Part of Universe's Missing Matter Discovered By XMM-Newton X-Ray Observatory
The European Space Agency's orbiting X-ray observatory XMM-Newton has
been used by a team of international astronomers to uncover part of the
missing matter in the universe.
10 years ago, scientists predicted that about half of the "ordinary" or
normal matter made of atoms exists in the form of low-density gas,
filling vast spaces between galaxies.
All the matter in the universe is distributed in a web-like structure.
At dense nodes of the cosmic web are clusters of galaxies, the largest
objects in the universe. Astronomers suspected that the low-density gas
permeates the filaments of the web.
The low density of the gas hampered many attempts to detect it in the
past. With XMM-Newton's high sensitivity, astronomers have discovered
its hottest parts. The discovery will help them understand the
evolution of the cosmic web.
Composite
optical and X-ray image of galaxy clusters Abell 222 and Abell 223. The
cluster pair is connected by a filament permeated by hot X-ray emitting
gas.
The optical
image was obtained by SuprimeCam at the Subaru telescope, the X-ray
image showing the distribution of the diffuse hot gas (yellow to red)
was obtained by XMM-Newton. Credits: ESA/ XMM-Newton/ EPIC/ ESO (J.
Dietrich)/ SRON (N. Werner)/ MPE (A. Finoguenov)
Only about 5% of our universe is made of normal matter as we know it,
consisting of protons and neutrons, or baryons, which along with
electrons, form the building blocks of ordinary matter. The rest of our
universe is composed of elusive dark matter (23%) and dark energy
(72%). Small as the percentage might be, half of the ordinary
baryonic matter is unaccounted for. All the stars, galaxies and gas
observable in the universe account for less than a half of all the
baryons that should be around.
Scientists predicted that the gas would have a high temperature and so
it would primarily emit low-energy X-rays. But its very low density
made observation difficult.
Astronomers using XMM-Newton were observing a pair of galaxy clusters,
Abell 222 and Abell 223, situated at a distance of 2300 million
light-years from Earth, when the images and spectra of the system
revealed a bridge of hot gas connecting the clusters.
"The hot gas that we see in this bridge or filament is probably the
hottest and densest part of the diffuse gas in the cosmic web, believed
to constitute about half the baryonic matter in the universe," says
Norbert Werner from SRON Netherlands Institute for Space Research,
leader of the team reporting the discovery.
This is a model
of the cosmic web. Clusters of galaxies are expected to develop at the
intersections of the web. Credits: Springel et al., Virgo Consortium
"The discovery of the warmest of the missing baryons is important.
That's because various models exist and they all predict that the
missing baryons are some form of warm gas, but the models tend to
disagree about the extremes," adds Alexis Finoguenov, a team member.
Even with XMM-Newton's sensitivity, the discovery was only possible
because the filament is along the line of sight, concentrating the
emission from the entire filament in a small region of the sky. The
discovery of this hot gas will help better understand the evolution of
the cosmic web.
"This is only the beginning. To understand the distribution of the
matter within the cosmic web, we have to see more systems like this
one. And ultimately launch a dedicated space observatory to observe the
cosmic web with a much higher sensitivity than possible with current
missions. Our result allows to set up reliable requirements for those
new missions." concludes Norbert Werner.
ESA's XMM-Newton Project Scientist, Norbert Schartel, comments on the
discovery, "This important breakthrough is great news for the mission.
The gas has been detected after hard work and more importantly, we now
know where to look for it. I expect many follow-up studies with
XMM-Newton in the future targeting such highly promising regions in the
sky."
From:
http://www.esa.int/esaCP/SEMQLPZXUFF_index_0.html