object

open cluster

A loosely bound group of young to intermediate-age stars found in a galaxy's disk.
101 related articles

Description

An open cluster is a group of stars born together from the same giant molecular cloud, typically containing from a few hundred to a few thousand members. These stars are loosely bound by gravity, so they drift through the disk of a galaxy together for hundreds of millions of years before gradually dispersing. Open clusters are found almost exclusively in the spiral arms and disk of galaxies, where gas and dust are dense enough to form new stars.

History

The first open cluster cataloged was the Pleiades, known since antiquity, but the concept of a physically related group of stars was established by the French astronomer Messier in the 18th century. The term 'open cluster' came into common use in the early 20th century as astronomers distinguished these loose groups from the denser, more tightly bound globular clusters.

How it works

Open clusters form when a large cloud of gas and dust collapses under its own gravity, fragmenting into many individual stars that share a common motion through space. The cluster's gravity holds the stars together, but it is weak compared to the tidal forces from the galaxy's overall mass distribution. Over time, encounters with giant molecular clouds and the differential rotation of the galaxy pull the cluster apart, scattering its stars into the general stellar population.

In practice

Open clusters serve as natural laboratories for studying stellar evolution, since all their stars share the same age and chemical composition, allowing astronomers to test models of how stars change over time.

Fun fact

The Hyades cluster, the nearest open cluster to Earth, is so spread out that its stars are currently passing through the constellation Taurus, and the cluster's core is already dissolving.

Concept graph →

Related articles · 102

Galaxies2026-08-303 minarXiv:2608.29637
A Star Cluster That Moved Out of the Galactic Core
A resident of a bustling city center one day packs a suitcase and moves to a quiet suburb. The same happens to galactic clusters, except instead of a suitcase, they have stars, and instead of a move, they have billions of years of drifting across the disk. Berkeley 36 is an open cluster, that is, a group of stars born together from a single cloud.
Galaxies2026-08-303 minarXiv:2608.29637
A Star Cluster That Moved Out of the Galactic Core
A resident of a bustling city center one day packs a suitcase and moves to a quiet suburb. The same happens to galactic clusters, except instead of a suitcase, they have stars, and instead of a move, they have billions of years of drifting across the disk. Berkeley 36 is an open cluster, that is, a group of stars born together from a single cloud.
Galaxies2026-08-263 minarXiv:2608.25673
Spirals with Quenched Cores: The Reverse Evolution of Galaxies
An old city gains new suburbs. In the center, narrow streets where life has nearly stopped, while on the outskirts construction is booming. That is what a spiral galaxy looks like when its core stars have long aged and new stars are still being born in the outer disk.
How a Neutron Vortex Gathers a Bouquet of Magnetic Filaments
Deep inside a neutron star, where matter is compressed to the density of an atomic nucleus, neutrons form a superfluid and protons form a superconductor. A neutron vortex is a quantized vortex in the superfluid, akin to a miniature whirlpool that cannot stop spinning.
A Pressure Cooker with Three Settings: How Disk Gas Forged the First Rocks
Three cabinets full of rocks. In one, metallic grains and the gray mineral enstatite; in the second, the same grains but with rusty streaks; in the third, layered clays swollen with water. All three sets were pulled from meteorites that fell to Earth: chondrites. They were born in the same gas-and-dust disk around the young Sun, yet somehow turned out so different.
Galaxies2026-08-191 minarXiv:2608.19326express
A Faint Ghost Galaxy in the Virgo Cluster
The night sky only looks black: telescopes reveal millions of galaxies, but some are so dim they blend into the background. Astronomers caught just such a "nearly invisible" one by chance while observing the Virgo Cluster with the two-meter telescope at Teide Observatory. The galaxy is named TTT J1237327+143535.
Galaxies2026-08-182 minarXiv:2608.17375express
Faint Galaxies Reveal Their Stellar Secrets
Faint galaxies scattered across the Perseus cluster are like ghosts among their bright neighbors. They are so diffuse that distant objects shine through them, and they contain hundreds of times fewer stars than our Milky Way.
Stellar2026-08-121 minarXiv:2608.11940express
How to Read a Star's Past from Its Chemical Makeup
Two stars circle each other like dancers who come together and drift apart. Over time, one swells, and its outer layers spill onto its neighbor. The star that receives foreign matter looks no different from a single star, but its surface remembers everything.
Exoplanets2026-08-032 minarXiv:2608.02204express
Exoplanets2026-07-301 minarXiv:2607.27765express
The Stellar Forge: A First Glimpse at the Birth of Cosmic Crystals
In the furnace of star formation, the heat reaches 900 degrees Celsius, like a glowing blast furnace. It is in this hellish heat that cosmic crystals are born. Astronomers have for the first time caught the moment when crystalline dust appears right during an accretion flare (when the star gobbles up surrounding gas) at the very young star EC 53, still cocooned in dense gas.
Galaxies2026-07-283 minarXiv:2607.26136
Cluster Crucible: Random Forest Identifies Returning Galaxies
Galaxy NGC 4254 lies 1.5 million light-years from the center of the Virgo cluster. It drags a long stream of cooling hydrogen — a sign that it's plowing headlong into the hot gas. Losing cold fuel quenches the birth of new stars.
Galaxies2026-07-282 minarXiv:2607.26205
Gravitational Rudder: How a Gas Disk Rips Binary Stars Apart in the Galactic Center
A gas disk with a mass of four hundred thousand suns encircles the black hole at the center of the Milky Way. Its gravity works like a gravitational rudder: slowly but inexorably turning the orbits of binary stars, driving them into the region where tidal forces tear the pair apart.
Galaxies2026-07-282 minarXiv:2607.26330
Contour Map of Stellar Nurseries: Computer Vision Finds Clusters in the Fireworks Galaxy
In the spiral galaxy Fireworks Galaxy — 6410 stellar nurseries. That's how many regions where massive stars are being born right now were identified by an algorithm on old ultraviolet radiation images from the Edwin Hubble. These aren't just blobs in a picture — each has a clear boundary, like a country on a contour map.
Stellar2026-07-242 minarXiv:2607.22060express
The Pulse of Young Stars Runs Hotter Than Expected
A young star cluster resembles an orchestra before a concert: each instrument tunes up in its own way, and the overall hum seems like chaos. But if you listen closely, you can pick out individual notes.
Cosmic Avalanches: How Vortex Traps Shape Pulsar Glitches
89 milliseconds. That's how long a vortex avalanche lasts that abruptly speeds up the rotation of the Vela pulsar — one of the most famous 'glitching' pulsars. Pulsars are rapidly spinning neutron stars born in the collapse of supernovae.
Galaxies2026-07-212 minarXiv:2607.19471express
Why Some Galaxies Are Blue and Others Red
Two cities endure a series of fires. In one, the wind carries ash far beyond the outskirts, leaving the sky clear. In the other, ash settles as a dense veil, painting sunsets crimson. Roughly the same thing, just on a galactic scale, happens with supernova explosions, the final flares of massive stars.
Galaxies2026-07-212 minarXiv:2607.19537express
How Scars on the Disk Reveal a Galaxy's Past
A galactic disk is like a frozen ripple on water: every disturbance leaves a trace that can be read billions of years later. When a dwarf satellite galaxy flies past or a head-on merger occurs, stars in the disk start to oscillate, like bobbers rocked by a wave.
Cosmology2026-07-153 minarXiv:2607.14034
Super-magnified stars: How ripples on the light ocean reveal dark matter's secrets
In 2016, astronomers saw something incredible: a distant star, named Icarus, flared up for several weeks, crossing the abyss of space. Gravitational lensing, an effect predicted by Einstein, had kicked in: a massive object bends spacetime and focuses light like a giant magnifying glass.
Galaxies2026-07-124 minarXiv:2607.10863
Symphony of Stellar Memory: How Chaos Preserves Galactic History
The formation of the Milky Way is a grand cosmic performance, in which mergers of satellite galaxies were woven into a single score. Each event left a trace in the dynamics and chemical composition of stars, much like notes capture the composer's intent.
Stellar2026-07-113 minarXiv:2607.10452
Local Big Bang: Explosive Outflows at the Birth of Massive Stars
In the quiet of cold molecular clouds, where interstellar gas under gravity condenses into dense clumps, the birth of massive stars is one of the great puzzles of astrophysics.
General Relativity2026-07-102 minarXiv:2607.09201express
Tiny Black Holes Build Giants
The James Webb Space Telescope peered into an era when the universe was less than a billion years old and spotted strange objects—'little red dots.' These are black holes with masses of millions of suns, but in very compact, chemically pristine galaxies. Standard scenarios can't grow such heavyweights that early.
Galaxies2026-07-064 minarXiv:2607.04942
Stellar Nurseries in the Jet's Shadow: JWST Explores Centaurus A
The cosmic spectacle unfolds on the stage of Galaxy галактики Centaurus A. In the lead role: a supermassive сверхмассивная чёрная дыра with a powerful jet that pierces space for hundreds of thousands of light-years.
The Forge of Black Holes: Stellar Mergers as a Source of Spin
In the heart of a dense star cluster, a true forge reigns: here stars, like glowing blanks, collide and merge under gravity, and these mergers are not a catastrophe but an opportunity. Each strike of the stellar hammer transfers spin to the future black hole.
Galaxies2026-07-063 minarXiv:2607.05509
Globular Clusters: A Palimpsest of Ancient Gas Clouds
Imagine an ancient manuscript, where a new story is written over an old text. Over time, the upper layer wears thin, and lines of the past show through. That’s exactly how globular clusters, the oldest stellar systems in the Universe, are structured, like a palimpsest.
How a Neural Network Combine Harvests Stellar Sprouts Across Hundreds of Thousands of Galaxies
In the young Universe, about ten billion years ago, galaxies resembled endless fields after a thunderstorm: everywhere, giant — thousands of light-years across — clumps of star formation were boiling up, where young stars were born with unbridled energy. Today, these patches are an almost vanished species: in nearby galaxies, raucous hotbeds are rare.
Galaxies2026-07-053 minarXiv:2607.04216
Quasi-interstellar objects: when the Solar System meets its own exiles
Remember the sensational comet 1I/‘Oumuamua — the first object to come to us from another star? Its hyperbolic trajectory left no doubt: it was a wanderer from the interstellar void. But astronomers wondered: could some of these visitors not be strangers at all, but our own, escaped from the Solar System millions of years ago?
Galaxies2026-07-013 minarXiv:2607.00982
The Hourglass of an Ancient Galaxy: JWST Spots Maturity That Arrived Too Soon
When we peer deep into space, we see the past. Edwin Hubble’s law turns redshift into a time machine: light from galaxy UDS 12999 traveled to us for 7.6 billion years — more than half the age of the Universe.
The Smoking Gun of Hierarchy: Black Holes Betray Their Ancestors
A detective story unfolded in the GWTC-5 catalog. Hundreds of signals from merging black holes, captured by the detectors of Rainer Weiss and his colleagues, held the secret to the origin of the most massive and rapidly spinning stellar-scale objects.
Galaxies2026-06-292 minarXiv:2606.30078express
Dark Matter Waves Stir Stars in Dwarf Galaxies
At the center of a tiny galaxy lies a dense clump of stars and dark matter. This clump, called a soliton, is not frozen in place: it quivers and oscillates like jelly on a plate.
Stellar2026-06-283 minarXiv:2606.29435
Cosmic Rings: How M92 Preserved the Memory of Supernovae
Imagine a forest planted in a single day. At first glance, all trees look alike, but their cross sections tell different stories: some grew on clean soil, others on the ashes of ancient fires.
The Quantum Tango of Neutrons: The Dineutron on the Edge of Stability
In nuclear physics, the belief long reigned that two neutrons cannot form a bound state — they attract too weakly and immediately fly apart. However, on the surface of neutron-rich nuclei, where the matter density drops to a thousandth of normal nuclear density, the situation changes dramatically.
High Energy2026-06-171 minarXiv:2606.19445express
Young Stars: Gamma Rays from Jets
Stars are born in cold clouds of cosmic dust and hydrogen. Inside these cocoons, protostars — the cores of future suns — were long thought to be just hot clumps. But it turns out many of them are powerful accelerators: they shoot out narrow jets of gas that, slamming into surrounding matter, produce invisible gamma-ray light.
Galaxies2026-06-162 minarXiv:2606.18350express
A Black Hole in a Stellar Beehive
For 23 years, Hubble and James Webb have peered into the heart of Omega Centauri, a globular cluster where millions of stars crowd into a space just 150 light-years across. In this stellar beehive, the motion of the stars betrayed an invisible partner: a main-sequence star (one that has not yet left the main evolutionary branch) seemed to be tugged in a dance with an unseen weight.
Exoplanets2026-06-091 minarXiv:2606.11292express
How a Neptune-like planet flipped its star
A planet the size of Neptune wandered too close to its star. The star begins to pull the planet's outer layers onto itself — gas streams off the planet like water from an overflowing bucket. This process is called Roche-lobe overflow (astronomers use this term for the boundary beyond which a star can tear material away from a planet).
Galaxies2026-06-054 minarXiv:2606.07357
The Cosmic Hump: How a New Spectrum Creates Massive Galaxies at the Dawn of Time
The Universe is singing. Not in the usual sense: its symphony is recorded in tiny density variations from which galaxies and ourselves grew. After the Big Bang, space was almost uniform, but quantum fluctuations during inflation left a faint pattern — slightly more matter here, slightly less there.
Galaxies2026-06-033 minarXiv:2606.04462
Gaia Sausage — A Palimpsest: Four Ancient Mergers that Rewrote the Galaxy's Heart
The stellar halo of the Milky Way is a galactic palimpsest: an ancient manuscript where earlier layers lie hidden beneath the visible text. For a long time, the Gaia-Sausage-Enceladus (GSE) structure was thought to be the final entry in this manuscript, the scar of a single catastrophic merger.
High Energy2026-05-293 minarXiv:2605.31362express
Cosmic Winds Dance in Step
In an orchestra, each musician plays their own part, but at a certain moment all instruments pause on a single note. Cosmic rays behave somewhat like this — particles flying toward us from distant stars.
Stellar2026-05-282 minarXiv:2605.29904express
A Cradle Carved by Light
In the heart of the Eagle Nebula, about 7000 light-years away, three giant pillars of gas and dust rise — the Pillars of Creation. Their shape is familiar to many from Hubble Space Telescope images. Now, Webb's infrared camera has allowed us to peer inside these dense cocoons where stars are born.
High Energy2026-05-212 minarXiv:2606.02593express
Stellar Wanderers in the Mass Gap
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.