Astronomers observe rare phenomenon of black holes emitting X-rays in nearby galaxy

Washington, Jan 10 : Astronomers have observed a rare phenomenon of X-ray jets originating from a black hole in a star system in the Centaurus A galaxy.

This source of the X-rays wasn't there during the last survey of the galaxy in 2003, but it shined throughout the time of the new observations, which were from March to May of 2007.

"Normally when astronomers study Centaurus A, it's the giant X-ray jets emanating from the heart of the galaxy that steal the show," explained Gregory Sivakoff, a postdoctoral researcher in astronomy at Ohio State University.

But when Sivakoff's team studied Centaurus A with NASA's Chandra X-ray Observatory starting in March 2007, they saw a new X-ray source, which was much smaller than the X-ray jets, but still glowing brightly.

Because it hadn't been seen before, the astronomers classified the object as a "transient" X-ray source, meaning that the object had been there before 2007, but had only recently brightened enough to stand out.

According to the researchers, the newly bright object, dubbed CXOU J132518.2-430304, is most likely a binary star system.

Though this type of star system is supposed to be rare, it's the second such system discovered in that galaxy.

These two stars likely formed at the same time, with one much more massive than the other. The more massive star evolved more quickly, and collapsed to form a black hole. It is now slowly devouring its companion.

"When we look at other galaxies like Centaurus A, we don't see these bright, transient X-ray binaries," said Sivakoff. "But now we've found two such objects in Centaurus A, and the implication is that we may not understand these objects as well as we thought we did," he added.

As astronomers piece together an explanation for the existence of the newly-discovered binary system, they may gain a better understanding of how black holes form from massive stars and how binary systems evolve.

"These binary systems are signposts of the massive stars that once existed in galaxies like Centaurus A. To understand the massive stars, we must first know how to read the signs," said Sivakoff.

ANI