The Maximum Mass of a Neutron Star is 2.25 Solar Masses

An outbursting, magnetically strong neutron star called a magnetar is seen here in an artist's illustration. Courtesy: NASA.
An outbursting, magnetically strong neutron star called a magnetar is seen here in an artist's illustration. Courtesy: NASA.

When stars grow old and die, their mass determines their ultimate fate. Many supermassive stars have futures as neutron stars. But, the question is, how massive can their neutron stars get? That’s one that Professor Fan Yizhong and his team at Purple Mountain Observatory in China set out to answer.

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Another Clue Into the True Nature of Fast Radio Bursts

Artist's concept of a magnetar. Credit: NASA/JPL-Caltech

Fast radio bursts (FRBs) are strange events. They can last only milliseconds, but during that time can outshine a galaxy. Some FRBs are repeaters, meaning that they can occur more than once from the same location, while others seem to occur just once. We still aren’t entirely sure what causes them, or even if the two types have the same cause. But thanks to a collaboration of observations from ground-based radio telescopes and space-based X-ray observatories, we are starting to figure FRBs out.

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Black Holes and Neutron Stars are Finally Linked to Supernovae

A star in a binary system dies in a catastrophic explosion. Such supernovae often result in neutron stars or black holes. Courtesy ESO/L. Calçada
This artist’s impression is based on the aftermath of a supernova explosion as seen by two teams of astronomers with both ESO’s Very Large Telescope (VLT) and ESO’s New Technology Telescope (NTT). The supernova observed, SN 2022jli, occurred when a massive star died in a fiery explosion, leaving behind a compact object — a neutron star or a black hole. This dying star, however, had a companion which was able to survive this violent event. The periodic interactions between the compact object and its companion left periodic signals in the data, which revealed that the supernova explosion had indeed resulted in a compact object.

Everybody knows that the explosive deaths of supermassive stars (called supernovae) lead to the creation of black holes or neutron stars, right? At least, that’s the evolutionary path that astronomers suggest happens. And, these compact objects exist throughout the Universe. But, no one’s ever seen the actual birth process of a neutron star or black hole in action before.

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Do Neutron Stars Have Mountains? Gravitational Wave Observatories Could Detect Them

Light bursts from the collision of two neutron stars. Credit: NASA's Goddard Space Flight Center/CI Lab

The surface gravity of a neutron star is so incredibly intense that it can cause atoms to collapse into a dense cluster of neutrons. The interiors of neutron stars may be dense enough to allow quarks to escape the bounds of nuclei. So it’s hard to imagine neutron stars as active bodies, with tectonic crusts and perhaps even mountains. But we have evidence to support this idea, and we could learn even more through gravitational waves.

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The Most Massive Neutron Stars Probably Have Cores of Quark Matter

Illustration of a quark core in a neutron star. Credit: Jyrki Hokkanen, CSC - IT Center for Science

Atoms are made of three things: protons, neutrons, and electrons. Electrons are a type of fundamental particle, but protons and neutrons are composite particles made of up and down quarks. Protons have 2 ups and 1 down, while neutrons have 2 downs and 1 up. Because of the curious nature of the strong force, these quarks are always bound to each other, so they can never be truly free particles like electrons, at least in the vacuum of empty space. But a new study in Nature Communications finds that they can liberate themselves within the hearts of neutron stars.

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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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Scientists Found Evidence Of A Nearby Kilonova 3.5 Million Years Ago

Most of the times astronomers reported dramatic, cataclysmic events like neutron star mergers or the creation of a black hole; they are taking place light years away, typically in in another galaxy. While we can observe their destructive power through the light they emit, they have minimal impact on Earth. However, a relatively recent discovery of certain types of isotopes at the bottom of the ocean hints at one of these events happening fairly close to home. And it probably didn’t happen all that long ago.

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When Stars Consume Their Partners, We Could Detect a Blast of Neutrinos

Three thousand light-years away, the Cat's Eye Nebula, a dying star throws off shells of glowing gas. This image from the Hubble Space Telescope reveals the nebula to be one of the most complex planetary nebulae known.The features seen in the Cat's Eye are so complex that astronomers suspect the central object may actually be a binary star system.
The Cat's Eye Nebula (NGC6543) is thought to be caused by a binary star system. Credit - NASA/HST

You might be familiar with the bizarre ritual of the female praying mantis which, I’m told, bites off the head and eats other body parts of the poor male they just mated with. It seems consuming partners is not unheard of.  It’s even seen in the lives of stars where binary stars orbit one another closely and one star ultimately consumes the other. If the victim is a neutron star a burst of neutrinos can be generated and a new study reveals they might just be detectable on Earth. 

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Astronomers are Hoping to Detect Gravitational Waves Coming from Supernova 1987A

This Hubble Space Telescope image shows Supernova 1987A within the Large Magellanic Cloud, a neighboring galaxy to our Milky Way.
Hubble Space Telescope image of SN1987A in the Large Magellanic Cloud (Credit : NASA)

A supernova explosion is a cataclysmic explosion that marks the violent end of a massive star’s life. During the event, the star releases immense amounts of energy, often outshining the combined light from all the stars in the host galaxy for a very brief period of time. The explosion produces heavy elements and spreads them out among the stars to contribute to the formation of new stars and planets. The closest supernova in recent years occurred in the Large Magellanic Cloud in 1987 (SN1987A) and now, a team of astronomers have searched through mountains of data to see if they can detect gravitational waves from the remnant. 

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If Neutron Stars Have Mountains, They Should Generate Gravitational Waves

Artist's depiction of a highly magnetize neutron star known as a magnetar. Credit: NASA's Goddard Space Flight Center/S. Wiessinger

A neutron star is 2 solar masses compressed into a ball only 12 kilometers wide. Its surface gravity is so immense it compresses atoms and molecules into raw nuclei and squeezes electrons into protons transforming them into neutrons. Given such immense pressures and densities, you might assume neutron stars have an almost perfectly smooth surface. But you’d be wrong because we know that neutron stars can have mountains.

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