“BLACK HOLES” - PART 2
A major mystery regarding the black holes is that they appear on two radically different size scales, which on one side shows us that there are countless numbers of black holes that are remnants of massive stars. Ten to twenty times as massive as the sun, these “stellar mass” black holes are found throughout the universe. When a star draws near enough for some of its matter around it to be snared by the black hole’s gravity, astronomers spot them and x-rays are in the process. Most stellar black holes lead isolated lives and can not be detected. Scientists estimate that there are as many as ten million to a billion black holes in just the Milky Way.
On the opposite side of the size spectrum are “super-massive” black holes which are millions, may be even billions of times as massive as the sun. It is believed that super-massive black holes lie at the center of many large galaxies, even our Milky Way. Because of the ways they affect nearby stars and gas, astronomers can detect them.
The Space Telescope Imaging Spectrograph (STIS) was an instrument, equipped in the Hubble Space Telescope in 1997, which separates visible light into various wavelengths. It can reveal the speed and other properties of gas as it swirls into a black hole and then reveals certain characteristics about the black hole such as its mass and how fast it spins.
Most, maybe all, of the large galaxies are home to a churning black hole is observed from Hubble. One black hole, fifty million light-years away in the constellation Virgo may have a mass equal to about three billion suns. The accretion disk is matter which surrounds a stellar black hole and is made up of gas and dust. The disk, which may include stars, is around a super-massive black hole in the middle of a galaxy. Chandra offered scientists data in 2004 which showed the first-ever glimpse of a black hole shredding a nearby star. Two super-massive black holes were spotted by Chandra later that same year. The holes were orbiting in the same galaxy and doomed to collide. In 2005, Chandra showed a series of stars probably spawned by the super-massive black hole at the center of the Milky Way.
A subject of present day research is whether black holes of intermediate mass exist. For years, scientists didn’t believe that such black holes existed. However, recent observations have led astronomers to believe differently. NASA is hopeful that future instruments will be able to directly image mass falling into a black hole. The Black Hole Imager is part of NASA’s ambitious “Beyond Einstein” program which will take a census of black holes in the Universe. Four x-ray telescopes that comprise the Constellation-x observatory are one hundred times more sensitive than any previous x-ray satellite mission. Amounts of data will be collected in a fraction of the time.
LISA, another key mission will be looking for the black holes in another way. Gravitational waves will be detected as they surround the black holes. Created by accelerated masses, the waves stream away through space and carry information about the masses and strong fields that create them.
This entry was posted on Friday, January 4th, 2008 at 3:57 am and is filed under Space Agency News. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
