New method to weigh stars found

Mathematicians at University of Southampton have now found a new way to measure the mass of pulsars.

PTI| Updated: Oct 06, 2015, 17:00 PM IST

London: Researchers have developed a new method for measuring the mass of pulsars - highly magnetised rotating neutron stars formed from the remains of massive stars after they explode into supernovae.

Until now, scientists have determined the mass of stars, planets and moons by studying their motion in relation to others nearby, using the gravitational pull between the two as the basis for their calculations.

However, in the case of young pulsars, mathematicians at University of Southampton have now found a new way to measure their mass, even if a star exists on its own in space.

"For pulsars, we have been able to use principles of nuclear physics, rather than gravity, to work out what their mass is ? an exciting breakthrough which has the potential to revolutionise the way we make this kind of calculation," Dr Wynn Ho, of Mathematical Sciences at Southampton, who led the research said.

"All previous precise measurements of pulsar masses have been made for stars that orbit another object, using the same techniques that were used to measure the mass of the Earth or Moon, or discover the first extrasolar planets. Our technique is very different and can be used for pulsars in isolation," Dr Cristobal Espinoza of the Pontificia Universidad Catolica de Chile said.

Pulsars emit a rotating beam of electromagnetic radiation, which can be detected by telescopes when the beam sweeps past the Earth, like observing the beam of a lighthouse.

They are renowned for their incredibly stable rate of rotation, but young pulsars occasionally experience so-called 'glitches', where they are found to speed up for a very brief period of time.

The prevailing theory is that these glitches arise as a rapidly spinning super-fluid within the star transfers its rotational energy to the star's crust, the component that is tracked by observations.

"Imagine the pulsar as a bowl of soup, with the bowl spinning at one speed and the soup spinning faster. Friction between the inside of the bowl and its contents, the soup, will cause the bowl to speed up. The more soup there is, the faster the bowl will be made to rotate," said Professor of Applied Mathematics at Southampton, Nils Andersson.

Ho collaborated with his colleague Andersson and external researchers Espinoza and Dr Danai Antonopoulou of the University of Amsterdam, to use new radio and X-ray data to develop a novel mathematical model that can be used to measure the mass of pulsars that glitch.

The idea relies on a detailed understanding of super-fluidity. The magnitude and frequency of the pulsar glitches depend on the amount of super-fluid in the star and the mobility of the super-fluid vortices within.

By combining observational information with the involved nuclear physics, one can determine the mass of the star.

The research was published in the journal Science Advances.