Black hole hunt

 

A NUI Galway researcher is using data recorded in an ongoing search for alien life as a source for new astronomical discoveries. John Moore reports

Hundreds of Irish computer owners are familiar with the SETI (Search for Extraterrestrial Intelligence) screensaver that uses a computer's idle time to search for aliens. SETI's headquarters at the University of California, Berkeley, uploads a small portion of data that might hold the final proof that our extraterrestrial friends are out there.

So far, no signal has yet been found in this, the first stage in the data analysis process. Yet the mountains of data gathered might contain many other signals of cataclysmic events happening in our universe that we haven't yet been able to see.

Astronomer Dr Aaron Golden, of the information technology department in NUI Galway, has begun to search the SETI data archive, looking for unique events called "evaporating primordial black holes".

Unlike "normal" black holes formed by the collapse of massive stars, primordial black holes are believed to have originated in the early universe, when fluctuations in space and time could have yielded sub-solar mass "mini" black holes.

"What is interesting about these mini black holes is that many theoretical models suggest that quite a substantial number of them should be evaporating [becoming extinct\] right about now," says Golden. There is one problem with this theory, however: no one has ever detected the great burst of energy that marks the passing of a black hole, he says.

"The explosions we expect to see should be in the form of gamma rays - yet satellite missions launched over the past number of years have failed to detect signatures from such phenomena. As we have no idea where to point a telescope to observe these events, the SETI archive is ideal to go back to and look for the occurrence of these events," he says.

As the violent fireball from an evaporating black hole expands, it should generate a powerful electromagnetic field that would become detectable as a coherent burst of radio waves. These might be easier to detect than the gamma ray emissions. The bursts, which only last one millionth of a second, could provide invaluable clues to the location of the dying black holes. As the signatures become distorted and stretched over time, they could provide an estimate for the distance they have travelled, says Golden. They might also tell us how close we are to black holes in our galactic neighbourhood, and how numerous they are.

"Detecting the radio burst could also provide us with a powerful observational constraint," says Golden. "All radio signals are dispersed (or delayed) as a function of their frequency as they transit the intervening plasma. What determines this dispersion are two things - the frequency of the radio waves, and the amount of plasma between the emission source and the detector," he explains.

Using very efficient computer programs to "de-disperse" the radio signals over a range of frequencies, it could determine the amount of intervening plasma. Astronomers could then build up a three-dimensional map of the interstellar plasma.

Even if he doesn't find the signal, Golden's time won't be wasted, however. The search will still allow him to place strong empirical limits and bounds to existing models. This would mean that current black hole theories might have to be reconsidered.

Although Golden's work is unusual in terms of astronomy research topics, the dataset already sits on computers on the Berkeley campus and invites examination. All that is required is some focused computing power to try to catch those faint and distant roars.

A key source of data for the Berkeley group is the Arecibo radio telescope in Puerto Rico, the largest in the world. It is effectively a gigantic reflecting bowl shaped like a satellite TV dish measuring 305 meters across and representing a surface of about 20 acres. It would take 10 billion normal bowls of cereal to fill the radio dish to the brim.

It is amazingly sensitive. It could detect a mobile telephone signal from as far away as the planet Saturn.

For more information about Berkeley's SETI programme visit the website:

http://setiathome.ssl.berkeley.edu