Light is shed on darkest galaxies

Light is shed on darkest galaxies

Computers were used to simulate galaxy formation
The mystery of how the darkest galaxies in the Universe came to exist may
have been solved by scientists.
Dwarf spheroidals are galaxies composed almost entirely of dark matter;
faint examples have been discovered orbiting the Milky Way and Andromeda
galaxies.

Scientists believe these dark systems were once gas-rich, but as they became
satellites of larger galaxies, most of their visible matter was stripped
away.

The study, reported in the journal Nature, may shed light on dark matter.

The scientists used computer simulations to uncover what might have happened
10 billion years ago as a gas-dominated dwarf galaxy hurtled into the orbit
of a larger, Milky-Way-sized system.

They found the drag force, or "ram pressure", created as a smaller galaxy
moved through the more massive one would have stripped away the dwarf
galaxy's interstellar gas.

The model also showed the gravitational tug from the larger system would
have wrenched away many of the dwarf system's luminous stars.

The result, said the international team, was a galaxy where most of the
visible matter was absent, leaving mainly dark matter behind.

'Grand challenge'

Stelios Kazantzidis, an astrophysicist from Stanford University and an
author of the paper, said: "These results are so exciting because they are
based on a combination of physical effects that has never before been
postulated.

"This is one step toward a more complete understanding of the formation of
structure in the Universe, which is one of the fundamental goals of
astrophysics."

The researchers believe all luminous galaxies should be surrounded by a few
extremely dark matter-dominated spheroidal galaxies.

And, said Dr Kazantzidis, studying them may provide insights into mysterious
dark matter.

He added: "Elucidating the nature of dark matter is one of the grandest
challenges of modern cosmology.

"In the next several years, numerous experiments will attempt to detect dark
matter using dwarf spherical galaxies as targets."


http://news.bbc.co.uk/2/hi/science/nature/6360757.stm


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