Sagittarius A*, abbreviated as Sgr A*, is the supermassive black hole at the Galactic Center of the Milky Way. The object was first detected in 1974 as a bright and very compact astronomical radio source. It has now been imaged by a world-wide network of radio observatories and its mass estimated observations of the orbits of nearby stars using very large infrared telescopes.
Observations by the W. M Keck Telescopes provided clear evidence for the existence of a supermassive black hole at the centre of our Milky Way galaxy. Because of dust, the galactic centre cannot be seen at visible, ultraviolet or soft x-rays wavelengths, but images of the stars and gas clouds at the centre of our Milky Way galaxy can be seen using infrared optics.
This image from the Keck telescopes shows the stars closest to the black hole hole and their orbits within the central 1.0 x 1.0 arcseconds of our Galaxy [http://www.galacticcenter.astro.ucla.edu/blackhole.html]. The superimposed orbits show the positions of the stars at earlier times in the period 1995-2014. The movements of these stars provide very convincing evidence for an invisible supermassive black hole at the centre of our Milky Way galaxy.
Go to https://www.eso.org/public/videos/eso1825e/ to see a time-lapse video from the NACO instrument on ESO’s Very Large Telescope in Chile showing stars orbiting the supermassive black hole at the heart of the Milky Way over a period of nearly 20 years ending in 2018.
The current best estimate of the mass of the black hole is 4.297±0.012 million solar masses. Although massive, the black hole in the centre of our galaxy is very modest compared to the black holes in some galaxies which exceed billions of solar masses
Image of Sgr A* captured by the Event Horizon Telescope (EHT), an array which linked together eight existing radio observatories across the planet to form a single “Earth-sized” virtual telescope.
In May 2022, astronomers released the first image of the accretion disk around the horizon of Sagittarius A*, confirming it to be a black hole. It was captured by the Event Horizon Telescope (EHT), an array which linked together eight existing radio observatories across the planet to form a single “Earth-sized” virtual telescope. The new view captures light bent by the powerful gravity of the black hole.
This is the first image of Sgr A*, the supermassive black hole at the centre of our galaxy. It’s the first direct visual evidence of the presence of this black hole. It was captured by the Event Horizon Telescope (EHT), an array which linked together eight existing radio observatories across the planet to form a single “Earth-sized” virtual telescope. Although we cannot see the event horizon itself, because it cannot emit light, glowing gas orbiting around the black hole reveals a telltale signature: a dark central region (called a shadow) surrounded by a bright ring-like structure.