First-ever Black Hole 'Accretion Disk' Captured

Korean researchers played a decisive role in simultaneously capturing the shadow and powerful jets of the supermassive black hole located at the center of the M87 galaxy for the first time. They also confirmed the appearance of the accretion disk of the M87 black hole for the first time in history.

An illustration depicting the accretion disk and jets of a black hole. Image source: Provided by Korea Astronomy and Space Science Institute.

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The Korea Astronomy and Space Science Institute (KASI) announced on the 27th that an international joint research team, including Senior Researcher Jongho Park, published these research results in the international academic journal Nature on the same day.

The international joint research team conducted observations using the Global Millimeter VLBI Array (GMVA), the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, and the Greenland Telescope (GLT). With the participation of these telescopes, they discovered physical phenomena that could not be confirmed in the existing Event Horizon Telescope (EHT) black hole images.

Black holes absorb surrounding matter with strong gravity, and it has been expected that this matter forms an accretion disk structure at the center of the black hole. A black hole itself emits no light. It emits light through accretion, which pulls nearby gases by gravity. Gases that are rotating even slightly become accreted and spin faster, forming an accretion disk. Until now, only indirect evidence of the existence of black hole accretion disks had been presented, but the structure of the accretion disk had never been resolved and imaged. This observation discovered that the light emitted from the accretion disk plays an important role in creating the ring structure around the black hole. It also confirmed the existing prediction that black holes in massive elliptical galaxies like M87 slowly absorb surrounding matter.

The international joint research team discovered the ring structure around the black hole at a wavelength of 3.5 mm, which is longer than the 1.3 mm wavelength used in EHT observations. The size of the observed ring structure appeared about 50% larger than the ring structure observed by EHT. In the EHT image observed at the 1.3 mm wavelength, only the photon ring around the black hole appeared, but in the GMVA+ALMA image observed at the longer wavelength, light from the plasma of the outer accretion disk, which is larger in scale than the black hole, was also captured along with the photon ring.

M87 black hole observed with GMVA+ALMA. The accretion disk structure of the black hole (left enlarged image) and the jet ejected from the black hole can be seen. Photo by KASI

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In particular, the shadow and jets (rapid flows of gases and liquids) of the M87 black hole were simultaneously captured for the first time. This result suggests that black holes not only absorb surrounding matter with strong gravity but also create jets moving at high speeds, which can influence the evolution of stars and galaxies far from the black hole.

ALMA, in which KASI participates in operation, played a significant role in this discovery. ALMA greatly improved the sensitivity and north-south directional resolution of the images, enabling the first-ever discovery of the ring structure at the 3.5 mm wavelength. Korean researchers contributed to the study by participating in error correction of the very long baseline interferometry data and the process of converting data into images. Korean researchers, including those from KASI, plan to conduct four intensive additional observations of the M87 black hole over one month using the Korean VLBI Network (KVN), the James Clerk Maxwell Telescope (JCMT) in Hawaii, which the Astronomy and Space Science Institute participates in operating, GMVA, and ALMA. Based on this, they will continue to study the formation mechanism of the strong jets observed in M87 and how the plasma around the black hole changes over time.

Theoretical explanation of the difference in ring structures observed by the previous EHT and the recent GMVA+ALMA. Image source: Provided by KASI

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Senior Researcher Park said, “This is an important turning point in black hole research as it directly imaged and proved the existence of the black hole accretion disk for the first time in history, which had only been predicted for decades.” He added, “It will provide an important clue to understanding how black holes absorb surrounding matter and how, in the process, they emit enormous energy that influences the evolution of stars and galaxies far from the black hole.”

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