What Is Dark Matter?

What Is Dark Matter?

By fitting a theoretical model of the composition of the universe to the combined set of cosmological observations, scientists have come up with the composition that we described above, ~68% dark energy, ~27% dark matter, ~5% normal matter. What is dark matter?

We are much more certain what dark matter is not than we are what it is. First, it is dark, meaning that it is not in the form of stars and planets that we see. Observations show that there is far too little visible matter in the universe to make up the 27% required by the observations. Second, it is not in the form of dark clouds of normal matter, matter made up of particles called baryons. We know this because we would be able to detect baryonic clouds by their absorption of radiation passing through them. Third, dark matter is not antimatter, because we do not see the unique gamma rays that are produced when antimatter annihilates with matter. Finally, we can rule out large galaxy-sized black holes on the basis of how many gravitational lenses we see. High concentrations of matter bend light passing near them from objects further away, but we do not see enough lensing events to suggest that such objects to make up the required 25% dark matter contribution.

Abell 2744: Pandora's Cluster Revealed

One of the most complicated and dramatic collisions between galaxy clusters ever seen is captured in this new composite image of Abell 2744. The blue shows a map of the total mass concentration (mostly dark matter).

However, at this point, there are still a few dark matter possibilities that are viable. Baryonic matter could still make up the dark matter if it were all tied up in brown dwarfs or in small, dense chunks of heavy elements. These possibilities are known as massive compact halo objects, or "MACHOs". But the most common view is that dark matter is not baryonic at all, but that it is made up of other, more exotic particles like axions or WIMPS (Weakly Interacting Massive Particles).

Dark Matter Goes Missing in Oddball Galaxy

Researchers were surprised when they uncovered galaxy NGC 1052-DF2 which is missing most, if not all, of its dark matter.

 

Recent Discoveries

Date	Discovery
January 8, 2020	Hubble Detects Smallest Known Dark Matter Clumps
September 9, 2019	Dark Matter in the Belly of the Whale – UGC 695
June 3, 2019	Heart of Lonesome Galaxy is Brimming with Dark Matter (Markarian 1216)
January 29, 2019	Astronomers Find Dark Energy May Vary Over Time
December 20, 2018	Faint Glow Within Galaxy Clusters Illuminates Dark Matter
July 17, 2018	From an Almost Perfect Universe to the Best of Both Worlds
June 20, 2018	XMM-Newton Finds Missing Intergalactic Material
April 18, 2018	Where is the Universe's Missing Matter?
March 28, 2018	Dark Matter Goes Missing in Oddball Galaxy Source :-https://science.nasa.gov/

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