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Posts Tagged ‘DARK MATTER

Fermi Space Telescope Fails to See Evidence Of Dark Matter

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If dark matter fills the universe, astronomers should see the gamma rays it produces. That evidence has so far failed to materialise
Among the most dramatic events in the universe are the death of stars as they collapse into black holes and the collision of black holes themselves. These events are so violent that they shake the firmament, generating gravity waves that ripple across the cosmos. They also generate huge blasts of neutrinos that can sometimes be picked up by giant neutrino telescopes on Earth.
But while these events are fascinating, not least because they almost certainly involve physics beyond our ken, they are hugely difficult to observe. That’s because neutrinos and gravity waves are notoriously shy.
Neutrinos usually pass straight through the Earth. In fact, astronomers have only once detected neutrinos from beyond the Solar System and that was almost 25 years ago during a supernova called SN1987A….. Read the rest of this entry »

Written by physicsgg

June 21, 2011 at 2:30 pm

The case for primordial black holes as dark matter

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M.R.S. Hawkins
The aim of this paper is to present the case that stellar mass primordial black holes make up the dark matter component of the Universe.
A near critical density of compact bodies implies that most lines of sight will be gravitationally microlensed, and the paper focuses on looking for the predicted effects on quasar brightness and spectral variations.
These signatures of microlensing include the shape of the Fourier power spectrum of the light curves, near achromatic and statistically symmetric variations, and the absence of time dilation in the timescale of variability.
For spectral changes, as the continuum varies there should be little corresponding change in the strength of the broad lines.
In all these cases, the observations are found to be consistent with the predictions for microlensing by a population of stellar mass compact bodies. For multiply lensed quasars where the images vary independently it is shown that stellar populations are too small to produce the observed microlensing effects, implying a population of compact dark matter bodies of around a stellar mass along the line of sight.
The most serious objection to dark matter in the form of compact bodies has come from observations of microlensing of stars in the Magellanic Clouds.
In this paper the expected event rate is re-analysed using more recent values for the structure and dynamics of the Galactic halo, and it is shown that there is then no conflict with the observations.
Finally, the possible identity of a near critical density of dark matter in the form of stellar mass compact bodies is reviewed, with the conclusion that by far the most plausible candidates are primordial black holes formed during the QCD epoch. The overall conclusion of the paper is that primordial black holes should be seen alongside elementary particles as viable dark matter candidates

Written by physicsgg

June 21, 2011 at 6:09 am

Posted in COSMOLOGY, RELATIVITY

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DARK STARS: A NEW LOOK AT THE FIRST STARS IN THE UNIVERSE

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Astronomers now believe that the cores of trillions of galaxies across the Universe are being powered by supermassive black hole. Recently, a team of experts proposed that these dark behemoths were produced by the collapse of massive stars made out of dark matter.

This is a view of the galaxy NGC 4151, nicknamed the Eye of Sauron

Unlike usual stars, which are made up of normal, baryonic matter, dark stars could have contained weirder elements, such as for supersymmetric particles. The scientific community now believes it has the necessary technology to try and detect signs of their existence.
Also worthy of mention is the fact that studies have demonstrated several times over that the gravitational pull of galaxies cannot be accounted for by the amount of normal mass they carry. As such, some other type of matter might be exerting its influence here.
Dark matter is the proposed explanation for the observed phenomena. It is currently believed to make up about 23 percent of the mass of the Universe, and to exist mostly in galactic halos. But there is no theoretical obstacle preventing it from enduring at the core of galaxies as well.
The associate director of the Michigan Center for Theoretical Physics, Katherine Freese, believes that the early stages of cosmic evolution were powered by dark matter instead of nuclear fusion.
She says that interactions between WIMP (Weakly Interacting Massive Particles) – which are their own antimatter particles – may have provided the necessary heat. At this point, WIMP are believed to be the particles making up dark matter.
Dark stars made of the stuff may have therefore existed in the early Universe. After the weird fuel was exhausted, these objects turned into heavy main sequence stars, which then went on to implode.
These powerful events gave birth to either neutron stars or black holes, depending on the size and mass of the original star. Over billions of years of cosmic evolution, these dark behemoths grew to the supermassive sizes we are observing today.
Freese and her team propose that the dark stars would have contained only 0.1 percent dark matter, and that the surface temperatures of these objects may have been less than 10,000 degrees Kelvin, Daily Galaxy reports.
The most interesting implication of the new work is that nuclear fusion began in these stars only after the dark matter fuel was exhausted. At that time, temperature levels spiked, allowing hydrogen atoms to start fusing and producing helium and energy.
http://news.softpedia.com/news/Dark-Matter-Stars-May-Have-Created-Supermassive-Black-Holes-202829.shtml
http://arxiv.org/PS_cache/arxiv/pdf/0903/0903.3070v1.pdf

Written by physicsgg

May 27, 2011 at 2:04 pm

Posted in ASTRONOMY, COSMOLOGY

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Some of the Universe’s Missing Mass Found

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An Australian science student managed to provide additional evidence that expert Fritz Zwicky was right in its theory on where the missing mass of the Universe may be hiding. The work done by Amelia Fraser-McKelvie, 22, has already been published in a scientific journal.

A 3-month study carried out by a 22-year-old reveals the location of the Universe's missing matter

The Monash University aerospace engineering/science student made the discovery during a six-week paid astrophysics research internship at the School of Physics (SP), Universe Today reports…. Read the rest of this entry »

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May 25, 2011 at 7:40 am

Posted in ASTRONOMY, COSMOLOGY, DARK MATTER

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The Alpha Magnetic Spectrometer (AMS)

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Cosmic ray detector blasts off on space shuttle

MS before lift-off.

AAn instrument for detecting cosmic rays – and possibly even dark matter – has finally been lifted into orbit on board the space shuttle Endeavour. The Alpha Magnetic Spectrometer (AMS), which is the brainchild of the Nobel-prize-winning physicist Samuel Ting, will soon be installed on the International Space Station (ISS). Ting first came up with the idea for the AMS in the 1990s but a series of setbacks, including the Columbia space shuttle disaster in 2003, has led to the mission being continually delayed….. Read the rest of this entry »

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May 17, 2011 at 1:20 pm

Dark matter without dark energy

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Newtonian Perturbations on Models with Matter Creation
Creation of Cold Dark Matter (CCDM) can macroscopically be described by a negative pressure, and, therefore, the mechanism is capable to accelerate the Universe, without the need of an additional dark energy component. In this framework we discuss the evolution of perturbations by considering a Neo-Newtonian approach where, unlike in the standard Newtonian cosmology, the fluid pressure is taken into account even in the homogeneous and isotropic background equations (Lima, Zanchin and Brandenberger, MNRAS 291, L1, 1997). The evolution of the density contrast is calculated in the linear approximation and compared to the one predicted by the ΛCDM model. The difference between the CCDM and ΛCDM predictions at the perturbative level is quantified by using three different statistical methods, namely: a simple χ^2 -analysis in the relevant space parameter, a Bayesian statistical inference, and, finally, a Kolmogorov-Smirnov test. We find that under
certain circumstances the CCDM scenario analysed here predicts an overall dynamics (including Hubble flow and matter fluctuation field) which fully recovers that of the traditional cosmic concordance model. Our basic conclusion is that such a reduction of the dark sector provides a viable alternative description to the accelerating ΛCDM cosmology…. Read more: http://arxiv.org/PS_cache/arxiv/pdf/1105/1105.1027v1.pdf

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May 7, 2011 at 5:19 pm

Posted in COSMOLOGY

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Νew dark matter signal

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…from CoGeNT Dark Matter Experiment

The CoGeNT dark matter experimental set-up at Soudan Underground Laboratory

“…..The annual modulation is the closest thing to a smoking gun [for dark matter],” says theorist Jonathan Feng at the University of California, Irvine, who is not part of the CoGeNT team. “This is the first evidence we’ve seen it somewhere other than DAMA……”

Read more: http://www.newscientist.com/article/dn20434-second-experiment-hints-at-seasonal-dark-matter-signal.html

Written by physicsgg

May 3, 2011 at 9:23 am

Posted in DARK MATTER

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