Did "Dark Matter" Create the First Stars? (Forwarded)

Press and Public Relations Department
Max Planck Society for the Advancement of Science
Munich, Germany

Contact:

Prof. Peter L. Biermann
Max Planck Institute for Radio Astronomy, Bonn, Germany
Tel.: +49 228 525-279

Prof. Alexander Kusenko
University of California at Los Angeles, USA, Los Angeles, USA
Tel.: +1 310-825-4814

Dr. Norbert Junkes, Public relations
Max Planck Institute for Radio Astronomy, Bonn, Germany
Tel.: +49 228 525-399

March 15th, 2006

News SP / 2006 (29)

Did "Dark Matter" Create the First Stars?

Dark matter could be "sterile" neutrinos, whose decay led to the formation
of stars in the early universe

Dark matter may have played a major role in creating stars at the very
beginnings of the universe. If that is the case, however, the dark matter
must consist of particles called "sterile neutrinos". Peter Biermann of
the Max Planck Institute for Radio Astronomy in Bonn, and Alexander
Kusenko, of the University of California, Los Angeles, have shown that
when sterile neutrinos decay, it speeds up the creation of molecular
hydrogen. This process could have helped light up the first stars only
some 20 to 100 million years after the big bang. This first generation of
stars then ionised the gas surrounding them, some 150 to 400 million years
after the big bang. All of this provides a simple explanation to some
rather puzzling observations concerning dark matter, neutron stars, and
antimatter (Physical Review Letters, March 10, 2006).

Scientists discovered that neutrinos have mass through neutrino
oscillation experiments. This led to the postulation that "sterile"
neutrinos exist -- also known as right-handed neutrinos. They do not
participate in weak interactions directly, but do interact through their
mixing with ordinary neutrinos. The total number of sterile neutrinos in
the universe is unclear. If a sterile neutrino only has a mass of a few
kiloelectronvolts (1 keV is a millionth of the mass of a hydrogen atom),
that would explain the huge, missing mass in the universe, sometimes
called "dark matter". Astrophysical observations support the view that
dark matter is likely to consist of these sterile neutrinos.

Biermann and Kusenko's theory sheds light on a number of still unexplained
astronomical puzzles. First of all, during the big bang, the mass of
neutrinos created in the Big Bang would equal what is needed to account
for dark matter. Second, these particles could be the solution to the
long-standing problem of why pulsars move so fast.

Pulsars are neutron stars rotating at a very high velocity. They are
created in supernova explosions and normally are ejected in one direction.
The explosion gives them a "push", like a rocket engine. Pulsars can have
velocities of hundreds of kilometres per second -- or sometimes even
thousands. The origin of these velocities remains unknown, but the
emission of sterile neutrinos would explain the pulsar kicks.

The Guitar Nebula (image) contains a very fast pulsar. If dark matter is
made of particles which reionized the universe -- as Biermann and Kusenko
suggest -- the pulsar's motion could have created this cosmic guitar.

Third, sterile neutrinos can help explain the absence of antimatter in the
universe. In the early universe, sterile neutrinos could have "stolen"
what is called the "lepton number" from plasma. At a later time, the lack
of lepton number was converted to a non-zero baryon number. The resulting
asymmetry between baryons (like protons) and antibaryons (like
antiprotons) could be the reason why the universe has no antimatter.

"The formation of central galactic black holes, as well as structure on
subgalactic scales, favours sterile neutrinos to account for dark matter.
The consensus of several indirect pieces of evidence leads one to believe
that the long sought-after dark-matter particle may, indeed, be a sterile
neutrino", says Peter Biermann.

Related links:

[1] Theory Group of Prof. Biermann at the Max-Planck-Institute for
Radioastronomy
http://www.mpifr-bonn.mpg.de/div/theory/

[2] Sterile neutrinos: references and links
http://www.nu.to.infn.it/Sterile_Neutrinos/

Original work:

P.L. Biermann & A. Kusenko
Relic keV sterile neutrinos and reionization
Physical Review Letters, 10 March 2006

IMAGE CAPTION:
[http://www.mpg.de/bilderBerichteDoku...ressebild.jpeg
(24KB)]
Head of the "guitar nebula". The formation contains a fast moving pulsar
followed by a tail of gas. Biermann and Kusenko's postulations about dark
matter could explain puzzlingly high pulsar velocities, which lead to such
cone-shaped features. Images are from the Planetary Camera aboard the
Hubble Space Telescope in 1994 (left) and 2001 (right).

Image: Hubble Space Telescope (NASA/ESA), Shami Shatterjee 200