This week in Cosmology

[Brian G Turner]

A few interesting developments this week in the world of Cosmology.

For starters, observations using the hubble Telescope and the Keck Telescope at Mauna Kea have discovered stars between galaxies - apparently ripped from their parent homes to form small clusters in the intergalactic voids:

Astronomers find 'cosmic vagabonds'

Astronomers have discovered clusters of stars drifting in what was thought to be the empty space between the galaxies.

The stars have been torn from their parent galaxies, and scattered into the intergalactic voids by gravity from other, passing galaxies.

Finding these cosmic "orphans" has pressed the capabilities of telescopes to their limits.

The scientists responsible have presented their work to the International Astronomical Union's (IAU) General Assembly in Sydney, Australia.

Droplets in space

Astronomers have known for more than a century that galaxies are surrounded by a swarm of ancient star clusters. Our own Milky Way galaxy has about 150 of these "globular clusters".

Globular clusters look like a droplet in space and can contain up to a million stars. Studies of them have provided many important insights into the formation of stars and galaxies.

Observations made by the Hubble Space Telescope and the giant 10-metre Keck Telescope on Mauna Kea, Hawaii, found the orphaned globular clusters.

Cosmic spill

"These clusters are no longer held within the gravitational grip of galaxies, and seem to be wandering freely through intergalactic space like cosmic vagabonds," says Dr Michael West of the University of Hawaii.

According to West, these globular star clusters probably once resided in galaxies just like most of the normal globular clusters that we see in nearby galaxies today.

However, the pull of gravity from a passing galaxy can rip stars and star clusters loose. In some cases, entire galaxies can be disrupted or destroyed by the gravitational pull from galactic neighbours.

It is thought that the partial or complete destruction of their parent galaxies spilled the globular star clusters into intergalactic space.

Astronomers also used the Hubble Telescope to develop a "mass map" of a distant galaxy, in the ongoing search to locate the presence - and eventually describe (assuming it exists!) Dark Matter:

'Mass map' probes dark matter

Astronomers have mapped of one of the most massive structures in the Universe, showing how much more there is to it than glowing stars and gas.

The object is a distant cluster of galaxies that contains dark matter, the unknown component that comprises most of the mass of the Universe.

The new "mass map" shows it is distributed in much the same way as are the visible stars.

Researchers believe it will lead to a better understanding of the mysterious dark matter, even though it does not help them find out exactly what it is.

Here, there and everywhere

Clusters of galaxies are the largest stable systems in the Universe. They contain not only stars, gas and dust but something else as well.

Astronomers do not know what that something is. They know it is there because they can see the effect its gravity has on the motions of the stars and galaxies.

Dark matter makes up about 80-85% of the matter in the Universe. Many types of objects are suspected, ranging from dead stars to hoards of sub-atomic particles.

In an attempt to pin down the distribution of dark matter, whatever it is, an international team of astronomers used the Hubble Space Telescope to make its mass map of the galaxy cluster called CL0024+1654.

The map enabled them to see how the dark matter is distributed with respect to the visible galaxies in the cluster.

Across the Universe

To produce the map, the researchers looked at more distant galaxies behind the cluster, noting that their shapes are distorted by the gravity of the foreground cluster - an effect called gravitational lensing.

The nature of the distortion provides information about the unseen mass of the cluster.

The project required more than 120 hours observing time - the largest amount of Hubble time ever devoted to studying a galaxy cluster.

The investigation has resulted in the most comprehensive study of the distribution of dark matter in a galaxy cluster so far.

The map reveals that the dark matter drops sharply with distance from the cluster centre, which is what astronomers expected.

"This confirms a picture that has emerged from recent detailed computer simulations," says Professor Richard Ellis of CalTech, US.

Ellis and colleagues presented their study at the General Assembly of the International Astronomical Union. They will also publish their results in a forthcoming issue of Astrophysical Journal.

And researchers in Cardiff and the Royal Observatory in Edinburgh have done a more extensive investigation of cosmic dust - which exists in space between stars, and contributes to the blocking of various electromagnetic waves. Their results - the dust is almost certainly formed primarily from supernovae:

Origin of cosmic dust discovered

UK astronomers say they have unlocked one of the Universe's oldest secrets - the origin of cosmic dust.

Cardiff University and Royal Observatory Edinburgh scientists found that some stars throw out huge quantities of this dust when they explode.

These explosions could be responsible for the Universe's first ever solid particles, they say in the journal Nature.

The scientists used the James Clerk Maxwell Telescope in Hawaii to make their discovery.

Cold space

Astronomers had thought space dust was mostly made in the winds from cool, giant stars in the late stages of their lives.

Researchers used the Scuba instrument on the James Clerk Maxwell Telescope to hunt for dust in the remains of a star called Cassiopeia A, which is 11,000 light-years distant and exploded 320 years ago as viewed from Earth.

Until recently, astronomers had only been able to detect warm dust.

"This is because it operates at longer sub-millimetre wavelengths than the infra-red instruments used previously," said Dr Steve Eales, an astrophysicist at Cardiff.

"With Scuba we can see dust which is very cold."

The dust found indicated stars might have been responsible for the earliest particles in the Universe, the team said.

Project leader Loretta Dunne added: "The origin of cosmic dust is, in fact, the basic question of the origin of our planet and others.

"Effectively, we live on a very large collection of cosmic dust grains and yet, until now, we have not been sure where cosmic dust is made."

Cosmic dust consists of tiny particles of solid material floating around in the space between the stars, but unlike house dust, it more closely resembles cigarette smoke and blocks out half of the light given off by stars and galaxies.

Dr Dunne added: "Dust has been swept under the cosmic carpet. For years, astronomers have treated it as a nuisance because of the way it hides the light from the stars.

"Now studies have shown that there is dust right at the edge of the Universe in the earliest stars and galaxies; we realise that we are ignorant of even its basic origin."

 

[Brian G Turner]

And here are a couple of the topics revisited from NewScientist magazine, with a little more information for those who want to read up further.

Dark matter map reveals galaxy cluster's appetite

Smoking supernova solves dusty mystery

And, also - a new story - polar mapping of high-energy neutrinos, using a special "telescope" named Amanda II

Polar observatory reveals first neutrino sky map