Astronomers create largest-ever 3D galactic map in hunt for dark energy

15 Jul 2016

A collaborative effort from international astronomers trying to understand the properties of mysterious dark energy has resulted in the largest-ever 3D galactic map.

To get a sense of how vast this 3D galactic map is, you must know that the team of astronomers led by Dr Florian Beutler at the University of Portsmouth has spent decades collating measurements of 1.2m galaxies as part of the Sloan Digital Sky Survey III (SDSS-III).

The team will now use new measurements carried out by the Baryon Oscillation Spectroscopic Survey (BOSS) programme of SDSS-III to help them measure the expansion rate of the universe.

Future Human

In doing so, they will be able to determine the amount of matter and dark energy that makes up the present-day universe, which is believed to be the driving force behind the proposed expansion of the universe.

BOSS of dark energy

BOSS does this by measuring major visible fluctuations in the 3D galactic map, more specifically referred to as baryonic acoustic oscillations (BAO), which are determined by the pressure waves remaining just 400,000 years after the Big Bang.

By taking these measurements from the earliest moments of the universe right up to the present day, the astronomers will be able to better determine how dark matter and dark energy have competed to govern the rate of expansion of the universe.

Galaxy map

Each dot in this picture indicates the position of a galaxy 6bn years into the past. The image covers about one-twentieth of the sky: a slice of the universe 6bn light years wide, 4.5bn light years high, and 500m light years thick. Each colour represents distance from Earth with yellow being the nearest. Image via Daniel Eisenstein and SDSS-III

Universe expanding very slowly, if at all

Speaking of this new enormous map, Beutler said: “This extremely detailed 3D map represents a colossal amount of work. The University of Portsmouth has worked with partner institutions for 10 years, helping to gather measurements of galaxies making up a quarter of the sky.

“Using this map we will now be able to make the most accurate possible measurements of dark energy, and the part it plays in the expansion of the universe.”

Initial analysis of the map, Beutler said, indicate that the dark energy readings show that the universe’s expansion is evolving very slowly, if at all. In fact, over the past 7bn years, the universe is likely to have only expanded by, at most, 20pc.

‘A great boon for cosmology’

Further important findings from the map have shown evidence that the movement of galaxies towards matter-filled regions of the universe due to gravity would add credence to Albert Einstein’s theory of general relativity. Therefore, the astronomers said, this would support the concept that the universe’s expansion is driven by vast cosmic scales, such as dark energy, rather than a breakdown of gravitational theory.

Dr Rita Tojeiro of the University of St Andrews, who partnered on the project, said of this discovery: “The ability to observe a single well-modelled physical effect from recombination until today is a great boon for cosmology.”

Night sky image via Shutterstock

Colm Gorey was a senior journalist with Silicon Republic