First insights from the Dark Energy Spectroscopic Instrument (DESI) have been released, bringing us a step closer to understanding our expanding universe.
DESI’s scientific mission is to try and understand the invisible and mysterious phenomenon known as “dark energy” that appears to be pushing everything in the cosmos apart.
You could be excused for thinking that the law of gravity should mean that all the galaxies must be coming closer together, not drifting apart. We can make sense of this spreading in terms of the big bang. 13.8 billion years ago the universe exploded out of a single point. It therefore makes sense that it might be expanding. But there’s more.
Not only are galaxies drifting apart, the expansion of the universe is accelerating – as if there’s more energy being added to that initial big bang.
This suggests an elusive force – dark energy – exists that is stretching the fabric of space-time itself.
By calculating the rate at which the universe’s expansion is accelerating, cosmologists believe that dark energy must account for 70% of the “stuff” in the universe. “Dark matter” accounts for a further quarter of the universe, leaving only about 5% that’s made up of ordinary matter we can see and interact with.
DESI represents an international effort to map all dark energy and, hopefully, to gain some insight into whatit is and how it has changed throughout the history of the universe.
The instrument – situated at about 2,000 metres elevation at Kitt Peak National Observatory, in Arizona, US – is operated by the Lawrence Berkeley National Laboratory. It is the world’s most powerful apparatus for imaging light ranges.
“The instrument is able to measure light from more than 100,000 galaxies in one night,” says University of Queensland astrophysicist Dr Rossana Ruggeri. “It uses 5,000 robotic positioners to move optical fibres that capture light from objects millions or billions of light-years away. That light tells researchers how far away an object is, helping them to build a three-dimensional cosmic map.”
Ruggeri and UQ colleagues play a leading role in ensuring DESI’s data quality, studying gravitational lensing, and examining galaxy migration and clustering.
DESI’s initial tranche of data has already made two significant findings: evidence of a mass migration of stars into the nearby Andromeda galaxy; and the discovery of incredibly distant quasars – the extremely bright, active supermassive black holes found at the centre of some galaxies.
But UQ professor Tamara Davis says there’s more to discover.
“DESI is currently two years into its five-year run and ahead of schedule on its quest to collect more than 40 million redshifts,” Davis says. “The survey has already catalogued more than 15 million galaxies in its science run and is adding more than a million per month.”
For the especially keen, DESI’s early data release can be accessed here.
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