Dead galaxies could be packed with dark matter

Dead galaxies in a cluster about 300 million light years from Earth could be packed with dark matter, keeping them from being ripped apart, a study by Australian scientists suggests.

Powerful computer simulations of the Coma Cluster, where thousands of galaxies are bound together by gravity, suggest it could contain as much as 100 times more dark matter than visible matter.

Dark matter cannot be seen directly but is thought to make up more than 80% of the matter in the Universe.

“The galaxies could have fallen into the cluster as early as seven billion years ago, which, if our current theories of galaxies evolution are correct, suggests they must have lots of dark matter protecting the visible matter from being ripped apart by the cluster,” said Cameron Yozin, an International Centre for Radio Astronomy Research PhD student who led the study.

Yozin, who is based at The University of Western Australia, says the galaxies he studied are about the same size as our own Milky Way but contain only 1% of the stars.

He says the galaxies appear to have stopped making new stars when they first fell into the cluster between seven and 10 billion years ago and have been dead ever since, leading astrophysicists to label them “failed” galaxies.

This end to star formation is known as “quenching”.

This can happen when the immense gravitational force of the cluster pulls in the galaxy, but its star-making gas is pushed out into the the cluster itself.

“For the first time, my simulations have demonstrated that these galaxies could have been quenched by the cluster as early as seven billion years ago. They have however avoided being ripped apart completely in this environment because they fell in with enough dark matter to protect their visible matter,” said Yozin.