Radio astronomers have captured the image of a giant black hole in the center of the Milky Way. This is the second time that a live image of the black hole has been taken since the first and most historic image of the same group being able to capture the farthest black hole from the black hole released in 2019.

The long-awaited results released by the Event Horizon Telescope Corporation on May 12 show a picture reminiscent of its predecessor: a ring of radiation around a dark disk of the same magnitude predicted by indirect observations and general relativity. By Albert Einstein.

“Today, at this time, we have direct evidence that this object is a black hole,” said Sarah Essen, an astronomer at the Harvard-Smithsonian Astronomical Center in Cambridge, Massachusetts, at a news conference in Corching, Germany. The team published its findings in a special issue of the Journal of Astronomy. Letters from the Journal of Astronomy. (K. Akkiyama And others. Astronomy. J. Let. 930, L12; 2022.)

“We have been preparing for this discovery for a long time,” said Katie Bowman, a former member of the Event Horizon Telescope team and a computational imaging researcher at the California Institute of Technology in Pasadena, at a news conference in Washington. The hole in the heart of our galaxy. “

Planet-sized telescope

During five nights in April 2017, the Event Horizon Telescope Collaboration used eight observatories around the world to collect data from the Milky Way galaxy – scientists named it Sagittarius A * after its discovery. Black hole M87 *, which is located at the center of the galaxy M87.

Observatory locations were distributed across Spain to Antarctica and from Chile to Hawaii (see:
Global effort)

The researchers released the 2019 image of the M87 * black hole, which provides the first direct evidence of the spherical “event horizon” surrounding the interior of the black hole.

But Sagittarius A Star data was very difficult to analyze. The two black holes have the same apparent size in the sky; Although the M87 * black hole is 1,600 times larger than the Sagittarius-A star, it is almost 2,000 times farther away. In addition, clusters of objects orbiting the M87 * black hole – regardless of their nature – are farther away (larger than Pluto’s orbit around the Sun), and unlike any black hole they emit, they are practically stable in the short term. Sagittarius A star, which can change rapidly even within a few hours of EHT monitoring every day.

“In the case of the M87 * black hole, over the course of a week, we see very little change,” said Heinaw Walke, an astronomer at the University of Rodbout in the Netherlands. It changes shape. In 5 to 15 minutes. “

As the shape of Sagittarius changes so quickly, scientists are careful to create thousands of images without even making a single image of it. Jose Gomez, a researcher at the Andalusian Institute for Astrophysics in Granada, Spain, and a member of the team said, “By averaging data from all these images, we can verify common features.

In addition to the radiation ring around a dark disk, the resulting image showed three bright “nodes”. “We see knots in every film we make,” says Asan, but their location is different in each photo. He said these knots often indicate defects caused by the researchers’ interferometry system.

This black hole differs in its shape from the M87 * hole, in that its brightest part was in the shape of a lunar quadrant (half full moon), which may indicate that dense clusters are accelerating along the line of sight.

Using a supercomputer that drives group simulations and compares their data with their results, the Sagittarius-A-star often rotates in the opposite direction, i.e. the axis that points up to the line of sight toward Earth, Gomez says.

Regina Kaputo, an astronomer at NASA’s Goddard Space Flight Center in Greenfield, Maryland, said: “What amazes me is that we see it from the opposite direction. The Sagittarius-A-Star wormhole occurred during intense activity in the past, but these shapes, known as Fermi bubbles, appear to orbit objects around the black hole, not from the front, but from the side when viewed from Earth.

The first signs of a black hole being a “Sagittarius-A-star” appeared in the 1970s, when radio astronomers discovered the source of a point-like radio wave located at the center of the galaxy.

This evidence became unusually opaque; Is dark as a normal star. Nevertheless, decades of observations of the motion of neighboring stars have shown that this object is very large: based on recent observations, scientists have been able to calculate its mass, i.e. 4.15 million solar masses, plus the margin of error. Or subtraction 0.3%. These calculations, made by observing the orbits of Sagittarius-A-stars, provide conclusive evidence that the source of these radio waves is as large and dense as a black hole.

It is noteworthy that the black hole “Sagittarius-A star” is practically invisible to optical telescopes; As dust and gas cover the galaxy disk. But since the late 1990s, Polk and others have realized that the shadow of a black hole can be large enough to be photographed by narrow radio waves that can escape from that envelope. However, scientists estimate that this will require an Earth-sized telescope. Fortunately, a technique called interferometry can help scientists in this endeavor. Technology can point multiple telescopes at the same object at the same time, making telescopes practically the same pieces of food.

The first attempts to monitor the Sagittarius-A-star by interferometry relied on radio waves with a wavelength of 7 millimeters, which was relatively long, and the observatories were several thousand kilometers away from each other. Thus, the cloudy space could not be overlooked by researchers.

Later various groups around the world worked hard to improve their methods and re-fit the added observatories into the network. In particular, researchers placed the Antarctic telescope and the $ 1.4 billion Atacama Large Millimeter / Submillimeter Telescope in Chile.

In 2015, research teams teamed up to create the event Horizon Telescope collaboration. The teams took part in a joint space-observation campaign in 2017, the first of which involved observations far enough away to reveal details of an object the size of a Sagittarius A star.

Future plans

The Event Horizon Telescope team collected additional data in 2018, but canceled scheduled observations in 2019 and 2020. Monitoring resumed in 2021 and 2022 with an upgraded network and sophisticated equipment.

Remo Telenos, a board member at the University of Arizona in Duson, said that in March, the team’s last observations could contribute to greater clarity at twice the rate of 2017, often at a wavelength of 0.87 millimeters. The resulting images.

Researchers hope to find out if the Sagittarius-A-star black hole has holes; Many black holes, including M87 *, appear to emit two rays of matter rapidly in opposite directions, and are believed to be caused by the intense heat of the gas falling towards the black hole and to be pushed by its rotation. . The Sagittarius-A-star may have had large jets in the past, marked by heated clouds above and below the galaxy. Its jets are now very weak, but their existence may reveal important details about our galaxy history.

“These eruptions can slow down or induce star formation, and they can push chemical elements around,” says Balk, which affects the evolution of an entire galaxy. “Now we see where all this is happening,” he added.