What would you do with a super-Hubble that could take snapshots of the sky not just in small patches but also in huge chunks? That’s a question NASA put to scientists, and they have duly answered. The agency recently selected 118 programs to use its shiny new Nancy Grace Roman Space Telescope, set to launch on August 30, in novel and exciting ways. Each project requires tasks that Roman is in pole position to carry out, such as scouring the cosmos for newborn black holes and investigating the stellar populations of nearby galaxies, as it prepares for its primary objectives of studying dark energy and dark matter, as well as discovering exoplanets by the tens of thousands.
Roman is more than a decade in the making at a cost of $4.3 billion, including its Hubble-sized panoramic mirror, sourced from the shadowy realm of U.S. spy satellites. Paired with a 300-megapixel infrared Wide-Field Instrument and a Coronagraph Instrument for high-contrast imaging, its 2.4-meter mirror will allow Roman to perform broad surveys of the universe, as well as breakthrough studies of exoplanets from its location 1.5 million kilometers (one million miles) from Earth, where the James Webb Space Telescope (JWST) also sits.
Roman’s mirror allows the telescope to see about 100 times more of the sky than Hubble or JWST in a single exposure, letting it study large numbers of galaxies and stars at the same time. This gives it unique capabilities that no other telescope can match but also poses a challenge for data management. NASA officials have said Roman is expected to produce 1.4 terabytes of science data per day and should beam back on the order of 500 terabytes of data per year; that annual figure is on par with the total amount of data that Hubble has produced across more than 35 years of operations. Many of the 118 newly selected “General Investigator” observer programs will seek to capitalize on that data deluge.
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A handful of Roman’s programs will be focused on little red dots (LRDs). Because of Roman’s wide, deep view, it can hunt for these mysterious objects in an entirely new way. Discovered by JWST in 2022, LRDs are strange, compact objects seen in the early universe that could be exotic black hole stars. LRDs, however, mysteriously fade away as the universe grows in age.
Vasily Kokorev of the University of Texas at Austin and his team will try to work out if LRDs really do fade away as the universe ages or if we just haven’t spotted them elsewhere yet, which will provide a big clue to their origin. Kokorev’s program, using Roman’s data, will begin its hunt two billion years after the big bang occurred 13.8 billion years ago. “When we try to find little red dots closer to us, we fail,” Kokorev says, although there have been hints of some within a few billion light-years of Earth—practically right next door, in cosmological terms.
Using JWST to look for more recent LRDs, Kokorev says, is like “trying to use an enormously large set of binoculars to read a book that’s right before you.” The numbers and ages of the LRDs that Roman finds should give us a better idea of their origins. If they contain humongous stars or black holes, thought to be the beginnings of groups of stars known as globular clusters, they should appear in similar numbers throughout the age of the universe. But if they are indeed black hole stars, growing supermassive black holes inside dense cocoons of gas, their number should drop off as matter in the universe spreads apart and the available fuel for these black holes runs dry.
Roman has been designed to study the more distant universe, too. Steven Finkelstein of the University of Texas at Austin is leading a program that will hunt for very bright, very distant galaxies that Roman and other observatories could nonetheless scrutinize in lavish detail. The most famous of these, called GN-z11, was discovered by Hubble in 2016 at just 400 million years after the big bang. Although JWST has since spotted more remote galaxies, GN-z11 stands alone as being particularly luminous, allowing easier in-depth follow-up study to determine its chemical composition and glean more about its history.
“It’s so much brighter than one would have expected to form at early times,” says Finkelstein, who hopes to find about 500 additional, similar objects with Roman. His program should also spot LRDs in the first two billion years of the universe, as well as large groups of galaxies, known as lensing clusters, that magnify the otherwise faint light of even more distant galaxies from farther back in the murky depths of cosmic time.
This simulated imagery highlights some of what NASA’s Roman Space Telescope could see in in one its deep-space surveys. More than a million supernovae flash and fade against a background of stars and faraway galaxies—representing just a small fraction of the dynamic, transient events Roman will capture during its five-year primary mission.
NASA’s Goddard Space Flight Center and M. Troxel
Finkelstein is also part of another program that will attempt to re-create Hubble and JWST’s famous deep-field images, which revealed millions of previously unseen galaxies by staring at seemingly empty patches of sky. Roman will do much the same but on a supercharged scale. Called the Roman eXtreme Deep Field (RXDF), this project will task the telescope with staring at an area 140 times larger than Hubble’s own extreme deep field, revealing millions of galaxies stretching back to 300 million years after the big bang, says Haojing Yan, the program’s lead and an observational astronomer at the University of Missouri. RXDF may even see supernovae from the first stars in the universe, known as Population III stars, Yan adds. “During most of their lifetimes, they are too faint to be detected,” he says. “But when they end their lives as supernovae, [with Roman] we’ll have a chance.”
As part of the 118 approved programs that will use data collected by Roman via its main surveys, there are several larger programs that will take their own bespoke observations. One of these, led by Karoline Gilbert of the Space Telescope Science Institute (STScI) in Maryland, will survey the nearby Andromeda and Triangulum galaxies, respectively located 2.5 million and three million miles from our Milky Way, in extraordinary detail.
Using Roman, Gilbert and her team will map half a billion stars in the two galaxies. Resolving individual stars in other galaxies is difficult, but Andromeda and Triangulum are close and large enough, and telescopes like Roman (and JWST and Hubble) are sufficiently eagle-eyed, to spot them. Roman, however, can uniquely sift through Andromeda’s stars much more minutely because of its wider field of view.
“Roman has this unprecedented combination of this panoramic view with really high resolution and precision,” Gilbert says. “We can study the ecosystem of these galaxies and the stars within them.”
Taking repeated images of Andromeda over several years, Roman will closely track the changing positions of stars in the galaxy, letting us discern its subtle dynamical history. Andromeda is thought to have merged with another galaxy in the past two billion years, and although the stars from that merger should now be widely scattered, they should still be detectable via their common motions. Gilbert’s program will also hunt for ultrafaint dwarf galaxies near Andromeda and Triangulum, which are dim objects so bereft of stars that they have mostly evaded other telescopes. As a class, “they are the most dark-matter-dominated objects in the universe,” Gilbert says. “This will be our first opportunity to find these ultrafaint dwarf galaxies around Andromeda or Triangulum.”
Ryan Foley of the University of California, Santa Cruz, will use Roman’s data for something a bit different—looking for failed supernovae in other galaxies. “It’s predicted that some massive stars should just collapse to black holes,” sans supernovae, Foley says, because they’d make that dark transformation before their supernovae’s shockwaves could escape. That means some stars should essentially wink out of existence as they expire—an oddity that we have seen hints before but never observed definitively. With Roman, Foley and his team will look at about 1,000 galaxies for such events.
There is much more to come as Roman gets up to speed and begins its unique study of the cosmos. “I’m just looking forward to another cool space telescope being launched,” Kokorev says. With it, astronomers will have a new tool to probe some of the universe’s greatest mysteries.