Ten months after the discovery of gravitational waves created by the merger of two black holes, scientists from the Tata Institute of Fundamental Research (TIFR), Mumbai, and Massachusetts Institute of Technology (MIT) have identified another celestial object that could be generating gravitational waves .
Two physicists have theoretically established that there is a strong indication that a population of neutron stars can generate continuous gravitational waves, making their detection possible.
Neutron stars, created by the death of a giant star, are the densest observable objects in the universe, with a star of a city’s size, having a mass about 1.4 times that of the sun.
The finding comes months after the discovery of gravitational waves created by the merger of two black holes, different by 7 times the mass of the Sun. Gravitational waves are faint ripples in the fabric of space-time, first predicted by Albert Einstein in 1916.
As gravitational waves are not absorbed or reflected by matter, they carry information on the motion of objects as stars and planets in the universe. This helps understand the creation of the universe and its history.
In the 1970s, it was theoretically worked out how fast these neutron stars could spin. This would predict relatively low spin rates of neutron stars, implying a weak possibility that they emitted gravitational waves.
“We have shown theoretically that while the spin rate can be very high (more than 1,000 times a second) for many neutron stars, it is not observed. The maximum spin rate observed is only slightly more than 700 times per second. This low observed spin rate could imply there is gravitational radiation, gravitational wave, which is slowing them down,” said Sudip Bhattacharyya, lead investigator, department of astronomy and astrophysics, TIFR. “So now there is a very strong indication that a population of neutron stars is continuously emitting gravitational waves.”
Previously, gravitational waves were found only from black hole mergers. “But these gravitational wave signals last only for a fraction of a second. Black hole mergers are a transient source, and therefore it is difficult to study gravitational waves for long. Neutron stars continuously generating gravitational waves can be studied almost permanently,” said Bhattacharyya, adding experimental physicists can now test their prediction by searching for these waves.
The study will be published in The Astrophysical Journal of the American Astronomical Society.
A century after Einstein said it
A century after Albert Einstein first predicted gravitational waves in 1916, the Laser Interferometer Gravitational-Wave Observatory (LIGO) Scientific Collaboration of 1,006 members from 15 countries announced the discovery of gravitational waves in February.
Gravitational waves: One of Einstein’s most important theories was proved right: what you need to know about gravity waves
What are they? Gravitational waves are faint ripples in the fabric of space-time first predicted by Albert Einstein in 1916 but never discovered because the equipment to detect them did not exist.
How are they created? They created by massive movements in the universe, such as two black holes colliding, massive stars exploding, or the birth of the Universe some 13.8 billion years ago
What is India’s role?
60 Indian scientists from nine Indian institutes were involved in the research and analysis of data generated from the detector.
2 black holes were merged to create the gravitational wave, which were separated by 7 milliseconds in the two LIGO detectors at Hanford and Lousiana.
1.33 billion light years taken by the gravity wave signals, which travelled to earth on September 14, 2015.
Mass of one black hole: 29 times the mass of the sun,
Mass of the second black hole: 36 times the mass of the sun.
The mass of the final black hole: 62 times the mass of the sun.
The power generated is equivalent to 3 solar masses, with 50 times the luminosity of all stars in the universe.
What is LIGO?
LIGO is a system of two identical detectors — in Livingston, Louisiana, and Hanford, Washington — built by scientists from the Massachusetts Institute of Technology and California Institute of Technology to detect incredibly tiny vibrations from passing gravitational waves.
US $ 620 million: Cost of the twin detectors
Source: LIGO Scientific Collaboration; Nature