Astronomers Discover MISSING LINK In Galaxy Evolution !!!

by **J The Kidd** Tue Nov 25, 2008 4:00 pm

Three galaxies from the Galaxy Zoo (top) and STAGES surveys (bottom)
show normal blue spiral galaxies (left), red spiral discoveries
(centre) and red ellipitical galaxies (right)

Astronomers have uncovered a type of galaxy that represents a 'missing link' in our understanding of the Universe.

Most normal galaxies are placed into two camps according to their
visual appearance: either spiral disk-like systems like our own Milky
Way, or round, rugby-ball shaped collections of stars known as
ellipticals.

Spiral galaxies have always been classed as blue because most of them
are still vigorously forming hot young stars. But elliptical galaxies
found in dense regions are mostly old and dead and emit a red light.

But two UK-led international studies have found one in five galaxies is a red spiral.

Dr Steven Bamford from the University of Nottingham, led the Galaxy Zoo
study, which studied more than one million galaxies using images from
the Sloan Digital Sky Survey.

He said: 'In order to have spiral arms, they must have been normal,
blue, spiral galaxies up until fairly recently. But for some reason
their star formation has been stopped, and they have turned red.

'Whatever caused them to stop forming stars can't have been
particularly violent, or it would have destroyed the delicate spiral
pattern.'

The discovery was made after they decided to look at the galaxies rather than rely on error-prone computer measurements.

The Galaxy Zoo team concluded that a more subtle process must be at
work, one that kills off star formation but does not disrupt the
overall shape of the galaxy.

Meanwhile a more direct search was undertaken by Christian Wolf from
Oxford University and Meghan Gray from Nottingham University in a
project called 'Stages.'

They trained the Hubble Space Telescope on areas of space where they
expected transformations between blue and red galaxies to occur. They
found a surprisingly large amount of red spiral galaxies in crowded
areas of space such as the A901/902 supercluster.

But despite their reddish colour, star formation has not been
completely killed off in these spiral galaxies. A shroud of dust meant
they were invisible on the visible light spectrum. But Dr Wolf's team
detected low levels of star formation using the infra red part of the
spectrum.

'For the STAGES galaxies, the Spitzer Space Telescope provided us with
additional images at infrared wavelengths. With them, we were able to
go further and peer through the dust to find the missing piece of the
puzzle,' Dr Wolf said.

The cosmic picture that emerges is a gentle one: the star formation in
blue spiral galaxies is gradually shut off and hidden behind dust,
before petering out to form smooth 'lenticular' (lens-shaped) red
galaxies with no trace of spiral arms.

To go further and transform the galaxy into an elliptical would require
more violent mechanisms, such as the wholesale collision of galaxies.

The two groups will publish their results in the Monthly Notices of the Royal Astronomical Society.