Sagittarius A* is a supermassive black hole located at the center of the Milky Way galaxy. It is situated in the constellation Sagittarius. Sagittarius A* is estimated to have a mass of about 4.3 million times that of our Sun, concentrated in a region less than the size of our solar system.

Sagittarius A* is small — just 30 times wider than our sun — and 27,000 light-years distant. Because it is relatively small, any activity on Sagittarius A* — such as the motion of the trillion-degree plasma that surrounds it — occurs 1,000 times faster than it does on M87’s black hole.

One of the significant discoveries related to Sagittarius A* is the observation of stars orbiting around it. These stars, known as S stars, follow elliptical paths, providing strong evidence for the existence of a massive black hole at the galactic center. The orbits of these stars have been studied over several decades, contributing to our understanding of black holes and the laws of gravity.

Details about the Black Hole

Diameter: 24 million km

Mass: 8.26×10^36 kg (4.3 million solar masses)

Discovered: February 13, 1974

Distance to Earth: 25,640 light-years

Constellation: Sagittarius

Discoverers: Reinhard Genzel, Harry Clive Minnett, Robert Brown, Bruce Balick
Credit: X-ray: NASA/CXC/SAO; IR. NASA/HST/STScl/. Inset: Radio (EHT Collaboration)

This is the first image of Sagittarius A* (or Sgr A* for short), 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. The telescope is named after the “event horizon”, the boundary of the black hole beyond which no light can escape.
Credit: EHT Collaboration

There’s no place like our home galaxy…or its supermassive black hole! Sagittarius A* (pronounced A-star) lies at the center of the Milky Way, surrounded by a disk of gas and dust. Webb may be able to detect that disk and tell us more about the “chicken and egg” problem of which came first — the galaxy, or the black hole?

Sagittarius A*: NASA Telescopes Support Event Horizon Telescope in Studying Milky Way’s Black Hole! This composite image of the supermassive black hole at the center of the Milky Way galaxy includes data from multiple NASA telescopes. The inset image from the Event Horizon Telescope shows the region around the black hole’s Event horizon, the boundary beyond which not even light can escape.