Dec. 8, 2011

A black hole recently found by scientists is so monstrous that it dwarfs any black hole found before. A black hole is an object in space so massive that nothing–not even light–can escape its gravitational pull. Located about 335 million light-years from Earth, the black hole has at least 20 billion times as much mass as the sun. It is also 2,000 times as massive as the black hole that resides in the center of the Milky Way Galaxy. A second black hole, found about 320 million light-years away, is nearly 10 billion times as massive as the sun. The previous record-holder among black holes is 6.7 billion times as massive as the sun.

The new black holes also have humongous event horizons (surfaces). At the event horizon, gravity is strong enough to capture even light. The event horizon of the larger of the black holes extends five times as far as the distance between the sun and the orbit of Pluto. If the sun collapsed into a black hole, its event horizon would be about 2 miles (3.4 kilometers) across.

A supermassive black hole sucks in a swirling disk of matter, shooting out beams of particles in this artist's illustration. A supermassive black hole has a mass from millions to billions of times that of the sun. NASA

Scientists think two black holes may be the remains of quasars, luminous objects seen in the early universe but not found in more recent times. Quasars are thought to be black holes that give off tremendous energy in the process of sucking in the matter around them. The newly identified black holes may be the remains of quasars that have dimmed after exhausting the supply of matter in their neighborhoods. Astronomers at the University of California, Berkeley, measured the mass of the black holes by clocking the speeds at which stars orbit (revolve around) them. The faster the stars orbit, the greater the mass of the black hole required to keep the stars from being flung into space.

Additional World Book articles:

• Astronomy
• Chandra X-ray Observatory
• Hawking, Stephen William

Three United States-born astronomers won the Nobel Prize in physics for their revolutionary discovery that the universe is expanding at an accelerating (increasingly faster) rate. The force driving this expansion is thought to be a mysterious antigravitational force known as dark energy. The prize winners were Saul Perlmutter of the University of California, Berkeley; Adam G. Riess of the Space Telescope Science Institute and Johns Hopkins University; and Brian P. Schmidt of the Australian National University. Schmidt is also a citizen of Australia.

The finding by the three astronomers expands on another revolutionary discovery about the universe made in 1929 by American astronomer Edwin Hubble. He had observed that the farther apart galaxies are from each other, the faster they are moving away from each other. From this, Hubble determined that the universe is expanding at a uniform rate. Later scientists found evidence that the expansion began 13.7 billion years ago with a cosmic explosion known as big bang. For many decades, astronomers believed that the expansion was slowing down because of the counter force of gravity on the universe.

Galaxies in the universe are speeding away from one another at a faster and faster rate. NASA/ESA/S. Beckwith (STScl) and the HUDF Team

Then in 1998, Perlmutter, Reiss, and Schmidt shocked the scientific community with their finding that galaxies are actually speeding away from each other at a faster and faster rate. Studies of the light from supernovae (exploding stars) indicate that this expansion began about 5 billion years ago. To account for the acceleration, scientists concluded that the universe was full of some kind of invisible energy, which was named dark energy. Later measurements confirmed that approximately 70 percent of the mass (amount of matter) of the universe consists of dark energy.

Additional World Book articles:

• Astronomy 2001 (Back in Time article)
• The Dark Side of the Universe (special report)