For Their Next Trick, Gravitational Wave Observatories Could Detect Collapsing Stars

After the death of a massive, spinning star, a disk of material forms around the central black hole. As the material cools and falls into the black hole, new research suggests that detectable gravitational waves are created. Ore Gottlieb

The merging of black holes and neutron stars are among the most energetic events in the universe. Not only do they emit colossal amounts of energy, they can also be detected through gravitational waves. Observatories like LIGO/Virgo (Laser Interferometer Gravitational Wave Observatory) and KAGRA (The Kamioka Gravitational Wave Detector) have detected their gravitational waves but new gravitational wave observatories are now thought to be able to detect the collapse of a massive rapidly spinning star before it becomes a black hole. According to new research, collapsing stars within 50 million light years should be detectable. 

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How a Black Hole Could Eat a Neutron Star from the Inside Out

Illustration of a neutron star. Credit: ESA

Primordial black holes are thought to have formed early in the evolution of the universe. None have been discovered yet but if they do exist and they may be plentiful, drifting almost invisibly through the cosmos, then they might account for dark matter. One possible way to search for them is to see the results of their meals and a bizarre new theory suggests low mass black holes could be captured by neutron stars and become trapped inside, devouring them from within. If these strange objects existed then it would make neutron stars less common in locations where black holes would proliferate as observed around Galactic centre.

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A Close Pulsar Measures 11.4 km Across

Animation of the millisecond pulsar PSR J0437-4715. On the left as seen from Earth. On the right as seen from the star's equatorial plane. (c) NASA/Sharon Morsink/Devarshi Choudhury et al.

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!

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Neutron Stars: Why study them? What makes them so fascinating?

Artist’s rendition of a neutron star. (Credit: ESO / L. Calçada)

Over the last several months, Universe Today has explored a plethora of scientific disciplines, including impact craters, planetary surfaces, exoplanets, astrobiology, solar physics, comets, planetary atmospheres, planetary geophysics, cosmochemistry, meteorites, radio astronomy, extremophiles, organic chemistry, black holes, cryovolcanism, planetary protection, dark matter, and supernovae, and how each of these unique disciplines continue to teach is about the cosmos and our place throughout its vastness.

Here, Universe Today discusses the field of neutron stars with Dr. Stuart Shapiro, who is a Professor of Physics and Astronomy and NCSA Senior Research Scientist at the University of Illinois at Urbana-Champaign, regarding the importance of studying neutron stars, the benefits and challenges, the most intriguing aspect about neutron stars he’s studied throughout his career, and any advice he can offer upcoming students who wish to pursue studying neutron stars. Therefore, what is the importance of studying neutron stars?

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Astronomers Will Get Gravitational Wave Alerts Within 30 Seconds

Astronomers and astrophysicists could use these alerts and information to understand how neutron stars behave and study nuclear interactions between neutron stars and black holes colliding.

Any event in the cosmos generates gravitational waves, the bigger the event, the more disturbance. Events where black holes and neutron stars collide can send out waves detectable here on Earth. It is possible that there can be an event in visible light when neutron stars collide so to take advantage of every opportunity an early warning is essential. The teams at LIGO-Virgo-KAGRA observatories are working on an alert system that will alert astronomers within 30 seconds fo a gravity wave event. If warning is early enough it may be possible to identify the source and watch the after glow. 

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A Neutron Star Merged with a Surprisingly Light Black Hole

Artwork of a neutron star–black hole merger. Credit: Carl Knox, OzGrav-Swinburne University.

Galactic collisions, meteor impacts and even stellar mergers are not uncommon events. neutron stars colliding with black holes however are a little more rare, in fact, until now, we have never observed one. The fourth LIGO-Virgo-KAGRA observing detected gravitational waves from a collision between a black hole and neutron star 650 million light years away. The black hole was tiny though with a mass between 2.5 to 4.5 times that of the Sun. 

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It Takes a Supercomputer to Properly Simulate a Neutron Star’s Surface

Neutron stars, the remains of massive stars that have imploded and gone supernova at the end of their life, can still create massive flares. These incredible bursts of energy release X-rays that propagate through space. It is a complex process to simulate but astronomers have turned to a supercomputer to help. Modelling the twisting magnetic fields, the interaction with gas and dust, the surface of flaring neutron stars has been revealed in incredible 3D.

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Neutron Stars are Jetting Material Away at 40% the Speed of Light

Artists impression of jets

It’s a well known fact that black holes absorb anything that falls into them. Often before material ‘vanishes’ inside it forms into an accretion disk around them. Like the progenitor stars, the black holes have powerful magnetic fields and these can generate jets that blast away from the black hole. A similar process occurs in neutron stars that are orbiting other stars and recent observations holes have shown that some material in the jets travel at speeds 35-40% the speed of light. 

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This Supernova Lit Up the Sky in 1181. Here’s What it Looks Like Now

A composite image of the remnant of supernova 1181. A spherical bright nebula sits in the middle surrounded by a field of white dotted stars. Within the nebula several rays point out like fireworks from a central star. G. Ferrand and J. English (U. of Manitoba), NASA/Chandra/WISE, ESA/XMM, MDM/R.Fessen (Dartmouth College), Pan-STARRS

Historical astronomical records from China and Japan recorded a supernova explosion in the year 1181. It was in the constellation Cassiopeia and it shone as bright as the star Vega for 185 days. Modern astronomers took their cue from their long-gone counterparts and have been searching for its remnant.

But it took them time to find it because they were looking for the wrong thing.

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Simulation Perfectly Matches What We See When Neutron Stars Collide

Numerical simulation of the resulting ejecta material of two merging neutron stars. Red colors refer to ejected material with a high fraction of neutrons which will appear typically redder than blue material that contains a higher fraction of protons. © I. Markin (University of Potsdam)
Numerical simulation of the resulting ejecta material of two merging neutron stars. Red colors refer to ejected material with a high fraction of neutrons which will appear typically redder than blue material that contains a higher fraction of protons. © I. Markin (University of Potsdam)

There are many mysteries in the world of astronomy and a fair number relate to the processes during the end of the life of a super massive star. Throw in the complexity of collisions and you have a real head scratching problem on your hands. In 2017 colliding neutron stars were detected and the data has allowed a new simulation to be tested with predictions beautifully matching observation.

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