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