Using the light of distant, dying galaxies, astronomers have produced the largest, three-dimensional map of the universe yet. Encompassing roughly 600,000 so-called luminous red galaxies--ancient galaxies with only old, red stars left that are uniquely brilliant--the map extends 5.6 billion light-years out into space, or 40 percent of the way to the edge of the visible universe.

Astrophysicists Nikhil Padmanabhan of Princeton University and David Schlegel of Lawrence Berkeley National Laboratories led a team of international colleagues that painstakingly surveyed the color and redshift of 10,000 of these unique galaxies. Using data from the Sloan Digital Sky Survey in New Mexico and from a telescope in Australia, the researchers were able to map a fan-shaped slice of the cosmos that covers a tenth of the sky in the Northern Hemisphere. They then applied these measurements to the broader sample to create their three-dimensional map.

"There's statistical uncertainty in applying a brightness-distance relation derived from 10,000 red luminous galaxies to all 600,000 without measuring them individually," Padmanabhan admits. "The game we play is, we have so many that the averages still give us very useful information about their distribution."

With such a measure of the distribution of matter, the researchers could test a proposed ruler based on regular variations in the grouping of ordinary matter every 450 million light-years or so. "Unfortunately, it's an inconveniently sized ruler," Schlegel says. "We had to sample a huge volume of the universe just to fit the ruler inside."

By showing such regular variations, the map confirms theories about dark energy--a mysterious force that accounts for the acceleration of the universe's expansion. As expected, its influence is outsized, making up nearly 75 percent of the universe's density. "By looking at where density variations were at the time of the cosmic microwave background and seeing how they evolve into a map that covers the last 5.6 billion years, we can see if our estimates of dark energy are correct," Padmanabhan notes. Now the astronomers just need to make even more precise maps--hard to do when so much of the matter is in the dark. The research is slated to appear in an upcoming issue of Monthly Notices of the Royal Astronomical Society.

1 Comments

1. 1. jtdwyer 01:57 PM 10/19/09

   Expanded Universe Perspective
   
   The perception of an accelerating universe may have simply arisen from our limited observational perspective. Since light emitted about 10B years ago from galaxies near the periphery of the observed universe indicate that the rate of universal expansion was greater than does light emitted about 5B years ago from nearer galaxies, it must be concluded that universal expansion has decelerated, as had been previously expected. Only this temporal, rather than spatial, interpretation produces a conclusion consistent with fundamental laws of physics.
   
   From this perspective, distant galaxies did not begin to more rapidly recede away from our own galaxy about 5B years ago, but rather, in the earlier universe all galaxies more rapidly receded away from all other galaxies. Observed more distant galaxies are further away than expected because, long ago, our own galaxy very rapidly receded away from their approaching light emissions. More recently, galaxies have less rapidly receded away from these ancient light emissions as well as the more recent emissions of nearer galaxies.
   
   The redshift of distant light indicates the relative velocity of the emitter and receiver, physically imparted to the wavelength of light by the relative velocity of its emitter as it is emitted and the receiver as it is received. The actual distance light traverses is determined by the separation distance of the emitter and receiver at emission and any subsequent relative motion of the receiver throughout the observed light's transit. The receiver's actual relative velocities, varying throughout transit, are not reflected in the redshift of observed light but are reflected in its traversal distance, as indicated by diminishment of its observed luminosity. The discrepancy between redshift and distance is produced by temporal variation in the velocity of the receiver.
   
   Events affecting the observed characteristics of light from other galaxies:
   
   1. As all galaxies receded away from each other in the earlier universe, their emitted light was redshifted by the relative velocity of the then current rate of spacetime expansion.
   
   2. As light emitted from other galaxies in the direction of our own galaxy independently traversed expanding spacetime, our galaxy continued its recession, initially at the relative velocity indicated by the emission redshift but varying over time.
   
   3. When the light from other galaxies is eventually received it is again redshifted by the now current recession velocity.
   
   4. The distance the observed light actually traversed exceeds the relative velocity indicated by the observed light's redshift. This discrepancy is proportionate to the variance of the receiver's recession velocity from emission to reception.
   
   In a decelerating universe, the receiver has moved farther during the observed light's transit than is indicated by its relative velocity at reception. This is consistent with observations, as more distant galaxies have been determined to be more distant than expected based solely on redshift.
   
   The apparent universe consisting of innumerable galaxies surrounding our own, all receding away from us, is an illusion of relative motion: it is we who have receded away from the ancient light emissions of all observed distant galaxies. While all distant galaxies recede away from each other, we observe only their light, emitted long ago. This light has independently traversed expanding spacetime in our direction as we continued to recede away from it. Observations previously concluded to indicate an accelerating universe instead indicate a decelerating universe, consistent with the second law of thermodynamics.

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