Heated Debate Surrounds Galaxy Seeming to Lack Dark Matter

Ultra-diffuse galaxy NGC1052-DF2
Image: Pieter van Dokkum/Ryan F. Mandelbaum

Strong skepticism ought to all the time accompany sturdy claims. One such current declare has generated a ton of speak about an odd, fuzzy galaxy that seems to be lacking its darkish matter.

That a galaxy would don’t have any darkish matter is a tremendous discovering, and it was coated slightly uncritically by a number of information retailers (including us!). Since then, some scientists have taken to social media and the arXiv science paper server to debate the scant knowledge used to make the shocking conclusion.

“The idea we were seeing a strong signature of a dark matter-free system seems incorrect,” Michelle Collins, astronomy lecturer on the University of Surrey within the United Kingdom, advised Gizmodo.

Last month, the distinguished science journal Nature printed a hanging remark from a workforce of astronomers with a title akin to astronomy clickbait: “A galaxy lacking dark matter.” Using their telescope, the Dragonfly Telephoto Array, they noticed a dim galaxy formed like a fuzzy and roughly the identical width because the Milky Way. They noticed the velocity of 10 brilliant collections of stars and realized that it appeared the galaxy was shifting method slower than they anticipated.

That would suggest to the researchers that NGC1052-DF2 was lacking the darkish matter that many astronomers suppose makes up the overwhelming majority of most galaxies’ mass.

Dark matter, you would possibly keep in mind, describes an issue greater than an answer. Observations of the universe’s gravity appear to show extra mass than astronomers can measure with their telescopes, maybe 5 to 6 instances extra. Physicists typically suppose there’s a brand new sort of matter but to be detected, although many as an alternative argue that the legal guidelines of gravity have a gap. You can inform a galaxy’s mass based mostly on how shortly it rotates—the extra mass it has, the quicker it must spin so as to not collapse. Most galaxies rotate too quick, whereas, based on Yale University scientist Pieter van Dokkum’s workforce, NGC1052-DF2 barely rotates in any respect.

Nearly all information retailers who coated the story (once more, together with me) typically reported the findings of the Nature paper with out severe doubt. But some astronomers aren’t satisfied.

At the middle of the dialogue is statistics. It’s mathematically difficult to make any conclusions utilizing very small datasets, particularly once you’re speaking about simply 10 clusters of stars in a whole galaxy, defined Nicolas Martin, astronomer on the Max Planck Institute for Astronomy in Germany, in a Twitter thread. He and others crunched the info in a different way, and located that positive, perhaps the galaxy was lacking darkish matter, however perhaps it wasn’t. “The current data set doesn’t warrant such a strong conclusion,” he wrote. He’s since printed the analysis with others, together with Collins, on the arXiv server.

One of the disagreements, for instance, stems from what to do with one of many 10 globular clusters that appears to be an outlier from the opposite 9 based mostly on the way it strikes. Both teams weigh it in a different way, Collins advised me.

Van Dokkum has since addressed some of the concerns on a private web site, and thought the talk was “missing the forest from the trees.” He famous to Gizmodo in an e-mail that folk typically agree with an analogous velocity unfold of the globular clusters, one that means far much less darkish matter than the common galaxy—so it’s nonetheless “lacking” darkish matter, however perhaps not “missing” darkish matter. But Collins responded to me that if you happen to attempt to base the mass of extra acquainted darkish matter-filled galaxies on simply 10 specifically chosen globular clusters, you can also make them, too, seem to not have any darkish matter.

There are different rebuttals to Van Dokkum’s claims, together with another arXiv paper discussing whether or not the remark actually challenges various theories to clarify the supply of the stuff we name “dark matter.” Another discusses the conduct of those “ultra-diffuse” galaxies more generally. 

And the talk has been occurring for a number of weeks on Twitter. One astronomy grad scholar, Mia de los Reyes at CalTech in California, even turned the dialogue into an American Chopper meme:

Original examine writer Van Dokkum himself doesn’t thoughts the talk—he calls it “excellent,” and “exactly what we are all supposed to do, trying to replicate each other’s results and looking for loopholes in the interpretation.” He advised Gizmodo he additionally thought it was good to see using social media and the arXiv preprint server to provide voice to youthful astronomers with good concepts.

It would take lots to persuade Collins that the galaxy was actually lacking darkish matter’s results. “You’d need significantly more data than they have presented here,” she stated.

But primarily this goes to point out science at its very core: It’s an ever-changing story the place proof and debate take us nearer to the reality. And it’s a superb reminder of one thing that a number of science writers, together with me, didn’t apply to this paper: We want to stay skeptical about any new outcomes till the bigger science neighborhood has had time to digest and debate them.

[arXiv 1, 2, 3, Twitter]

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