Free Astronomy Magazine March-April 2016

COSMOLOGY spokesperson and professor of physics and astronomy at Loui- siana State University. “With this discovery, we hu- mans are embarking on a mar- velous new quest: the quest to explore the warped side of the universe—objects and pheno- mena that are made from warped spacetime. Colliding black holes and gravitational waves are our first beautiful examples,” says Thorne. Virgo research is carried out by the Virgo Collaboration, con- sisting of more than 250 physicists and engi- neers belonging to 19 different European research groups: 6 from Centre National de la Recherche Scientifique (CNRS) in France; 8 from the Istituto Nazionale di Fisica Nucleare (INFN) in Italy; 2 in The Netherlands with Nikhef; the Wigner RCP in Hungary; the POL- GRAW group in Poland; and the European Gravitational Observatory (EGO), the labora- tory hosting the Virgo detector near Pisa in Italy. Fulvio Ricci, Virgo Spokesperson, notes that, “This is a significant milestone for phys- T he side com- puter simula- tion shows the collision of two black holes, a tremendously powerful event detected for the first time ever by the LIGO. [Simulat- ing eXtreme Space- times Project] The plots below show the signals of gravitational waves detected by the twin LIGO observatories at Livingston and Hanford, The sig- nals came from two merging black holes, each about 30 times the mass of our Sun, lying 1.3 bil- lion light-years away. The top two plots show data received at Livingston and Hanford, along with the predicted shapes for the waveform. These predicted wave- forms show what two merging black holes should look like accord- ing to the equa- tions of Albert Einstein's general theory of relativi- ty, along with the instrument's ever- present noise. The final plot compares data from both detec- tors. As the plots reveal, the LIGO data very closely match Ein- stein's predic- tions. [Caltech/ MIT/LIGO Lab] ics, but more importantly merely the start of many new and exciting astrophysical discov- eries to come with LIGO and Virgo.” Bruce Allen, managing director of the Max Planck Institute for Gravitational Physics (Albert Einstein Institute), adds, “Einstein thought gravitational waves were too weak to detect, and didn’t believe in black holes. But I don’t think he’d have minded being wrong!” At each observatory, the two-and-a-half- mile (4-km) long L-shaped LIGO interferome- ter uses laser light split into two beams that travel back and forth down the arms (four- foot diameter tubes kept under a near-per- fect vacuum). The beams are used to moni- tor the distance between mirrors precisely positioned at the ends of the arms. Accord- ing to Einstein’s theory, the distance bet- ween the mirrors will change by an infinites- imal amount when a gravitational wave pas- ses by the detector. A change in the lengths of the arms smaller than one-ten-thousandth the diameter of a proton (10 -19 meter) can be detected. Independent and widely separat- ed observatories are necessary to determine the direction of the event causing the gravi- tational waves, and also to verify that the sig- nals come from space and are not from some other local phenomenon. “Hopefully this first observationwill accelerate the construction of a global network of detec- tors to enable accurate source location in the era of multi-messenger astronomy,” concludes David McClelland, professor of physics and director of the Centre for Gravitational Phys- ics at the Australian National University. n