Tuesday, November 4, 2014

Standard Model may account for Dark Matter and it may be massive

A massive cluster of yellowish galaxies, seemingly caught in a red and blue spider web of eerily distorted background galaxies, makes for a spellbinding picture from the new Advanced Camera for Surveys (ACS) aboard NASA's Hubble Space Telescope. 

To make this unprecedented image of the cosmos, Hubble peered straight through the center of one of the most massive galaxy clusters known, called Abell 1689

The gravity of the cluster's trillion stars, plus dark matter, acts as a 2-million-light-year-wide lens in space. 

This gravitational lens bends and magnifies the light of the galaxies located far behind it. Some of the faintest objects in the picture are probably over 13 billion light-years away (redshift value 6). 

Strong gravitational lensing as observed by the Hubble Space Telescope in Abell 1689 indicates the presence of dark matter. 

Credit: NASA, N. Benitez (JHU), T. Broadhurst (Racah Institute of Physics/The Hebrew University), H. Ford (JHU), M. Clampin (STScI),G. Hartig (STScI), G. Illingworth (UCO/Lick Observatory), the ACS Science Team and ESA

The physics community has spent three decades searching for and finding no evidence that dark matter is made of tiny exotic particles.

Case Western Reserve University theoretical physicists suggest researchers consider looking for candidates more in the ordinary realm and, well, more massive.

Dark matter is unseen matter, that, combined with normal matter, could create the gravity that, among other things, prevents spinning galaxies from flying apart.

Physicists calculate that dark matter comprises 27 percent of the universe; normal matter 5 percent.

Instead of WIMPS, weakly interacting massive particles, or axions, which are weakly interacting low-mass particles, dark matter may be made of macroscopic objects, anywhere from a few ounces to the size of a good asteroid, and probably as dense as a neutron star, or the nucleus of an atom, the researchers suggest.

Physics professor Glenn Starkman and David Jacobs, who received his PhD in Physics from CWRU in May and is now a fellow at the University of Cape Town, say published observations provide guidance, limiting where to look.

They lay out the possibilities in a paper "Macro Dark Matter"

The Macros, as Starkman and Jacobs call them, would not only dwarf WIMPS and axions, but differ in an important way.

They could potentially be assembled out of particles in the Standard Model of particle physics instead of requiring new physics to explain their existence.

"We've been looking for WIMPs for a long time and haven't seen them," Starkman said. "We expected to make WIMPS in the Large Hadron Collider (LHC), and we haven't."

WIMPS and axions remain possible candidates for dark matter, but there's reason to search elsewhere, the theorists argue.

"The community had kind of turned away from the idea that dark matter could be made of normal-ish stuff in the late '80s," Starkman said.

"We ask, was that completely correct and how do we know dark matter isn't more ordinary stuff— stuff that could be made from quarks and electrons?"

After eliminating most ordinary matter, including failed Jupiters, white dwarfs, neutron stars, stellar black holes, the black holes in centers of galaxies and neutrinos with a lot of mass, as possible candidates, physicists turned their focus on the exotics.

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