neutron star mass limit

Pulsar PSR J0614-3329 spins 318 times per second. A point on its equator moves at about 10% of the speed of light. From a distance, the star looks like a lighthouse spinning so fast that its beam blurs into a continuous ring.

It's like a sprint record: to break it, you need a perfect run-up. But for sub-millisecond pulsars, the run-up is too short. The fastest known pulsar, PSR J1748-2446ad, spins 716 times per second — faster than a kitchen blender. If it were the size of Earth, a point on its equator would move at about 0.24 times the speed of light. But why doesn't any pulsar spin even faster?

A sculptor shapes mountains from magnetic fields and heat, but the stone resists. A neutron star, the ultra-dense remnant of a supernova explosion, in a binary system pulls matter from its companion star. This infalling matter heats the star's crust unevenly, while the magnetic field tugs from within.

Atomic batteries powered by plutonium decay have been running pacemakers and space probes for over sixty years. But the raw material is scarce: worldwide, only a few kilograms of plutonium-238 are produced each year, barely enough for the most critical missions.

A campfire that doesn't go out all at once but smolders for hours because the wood inside still holds the heat of the past flame. That's roughly how the memory effect works for black holes. Normally, a tiny black hole with the mass of a mountain should evaporate in fractions of a second, scattering particles like sparks.

The merger of two neutron stars is not just a collision. Even before they touch, they deform each other through tidal forces, and this deformation depends on how 'soft' or 'stiff' the matter inside is. Stiff matter resists more; soft matter changes shape more easily.

The most massive stars are like overinflated balloons: their envelope stops stretching and instead begins to furiously vent material. At a certain stage, the mass loss becomes so intense that the star stops growing in size. Astronomers see this moment as a kink in the diagram where stars are sorted by luminosity and temperature.

A supernova explosion blasts off the outer layers of a dying star. What remains is the core — a neutron star, packed into a sphere the size of a city. The existence of such stars was predicted back in 1934 by Fritz Zwicky.

Through three minutes after the Big Bang, the Universe played its first symphony. It was the big bang nucleosynthesis — the formation of light nuclei, where each element sounded its own note, and the tempo was set by the expansion of space.

In August 2019, the LIGO and Virgo detectors picked up gravitational waves from the merger of two compact objects in a binary star. One weighed 23 solar masses — a standard black hole. The other came in at 2.5–2.67 M⊙.

The universe cooled like a giant bathtub after a hot start. At 400 000 years after the Big Bang, hydrogen was ready to recombine — protons capturing electrons to become neutral atoms. But somewhere in this dark water, a tap kept dripping.

For thirteen billion years, light battled through cosmic emptiness. It bent around massive galaxy clusters that, as Einstein predicted, acted as giant lenses — amplifying and distorting the distant glow. In 2023, the NIRSpec instrument on the James Webb Space Telescope captured this light and spread it into spectra.

Dark matter is invisible to telescopes, but its gravity was revealed half a century ago by Vera Rubin. Since then, physicists have explored dozens of hypotheses, and one of the most elegant is primordial black holes, formed in the first moments after the Big Bang.

Dark matter remains the inaudible bass line of the cosmic symphony — it emits no light, but its gravitational pull shapes galaxies. Vera Rubin first caught this rhythm in the 1970s by observing the rotation of stars.

In 2021, the LHAASO observatory registered gamma quanta with energies above a petaelectronvolt from sources like the Crab Nebula — a supernova remnant with a pulsating neutron star at its heart.

Cosmology is like an orchestra where different sections suddenly start playing out of sync. Measurements of the universe's expansion rate (the Hubble constant) from the early and late universe give different numbers.

Think of a merry-go-round: it's easier to spin a light one, harder to spin a heavy one. Neutron stars, the ultra-dense remnants of exploded stars, behave in a similar way. Astronomers looked at fifty binary systems where one neutron star orbits another and noticed: the heavier the star, the longer its spin period. The link isn't strict, but it's statistically noticeable.

A teaspoon of neutron star matter weighs as much as a mountain. But this mountain may have an invisible twin. Deep inside a neutron star, ordinary matter is compressed to unimaginable densities. There, protons and neutrons can dissolve into a quark soup.

A hot infant and a cold adult — the same neutron star looks different. Just born in a supernova explosion, it is scorching hot at tens of billions of degrees. But as time passes, it cools, contracting like cooling metal. For the star PSR J1012+5307, this transition means an almost twofold reduction in radius.

Neutron stars are the final chord in the evolution of massive suns. Born in the cataclysm of a supernova, they pack a mass comparable to the Sun's into a sphere the size of an earthly metropolis.

A neutron star is the core left behind after a massive star explodes. Its matter is so compressed that a teaspoonful would weigh billions of tons. But the exact size and mass of such objects remain debated. A team of astronomers studied the system EXO 0748-676, where a neutron star pulls matter from a normal companion star. It occasionally flares up and then quiets down.

Hidden in the globular cluster Terzan 5 is the binary system IGR J17480-2446. One of its members is a neutron star that behaves strangely. It spins at just 11 hertz (11 revolutions per second) and cools suspiciously slowly after an outburst. Usually, such stars spin hundreds of times faster and cool briskly — here, it's the opposite.

In the depths of a neutron star, the remnant of an exploded star, matter is compressed so tightly that a teaspoon would weigh billions of tons. Within this superdense material, a special kind of force might be at work, one that affects only muon and tau neutrinos.

The Sun is a giant nuclear reactor that continuously sends us light and heat. But it also has another, almost silent postal service: every second, tens of billions of neutrinos, ghostly particles born in the thermonuclear furnace, fly through a square centimeter of your palm. Most of them leave no trace.

A giant baby planet is still pulling in leftover building material from its surrounding cloud. That's the scene the Hubble Space Telescope captured when it aimed its cameras at an object catalogued as SR 12 c. This companion planet orbits a young star at a wide distance — farther out than Neptune is from the Sun.

Atomic nuclei are rarely perfect spheres. More often, they resemble a slightly squashed ball — the electric charge inside is unevenly distributed, and protons may shift a bit, creating a tiny 'pear-shaped' bulge.

The universe is full of the invisible. We know about dark matter from galaxy rotation and gravitational lensing, but its nature has eluded us for a century.

A neutron star is a gravitational lens that focuses our attempts to glimpse dark matter. Through its ultra-dense matter, like exotic glass, we search for the axion — an elusive particle that could explain the hidden mass of the universe.

Somewhere in the galactic bulge, a massive star lies dormant, ready to trade quiet burning for collapse. Its core will exhaust its fuel, and in a fraction of a second, a neutron star or black hole will be born, releasing 10⁵⁸ neutrinos — almost all the energy of the explosion.

Cosmic black holes at the centers of galaxies are like giant banyan trees: their aerial root‑filaments stretch for kiloparsecs to harvest nourishing matter. For decades astronomers have debated: how does cooling gas from cluster atmospheres fall into the sphere of influence of a supermassive hole?

A lump of dark matter drifts through the void — invisible, almost intangible. No one knows what it's made of, but a new study suggests viewing it as a drop of quantum liquid. Two kinds of fermion particles — call them "heavy" (ψ) and "light" (χ)—exchange signals via a third mediator particle (φ), like floats tied to a single line.

Deep underground in Japan, a huge tank of ultrapure water waits for rare visitors — neutrinos arriving from distant stellar explosions. Such guests are few and far between: over years of observation, Super-Kamiokande registers only a handful of events.

A neutron star is a city the size of Manhattan, compressed to such a density that a teaspoon of its material weighs as much as Mount Everest. To understand what it's made of inside, scientists measure its radius. But there's a catch: many measurements suffer from systematic errors, like trying to measure the height of someone who keeps fidgeting and bending over.

A figure skater pulls their arms in, and their spin suddenly accelerates. When a massive star exhausts its fuel and its core collapses, something similar happens, but on a cosmic scale. The core shrinks to a city-sized sphere, and if it is spinning rapidly, a peculiar instability can arise.

The universe is filled with invisible dark matter. Just as a drop of water, as it evaporates, leaves behind a tiny salt crystal, so too can a black hole evaporate, leaving behind a minuscule stable remnant.

At the heart of our stellar metropolis — the Galaxy — lurks the supermassive black hole Sagittarius A*. Around it, star S2 whirls in a swift dance. But its movements reveal more than just the hole's pull: an invisible partner joins the dance — dark matter.

For a long time, a void yawned in the family of ultra-dense remnants of dead stars. Neutron stars, swift city-sized tops, rarely weigh more than two Suns. Black holes start at about five solar masses. Between them lies a 'gap' where for decades no object could be found.

A sugar cube weighs about a gram. But a black hole that could hide inside such a cube would weigh as much as a small mountain — billions of tons. Yet even such tiny things, born in the first instants after the Big Bang, should have vanished long ago.

In the standard picture, black holes are the undisputed density champions: all their matter is squeezed into a single point. Imagine the entire mass of Mount Everest packed into a grain of salt. But physicists have found a theoretical trick.

A giant tank of ultrapure water sits deep underground in Japan. Its walls are lined with thousands of light-sensitive sensors that catch faint flashes — the traces of ghostly particles passing through the water.