NASA JPL | Space Telescope Science Institute | STScI-2010-26 | 19 Aug 2010
Astronomers take a step towards revealing the Universe's biggest mysteryAn international team of astronomers using NASA's Hubble Space Telescope has devised a new method for measuring perhaps the greatest puzzle of our universe — dark energy. This mysterious phenomenon, discovered in 1998, is pushing our universe apart at ever-increasing speeds. The team's results appear in the August 20, 2010 issue of the journal Science.
Astronomers have devised a new method for measuring perhaps the greatest puzzle of our universe — dark energy. This mysterious force, discovered in 1998, is pushing our universe apart at ever-increasing speeds.
For the first time, astronomers using NASA's Hubble Space Telescope were able to take advantage of a giant magnifying lens in space — a massive cluster of galaxies — to narrow in on the nature of dark energy. Their calculations, when combined with data from other methods, significantly increase the accuracy of dark energy measurements. This may eventually lead to an explanation of what the elusive phenomenon really is.
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In their new study, the science team used images from Hubble to examine a massive cluster of galaxies, named Abell 1689, which acts as a magnifying, or gravitational, lens. The gravity of the cluster causes galaxies behind it to be imaged multiple times into distorted shapes, sort of like a fun-house mirror reflection that warps your face.
Using these distorted images, the scientists were able to figure out how light from the more distant, background galaxies had been bent by the cluster — a characteristic that depends on the nature of dark energy. Their method also depends on precise ground-based measurements of the distance and speed at which the background galaxies are traveling away from us. The team used these data to quantify the strength of the dark energy that is causing our universe to accelerate.
Credit: NASA, ESA, E. Jullo (Jet Propulsion Laboratory), P. Natarajan (Yale University), and J.-P. Kneib (Laboratoire d'Astrophysique de Marseille, CNRS, France)
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ESA | Hubble European Information Center | heic1014 | 19 Aug 2010
Astronomers Use Galactic Magnifying Lens to Probe Elusive Dark EnergyAn international team of astronomers using gravitational lensing observations from the NASA/ESA Hubble Space Telescope has taken an important step forward in the quest to solve the riddle of dark energy, a phenomenon which mysteriously appears to power the Universe's accelerating expansion. Their results appear in the 20 August 2010 issue of the journal Science.
Normal matter like that found in stars, planets and dust clouds only makes up a tiny fraction of the mass–energy content of the Universe. It is dwarfed by the amount of dark matter — which is invisible, but can be detected by its gravitational pull. In turn, the amount of dark matter in the Universe is itself overwhelmed by the diffuse dark energy that permeates the entire Universe. Scientists believe that the pressure exerted by this dark energy is what pushes the Universe to expand at an ever-increasing rate.
Probing the nature of dark energy is, therefore, one of the key challenges in modern cosmology. Since its discovery in 1998, the quest has been to characterise and understand it better. This work presents an entirely new way to do so.
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The team measured the properties of the gravitational lensing in the galaxy cluster Abell 1689. Gravitational lensing is a phenomenon predicted by Einstein’s theory of general relativity, and was here used by the team to probe how the cosmological distances (and thus the shape of space-time) are modified by dark energy. At cosmic distances, a huge cluster of galaxies in the foreground has so much mass that its gravitational pull bends beams of light from very distant galaxies, producing distorted images of the faraway objects. The distortion induced by the lens depends in part on the distances to the objects, which have been precisely measured with large ground-based telescopes such as ESO’s Very Large Telescope and the Keck Telescopes.
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Looking at the distorted images allows astronomers to reconstruct the path that light from distant galaxies takes to make its long journey to Earth. It also lets them study the effect of dark energy on the geometry of space in the light path from the distant objects to the lensing cluster and then from the cluster to us. As dark energy pushes the Universe to expand ever faster, the precise path that the light beams follow as they travel through space and are bent by the lens is subtly altered. This means that the distorted images from the lens encapsulate information about the underlying cosmology, as well as about the lens itself.
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The real strength of this new result is that it devises a totally new way to extract information about the elusive dark energy. It is a unique and powerful one, and offers great promise for future applications.
Yale University | Science & Engineering | 19 Aug 2010
Cosmological Constraints from Strong Gravitational Lensing in Clusters of Galaxies - E Jullo et alA team of astronomers has used a massive galaxy cluster as a cosmic magnifying lens to study the nature of dark energy for the first time. When combined with existing techniques, their results significantly improve current measurements of the mass and energy content of the universe. The findings appear in the August 20 issue of the journal Science.
Astronomers employ a number of methods to study the geometry of the universe, which tells us something about the nature of dark energy—a mysterious force discovered in 1998 that speeds up the expansion of the universe, but about which little else is known. Uncovering the nature of dark energy, which makes up about 72 percent of all the mass and energy in the universe and will ultimately determine its fate, is one of the holy grails of modern-day cosmology.
Now an international team including Yale University cosmologist Priyamvada Natarajan has used gravitational lensing to learn more about this elusive force. Using data taken by the Hubble Space Telescope as well as ground-based telescopes, the team analyzed images of 34 extremely distant galaxies situated behind Abell 1689, one of the biggest and most massive known galaxy clusters in the universe.
Through the gravitational “lens” of Abell 1689, astronomers were able to detect the faint, distant background galaxies—whose light was bent and projected by the cluster’s massive gravitational pull—in a similar way that the lens of a magnifying lens distorts an object’s image.
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Using theoretical models of the distribution of both ordinary and dark matter in space, Natarajan and the team were able to narrow the range of current estimates about dark energy’s effect on the universe, denoted by the value w, by 30 percent. The team combined their new technique with other methods, including using supernovae, X-ray galaxy clusters and data from the Wilkinson Microwave Anisotropy Probe (WMAP) spacecraft, to constrain the value for w.
The result confirms previous findings that the nature of dark energy likely corresponds to a flat universe. In this scenario, the expansion of the universe will continue to accelerate and the universe will expand forever.
- Science 329(5994) (20 Aug 2010) DOI: 10.1126/science.1185759
