A strip of sky reveals half of all time
Peering through a tiny strip of sky, astronomers are looking back over half the age of our universe to times when galaxies were young. Their goal is to study the universe as it was back then. That includes learning more about how galaxies evolve as they transition from adolescence to adulthood.
Research teams have scarcely begun to crunch through the data. Yet to their surprise and delight, one team has already discovered a fundamental organizing principle that shapes all galaxies. It seems to have been built into the fabric of our universe when it was born some 13.7 billion years ago.
It's an early payoff for an ambitious project with a ham-handed name: All-wavelength Extended Groth Strip International Survey.
Its participants call it AEGIS.
Named after Princeton University physicist Edward Groth, the strip is a slot about the length of two full moons near the Big Dipper's handle. Just as you can see a lot through a crack in a fence, astronomers are seeing a lot through the Groth Strip. Results released last week include a mosaic of Hubble Space Telescope images showing color images of at least 50,000 galaxies.
Nearly 100 scientists in six countries are engaged in the five-year AEGIS project. Their 10 instrument teams have the services of four orbiting observatories plus various ground-based installations. Together, these instruments cover a wavelength range from radio waves to X-rays. They give what Sandra Faber at the University of California in Santa Cruz calls "the first truly panchromatic look at the universe more than halfway back in time."
Results posted on the AEGIS website (aegis.ucolick.org) last week have fired the enthusiasm of AEGIS researchers. Summing up their scientific significance, Marc Davis at the University of California in Berkeley said simply, "They knock your socks off."
Dr. Faber has special reason for elation. There are three types of galaxies – neat spirals, cloudlike ellipticals, and "train wrecks" left by galaxy collisions that look like they had a bad hair day. There's a long-standing mathematical relationship that lets astronomers calculate a spiral galaxy's mass from the way stars move around it. Faber co-wrote a study that extended this relationship to include less organized star motions in elliptical galaxies. Now Faber's colleague, Susan Kassin, has used AEGIS data to come up with a star speed index that extends the relationship to cover all galaxies, even the disordered motion of stars in the train wreck galaxies.
Measure representative star motion in any type of galaxy whatsoever. Calculate the new speed index. Then you can predict the total mass of the galaxy's stars. This generality looks like an organizing principle that reflects a fundamental property of the universe. If so, Faber says these speed/mass relationships, including her own, "were imprinted by the nature of the fluctuations that made galaxies in the first place." Those were fluctuations in density that occurred at the very birth of our universe.
To your eye, the Groth Strip is empty sky. To AEGIS astronomers, it's a ripe harvest field.
If researchers have already lost their socks, they better stay barefoot as they traipse through it still farther.