Scientists closer to understanding the Universe

Scientists today announced that they have made the most precise distance measurements to galaxies six billion light years away ever.

The Baryon Oscillation Spectroscopic Survey (BOSS) has measured the distance to these galaxies to a precision of one percent using the largest volume of the Universe ever surveyed in this way.

Such measurements are key to determining the nature of dark energy, the mysterious force which cosmologists believe to be causing the expansion of the Universe to speed up.

Artist's concept of the new measurement

Artist’s concept of the new measurement of the size of the Universe. The grey spheres show the pattern of the ‘baryon acoustic oscillations’ from the early Universe.

Dr Rita Tojeiro a BOSS collaborator at the Institute of Cosmology and Gravitation (ICG) based at the University of Portsmouth said: “I’m incredibly proud of this result. Measuring anything to this level of accuracy in astronomy is very rare and requires hard and gruelling work. But precise measurements are what we need to unlock the secrets of our Universe. One percent precision will be the definitive measurement for at least the next decade.”

The measurement was done using the Sloan Foundation Telescope at the Apache Point Observatory in New Mexico. BOSS, the largest program in the Sloan Digital Sky Survey III (SDSS III) has recorded high-precision positions of 1,009,172 galaxies, looking back over six billion years into the Universe’s past and covering one fifth of the sky.

BOSS measures the regular spacing of galaxies during key epochs in cosmic history and provides us with a “standard ruler” which is used to measure the evolution of the Universe’s structure.

Dr Ashley Ross, a researcher at the ICG and BOSS collaborator, said: “Nature has presented us with a beautiful ruler, and it happens to be half a billion light years long, so we can measure it precisely even from very far away.”

Accurate measurements dramatically sharpen our knowledge of fundamental cosmic properties, including how dark energy accelerates the expansion of the Universe. However measuring the positions of the galaxies is only the beginning of the process.

Angela Burden a PhD student at the ICG who performed part of the analyses said: “Observing the positions of galaxies is only the start of the process. We had to develop complex algorithms using computer simulations of fake Universes to ensure that we can get the most precise measurements of this ruler as possible.

“The positions look distorted when galaxies that are close to one another move each other around due to their mutual gravitational attraction. Part of the analyses is undoing these effects to sharpen our measurement signal.

“Measurements of this level of precision required a huge amount of work from the collaboration resulting in a total of 10 papers published describing the development and testing of our algorithms.”

The BOSS results combined with recent measurements of variation in the cosmic microwave background radiation (CMB) by the European Space Agency’s Planck satellite, dramatically sharpen our knowledge of how dark energy accelerates the expansion of the Universe. Combined they suggest that dark energy is a “cosmological constant”, whose strength does not vary in space or time. What we perceive as dark energy is unlikely to be a flaw in Einstein’s theory of General Relativity.

Dr Lado Samushia, another BOSS collaborator at the ICG said: “Remarkably, these results are fully consistent with Einstein’s General Relativity, and as such 100 years on and with all of these high precision measurements, his theory is yet to be disproven.

“Each new measurement made is like another bolt locking down the “cosmological constant” theory. Increasing the precision of a measurement is like tightening a bolt another turn, which really tests its endurance.”

Precise as they are, the new BOSS results are just the beginning. Greater coverage and better resolution in scale are essential to help us understand dark energy itself.

“Understanding the physical cause of the accelerated expansion remains one of the greatest goals in modern physics,” Dr Samushia added.

Meanwhile BOSS, ahead of schedule for completion in June, 2014, is continuing to collect data to expand our galaxy map of the Universe.

The BOSS analysis is based on SDSS III’s Data Releases 10 and 11 (DR 10 and DR 11) and has been submitted for publication in the Monthly Notices of the Royal Astronomical Society (MNRAS); the analysis is available online at [arXiv URL TK].

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