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Sagittarius A supermassive black hole:
Violent Heart of the Milky Way
Astronomers see a supermassive black hole – known as Sagittarius A – sitting at the center of our Milky Way galaxy. But, could the big black hole, itself, be surrounded by a swarm of small black holes that may have been accumulating nearby for billions of years?
[click to enlarge NASA/CXC/MIT/ photo]
Astronomers at the University of California at Los Angeles used NASA's Chandra X-ray Observatory to look at stars within 70 lightyears of Sagittarius A.
They say there is such a swarm and the smaller black holes are likely to fall into the supermassive black hole eventually. That, of course, will just make the big black hole even bigger.
The Chandra Observatory is an X-ray telescope in orbit above Earth.
A lightyear is the distance light travels in one year at the speed of 299,792 kilometers per second. That is 186,282 miles per second. With 31,557,600 seconds in a year, one lightyear equals a distance of 9.46 trillion kilometers or 5.87 trillion miles.
The UCLA astronomers spotted four objects that seem to be black holes and neutron stars in binary systems within just three lightyears of the central black hole.
That led the team of astronomers to estimate that 10,000 or more black holes and neutron stars are swarming around Sagittarius A.
That central region of our Milky Way galaxy has been described as a stellar graveyard because of the dense clutch of dead and dying stars.
Every million years, a black hole or neutron star is swallowed by the supermassive black hole. That will bloat Sagittarius A by about three percent over the next billion years.
Sagittarius A already may be three million times as massive as our star, the Sun.
How are black holes born?
Astronomers believe a black hole forms when a supermassive object – a dying giant star – collapses in on itself to form a very small point of infinite gravity.
What is a Singularity?
The center of a black hole is a singularity.
NASA's glossary defines it as, "A place where spacetime becomes so strongly curved that the laws of Einstein's general relativity break down and quantum gravity must take over."
It also has been defined as:
- the point where the curvature of space-time is infinite.
- the point at which spacetime becomes compressed to the point of being infinitely dense and infinitely small.
- the zero-dimensional point at the center of a black hole or other significant object – such as the Universe at the instant of the Big Bang – at which all conceptions of space and time break down and become incomprehensible.
- the dimensionless point at the center of a black hole, where all the mass of the collapsing star has shrunk to infinite density.
- the object of zero radius into which the matter in a black hole is believed to fall.
That point is called a singularity.
A special region in space surrounds the singularity. The border of that region is known as the event horizon.
Any object that crosses the event horizon is pulled into the black hole, never to return. That means that not even light can escape from a black hole.
How big is a black hole? The diameter of the event horizon depends on the mass of the object that formed it. For instance:
Physicists don't know what lies between the event horizon and the singularity. That is, they don't know what is inside a black hole. There may be no structure or anything measurable inside the event horizon. The inside of a black hole may or may not be uniform and featureless throughout.
- If the Sun were to collapse into a singularity, its event horizon would be about 1.9 miles across.
- If the collapsing body were Earth, its event horizon would be only 0.4 inches across.
- Chandra – Gateway to the University
- Chandra – Sagittarius A: Milky Way Monster Stars in Cosmic Reality Show
- NASA – Beyond Einstein
- NASA – Glossary
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