Dark Matter Punched Gargantuan Holes Through a Jet Stream of Stars

We can't see dark matter, but we can see the havoc it wreaks.

V. Belokurov, D. Erkal, S.E. Koposov (IoA, Cambridge)

Scientists from the University of Cambridge have discovered a pair of incredibly massive holes punched through a trail of Milky Way galaxy stars — and they think big clumps of dark matter were responsible.

The globs of dark matter that did the deed are insanely large — about one million to 100 million times the mass of the sun — and yet are the smallest bits of dark matter scientists have detected yet, according to a new study uploaded to the arXiv repository and last updated Wednesday.

Don’t take that literally — dark matter, for those who might not know, has never been directly observed, even though it comprises about 85 percent of the known universe. The reason we know dark matter exists is because it’s the only way to explain some of the weird gravitational effects influencing big celestial bodies in the universe.

Moreover, it’s the only way to explain exactly how an otherwise elegant stellar stream in the Palomar 5 globular cluster — itself 5,000 times the mass of the sun and 30,000 light-years long — possesses a bunch of vacant splotches.

The results, submitted to the Monthly Notices of the Royal Astronomical Society, could be critical in helping scientists actually characterize dark matter. The research team ran some calculations based on the new data that suggests dark matter is more massive and slower moving than we previously imagined.

“While we do not yet understand what dark matter is formed of, we know that it is everywhere,” said Denis Erkal from Cambridge’s Institute of Astronomy, the paper’s lead author, in a news release. “It permeates the universe and acts as scaffolding around which astrophysical objects made of ordinary matter — such as galaxies — are assembled.”

A dark matter clump blasting through a stellar stream would presumably create a gap that’s proportional the mass of the dark matter itself. Based on this assumption, the researchers studied Palomar 5 and ran some simulations to determine the gaps in the trail of stars lined up with a theoretical fly-by of dark matter.

Composite color image of the stars near the Pal 5 cluster.

S.E. Koposov, D. Erkal, V. Belokurov (IoA, Cambridge) with data from the Sloan Digital Sky Survey

“If dark matter can exist in clumps smaller than the smallest dwarf galaxy, then it also tells us something about the nature of the particles which dark matter is made of – namely that it must be made of very massive particles,” said study coauthor Vasily Belokurov. “This would be a breakthrough in our understanding of dark matter.”

If the team can further validate this new technique for determining the effects of dark matter, it would be another way to discern where smaller clumps of the hidden stuff might be zipping around.

“It’s like putting dark matter goggles on and seeing thousands of dark clumps each more massive than a million suns whizzing around,” said Erkal.

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