[ExI] cosmological model gets it mostly right
thespike at satx.rr.com
Sat Jan 23 00:14:01 UTC 2010
Galaxies shaped by dark past
Friday, 22 January 2010
by Heather Catchpole
SYDNEY: Using a detailed cosmological model that includes dark energy
and dark matter, two American astrophysicists have been able to
correctly predict the shapes and proportions of the different types of
galaxies in the universe and discover the Milky Way’s past.
The shape of galaxies depends on their turbulent history, and
understanding how they evolve is a major task.
Astrophysicists Nick Devereux of Embry-Riddle University in Arizona and
Andrew Benson of the California Institute of Technology used a
sophisticated computer model called GALFORM, combined with data from the
infrared Two Micron All Sky Survey, which scanned 70% of the sky between
1997 and 2001.
Researchers were ”completely astonished”
GALFORM simulates galaxy formation in a universe dominated by the
enigmatic dark energy and dark matter. It’s based on a cosmological
model of the universe called the Lambda Cold Dark Matter (LCDM) that
predicts how matter flows and lumps together. The Lambda component is
represents ‘dark energy’, which drives the expansion of the universe.
The model was able to reproduce the evolutionary history of the universe
over its 13.7 billion years. Moreover it not only got the shapes but
also the numbers of various galaxies right and the rate at which galaxy
“We were completely astonished that our model predicted both the
abundance and diversity of galaxy types so precisely,” said
astrophysicist Nick Devereux of Embry-Riddle University in Arizona.
“It really boosts my confidence in the model,” said Benson.
If galaxies are close enough together, then gravity can cause them to
merge, with spiral galaxies morphing to elliptical galaxies. The Milky
Way and its neighbour Andromeda are close enough that this will happen,.
Benson and Devereaux said that their model, published in the Monthly
Notices of the Royal Astronomical Society shows that the Milky Way has a
complex past but so far has only undergone minor collisions and the
gravitational collapse of its inner disk to form the central bar.
A galaxy’s shape depends on how it formed – and can vary from elliptical
and lens shapes to spirals. Our own Milky Way galaxy is classified as a
American astronomer Edwin Hubble defined these ranges of galactic shapes
as the ‘Hubble sequence’. They appear as elliptical blobs, or spiral
disks with circles or bars at the centre. Our own Milky Way is
classified as a barred spiral.
But the story of how the shapes arise is incredibly complex, so much so
that it stretches the limit of current computing capacity. To understand
it, astrophysicists use analytical models that can give an approximation
of the physics involved in everything from the evolution of stars to the
merging of entire galaxies.
Benson and Devereaux were able to predict the shapes and proportions of
galaxies with buldges, bulges and discs or just discs.
Model predicts too many dwarves
Australian astrophysicist Geraint Lewis from the University of Sydney
says while the results are very encouraging, there’s still a few holes
in the LDCM model, which the authors acknowledge.
“These guys have refined the recipe – what’s coming out is not only
elliptical and spiral galaxies but the right proportion of these
galaxies – which is very encouraging, but it’s not the end of the
answer,” Lewis said.
While the model is working well large scales, it predicts a greater
number of dwarf galaxies (small galaxies like the nearby Magellanic
Clouds) than we actually observe, says Lewis.
“The [dwarf galaxies] are inconsequential in some way but the number of
them is important. If your recipe was right you should get dark blobs
with nothing in, but if these are not there, it’s a problem for the LCDM.”
[[comment: obviously they've been harvested...]]
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