Dark energy discovery a decade in the making: New supernova insights offer clues to the expansion of the universe

Researchers at Swinburne College of Expertise have contributed to a landmark examine that complicates our understanding of the universe.

The work is published on the arXiv preprint server.

The Darkish Vitality Survey (DES), which launched outcomes at this time, represents the work of over 400 astrophysicists, astronomers and cosmologists from over 25 establishments.

DES scientists took information for 758 nights throughout six years to grasp the character of dark energy and measure the growth charge of the universe. They discovered that the density of darkish power within the universe may have diversified over time, in accordance with a brand new complicated principle.

Dr. Anais Möller from Swinburne College of Expertise’s Centre for Astrophysics and Supercomputing was a part of the group engaged on this revolutionary evaluation, alongside Swinburne’s Mitchell Dixon, Professor Karl Glazebrook and Emeritus Professor Jeremy Mould.

“These outcomes, a collaboration between a whole bunch of scientists around the globe, are a testomony to the facility of cooperation and exhausting work to make main scientific progress,” says Dr. Möller.

“I’m very happy with the work we now have achieved as a group; it’s an extremely thorough evaluation which reduces our uncertainties to new ranges and exhibits the facility of the Darkish Vitality Survey. We not solely used state-of-the-art information, but in addition developed pioneering strategies to extract the utmost info from the Supernova Survey. I’m notably happy with this, as I developed the strategy to pick out the supernovae used for the survey with machine studying.”

In 1998, astrophysicists found that the universe is increasing at an accelerating charge, attributed to a mysterious entity known as darkish power, which makes up about 70% of our universe. On the time, astrophysicists agreed that the universe’s growth needs to be slowing down due to gravity.

This revolutionary discovery, which astrophysicists achieved with observations of particular sorts of exploding stars, known as kind 1a supernovae, was acknowledged with the Nobel Prize in Physics in 2011.

Now, 25 years after the preliminary discovery, the Darkish Vitality Survey is a end result of a decade’s value of analysis from scientists worldwide, who analyzed greater than 1,500 supernovas utilizing the strongest constraints on the growth of the universe ever obtained. That is the most important variety of kind 1a supernovae ever used for constraining darkish power from a single survey probing giant cosmic occasions.

The result outcomes are per the now-standard cosmological mannequin of a universe with an accelerated growth. But, the findings are usually not definitive sufficient to rule out a probably extra complicated mannequin.

“There may be nonetheless a lot to find about darkish power, however this evaluation may be thought-about because the gold normal in supernova cosmology for fairly a while,” says Dr. Moller. “This evaluation additionally brings revolutionary strategies that can be used within the subsequent era of surveys, so we’re taking a leap in the way in which we do science. I am excited to uncover extra in regards to the thriller that’s darkish power within the upcoming decade.”

Pioneering a brand new strategy

The brand new examine pioneered a brand new strategy to utilizing photometry—with an unprecedented 4 filters—to seek out the supernovae, classify them and measure their mild curves. Dr. Möller created the strategy to pick out these kind 1a supernovae utilizing fashionable machine studying.

“It is vitally thrilling occasions to see this revolutionary know-how harness the facility of huge astronomical surveys,” she says. “Not solely we’re capable of receive extra kind 1a supernovae than earlier than, however we examined these strategies totally as we wish to do extra precision measurements on the basic physics of our universe.”

This system requires information from kind 1a supernovae, which happen when an especially dense lifeless star, referred to as a white dwarf, reaches a critical mass and explodes. Because the crucial mass is sort of the identical for all white dwarfs, all kind 1a supernovae have roughly the identical precise brightness and any remaining variations may be calibrated out. So, when astrophysicists examine the obvious brightnesses of two kind 1a supernovae as seen from Earth, they will decide their relative distances from us.

Astrophysicists hint out the historical past of cosmic growth with giant samples of supernovae spanning a variety of distances. For every supernova, they mix its distance with a measurement of its redshift—how rapidly it’s transferring away from Earth as a result of growth of the universe. They will use that historical past to find out whether or not the darkish power density has remained fixed or modified over time.

The outcomes discovered w = –0.80 +/- 0.18 utilizing supernovae alone. Mixed with complementary information from the European Area Company’s Planck telescope, w reaches –1 throughout the error bars. To return to a definitive conclusion, scientists will want extra information utilizing a brand new survey.

The DES researchers used superior machine-learning strategies to assist in supernova classification. Among the many information from about two million distant noticed galaxies, DES discovered a number of thousand supernovae. Scientists in the end used 1,499 kind 1a supernovae with high-quality information, making it the most important, deepest supernova pattern from a single telescope ever compiled. In 1998, the Nobel-winning astronomers used simply 52 supernovae to find out that the universe is increasing at an accelerating charge.