“It seems to be the final
nail in the coffin of the dark matter interpretation,” says astroparticle physicist
Ben Safdi of the University of Michigan in Ann Arbor.
The tantalizing glows were first
detected in 2014 as an excess of X-rays with an energy of 3.5 kiloelectron volts, or keV, coming from faraway galaxy clusters. Some
astronomers argued that the X-rays could come from decaying particles of dark
matter — the ubiquitous, inert material that makes up more than 80 percent of
the universe’s matter. The X-rays’ energy, in particular, suggested that the
light could be coming from hypothetical dark matter particles called sterile neutrinos (SN: 6/1/18).
All images of the sky look
through some portion of the Milky Way’s dark matter halo, even if that’s not
what a telescope is aiming at. So the researchers sifted through every
observation that the European Space Agency’s XMM-Newton space telescope ever
made, about 347 days of total exposure time, in search of X-rays at the right
energy. The team saw none.
“The jury is still out on
what is producing the 3.5 keV” signal, Safdi says. “What’s clear, though, is
it’s not dark matter.”