Eighty-five p.c of the universe consists of darkish topic, however we don’t know what, precisely, it’s.
A brand new learn about from the University of Michigan, Lawrence Berkeley National Laboratory (Berkeley Lab) and University of California, Berkeley has dominated out darkish topic being accountable for mysterious electromagnetic alerts up to now noticed from within sight galaxies. Prior to this paintings there have been top hopes that those alerts would give physicists arduous proof to lend a hand establish darkish topic.
Dark topic can’t be noticed at once as it does now not soak up, mirror or emit mild, however researchers realize it exists as a result of of the impact it has on different topic. We want darkish topic to provide an explanation for gravitational forces that hang galaxies in combination, for instance.
Physicists have advised darkish topic is a carefully similar cousin of the neutrino, referred to as the sterile neutrino. Neutrinos — subatomic debris with out a rate and which infrequently engage with topic — are launched throughout nuclear reactions happening throughout the solar. They have a tiny quantity of mass, however this mass isn’t defined by means of the Standard Model of Particle Physics. Physicists recommend that the sterile neutrino, a hypothetical particle, may just account for this mass and in addition be darkish topic.
Researchers must be capable of discover the sterile neutrino as a result of it’s volatile, says Ben Safdi, co-author and an assistant professor of physics at U-M. It decays into odd neutrinos and electromagnetic radiation. To discover darkish topic, then, physicists scan galaxies to seek for this electromagnetic radiation within the shape of X-ray emission.
In 2014, a seminal paintings found out extra X-ray emission from within sight galaxies and galaxy clusters. The emission gave the impression to be in step with that which might stand up from decaying sterile neutrino darkish topic, Safdi mentioned.
Now, a meta research of uncooked knowledge taken by means of the XMM-Newton house X-ray telescope of items within the Milky Way over a length of 20 years has discovered no proof that the sterile neutrino is what contains darkish topic. The analysis workforce comprises U-M doctoral pupil Christopher Dessert and Nicholas Rodd, a physicist with the Berkley Lab idea staff and the Berkley Center for Theoretical Physics. Their effects are revealed within the magazine Science.
“This 2014 paper and follow-up works confirmed the signal generated a significant amount of interest in the astrophysics and particle physics communities because of the possibility of knowing, for the first time, precisely what dark matter is at a microscopic level,” Safdi mentioned. “Our finding does not mean that the dark matter is not a sterile neutrino, but it means that — contrary to what was claimed in 2014 — there is no experimental evidence to-date that points towards its existence.”
Space-based X-ray telescopes such as the XMM-Newton telescope, level at dark-matter-rich environments to seek for this faint electromagnetic radiation within the shape of X-ray alerts. The 2014 discovery named the X-ray emission the “3.5 keV line” — keV stands for kilo-electronvolts — as a result of of the place the sign gave the impression on X-ray detectors.
The analysis workforce looked for this line in our personal Milky Way the use of 20 years of archival knowledge taken by means of the XMM-Newton house X-ray telescope. Physicists know darkish topic collects round galaxies, so when earlier analyses checked out within sight galaxies and galaxy clusters, each and every of the ones photographs would have captured some column of the Milky Way darkish topic halo.
The workforce used the ones photographs to take a look at the “darkest” phase of the Milky Way. This considerably advanced the sensitivity of earlier analyses on the lookout for sterile neutrino darkish topic, Safdi mentioned.
“Everywhere we look, there should be some flux of dark matter from the Milky Way halo,” mentioned the Berkeley Lab’s Rodd, as a result of of our sun machine’s location within the galaxy. “We exploited the fact that we live in a halo of dark matter” within the learn about.
Christopher Dessert, a learn about co-author who’s a physics researcher and Ph.D. pupil at U-M, mentioned galaxy clusters the place the three.five keV line had been noticed even have huge background alerts, which serve as noise in observations and will make it tricky to pinpoint particular alerts that can be related to darkish topic.
“The reason why we’re looking through the galactic dark matter halo of our Milky Way galaxy is that the background is much lower,” Dessert mentioned.
For instance, XMM-Newton has taken photographs of remoted items like particular person stars within the Milky Way. The researchers took those photographs and masked the items of authentic passion, leaving pristine and darkish environments by which to seek for the glow of darkish topic decay. Combining 20 years of such observations allowed for a probe of sterile neutrino darkish topic to extraordinary ranges.
If sterile neutrinos have been darkish topic, and if their decay ended in an emission of the three.five keV line, Safdi and his fellow researchers must have noticed that line of their research. But they discovered no proof for sterile neutrino darkish topic.
“While this work does, unfortunately, throw cold water on what looked like what might have been the first evidence for the microscopic nature of dark matter, it does open up a whole new approach to looking for dark matter which could lead to a discovery in the near future,” Safdi mentioned.
Reference: “The dark matter interpretation of the 3.5-keV line is inconsistent with blank-sky observations” by means of C. Dessert; B.R. Safdi at University of Michigan, Ann Arbor in Ann Arbor, MI; N.L. Rodd at University of California, Berkeley in Berkeley, CA; N.L. Rodd at Lawrence Berkeley National Laboratory in Berkeley, CA., 26 March 2020, Science.DOI: 10.1126/science.aaw3772
Researchers within the learn about have been supported by means of the U.S. Department of Energy’s Early Career Research Program, Leinweber Center for Theoretical Physics at U-M and Miller Institute for Basic Research in Science at UC Berkeley. The analysis was once supported by means of Advanced Research Computing at U-M.