dark matter

American  

noun

1. a hypothetical form of matter invisible to electromagnetic radiation, postulated to account for gravitational forces observed in the universe.

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dark matter British  

noun

1. astronomy matter known to make up perhaps 90% of the mass of the universe, but not detectable by its absorption or emission of electromagnetic radiation

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dark matter Scientific  

1. Matter that emits little or no detectable radiation. Gravitational forces observed on many astronomical objects suggest the significant presence of such matter in the universe, accounting for approximately 23 percent of the total mass and energy of the universe. Its exact nature is not well understood, but it may be largely composed of varieties of subatomic particles that have not yet been discovered, as well as the mass of black holes and of stars too dim to observe.

2. Also called missing mass

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dark matter Cultural  

1. Unseen matter that may make up more than ninety percent of the universe. As the name implies, dark matter does not interact with light or other electromagnetic radiation, so it cannot be seen directly, but it can be detected by measuring its gravitational effects. It is believed that dark matter was instrumental in forming galaxies early in the Big Bang.

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Usage

What does dark matter mean? Dark matter is speculated to be a type of matter that cannot be directly observed. It has an unknown nature, a high mass, and astronomers hypothesize that it makes up much of the universe. How is dark matter pronounced?[ dahrk mat-er ]

Closer Look

What is the universe made of? We know that galaxies consist of planets, stars, and huge gas and dust clouds—all of these objects are observable by the radiation they give off, such as radio, infrared, optical, ultraviolet, x-ray, or gamma-ray radiation, and all can be observed using various kinds of telescopes. But there are reasons to suspect the existence of far more matter than this, matter that is not directly observable. Evidence for such dark matter comes from observations of certain gravitational effects. For example, astronomers have found that galaxies rotate much faster than they would be expected to rotate based solely on their observable mass—in fact, they should be flying apart. One explanation for this apparent anomaly is to assume that the galaxies have much more mass than we can see, and this invisible mass holds them together gravitationally. Various theories of the composition of this invisible dark matter have been proposed, from exotic yet-to-be discovered particles to planet-sized objects made of ordinary matter that are too small or far away to be detected by present-day instruments. But none of these theories are entirely satisfactory, and the fundamental question of what makes up most of the universe remains unanswered.

Etymology

Origin of dark matter

First recorded in 1985–90

Example Sentences

Some of the unseen matter we attribute to dark matter could, in fact, be made of such relics.

From Science Daily • May 22, 2026

Out of the 28 strongest signals examined, GW190728 was the only event that showed agreement with the dark matter scenario.

From Science Daily • May 19, 2026

“Living in the deepest corners of our vast cosmos or our mathematical constructs,” the authors write, are still-unsolved scientific mysteries, including dark matter and dark energy.

From The Wall Street Journal • May 19, 2026

"The statistical significance of this is not high enough to claim a detection of dark matter, and further checks should be performed by independent groups," Aurrekoetxea says.

From Science Daily • May 19, 2026

I rushed back to my room, skirting past my parents and their ever-growing dark matter, and got to work on mapping out a plan.

From "Sir Fig Newton and the Science of Persistence" by Sonja Thomas