Natural Science Forum / Physics / General Physics / November 2007

Proto-galaxies tip cold dark matter
  http://physicsworld.com/cws/article/news/32010

  Astronomers have spotted some of the first galaxies ever to form.
  These so-called proto-galaxies existed over 11 billion years ago and
  their discovery supports the "cold dark matter" model of how the
  universe evolved after the Big Bang.

  In all, 27 proto-galaxies were found by an international team using
  the using the Very Large Telescope in Chile. Data from the
  observation should help astrophysicists refine models of galaxy
  formation.

  The first galaxies are believed to have formed about one billion
  years after the universe was created in the Big Bang -- which itself
  happened nearly 14 billion years ago. Astrophysicists believe that
  around this time, cold dark matter -- invisible stuff that accounts
  for 95% of the mass of the universe -- began to gather in small
  clumps under its own gravitational attraction. These clumps joined
  together to create larger clumps, which in turn combined to make even
  larger clumps and so on.

  The first stars

  Astrophysicists believe that normal matter such as hydrogen simply
  tagged along with the dark matter because of its gravitational
  attraction. Eventually, these clumps of matter and dark matter became
  proto-galaxies -- structures about 1000-times smaller than our Milky
  Way galaxy -- which contained the first stars. These galaxies are
  then believed to join together to form the galaxies we know today.

  In principle, proto-galaxies should still be visible because the
  light from some of these very distant structures is only now reaching
  Earth. However, this light is very faint and astronomers have
  struggled to detect it -- and instead they have had to infer the
  existence of proto-galaxies from their apparent ability to block
  radiation from even further away.

  The astronomers discovered the proto-galaxies in a small patch of sky
  using the European Southern Observatory's Very Large Telescope (VLT)
  (arXiv 0711.1354v1). The observations were made between 2004 and 2006
  for a total of 92 hours, which allowed the team to resolve extremely
  faint and distant objects.

  Damped Lyman alpha system

  The galaxies were identified by their distinct ultraviolet light --
  called Lyman alpha light - that is given off by hydrogen gas when it
  is ionized by radiation from a star. Proto-galaxies are expected to
  contain large amounts of gaseous hydrogen at relatively high
  densities, which gives the Lyman alpha light the spectral
  characteristics of a "damped Lyman alpha system" (DLAS). DLAS light
  was spotted coming from 27 distant objects and the shifts in
  wavelength of the DLAS light confirmed that the galaxies existed
  about 2 billion years after the Big Bang.

  "The new observations confirm theoretical research proposing that
  galaxies like our own have formed by the amalgamation of small
  proto-galaxies early on in the history of the Universe", said Andy
  Bunker of the Anglo-Australian Observatory in Sydney, who is one of
  the leaders of the study.

  According to team member Cedric Lacey, who is an astrophysicist at
  Durham University in the UK, the VLT data will allow astronomers to
  work out how many stars each proto-galaxy contains. This and other
  parameters extracted from the observations will then be used to
  improve current models of galaxy formation.

  Lacey also told physicsworld.com that there is "nothing special"
  about the part of the sky where the proto-galaxies were found. "It's
  an average bit of the sky", he said, "which means that we should see
  [proto-galaxies] in all directions".

  As is often the case with scientific discoveries, the proto-galaxies
  were found by mistake. The team were actually looking for evidence of
  Lyman alpha fluorescence, whereby radiation created shortly after the
  Big Bang interacts with hydrogen throughout the universe, causing it
  to glow in the ultraviolet. According to Lacey, the team also saw
  evidence of this fluorescence and have asked for more time on the VLT
  to study it in more detail.