United Kingdom – Researchers from the University of Southampton has announced a new method to measure the mass of a pulsar even when existing in the Universe with no other nearby objects. These findings, published in the journal Science Advances, were possible thanks to a special property of pulsars.

A pulsar is a celestial object  – thought to be a rapidly rotating neutron star – formed out of the debris left over when massive stars explode. The traditional way to determine its mass is to study the motion of the object in relation to other nearby bodies, calculating the mass by the gravitational attraction each one exercise on the other.

Schematic view of a pulsar. The sphere in the middle represents the neutron star, the curves indicate the magnetic field lines and the protruding cones represent the emission beams. Credit: Mysid in Inkscape by Roy Smits/Wikipedia

However, British scientists have come up with a new method. “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 revolutionize the way we make this kind of calculation,” said university mathematician Wynn Ho, lead author of the study, in a press release.

The new method

The method makes use of a special property of pulsars: rotating electromagnetic beams of radiation that can be detected by telescopes when they sweep past Earth.

The rotation of some pulsars is very stable. However, young pulsars can occasionally exhibit “glitches” in which they briefly speed up. These glitches are the result of the spinning of superfluids inside the star that transfer their rotational energy outward to the star’s outer crust. This affects the rotation rate and the timing of the observed beams.

“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 Nils Andersson, a professor of applied mathematics at Southampton, in a press release.

X-ray and radio data were used on pulsars to create a mathematical model to determine the mass of the celestial object that exhibits glitches.

This was possible when scientists understood pulsar’s superfluids. The magnitude and frequency of the pulsar glitches depend on the amount of superfluid present in the star and its movement as partially noted before. Scientists were able to know the mass of a pulsar by combining observational information and known nuclear physics.

“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 Earth or the Moon or discover the first extrasolar planets. Our technique is very different and can be used for pulsars in isolation,” said Cristobal Espinoza of the Pontificia Universidad Catolica de Chile.

Source: Science Advances