Physicists brawl over new dark matter claim | Science
For a long time, astrophysicists have thought some kind of invisible dark matter should pervade the galaxies and maintain them collectively, though its nature stays a thriller. Now, three physicists claim their observations of empty patches of sky rule out one doable rationalization of the unusual substance—that it’s made out of bizarre particles referred to as sterile neutrinos. But others argue the info present no such factor.
“I think that for most of the people in the community this is the end of the story,” says research writer Benjamin Safdi, an astroparticle physicist on the University of Michigan, Ann Arbor. But Kevork Abazajian, a theoretical physicist on the University of California, Irvine, says the new evaluation is badly flawed. “To be honest, this is one of the worst cases of cherry picking the data that I’ve seen,” he says. In unpublished work, one other group checked out comparable patches of sky and noticed the exact same signal of sterile neutrinos that eluded Safdi.
Astrophysicists assume every galaxy types and resides inside an enormous clump, or “halo,” of dark matter, just like the pit in a peach. The gravity of the invisible substance helps stop the celebrities inside from flying off into empty house. Theoretical physicists have dreamed up quite a few hypothetical particles which may make up dark matter, amongst them cousins to just about massless, barely detectable subatomic particles referred to as neutrinos, which gush out of the Sun and nuclear reactors. The particles that make up dark matter could be hypothetical “sterile” neutrinos, heavier and much more elusive. An odd neutrino can work together with an atomic nucleus; sterile neutrinos would solely work together with different neutrinos, arising when an odd neutrino morphs right into a sterile one by means of a course of referred to as neutrino mixing.
The concept that sterile neutrinos would possibly make up dark matter obtained a lift in 2014. Observations of close by galaxies and the middle of our personal Milky Way revealed a faint glow of x-rays with a selected vitality, three.5 kilo-electron volts (keV). That glow could be anticipated if sterile neutrinos with a mass of seven keV pervaded the galaxies. Very hardly ever, a sterile neutrino would decay into an odd neutrino and an x-ray, which might have an vitality equal to half the sterile neutrino’s mass.
But a new evaluation of astronomical observations reveals the telltale glow can’t come from dark matter, Safdi and colleagues report right this moment in Science. They checked out information not from distant galaxies, however from clean spans of sky between the celebrities in additional than 4000 archival pictures snapped by XMM-Newton, an x-ray house telescope launched in 1999 by the European Space Agency. If our personal galaxy lies inside an enormous cloud of sterile neutrinos, then the telescope should be peering by means of that cloud—and the sky between the celebrities also needs to faintly glow with three.5-keV x-rays.
Safdi’s staff discovered no signal of such a glow. The no-show suggests the glow in distant galaxies isn’t coming from dark matter, however from some extra odd supply equivalent to scorching fuel, Safdi says.
Alexey Boyarsky, an astroparticle theorist at Leiden University, is unconvinced. “I think this paper is wrong,” he says. Boyarsky says he and his colleagues carried out an identical, unpublished evaluation in 2018, additionally utilizing pictures from XMM-Newton, and did see a three.5-keV glow from the empty sky, simply anticipated from peering by means of a halo of sterile neutrinos.
How do two teams take a look at the identical information and are available to reverse conclusions? The distinction lies of their strategies, Boyarsky says. Because our galaxy is full of a skinny ionized fuel, the sky emits x-rays, which might peak as particular energies even and not using a contribution from dark matter. The XMM-Newton telescope itself can even glow and emit x-rays at sure energies. And some x-rays come from past our galaxy, too. To see a three.5-keV glow from dark matter, researchers should sift it from these background contributions.
To do this, Boyarsky and colleagues analyzed your complete spectrum of x-ray energies that XMM-Newton can detect, modeled your complete background, and subtracted it from the info. Crucially, Boyarsky says, his staff eliminated recognized peaks at three.three keV and three.7 keV to disclose the unexplained three.5-keV peak. Safdi says his staff took a unique strategy. Borrowing statistical methods developed at atom smashers, they analyzed the spectrum from every picture individually and analyzed information solely over a a lot narrower vary of energies.
However, that vitality vary isn’t a lot wider than the height the staff is in search of, Abazajian says. Boyarsky provides that as a result of Sadfi and his staff didn’t take out the 2 different background peaks, they could have mistaken a plateau created by the three overlapping peaks for a flat spectrum.
Not so, Safdi Says. His staff discovered that subtracting the opposite peaks and widening the vitality window doesn’t change the outcome. If a three.5-keV peak exists, he says, his staff’s extra refined method would have revealed it.
Boyarsky says he’s going to attempt to publish his blank-sky evaluation. A physics journal turned it down, saying it wasn’t sufficiently “interesting,” he says. Now, he says he’ll submit it to Science. “I don’t care if it gets published, but I would like it to be peer reviewed,” he says. “They can’t say it isn’t interesting.”