By PAUL RECER=
AP Science Writer=
WASHINGTON (AP)
Supermassive black holes were once only a
theory, but astronomers have now found and studied enough of them
to draw some conclusions about how they form and where they can
exist.
At least 33 supermassive black holes now have been found in the centers of distant galaxies, astronomers reported Monday at a meeting in Rochester, N.Y. of the American Astronomical Society. John Kormendy of the University of Texas said that it is clear now that big galaxies, with massive bulges of stars around their center, contain huge black holes, some with a mass equal to a billion or more suns.
Galaxies with smaller bulges, such as the Milky Way, the home galaxy of the sun, contain smaller black holes. The Milky Way's central black hole is thought to contain a mass equal to about three million suns.
The studies also suggest that disc galaxies, which have no center bulge, do not have a black hole at their center, or have black holes too small to be detected. Kormendy said an analysis also shows that galaxies with stars that are moving more rapidly are more likely to have the biggest supermassive black holes.
Stars in a galaxy tend to orbit about the center of the galaxy and the more massive the black hole, the more rapid the motion, he said. Astronomers also have a better understanding of how black holes formed. Once, there was a question of which came first -- the black hole or the galaxy.
Now, said Kormendy, it is clear that black holes and the galaxy around them formed together, with the black holes growing from a diet of gas and stars sucked in from the host galaxy.
A black hole is an object in space with such a great mass that it has collapsed under its own gravity. The force of its gravity so intense that nothing can escape, not even light. Thus, the black hole, itself, cannot be seen.
Instead, astronomers observe the rapid motion of stars and gas swirling around the black hole. As the matter is accelerated to extremely high speeds, it heats to temperatures and gives streams of electromagnetic radiation. Some black holes have jets of X-rays and gamma rays that move at millions of miles an hour away from the center.
Understanding of black holes has been advanced by observations from the Hubble Space Telescope, which has identified 10 galaxies with black holes. The orbiting observatory is able to precisely measure the movement of gas and stars around a galactic center. From this motion, the mass of the galaxy's black hole can be calculated.
For the first time, there is clear evidence that a solar system other than our own exists, researchers said Thursday.
Three huge planets are spinning around the star Upsilon Andromedae 44 light years from Earth in our Milky Way galaxy, San Francisco State University researchers said at a news conference.
Their presence indicates that many of the Milky Way's 200 billion stars are likely to have planetary systems.
``It implies that planets can form more easily than we ever imagined, and that our Milky Way is teeming with planetary systems,'' said Debra Fischer, one of the researchers.
The researchers began their search for planets 12 years ago. They and their colleagues are responsible for finding 14 of the 20 planets known to exist outside the Earth's solar system.
However, those planets were single bodies surrounding a star. This is the first time multiple planets around a star have been found.
The innermost of the three planets, spotted in 1996, has at least 75 percent of the mass of Jupiter and is very close to its sun, orbiting once every 4.6 days. Jupiter is the largest planet in the solar system, 318 times the size of Earth.
The middle planet is twice Jupiter's mass and orbits the star every 242 days from a location about as far as Venus from the sun. The outer planet has the mass of four Jupiters and orbits its star every 3 1/2 to 4 years. It is more than twice as far from its star as Earth is from the sun.
Earthlike planets are unlikely to be found in such systems, the scientists said, because the forces generated by huge Jupiterlike planets moving in elliptical rather than circular orbits would kick smaller planets out into oblivion.
``Now we have a multiple system, maybe a Rosetta stone to help us understand a lot of these weird planets we're finding,'' said R. Paul Butler by telephone from the Anglo-Australian Observatory in Epping, Australia.
The Rosetta stone is an ancient inscription in three languages that allowed scientists to decipher Egyptian hieroglyphics.
Upsilon Andromedae is easily visible with the naked eye, although it is currently behind the sun and will not be seen until June.
The planets were discovered using a method that measures their gravitational pull on their star, not by direct observation. Planets' gravity tugs on their stars, causing them to wobble slightly. By examining the star's ultraviolet light transmissions, astronomers can calculate back-and-forth shifts in the ultraviolet wavelengths. A larger wobble indicates the orbiting planet is large.
``I am mystified at how such a system of Jupiterlike planets might have been created,'' said Geoffrey Marcy, professor of physics and astronomy at San Francisco State.
``This will shake up the theory of planet formation.'' Alex Wolszczan, an astronomy professor at Penn State University, called the discovery an important step toward understanding the cosmos.
``It has been anticipated and awaited by the scientific community. It's nice to see it's finally happened,'' he said. ``What I get right away from this particular discovery is that it emphasizes even more how different those systems are from our own.''
Solar System Live
The interactive Orrery of the Web. You can view
the entire Solar System, or just the inner planets (through the orbit of Mars).
