April 30, 2012
Chandra Reveals Outburst From Old Black Holes
Astronomers using NASA's Chandra X-ray Observatory have found evidence for a population of old stellar black holes.
The discovery provides new insight into the nature of stellar black holes, which is a class that can produce as much energy in X-rays as what a million suns could radiate at all wavelengths.
The astronomers used Chandra to find an outburst that was produced by a black hole in the spiral galaxy M83, which is located about 15 million light years from Earth.
Chandra helped the researchers discover a new ultra luminous X-ray source, or ULX. NASA said these objects give off more X-rays than most binary systems, in which a companion star orbits the remains of a collapsed star.
These collapsed stars form either a dense core known as a neutron star, or a black hole. The space agency said the extra X-ray emission suggests ULXs contain black holes that might be more massive than the ones found other places in the galaxy.
The companion stars to ULXs are young, massive stars, and the new research provides evidence that ULXs can contain much older black holes.
Astronomers compared the ULX discovery from 2010 with data from Chandra images taken from 2000 and 2001.
The compared images showed that the source had increased in X-ray brightness by at least 3,000 times and has since become the brightest X-ray source in M83.
The sudden brightening of the M83 ULX is one of the largest changes in X-rays that has even been seen for this type of object, according to NASA.
"The flaring up of this ULX took us by surprise and was a sure sign we had discovered something new about the way black holes grow," Roberto Soria of Curtin University in Australia, who led the new study, said in a press release.
The researchers said that the jump in X-ray brightness occurred because of a sudden increase in the amount of material falling into the black hole.
They found that the object had not been previously observed in Magellan Telescope images that was taken in April 2009, or a Hubble image that was taken back in August 2009.
The lack of blue source in the previous images indicates the black hole's companion star is fainter, redder and has a lower mass than most of the companions that previously had been linked to ULXs.
"If the ULX only had been observed during its peak of X-ray emission in 2010, the system easily could have been mistaken for a black hole with a massive, much younger stellar companion, about 10 to 20 million years old," co-author William Blair of Johns Hopkins University in Baltimore said in a press release.
The companion to the black hole in M83 is likely a red giant star 500 million years old, with a mass four times the our Sun.
"With these two objects, it's becoming clear there are two classes of ULX, one containing young, persistently growing black holes and the other containing old black holes that grow erratically," Kip Kuntz, a co-author of the new M83 paper, also of Johns Hopkins University, said in a press release. "We were very fortunate to observe the M83 object at just the right time to make the before and after comparison."
The researchers will be reporting their findings in the May 10th issue of The Astrophysical Journal.
Image Caption: Composite image of spiral galaxy M83. (X-ray: NASA/CXC/Curtin University/R. Soria et al., Optical: NASA/STScI/ Middlebury College/F. Winkler et al.)