X-rays of a specific wavelength emanating from the hearts of nearby galaxies and galaxy clusters could be signs of particles of dark matter decaying in space, two independent teams of astronomers report. If that interpretation is correct, then dark matter could consist of strange particles called sterile neutrinos that weigh about 1/100 as much as an electron. However, some other researches are skeptical.
For decades, astronomers and astrophysicists have thought that some
sort of mysterious dark matter must provide the gravity that keeps
individual galaxies from falling apart. In fact, the current standard
model of cosmology indicates that a typical galaxy forms within a vast
clump, or halo, of dark matter whose gravity keeps the stars from flying
out into space. However, scientists do not know what dark matter is, as
they have never detected it by any means other than sensing its
gravity.
Now, two teams report possible signs of dark matter particles
revealing themselves in another way—by very, very slowly decaying into
normal photons. Both groups relied on data from one of the most
successful space observatories, the European Space Agency's X-ray
Multi-Mirror Mission (XMM-Newton), which launched in December 1999 and
is still taking data. Esra Bulbul, an astrophysicist at the
Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts,
and colleagues discovered x-rays of a specific energy—3.5 kiloelectron
volts (keV)—shining from 73 galaxy clusters, including the Perseus
cluster. The Harvard group also used data from NASA's orbiting Chandra
X-ray Observatory launched by NASA in July 1999, as it reports in a
paper submitted to The Astrophysical Journal.
