Astronomers' Doubts About the Dark Side: Errors in Big Bang Data
Astronomers' Doubts About the Dark Side: Errors in Big Bang Data
Larger Than Thought?
http://www.sciencedaily.com/releases...0613212708.htm
ScienceDaily (June 11, 2010) — New research by astronomers in the
Physics Department at Durham University suggests that the conventional
wisdom about the content of the Universe may be wrong.
Graduate student Utane Sawangwit and Professor Tom Shanks looked at
observations from the Wilkinson Microwave Anisotropy Probe (WMAP)
satellite to study the remnant heat from the Big Bang. The two
scientists find evidence that the errors in its data may be much
larger than previously thought, which in turn makes the standard model
of the Universe open to question. The team publish their results in a
letter to the journal Monthly Notices of the Royal Astronomical
Society.
Launched in 2001, WMAP measures differences in the Cosmic Microwave
Background (CMB) radiation, the residual heat of the Big Bang that
fills the Universe and appears over the whole of the sky. The angular
size of the ripples in the CMB is thought to be connected to the
composition of the Universe. The observations of WMAP showed that the
ripples were about twice the size of the full Moon, or around a degree
across.
With these results, scientists concluded that the cosmos is made up of
4% 'normal' matter, 22% 'dark' or invisible matter and 74% 'dark
energy'. Debate about the exact nature of the 'dark side' of the
Universe -- the dark matter and dark energy -- continues to this day.
Sawangwit and Shanks used astronomical objects that appear as
unresolved points in radio telescopes to test the way the WMAP
telescope smoothes out its maps. They find that the smoothing is much
larger than previously believed, suggesting that its measurement of
the size of the CMBR ripples is not as accurate as was thought. If
true this could mean that the ripples are significantly smaller, which
could imply that dark matter and dark energy are not present after
all.
Prof. Shanks comments "CMB observations are a powerful tool for
cosmology and it is vital to check for systematic effects. If our
results prove correct then it will become less likely that dark energy
and exotic dark matter particles dominate the Universe. So the
evidence that the Universe has a 'Dark Side' will weaken!"
In addition, Durham astronomers recently collaborated in an
international team whose research suggested that the structure of the
CMB may not provide the robust independent check on the presence of
dark energy that it was thought to.
If dark energy does exist, then it ultimately causes the expansion of
the Universe to accelerate. On their journey from the CMB to the
telescopes like WMAP, photons (the basic particles of electromagnetic
radiation including light and radio waves) travel through giant
superclusters of galaxies. Normally a CMB photon is first blueshifted
(its peak shifts towards the blue end of the spectrum) when it enters
the supercluster and then redshifted as it leaves, so that the two
effects cancel. However, if the supercluster galaxies are accelerating
away from each other because of dark energy, the cancellation is not
exact, so photons stay slightly blueshifted after their passage.
Slightly higher temperatures should appear in the CMB where the
photons have passed through superclusters.
However, the new results, based on the Sloan Digital Sky Survey which
surveyed 1 million luminous red galaxies, suggest that no such effect
is seen, again threatening the standard model of the Universe.
Utane Sawangwit says, "If our result is repeated in new surveys of
galaxies in the Southern Hemisphere then this could mean real problems
for the existence of dark energy."
If the Universe really has no 'dark side', it will come as a relief to
some theoretical physicists. Having a model dependent on as yet
undetected exotic particles that make up dark matter and the
completely mysterious dark energy leaves many scientists feeling
uncomfortable. It also throws up problems for the birth of stars in
galaxies, with as much 'feedback' energy needed to prevent their
creation as gravity provides to help them form.
Prof. Shanks concludes "Odds are that the standard model with its
enigmatic dark energy and dark matter will survive -- but more tests
are needed. The European PLANCK satellite, currently out there
collecting more CMB data will provide vital new information and help
us answer these fundamental questions about the nature of the Universe
we live in."
Story Source:
The above story is reprinted (with editorial adaptations by
ScienceDaily staff) from materials provided by Royal Astronomical
Society (RAS).
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