stellar radius

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.

A light ray passing by a massive body slightly changes its direction, like a stream of water bending around a rock in a creek. In the solar system, there are many such "rocks": planets, their moons, asteroids. And each one, with its own gravity, bends the path of light coming from distant stars.

A galaxy is like a city: bright lights and dense buildings at the center, sparse lights and emptiness toward the outskirts. But if you watch how gas rotates in a galaxy's disk, you see that its speed barely drops at the edges. As if invisible neighborhoods keep the motion going. Astronomers have found a way to map this invisible city.

A cosmic "caliper" will soon measure a neutron star to within a hundred meters. For an object a couple dozen kilometers across, that's like measuring the thickness of a human hair from a kilometer away. A neutron star is the remnant of an exploded supernova.

Betelgeuse, the red supergiant familiar from Orion's shoulder, keeps surprising us. After the mysterious Great Dimming of 2019–2020, when the star suddenly dimmed, it didn't just recover; it changed its ways.

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 neutron star is the collapsed core of a massive star, squeezed to the size of a city. A teaspoon of its material weighs as much as a mountain. But inside this superdense sphere, a surprise may lurk: under unimaginable pressure, neutrons break apart into quarks, giving the star a new, more compact core.

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.

When the James Webb Space Telescope turned its gaze deep into time, astronomers expected to see familiar galaxies. Instead, the images were dotted with a scattering of bright, incredibly compact red dots.

A regular rangefinder sends a single light pulse and waits for it to return — like a person shouting into the void and listening for an echo. But if you use multiple sources that glow in unison, and analyze not the volume but the rhythm of the echo of reflected flashes, the picture becomes sharper.

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.

Hydrogen is the most common element. Its atoms are like antennas: they emit and absorb light at very specific frequencies. Einstein predicted that spacetime can ripple: these are gravitational waves.

Edwin Hubble and Georges Lemaître discovered the expansion of the Universe nearly a century ago. One way to test it is the surface brightness test: in an expanding cosmos, the light of a distant galaxy should fade like a pattern on a stretching film.

A galaxy is like a glowing pancake studded with stars. If you look at it face-on, you see everything at once — both the bright spiral arms and the dark dust lanes. But tilt the pancake, and the picture changes: layers overlap, light blends together. This very effect, it turns out, creates the illusion of a tight link between radio and gamma-ray emission in distant star systems.

At the center of the Milky Way lurks something invisible but extremely massive — about four million times heavier than the Sun. It is usually called a black hole and designated Sagittarius A*. But astronomers are not letting their guard down: what if it is not a hole but something more exotic, like a giant ball of ultralight particles — a boson star?

The halo of our Galaxy is a huge, sparse cloud of old stars that envelops the familiar disk. It holds the story of how the Milky Way grew by gobbling up neighboring dwarf galaxies.

The universe keeps a tally of every newborn star. Over 13.8 billion years, galaxies have ignited so many stars that their 'census' can reveal the nature of the cosmos itself, just as tree rings reveal past climates.

In the vast cosmic web, the James Webb Space Telescope spotted something unusual — tiny but bright red sparks that astronomers have nicknamed 'little red dots.' They shine as if an invisible fire is raging inside: their spectrum looks like a letter V, and the hydrogen lines are broadened, as if someone smeared paint across a canvas.

The night sky looks still, but many stars tremble like a drum after a strike. For seven straight years, the TESS satellite stared at the same patches of sky and caught this trembling in 19,151 red giants — old, bloated stars. Previously, far fewer of these 'singing' giants were known, and now the list has grown by 80%.

Every molecule is like a set of building blocks: the same pieces can be assembled in different ways. Two assemblies with the same atoms but different geometry are called isomers. If one can be turned into the other by a simple rotation around a bond, they are conformers, like a bent arm versus a straight one.

The Sun is not a perfectly steady lightbulb. Its brightness quivers slightly: it dims a bit, then brightens. For Earth's climate, even slow variations stretched over thousands and millions of years matter. They could have left their mark in the geological record of the last 540 million years. Astronomer [scientist:A. M.

Light from distant stars, as it travels through cosmic dust, loses some of its energy. Dust grains absorb and scatter light, and the way they do so at different wavelengths reveals their composition and size. Astronomers call this the dust extinction curve.

A galaxy is like a giant merry-go-round: stars and gas whirl around the center, and their speeds reveal how much stuff is on the ride. If we only saw the luminous matter, the outer parts would spin slower than observations show. So there must be invisible mass, dark matter, that holds the galaxy together.

A star like the Sun doesn't just shine: it hums quietly. Inside, plasma churns, and these motions make the surface rise and fall rhythmically. Catching such a tremor from Earth is nearly impossible: it gets lost in the noise of the atmosphere and the instrument itself. That's why astronomers listen to stars from space, where it's quieter.

The gas in a galaxy glows like a neon sign, and by the color of that glow, astronomers can tell how hot it is. The logic is simple: the more heavy elements (which astronomers call metals) in the gas, the better it cools. So galaxies rich in metals should have cooler gas. But new observations show the opposite.

If you build a giant blanket around a star, you get a Dyson sphere. It absorbs all the radiation and glows in invisible heat rays. No such sphere has been seen yet, but astronomers know: to find it, look for this thermal glow.

Two spotlights placed side by side: from a distance, their light blends into one patch, and it seems there's a single source. The same happens in space: about 10–20% of faint stars are actually close pairs of identical stars. Individually, they can't be resolved, but together they shine noticeably brighter than a single star with the same parameters.

A planet hugging its star is like an ice cube forgotten on a scorching skillet. The ice melts and evaporates, except instead of water, it's hydrogen and helium from the planet's upper layers.

If you spill a handful of colorful beads on the floor, they will land differently: some will clump together, others will scatter into corners. Roughly the same way, galaxies of different colors (blue, green, and red) are scattered across the universe. Scientists decided to measure how 'clumpy' their distribution is using a number called the fractal dimension.

A radio telescope has caught signals from three galaxies that existed when the universe was less than a billion years old. Their radio glow is so powerful that each seems to be birthing a thousand suns per year in a short span. For comparison, our Milky Way produces only a couple of stars per year.

Light from a streetlamp passing through blinds flickers: the stripes shift, and brightness rises and falls. From that rhythm, you can guess how wide the lamp is. The new method for measuring stars works similarly: instead of capturing a sharp image, astronomers monitor the "twinkling" of light collected by two or more telescopes simultaneously.

At night, the sky is never completely black. Even far from cities, the upper atmosphere glows faintly: sunlight makes hydrogen atoms emit a reddish glow that astronomers call geocoronal emission. For a telescope, it's like a fogged-up window: it adds extra light and hinders seeing distant galaxies.

In the dark clouds of interstellar gas where stars are born, matter gathers into dense knots — future cradles of stars. Astronomers measure distances between these knots from sky photographs, but a photograph is flat while the cloud is volumetric. Converting from plane to volume is not as simple as it seems.

Light from a distant source passing near a neutron star bends like a flashlight beam in a funhouse mirror. Astrophysicists ran a numerical experiment: they traced rays backward from the observer to the star and looked at what picture a telescope would see.

Dust in space is not just grime: it's the raw material for future stars and planets. But how it is distributed in our galaxy has long been a puzzle: dust is hard to measure directly, and it blocks the light of distant stars. Now astronomers have peered through this veil using data on five million stars: their brightness, color, and precise positions in the sky.

The James Webb Space Telescope peered 11 billion years back in time and spotted galaxies turned edge-on toward us. To measure their thickness, scientists devised a clever method: they calculated it the same way you'd measure the thickness of a slightly tilted pancake, not a perfectly flat one. Previous estimates were imprecise because they assumed an ideal angle.

Betelgeuse is a giant star ready to explode as a supernova. But it may not be alone: a small companion star, Sivarkha, circles in a tight orbit. Every 2000 days, it plunges through Betelgeuse’s outer layers, like a boat cutting through water, leaving waves of superheated gas.

Fast radio bursts are brilliant cosmic flashes that, like a starting signal, set off a race of radio waves across the universe. Astronomers used them as a natural laboratory to test whether the photon, the quantum of light and the carrier particle of the electromagnetic interaction, has mass.

The galaxy NGC 1560 is a modest island of stars and gas ten million light-years away. Its rotation curve, first measured in 1991, became an icon for those seeking an alternative to dark matter. The plot of rotation speed versus radius shows bends that seem to exactly mirror the bends in the distribution of ordinary matter.

The Solar System takes 210 million years to complete one orbit around the center of the Milky Way. The last time we were on this same side of the Galaxy, early dinosaurs were roaming the Earth. That number, 243.72 km/s, has now been refined thanks to rare stars that streak through the Galaxy like cannonballs.