Evidence for more dark-matter-deficient dwarf galaxies found

Scientists identified 19 dwarf galaxies with less dark matter.


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The standard cosmological theory proposes that dark matter drives the formation of galaxies and the gravity wells in which they structure. Likewise, dwarf galaxies in the Local Group are also dominated by dark matter.

However, recently, it has been argued that not all dwarf galaxies are dominated by dark matter.

In a new study, scientists determined 19 dwarf galaxies with amounts of dark matter that do not conform to theory. The study presents a new evidence for more dark-matter-deficient dwarf galaxies.

For the study, scientists analyzed the data from the Arecibo radio telescope to calculate galactic weights by measuring how fast hydrogen moves around them. The higher the speed, the more mass a galaxy has.

They next added the mass of the hydrogen and all the stars (using starlight data) to come up with a total non-dark matter mass for the galaxy. The difference between this number and the total mass was attributable to dark matter.

An example of the baryonic dominated dwarf galaxies—UGC7920.(Credit: DECaLS-DR8)
An example of the baryonic dominated dwarf galaxies—UGC7920.(Credit: DECaLS-DR8)

Normally, just 2 percent of the mass of a dwarf galaxy is made up of non-dark matter. But, scientists found that one galaxy, for example, weighed in at approximately 14 billion suns, and its total non-dark matter mass made up roughly 27 percent of its total mass.

Scientists analyzed a total of 324 dwarf galaxies. Among them, 19 dwarf galaxies were found to have less dark matter than theory has suggested they should.

Scientists noted, “the “missing” dark matter might be attributed to neighbors pulling it off and keeping it to themselves—but some of the exceptions they found had no neighbors that were near enough to be considered suspects. This study has the potential to challenge the formation theory as it applies to dwarf galaxies.”

The study is published in the journal Nature Astronomy.