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A New Type of Black Hole?

A New Type of Black Hole?Tufts’ Rosanne Di Stefano recently led a study that may suggest the existence of a new intermediate class of black holes. Medford/Somerville, Mass.

Medford/Somerville, Mass. [03.12.04] Using an innovative method to detect and measure x-rays in space, a Tufts scientist may have stumbled onto something much larger: a new class of space objects several hundred times the mass of the sun. While the findings are preliminary, they could represent a new type of black hole.

"Until a few years ago, astronomers only knew of two sizes of black holes: stellar black holes, with masses about ten times the sun, and supermassive black holes located at the centers of galaxies, with masses ranging from millions to billions times the sun," reported NASA. "Recent evidence [discovered by Tufts' Rosanne Di Stefano] suggests a class of ‘intermediate-mass' black holes may exist."

Clues to this new phenomenon were discovered by Di Stefano - visiting associate professor in Tufts' physics department - who was conducting research at NASA's Chandra observatory at the Harvard-Smithsonian Center for Astrophysics.

"We're finding objects in the temperature range for an accreting black hole that is more massive than a stellar black hole," Di Stefano told "A big clue that we may be seeing intermediate black holes are the [powerful x-ray signals]."

Di Stefano, the lead author of a series of papers published in The Astrophysical Journal, said that the finding provokes questions for scientists in the field.

"The challenge raised by the discovery of these sources is to understand how they produce so much X-ray power at temperatures of a few million degrees," Di Stefano said in a statement from NASA.

Though the mysterious x-ray sources certainly suggest the presents of a mid-sized black hole, the Tufts expert says the data is very preliminary.

"There's no direct evidence for intermediate black holes," Di Stefano told "And it will be very difficult to establish them in the same way that we have for supermassive black holes, at the center of galaxies, or stellar black holes."

According to the Tufts scientist, other theories could explain the phenomenon.

"Di Stefano cautioned that it's not certain that the objects her team found are definitely black holes," reported "They could be neutron stars or stellar black holes that are behaving unlike anything ever seen before."

But the innovative method the Tufts expert used to detect the x-ray sources "could eventually be used to detect a definite black hole middleweight," according to

"Di Stefano and her colleagues determined the temperatures of individual X-ray emitting objects in four galaxies by measuring their X-ray spectra, or distribution of X-rays with energy," reported NASA. "They found that between 15 percent and 20 percent of all detected sources fell in the quasisoft temperature range [between 1 million and 4 million degrees Celsius]."

The Tufts scientist told that more work needs to be done in order to better understand all quasisoft temperature sources.

"Di Stefano said more quasisoft X-ray sources need to be catalogued in order to differentiate which objects are ordinary black holes which may be middleweights," reported


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