Dark matter and Dark energy

As you know,the unknown nature of dark matter and dark energy are important problems of cosmologists today.Here we want to share our information and latest news about them.

http://up6.iranblog.com/files/eaDark...-CL0024-17.jpg

I have attached a power point file which is a lecture on dark matter as an introduction.
http://sfwdmotahari.persiangig.com/d...artment%29.pps
It contains the definitions of the latest theories for the nature of dark matter and the effects that help astronomers to find it
The essence of dark energy is really more complex and unknown and it seems to be a created amazing factor which seems essentials for calculations on cosmological models to correspond with observations but there is no powerful theory for its nature till now!

It was really the most exciting news that I've ever heard in Physics world!!:explode:
It is really amazing if all these improvements on dark matter may be questioned by this new theory!

http://www.physorg.com/news/2011-08-...um-vacuum.html

http://sfwdmotahari.persiangig.com/image/dipole.jpg

If i want to say a summary about it:
The important key of this article is that maybe the effect of dark matter is caused by the gravitational polarization of quantum vacuum and so there would be nothing called dark matter!
Hajdukovic(The author of article) says: “The first entity is our ‘normal’ matter (hence we do not assume the existence of dark matter and dark energy), immersed in the second entity, the quantum vacuum, considered as a sea of different kinds of virtual dipoles, including gravitational dipoles.”
and if it exists,these gravitational dipoles may become gravitationally polarized by the nearby baryonic matters and when these virtual dipoles align,they can produce an additional gravitational field which we thought it is the effect of dark matter!:OSMILEY:
It is amazing that this theory have described some famous observational effects like Tully-Fisher relation!
!...awesome

نقل قول:

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نوشته اصلی توسط Fowad

It was really the most exciting news that I've ever heard in Physics world!!:explode:
It is really amazing if all these improvements on dark matter may be questioned by this new theory!
http://www.physorg.com/news/2011-08-...um-vacuum.html
It is amazing that this theory have described some famous observational effects like Tully-Fisher relation!
!...awesome

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But it seems that there are some other important observational results that are described much better with Dark matter like:
rotational curves of Galaxies and their unusual behavior nearby the edge,which guide us to thinking about a mass inside and also other effects like observations of cosmic microwave background(CMB),gravitational lensing,supernovaes and etc.
So it seems that there is still a long way for this new idea to replace the old theory of dark matter...!
I've also heard that there was such an idea for this extra gravitational field caused by gravitational dipoles previously and it was an idea for the nature of dark matter itself!Maybe the reason that cosmologists did not consider to it, was their output new results of fundamental particles on CERN!we should ask them?!

Astrophile: How to spot a dark-matter galaxy

18 January 2012 by Lisa Grossman

*Astrophile is a weekly column on curious cosmic objects, from the solar system to the far reaches of the multiverse

http://www.newscientist.com/data/ima...1370-1_300.jpg

If there was a dark matter galaxy hiding in front of this kangaroo, this is what we would see
Image: Nature and Robert Schmidt

Object type: Dwarf galaxy
Mass: 190,000,000 times the mass of the sun
Composition: Mostly dark matter

If we could don dark matter glasses and look at the universe around us, we might see thousands of miniature galaxies swarming about the luminous spirals that make up the Milky Way and Andromeda.

We can't – but we have the next best thing. A technique known as gravitational lensing has allowed one of these dark dwarfs to be glimpsed, suggesting the Milky Way isn't as lonely as it looks to us Earthlings.

Astronomers think that galaxies usually grow by devouring smaller nearby clusters of stars called dwarf galaxies, no bigger than 100 million times the mass of the sun. According to this theory, the Milky Way and all other full-size galaxies should keep company with thousands of dwarfs. However, only 30 such companions have been spotted in our neighbourhood.

Where are all the missing minis hiding? One explanation is that they're mostly made of dark matter, the mysterious, aloof substance thought to make up 83 per cent of the mass in the universe but which is reluctant to interact with regular matter.

"They are there, but we just don't see them," says Simona Vegetti of the Massachusetts Institute of Technology.

Warped lens

Some of the Milky Way's known satellites, such as the Sagittarius dwarf galaxy, do seem to be mostly dark matter, hosting just 100 or fewer visible stars. It's hard to know how many more are lurking undercover, though. And it's especially hard to know if distant galaxies host any dark satellites at all.

"When you're trying to test theories using the Milky Way, at a certain point you have to ask, is the Milky Way a special place or not?" Vegetti says. "It's important to test in other galaxies."

Now, Vegetti and colleagues have tracked down a dark dwarf galaxy orbiting a massive elliptical galaxy 10 billion light years away. The invisible entity, part of a system called JVAS B1938+666, weighs in at about 190 million times the mass of the sun, making it similar in size to the Sagittarius dwarf.

The team found the dark galaxy by looking at the way its gravity warped the space-time around it, a technique called gravitational lensing. When the dwarf's vast companion passed in front of an even more distant galaxy, its gravity made the background galaxy look stretched out in a ring of light. Normally these rings, called Einstein rings, form nearly perfect circles. But the presence of the otherwise invisible dwarf galaxy introduced a small flaw, making the further galaxy look like a perfect china bowl with a chip in it.

Purely dark

"The great thing about the technique is that we can use it to detect satellite galaxies that are purely dark matter," says study co-author Chris Fassnacht of the University of California, Davis – although it's hard to tell from here whether the galaxy has a handful of stars or not.

This is the second dark galaxy to be spotted outside our galactic system, but the first that is as small as the Milky Way's known companions. The other galaxy was just 2.6 billion light years away and 18 times as massive.

"These two together are telling us that it's not something special to have a satellite that small," Vegetti says. The universe may be swarming with small, dark galaxies, she says, though she and her team will have to keep looking to know for sure.

"We've found two, so everything looks promising," she says.

From: Newscientist

some thing in our universe I think are fantastic and one of them is dark energy I put a general definition of dark energy from NASA , I hope you enjoy this article :
In the early 1990's, one thing was fairly certain about the expansion of the Universe. It might have enough energy density to stop its expansion and recollapse, it might have so little energy density that it would never stop expanding, but gravity was certain to slow the expansion as time went on. Granted, the slowing had not been observed, but, theoretically, the Universe had to slow. The Universe is full of matter and the attractive force of gravity pulls all matter together. Then came 1998 and the Hubble Space Telescope (HST) observations of very distant supernovae that showed that, a long time ago, the Universe was actually expanding more slowly than it is today. So the expansion of the Universe has not been slowing due to gravity, as everyone thought, it has been accelerating. No one expected this, no one knew how to explain it. But something was causing it.
http://science.nasa.gov/media/medial.../image_preview
Eventually theorists came up with three sorts of explanations. Maybe it was a result of a long-discarded version of Einstein's theory of gravity, one that contained what was called a "cosmological constant." Maybe there was some strange kind of energy-fluid that filled space. Maybe there is something wrong with Einstein's theory of gravity and a new theory could include some kind of field that creates this cosmic acceleration. Theorists still don't know what the correct explanation is, but they have given the solution a name. It is called dark energy.
What Is Dark Energ
More is unknown than is known. We know how much dark energy there is because we know how it affects the Universe's expansion. Other than that, it is a complete mystery. But it is an important mystery. It turns out that roughly 70% of the Universe is dark energy. Dark matter makes up about 25%. The rest - everything on Earth, everything ever observed with all of our instruments, all normal matter - adds up to less than 5% of the Universe. Come to think of it, maybe it shouldn't be called "normal" matter at all, since it is such a small fraction of the Universe.
One explanation for dark energy is that it is a property of space. Albert Einstein was the first person to realize that empty space is not nothing. Space has amazing properties, many of which are just beginning to be understood. The first property that Einstein discovered is that it is possible for more space to come into existence. Then one version of Einstein's gravity theory, the version that contains a cosmological constant, makes a second prediction: "empty space" can possess its own energy. Because this energy is a property of space itself, it would not be diluted as space expands. As more space comes into existence, more of this energy-of-space would appear. As a result, this form of energy would cause the Universe to expand faster and faster. Unfortunately, no one understands why the cosmological constant should even be there, much less why it would have exactly the right value to cause the observed acceleration of the Universe.

Astronomers Reach New Frontiers of Dark Matter

ScienceDaily (Jan. 9, 2012) — Astronomers have mapped dark matter on the largest scale ever observed. New findings reveal a Universe comprising an intricate cosmic web of dark matter and galaxies spanning more than one billion light years.

The School's Dr Catherine Heymans and Associate Professor Ludovic Van Waerbeke of the University of British Columbia, Vancouver, Canada, will present the results January 9 to the American Astronomical Society meeting in Austin, Texas.

An international team of researchers led by Van Waerbeke and Heymans achieved their results by analysing images of about 10 million galaxies in four different regions of the sky. They studied the distortion of the light emitted from these galaxies, which is bent as it passes massive clumps of dark matter during its journey to Earth


Their project -- known as the Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS) -- uses data from the Canada-France-Hawaii Telescope Legacy Survey. This accumulated images over five years using the wide field imaging camera MegaCam, a 1 degree by 1 degree field-of-view, 340 Megapixel camera on the CFHT in Hawaii.

Galaxies included in the survey are typically six billion light years away. The light captured by the images used in the study was emitted when the Universe was six billion years old -- roughly half the age it is today.

The team's result has been suspected for a long time from studies based on computer simulations, but was difficult to verify owing to the invisible nature of dark matter. This is the first direct glimpse of dark matter on large scales showing the cosmic web in all directions.

Dr Thomas Kitching is the Cosmology Working Group coordinator, based in the School's Institute for Astronomy. "The dark matter map we have produced looks back over 75% of the age of the Universe, to a time when it was very different to today. By tracking the evolution of the Universe over cosmic time, the team at Edinburgh will investigate how dark energy has come to dominate the present day Universe.

"Over the next few months we will be using this data to map the evolution of the expansion of the Universe and learn about dark energy, which is causing the expansion of the Universe to accelerate. We will test theories of gravity itself to determine if Einstein's general relativity is correct or not. We will also use it to determine the properties of neutrinos, ghostly particles that interact with normal matter only very weakly."

The research was supported by the European Research Council, Natural Sciences and Engineering Research Council of Canada, the Canadian Institute for Advanced Research and the Canadian Astronomy Data Centre

http://images.sciencedaily.com/2012/01/120109132703.jpgThe observations show that dark matter in the Universe is distributed as a network of gigantic dense (white) and empty (dark) regions, where the largest white regions are about the size of an Earth moon on the sky. (Credit: Van Waerbeke, Heymans and the CFHTLenS Collaboration)