TRANSCRIPT
When a massive star runs out of fuel and collapses, it triggers what's known as a supernova - one of the largest explosions in the universe.
The flash of light caused by the blast lasts just seconds.
But the debris that is propelled into space can be studied for millennia.
The collapsed remnants are known as neutron stars.
There are thousands of them in our galaxy, and they're the densest observable objects in the universe.
Astrophysicist Daniel Reardon says a teaspoon of neutron star material would weigh about 1 trillion kilograms on Earth – that's about as much as a mountain.
"Neutron stars are these incredible dense remnants of massive stars that exploded, and some of them emit beams of radiation from the magnetic fields. These are radio waves, and as these neutron stars spin, the radio waves point towards us and we see that as a pulse of light. And when we see neutron stars in this way, we call them a pulsar."
Dr Reardon is a postdoctoral researcher at Swinburne University of Technology's Centre for Astrophysics and Supercomputing and a member of OzGrave, also known as the ARC Centre of Excellence for Gravitational Wave Discovery.
For the past decade, he's been studying one of the closest neutron stars to earth, known as a millisecond pulsar.
It's rotating at 174 times per second - that's as fast as a blender.
"The particular one we've been studying is actually the nearest and brightest millisecond pulsar. So it spins a lot faster than most of these neutron stars. And it emits beams of radio radiation from the poles that we see as pulses with our radio telescopes on earth. This one is 500 light years away, which is relatively close in our galaxy. And that makes it very important because it's very bright and that means we can do some precise science with it."
Up until now, much of its characteristics have remained a mystery.
But, thanks to a collaboration between Australian scientists and NASA, we now have an accurate measurement of both the mass and radius of the neutron star.
Dr Reardon, who is one of the lead researchers, says it's a significant breakthrough because it "advances our fundamental understanding of how the Universe operates.”
“It is very exciting because this is only the third precise measurement of a neutron star size from this NASA mission. But it is the most precise, and it's the one for this very important central anchor point for our theories of physics. These cores of neutron stars are filled with unique states of matter that we can't possibly replicate on earth. So it's a very important test of our fundamental theories of physics. Going forward into the future these will be the basis of our new theories.”
This latest breakthrough was made possible thanks to 30 years of observations from Australia's Murriyang radio telescope in Parkes, in central west New South Wales.
For years , NASA has been trying to study the interior physics of neutron stars - including mass and radius – through an X-ray telescope on the International Space Station.
The telescope, known as Neutron star Interior Composition Explorer, or NICER, explores how matter behaves under extreme conditions inside neutron stars.
"NASA's attempt to measure the mass and radius of this particular neutron star was complicated by the fact that there's background noise from an active galaxy near this neutron star. They actually struggled to separate the mass and size of this neutron star. "
And that's where Australia came in.
"We were observing this neutron star for almost 30 years using this Murriyang Parkes radio telescope and that data over that 30 years, we tracked very tiny time delays in the arrival times of radio pulses, which allowed us to measure the mass of the neutron star. So with the mass measured to high precision from us, this NASA team was able to infer the radius and give us an understanding of what's happening inside this neutron star."
In a series of three papers published on Thursday, Dr Reardon, along with a team of international scientists detail how they were able to accurately measured the mass and radius of the nearby neutron star.
