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VLBA Helps with First ‘Complete Description’ of a Black Hole

November 18, 2011 Leave a comment

Credit: Chandra X-Ray Observatory, NASA

Credit: Chandra X-Ray Observatory, NASA

For the first time, astronomers have produced a complete description of a black hole, a concentration of mass so dense that not even light can escape its powerful gravitational pull. Their precise measurements have allowed them to reconstruct the history of the object from its birth some six million years ago.

Using several telescopes, both ground-based and in orbit, the scientists unravelled longstanding mysteries about the object called Cygnus X-1, a famous binary-star system discovered to be strongly emitting X-rays nearly a half-century ago. The system consists of a black hole and a companion star from which the black hole is drawing material. The scientists’ efforts yielded the most accurate measurements ever of the black hole’s mass and spin rate.

“Because no other information can escape from a black hole, knowing its mass, spin, and electrical charge gives a complete description of it,” said Mark Reid, of the Harvard-Smithsonian Center for Astrophysics (CfA). “The charge of this black hole is nearly zero, so measuring its mass and spin make our description complete,” he added.

Full Story: http://www.nrao.edu/pr/2011/cygx1/

City Lights Could Reveal E.T. Civilization

November 7, 2011 Leave a comment

Credit: David A. Aguilar (CfA)

Credit: David A. Aguilar (CfA)

In the search for extraterrestrial intelligence, astronomers have hunted for radio signals and ultra-short laser pulses. In a new paper, Avi Loeb (Harvard-Smithsonian Center for Astrophysics) and Edwin Turner (Princeton University) suggest a new technique for finding aliens: look for their city lights. “Looking for alien cities would be a long shot, but wouldn’t require extra resources. And if we succeed, it would change our perception of our place in the universe,” said Loeb.

As with other SETI methods, they rely on the assumption that aliens would use Earth-like technologies. This is reasonable because any intelligent life that evolved in the light from its nearest star is likely to have artificial illumination that switches on during the hours of darkness.

How easy would it be to spot a city on a distant planet? Clearly, this light will have to be distinguished from the glare from the parent star. Loeb and Turner suggest looking at the change in light from an exoplanet as it moves around its star.

Full Story: http://www.cfa.harvard.edu/news/2011/pr201130.html

Chandra Finds Nearest Pair of Supermassive Black Holes

August 31, 2011 Leave a comment

Credit: X-ray: NASA/CXC/SAO/G.Fabbiano et al; Optical: NASA/STScI

Astronomers have used NASA’s Chandra X-ray Observatory to discover the first pair of supermassive black holes in a spiral galaxy similar to the Milky Way. At a distance of 160 million light years, it is also the nearest known pair of supermassive black holes.

The black holes are located near the center of the spiral galaxy NGC 3393. Separated by only 490 light years, the black holes are likely the remnant of a merger of two galaxies of unequal mass a billion or more years ago.

“If this galaxy wasn’t so close we’d have no chance of separating the two black holes in the way we have here,” said Pepi Fabbiano of the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Mass., who led the study that appears in this week’s electronic issue of the journal Nature. “Since this galaxy was right under our noses by cosmic standards, it makes us wonder how many of these black hole pairs we’ve been missing.”

Full Story: http://chandra.si.edu/press/11_releases/press_083111.html