A Close Pulsar Measures 11.4 km Across

When massive stars detonate as supernovae, they leave often behind a pulsar. These fast rotating stellar corpses have fascinated scientists since their discovery in 1967. One nearby pulsar turns 174 times a second and now, its size has been precisely measured. An instrument on board the International Space Station was used to measure x-ray pulses  from the star. A supercomputer was then used to analyse its properties and found it was 1.4 times the mass of the Sun and measured only 11.4 km across!

The death of a massive stars leads to one of a number of objects but two of them are closely related, the neutron star and the pulsar. Both are formed during the core collapse and supernova explosion that marks the death of a star. All of the components of the atom are squashed together removing all the space between the neutrons to form one MASSIVE neutron. Pulsars are rotating neutron stars with strong magnetic fields that emit beams of electromagnetic radiation from their magnetic poles. These beams become visible from Earth when aligned with our line of sight, creating a pulsating effect, hence the term “pulsar.”

One of the nearest pulsars, PSR J0437-4725 lies at 510 light years in the constellation Pictor. It rotates 174 times per second which means it rotates once in just 5.75 milliseconds. Perhaps more mind blowing than its rotational velocity is its size. Imagine 1.4 times the mass of the Sun squashed up into a ball just 11.4 kilometres across – the Sun is 1.39 million kilometres across by comparison! 

This astonishing result of the pulsars diminutive size are the results of precision measurements by a team fo astronomers at the University of Amsterdam. The scientists used data from the NICER X-ray telescope on the ISS, combining it with a method called pulse profile modelling. The data was fed into Snellius, the Dutch national supercomputer and complex statistical models were created. This allowed them to calculate the star’s radius, assisted by mass measurements from Daniel Reardon (Swinburne University of Technology, Australia) and his colleagues at the Parkes Pulsar Timing Array. Not only were the team able to identify precise dimensions, they were also able to map the temperature distribution of the magnetic poles.

The lead researcher, Devarshi Choudhury was very happy with the results ”Before, we were hoping to be able to calculate the radius accurately. And it would be great if we could show that the hot magnetic poles are not directly opposite each other on the stellar surface. And we just managed to do both!”

The team’s paper reports something known as a softer equation of state. This means there is a smaller increase of pressure for a change in density. This implies that the maximum mass of neutron stars is likely lower than previous theories have predicted. An observation that sits well with gravitational wave observations from neutron stars.

Source : Nearest millisecond pulsar has radius of 11.4 kilometres and is 1.4x as heavy as the sun