Gravitational Waves Could Give Us Insights into Fast Radio Bursts

This artist's illustration shows a neutron star with a powerful magnetic field, a magnetar. Scientists want to know if magnetars can generate both Fast Radio Bursts and Gravitational Waves. Image Credit: ESO/L. Calçada

Fast Radio Bursts (FRBs) are mysterious pulses of energy that can last from a fraction of a millisecond to about three seconds. Most of them come from outside the galaxy, although one has been detected coming from a source inside the Milky Way. Some of them also repeat, which only adds to their mystery.

Though astrophysicists think that a high-energy astrophysical process is the likely source of FRBs, they aren’t certain how they’re generated. Researchers used gravitational waves (GWs) to observe one nearby, known source of FRBs to try to understand them better.

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Neutron Stars With Less Mass Than A White Dwarf Might Exist, and LIGO and Virgo Could Find Them

Illustration of a neutron star. Credit: NASA’s Goddard Space Flight Center/Chris Smith (USRA/GESTAR)

Most of the neutron stars we know of have a mass between 1.4 and 2.0 Suns. The upper limit makes sense, since, beyond about two solar masses, a neutron star would collapse to become a black hole. The lower limit also makes sense given the mass of white dwarfs. While neutron stars defy gravitational collapse thanks to the pressure between neutrons, white dwarfs defy gravity thanks to electron pressure. As first discovered by Subrahmanyan Chandrasekhar in 1930, white dwarfs can only support themselves up to what is now known as the Chandrasekhar Limit, or 1.4 solar masses. So it’s easy to assume that a neutron star must have at least that much mass. Otherwise, collapse would stop at a white dwarf. But that isn’t necessarily true.

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Do the Fastest Spinning Pulsars Contain Quark Matter?

Illustration of a pulsar with powerful magnetic fields. Credit: NASA's Goddard Flight Center/Walt Feimer

Neutron stars are so named because in the simplest of models they are made of neutrons. They form when the core of a large star collapses, and the weight of gravity causes atoms to collapse. Electrons are squeezed together with protons so that the core becomes a dense sea of neutrons. But we now know that neutron stars aren’t just gravitationally bound neutrons. For one thing, neutrons are comprised of quarks, which have their own interactions both within and between neutrons. These interactions are extremely complex, so the details of a neutron star’s interior are something we don’t fully understand.

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Are Fast Radio Bursts Caused by Interstellar Objects Crashing Into Neutron Stars?

This magnetar is a highly magnetized neutron star. This artist's illustration shows an outburst from a magnetar. Neutron stars that spin rapidly and give out radiation are called pulsars, and specific pulsars are rare in the core of the Milky Way. Credit: NASA/JPL-CalTech
This magnetar is a highly magnetized neutron star. This artist's illustration shows an outburst from a magnetar. Neutron stars that spin rapidly and give out radiation are called pulsars, and specific pulsars are rare in the core of the Milky Way. Credit: NASA/JPL-CalTech

Every now and then, astronomers will detect an odd kind of radio signal. So powerful it can outshine a galaxy, but lasting only milliseconds. They are known as fast radio bursts (FRBs). When they were first discovered a couple of decades ago, we had no idea what might cause them. We weren’t even sure if they were astronomical in origin. FRB’s were so localized and so short-lived, it was difficult to gather data on them. But with wide-field radio telescopes such as CHIME we can now observe FRBs regularly and have a pretty good idea of their source: magnetars.

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The Strange Pulsar at the Center of the Crab Nebula

Hubble image of the Crab Nebula supernova remnant captured with the Wide Field and Planetary Camera 2. Credit: NASA, ESA, J. Hester and A. Loll (ASU)

Thanks to the Hubble Space Telescope, we all have a vivid image of the Crab Nebula emblazoned in our mind’s eyes. It’s the remnant of a supernova explosion Chinese astronomers recorded in 1056. However, the Crab Nebula is more than just a nebula; it’s also a pulsar.

The Crab Pulsar pulsates in an unusual ‘zebra’ pattern, and an astrophysicist at the University of Kansas thinks he’s figured out why.

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The Aftermath of a Neutron Star Collision Resembles the Conditions in the Early Universe

This artist's illustration shows a neutron star collision leaving behind a rapidly expanding cloud of radioactive material. The conditions in the cloud are similar to the conditions in the early Universe, shortly after the Big Bang. Image Credit: NASA GODDARD SPACE FLIGHT CENTER, CI LAB

Neutron stars are extraordinarily dense objects, the densest in the Universe. They pack a lot of matter into a small space and can squeeze several solar masses into a radius of 20 km. When two neutron stars collide, they release an enormous amount of energy as a kilonova.

That energy tears atoms apart into a plasma of detached electrons and atomic nuclei, reminiscent of the early Universe after the Big Bang.

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Astronomers Have Found the Fastest Spinning Neutron Star

Illustration of a millisecond pulsar consuming material from a companion star. Pulsars that evaporate their companions rather than consuming them could serve as stellar engines. Credit: NASA / GSFC SVS / Dana Berry

Neutron stars are as dense as the nucleus of an atom. They contain a star’s worth of matter in a sphere only a dozen kilometers wide. And they are light-years away. So how can we possibly understand their interior structure? One way would be to simply spin it. Just spin it faster and faster until it reaches a maximum limit. That limit can tell us about how neutron stars hold together and even how they might form. Obviously, we can’t actually spin up a neutron star, but it can happen naturally, which is one of the reasons astronomers are interested in these maximally spinning stars. And recently a team has discovered a new one.

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Neutron Star Mergers Could Be Producing Quark Matter

An artist's impression of a neutron star merger as the two stars merge, change shape, and heat up. Courtesy: University of Warwick/Mark Garlick.
An artist's impression of a neutron star merger as the two stars merge, change shape, and heat up. Courtesy: University of Warwick/Mark Garlick.

When neutron stars dance together, the grand smash finale they experience might create the densest known form of matter known in the Universe. It’s called “quark matter, ” a highly weird combo of liberated quarks and gluons. It’s unclear if the stuff existed in their cores before the end of their dance. However, in the wild aftermath a neutron-star merger, the strange conditions could free quarks and gluons from protons and neutrons. That lets them move around freely in the aftermath. So, researchers want to know how freely they move and what conditions might impede their motion (or flow).

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The Aftermath of Neutron Star Mergers

An artistic rendering of two neutron stars merging. Credit: NSF/LIGO/Sonoma State/A. Simonnet

Neutron stars (NS) are the collapsed cores of supermassive giant stars that contain between 10 and 25 solar masses. Aside from black holes, they are the densest objects in the Universe. Their journey from a main sequence star to a collapsed stellar remnant is a fascinating scientific story.

Sometimes, a binary pair of NS will merge, and what happens then is equally as fascinating.

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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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