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Black Holes Encyclopedia

Milky Way

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Alternate Names

Sagittarius A*




In the constellation Sagittarius

Finder Chart


27,000 million light-years (8 kiloparsecs)


4.1 million times the mass of the Sun


Diameter roughly 15 million miles (24 million km).

Discovery Methods


Milky Way

The center of the Milky Way galaxy is a turbulent, dynamic region of bright star clusters, clouds of hot gas, and monstrous magnetic fields. And they all seem to center on a small, dense object known as Sagittarius A* (Sgr A*). Observations of stars orbiting this point suggest that it is a supermassive black hole. There is little gas spiraling into Sagittarius A*, perhaps because exploding stars have blown away much of the gas and dust from the Milky Way's core.

Although this is by far the closest supermassive black hole, it is still relatively difficult to study because it lies behind many thick clouds of interstellar dust, which absorb visible light. Astronomers rely on X-rays, radio waves, and other wavelengths of energy to study the Milky Way's core.

Audio Podcasts

Zeroing in on the Black Hole

Researchers discuss the techniques used to measure the mass of the galaxy's supermassive black hole.

Not-So-Active Heart

UCLA researchers Andrea Ghez and Mark Morris discuss why the Milky Way's central black hole is much quieter than many others.


Stretching Out (European Southern Observatory)
A giant gas cloud is being ripped apart as it loops around the supermassive black hole at the center of the Milky Way galaxy.

Getting Closer (UCLA Newsroom)
Using techniques that cancel out much of the blurring effects of Earth's atmosphere, astronomers have discovered a star that races around the supermassive black hole at the heart of the Milky Way once every 11 years, which puts it closer to the black hole than any other star yet seen. The discovery will allow scientists to probe the black hole's effects on spacetime.

Little Snacks for the Milky Way's Black Hole (Chandra Web Site)
Small flares in the X-ray light from the supermassive black hole at the center of the galaxy may erupt when the black hole "snacks" on asteroids.

Whirling Around the Milky Way (ESO News)
European astronomers have monitored the orbits of about 30 stars in the center of the Milky Way galaxy to learn more about the galaxy's central black hole and the environment around it.

Astronomers Get Closest Look Yet At Milky Way's Mysterious Core (National Radio Astronomy Observatory)
Using a planet-wide array of radio telescopes, astronomers have come closer than ever to measuring the size of the suspected black hole at the center of the Milky Way. They determined that a source of radio waves in the galaxy's core is no larger than the distance between Earth and the Sun. The radio waves probably come from a ring of material that encircles the black hole.

Milky Way's Quiet Black Hole Flared in Past (StarDate)
Oliver Cromwell had Charles I beheaded, toppling the British monarchy. An outbreak of plague shut down Cambridge University, leaving 22-year-old student Isaac Newton to return home and spend his leisure hours creating, among other things, the theory of gravity. And had they existed then, space-borne gamma-ray telescopes would have seen the black hole at the center of our Milky Way galaxy flare to life.

Scientists Look into Milky Way Core (BBC News)
A team of astronomers led by Andrea Ghez at UCLA has pinpointed the location of Sagittarius A* with the greatest accuracy to date by observing three stars that orbit it. Ghez and colleagues collected infrared images of the Milky Way's core over a four-year period. The positions of the stars nearest Sagittarius A* change significantly in only a few years, implying that they orbit a compact, massive body.



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This document was last modified: July 15, 2015.


Center of Milky Way Sagittarius A*
Ground-Based Photo

Radio Image of Sgr A*
Ground-Based Photo

Hiding a Black Hole
Ground-Based Photo

Center of the Milky Way
Ground-Based Photo

Milky Way Sagittarius A*
Space-Based Photo

Glowing Heart
Space-Based Photo

Sagittarius A*
Space-Based Photo

Motions of Stars Around Sgr A*


Flares from the Center of the Milky Way
Flares from the accretion disk around the black hole at the center of the galaxy.