What is Sagittarius A*?

Sagittarius A * (abbreviated as Sgr A *, the asterisk * pronounced "star" or "star") is a very bright and dense radio wave source located in the galaxy's galaxy, rotating about every 11 minutes ^{[1 ] Is} part of Sagittarius A. Sagittarius A * is likely to be the closest supermassive black hole to us ^[2] , so it is also considered to be the best target for studying black hole physics ^[3] .

Sagittarius A *

Multiple research teams have tried to use

Stars near Sagittarius A * observed over several years using time-lapse photography

Sagittarius A * was first discovered in February 1974. ^[8] Its observations mainly rely on light-variable observations.

The Max Planck Institute for Extraterrestrial Physics, an international research team led by Rainer, observed the astral S2 close to Sagittarius A * for ten years, and announced Sagittarius A on October 16, 2002. * Evidence for a mass of dense body ^[9] . From the Kepler orbit of S2, Sagittarius A * has a mass of 260 ± 200,000 solar masses and a radius of 120 astronomical units ^[10] . Subsequent observations estimate that the mass of Sagittarius A * should be 4.1 million solar masses with a volume radius of less than 45 astronomical units ^[11] .

In November 2004, astronomers discovered that GCIRS 13E, which may be a medium-mass black hole, has an orbit about 3 light years from Sagittarius A *. GCIRS 13E has a mass of 1300 solar masses and belongs to a cluster of 7 stars. This observation supports the claim that overweight black holes will absorb smaller black holes and stars to grow.

Sagittarius A * (center) and two light echoes (inside)

After observing Sagittarius A * for about 16 years, it is believed that its mass is 431 ± 380,000 solar masses. Researcher Reinhard Genzel believes that there is preliminary evidence for the existence of overweight black holes ^[12] .

On April 10, 2019, the "Event Horizon Telescope" project, a collaboration of scientific researchers from multiple countries around the world, released a "groundbreaking achievement". It is generally believed that this will be the first black hole photo ever obtained by human beings.

The "Event Horizon Telescope" project is composed of scientists from many countries and regions around the world. They use radio telescopes distributed around the world to form a huge virtual telescope with a caliber equivalent to the diameter of the earth. The key objects for taking photos with this virtual telescope are black holes located at the center of the galaxy code M87 and Sagittarius A * black holes at the center of the Milky Way. Unfortunately, for various reasons, the "Event Horizon Telescope" project on April 10, 2019 only published photos of the M87 black hole, and Sagittarius A * photos could not be released.