"Long before it's in the papers"
January 27, 2015


Hint of dark matter found?

Oct. 17, 2014
Courtesy of the University of Leicester
and World Science staff

Space sci­en­tists have measured a cu­ri­ous sig­nal that they say might come from the mys­te­ri­ous “dark mat­ter,” an in­vis­i­ble sub­stance de­tected so far only through its gra­vity.

The re­search­ers at the Uni­vers­ity of Leices­ter in the U.K. re­ported what seems to be a sig­na­ture of par­t­i­cles thought to pos­sibly make up dark mat­ter, called ax­ions. The sci­en­tists spec­u­late that the Earth’s mag­net­ic field is turn­ing some of these in­to X-rays.

A sketch (not to scale) showing axions (blue) streaming out from the Sun, converting in the Earth's magnetic field (red) into X-rays (orange), which are then detected by the XMM-Newton observatory. (Credit: U. of Leicester)

“If con­firmed, it will be the first di­rect de­tec­tion and iden­ti­fica­t­ion of the elu­sive dark mat­ter par­t­i­cles and will have a fun­da­men­tal im­pact on our the­o­ries of the Uni­verse,” said Uni­vers­ity of Leices­ter phys­i­cist Mar­tin Bar­stow, who is al­so Pres­ident of the Roy­al As­tro­nom­i­cal So­ci­e­ty.

In a study to be pub­lished Oct. 20 in the jour­nal Monthly No­tices of the Roy­al As­tro­nom­i­cal So­ci­e­ty, the sci­en­tists said the sig­nal has no con­ven­tion­al ex­plana­t­ion. The first au­thor of the stu­dy, George Fra­ser of the Uni­vers­ity of Leices­ter, died last March.

“The di­rect de­tec­tion of dark mat­ter has pre­oc­cu­pied phys­ics for over thir­ty years,” Fra­ser wrote. Dark mat­ter, a kind of in­vis­i­ble mass of un­known or­i­gin, can­not be seen di­rectly with tele­scopes, but is in­stead in­ferred from its gravita­t­ional pull. It is be­lieved to make up most of the mat­ter of the Uni­verse.

Fra­ser and col­leagues worked by stu­dying the X-ray back­ground, the sky as viewed in X-ray light.

“The X-ray back­ground – the sky, af­ter the bright X-ray sources are re­moved – ap­pears to be un­changed when­ev­er you look at it,” ex­plained An­dy Read, lead au­thor of the pa­per, al­so from the Uni­vers­ity of Leices­ter. But “we have disco­vered a sea­son­al sig­nal in this X-ray back­ground, which has no con­ven­tion­al ex­plana­t­ion, but is con­sist­ent with the disco­very of ax­ions.”

The re­search­ers stud­ied al­most the en­tire ar­chive of da­ta from the Eu­ro­pe­an Space Agen­cy’s X-ray ob­serv­a­to­ry, XMM-Newton.

“It ap­pears plau­si­ble that ax­ions – dark mat­ter par­t­i­cle can­di­dates – are in­deed pro­duced in the co­re of the Sun and do in­deed con­vert to X-rays in the mag­net­ic field of the Earth,” the sci­en­tists wrote in the pa­per. “It is pre­dicted that the X-ray sig­nal due to ax­ions will be great­est when look­ing through the sun­ward side of the mag­net­ic field be­cause this is where the field is strongest.”

Pre­vi­ous searches for ax­ions had proved un­suc­cess­ful.

“These ex­cit­ing disco­veries, in George’s fi­nal pa­per, could be truly ground break­ing, po­ten­tially open­ing a win­dow to new phys­ics, and could have huge im­plica­t­ions, not only for our un­der­stand­ing of the true X-ray sky, but al­so for iden­ti­fy­ing the dark mat­ter that dom­i­nates the mass con­tent of the cos­mos,” Read said.

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Space scientists have detected a curious signal that they say might be an effect of the mysterious “dark matter,” an invisible substance detected so far only through its gravity. The researchers at the University of Leicester in the U.K. reported what seems to be a signature of particles thought to possibly make up dark matter, called axions. The scientists speculate that the Earth’s magnetic field is turning some of these into X-rays. “If confirmed, it will be the first direct detection and identification of the elusive dark matter particles and will have a fundamental impact on our theories of the Universe,” said University of Leicester physicist Martin Barstow, who is also President of the Royal Astronomical Society. In a study to be published Oct. 20 in the journal Monthly Notices of the Royal Astronomical Society, the scientists said the signal has no conventional explanation. The first author of the study, George Fraser of the University of Leicester, died last March. “The direct detection of dark matter has preoccupied physics for over thirty years,” Fraser wrote. Dark matter, a kind of invisible mass of unknown origin, cannot be seen directly with telescopes, but is instead inferred from its gravitational pull. It is believed to make up most of the matter of the Universe. Fraser and colleagues worked by studying the X-ray background, the sky as viewed in X-ray light. “The X-ray background – the sky, after the bright X-ray sources are removed – appears to be unchanged whenever you look at it,” explained Andy Read, lead author of the paper, also from the University of Leicester. But “we have discovered a seasonal signal in this X-ray background, which has no conventional explanation, but is consistent with the discovery of axions.” The researchers studied almost the entire archive of data from the European Space Agency’s X-ray observatory, XMM-Newton. “It appears plausible that axions – dark matter particle candidates – are indeed produced in the core of the Sun and do indeed convert to X-rays in the magnetic field of the Earth,” the scientists wrote in the paper. “It is predicted that the X-ray signal due to axions will be greatest when looking through the sunward side of the magnetic field because this is where the field is strongest.” Previous searches for axions had proved unsuccessful. “These exciting discoveries, in George’s final paper, could be truly ground breaking, potentially opening a window to new physics, and could have huge implications, not only for our understanding of the true X-ray sky, but also for identifying the dark matter that dominates the mass content of the cosmos,” Read said.