Black holes are dark monsters that warp spacetime, but counterintuitively, some black holes are quite bright—not strictly speaking the black hole itself, but a glowing “accretion disk” surrounding the black hole, sometimes brighter than an entire galaxy. high.
Astronomers have discovered that the brightness of these extremely bright huge black holes called “quasars” is not constant, but varies over time. This phenomenon may be related to how black hole accretion disks devour celestial bodies. of relevance.
Tang Jijia and his research team from Taiwan, who are currently studying in the doctoral program at the Department of Astronomy and Astrophysics (RSAA) of the Australian National University (ANU), observed more than 5,000 black holes, analyzed the observation data for five years, and used the magnetohydrodynamic model Find very clear rules. The research was published in the prestigious journal Nature Astronomy in February.
▲ The central black hole of the Milky Way taken by EHT, the halo is the accretion disk glowing. (Source: EHT)
In the extreme environment around the black hole, many physical laws are quite different from the daily rules of the earth, and the interaction between gravity and magnetic field is a key factor that cannot be ignored. However, the structure of the black hole’s accretion disk is very chaotic and rotates at a high speed. How to explain the luminosity changes of quasars from the activities of the accretion disk has always puzzled astronomers.
▲ The black hole and accretion disk imagined by the artist. How to explain the physical phenomenon of turbulent flow above the accretion disk is a big problem. (Source: NASA)
The latest research, thanks to the long-term survey observations of NASA’s ATLAS telescope in Hawaii, the research team was able to record in detail the brightness changes of each quasar at different time points, and use statistical methods to analyze the data. Looking closely at the 5,000 brightest quasars, the team found that when sorted by disk size, brightness, and color, patterns of brightness variation were generally correlated with the rate at which the disk orbited the black hole.
In the past, when astronomers studied the brightness changes of accretion disks, they would take into account the properties of many and various quasars, forming a very long and complicated relationship. However, this study is based on a large amount of observational data. When the time difference is replaced by the thermal equilibrium time scale as the unit, the brightness change of the accretion disk and the time difference will show a simple linear relationship, that is to say, no matter the size, brightness or color of the accretion disk, as long as the The thermal equilibrium time scale is unit, and the quasar brightness variation pattern is the same. This result is very consistent with the prediction result based on magnetohydrodynamics, which is called the theory of magnetic rotation instability, and it can be said to point out a clear path for the study of black hole accretion disks.
▲ The left picture shows the relationship between the time difference and the quasar luminosity change. The right picture shows the redrawn coordinates of this study after reconsidering the thermal equilibrium time scale of the accretion disk. (Source: Nature)
The theory of magnetic rotation instability was proposed in 1998, and this research confirms that it can explain how the magnetic field interacts with the matter on the black hole’s accretion disk, which eventually leads to changes in brightness over time. This discovery opens up new avenues for studying the properties of black hole accretion disks. The next step is to examine more closely the subtle differences in the brightness of different quasars to see if this information contains clues to identify the angle of the black hole’s accretion disk, allowing us to more fully understand properties of black holes.
(This article is reproduced with the authorization of Taipei Planetarium; the source of the first image: Pixabay)
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