Capturing a giant black hole at the center of our galaxy

Sagittarius is an image of a black hole.  The black part in the center is the black hole (the event horizon) and the shadow containing the black hole, and the bright part of the ring bends light by the black hole's gravity.  Source: EHT
Sagittarius is an image of a black hole. The black part in the center is the black hole (the event horizon) and the shadow containing the black hole, and the bright part of the ring bends light by the black hole’s gravity. Source: EHT

On May 12, a joint international research team captured images of the supermassive arc black hole (Sgr A*) located at the center of the Milky Way. The research team has successfully observed black holes using the Event Horizon Telescope (EHT), which connects eight radio telescopes based on a global collaboration. The Event Horizon Telescope (EHT) is an international collaborative project that aims to capture images of black holes connecting radio telescopes scattered around the world to create a virtual Earth-sized telescope and the name of this virtual telescope. The event horizon is the region that connects the black hole’s inside and outside.

The arc black hole is the second black hole imaged by the EHT team after M87. Sagittarius: The black hole is located at the center of the Milky Way, about 27,000 light-years from Earth and has a mass about 4 million times the mass of the Sun. Compared to the M87 black hole, its distance from the solar system is about 1/2000, making it a strong target for black hole research. However, it is more than 1,500 times smaller than the mass of M87, so the gas flow around the black hole changes rapidly and the image suffers from severe scattering effects, which makes observation difficult compared to M87.

Sagittarius image of a black hole divided into four groups.  The researchers created thousands of images of Arc using data from the eight radio telescopes that make up the Event Horizon Telescope.  All of these videos have been combined to produce the representative video shown above.  Each image was divided into 4 groups based on morphological similarity.  The three groups on the left show the structure of the ring, but the brightness around the ring is different.  The fourth set consists of images that match the data but do not show a loop structure.  The bar graph at the bottom of each image indicates the relative proportion of images that belong to each group.  The first three groups contain thousands of images, while the fourth and smallest group contains only hundreds of images.  This means that the image with the toroidal structure has more weight than the fourth group image in the final representative image.  The researchers obtained the final top panel image by weighting the average of the images from these four groups according to their relative weights.  Source: EHT
Sagittarius image of a black hole divided into four groups. The researchers created thousands of images of Arc using data from the eight radio telescopes that make up the Event Horizon Telescope. All of these videos have been combined to produce the representative video shown above. Each image was divided into 4 groups based on morphological similarity. The three groups on the left show the structure of the ring, but the brightness around the ring is different. The fourth set consists of images that match the data but do not show a loop structure. The bar graph at the bottom of each image indicates the relative proportion of images that belong to each group. The first three groups contain thousands of images, while the fourth and smallest group contains only hundreds of images. This means that the image with the toroidal structure has more weight than the fourth group image in the final representative image. The researchers obtained the final top panel image by weighting the average of the images from these four groups according to their relative weights. Source: EHT

More than 300 EHT researchers from 80 institutions around the world participated in this study. In particular, for large-scale processing of black hole observation data, supercomputers were used to analyze the data and at the same time reproduce and compare a large amount of black hole images over a period of 5 years. After calibration and imaging, the researchers found a ring-shaped structure and shadows of the black hole, a central dark region.

As a follow-up study, EHT researchers set out to develop a theory to analyze suspended flow around supermassive black holes. With this, it will be possible to clarify the process of formation and evolution of galaxies, and with further research, new results are expected, such as careful verification of the theory of general relativity.

What is the EHT Project?

When you think of a “black hole,” you think of a black hole. No one has ever seen a black hole in person, and no one has ever seen a black hole in person. Even black holes absorb light and cannot be directly observed. The images of black holes that we have seen in videos and articles are purely theoretical.

The Event Horizon Telescope (EHT) translates to “Event Horizon Telescope” and the “event horizon” means a broad line separating the black hole and its interior. When matter goes beyond the event horizon and is sucked into a black hole, some of it is released as energy; So if you use high-resolution monitoring equipment, you can see the edge of the event horizon.

Near the event horizon, a phenomenon occurs due to the strong gravitational influence. A typical example is the shadow of a black hole. Matter approaching the event horizon of the disk around the black hole rotates around the black hole at a speed close to the speed of light and is pulled into the black hole. The strong light from the friction generated at this moment makes the dial glow brightly. The shape of this disk is distorted and bent by the black hole’s gravitational pull. Think of the black hole in the movie Interstellar.

Source: © EHT
Source: © EHT

To the viewer, the edge of this turntable moving toward the viewer appears brighter than the edge farthest from the viewer. These observations of phenomena that occur in the extreme environment around black holes provide strong evidence for the general theory of relativity and the understanding of supermassive black holes. A giant screen is required for this note. So radio astronomers from Global Village connected eight radio telescopes into one and used it as a giant Earth-sized telescope. Since 2018, additional telescopes have been added to the EHT observation network, bringing the total number to 11 in 2020.

Previous International Joint Research Achievements of EHT

A supermassive black hole in the center of galaxy M87
A supermassive black hole in the center of galaxy M87

The black part in the center is the shadow of the black hole, including the event horizon, and the bright part of the ring is bent by the black hole’s gravitational light. The part where the light is directed toward the viewer appears brighter. It was released in April 2019.

Polarized image of a supermassive black hole in the center of galaxy M87
Polarized image of a supermassive black hole in the center of galaxy M87

Shows how the black hole’s edge region is polarized. The glowing spiral lines in the figure indicate the direction of polarization with respect to the magnetic field around the M87 black hole. Released March 2021.

Video of simultaneous observations of multiple wavelengths from the black hole in the center of galaxy M87 to galaxies and jets.
Produced by simultaneous multi-wavelength observations of the black hole at the M87 center of galaxies and jets

This is a multi-wavelength observing image of the center of M87 as a supermassive black hole ejecting a powerful jet through a very large synchronous observing network using telescopes from 19 astronomical observatories. Released in April 2021.

Sagittarius is a black hole at the center of our galaxy
Sagittarius is a black hole at the center of our galaxy

It was discovered by observations in the 7 mm and 13 mm wavelength bands of the East Asian VLBI Observation Network (EAVN) that the structure of the black hole, which is in the center of the Milky Way and closest to Earth, is circular. The data was released in February 2022.

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