Neutron star key facts<\/strong><\/h2>A neutron star forms when a medium-sized star reaches the end of its life and explodes as a supernova<\/a>, after which it leaves an incredibly dense core behind.<\/p>The name ‘neutron star’ comes from the sub-atomic particles called neutrons, which you usually find inside the nuclei of atoms.<\/p>
The intense pressure inside a neutron star takes the other two mainstays of the atom \u2013 protons and electrons \u2013 and crushes them together to form yet more neutrons.<\/p>
In total, a neutron star is 90% neutrons \u2013 effectively, each one is a giant, city-sized atomic nucleus.<\/p>
The anatomy of a neutron star<\/strong><\/h2>![\"\"](\"https:\/\/c02.purpledshub.com\/uploads\/sites\/48\/2021\/11\/neutron-star-anatomy-eaf5fe2.jpg\" "\\"\\"\/")
Credit: Paul Wootton<\/figcaption><\/figure>A neutron star has a similar structure to our planet, with an atmosphere, crust and core. But what goes on inside is very different.<\/p>
Atmosphere<\/strong><\/h3>The gravity of the neutron star maintains an atmosphere of hydrogen, helium and carbon heated to around 2 million \u00b0C. It\u2019s just a few thousandths ofa millimetre thick.<\/p>
Outer crust<\/strong> <\/h3>The outer crust is made of a mixture of electrons and atoms that have had some or all of their electrons removed (known as ions).<\/p>
Outer core<\/strong><\/h3>Here you will find superconducting protons. A superconducting material offers no resistance to electrical current and so the current can flow through it without losing any energy.<\/p>
Inner core<\/strong><\/h3>The least understood part of a neutron star, the inner core could be made of a soup of quarks \u2013 the particles that make up protons and neutrons.<\/p>
Inner crust<\/strong><\/h3>The neutron star\u2019s magnetic field holds a lot of sway in this region. It could help fragment the crust and generate starquakes. Material in the inner crust takes the form of electrons, neutrons and atomic nuclei.<\/p>![\"The](\"https:\/\/c02.purpledshub.com\/uploads\/sites\/48\/2020\/01\/Vela_pulsar-c87f4d0.jpg\")
The Vela pulsar, as seen by the Chandra X-ray Observatory. Pulsars are neutron stars that spin andemit a regular pulse of charged particles in the direction of Earth as they do so. Credit: NASA\/CXC\/Univ of Toronto\/M.Durant et al<\/figcaption><\/figure>Neutron stars and gravity<\/strong><\/h2>Neutron stars exist because of a delicate balance of forces. On one hand you have gravity trying to collapse the star.<\/p>
Research published in July 2021 found that the gravity of neutron stars is so extreme, mountains on their surface can barely reach a millimetre in height.<\/p>
Yet resistance to gravitational collapse comes in the form of something called degeneracy pressure.<\/p>
This is generated because there comes a point when it is too hard to squash nuclear material closer together and so the two opposing forces balance each other out.<\/p>
This means that the most massive neutron stars should also be the smallest \u2013 more mass means stronger gravity and therefore a more compact, tightly squeezed object.<\/p>
The neutron star that makes no sense<\/strong><\/h2>![\"\"](\"https:\/\/c02.purpledshub.com\/uploads\/sites\/48\/2021\/11\/E2YP3RIXMAIWco5-440cfaf.jpg\" "\\"\\"\/")
An image of J0740 and its binary companion 6620, as taken by the NICER instrument on the ISS, using data from the XMM-Newton space telescope. Credit: ESA<\/figcaption><\/figure>At least, that is how it is supposed to work.<\/p>
Imagine the surprise for astronomers when in 2019 they stumbled across a seemingly impossible neutron star.<\/p>
This neutron star currently makes no sense: a neutron star that has a density far greater than its vast size should allow.<\/p>
Explaining its existence wouldn’t just answer important questions about neutron stars that we\u2019ve been asking for decades, it could also tell us more about nuclear physics and gravity to boot.<\/p>
The neutron star in question is called J0740 and sits 3,600 lightyears away in the constellation of Camelopardalis, the Giraffe.<\/p>
Like many stars<\/a>, it exists in a pair (or binary star<\/a> system). Its partner, 6620, is a white dwarf<\/a>, another type of dead star.<\/p>Studying neutron star J0740<\/strong><\/h2>![\"\"](\"https:\/\/c02.purpledshub.com\/uploads\/sites\/48\/2021\/11\/iss057e055460orig-80dd7ec.jpg\" "\\"\\"\/")
The Neutron Star Interior Composition ExploreR (NICER) X-ray telescope looks out into deep space from its perch on the ISS. Credit: NASA<\/figcaption><\/figure>Anna Watts from the University of Amsterdam is part of team that\u2019s been studying J0740 and other neutron stars using NASA\u2019s Neutron star Interior Composition Explorer (NICER), an X-ray telescope attached to the International Space Station<\/a> (ISS).<\/p>“As these objects spin, their brightness changes because there are hotspot regions on their surfaces,” says Watts. “We can use this characteristic to build up maps of those surfaces.”<\/p>
To accurately chart the surface detail of an object the size of London from a distance of over 3,600 lightyears (or 34 quadrillion kilometres) is quite some feat.<\/p>![\"\"](\"https:\/\/c02.purpledshub.com\/uploads\/sites\/48\/2021\/11\/Screenshot-2021-11-30-at-10.59.49-be0d00d-e1638270061133.png\" "\\"\\"\/")
At around 30km wide, J0740 would fit easliy within London\u2019s orbital motorway, the M25. Credit: FrankRamspott\/iStock\/Getty<\/figcaption><\/figure>It takes 3 to 4 weeks of observations over the course of a year. These surface maps are one of the tools Watts and her colleagues use to estimate the mass and size (radius) of neutron stars such as J0740.<\/p>
It turns out that J0740 is the most massive neutron star we\u2019ve ever found, tipping the scales at 2.1 times the mass of the Sun.<\/p>
So it should also have the smallest radius. Except it doesn\u2019t. It\u2019s just as wide as another neutron star with only two-thirds as much mass.<\/p>
That means the material inside J0740 isn\u2019t as compressible \u2013 or \u2018squishy\u2019 as astronomers tend to refer to it \u2013 as they thought.<\/p>
That potentially gives us clues about what\u2019s going on inside the core, which is important because of all the layers a neutron star has, the core is the least understood.<\/p>
Understanding quarks<\/strong><\/h2>Quarks are the particles that make up protons and neutrons. The intense pressure in the core of a neutron star could break the neutrons apart, forming a quark \u2018soup\u2019.<\/p>
It takes energy to break the neutrons down, which means there would be less available to resist gravity.<\/p>
That should make the neutron star more compressible and smaller, but Watts argues that\u2019s now harder to justify given J0740\u2019s surprisingly large size.<\/p>
“It doesn\u2019t rule them out completely, but those models look quite unlikely,” she says.<\/p>
Joseph Kapusta, from the University of Minnesota, is one of the researchers examining the possibility of quarks in the core of a neutron star.<\/p>
“A mixture of quarks and ordinary nuclear matter could support a star up to 2.2 solar masses,” he says, enough to encompass J0740 at 2.1 solar masses.<\/p>
He isn\u2019t convinced the NICER findings are enough to rule out his theory.<\/p>
“There are uncertainties in the estimates of the radius,” he says. That could leave some wiggle room for a quark soup core.<\/p>
Watts is busy hunting down other massive neutron stars to see if they also have unexpectedly large radii.<\/p>
NICER should be able to look at six neutron stars in total.<\/p>
“The dream is about 20,” Watts says, but that will have to wait until the next generation of X-ray telescopes.<\/p>
In the meantime, other teams of researchers have been busy trying to explain why J0740 isn\u2019t as squishy as it should be.<\/p>
Neutron stars and dark matter<\/strong><\/h2>![\"\"](\"https:\/\/c02.purpledshub.com\/uploads\/sites\/48\/2018\/12\/Dark-matter-abell-1689-f220708.jpg\" "\\"\\"\/")
A dark matter halo mapped in galaxy Abell 1689. Credit: NASA, ESA, E. Jullo (Jet Propulsion Laboratory), P. Natarajan (Yale University), and J.-P. Kneib (Laboratoire d’Astrophysique de Marseille, CNRS, France); Acknowledgment: H. Ford and N. Benetiz (Johns Hopkins University), and T. Broadhurst (Tel Aviv University)<\/figcaption><\/figure>Adrian Abac, from the University of San Carlos in the Philippines, argues that there\u2019s something our current neutron star models aren\u2019t accounting for: dark matter<\/a>.<\/p>Dark matter is the mysterious, invisible glue thought to stick galaxies together. It\u2019s spread sparsely throughout space.<\/p>
In fact, just one milligram of dark matter will pass through you over the course of your life.<\/p>
Abac argues that it also gets caught up in the cores of neutron stars.<\/p>
When he added dark matter to his neutron star models, he found that it offered up an additional source of resistance to gravity, perhaps explaining why J0740 isn\u2019t as compressible as we expected.<\/p>
Nuclear pasta<\/strong><\/h2>![\"\"](\"https:\/\/c02.purpledshub.com\/uploads\/sites\/48\/2021\/11\/Nuclear-pasta-label-747189a.jpg\" "\\"\\"\/")
The intense gravity of neutron stars is thought to have strange effects on the material within them, forming it into different \u2018nuclear pasta\u2019 shapes at different depths. Credit: M. E. Caplan, C. J. Horowitz<\/figcaption><\/figure>Fan Ji, from Nankai University in China, has taken a different approach.<\/p>
He thinks the answer lies in the neutron star\u2019s inner crust rather than the core.<\/p>
Matter between the core and surface forms odd materials that physicists refer to as \u2018nuclear pasta<\/a>\u2019.<\/p>He found that if the inner crust is made of bubble-shaped material called \u2018gnocchi\u2019, then it can lead to a neutron star with a larger radius because the star is less compressible.<\/p>
Crucially however, this was the case for low mass neutron stars, not huge ones like J0740.<\/p>
Magnetic pasta<\/strong><\/h2>![\"\"](\"https:\/\/c02.purpledshub.com\/uploads\/sites\/48\/2021\/11\/GettyImages-758305407-10fe761-e1638270521838.jpg\" "\\"\\"\/")
Artist’s illustration of magnetic field lines around a neutron star. Credit: Mark Garlick \/ Science Photo Library<\/figcaption><\/figure>There is another force that could be playing a role: magnetism.<\/p>
The name ‘neutron star’ comes from the sub-atomic particles called neutrons, which you usually find inside the nuclei of atoms.<\/p>
The intense pressure inside a neutron star takes the other two mainstays of the atom \u2013 protons and electrons \u2013 and crushes them together to form yet more neutrons.<\/p>
In total, a neutron star is 90% neutrons \u2013 effectively, each one is a giant, city-sized atomic nucleus.<\/p>
The anatomy of a neutron star<\/strong><\/h2>Credit: Paul Wootton<\/figcaption><\/figure>A neutron star has a similar structure to our planet, with an atmosphere, crust and core. But what goes on inside is very different.<\/p>
Atmosphere<\/strong><\/h3>The gravity of the neutron star maintains an atmosphere of hydrogen, helium and carbon heated to around 2 million \u00b0C. It\u2019s just a few thousandths ofa millimetre thick.<\/p>
Outer crust<\/strong> <\/h3>The outer crust is made of a mixture of electrons and atoms that have had some or all of their electrons removed (known as ions).<\/p>
Outer core<\/strong><\/h3>Here you will find superconducting protons. A superconducting material offers no resistance to electrical current and so the current can flow through it without losing any energy.<\/p>
Inner core<\/strong><\/h3>The least understood part of a neutron star, the inner core could be made of a soup of quarks \u2013 the particles that make up protons and neutrons.<\/p>
Inner crust<\/strong><\/h3>The neutron star\u2019s magnetic field holds a lot of sway in this region. It could help fragment the crust and generate starquakes. Material in the inner crust takes the form of electrons, neutrons and atomic nuclei.<\/p>The Vela pulsar, as seen by the Chandra X-ray Observatory. Pulsars are neutron stars that spin andemit a regular pulse of charged particles in the direction of Earth as they do so. Credit: NASA\/CXC\/Univ of Toronto\/M.Durant et al<\/figcaption><\/figure>Neutron stars and gravity<\/strong><\/h2>Neutron stars exist because of a delicate balance of forces. On one hand you have gravity trying to collapse the star.<\/p>
Research published in July 2021 found that the gravity of neutron stars is so extreme, mountains on their surface can barely reach a millimetre in height.<\/p>
Yet resistance to gravitational collapse comes in the form of something called degeneracy pressure.<\/p>
This is generated because there comes a point when it is too hard to squash nuclear material closer together and so the two opposing forces balance each other out.<\/p>
This means that the most massive neutron stars should also be the smallest \u2013 more mass means stronger gravity and therefore a more compact, tightly squeezed object.<\/p>
The neutron star that makes no sense<\/strong><\/h2>An image of J0740 and its binary companion 6620, as taken by the NICER instrument on the ISS, using data from the XMM-Newton space telescope. Credit: ESA<\/figcaption><\/figure>At least, that is how it is supposed to work.<\/p>
Imagine the surprise for astronomers when in 2019 they stumbled across a seemingly impossible neutron star.<\/p>
This neutron star currently makes no sense: a neutron star that has a density far greater than its vast size should allow.<\/p>
Explaining its existence wouldn’t just answer important questions about neutron stars that we\u2019ve been asking for decades, it could also tell us more about nuclear physics and gravity to boot.<\/p>
The neutron star in question is called J0740 and sits 3,600 lightyears away in the constellation of Camelopardalis, the Giraffe.<\/p>
Like many stars<\/a>, it exists in a pair (or binary star<\/a> system). Its partner, 6620, is a white dwarf<\/a>, another type of dead star.<\/p>Studying neutron star J0740<\/strong><\/h2>The Neutron Star Interior Composition ExploreR (NICER) X-ray telescope looks out into deep space from its perch on the ISS. Credit: NASA<\/figcaption><\/figure>Anna Watts from the University of Amsterdam is part of team that\u2019s been studying J0740 and other neutron stars using NASA\u2019s Neutron star Interior Composition Explorer (NICER), an X-ray telescope attached to the International Space Station<\/a> (ISS).<\/p>“As these objects spin, their brightness changes because there are hotspot regions on their surfaces,” says Watts. “We can use this characteristic to build up maps of those surfaces.”<\/p>
To accurately chart the surface detail of an object the size of London from a distance of over 3,600 lightyears (or 34 quadrillion kilometres) is quite some feat.<\/p>At around 30km wide, J0740 would fit easliy within London\u2019s orbital motorway, the M25. Credit: FrankRamspott\/iStock\/Getty<\/figcaption><\/figure>It takes 3 to 4 weeks of observations over the course of a year. These surface maps are one of the tools Watts and her colleagues use to estimate the mass and size (radius) of neutron stars such as J0740.<\/p>
It turns out that J0740 is the most massive neutron star we\u2019ve ever found, tipping the scales at 2.1 times the mass of the Sun.<\/p>
So it should also have the smallest radius. Except it doesn\u2019t. It\u2019s just as wide as another neutron star with only two-thirds as much mass.<\/p>
That means the material inside J0740 isn\u2019t as compressible \u2013 or \u2018squishy\u2019 as astronomers tend to refer to it \u2013 as they thought.<\/p>
That potentially gives us clues about what\u2019s going on inside the core, which is important because of all the layers a neutron star has, the core is the least understood.<\/p>
Understanding quarks<\/strong><\/h2>Quarks are the particles that make up protons and neutrons. The intense pressure in the core of a neutron star could break the neutrons apart, forming a quark \u2018soup\u2019.<\/p>
It takes energy to break the neutrons down, which means there would be less available to resist gravity.<\/p>
That should make the neutron star more compressible and smaller, but Watts argues that\u2019s now harder to justify given J0740\u2019s surprisingly large size.<\/p>
“It doesn\u2019t rule them out completely, but those models look quite unlikely,” she says.<\/p>
Joseph Kapusta, from the University of Minnesota, is one of the researchers examining the possibility of quarks in the core of a neutron star.<\/p>
“A mixture of quarks and ordinary nuclear matter could support a star up to 2.2 solar masses,” he says, enough to encompass J0740 at 2.1 solar masses.<\/p>
He isn\u2019t convinced the NICER findings are enough to rule out his theory.<\/p>
“There are uncertainties in the estimates of the radius,” he says. That could leave some wiggle room for a quark soup core.<\/p>
Watts is busy hunting down other massive neutron stars to see if they also have unexpectedly large radii.<\/p>
NICER should be able to look at six neutron stars in total.<\/p>
“The dream is about 20,” Watts says, but that will have to wait until the next generation of X-ray telescopes.<\/p>
In the meantime, other teams of researchers have been busy trying to explain why J0740 isn\u2019t as squishy as it should be.<\/p>
Neutron stars and dark matter<\/strong><\/h2>A dark matter halo mapped in galaxy Abell 1689. Credit: NASA, ESA, E. Jullo (Jet Propulsion Laboratory), P. Natarajan (Yale University), and J.-P. Kneib (Laboratoire d’Astrophysique de Marseille, CNRS, France); Acknowledgment: H. Ford and N. Benetiz (Johns Hopkins University), and T. Broadhurst (Tel Aviv University)<\/figcaption><\/figure>Adrian Abac, from the University of San Carlos in the Philippines, argues that there\u2019s something our current neutron star models aren\u2019t accounting for: dark matter<\/a>.<\/p>Dark matter is the mysterious, invisible glue thought to stick galaxies together. It\u2019s spread sparsely throughout space.<\/p>
In fact, just one milligram of dark matter will pass through you over the course of your life.<\/p>
Abac argues that it also gets caught up in the cores of neutron stars.<\/p>
When he added dark matter to his neutron star models, he found that it offered up an additional source of resistance to gravity, perhaps explaining why J0740 isn\u2019t as compressible as we expected.<\/p>
Nuclear pasta<\/strong><\/h2>The intense gravity of neutron stars is thought to have strange effects on the material within them, forming it into different \u2018nuclear pasta\u2019 shapes at different depths. Credit: M. E. Caplan, C. J. Horowitz<\/figcaption><\/figure>Fan Ji, from Nankai University in China, has taken a different approach.<\/p>
He thinks the answer lies in the neutron star\u2019s inner crust rather than the core.<\/p>
Matter between the core and surface forms odd materials that physicists refer to as \u2018nuclear pasta<\/a>\u2019.<\/p>He found that if the inner crust is made of bubble-shaped material called \u2018gnocchi\u2019, then it can lead to a neutron star with a larger radius because the star is less compressible.<\/p>
Crucially however, this was the case for low mass neutron stars, not huge ones like J0740.<\/p>
Magnetic pasta<\/strong><\/h2>Artist’s illustration of magnetic field lines around a neutron star. Credit: Mark Garlick \/ Science Photo Library<\/figcaption><\/figure>There is another force that could be playing a role: magnetism.<\/p>
A neutron star has a similar structure to our planet, with an atmosphere, crust and core. But what goes on inside is very different.<\/p>
Atmosphere<\/strong><\/h3>The gravity of the neutron star maintains an atmosphere of hydrogen, helium and carbon heated to around 2 million \u00b0C. It\u2019s just a few thousandths ofa millimetre thick.<\/p>
Outer crust<\/strong> <\/h3>The outer crust is made of a mixture of electrons and atoms that have had some or all of their electrons removed (known as ions).<\/p>
Outer core<\/strong><\/h3>Here you will find superconducting protons. A superconducting material offers no resistance to electrical current and so the current can flow through it without losing any energy.<\/p>
Inner core<\/strong><\/h3>The least understood part of a neutron star, the inner core could be made of a soup of quarks \u2013 the particles that make up protons and neutrons.<\/p>
Inner crust<\/strong><\/h3>The neutron star\u2019s magnetic field holds a lot of sway in this region. It could help fragment the crust and generate starquakes. Material in the inner crust takes the form of electrons, neutrons and atomic nuclei.<\/p>The Vela pulsar, as seen by the Chandra X-ray Observatory. Pulsars are neutron stars that spin andemit a regular pulse of charged particles in the direction of Earth as they do so. Credit: NASA\/CXC\/Univ of Toronto\/M.Durant et al<\/figcaption><\/figure>Neutron stars and gravity<\/strong><\/h2>Neutron stars exist because of a delicate balance of forces. On one hand you have gravity trying to collapse the star.<\/p>
Research published in July 2021 found that the gravity of neutron stars is so extreme, mountains on their surface can barely reach a millimetre in height.<\/p>
Yet resistance to gravitational collapse comes in the form of something called degeneracy pressure.<\/p>
This is generated because there comes a point when it is too hard to squash nuclear material closer together and so the two opposing forces balance each other out.<\/p>
This means that the most massive neutron stars should also be the smallest \u2013 more mass means stronger gravity and therefore a more compact, tightly squeezed object.<\/p>
The neutron star that makes no sense<\/strong><\/h2>An image of J0740 and its binary companion 6620, as taken by the NICER instrument on the ISS, using data from the XMM-Newton space telescope. Credit: ESA<\/figcaption><\/figure>At least, that is how it is supposed to work.<\/p>
Imagine the surprise for astronomers when in 2019 they stumbled across a seemingly impossible neutron star.<\/p>
This neutron star currently makes no sense: a neutron star that has a density far greater than its vast size should allow.<\/p>
Explaining its existence wouldn’t just answer important questions about neutron stars that we\u2019ve been asking for decades, it could also tell us more about nuclear physics and gravity to boot.<\/p>
The neutron star in question is called J0740 and sits 3,600 lightyears away in the constellation of Camelopardalis, the Giraffe.<\/p>
Like many stars<\/a>, it exists in a pair (or binary star<\/a> system). Its partner, 6620, is a white dwarf<\/a>, another type of dead star.<\/p>Studying neutron star J0740<\/strong><\/h2>The Neutron Star Interior Composition ExploreR (NICER) X-ray telescope looks out into deep space from its perch on the ISS. Credit: NASA<\/figcaption><\/figure>Anna Watts from the University of Amsterdam is part of team that\u2019s been studying J0740 and other neutron stars using NASA\u2019s Neutron star Interior Composition Explorer (NICER), an X-ray telescope attached to the International Space Station<\/a> (ISS).<\/p>“As these objects spin, their brightness changes because there are hotspot regions on their surfaces,” says Watts. “We can use this characteristic to build up maps of those surfaces.”<\/p>
To accurately chart the surface detail of an object the size of London from a distance of over 3,600 lightyears (or 34 quadrillion kilometres) is quite some feat.<\/p>At around 30km wide, J0740 would fit easliy within London\u2019s orbital motorway, the M25. Credit: FrankRamspott\/iStock\/Getty<\/figcaption><\/figure>It takes 3 to 4 weeks of observations over the course of a year. These surface maps are one of the tools Watts and her colleagues use to estimate the mass and size (radius) of neutron stars such as J0740.<\/p>
It turns out that J0740 is the most massive neutron star we\u2019ve ever found, tipping the scales at 2.1 times the mass of the Sun.<\/p>
So it should also have the smallest radius. Except it doesn\u2019t. It\u2019s just as wide as another neutron star with only two-thirds as much mass.<\/p>
That means the material inside J0740 isn\u2019t as compressible \u2013 or \u2018squishy\u2019 as astronomers tend to refer to it \u2013 as they thought.<\/p>
That potentially gives us clues about what\u2019s going on inside the core, which is important because of all the layers a neutron star has, the core is the least understood.<\/p>
Understanding quarks<\/strong><\/h2>Quarks are the particles that make up protons and neutrons. The intense pressure in the core of a neutron star could break the neutrons apart, forming a quark \u2018soup\u2019.<\/p>
It takes energy to break the neutrons down, which means there would be less available to resist gravity.<\/p>
That should make the neutron star more compressible and smaller, but Watts argues that\u2019s now harder to justify given J0740\u2019s surprisingly large size.<\/p>
“It doesn\u2019t rule them out completely, but those models look quite unlikely,” she says.<\/p>
Joseph Kapusta, from the University of Minnesota, is one of the researchers examining the possibility of quarks in the core of a neutron star.<\/p>
“A mixture of quarks and ordinary nuclear matter could support a star up to 2.2 solar masses,” he says, enough to encompass J0740 at 2.1 solar masses.<\/p>
He isn\u2019t convinced the NICER findings are enough to rule out his theory.<\/p>
“There are uncertainties in the estimates of the radius,” he says. That could leave some wiggle room for a quark soup core.<\/p>
Watts is busy hunting down other massive neutron stars to see if they also have unexpectedly large radii.<\/p>
NICER should be able to look at six neutron stars in total.<\/p>
“The dream is about 20,” Watts says, but that will have to wait until the next generation of X-ray telescopes.<\/p>
In the meantime, other teams of researchers have been busy trying to explain why J0740 isn\u2019t as squishy as it should be.<\/p>
Neutron stars and dark matter<\/strong><\/h2>A dark matter halo mapped in galaxy Abell 1689. Credit: NASA, ESA, E. Jullo (Jet Propulsion Laboratory), P. Natarajan (Yale University), and J.-P. Kneib (Laboratoire d’Astrophysique de Marseille, CNRS, France); Acknowledgment: H. Ford and N. Benetiz (Johns Hopkins University), and T. Broadhurst (Tel Aviv University)<\/figcaption><\/figure>Adrian Abac, from the University of San Carlos in the Philippines, argues that there\u2019s something our current neutron star models aren\u2019t accounting for: dark matter<\/a>.<\/p>Dark matter is the mysterious, invisible glue thought to stick galaxies together. It\u2019s spread sparsely throughout space.<\/p>
In fact, just one milligram of dark matter will pass through you over the course of your life.<\/p>
Abac argues that it also gets caught up in the cores of neutron stars.<\/p>
When he added dark matter to his neutron star models, he found that it offered up an additional source of resistance to gravity, perhaps explaining why J0740 isn\u2019t as compressible as we expected.<\/p>
Nuclear pasta<\/strong><\/h2>The intense gravity of neutron stars is thought to have strange effects on the material within them, forming it into different \u2018nuclear pasta\u2019 shapes at different depths. Credit: M. E. Caplan, C. J. Horowitz<\/figcaption><\/figure>Fan Ji, from Nankai University in China, has taken a different approach.<\/p>
He thinks the answer lies in the neutron star\u2019s inner crust rather than the core.<\/p>
Matter between the core and surface forms odd materials that physicists refer to as \u2018nuclear pasta<\/a>\u2019.<\/p>He found that if the inner crust is made of bubble-shaped material called \u2018gnocchi\u2019, then it can lead to a neutron star with a larger radius because the star is less compressible.<\/p>
Crucially however, this was the case for low mass neutron stars, not huge ones like J0740.<\/p>
Magnetic pasta<\/strong><\/h2>Artist’s illustration of magnetic field lines around a neutron star. Credit: Mark Garlick \/ Science Photo Library<\/figcaption><\/figure>There is another force that could be playing a role: magnetism.<\/p>
The outer crust is made of a mixture of electrons and atoms that have had some or all of their electrons removed (known as ions).<\/p>
Outer core<\/strong><\/h3>Here you will find superconducting protons. A superconducting material offers no resistance to electrical current and so the current can flow through it without losing any energy.<\/p>
Inner core<\/strong><\/h3>The least understood part of a neutron star, the inner core could be made of a soup of quarks \u2013 the particles that make up protons and neutrons.<\/p>
Inner crust<\/strong><\/h3>The neutron star\u2019s magnetic field holds a lot of sway in this region. It could help fragment the crust and generate starquakes. Material in the inner crust takes the form of electrons, neutrons and atomic nuclei.<\/p>The Vela pulsar, as seen by the Chandra X-ray Observatory. Pulsars are neutron stars that spin andemit a regular pulse of charged particles in the direction of Earth as they do so. Credit: NASA\/CXC\/Univ of Toronto\/M.Durant et al<\/figcaption><\/figure>Neutron stars and gravity<\/strong><\/h2>Neutron stars exist because of a delicate balance of forces. On one hand you have gravity trying to collapse the star.<\/p>
Research published in July 2021 found that the gravity of neutron stars is so extreme, mountains on their surface can barely reach a millimetre in height.<\/p>
Yet resistance to gravitational collapse comes in the form of something called degeneracy pressure.<\/p>
This is generated because there comes a point when it is too hard to squash nuclear material closer together and so the two opposing forces balance each other out.<\/p>
This means that the most massive neutron stars should also be the smallest \u2013 more mass means stronger gravity and therefore a more compact, tightly squeezed object.<\/p>
The neutron star that makes no sense<\/strong><\/h2>An image of J0740 and its binary companion 6620, as taken by the NICER instrument on the ISS, using data from the XMM-Newton space telescope. Credit: ESA<\/figcaption><\/figure>At least, that is how it is supposed to work.<\/p>
Imagine the surprise for astronomers when in 2019 they stumbled across a seemingly impossible neutron star.<\/p>
This neutron star currently makes no sense: a neutron star that has a density far greater than its vast size should allow.<\/p>
Explaining its existence wouldn’t just answer important questions about neutron stars that we\u2019ve been asking for decades, it could also tell us more about nuclear physics and gravity to boot.<\/p>
The neutron star in question is called J0740 and sits 3,600 lightyears away in the constellation of Camelopardalis, the Giraffe.<\/p>
Like many stars<\/a>, it exists in a pair (or binary star<\/a> system). Its partner, 6620, is a white dwarf<\/a>, another type of dead star.<\/p>Studying neutron star J0740<\/strong><\/h2>The Neutron Star Interior Composition ExploreR (NICER) X-ray telescope looks out into deep space from its perch on the ISS. Credit: NASA<\/figcaption><\/figure>Anna Watts from the University of Amsterdam is part of team that\u2019s been studying J0740 and other neutron stars using NASA\u2019s Neutron star Interior Composition Explorer (NICER), an X-ray telescope attached to the International Space Station<\/a> (ISS).<\/p>“As these objects spin, their brightness changes because there are hotspot regions on their surfaces,” says Watts. “We can use this characteristic to build up maps of those surfaces.”<\/p>
To accurately chart the surface detail of an object the size of London from a distance of over 3,600 lightyears (or 34 quadrillion kilometres) is quite some feat.<\/p>At around 30km wide, J0740 would fit easliy within London\u2019s orbital motorway, the M25. Credit: FrankRamspott\/iStock\/Getty<\/figcaption><\/figure>It takes 3 to 4 weeks of observations over the course of a year. These surface maps are one of the tools Watts and her colleagues use to estimate the mass and size (radius) of neutron stars such as J0740.<\/p>
It turns out that J0740 is the most massive neutron star we\u2019ve ever found, tipping the scales at 2.1 times the mass of the Sun.<\/p>
So it should also have the smallest radius. Except it doesn\u2019t. It\u2019s just as wide as another neutron star with only two-thirds as much mass.<\/p>
That means the material inside J0740 isn\u2019t as compressible \u2013 or \u2018squishy\u2019 as astronomers tend to refer to it \u2013 as they thought.<\/p>
That potentially gives us clues about what\u2019s going on inside the core, which is important because of all the layers a neutron star has, the core is the least understood.<\/p>
Understanding quarks<\/strong><\/h2>Quarks are the particles that make up protons and neutrons. The intense pressure in the core of a neutron star could break the neutrons apart, forming a quark \u2018soup\u2019.<\/p>
It takes energy to break the neutrons down, which means there would be less available to resist gravity.<\/p>
That should make the neutron star more compressible and smaller, but Watts argues that\u2019s now harder to justify given J0740\u2019s surprisingly large size.<\/p>
“It doesn\u2019t rule them out completely, but those models look quite unlikely,” she says.<\/p>
Joseph Kapusta, from the University of Minnesota, is one of the researchers examining the possibility of quarks in the core of a neutron star.<\/p>
“A mixture of quarks and ordinary nuclear matter could support a star up to 2.2 solar masses,” he says, enough to encompass J0740 at 2.1 solar masses.<\/p>
He isn\u2019t convinced the NICER findings are enough to rule out his theory.<\/p>
“There are uncertainties in the estimates of the radius,” he says. That could leave some wiggle room for a quark soup core.<\/p>
Watts is busy hunting down other massive neutron stars to see if they also have unexpectedly large radii.<\/p>
NICER should be able to look at six neutron stars in total.<\/p>
“The dream is about 20,” Watts says, but that will have to wait until the next generation of X-ray telescopes.<\/p>
In the meantime, other teams of researchers have been busy trying to explain why J0740 isn\u2019t as squishy as it should be.<\/p>
Neutron stars and dark matter<\/strong><\/h2>A dark matter halo mapped in galaxy Abell 1689. Credit: NASA, ESA, E. Jullo (Jet Propulsion Laboratory), P. Natarajan (Yale University), and J.-P. Kneib (Laboratoire d’Astrophysique de Marseille, CNRS, France); Acknowledgment: H. Ford and N. Benetiz (Johns Hopkins University), and T. Broadhurst (Tel Aviv University)<\/figcaption><\/figure>Adrian Abac, from the University of San Carlos in the Philippines, argues that there\u2019s something our current neutron star models aren\u2019t accounting for: dark matter<\/a>.<\/p>Dark matter is the mysterious, invisible glue thought to stick galaxies together. It\u2019s spread sparsely throughout space.<\/p>
In fact, just one milligram of dark matter will pass through you over the course of your life.<\/p>
Abac argues that it also gets caught up in the cores of neutron stars.<\/p>
When he added dark matter to his neutron star models, he found that it offered up an additional source of resistance to gravity, perhaps explaining why J0740 isn\u2019t as compressible as we expected.<\/p>
Nuclear pasta<\/strong><\/h2>The intense gravity of neutron stars is thought to have strange effects on the material within them, forming it into different \u2018nuclear pasta\u2019 shapes at different depths. Credit: M. E. Caplan, C. J. Horowitz<\/figcaption><\/figure>Fan Ji, from Nankai University in China, has taken a different approach.<\/p>
He thinks the answer lies in the neutron star\u2019s inner crust rather than the core.<\/p>
Matter between the core and surface forms odd materials that physicists refer to as \u2018nuclear pasta<\/a>\u2019.<\/p>He found that if the inner crust is made of bubble-shaped material called \u2018gnocchi\u2019, then it can lead to a neutron star with a larger radius because the star is less compressible.<\/p>
Crucially however, this was the case for low mass neutron stars, not huge ones like J0740.<\/p>
Magnetic pasta<\/strong><\/h2>Artist’s illustration of magnetic field lines around a neutron star. Credit: Mark Garlick \/ Science Photo Library<\/figcaption><\/figure>There is another force that could be playing a role: magnetism.<\/p>
The least understood part of a neutron star, the inner core could be made of a soup of quarks \u2013 the particles that make up protons and neutrons.<\/p>
Inner crust<\/strong><\/h3>The neutron star\u2019s magnetic field holds a lot of sway in this region. It could help fragment the crust and generate starquakes. Material in the inner crust takes the form of electrons, neutrons and atomic nuclei.<\/p>The Vela pulsar, as seen by the Chandra X-ray Observatory. Pulsars are neutron stars that spin andemit a regular pulse of charged particles in the direction of Earth as they do so. Credit: NASA\/CXC\/Univ of Toronto\/M.Durant et al<\/figcaption><\/figure>Neutron stars and gravity<\/strong><\/h2>Neutron stars exist because of a delicate balance of forces. On one hand you have gravity trying to collapse the star.<\/p>
Research published in July 2021 found that the gravity of neutron stars is so extreme, mountains on their surface can barely reach a millimetre in height.<\/p>
Yet resistance to gravitational collapse comes in the form of something called degeneracy pressure.<\/p>
This is generated because there comes a point when it is too hard to squash nuclear material closer together and so the two opposing forces balance each other out.<\/p>
This means that the most massive neutron stars should also be the smallest \u2013 more mass means stronger gravity and therefore a more compact, tightly squeezed object.<\/p>
The neutron star that makes no sense<\/strong><\/h2>An image of J0740 and its binary companion 6620, as taken by the NICER instrument on the ISS, using data from the XMM-Newton space telescope. Credit: ESA<\/figcaption><\/figure>At least, that is how it is supposed to work.<\/p>
Imagine the surprise for astronomers when in 2019 they stumbled across a seemingly impossible neutron star.<\/p>
This neutron star currently makes no sense: a neutron star that has a density far greater than its vast size should allow.<\/p>
Explaining its existence wouldn’t just answer important questions about neutron stars that we\u2019ve been asking for decades, it could also tell us more about nuclear physics and gravity to boot.<\/p>
The neutron star in question is called J0740 and sits 3,600 lightyears away in the constellation of Camelopardalis, the Giraffe.<\/p>
Like many stars<\/a>, it exists in a pair (or binary star<\/a> system). Its partner, 6620, is a white dwarf<\/a>, another type of dead star.<\/p>Studying neutron star J0740<\/strong><\/h2>The Neutron Star Interior Composition ExploreR (NICER) X-ray telescope looks out into deep space from its perch on the ISS. Credit: NASA<\/figcaption><\/figure>Anna Watts from the University of Amsterdam is part of team that\u2019s been studying J0740 and other neutron stars using NASA\u2019s Neutron star Interior Composition Explorer (NICER), an X-ray telescope attached to the International Space Station<\/a> (ISS).<\/p>“As these objects spin, their brightness changes because there are hotspot regions on their surfaces,” says Watts. “We can use this characteristic to build up maps of those surfaces.”<\/p>
To accurately chart the surface detail of an object the size of London from a distance of over 3,600 lightyears (or 34 quadrillion kilometres) is quite some feat.<\/p>At around 30km wide, J0740 would fit easliy within London\u2019s orbital motorway, the M25. Credit: FrankRamspott\/iStock\/Getty<\/figcaption><\/figure>It takes 3 to 4 weeks of observations over the course of a year. These surface maps are one of the tools Watts and her colleagues use to estimate the mass and size (radius) of neutron stars such as J0740.<\/p>
It turns out that J0740 is the most massive neutron star we\u2019ve ever found, tipping the scales at 2.1 times the mass of the Sun.<\/p>
So it should also have the smallest radius. Except it doesn\u2019t. It\u2019s just as wide as another neutron star with only two-thirds as much mass.<\/p>
That means the material inside J0740 isn\u2019t as compressible \u2013 or \u2018squishy\u2019 as astronomers tend to refer to it \u2013 as they thought.<\/p>
That potentially gives us clues about what\u2019s going on inside the core, which is important because of all the layers a neutron star has, the core is the least understood.<\/p>
Understanding quarks<\/strong><\/h2>Quarks are the particles that make up protons and neutrons. The intense pressure in the core of a neutron star could break the neutrons apart, forming a quark \u2018soup\u2019.<\/p>
It takes energy to break the neutrons down, which means there would be less available to resist gravity.<\/p>
That should make the neutron star more compressible and smaller, but Watts argues that\u2019s now harder to justify given J0740\u2019s surprisingly large size.<\/p>
“It doesn\u2019t rule them out completely, but those models look quite unlikely,” she says.<\/p>
Joseph Kapusta, from the University of Minnesota, is one of the researchers examining the possibility of quarks in the core of a neutron star.<\/p>
“A mixture of quarks and ordinary nuclear matter could support a star up to 2.2 solar masses,” he says, enough to encompass J0740 at 2.1 solar masses.<\/p>
He isn\u2019t convinced the NICER findings are enough to rule out his theory.<\/p>
“There are uncertainties in the estimates of the radius,” he says. That could leave some wiggle room for a quark soup core.<\/p>
Watts is busy hunting down other massive neutron stars to see if they also have unexpectedly large radii.<\/p>
NICER should be able to look at six neutron stars in total.<\/p>
“The dream is about 20,” Watts says, but that will have to wait until the next generation of X-ray telescopes.<\/p>
In the meantime, other teams of researchers have been busy trying to explain why J0740 isn\u2019t as squishy as it should be.<\/p>
Neutron stars and dark matter<\/strong><\/h2>A dark matter halo mapped in galaxy Abell 1689. Credit: NASA, ESA, E. Jullo (Jet Propulsion Laboratory), P. Natarajan (Yale University), and J.-P. Kneib (Laboratoire d’Astrophysique de Marseille, CNRS, France); Acknowledgment: H. Ford and N. Benetiz (Johns Hopkins University), and T. Broadhurst (Tel Aviv University)<\/figcaption><\/figure>Adrian Abac, from the University of San Carlos in the Philippines, argues that there\u2019s something our current neutron star models aren\u2019t accounting for: dark matter<\/a>.<\/p>Dark matter is the mysterious, invisible glue thought to stick galaxies together. It\u2019s spread sparsely throughout space.<\/p>
In fact, just one milligram of dark matter will pass through you over the course of your life.<\/p>
Abac argues that it also gets caught up in the cores of neutron stars.<\/p>
When he added dark matter to his neutron star models, he found that it offered up an additional source of resistance to gravity, perhaps explaining why J0740 isn\u2019t as compressible as we expected.<\/p>
Nuclear pasta<\/strong><\/h2>The intense gravity of neutron stars is thought to have strange effects on the material within them, forming it into different \u2018nuclear pasta\u2019 shapes at different depths. Credit: M. E. Caplan, C. J. Horowitz<\/figcaption><\/figure>Fan Ji, from Nankai University in China, has taken a different approach.<\/p>
He thinks the answer lies in the neutron star\u2019s inner crust rather than the core.<\/p>
Matter between the core and surface forms odd materials that physicists refer to as \u2018nuclear pasta<\/a>\u2019.<\/p>He found that if the inner crust is made of bubble-shaped material called \u2018gnocchi\u2019, then it can lead to a neutron star with a larger radius because the star is less compressible.<\/p>
Crucially however, this was the case for low mass neutron stars, not huge ones like J0740.<\/p>
Magnetic pasta<\/strong><\/h2>Artist’s illustration of magnetic field lines around a neutron star. Credit: Mark Garlick \/ Science Photo Library<\/figcaption><\/figure>There is another force that could be playing a role: magnetism.<\/p>
Neutron stars and gravity<\/strong><\/h2>Neutron stars exist because of a delicate balance of forces. On one hand you have gravity trying to collapse the star.<\/p>
Research published in July 2021 found that the gravity of neutron stars is so extreme, mountains on their surface can barely reach a millimetre in height.<\/p>
Yet resistance to gravitational collapse comes in the form of something called degeneracy pressure.<\/p>
This is generated because there comes a point when it is too hard to squash nuclear material closer together and so the two opposing forces balance each other out.<\/p>
This means that the most massive neutron stars should also be the smallest \u2013 more mass means stronger gravity and therefore a more compact, tightly squeezed object.<\/p>
The neutron star that makes no sense<\/strong><\/h2>An image of J0740 and its binary companion 6620, as taken by the NICER instrument on the ISS, using data from the XMM-Newton space telescope. Credit: ESA<\/figcaption><\/figure>At least, that is how it is supposed to work.<\/p>
Imagine the surprise for astronomers when in 2019 they stumbled across a seemingly impossible neutron star.<\/p>
This neutron star currently makes no sense: a neutron star that has a density far greater than its vast size should allow.<\/p>
Explaining its existence wouldn’t just answer important questions about neutron stars that we\u2019ve been asking for decades, it could also tell us more about nuclear physics and gravity to boot.<\/p>
The neutron star in question is called J0740 and sits 3,600 lightyears away in the constellation of Camelopardalis, the Giraffe.<\/p>
Like many stars<\/a>, it exists in a pair (or binary star<\/a> system). Its partner, 6620, is a white dwarf<\/a>, another type of dead star.<\/p>Studying neutron star J0740<\/strong><\/h2>The Neutron Star Interior Composition ExploreR (NICER) X-ray telescope looks out into deep space from its perch on the ISS. Credit: NASA<\/figcaption><\/figure>Anna Watts from the University of Amsterdam is part of team that\u2019s been studying J0740 and other neutron stars using NASA\u2019s Neutron star Interior Composition Explorer (NICER), an X-ray telescope attached to the International Space Station<\/a> (ISS).<\/p>“As these objects spin, their brightness changes because there are hotspot regions on their surfaces,” says Watts. “We can use this characteristic to build up maps of those surfaces.”<\/p>
To accurately chart the surface detail of an object the size of London from a distance of over 3,600 lightyears (or 34 quadrillion kilometres) is quite some feat.<\/p>At around 30km wide, J0740 would fit easliy within London\u2019s orbital motorway, the M25. Credit: FrankRamspott\/iStock\/Getty<\/figcaption><\/figure>It takes 3 to 4 weeks of observations over the course of a year. These surface maps are one of the tools Watts and her colleagues use to estimate the mass and size (radius) of neutron stars such as J0740.<\/p>
It turns out that J0740 is the most massive neutron star we\u2019ve ever found, tipping the scales at 2.1 times the mass of the Sun.<\/p>
So it should also have the smallest radius. Except it doesn\u2019t. It\u2019s just as wide as another neutron star with only two-thirds as much mass.<\/p>
That means the material inside J0740 isn\u2019t as compressible \u2013 or \u2018squishy\u2019 as astronomers tend to refer to it \u2013 as they thought.<\/p>
That potentially gives us clues about what\u2019s going on inside the core, which is important because of all the layers a neutron star has, the core is the least understood.<\/p>
Understanding quarks<\/strong><\/h2>Quarks are the particles that make up protons and neutrons. The intense pressure in the core of a neutron star could break the neutrons apart, forming a quark \u2018soup\u2019.<\/p>
It takes energy to break the neutrons down, which means there would be less available to resist gravity.<\/p>
That should make the neutron star more compressible and smaller, but Watts argues that\u2019s now harder to justify given J0740\u2019s surprisingly large size.<\/p>
“It doesn\u2019t rule them out completely, but those models look quite unlikely,” she says.<\/p>
Joseph Kapusta, from the University of Minnesota, is one of the researchers examining the possibility of quarks in the core of a neutron star.<\/p>
“A mixture of quarks and ordinary nuclear matter could support a star up to 2.2 solar masses,” he says, enough to encompass J0740 at 2.1 solar masses.<\/p>
He isn\u2019t convinced the NICER findings are enough to rule out his theory.<\/p>
“There are uncertainties in the estimates of the radius,” he says. That could leave some wiggle room for a quark soup core.<\/p>
Watts is busy hunting down other massive neutron stars to see if they also have unexpectedly large radii.<\/p>
NICER should be able to look at six neutron stars in total.<\/p>
“The dream is about 20,” Watts says, but that will have to wait until the next generation of X-ray telescopes.<\/p>
In the meantime, other teams of researchers have been busy trying to explain why J0740 isn\u2019t as squishy as it should be.<\/p>
Neutron stars and dark matter<\/strong><\/h2>A dark matter halo mapped in galaxy Abell 1689. Credit: NASA, ESA, E. Jullo (Jet Propulsion Laboratory), P. Natarajan (Yale University), and J.-P. Kneib (Laboratoire d’Astrophysique de Marseille, CNRS, France); Acknowledgment: H. Ford and N. Benetiz (Johns Hopkins University), and T. Broadhurst (Tel Aviv University)<\/figcaption><\/figure>Adrian Abac, from the University of San Carlos in the Philippines, argues that there\u2019s something our current neutron star models aren\u2019t accounting for: dark matter<\/a>.<\/p>Dark matter is the mysterious, invisible glue thought to stick galaxies together. It\u2019s spread sparsely throughout space.<\/p>
In fact, just one milligram of dark matter will pass through you over the course of your life.<\/p>
Abac argues that it also gets caught up in the cores of neutron stars.<\/p>
When he added dark matter to his neutron star models, he found that it offered up an additional source of resistance to gravity, perhaps explaining why J0740 isn\u2019t as compressible as we expected.<\/p>
Nuclear pasta<\/strong><\/h2>The intense gravity of neutron stars is thought to have strange effects on the material within them, forming it into different \u2018nuclear pasta\u2019 shapes at different depths. Credit: M. E. Caplan, C. J. Horowitz<\/figcaption><\/figure>Fan Ji, from Nankai University in China, has taken a different approach.<\/p>
He thinks the answer lies in the neutron star\u2019s inner crust rather than the core.<\/p>
Matter between the core and surface forms odd materials that physicists refer to as \u2018nuclear pasta<\/a>\u2019.<\/p>He found that if the inner crust is made of bubble-shaped material called \u2018gnocchi\u2019, then it can lead to a neutron star with a larger radius because the star is less compressible.<\/p>
Crucially however, this was the case for low mass neutron stars, not huge ones like J0740.<\/p>
Magnetic pasta<\/strong><\/h2>Artist’s illustration of magnetic field lines around a neutron star. Credit: Mark Garlick \/ Science Photo Library<\/figcaption><\/figure>There is another force that could be playing a role: magnetism.<\/p>
At least, that is how it is supposed to work.<\/p>
Imagine the surprise for astronomers when in 2019 they stumbled across a seemingly impossible neutron star.<\/p>
This neutron star currently makes no sense: a neutron star that has a density far greater than its vast size should allow.<\/p>
Explaining its existence wouldn’t just answer important questions about neutron stars that we\u2019ve been asking for decades, it could also tell us more about nuclear physics and gravity to boot.<\/p>
The neutron star in question is called J0740 and sits 3,600 lightyears away in the constellation of Camelopardalis, the Giraffe.<\/p>
Like many stars<\/a>, it exists in a pair (or binary star<\/a> system). Its partner, 6620, is a white dwarf<\/a>, another type of dead star.<\/p> Anna Watts from the University of Amsterdam is part of team that\u2019s been studying J0740 and other neutron stars using NASA\u2019s Neutron star Interior Composition Explorer (NICER), an X-ray telescope attached to the International Space Station<\/a> (ISS).<\/p> “As these objects spin, their brightness changes because there are hotspot regions on their surfaces,” says Watts. “We can use this characteristic to build up maps of those surfaces.”<\/p> To accurately chart the surface detail of an object the size of London from a distance of over 3,600 lightyears (or 34 quadrillion kilometres) is quite some feat.<\/p> It takes 3 to 4 weeks of observations over the course of a year. These surface maps are one of the tools Watts and her colleagues use to estimate the mass and size (radius) of neutron stars such as J0740.<\/p> It turns out that J0740 is the most massive neutron star we\u2019ve ever found, tipping the scales at 2.1 times the mass of the Sun.<\/p> So it should also have the smallest radius. Except it doesn\u2019t. It\u2019s just as wide as another neutron star with only two-thirds as much mass.<\/p> That means the material inside J0740 isn\u2019t as compressible \u2013 or \u2018squishy\u2019 as astronomers tend to refer to it \u2013 as they thought.<\/p> That potentially gives us clues about what\u2019s going on inside the core, which is important because of all the layers a neutron star has, the core is the least understood.<\/p> Quarks are the particles that make up protons and neutrons. The intense pressure in the core of a neutron star could break the neutrons apart, forming a quark \u2018soup\u2019.<\/p> It takes energy to break the neutrons down, which means there would be less available to resist gravity.<\/p> That should make the neutron star more compressible and smaller, but Watts argues that\u2019s now harder to justify given J0740\u2019s surprisingly large size.<\/p> “It doesn\u2019t rule them out completely, but those models look quite unlikely,” she says.<\/p> Joseph Kapusta, from the University of Minnesota, is one of the researchers examining the possibility of quarks in the core of a neutron star.<\/p> “A mixture of quarks and ordinary nuclear matter could support a star up to 2.2 solar masses,” he says, enough to encompass J0740 at 2.1 solar masses.<\/p> He isn\u2019t convinced the NICER findings are enough to rule out his theory.<\/p> “There are uncertainties in the estimates of the radius,” he says. That could leave some wiggle room for a quark soup core.<\/p> Watts is busy hunting down other massive neutron stars to see if they also have unexpectedly large radii.<\/p> NICER should be able to look at six neutron stars in total.<\/p> “The dream is about 20,” Watts says, but that will have to wait until the next generation of X-ray telescopes.<\/p> In the meantime, other teams of researchers have been busy trying to explain why J0740 isn\u2019t as squishy as it should be.<\/p> Adrian Abac, from the University of San Carlos in the Philippines, argues that there\u2019s something our current neutron star models aren\u2019t accounting for: dark matter<\/a>.<\/p> Dark matter is the mysterious, invisible glue thought to stick galaxies together. It\u2019s spread sparsely throughout space.<\/p> In fact, just one milligram of dark matter will pass through you over the course of your life.<\/p> Abac argues that it also gets caught up in the cores of neutron stars.<\/p> When he added dark matter to his neutron star models, he found that it offered up an additional source of resistance to gravity, perhaps explaining why J0740 isn\u2019t as compressible as we expected.<\/p> Fan Ji, from Nankai University in China, has taken a different approach.<\/p> He thinks the answer lies in the neutron star\u2019s inner crust rather than the core.<\/p> Matter between the core and surface forms odd materials that physicists refer to as \u2018nuclear pasta<\/a>\u2019.<\/p> He found that if the inner crust is made of bubble-shaped material called \u2018gnocchi\u2019, then it can lead to a neutron star with a larger radius because the star is less compressible.<\/p> Crucially however, this was the case for low mass neutron stars, not huge ones like J0740.<\/p> There is another force that could be playing a role: magnetism.<\/p>Studying neutron star J0740<\/strong><\/h2>
Understanding quarks<\/strong><\/h2>
Neutron stars and dark matter<\/strong><\/h2>
Nuclear pasta<\/strong><\/h2>
Magnetic pasta<\/strong><\/h2>
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