28-01-11

Hunt for dark matter closes in at Large Hadron Collider

 

Wednesday 26 January 2011


Physicists are closer than ever to finding the source of the Universe's mysterious dark matter, following a better than expected year of research at the Compact Muon Solenoid (CMS) particle detector, part of the Large Hadron Collider (LHC) at CERN in Geneva.

 

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Max Braun on Flickr

 

 

The scientists have now carried out the first full run of experiments that smash protons together at almost the speed of light.

 

When these sub-atomic particles collide at the heart of the CMS detector, the resultant energies and densities are similar to those that were present in the first instants of the Universe, immediately after the Big Bang some 13.7 billion years ago.

 

The unique conditions created by these collisions can lead to the production of new particles that would have existed in those early instants and have since disappeared.

 

The researchers say they are well on their way to being able to either confirm or rule out one of the primary theories that could solve many of the outstanding questions of particle physics, known as Supersymmetry (SUSY).

 

Many hope it could be a valid extension for the Standard Model of particle physics, which describes the interactions of known subatomic particles with astonishing precision but fails to incorporate general relativity, dark matter and dark energy.

 

Dark matter is an invisible substance that we cannot detect directly but whose presence is inferred from the rotation of galaxies.

 

Physicists believe that it makes up about a quarter of the mass of the Universe whilst the ordinary and visible matter only makes up about 5% of the mass of the Universe.

 

Its composition is a mystery, leading to intriguing possibilities of hitherto undiscovered physics.

 

Professor Geoff Hall from the Department of Physics at Imperial College London, who works on the CMS experiment, said:

"We have made an important step forward in the hunt for dark matter, although no discovery has yet been made.

 

These results have come faster than we expected because the LHC and CMS ran better last year than we dared hope and we are now very optimistic about the prospects of pinning down Supersymmetry in the next few years."

 


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16-01-11

Dark-Matter Galaxy Detected: Hidden Dwarf Lurks Nearby?

 

Richard A. Lovett in Seattle, Washington


for National Geographic News


Published January 14, 2011

 

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An entire galaxy may be lurking, unseen, just outside our own, scientists announced Thursday.

 


The invisibility of "Galaxy X"—as the purported body has been dubbed—may be due less to its apparent status as a dwarf galaxy than to its murky location and its overwhelming amount of dark matter, astronomer Sukanya Chakrabarti speculates.

 

Detectable only by the effects of its gravitational pull, dark matter is an invisible material that scientists think makes up more than 80 percent of the mass in the universe.

 

Chakrabarti, of the University of California, Berkeley, devised a technique similar to that used 160 years ago to predict the existence of Neptune, which was given away by the wobbles its gravity induced in Uranus's orbit.

 

Based on gravitational perturbations of gases on the fringes of our Milky Way galaxy, Chakrabarti came to her conclusion that there's a unknown dwarf galaxy about 260,000 light-years away.


With an estimated mass equal to only one percent the mass of the Milky Way, Galaxy X is still the third largest of the Milky Way's satellite galaxies, Chakrabarti predicts.


The two Magellanic are each about ten times larger.


If it exists, Galaxy X isn't likely to be composed entirely of dark matter.


It should also have a sprinkling of dim stars, Chakrabarti said.


"These should provide enough light for astronomers to see it, now that they know where to look," she said.


The reason the dark matter galaxy hasn't yet been seen, she added, is because it lies in the same plane as the Milky Way disc.


Clouds of gas and dust stand between us and Galaxy X, confounding telescopes.

 

 

 

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14-01-11

Harvard-Smithsonian Center For Astrophysics - Better Measuring Dark Energy

 

 

Press Release

Release No.: 2011-04

For Release: Thursday, January 13, 2011 09:00:00 AM EST

 

Dark Energy.jpg

 

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The Best Way to Measure Dark Energy Just Got Better

 

Seattle, WA

 

Dark energy is a mysterious force that pervades all space, acting as a "push" to accelerate the Universe's expansion.

 

Despite being 70 percent of the Universe, dark energy was only discovered in 1998 by two teams observing Type Ia supernovae.

 

A Type 1a supernova is a cataclysmic explosion of a white dwarf star.

 

These supernovae are currently the best way to measure dark energy because they are visible across intergalactic space.

 

Also, they can function as "standard candles" in distant galaxies since the intrinsic brightness is known.

 

Just as drivers estimate the distance to oncoming cars at night from the brightness of their headlights, measuring the apparent brightness of a supernova yields its distance (fainter is farther).

 

Measuring distances tracks the effect of dark energy on the expansion of the Universe.

 

The best way of measuring dark energy just got better, thanks to a new study of Type Ia supernovae led by Ryan Foley of the Harvard-Smithsonian Center for Astrophysics. 

 

He has found a way to correct for small variations in the appearance of these supernovae, so that they become even better standard candles.

 

The key is to sort the supernovae based on their color.

 

"Dark energy is the biggest mystery in physics and astronomy today.

 

Now, we have a better way to tackle it," said Foley, who is a Clay Fellow at the Center.

 

He presented his findings in a press conference at the 217th meeting of the American Astronomical Society.

 

The new tool also will help astronomers to firm up the cosmic distance scale by providing more accurate distances to faraway galaxies.

 

Type Ia supernovae are used as standard candles, meaning they have a known intrinsic brightness.

 

However, they're not all equally bright.

 

Astronomers have to correct for certain variations.

 

In particular, there is a known correlation between how quickly the supernova brightens and dims (its light curve) and the intrinsic peak brightness.

 

Even when astronomers correct for this effect, their measurements still show some scatter, which leads to inaccuracies when calculating distances and therefore the effects of dark energy.

 

Studies looking for ways to make more accurate corrections have had limited success until now.

 

"We've been looking for this sort of 'second-order effect' for nearly two decades," said Foley.

 

Foley discovered that after correcting for how quickly Type Ia supernovae faded,

they show a distinct relationship between the speed of their ejected material and their color: the faster ones are slightly redder and the slower ones are bluer.

 

Previously, astronomers assumed that redder explosions only appeared that way because of intervening dust, which would also dim the explosion and make it appear farther than it was.

 

Trying to correct for this, they would incorrectly calculate that the explosion was closer than it appeared.

 

Foley's work shows that some of the color difference is intrinsic to the supernova itself.

 

The new study succeeded for two reasons.

 

First, it used a large sample of more than 100 supernovae.

 

More importantly, it went back to "first principles" and reexamined the assumption that Type Ia supernovae are one average color.

 

The discovery provides a better physical understanding of Type Ia supernovae and their intrinsic differences.

 

It also will allow cosmologists to improve their data analysis and make better measurements of dark energy - an important step on the road to learning what this mysterious force truly is, and what it means for the future of the cosmos.

 

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

 


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