Roman telescope will track the changing universe

NASA’s Nancy Grace Roman Space Telescope is designed to show the universe in motion. By repeatedly photographing the same regions, it will allow astronomers to study changes that unfold over hours, years and longer periods, from exploding stars to the activity of faint, nearby suns.

The telescope is named for Nancy Grace Roman, NASA’s first chief of astronomy and its first female executive. Evening Report reports that Roman’s main advantage will come from combining three abilities that are usually difficult to achieve at the same time: detailed images, a very broad field of view and regular monitoring.

That combination could turn observations of the sky into something closer to a time-based record than a collection of isolated pictures. Changes in brightness and position can reveal the physical processes taking place across the cosmos.

A wide and detailed view

Roman is often compared with the Hubble Space Telescope. The two observatories have mirrors of the same size and both work with visible and infrared light. Roman, however, can observe an area of sky as much as 200 times larger.

A wider view generally comes with a loss of detail. Kepler and the Transiting Exoplanet Survey Satellite, or TESS, have surveyed huge numbers of stars, but their lower spatial resolution can cause neighbouring objects to merge into one apparent source. The James Webb Space Telescope provides sharper images, yet its smaller field of view prevents it from efficiently following millions of objects simultaneously.

Roman is intended to occupy the space between those approaches. Its resolution should allow astronomers to separate individual stars in crowded regions, while its large viewing area will let the telescope examine many targets in one observation. Returning to the same fields will add the third dimension: time.

Different kinds of objects change at different speeds. A pattern lasting only hours can point to a different event from one that develops over years. Measuring these shifts in light should help researchers identify what is happening without relying on a single snapshot.

Searching the crowded galactic centre

Two major surveys will use Roman’s time-based observing strategy in different parts of the sky. The High-Latitude Time-Domain Survey will look for remote events such as supernovae. The Galactic Bulge Time-Domain Survey will focus on the dense central region of the Milky Way.

From Earth, the galactic bulge appears as a pale, blurred band because huge numbers of stars, together with gas and dust, lie along the line of sight. Roman’s resolution and infrared observations will help distinguish those stars individually, creating a backdrop for searches that depend on brief changes in brightness.

One such technique is microlensing. When a foreground object passes between a distant star and the telescope, its gravity can bend and amplify the star’s light. The intervening object may be a star, a planet roughly the size of Mars or a black hole with a mass hundreds of times greater than the Sun’s.

Roman will also look for transits, which occur when a planet crosses the face of its star and causes a small drop in the star’s light. Because the galactic bulge contains so many stars, astronomers expect the survey to identify about 100,000 transiting planets.

Following small, active stars

Repeated observations will also reveal how stars spin and how features on their surfaces change. This is especially valuable for the smallest and coolest stars, whose faint, reddish light makes them difficult to study in large numbers.

Stars cooler than approximately 2,500 degrees Celsius are expected to have both magnetic spots and clouds on their surfaces. As a star rotates, those features move into and out of view, producing changes that can be used to calculate its rotation period.

Comparing those periods across many stars could show how stellar activity develops over long timescales. It may also provide clues about the environments surrounding planets orbiting these stars.

TESS has surveyed almost the whole sky during the past eight years and has measured rotation periods for hundreds of these very small stars. But its visible-light observations make the stars appear relatively dim, while its lower resolution creates problems in densely populated fields.

Roman’s combination of near-infrared sensitivity, detailed imaging and broad coverage is expected to expand that sample substantially. A larger collection of stars, drawn from a wider range of environments, could help astronomers understand how stellar behaviour varies—and what that means for worlds around them.

From distant supernovae to planets and compact stars near the Milky Way’s centre, Roman will examine a sky that changes far more than unaided vision suggests.