National Radio Astronomy Observatory | 21 July 2010
Green Bank Telescope Enables "Intensity Mapping" to Shed Light on Mysteries of Dark EnergyPioneering observations with the National Science Foundation's giant Robert C. Byrd Green Bank Telescope (GBT) have given astronomers a new tool for mapping large cosmic structures. The new tool promises to provide valuable clues about the nature of the mysterious "dark energy" believed to constitute nearly three-fourths of the mass and energy of the Universe.
Dark energy is the label scientists have given to what is causing the Universe to expand at an accelerating rate. While the acceleration was discovered in 1998, its cause remains unknown. Physicists have advanced competing theories to explain the acceleration, and believe the best way to test those theories is to precisely measure large-scale cosmic structures.
Sound waves in the matter-energy soup of the extremely early Universe are thought to have left detectable imprints on the large-scale distribution of galaxies in the Universe. The researchers developed a way to measure such imprints by observing the radio emission of hydrogen gas. Their technique, called intensity mapping, when applied to greater areas of the Universe, could reveal how such large-scale structure has changed over the last few billion years, giving insight into which theory of dark energy is the most accurate.
National Science Foundation | PR 10-124 | 21 July 2010
New Galaxy Maps to Help Find Dark Energy Proof?Carnegie Mellon researcher Jeff Peterson describes new technique developed by international research team to expand understanding of the expanding universe.
Using the world's largest, fully steerable radio telescope--the National Science Foundation's Robert C. Byrd Green Bank Telescope (GBT) in W.Va.--an international team of researchers has given astronomers the promise of a new tool for mapping the universe and gaining valuable clues about the nature of the mysterious "dark energy" believed to constitute nearly three-fourths of the universe's mass and energy. "Intensity Mapping" offers the potential for significant contributions to the field and further discovery. This research is detailed in the July 22 issue of the journal Nature.
In the matter-energy soup of the extremely early universe, sound waves are thought to have left detectable imprints on the large-scale distribution of galaxies. The researchers developed a way to measure such imprints by observing the radio emission of hydrogen gas. Their technique, called intensity mapping, when applied to greater areas of the universe, could reveal how such a large-scale structure has changed over the last few billion years, giving insight into which theory of dark energy is the most accurate.
This new technique was developed by an international collaborative team that consists of Tzu-Ching Chang, of the Academia Sinica in Taiwan and the University of Toronto, Ue-Li Pen of the University of Toronto, and Jeffrey Peterson and Kevin Bandura of Carnegie Mellon University (CMU).
National Geographic | Daily News | 21 July 2010
A New Way to Map the UniverseRadio maps may reveal impact of cosmic sound waves.
A newly developed technique could one day help astronomers use giant sound waves to test theories of dark energy, the mysterious force thought to be causing the universe to fly apart faster over time.
Called intensity mapping, the technique looks for unique radio emissions of hydrogen gas in galaxies and galaxy clusters to map the large-scale structure of the universe. Hydrogen is the lightest and most abundant element in the universe, and it tends to cluster around galaxies because of their strong gravitational pull.
Until now, astronomers have been mapping large cosmic structures by identifying the galaxies and clusters themselves—a process akin to mapping forests on Earth by counting individual trees. The new method is more like mapping forests by looking for large patches of green.
By speeding up large-scale mapping efforts, the method should reveal how structures in the universe have evolved since the big bang.
In particular, the new maps might help astronomers detect variations in matter distribution caused by enormous sound waves called baryon acoustic oscillations, or BAOs, which were created shortly after the big bang.
Using the cosmic sound waves as rulers to measure the size of the universe over time can help scientists understand how dark energy has affected the cosmos.
Science NOW | 21 July 2010
An intensity map of hydrogen 21-cm emission at redshift z ≈ 0.8[img3="Cosmic scaffolding. The "cosmic web" of dark matter as simulatedA new technique might soon enable cosmologists to map the universe even when they can't pick out individual galaxies. If it works, researchers would be able to probe the structure of 500 times as much of the universe as they have studied so far. "This is the first pioneering experiment that shows that this can be done," says Avi Loeb, a theoretical astrophysicist at Harvard University, who was not involved in the work.
on a computer. A new technique could enable scientists to
detect much more of the enormous structure than before.
Credit: Nickolay Y. Gnedin, Nature, 435 (2 June 2005)"]http://news.sciencemag.org/sciencenow/a ... o-3873.jpg[/img3]
Our galaxy resides within a huge "cosmic web" of dark matter, mysterious stuff that so far has revealed itself only through its gravity. Galaxies lie inside the dark-matter filaments, and scientists have made great strides in tracing this "large-scale structure" by mapping those luminous beacons. Astronomers working with the Sloan Digital Sky Survey have used a 2.5-meter telescope at the Apache Point Observatory in Sunspot, New Mexico, to map the location of more than 930,000 nearby galaxies, determining the distance to each by how much the expansion of the universe has stretched, or "redshifted," the wavelength of the galaxy's light.
Unfortunately, galaxies more than 5 billion light-years away are so dim that the Sloan survey can't spot them. In contrast, the afterglow of the big bang provides a kind of celestial wallpaper that's about 45 billion light-years away. So scientists have surveyed only 0.1% of the observable universe, Loeb says.
But that could change, thanks to work led by cosmologist Tzu-Ching Chang of Academia Sinica in Taipei and the University of Toronto in Canada. Instead of searching for the light from individual galaxies with an optical telescope, the team stalked a different quarry, red-shifted radio waves emitted by hydrogen atoms floating in huge clouds within the galaxies. That distinctive "21 centimeter" radiation can be traced with a radio telescope even if the scope does not have enough angular resolution to resolve individual galaxies, Chang says.
- Nature 466 (22 July 2010) | doi: 10.1038/nature09187
