49 Fun Facts About Neutron Stars

A neutron star is the gravitationally collapsed core of what kind of object?

A massive supergiant has a core heavy enough to collapse when its fuel runs out, whereas a star like the Sun simply fades into a white dwarf and never explodes.

A typical neutron star packs more mass than the Sun into a ball about as wide as what?

A city is the usual comparison: the star is only about 20 kilometres across, and its gravity is strong enough to bend light from its far side into view, so it looks bigger than it really is.

Which class of objects is the only one denser than neutron stars?

Black holes are what a collapsing core becomes when it is too heavy even for packed neutrons to hold up, which leaves a neutron star as the densest object astronomers can observe directly.

Collisions between neutron stars are thought to forge much of the universe's supply of which element?

Gold and platinum were among the freshly made heavy elements reported in the glow of the first neutron-star collision ever observed, while carbon, oxygen and iron are forged inside ordinary stars.

About how many neutron stars are thought to exist in the Milky Way?

Around one billion is the usual estimate, worked out from how many stars have exploded over the galaxy's history, and most of them have long since cooled and gone dark.

A teaspoon of neutron-star material has a mass roughly 900 times that of which famous structure?

The Great Pyramid of Giza weighs about six million tonnes, yet a teaspoon outweighs 900 of them because the collapse crushes protons and electrons together into tightly packed neutrons.

Which pair of astronomers proposed neutron stars in December 1933, less than two years after the neutron was discovered?

Baade and Zwicky told a meeting of the American Physical Society that an exploding star's core could collapse into a ball of neutrons, 34 years before anyone actually found one.

Who discovered the neutron in 1932, setting up the idea of neutron stars?

James Chadwick proved in 1932 that a puzzling radiation others took for gamma rays was really the neutral particle his mentor Ernest Rutherford had predicted years before.

Jocelyn Bell found the first pulsar as a 'bit of scruff' while reading her radio telescope's output by eye on what?

Paper charts poured off her pen recorders at 96 feet a day and she analysed them all by hand, which is how she spotted a smudge that kept returning from the same patch of sky.

The first pulsar's discoverers half-jokingly labelled its steady pulses after what?

Little green men gave the signal its label, LGM-1, because pulses that steady briefly looked like a beacon from an alien civilisation before a natural cause was found.

The steadiest pulsars spin so regularly that astronomers compare their timekeeping with what?

Atomic clocks are the benchmark, and astronomers now time dozens of these steady pulsars across the sky to catch gravitational waves gently stretching the space in between.

Which band put a plot of the first pulsar's radio pulses on the cover of its 1979 debut album Unknown Pleasures?

A Joy Division member spotted the stacked pulses in The Cambridge Encyclopaedia of Astronomy, and the plot traces back to Harold Craft's 1970 PhD thesis.

Which of Bell's colleagues shared the 1974 Nobel Prize in Physics for the discovery of pulsars, while she was left out?

Antony Hewish shared the prize with Martin Ryle, and Fred Hoyle protested publicly that Bell, who actually found the signal, had been passed over.

Jocelyn Bell Burnell gave away her entire $3 million Breakthrough Prize in 2018 to pay for what?

Physics scholarships were her choice: the money set up an Institute of Physics fund that helps women, ethnic-minority and refugee students train as research physicists.

In which part of the UK was pulsar discoverer Bell Burnell born?

Northern Ireland was home: she grew up in Lurgan, and staff at the nearby Armagh Observatory encouraged her interest in astronomy when she visited as a girl.

The explosion that left the Crab Pulsar shone in daylight for weeks in 1054, recorded as a 'guest star' where?

China's court astronomers logged the guest star as visible in daylight for 23 days, and their notes on its position let twentieth-century astronomers match it to the Crab Nebula.

How many times per second does the Crab Pulsar rotate?

About 30 turns a second, and the spin is slowing by just 38 billionths of a second each day, yet that lost energy is enough to keep the whole Crab Nebula glowing.

Timing the Crab Pulsar's rapid pulses in 1968 convinced scientists that pulsars were spinning neutron stars rather than what?

Pulsating white dwarfs were the main rival idea, but a star that size cannot throb or spin that quickly without tearing itself apart, which left only something far smaller and denser.

A magnetar's magnetic field would be lethal from 1,000 kilometres away because it stretches what out of shape?

Atoms get squeezed into cigar shapes by a field that strong, and near the star's surface into needles a hundred times longer than wide, so the chemistry that keeps a body alive stops working.

In 1998 a magnetar flare from 20,000 light-years away made the night-time upper atmosphere behave as if it were what?

Daytime conditions returned for five minutes as the gamma rays pushed the electrically charged layer down to its sunlit height, a jolt spotted by Stanford engineers monitoring Navy radio signals to submarines.

How fast do most magnetars spin, next to ordinary pulsars?

More slowly, once every two to ten seconds, because the colossal magnetic field acts as a brake, carrying off energy and dragging a newborn's rapid spin down within a few thousand years.

In December 2004 a magnetar's flare from across the galaxy was so bright that its flash bounced off what?

The Moon scattered some of the gamma rays back towards a Russian satellite, and for a tenth of a second the blast rivalled a full moon in brightness.

In 2020 a magnetar in our own galaxy was caught producing which mysterious signal, previously seen only from other galaxies?

Fast radio bursts last only milliseconds and had puzzled astronomers since 2007, so catching one from a magnetar in the Milky Way on 28 April 2020 finally gave them a culprit.

The fastest-spinning pulsar known rotates roughly how many times every second?

About 700, or 716 to be exact, which beats the blades of a kitchen blender, and at that rate any star wider than about 30 kilometres would fling its own surface into space.

Like Jocelyn Bell with the first pulsar, Jason Hessels found a record-fast pulsar in 2004 while he was what?

A graduate student, at McGill in Montreal, which fits a pattern: Bell was one when she spotted the first pulsar, and so was Russell Hulse when he made a find that later won the Nobel Prize.

Millisecond pulsars are old, yet spin far faster than young ones like the Crab; what spun them up?

Gas from a companion star spills onto the old pulsar and whips it back up to speed, which is why these stars are nicknamed recycled pulsars and are so often found with a partner.

A 'glitch' in a neutron star is a sudden small change of what kind?

A spin-up of a millionth or less: a glitch interrupts a pulsar's steady slowing, probably when the faster-spinning fluid inside briefly grips the crust and passes on some of its spin.

In 1974 Hulse and Taylor noticed a pulsar's ticks arriving early, then late, in an eight-hour cycle; what had they found?

The first binary pulsar: its ticks bunched up as it swung toward Earth and spread out as it swung away, betraying an unseen partner that proved to be a second neutron star.

The Hulse-Taylor pulsar's orbit is slowly shrinking, exactly as predicted by whose theory of gravity?

Albert Einstein's general relativity says such a pair must leak energy as gravitational waves, and the orbit duly gets about 75 millionths of a second shorter each year, within half a percent of the forecast.

Which telescope did Hulse and Taylor use to make their Nobel-winning pulsar discovery in 1974?

The Arecibo 305 m dish in Puerto Rico was the world's largest for 53 years and the setting for the climax of a 1995 James Bond film, but it collapsed in December 2020 after support cables failed.

Which observatory recorded the 2017 neutron-star collision as a 100-second ripple in space-time, before any telescope saw its light?

LIGO's twin detectors in Washington State and Louisiana felt the two stars spiral together for about 100 seconds, and the alert set telescopes hunting: within half a day they had found the fading glow.

The 2017 neutron-star crash happened about 130 million years ago, when what lived on Earth?

Dinosaurs walked the Earth when the two stars merged, because the galaxy they sat in is about 130 million light-years away and the ripples and light needed that long to cross the gap.

The 2017 neutron-star collision's glow changed colour within days, from blue to what?

Red: as the debris cloud expanded and cooled, its light slid from very blue to very red in just a few days.

Gamma rays and gravitational waves from the 2017 collision arrived together, showing gravity travels how fast?

The speed of light, to within a few parts in a thousand trillion: after a journey of some 130 million years, the two signals reached Earth less than two seconds apart.

What name is given to the glowing cloud of radioactive debris left after two neutron stars collide?

A kilonova shines about a thousand times brighter than an ordinary nova. Theorists predicted such blasts decades ago, but the first confirmed one was only seen in 2017.

Deep in a neutron star's crust, nuclei are thought to squash into blobs, tubes and sheets that physicists nickname nuclear what?

Pasta: the blobs are called gnocchi, the tubes spaghetti and the sheets lasagne. A 2018 simulation suggested nuclear pasta may be the strongest material in the universe, about ten billion times stronger than steel.

In 1992, tiny wobbles in a pulsar's ticking revealed the first known examples of what?

Exoplanets: the first worlds confirmed beyond the Solar System circle the corpse of a star, not a sun. Their names play on it: Poltergeist and Phobetor, joined two years later by Draugr, after the undead of Norse myth.

Seven neutron stars share a film's nickname, and an eighth is named Calvera after its villain; which film?

The Magnificent Seven: astronomers named the newcomer after the bandit chief who fights the film's seven gunmen, and in 2026 the International Astronomical Union made the joke the star's official name.

Which physicist worked with George Volkoff in 1939 to calculate a maximum mass for neutron stars, a limit that bears his name?

J. Robert Oppenheimer got about 0.7 Suns, only half the mass of a typical neutron star, because his sums ignored the repulsion between neutrons. A few years later he was leading the Manhattan Project.

NASA's Pioneer plaque shows aliens where the Sun is using 14 pulsars, each labelled in code with what?

How fast it spins: every pulsar ticks at its own rate, so the 14 numbers work like fingerprints. And because pulsars slow down with age, the numbers also reveal how long ago the probe was launched.

Dropped from one metre above a neutron star 12 km in radius, roughly how fast would an object hit the surface?

About 1,400 km/s, some five million kilometres an hour, after a fall of just one metre: gravity at the surface is more than a hundred billion times stronger than on Earth.

Which film turns on the same effect of gravity that makes time run noticeably slower on a neutron star's surface?

Interstellar: on one of its planets, one hour costs the crew seven years back home. A neutron star is gentler, but a clock on its surface would still fall a couple of years behind Earth's every decade.

A 2020 study suggested that 'mountains' on a neutron star's surface may be no taller than what?

Fractions of a millimetre, far smaller than older estimates, because the gravity flattens anything taller. Bumps that slight make only feeble gravitational waves, and none has yet been detected from a spinning star.

A pulsar that slowly destroys its tiny partner star is nicknamed after which creature?

A black widow, after the spider said to eat its mate: the pulsar's radiation slowly boils its partner star away. Cousins with heavier partners are called redbacks, after an Australian spider with the same habit.

In a 2017 NASA test aboard the space station, a telescope timed distant pulsars to do the job of which everyday technology?

GPS, in effect: by timing the arrival of pulses from distant pulsars, the telescope worked out its own position in orbit. NASA hopes future probes will find their way through deep space like this, without help from Earth.

Which of these stars is heavy enough to end its life as a neutron star?

Betelgeuse was born with well over ten times the Sun's mass, clearing the bar of about eight, so when it explodes its core will probably be crushed into a neutron star. The other three are far too light and will end their lives quietly.

What sits beneath a neutron star's millimetres-thin atmosphere, above its solid crust?

An 'ocean' of Coulomb liquid, a fluid of bare, charged nuclei, lies there, and it is only metres to tens of metres deep. The star's spin and magnetic field shape its currents.

A 1962 rocket flight found the first known source of which radiation outside the Solar System, later traced to a neutron star?

X-rays cannot get through Earth's atmosphere, so it took a rocket to see them, and this one made the find by accident while looking at something closer to home. Team leader Riccardo Giacconi shared the 2002 Nobel Prize in Physics.

In 2024, which telescope found the best evidence yet of the neutron star left by the supernova of 1987?

The James Webb Space Telescope picked up argon gas glowing at the heart of the wreckage, energised by something hot and compact. Astronomers had been searching for the star ever since the blast was seen in 1987.