* Astronomy

Blobrana · L

RE: Dark Energy

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Voiding the Cosmic Void: We're not at Center of the Universe After All
Models of the universe that place us near the center of a large, sparse region don't jibe with astronomical observations. Cosmologists at the University of British Columbia reached the conclusion through a new analysis that reaffirms the presence of a perplexing dark energy.

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Astronomers will hold a media teleconference Tuesday, Dec. 16 at 1 p.m. EST to announce important new results on dark energy that were made using NASA's Chandra X-ray Observatory.

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Is Earth at the heart of a giant cosmic void?
It was the evolutionary theory of its age. A revolutionary hypothesis that undermined the cherished notion that we humans are somehow special, driving a deep wedge between science and religion. The philosopher Giordano Bruno was burned at the stake for espousing it; Galileo Galilei, the most brilliant scientist of his age, was silenced. But Nicolaus Copernicus's idea that Earth was just one of many planets orbiting the sun - and so occupied no exceptional position in the cosmos - has endured and become a foundation stone of our understanding of the universe.

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The GRavitational lEnsing Accuracy Testing 2008 (GREAT08) PASCAL Challenge is being set by 38 scientists across 19 international institutions, with the aim of enticing other researchers to crack it by 30 April 2009.

"The GREAT08 PASCAL Challenge will help us answer the biggest question in cosmology today: what is the dark energy that seems to make up most of the universe? We realised that solving our image processing problem doesn't require knowledge of astronomy, so we're reaching out to attract novel approaches from other disciplines" - Dr Sarah Bridle, UCL Physics and Astronomy, who is leading the challenge alongside Professor John Shawe-Taylor, Director of the UCL Centre for Computational Statistics and Machine Learning.

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Theorists Tackle Universe's 'Coincidence Problem'
Australian scientists have come up with a simple solution to one of the deepest puzzles in our understanding of the cosmos -- why life on Earth coincides with a momentous shift in the makeup of the universe.
Ph.D. student Chas Egan and Charley Lineweaver from Australian National University publish their solution to the so-called "coincidence problem" this week in the journal Physical Review D.
The conundrum has its roots in the way the universe changes as it expands

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Dark energy site open for business!
Nearly 3/4 chunk of the cosmic budget is dark energy, the mysterious force (or pressure, really) that appears to be making the expansion of the Universe accelerate. Weve known the Universe is expanding since the early 20th century, but everyone assumed, logically, that the combined gravity of all the objects in space was slowing the expansion, like tension in a rubber band.
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A universe riddled with holes would do away with the need for dark energy. Unfortunately that idea itself now seems to have a few holes.
In 1998, astronomers found that distant supernovae were dimmer, and thus farther away, than expected. According to the standard model of cosmology, which assumes that the universe is homogenous on large scales, this suggested that the expansion of the universe was speeding up. That acceleration was attributed to a mysterious "dark energy" inherent in the fabric of space-time.
Then, last year, Edward Kolb of the Fermi National Accelerator Laboratory in Batavia, Illinois, and colleagues re-examined the supernovae data in the context of the "Swiss-cheese" model, which assumes the universe is full of holes or voids with less matter than other regions. It was inspired by the accidental discovery of a giant void about 1 billion light years across.

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Title: Constraints on dark energy models from radial baryon acoustic scale measurements.
Authors: Lado Samushia, Bharat Ratra .

We use the radial baryon acoustic oscillation (BAO) measurements of Gaztanaga et al. (2008) to constrain parameters of dark energy models. These constraints are comparable with constraints from other "non-radial" BAO data. The radial BAO data are consistent with the time-independent cosmological constant model but do not rule out time-varying dark energy.

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Astronomers searching for evidence of the mysterious energy that is speeding up the expansion of the Universe have discovered three new galaxy clusters. They used a microwave survey technique that could rival existing ways of searching for dark energy.
The discovery is the first step towards a catalogue of thousands of galaxy clusters, whose evolution in the early Universe reflects the tug of war between gravity and dark energy, the repulsive force that seems to make up three-quarters of the total mass-energy in the Universe.

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