”says co-author Xin Liu University of Illinois.
Video: Artist’s impression of the flickering of light in a supermassive black hole. (Credit: Mark A. Garlick / Simons Foundation)
Source: University of Illinois at Urbana Champaign, Article: Science, doi: 10.1126 / science.abg9933