How NASA’s Roman Space Telescope Will Turn the Universe Back

In this side view of the simulated universe, each point represents a galaxy whose size and brightness correspond to its mass. Slides from different eras show how the Romans would view the universe throughout cosmic history. Astronomers will use such observations to piece together how cosmic evolution led to the web-like structure we see today. Image credit: NASA’s Goddard Space Flight Center and A. Young

New simulation shows how[{” attribute=””>NASA’s Nancy Grace Roman Space Telescope will turn back the cosmic clock, unveiling the evolving universe in ways that have never been possible before when it launches by May 2027. With its ability to rapidly image enormous swaths of space, Roman will help us understand how the universe transformed from a primordial sea of charged particles to the intricate network of vast cosmic structures we see today.

“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,” said Aaron Yung, a postdoctoral fellow at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, who led the study. “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.”

Combining Roman’s large view with Hubble’s broader wavelength coverage and Webb’s more detailed observations will offer a more comprehensive view of the universe.


In this deep universe simulated view, every point represents a galaxy. The three small squares show Hubble’s field of view, each revealing a different region of the artificial universe. Roman will be able to quickly scan an area as large as the entire zoomed image, which will give us a glimpse of the largest structures of the universe. Image credit: NASA’s Goddard Space Flight Center and A. Young

The simulation covers a swath of sky two square degrees in size, which is about 10 times the apparent size of the full moon, which contains more than 5 million galaxies. It is based on a well-tested galaxy formation model and represents our current understanding of how the universe works. Using highly efficient technology, the team can simulate tens of millions of galaxies in less than a day — something that would take years using conventional methods. When Roman launches and starts providing real data, scientists can compare it to a set of these simulations, and put their models to the ultimate test. This will help reveal the physics of galaxy formation, dark matter – a mysterious substance only observed through gravitational effects – and much more.

A paper describing the results has been published in Monthly Notices of the Royal Astronomical Society in December 2022.

Cosmic Web Uncovered

Galaxies and clusters of galaxies glow in clumps along invisible filaments of dark matter in a tapestry the size of the visible universe. With a wide enough view of this tapestry, we can see that the large-scale structure of the universe is like a web, with filaments spanning hundreds of millions of light-years. Galaxies are mainly found at the intersections of the filaments, with vast “cosmic voids” between all the bright filaments.

This is what the universe looks like now. But if we could turn the universe back in time, we would see something completely different.

Hubble versus the Roman field of view

This image, which contains millions of simulated galaxies scattered across space and time, shows regions that Hubble (white) and Roman (yellow) could capture in a single shot. It would take Hubble about 85 years to map the entire region shown in the image at the same depth, but Roman could do it in just 63 days. Roman’s greater vision and fast scanning speeds will reveal the evolving universe in ways never before possible. Image credit: NASA’s Goddard Space Flight Center and A. Young

Instead of glowing giant stars scattered throughout galaxies that are greater distances apart, we would find ourselves immersed in a sea of[{” attribute=””>plasma (charged particles). This primordial soup was almost completely uniform, but thankfully for us, there were tiny knots. Since those clumps were slightly denser than their surroundings, they had slightly larger gravitational pull.

Over hundreds of millions of years, the clumps drew in more and more material. They grew large enough to form stars, which were gravitationally drawn toward the dark matter that forms the invisible backbone of the universe. Galaxies were born and continued to evolve, and eventually, planetary systems like our own emerged.


In this side view of the simulated universe, each point represents a galaxy whose size and brightness correspond to its mass. Slides from different eras show how the Romans would view the universe throughout cosmic history. Astronomers will use such observations to piece together how cosmic evolution led to the web-like structure we see today. Image credit: NASA’s Goddard Space Flight Center and A. Young

Roman’s panoramic view will help us see what the universe looked like in different phases and fill in many gaps in our understanding. For example, while astronomers have detected “halos” of dark matter that surround galaxies, they aren’t sure how they form. By seeing how gravitational lensing caused by dark matter distorts the appearance of distant objects, Roman will help us see how halos have evolved through cosmic time.

“Simulations like this will be crucial in connecting unprecedentedly large galaxy surveys from Roman times to the invisible scaffolding of dark matter that defines the distribution of those galaxies,” said Sangeeta Malhotra, an astrophysicist at Goddard and one of the authors of the paper.

See the bigger picture

Studying such vast cosmic structures with other space telescopes is not practical because it can take hundreds of years of observations to piece together enough images to see them.

“Roman will have the unique ability to match the depth of the Hubble Ultra Deep Field, but it covers many times more sky area than wide surveys like Scan CandlesYoung said. “This complete view of the early universe will help us understand how representative the Hubble and Webb snapshots are of what it was like at the time.”

The Roman Wide View will also serve as a roadmap that Hubble and Webb can use to zoom in on areas of interest.

NASA's Nancy Grace Romanian Space Telescope

The Romanian Space Telescope is a NASA observatory designed to uncover the mysteries of dark energy and dark matter, search for and image exoplanets, and explore many topics in infrared astrophysics. Credit: NASA

Roman’s comprehensive sky surveys will be able to map the universe a thousand times faster than the Hubble telescope. This would be possible because of the observatory’s rigid structure, fast rotational speed, and large telescope field of view. The Romans will quickly move from one cosmic goal to another. Once a new target is obtained, the vibrations will quickly stabilize because potentially oscillating structures such as solar arrays are held in place.

“Roman will take about 100,000 images each year,” said Jeffrey Crook, an astrophysicist at Goddard. “Given Roman’s larger field of view, it would take longer than our lifetimes for even powerful telescopes like Hubble or Webb to cover as much of the sky.”

By providing a giant, clear view of cosmic ecosystems and collaborating with observatories like Hubble and Webb, Roman will help us solve some of astrophysics’ most profound mysteries.

Reference: “Semi-Analytic Predictions of Roman – Beginning of a New Era of Deep Surveys of Galaxies” by LY Aaron Yung, Rachel S Somerville, Steven L Finkelstein, Peter Behroozi, Romeel Davé, Henry C Ferguson, Jonathan P Gardner, Gergo Popping, Sangeeta Malhotra, Casey Babovich, James E. Rhodes, Michaela P. Bagley, Michaela Hirschman and Anton M Cockeymore, December 8, 2020, Available Here. Monthly Notices of the Royal Astronomical Society.
DOI: 10.1093/mnras/stac3595

At NASA’s Goddard Space Flight Center, he oversees the Nancy Grace Roman Space Telescope in collaboration with NASA’s Jet Propulsion Laboratory and Caltech/IPAC in Southern California, as well as the Space Telescope Science Institute in Baltimore. A diverse team of scientists from various research institutions forms the core of the project’s scientific team. The project is supported by major industry partners, including Ball Aerospace and Technologies of Boulder, Colorado, L3Harris Technologies of Melbourne, Florida, and Teledyne Scientific & Imaging of Thousand Oaks, California.

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