M77 is a brilliant barred spiral galaxy located 47 million light-years away in the constellation Cetus. In a recent study, astronomers provided important evidence for a 30-year-old "unified model" after exhaustive observations of the center of M77.
M77, also known as NCG 1068. | Image source: ESO
Unified model
At the centers of most galaxies, astronomers have discovered the existence of supermassive black holes. The mass of these black holes is millions, if not billions, of times the mass of the Sun. But at any given time, only a few of them are "active." To become an "active galactic nucleus (AGN)," the black hole must accumulate large amounts of gas around it, which is heated and emits bright light.
Although the active galactic nucleus occupies a region not as large as the solar system, it emits even brighter light than the light emitted by all the stars in the galaxy combined. In some cases, black holes also produce huge jets of matter that extend outward at nearly the speed of light.
Since its first discovery in the 1950s, AGN has been an object of keen study by astronomers. Astronomers have also found different types of AGNs, such as quasars, radio galaxies, Seiffert galaxies, etc.
Active galactic nuclei are high-energy regions at the centers of some galaxies, driven by supermassive black holes. When jets are pointing at Earth, AGNs look unusually bright, and such AGNs are called "flares." When jets don't point to Earth or black holes don't produce jets, AGN looks completely different. | Image credit: ESO/M. Kornmesser and L. Cal ada
By the 1980s, astronomers had proposed a unified model of AGN, arguing that all AGNs were essentially the same, and that they all had the same basic structure, including a supermassive black hole at the center and a thick ring of dust around the black hole.
Based on this model, we determine the differences in their appearance from the perspective of observing AGNs on Earth. The type of AGN we see depends on how well the dust ring obscures the black hole, and in some cases, the black hole is completely obscured.
In the past, astronomers have found some evidence to support a unified model, including warm dust found at the center of M77. However, astronomers remain skeptical that this dust could completely obscure the black hole.
According to the spectrum of AGN, they can be divided into two categories: type I and type II. The spectrum of type I AGN shows both wide and narrow line areas; the spectrum of type II AGN shows only narrow line areas.
Sharp images
The Very Large Telescope (VLT) in Chile's Atacama Desert is one of the most advanced optical telescopes in the world, containing four fixed-position telescopes with a diameter of 8.2 meters.
The VLT consists of four fixed-position 8.2-meter telescopes and four movable 1.8-meter auxiliary telescopes. These telescopes can work together to form a huge Very Large Telescope Interferometer (VLTI), which captures far more detail than a telescope alone can see. | Image credit: ESO/H.H. Heyer
The new observations come from a powerful instrument called MATISSE, which can pass through dust and allow astronomers to accurately make temperature measurements. Such a powerful instrument combines the number of infrared rays collected by VLT's 4 telescopes, a technique that combines light, an interferometry commonly used in astronomy, to capture details that even the world's largest telescope cannot distinguish.
After combining radio data from ALMA and VLBA, the researchers were able to clearly map out a detailed image of the M77 center. They found a thick ring of cosmic dust and gas with a supermassive black hole hidden in its center. As shown in the image below (right), the black dot shows the most likely location of the black hole, and the two ellipses show the extent of the dust ring. Such a detailed picture depicts exactly what the unified model would expect.
VLTI observed a thick ring of cosmic dust and gas in the center of M77, and a supermassive black hole completely embedded in the center of the ring. | Image credit: ESO/Jaffe, Gámez-Rosas et al.
Next, the researchers hope to use MATISSE to observe more AGNs to look for more observational evidence about the unified model. Because the evolution of galaxies is closely related to the active galactic nuclei at their centers, a better understanding of AGNs could also help us gain a more complete understanding of how galaxies formed, evolved, and died.
#创作团队:
Author: No. 2 Beidou
Typography/Design: Wenwen
#参考来源:
https://www.eso.org/public/teles-instr/paranal-observatory/vlt/
https://www.eso.org/public/news/eso2203/
https://astronomy.com/news/2022/02/m77s-active-nucleus-is-hiding
http://www.natureasia.com/ko-kr/earth-env/research/13983
#图片来源:
首图:ESO/Jaffe, Gámez-Rosas et al.