A second type of black hole is the supermassive variety, which is thought to exist at the center of each galaxy, including the Milky Way. These black holes can be detected by the way their gravity distorts nearby stars, said Morgan, the MIT astrophysicist.
Though scientists are uncertain how supermassive black holes form, they appear to be closely related to the growth of galaxies.
"For example, many astronomers have recently found that the huge black holes at the centers of galaxies undergo growth spurts at the same time as the galaxies themselves are having growth spurts," Edmonds said.
The future of black hole detection may be even brighter if NASA moves forward with its proposed Nuclear Spectroscopic Telescopic Array (NuSTAR).
Current x-ray telescopes are limited to detecting relatively low-energy x-rays, which are more easily blocked by gas and dust than are high-energy x-rays. NuSTAR will be able to detect significantly higher-energy x-rays, said Fiona Harrison, an astrophysicist at the California Institute of Technology in Pasadena.
"As you go to higher and higher energy, you are capable of uncovering those black holes that are surrounded by dust and gas. We know there are a lot of those out there," said Harrison, who also serves as NuStar's principle investigator.
The proposed array is in the final stage of a review process. A final funding decision is due in February 2006. If approved by NASA, NuSTAR would launch in February 2009.
The array would survey and reveal black holes in areas of the sky previously examined with the less-powerful Chandra X-Ray Observatory. NuSTAR should help astronomers understand how black holes came to be in the universe and how they have grown over cosmic time.
"Every large galaxy has a black hole in the center and we are trying to understand this process," Harrison said. "They are turning out to be quite important in forming structure in the universe."
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