August 8, 2012

New 3-D Map Offers Clues To Dark Matter And Dark Energy

April Flowers for - Your Universe Online

The largest-ever 3-D map of massive galaxies and distant black holes was released this week in the hopes that it will help explain the mysteries of "dark matter" and "dark energy."

This new sky map is the work of the Sloan Digital Sky Survey III (SDSS-111) collaboration. SDSS-III is mission is to map the Milky Way, search for extrasolar planets, and solve the mystery of dark matter. The research team began to gather data in 2008 for a six-year project using the Sloan Foundation 2.5-meter Telescope at Apache Point Observatory in New Mexico.

Early last year, the SDSS-III released an image of the sky that was, to that date, the largest ever. It covers one-third of the night sky. With Data Release 9 (DR9), they have begun to expand this image into a fully functional three-dimensional map. DR9, posted online last week, makes available the first third of the galaxy map that the project is designed to create.

"What really makes me proud of this survey is our commitment to creating a legacy for the future," said Michael Blanton, a professor at New York University who led the team that prepared DR9. "Our goal is to create a map of the Universe that will be used long after we are done, by future generations of astronomers, physicists, and the general public."

DR9 is the latest in a series of data releases stretching back to 2001. This new release includes data from the ongoing Baryon Oscillation Spectroscopic Survey (BOSS). BOSS uses baryon acoustic oscillations (regular, periodic fluctuations in the density of the visible baryonic matter of the universe) to complete its very ambitious project. BOSS will eventually measure the positions of 1.5 million massive galaxies over the past six billion years of cosmic time, as well as 160,000 quasars — giant black holes actively feeding on stars and gas — from as long ago as 12 billion years in the past.

BOSS is targeting these particular big, bright galaxies because they live in the same places as other galaxies and they are easy to spot, even so far away in the Universe. Mapping these big galaxies provides an effective way to make a map of the rest of the Universe.

Scientist will be able to retrace the history of the universe over the last six billion years with such a map. This will allow them to create better estimates for how much of the Universe is made up of dark matter and dark energy. Dark matter is matter that we cannot directly see because it doesn't emit or absorb light, and dark energy seems to be the force that drives the accelerating expansion of the Universe.

"Dark matter and dark energy are two of the greatest mysteries of our time," said David Schlegel of Lawrence Berkeley National Laboratory, who led the SDSS-III effort to map these galaxies and quasars. "We're confident this new map will guide us, or someone else, in solving these mysteries."

That map is the centerpiece of DR9 and includes new spectra from 540,000 galaxies from when the Universe was half its present age. A spectrum is a measure of light from a galaxy at different wavelengths; from this information, we can measure the distances to those galaxies. This distance information provides the third dimension in the DR9 map, providing a more detailed view of the structure of the Universe than has been measured before.

The new map pinpoints the locations and distances of over a million galaxies. It covers a total volume equivalent to that of a cube four billion light-years on a side.

"We want to map the largest volume of the universe yet, and to use that map to understand how the expansion of the universe is accelerating," said Daniel Eisenstein (Harvard-Smithsonian Center for Astrophysics), the director of SDSS-III.

Further details, and another way to measure the distribution of matter in the Universe, are added to the map by quasars. Quasars are the brightest objects in the distant Universe, and their spectra reveal intricate patterns imprinted by large scale clumping of intergalactic gas and the underlying dark matter that lies between each quasar and the Earth.

DR9 is not only helping us to understand the distant Universe, but also our own cosmic backyard, the Milky Way galaxy. DR9 includes better estimates for the temperatures and chemical compositions of more than half a million stars in our own galaxy.

"With these better estimates, we can look back at the history of our galaxy," said Connie Rockosi of the University of California, Santa Cruz, who leads the SDSS- III's Milky Way study. "This new information can help us tell the story of how our galaxy formed, and how it came to be the Milky Way that we see today."

With all the new images and spectra come the promise of new discoveries about our Universe, but SDSS-III isn't nearly done. They are only halfway through their six-year survey and expect to release three times as much data before completion in 2014.

Doubtless, DR9 contains many surprises beyond the data already gleaned.

"The most fun part of making this data available online is knowing that anyone on the Internet can now access the very same data and search tools that professional astronomers use to make exciting discoveries about our Universe," said Ani Thakar of Johns Hopkins University. Thakar works hard behind-the-scenes to distribute the terabytes of SDSS-III data to astronomers and the public.

According to the scientific spokesperson for the SDSS-III, Michael Wood-Vasey, this is science at its collaborative best. SDSS-III shares all of its data with the world to allow anyone to make the next big discovery. The project is a sort of open-source astronomy experiment, with websites releasing all of their data, resources for teachers (including lesson plans to teach astronomy, science, technology, and math using DR9), and they are participating in the new release of Galaxy Zoo, a citizen science project which allows online volunteers to contribute to cutting edge astronomy research.

The team published their findings about the DR9 data, " The Ninth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the SDSS-III Baryon Oscillation Spectroscopic Survey" in Astrophysical Journal Supplement Series.