Copyright: Chandra: NASA/CXC/SAO/E.Bulbul, et al.; XMM: ESA)
A new study of the Perseus galaxy cluster, shown in this image, and
others using Chandra and XMM-Newton has revealed a mysterious X-ray
signal in the data. The signal is also seen in over 70 other galaxy
clusters using XMM-Newton. This unidentified signal requires further
investigation to confirm both its existence and nature, but one
possibility is that it represents the decay of ‘sterile neutrinos’, one
proposed candidate to explain dark matter.
A new study of the Perseus galaxy cluster, shown in this image, and
others using Chandra and XMM-Newton has revealed a mysterious X-ray
signal in the data. This signal is represented in the circled data
points in the inset, which is a plot of X-ray intensity as a function of
X-ray energy. The signal is also seen in over 70 other galaxy clusters
using XMM-Newton. This unidentified X-ray emission line – a spike of
intensity centred on about 3.56 keV – requires further investigation to
confirm both the signal’s existence and nature. One possibility is this
signal is the decay of ‘sterile neutrinos’, one proposed candidate to
explain dark matter.
Astronomers using ESA and NASA high-energy observatories have discovered
a tantalising clue that hints at an elusive ingredient of our Universe:
dark matter.
Although thought to be invisible, neither emitting nor absorbing light,
dark matter can be detected through its gravitational influence on the
movements and appearance of other objects in the Universe, such as stars
or galaxies.
Based on this indirect evidence, astronomers believe that dark matter is
the dominant type of matter in the Universe – yet it remains obscure.
Now a hint may have been found by studying galaxy clusters, the largest cosmic assemblies of matter bound together by gravity.
Galaxy clusters not only contain hundreds of galaxies, but also a huge amount of hot gas filling the space between them.
However, measuring the gravitational influence of such clusters shows
that the galaxies and gas make up only about a fifth of the total mass –
the rest is thought to be dark matter.
The gas is mainly hydrogen and, at over 10 million degrees celsius, is
hot enough to emit X-rays. Traces of other elements contribute
additional X-ray ‘lines’ at specific wavelengths.
Examining observations by ESA’s XMM-Newton and NASA’s Chandra spaceborne
telescopes of these characteristic lines in 73 galaxy clusters,
astronomers stumbled on an intriguing faint line at a wavelength where
none had been seen before.
“If this strange signal had been caused by a known element present in
the gas, it should have left other signals in the X-ray light at other
well-known wavelengths, but none of these were recorded,” says Dr Esra
Bulbul from the Harvard-Smithsonian Center for Astrophysics in
Cambridge, Massachusetts, USA, lead author of the paper discussing the
results.
“So we had to look for an explanation beyond the realm of known, ordinary matter.”
The astronomers suggest that the emission may be created by the decay of
an exotic type of subatomic particle known as a ‘sterile neutrino’,
which is predicted but not yet detected.
Ordinary neutrinos are very low-mass particles that interact only rarely
with matter via the so-called weak nuclear force as well as via
gravity. Sterile neutrinos are thought to interact with ordinary matter
through gravity alone, making them a possible candidate as dark matter.
“If the interpretation of our new observations is correct, at least part
of the dark matter in galaxy clusters could consist of sterile
neutrinos,” says Dr Bulbul.
The surveyed galaxy clusters lie at a wide range of distances, from more
than a hundred million light-years to a few billion light-years away.
The mysterious, faint signal was found by combining multiple
observations of the clusters, as well as in an individual image of the
Perseus cluster, a massive structure in our cosmic neighbourhood.
The implications of this discovery may be far-reaching, but the
researchers are being cautious. Further observations with XMM-Newton,
Chandra and other high-energy telescopes of more clusters are needed
before the connection to dark matter can be confirmed.
“The discovery of these curious X-rays was possible thanks to the large
XMM-Newton archive, and to the observatory’s ability to collect lots of
X-rays at different wavelengths, leading to this previously undiscovered
line,” comments Norbert Schartel, ESA’s XMM-Newton Project Scientist.
“It would be extremely exciting to confirm that XMM-Newton helped us find the first direct sign of dark matter.
“We aren't quite there yet, but we’re certainly going to learn a lot
about the content of our bizarre Universe while getting there.”
More information
“Detection of an unidentified emission line in the stacked X-ray spectrum of galaxy clusters,” by E. Bulbul et al. is published in the 1 July 2014 issue of the Astrophysical Journal.
For further information, please contact:
Markus Bauer
ESA Science and Robotic Exploration Communication Officer
Tel: +31 71 565 6799
Mob: +31 61 594 3 954
Email: markus.bauer@esa.int
ESA Science and Robotic Exploration Communication Officer
Tel: +31 71 565 6799
Mob: +31 61 594 3 954
Email: markus.bauer@esa.int
Esra Bulbul
Harvard-Smithsonian Center for Astrophysics
Cambridge, MA, USA
Phone: +1-617-496-7565
Email: ebulbul@cfa.harvard.edu
Harvard-Smithsonian Center for Astrophysics
Cambridge, MA, USA
Phone: +1-617-496-7565
Email: ebulbul@cfa.harvard.edu
Norbert Schartel
XMM-Newton Project Scientist
Tel: +34 91 8131 184
Email: Norbert.Schartel@sciops.esa.int
XMM-Newton Project Scientist
Tel: +34 91 8131 184
Email: Norbert.Schartel@sciops.esa.int
Source: ESA
