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Showing posts with label dark energy. Show all posts
Showing posts with label dark energy. Show all posts

Wednesday 22 July 2015

Dead galaxies in Coma Cluster may be packed with dark matter



New computer simulations show that these galaxies stopped star formation as early as 7 billion years ago but haven’t been ripped apart due to their dark matter.

Galaxies in a cluster roughly 300 million light-years from Earth could contain as much as 100 times more dark matter than visible matter, according to an Australian study.

The research used powerful computer simulations to study galaxies that have fallen into the Coma Cluster, one of the largest structures in the universe in which thousands of galaxies are bound together by gravity.

It found the galaxies could have fallen into the cluster as early as 7 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.

Dark matter cannot be seen directly, but the mysterious substance is thought to make up about 84 percent of the matter in the universe.

Cameron Yozin from the University of Western Australia, who led the study, says the paper demonstrates for the first time that some galaxies that have fallen into the cluster could plausibly have as much as 100 times more dark matter than visible matter.

Yozin says the galaxies he studied in the Coma Cluster are about the same size as our Milky Way but contain only 1 percent of the stars.

He says the galaxies appear to have stopped making new stars when they first fell into the cluster between 7 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.”

“Galaxies originally form when large clouds of hydrogen gas collapse and are converted to stars; if you remove that gas, the galaxy cannot grow further,” Yozin said.

“Falling into a cluster is one way in which this can happen. The immense gravitational force of the cluster pulls in the galaxy, but its gas is pushed out and essentially stolen by hot gas in the cluster itself.

“For the first time, my simulations have demonstrated that these galaxies could have been quenched by the cluster as early as 7 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,” Yozin said.

Source : Astronomy Magzine

Saturday 1 November 2014

Universe may face a darker future

Artist’s impression of exocomets around Beta Pictoris

New research offers a novel insight into the nature of dark matter and dark energy and what the future of our Universe might be.

Researchers in Portsmouth and Rome have found hints that dark matter, the cosmic scaffolding on which our Universe is built, is being slowly erased, swallowed up by dark energy.

The findings appear in the journal Physical Review Letters, published by the American Physical Society. In the journal cosmologists at the Universities of Portsmouth and Rome, argue that the latest astronomical data favours a dark energy that grows as it interacts with dark matter, and this appears to be slowing the growth of structure in the cosmos.

Professor David Wands, Director of Portsmouth's Institute of Cosmology and Gravitation, is one of the research team.

He said: "This study is about the fundamental properties of space-time. On a cosmic scale, this is about our Universe and its fate.

"If the dark energy is growing and dark matter is evaporating we will end up with a big, empty, boring Universe with almost nothing in it.

"Dark matter provides a framework for structures to grow in the Universe. The galaxies we see are built on that scaffolding and what we are seeing here, in these findings, suggests that dark matter is evaporating, slowing that growth of structure."

Cosmology underwent a paradigm shift in 1998 when researchers announced that the rate at which the Universe was expanding was accelerating. The idea of a constant dark energy throughout space-time (the "cosmological constant") became the standard model of cosmology, but now the Portsmouth and Rome researchers believe they have found a better description, including energy transfer between dark energy and dark matter.

Research students Valentina Salvatelli and Najla Said from the University of Rome worked in Portsmouth with Dr Marco Bruni and Professor Wands, and with Professor Alessandro Melchiorri in Rome. They examined data from a number of astronomical surveys, including the Sloan Digital Sky Survey, and used the growth of structure revealed by these surveys to test different models of dark energy.
Professor Wands said: "Valentina and Najla spent several months here over the summer looking at the consequences of the latest observations. Much more data is available now than was available in 1998 and it appears that the standard model is no longer sufficient to describe all of the data. We think we've found a better model of dark energy.

"Since the late 1990s astronomers have been convinced that something is causing the expansion of our Universe to accelerate. The simplest explanation was that empty space – the vacuum – had an energy density that was a cosmological constant. However there is growing evidence that this simple model cannot explain the full range of astronomical data researchers now have access to; in particular the growth of cosmic structure, galaxies and clusters of galaxies, seems to be slower than expected."
Professor Dragan Huterer, of the University of Michigan, has read the research and said scientists need to take notice of the findings.

He said: "The paper does look very interesting. Any time there is a new development in the dark energy sector we need to take notice since so little is understood about it. I would not say, however, that I am surprised at the results, that they come out different than in the simplest model with no interactions. We've known for some months now that there is some problem in all data fitting perfectly to the standard simplest model."