The Nancy Grace Roman Space Telescope will 'rewind' the universe. Here's how

A new simulation of millions of galaxies has shown just how powerful the forthcoming Nancy Grace Roman Space Telescope (Roman) will be when it opens its eye to the universe. 

NASA says that the telescope will turn back the "cosmic clock" and allow astronomers to see space in a way they never have before. This should help scientists understand how the universe evolved from a sea of densely packed particles into the cosmos we see today full of stars and galaxies.

Set to launch no sooner than May 2027, Roman's power to revolutionize astronomy lies in the fact that it will have the ability to capture vast regions of space in a single image. As a startling example of this boosted observing power, the simulation demonstrates how in just 63 days Roman can image an amount of sky that it would take the Hubble Space Telescope 85 years to capture. 

The real benefit of the Nancy Grace Roman Space Telescope will be felt when it is teamed up with its fellow space telescopes, with Hubble able to see a broader spectrum of light and the James Webb Space Telescope (JWST) offering deeper observations.

Related: What is the Nancy Grace Roman Space Telescope? 

"The Hubble and James Webb Space Telescopes are optimized for studying astronomical objects in-depth and up close, so they're like looking at the universe through pinholes," leader of a study describing the simulation and postdoctoral fellow at NASA's Goddard Space Flight Center in Greenbelt, Maryland, Aaron Yung, said in a NASA statement. "To solve cosmic mysteries on the biggest scales, we need a space telescope that can provide a far larger view. That's exactly what Roman is designed to do."

The simulation created by Yung and the team shows a patch of sky measuring 2 square degrees, equivalent to 10 times the apparent size of the full moon in the night sky. Within this patch of simulated space, over 5 million galaxies are represented. 

The same simulation can model tens of millions of galaxies in less than a day, something that would take years with more conventional methods. When Roman launches and reaches an operational state, researchers can then take its observations and compare them to the simulation, helping them unravel some of the greatest mysteries in the universe. 

This could include investigating the nature of dark energy  —  the force that is driving the accelerating expansion of the universe  —  and dark matter, the substance that is almost completely invisible despite composing around 85% of the matter in the cosmos. 

How Roman will investigate dark matter and dark energy 

Both galaxies and the clusters they sometimes form grow in "clumps" throughout the universe that are connected by invisible threads of dark matter. Galaxies are positioned along these dark matter filaments at the points at which they intersect. Between these strands are tremendous cosmic voids. 

This creates a tapestry of the universe with a web-like structure extending for hundreds of millions of light-years that can only be seen with an incredibly broad view. Yet this picture would look very different to astronomers if they could view it as it appeared much earlier in the universe's 13.7-billion-year history.

Rewinding cosmic time would reveal the early universe as a uniform primordial sea of plasma composed of charged particles with overly dense patches that would collapse under their own gravity to birth the first stars over the course of hundreds of millions of years. Drawn towards the gravitational pull of dark matter, these first stars would then group into galaxies that will go on to evolve to be populated by planetary systems like our solar system.

Roman will be able to look back at various stages of this progression as the universe began to take shape. Because dark matter's gravitational influence helps determine the distribution of galaxies, watching it aid in the formation of early galaxies could shed light on the nature of this mysterious form of matter as it plays its role as the universe's "invisible backbone." On a smaller scale, this look back in time could also allow astronomers to see the effect of dark matter as it forms invisible haloes around early galaxies, thus revealing how they evolve individually. 

Roman will also allow astronomers to rewind the recent accelerating expansion of the universe to learn more about dark energy, the force that drives this expansion. 

"Most capabilities of the Nancy Grace Roman telescope will make it a suitable instrument to study the nature of dark energy," cosmology postdoctoral researcher at Universidad ECCI in Bogotá, Colombia, Luz Ángela García recently told Space.com. "Because of its broad coverage of the sky, the telescope will capture an unprecedented number of galaxies in its field of view and the distribution of those galaxies in our universe, which will allow us to understand the effect of dark energy on large cosmological scales and the clustering and evolution of galaxies."

NASA points out that Roman's sweeping celestial surveys will be able to map the universe up to a thousand times faster than Hubble, with the telescope moving rapidly from one observational target to the next. 

"Roman will take around 100,000 pictures every year," Goddard research astrophysicist, Jeffrey Kruk, said in NASA's statement. "Given Roman's larger field of view, it would take longer than our lifetimes even for powerful telescopes like Hubble or Webb to cover as much sky."

Beginning life as the Wide Field Infrared Survey Telescope (WFIRST) Roman was renamed in May 2020 in honor of Nancy Grace Roman, a pioneering scientist who served as NASA's first chief astronomer from 1961 to 1963. 

Roman, who passed away on December 26, 2018 at the age of 93, was affectionately known as "the mother of Hubble," the nickname she earned as a result of her tireless advocacy for new tools that would allow astronomers to study the broader universe. This push would eventually lead to the launch of the Hubble Space Telescope in 1990.

The simulation showing the observing power of the Roman Telescope is available for download here. A paper discussing the simulation was published in December in the journal Monthly Notices of the Royal Astronomical Society. 

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