How Much Dark Matter

[Robert_Stephens]

How Much Dark Matter?

How Much Dark Matter Do Some Galaxies Need? 300 Billion Suns | Dark Matter, Dark Energy | Strangest Things In Space | Space.com

It appears, what they are calling dark matter, is now being estimated to run at about a mass of some 300 billion sun size volume.

Active galaxies show the way

Star formation is especially high within so-called submillimeter galaxies, which are some of the most active stellar cradles in the 13.7-billion-year-old universe. (The galaxies get their name from the emissions we detect from them as they rapidly move away from Earth. The wavelength of the emissions is less than a millimeter long.) In these old, bright galaxies, new stars are created at the rate of up to a few thousand per year. By comparison, the Milky Way produces about 10 stars annually.

"These are the galaxies that formed when the universe was about 2 or 3 billion years old," Cooray said.

After measuring the brightness of the galaxies within the patch of sky, the researcher calculated the minimum dark halo mass needed to develop and sustain a submillimeter galaxy when the universe's star formation was at its peak.

That number, 300 billion solar masses, is substantially less than previous estimates.

"There could be many reasons for this," Cooray said. For example, "it could be that there are more galaxies in the universe actively undergoing star formation than assumed by current simulations."

Or it could be something else entirely.

Whatever the cause, the link between halo mass and star formation will require another look at current theoretical models for these ancient star-forming galaxies, as well as galaxy formation and evolution as a whole, researchers said.

I find this quite compelling in that it is still a postulate, but plausible since there is no other models to work with.

Comments welcome.

Robert

 

[waltky]

Scientists hope to detect that rare event when a particle of dark "stuff" bumps into regular matter...

Dark Matter: Experiment to shed light on dark particles
5 February 2013 - BBC World Service science reporter Rebecca Morelle has been inside the Darkside50 experiment

In a man-made cavern, deep beneath a mountain, scientists are hoping to shed light on one of the most mysterious substances in our Universe - dark matter. The Gran Sasso National Laboratory seems more like a Bond villain's lair than a hub for world class physics. It's buried under the highest peak of Italy's Gran Sasso mountain range; the entrance concealed behind a colossal steel door found halfway along a tunnel that cuts through the mountain. But there's a good reason for its subterranean location. The 1,400m of rock above means that it is shielded from the cosmic rays that constantly bombard the surface of our planet.

It provides scientists with the "silence" they need to understand some of the strangest phenomena known to physics. Inside three vast halls, a raft of experiments are running - but with their latest addition, DarkSide50, scientists are setting their sights on dark matter. Everything we know and can see in the Universe only makes up about 4% of the stuff that is out there. They predict that about 73% of the Universe is made up of dark energy - a pervasive energy field that acts as a sort of anti-gravity to stop the Universe from contracting back in on itself. The other 23%, researchers believe, comes in the form of dark matter. The challenge is that until now nobody has seen it.

As dark matter particles steam through the detector, scientists hope that a few will collide with the argon atoms. This will generate two flashes of light - one in the liquid argon and another in the gas - which will be detected by the receptors.

Dr Chamkaur Ghag, a particle physicist from University College London, explains: "We think it is in the form of a particle. "We have protons, neutrons and electrons and all these regular normal particles that you associate building things with. We think dark matter is a particle too, it's just an odd form of matter in the fact that we don't perceive it very readily. "And that is because it doesn't feel the electromagnetic force - light doesn't bounce off it, we don't interact with it very strongly." Physicists have called these dark matter contenders Weakly Interacting Massive Particles - or WIMPS. They believe millions of them are passing through us every second without a trace.

But very occasionally one will bump into a piece of "regular" matter - and that is what they are hoping to detect with DarkSide50. The rest, scientists believe, comes in two enigmatic forms. Inside a house-sized tank, a large metal sphere holds a particle detector called a scintillator. This container is filled with 50kg of liquid argon and a thick layer of the element in its gas form. "If a dark matter particle comes in and hits the argon, the recoiling atom gets a kick of energy and it quickly tries to get rid of it," says Dr Ghag. "In argon it gets rid of it by kicking out light; it sheds photons. "But it also gives charge: some electrons that are liberated from the interaction site. And those electrons drift up into a gas layer, and when they hit the gas and you get another flash of light."

More BBC News - Dark Matter: Experiment to shed light on dark particles

 

[waltky]

Granny says dat don't look like dark matter to her - dat looks like a copper thing-a-ma-jiggy...

Dark matter experiment CDMS sees three tentative clues
15 April 2013 - Researchers have revealed the first potential hints of the elusive material called dark matter at an underground laboratory in the US.

Though it is believed to make up a quarter of our Universe, dark matter - true to its name - has never been seen. Scientists at the American Physical Society meeting showed three promising clues to it from the CDMS experiment. However, they stressed the preliminary nature of the results and that more data are needed to confirm it. Physics has a well-defined threshold for claiming that a new particle has been discovered, and this result still falls far short of that.

The CDMS experiment is based underground at the Soudan mine in Minnesota, US

Nevertheless, given the feverish pitch of the hunt for dark matter - in other underground labs, at the Large Hadron Collider in Switzerland, and even in space - these three early hints have caused a stir at the meeting. "It's certainly something we want to be investigating," CDMS collaborator Blas Cabrera of Stanford University told BBC News. "This is science, and the further tightening up of what we see - or excluding it - is very important for us to do."

Four-way search

Dark matter is believed to interact only very rarely with the normal matter we know well. Deep within a mine in the US state of Minnesota, CDMS - which stands for Cryogenic Dark Matter Search - tries to catch those rare interactions as dark matter particles bump into the nuclei of atoms in a detector that is held at temperatures near that of deep space. The facility reported two potential dark matter sightings in 2010, but those later turned out to come from the instrument itself. The new results - to be posted to the preprint server Arxiv - show three signals that should only have a 0.19% chance of showing up if there were no particle causing them, around the level of what physicists call a "three-sigma" result. They suggest a less massive dark matter particle than commonly considered - about seven times that of the proton - but one that is still consistent with some theories. Further, it does not match up with results published in Physical Review Letters from another underground experiment in Italy called Xenon.

More clarity will come, as is often the case, with more data. "We're actually in a good situation in the whole of the field," said Bernard Sadoulet of the University of California Berkeley, referring to the four types of experiments being used around the world - and within it and below it - to finally track dark matter down. "These four ways… we can rely on to help us work through these hints," he told the meeting. The hint-laden data were taken when CDMS used detectors made of silicon; it has since moved on to germanium detectors. But Prof Cabrera said the team was aiming to re-install the silicon, just to check on the unexpected hints announced here. "The fact that we're looking at changing our strategies to include silicon means it's certainly exciting."

BBC News - Dark matter experiment CDMS sees three tentative clues