Dark matter is likely ‘cold,’ not ‘fuzzy,’ scientists report after new simulations

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July 24, 2017








Dark matter is the aptly named unseen material that makes up the bulk of matter in our universe. But what dark matter is made of is a matter of debate.
Scientists have never directly detected dark matter. But over decades, they have proposed a variety of theories about what type of material — from new particles to primordial black holes — could comprise dark matter and explain its many effects on normal matter. In a paper published July 20 in the journal Physical Review Letters, an international team of cosmologists uses data from the intergalactic medium — the vast, largely empty space between galaxies — to narrow down what dark matter could be.
The team’s findings cast doubt on a relatively new theory called “fuzzy dark matter,” and instead lend credence to a different model called “cold dark matter.” Their results could inform ongoing efforts to detect dark matter directly, especially if researchers have a clear idea of what sorts of properties they should be seeking.
“For decades, theoretical physicists have tried to understand the properties of the particles and forces that must make up dark matter,” said lead author Vid Iršič, a postdoctoral researcher in the Department of Astronomy at the University of Washington. “What we have done is place constraints on what dark matter could be — and ‘fuzzy dark matter,’ if it were to make up all of dark matter, is not consistent with our data.”

A depiction of hydrogen gas within the intergalactic medium, or IGM, with bright areas indicating high gas density.Vid Iršič

Scientists had drawn up both the “fuzzy” and “cold” dark-matter theories to explain the effects that dark matter appears to have on galaxies and the intergalactic medium between them.
Cold dark matter is the older of these two theories, dating back to the 1980s, and is currently the standard ...

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