substance

interstellar gas

The diffuse gas in the space between stars, which can interact with cosmic rays.
65 related articles

Description

Interstellar gas is the diffuse matter that fills the space between stars in a galaxy. It consists primarily of hydrogen (atomic and molecular) and helium, with trace amounts of heavier elements, dust, and cosmic rays. This gas is the raw material for star formation and is constantly recycled through stellar birth and death. It also serves as a medium through which cosmic rays propagate, and its interactions with radiation reveal the structure and chemistry of galaxies.

History

The existence of interstellar gas was first inferred in the early 20th century from the absorption lines of calcium and sodium in starlight, and later confirmed by the detection of interstellar hydrogen via the 21-cm line in 1951.

How it works

Interstellar gas exists in multiple phases: cold molecular clouds (10–20 K), warm neutral and ionized gas (10⁴ K), and hot ionized gas (10⁶ K) from supernova remnants. Cosmic rays, high-energy charged particles, travel through this gas, ionizing atoms and exciting molecular emissions. The gas is also influenced by magnetic fields, which shape its structure and affect star formation rates.

In practice

Interstellar gas is studied using radio, infrared, and X-ray observations to map the structure of the Milky Way, identify regions of star formation, and understand the life cycle of matter in galaxies. It is also relevant to the search for complex organic molecules in space.

Fun fact

Interstellar gas is so sparse that a cubic centimeter of space contains only about one atom on average, yet it is dense enough to block visible light in some regions, creating dark nebulae.

Concept graph →

Related articles · 65

Dusty Plasma Sorts Microspheres Like Escalators of Different Heights
In a ring-shaped channel between two toothed rings, microspheres are suspended: some with a radius of 8 micrometers, others 14. The discharge is switched on, and the particles start moving. The small ones go one way, the large ones the other. It is like a shopping mall where escalators for people of different heights run in opposite directions.
Galaxies2026-08-272 minarXiv:2608.27067
Dancing Clouds: Measuring the Transverse Motion of Gas in L1688
The cloud L1688 in the constellation Ophiuchus resembles a dance floor where partners don't always hold hands. Astronomers have long assumed that gas in molecular clouds moves together with the young stars born within them.
Two Hands Painting the Sky: Supernova Remnants and Microquasars
The night sky in neutrino light resembles a canvas worked on by two hands. One holds a broad, soft brush: these are supernova remnants, the shells left behind after stellar explosions. The other grips a fine, hard pen — microquasars, binary systems where a black hole twists matter into narrow jets.
Generative AI Reconstructs Neutron Star Matter
An interpreter gets distracted by every rustle in the hall, and a one-hour meeting stretches into two. A neutron star compresses a solar mass into a sphere the size of a city, and the matter in its core is denser than an atomic nucleus. Physicists cannot probe its structure in the lab: the required pressures are unattainable.
Galaxies2026-08-141 minarXiv:2608.14023express
Dust in Galaxies: Clumps Instead of Haze
Light from a distant galaxy reaches us through its own dust. This dust is not a smooth haze but ragged clouds, like wisps of cotton. Old models treated it as a uniform mist, and then the galaxy didn't add up energetically: too much light disappeared in the ultraviolet and too little came back in the infrared. Astronomers did what a cook does when they dice a potato instead of tossing it in whole.
Galaxies2026-08-111 minarXiv:2608.10719express
A Wanderer That Feeds on the Go
A black hole with a mass of 35,000 Suns drifts through a galaxy's gas like a barge through fog. Its gravity rakes the material ahead of it, leaving a dense trail behind — a wake of gas. Some of that gas gets pulled into the black hole, and it grows.
Galaxies2026-08-102 minarXiv:2608.09587express
Neon Backlight of the Solar System
Every morning, a janitor sweeps leaves into a pile. The Sun, as it travels through the galaxy, does something similar: its gravity gathers diffuse interstellar gas into an invisible cone — a giant funnel.
Stellar2026-08-102 minarXiv:2608.09896
Planetary Kitchens: What the Pantries of Taurus Hide
In the dark kitchen of the Taurus molecular cloud, 450 light-years away, dozens of planetary systems are being prepared. Each young star is a chef, and its protoplanetary disk is a counter piled with flour-like dust and steam-like gas.
Galaxies2026-08-082 minarXiv:2608.08014express
First Light from a Tiny Builder
In a dense molecular cloud, at the edge of glowing gas, an invisible assembly line is at work. It takes simple scraps — single atoms and light pairs — and glues them together step by step into long carbon chains and rings. The first piece of this assembly line has long eluded our eyes. Now it has been found.
Chemical Physics2026-08-062 minarXiv:2608.05590express
Space Chemistry on a Grain of Sand
In dark interstellar clouds where new stars are born, chemistry starts with a tiny particle — the trihydrogen ion (H₃⁺). It collides with other atoms and sets off a cascade of reactions that build ever more complex molecules. For a long time, it was thought that the main reaction producing it, H₂⁺ colliding with H₂, only happens in the gas phase.
High Energy2026-08-041 minarXiv:2608.03858express
Dark Matter Speaks in Gamma-Ray Light
Dark matter is the invisible scaffolding of the universe. It's there, we know from the motion of stars and galaxies, but what this scaffolding is made of remains unknown. One guess is ultra-light particles similar to axions. They barely interact with ordinary matter, yet occasionally they do get involved.
Stellar2026-07-291 minarXiv:2607.26814express
Proteins from Cosmic Ice
In the black depths of space, on the surfaces of tiny icy dust grains, a quiet construction is underway. There, where temperatures drop to near absolute zero and harsh radiation abounds, the ordinary amino acid glycine, the simplest protein building block, links up with itself.
Galaxies2026-07-272 minarXiv:2607.24929
Cosmic Cross-Pollination: How Galaxies Enrich Their Neighbors with Metals
In 1,433 pairs of galaxies scattered across the sky, astronomers noticed an unusual pattern. Neighbors located 'above' or 'below' a massive stellar system contain up to a quarter more oxygen than those lying in the plane of its disk.
Galaxies2026-07-253 minarXiv:2607.22966
A Chick in a Dust Shell: How a Red Quasar Emerges
In the deep field of JWST, among thousands of galaxies, astronomers zoomed in on the source JADES-GS 209777 – and saw a cosmic chick. Its "shell" is a thick cocoon of gas and cosmic dust that long hid the growing black hole at its center. But at a redshift of 3,711 (1,8 billion years after the Big Bang), the shell began to crack.
Galaxies2026-07-233 minarXiv:2607.21719
Cosmic Searchlight in the Fog: How Quasars Illuminate Their Halos
Eight hundred million years after the Big Bang, and at the heart of a young galaxy a monstrous engine is already throbbing. A black hole with a mass of ten billion suns devours matter so greedily that its radiation should outshine everything around it. But outside, silence.
Galaxies2026-07-223 minarXiv:2607.19808
Embroidery on a Dark Canvas: How a Neural Network Creates Galaxies in Seconds
The cosmos resembles silk fabric with threads of the dark web showing through. We only glimpse tiny swatches of the real tapestry — through telescopes, in actual galaxy catalogs. To separate the fundamental signal from astrophysical noise in the cosmic pattern, statistical analysis demands thousands of plausible sketches — synthetic sky maps.
Stellar2026-07-223 minarXiv:2607.20617
The Cosmic Matryoshka: How Supermassive Stars Grow Black Holes
In the early universe, just a few hundred million years after the Big Bang, astronomers see strange objects — little red dots. They are compact, red, and in their spectra, broad Balmer lines scream the presence of supermassive black holes. But how did the hole manage to accumulate millions of solar masses in such a short time?
Galaxies2026-07-173 minarXiv:2607.15515
Star Chefs of the Early Universe: Nitrogen Excess
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.
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.
Galaxies2026-07-083 minarXiv:2607.07973
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.
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.
Exoplanets2026-06-301 minarXiv:2607.00202express
Can life travel between stars on icy comets?
Tiny seeds of life can cross the black void on icy wanderers like comet 3I/ATLAS. The James Webb Space Telescope found water and methane on it for the first time, and light analysis revealed an unusual gas composition.
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.
Exoplanets2026-06-252 minarXiv:2606.27535express
An Interstellar Visitor Wrapped in Amorphous Glass Dust
In 2019, an unusual visitor, comet 3I/ATLAS, zoomed into the Solar System. It came from another star, and for the first time, astronomers were able to see what its dusty tail is made of.
Galaxies2026-06-022 minarXiv:2606.03313
Exoplanets2026-05-311 minarXiv:2606.01377express
Interstellar Visitor Slims Down Before Our Eyes
Among the icy chunks hurtling through the void, there are special travelers — interstellar comets. They were born around distant stars and happened to wander into our neighborhood. One of them, 3I/ATLAS, came under the gaze of telescopes as it approached the Sun. Its material, frozen gases and refractory dust, began to evaporate, leaving a glowing tail behind.
Galaxies2026-05-282 minarXiv:2605.29616express
A Dusty Flare at the Heart of a Galaxy
A bonfire that no one sees, but everyone feels the warmth: that's how astronomers found a flare in a distant galaxy. Not by its light, but by the infrared radiation of heated dust. The galaxy SDSS J010320.39+140152.5 caught attention when its center suddenly blazed in the infrared, as if someone had thrown logs onto an invisible fire.
Stellar2026-05-162 minarXiv:2605.16760express
How Stars Lose Their Hydrogen Envelope
In the crowded center of the galaxy, two stars orbit so close together that one strips the outer layers off the other, like wind blowing off a coat. What remains is a hot helium core, a star without a hydrogen envelope.
Galaxies2026-05-082 minarXiv:2605.07159express
Glycine Isomer Found in Molecular Cloud Around Protostar
For nearly half a century, astronomers have been searching for glycine, the simplest amino acid and one of the fundamental building blocks of proteins, in the interstellar medium.
HEP Phenomenology2026-05-081 minarXiv:2605.08010express
Galaxies2026-04-262 minarXiv:2604.23686express
The Milky Way's Magnesium Haze Gets Mapped
A distant city seen through a fogged-up window: bright lights blur, details are lost. That's roughly how astronomers see gas with magnesium ions (magnesium) in our galaxy — the strongest spectral lines "peg the needle," preventing us from knowing how much material is really there.
Galaxies2026-04-232 minarXiv:2604.21218express
Galaxies2026-04-201 minarXiv:2604.17955express
Gas Jumps Over the Ring
A river flows toward a whirlpool, but a dam with a notch blocks the way. Most water piles up before the dam, but some, gaining height, leaps over it and falls straight into the funnel. So it is with gas in a galaxy: it streams toward the center but hits a ring of stars and gas, like a dam. Usually, everything stops there, swirling into a dense vortex.
Exoplanets2026-04-202 minarXiv:2604.18332express
Dust Halos Around Young Stars
A young star is surrounded by a flat, rotating disk of gas and dust, like pizza dough that's been spun out. Planets are born inside such a disk. But around three stars (Elias 2-24, IM Lup, and DM Tau) astronomers noticed something odd: far beyond the edge of the bright disk stretches a barely visible but enormous dust halo.
High Energy2026-04-171 minarXiv:2604.16650express
Stellar Ash
A neutron star is the remnant of an exploded star, compressed to the size of a city. On its surface, a thermonuclear fire sometimes erupts: accumulated gas explodes like a giant hydrogen bomb. After the burst, ash remains — a mixture of heavy elements that rises to the surface and forms a hot atmosphere.
High Energy2026-04-061 minarXiv:2604.04814express
Cosmic Rays Wander Between Clouds
Interstellar space is not empty: it is filled with tenuous gas, which is warm in some places and cold in others. The boundaries between such regions resemble the walls between soap bubbles.
Stellar2026-04-062 minarXiv:2604.05221express
Stars and Their Disks: The Carbon Puzzle
Two very small, cool stars, similar to the famous TRAPPIST-1, reside in the young Upper Scorpius star cluster. They are only 5–10 million years old — by cosmic standards, mere infants. Each is surrounded by a disk of gas and dust from which planets may eventually assemble.