LONDON: Scientists have for the first time measured the distance to galaxies more than six billion light years away accurate to 1%.
The analysis revealed on Thursday incorporates spectra of 1,277,503 galaxies and covers 8,509 square degrees of the sky visible from the northern hemisphere. This is the largest sample of the universe ever surveyed at this density.
Nearly all of these stars are a few thousand light-years away and all are still within our own Milky Way galaxy according to researchers from the Baryon Oscillation Spectroscopic Survey (BOSS), the largest of four cosmological surveys currently underway on the Sloan Foundation Telescope in the US.
When complete the project will have collected high-quality spectra of 1.3 million galaxies plus 160,000 quasars and thousands of other astronomical objects covering 10,000 square degrees.
David Schlegel, a physicist at Lawrence Berkeley National Laboratory (LBNL) and the principal investigator of BOSS said, “I now know the size of the Universe better than I know the size of my house.”
“Determining distance is a fundamental challenge of astronomy,” said Daniel Eisenstein, director of the Sloan Digital Sky Survey III (SDSS-111), an international collaboration of four surveys including BOSS. “Once you know how far away it is, learning everything else about it is suddenly much easier,” he added.
“Astronomers were arguing about estimates that differed by up to 50% 20 years ago. Five years ago we’d refined that uncertainty to 5%; a year ago it was 2%. The 1% accuracy will be the standard for a long time,” he said. With the highly accurate distance measurements, BOSS astronomers are hoping to understand ‘dark energy’, thought to permeate empty space accelerating the expansion of the Universe. BOSS uses a specialized instrument that can make detailed measurements of 1000 galaxies at a time. The BOSS measurements are consistent with a form of dark energy that stays constant through the history of the Universe.
This “cosmological constant” is one of just six numbers needed to make a model that matches the shape and scale structure of the Universe.
“We don’t yet understand what dark energy is but we can measure its properties. Then, we compare those values to what we expect them to be given our current understanding of the Universe. The better our measurements, the more we can learn,” Eisenstein said.
It uses ripples – imprints of pressure waves that moved through the early Universe which was so hot and dense that particles of light (photons) moved along with the protons and neutrons (known collectively as baryons) that today make up the nuclei of atoms. The original size of these ripples is known, and their size today can be measured by mapping galaxies.
Making these measurements required mapping the locations of 1.2 million galaxies.
Since 2009, BOSS has used the Sloan Foundation Telescope at the Apache Point Observatory in New Mexico. BOSS will continue gathering data until June, 2014.