A bacteria-size deformation detected in a neutron star
doi:10.1038/nindia.2020.130 Published online 28 August 2020
An astrophysicist from the Tata Institute of Fundamental Research (TIFR) in Mumbai has inferred that a rotating neutron star, located 4500 light-years away from the Earth, emits gravitational waves continuously1. He has also measured a bacteria-size deformation in this star.
These findings, the scientist says, will be extremely useful for understanding the emission of continuous gravitational waves from a neutron star and how such a star evolves into a binary star system.
Neutron stars form when massive stars run out of fuel and collapse. However, scientists have not yet detected a continuous emission of gravitational waves from a spinning neutron star with a slight deformation.
“A way to indirectly infer such waves and to measure deformation is to estimate the contribution of the gravitational waves that slow down the spin of a neutron star, which was not possible till now,” says TIFR astrophysicist Sudip Bhattacharyya.
Neutron stars slow down their spin (spin-down) over time. Such a spin-down takes a very long time. With the help of observational results and theoretical calculations, Bhattacharyya measured two spin-down rates for the neutron star: one of them in the phase of mass transfer from a companion star and the other in the phase when there is no mass transfer.
Using these values, he calculated the bacteria-size deformation in the neutron star. Deformation around the spin axis of such a star would cause the continuous emission of gravitational waves, he adds.
1. Bhattacharyya, S. The permanent ellipticity of the neutron star in PSR J1023+0038. Mon. Not. Roy. Astron. Soc. (2020) doi: 10.1093/mnras/staa2304