When a massive star dies, first there is a supernova explosion. Then, what’s left over becomes either a black hole or a neutron star.

That neutron star is the densest celestial body that astronomers can observe, with a mass about 1.4 times the size of the sun. However, there is still little known about these impressive objects. Now, a Florida State University researcher has published a piece^[1] in Physical Review Letters arguing that new measurements related to the neutron skin of a lead nucleus may require scientists to rethink theories regarding the overall size of neutron stars.

New research is helping to explain one of the big questions that has perplexed astrophysicists for the past 30 years — what causes the changing brightness of distant stars called magnetars.

Magnetars were formed from stellar explosions or supernova e and they have extremely strong magnetic field s, estimated to be around 100 million, million times greater than the magnetic field found on earth.

The magnetic field on each magnetar generates intense heat and x-rays. It is so strong it affects the physical properties of matter, most notably the way that heat is co nducted through the crust of the star and across its surface, creating the variations in brightness which has puzzled astrophysicists and astronomers.

We know dark matter exists because we can observe its effects on all the stuff that’s swirling around in the universe. Scientists estimate that about 27% of the universe is made of dark matter (68% is dark energy, and the last 5% is ordinary matter and energy). The questions on everyone’s mind: Where exactly is all that elusive stuff located? And how is it distributed throughout the universe?

An international project of over 400 scientists called the Dark Energy Survey is working on answering them. It has just released the largest and most detailed map of dark matter in the universe—with some unexpected findings that don’t yet neatly align with ideas in physics that date all the way back to Albert Einstein and his theory of general relativity.

Five years on from the first discovery of gravitational waves, an international team of scientists, including from the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav), are continuing the hunt for new discoveries and insights into the Universe. Using the super-sensitive, kilometer-sized LIGO detectors in the United States, and the Virgo detector in Europe, the team have witnessed the explosive collisions of black holes and neutron stars. Recent studies, however, have been looking for something quite different: the elusive signal from a solitary, rapidly-spinning neutron star.

Take a star similar in size to the Sun, squash it down to a ball about twenty kilometers across — roughly the distance from Melbourne airport to the city center — and you’d get a neutron star: the densest object in the known Universe. Now set your neutron star spinning at hundreds of revolutions per second and listen carefully. If your neutron star isn’t perfectly spherical, it will wobble about a bit, and you’ll hear a faint “humming” sound. Scientists call this a continuous gravitational wave.

So far, these humming neutron stars have proved elusive. As OzGrav postdoctoral researcher Karl Wette from the Australian National University explains: Imagine you’re out in the Australian bush listening to the wildlife. The gravitational waves from black hole and neutron star collisions we’ve observed so far are like squawking cockatoos — loud and boisterous, they’re pretty easy to spot!