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Black Holes Encyclopedia
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« Zeroing in on a Dark Heart

Best-Case Scenario

Black Hole Binge?

But it's an anemic black hole.

The supermassive black holes in the centers of many other galaxies are surrounded by large, turbulent disks of infalling material, known as accretion disks. As the gas, dust, and demolished stars spiral toward the black hole's "surface," the event horizon, they are heated to millions or billions of degrees. That produces enormous amounts of energy, particularly X-rays.

Streamers of stars and gas orbit the central black hole in this false-color image, which combines views in infrared and radio wavelengths. [NRAO/AUI]

An X-ray view of the center of the galaxy. The black hole is at the center, but is too small to see. [NASA/CXC/MIT/F.K.Baganoff et al.]

Magnetic fields in the disk funnel some of the material from the innermost region of the accretion disk into thin jets that shoot into space at near the speed of light. The jets produce lots of radio energy, which radio telescopes on Earth detect as active galactic nuclei (AGNs). In fact, it was the discovery of AGNs that motivated the earliest searches for a supermassive black hole at the center of the Milky Way.

Yet the Milky Way's black hole is an inactive galactic nucleus. It does have a small accretion disk, which produces a faint glow in visible, infrared, and other wavelengths. But the total amount of material in the disk probably equals the mass of a pulverized asteroid or two, not a star.

"We have these young stars in this region losing mass," says Ghez. "The mass should fall into the black hole, and this is one of the reasons why it's odd that the black hole today is so quiet. ... That's an interesting problem that people are currently scratching their heads about."

The black hole probably hasn't always been so quiet, though. A century ago or longer, it seems to have gorged itself on something — either a star or two or a vast amount of gas. Space-based X-ray telescopes have seen evidence of the feast as "light echoes" — the sudden brightening of large gas clouds near the galactic center as they are illuminated by an older source of energy, which could be superheated gas as it spiraled into the black hole.

"We're seeing evidence that there was a tremendous flash of X-rays, one or a few hundred years ago, at or near the center of the galaxy," Morris says. "We can't really pinpoint exactly where, but it could easily have been the central supermassive black hole eating a star. [It] is the kind of flash that you would get if a black hole ate a star, and that happens once in a while."

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Related Info

Research Question

Is there a supermassive black hole at the center of the Milky Way galaxy?

Research Methods

Measuring the motions of stars

Key Researchers

Andrea Ghez
Reinhard Genzel

Results to Date

There is a supermassive black hole, roughly 4.1 million times the mass of the Sun, at the center of the galaxy.

Resources

UCLA Galactic Center Group

The Galactic Center Massive Black Hole and Nuclear Star Cluster, by
Reinhard Genzel, et. al.

The Black Hole at the Center of Our Galaxy, by Fulvio Melia, 2003

Fun Fact

Sagittarius A*, the black hole at the center of the Milky Way, is about 16 million miles (25 million km) in diameter, or about half the distance from the Sun to Mercury, the innermost planet.

A view of the star cluster and gas clouds at the center of the Milky Way. [ESO/S. Gillessen et al.]

Young stars crowd near central black hole