How To Detect Black Holes?

Astrophysicists are gearing up to detect 
waves emanated from black holes, reports Biplab Das 

Astrophysicists are all set to look at a new window of the Universe, the so-called gravitional waves. "Einstein first predicted the existence of gravitational waves in 1916," said Dr. Biplab Bhawal from the California Institute of Technology (Caltech). "They are literally quakes in space-time that emanate from the most violent events in the Universe - the collision of two black holes or an exploding star." 

He was speaking on 'Introduction of Gravitational Waves and Their Detection' at a seminar on 'Identifying Black Holes Through Gravitational and Electromagnetic Waves' organised by the Centre for Space Physics (CSP) in the city recently. 

Gravitational waves are emitted by large accelerating masses. "So, they will tell scientists how large amounts of matter move, twirl, and collide throughout the Universe and how they could warp the space around them," Bhawal said. "This new tool may even record the first murmur of creation, the moment when the Universe popped into existence through a fiery birth known as Big Bang." 

According to him, any planet in the vicinity of such waves would be torn apart. "Fortunately, by the time such waves reach earth, this cosmic tsunami would be reduced to a mild flutter," Bhawal said. Were such gravity to hit this page you read, they would be so weak that they would squeeze and stretch the sheet's dimension by a length thousands of times smaller than the size of a proton. 

It is because of the faintness of the ripples that physicists need a powerful detection system to catch them on earth. A team of experts from Caltech and Massachusetts Institute of Technology (MIT) has designed an observatory known as the Laser Interferometre Gravitational-wave Observatory (LIGO). Its own L-shaped detectors-one in Livingstone, Louisiana, and the other in Hanford, Washington, work in concert across the nearly 3,000 kilometres that separate them. 

With the help of laser, each LIGO detector uses its two 4-kilometre arms-positioned at a 90-degree angle-to measure gravitational waves. "LIGO will be most receptive to frequencies from 100 to 3,000 hertz, which coincides with the same frequencies our ear pick up sound," Bhawal said. 

One could actually listen to the signal, once it is electronically recorded. The biggest prize of all will be the detection of gravitational waves from two black holes colliding, said Prof. Sandip Chakrabarti of the S. N. Bose National Centre for Basic Sciences (SNBNCBS). 

According to him, as the two black holes are about to meet, spiralling inward faster and faster at speeds close to that of light, computer models predict that the whine will turn into a chirp, a birdlike trill that races up the scales in a matter of seconds. "If such phenomenon is detected it would be the first direct evidence that black holes truly exist," Chakrabarti said.