Secrets of physics in ‘flywheel’ star

Earth has a new neighbour after Australian scientists uncovered the secrets of the closest pulsar neutron star, a rapidly spinning body on the brink of becoming a black hole.

Lead researcher from the ARC Centre of Excellence in Gravitational Wave Discovery (OzGrav) and Swinburne University of Technology Daniel Reardon. Picture: Jessie Xu / SUT

Earth has a new neighbour after Australian scientists uncovered the secrets of the closest pulsar neutron star, a rapidly spinning body on the brink of becoming a black hole.

The star is known as a millisecond pulsar and rotates 174 times a second. For years it has been almost impossible to evaluate, until new research allowed scientists to determine its mass and radius.

This could be key to understanding the intricacies of physics and chemistry.

The pulsar has no name beyond the coordinates for its location: PSRJ 0437, -4715. It spins as fast as a blender and is 42 per cent heavier than our sun, but confined to a radius of 11.4km.

Lead researcher from the ARC Centre of Excellence in Gravitational Wave Discovery (OzGrav) and Swinburne University of Technology Daniel Reardon has been observing the pulsar for over a decade.

“It’s so dense that if you took a teaspoon of this mat­erial, it would weigh as much as all of the people on the planet,” Dr Reardon said. “The matter is compressed to its absolute limit.”

Millisecond pulsars are the fastest category of pulsars, a term for all rapidly spinning stars that emit radio waves. Over millions of years, the pulsar has ripped away mass from a neighbouring star, growing faster as it pulled away this cosmic mass.

“As the material falls on to the surface of the neutron star, it spins it up, very much like how a figure skater, if they’re spinning around and they pull their arms in, will spin a lot faster.

“Once they’ve been spun up … they basically stay there forever because they’re a huge flywheel that contains a lot of energy. This pulsar was spun up maybe a billion years ago.”

The Murriyang radio telescope was used along with the ISS’s X-ray telescope to discover the neutron star.

The companion star from which the pulsar pulled its mass was always lighter and with a lower gravitational pull, but the siphoning of its mass has left it reduced to a white dwarf; a floating nebula exhausted of the nuclear fuel that drives the fusion power at the core of a sun, leaving it burning dull and low.

Neutron stars are categorised by their extreme density.

At the core of the star is a form of matter impossible to replicate on Earth, a “soup” of clustered neutrons and quarks, an elementary particle that atoms are formed from.

“This is a kind of matter that we’re completely unable to form on earth,” Dr Reardon said.

“Which is why these neutron stars are very valuable laboratories of physics.”

A graphic representation showing the mass and orbit of a white dwarf around a neutron star.

Astronomers have been watching and measuring the star for 30 years, and will continue. “200 years into the future, we will still be monitoring this pulsar to do exciting science,” Dr Reardon said. “I know that the astronomers of that time will be using the observations that I made now.”

The most recent findings were published across three papers, describing how the Murriyang radio telescope housed at CSIRO’s Parkes Observatory, along with NASA’s X-ray telescope on the International Space Station, have accurately measured the star’s mass and radius.

It was completed by OzGrav, Swinburne, the Neutron Star Interior Composition Explorer (NICER) and NASA.