Astronomers have been studying black holes for decades and are able to "see" them due to the fact that gas gets extremely hot and emits X-rays before it is swallowed completely and is lost forever.

The new research found that X-rays are being emitted as a regular signal from the super-massive black hole. The frequency of the pulse is related to the size of the black hole.

This Hubble Space Telescope image, taken December 29, 2005 and released on October 2, 2007 shows giant star-forming nebula with massive young stellar clusters. Astronomers who stumbled upon a powerful burst of radio waves said that they had never seen anything like it before, and it could offer a new way to search for colliding stars or dying black holes.(Xinhua/Reuters Photo)

"Such signals are a well known feature of smaller black holes in our Galaxy when gas is pulled from a companion star," said lead researcher Marek Gierlinski. "The really interesting thing is that we have now established a link between these light-weight black holes and those millions of times as heavy as our Sun."

Scientists hope future research will tell why some super-massive black holes show this behavior while others do not.

(Xinhua News Agency September 19, 2008)