An artist's impression of the three layers of a neutron star. Credit:Carl Knox, OzGrav “It’s the densest form of matter,” says Monash University-based astronomer Dr Greg Ashton. “You take something like the mass of the sun and you crush it down to about 10 kilometres in radius. And that object rotates very rapidly.” Stars like our sun are made of hydrogen, which burn in giant nuclear reactors at their heart. They are so massive they have an extremely strong gravitational pull. That gravity is always compressing the star but is balanced out by the enormous energy the star generates.

But, eventually, stars run out of fuel and can no longer fight their own gravity. They get crushed inward. In some giant stars, the atoms get crushed together so hard they become a different type of matter: neutrons. The star turns from a giant fiery orb into a small, spinning, extremely radioactive neutron star – with a hard crust. Loading Replay Replay video Play video Play video Neutron stars generate extremely powerful magnetic fields. These fields channel the star's radiation into a thin beam. As the star spins, the beam spins too – Dr Ashton likens it to the rotating beam of a lighthouse. Australian scientists have been watching the spinning beam coming from a neutron star known as Vela – and waiting for a glitch.

Loading Vela, and other neutron stars, rotate with great regularity. Until they don’t. Sometimes, with no warning, the rotation speeds up or slows down temporarily. This is called a glitch, and they have fascinated scientists for years. These glitches happen semi-randomly, so no one had seen one in real time. In 2016 a team from the University of Tasmania set the 26-metre radio telescope atop Mount Pleasant, just outside Hobart, to focus on Vela. Then they watched, and waited. “They took a risk to do it,” says Dr Ashton. “It could have glitched when the telescope was offline for technical reasons.”

And suddenly, there it was. The star’s spin first slowed down, and then sped up until it was racing, before finally settling into its normal rhythm. The whole thing lasted about 13 seconds. Dr Ashton's ARC Centre for Gravitational Wave Discovery team were then able to do some detective work about what could be causing the glitch, which they published on Tuesday in Nature Astronomy. Inside the star, they speculate, the neutrons are crushed together so hard they start behaving like a fluid. But neutrons are much smaller than atoms. That means they are governed by the strange physical laws of very small things – known as quantum physics. This quantum fluid – known as a superfluid – sloshes around inside the star in strange ways, creating whirlpools and vortexes.