Gravitational waves: Neutron stars continuously emit ripples, claim Indian scientists

Indian scientists have said that many dense neutron stars that spin fast generate gravitational waves continuously. In order to detect such waves, careful observations should be made, they said.

Neutron stars, which contain a fistful of stellar material outweighing a mountain on Earth, are the densest observable objects in the universe. The neutron stars have more material than in the Sun crammed inside them, although they are not bigger than a city in size.

Sudip Bhattacharyya from the Tata Institute of Fundamental Research (TIFR) in Mumbai and Deepto Chakrabarty from Massachusetts Institute of Technology (MIT) in the US have shown that a population of neutron stars should spin around their axes much faster than the highest observed spin rate of any neutron star.

If the neutron stars emit gravitational waves continuously and hence spin down then only the observed lower spin rates are possible, they pointed out.

The transfer of matter from a normal companion star can increase the spin rate of a population of neutron stars. Some of them even spin several hundred times in a second around their own axes.

It was theoretically worked out in the 1970s that how fast the neutron stars could spin. This has formed the basis of studies of neutron stars since then.

The new study has however shown that for episodic mass transfer, which happens for many neutron stars, the stellar spin rate should be much higher. And the star could easily attain a spin rate more than a thousand times per second.

Because no neutron star has been observed with a high spin rate, the team has pointed out that many of these stars may slow down by continuously emitting gravitational waves.

Einstein’s general theory of relativity predicted the gravitational waves emitted by massive objects. This was recently discovered during transient phenomena of black hole mergers.

Continuous gravitational waves could provide an opportunity to study these waves almost permanently. However, the detection of continuous gravitational waves is still elusive.

The research provides a strong indication that many fast spinning neutron stars generate gravitational waves continuously, and careful observations should be made to detect such waves.

The study was published in The Astrophysical Journal. 

(With inputs from PTI)