Jacquelyn Mitchell

Look up at the night sky with your naked eye and it may seem like it rarely changes. Yet the universe is in constant flux. Stars drift through space, orbiting the centre of the Milky Way as planets orbit them. They rotate, showing off spots on their surfaces and sometimes producing violent outbursts that affect planetary atmospheres much like solar storms produce auroras on the Earth. As stars age, they can die dramatically as supernovae, releasing material that will form the next generation of stars and planets. A new NASA telescope – named after NASA’s first chief of astronomy and first female executive, Nancy Grace Roman – will let us observe these changes to the night sky, almost as if we are watching a cosmic high-definition movie. This is thanks to three capabilities working together: sharp images, a huge field of view and repeated observations.  

Watching the sky change

The Nancy Grace Roman Telescope is often described as the successor to the Hubble Space Telescope. It has the same size mirror as Hubble and also observes visible and infrared light. But it is capable of observing a much larger patch of the sky – up to 200 times larger.

Usually, seeing a bigger patch of sky means sacrificing spatial resolution. Both the Kepler and the Transiting Exoplanet Survey Satellite planet-hunting telescopes have watched enormous numbers of stars, but their lower spatial resolution means nearby stars can blend together. On the other hand, the James Webb Space Telescope can see more sharply, but its much smaller field of view makes it impractical for monitoring millions of objects at once. The Roman telescope is notable for combining high resolution with a wide field of view.

The final key to Roman’s power is time: by repeatedly observing the same patches of sky, Roman will reveal changes that a single image could never capture. Those changes unfold on timescales ranging from hours to years, revealing different physical processes. By simply tracking how the light of objects changes over time, Roman is able to distinguish different patterns and use them to uncover what is happening throughout the universe. Two of Roman’s core surveys are designed to watch different parts of the sky for different kinds of change. The High-Latitude Time-Domain Survey will capture distant phenomena such as supernovae, while the Galactic Bulge Time-Domain Survey will monitor the packed centre of the Milky Way.  

A window into the Milky Way

In the galactic bulge, thousands of stars (along with gas and dust) obscure our view of the centre of the galaxy. These same stars appear to our eyes as almost a solid white, smeary “Milky Way.” Roman, however, can see the individual stars to use them as a backdrop for interesting science. One of the primary focuses of the Galactic Bulge Time-Domain Survey is finding objects through microlensing. This is a process through which gravity from a passing object can warp and magnify light from a distant star behind it, allowing us to have a better view of that distant star. These passing foreground objects can include stars, Mars-sized planets and even black holes hundreds of times the mass of the Sun.

Roman will also find planets using the transit method, when planets dim starlight by passing in front of their star, revealing their presence. The sheer number of stars in the galactic bulge means astronomers predict they will find around 100,000 transiting planets.  

What changing starlight reveals

Staring at stars can also reveal how stars themselves rotate and change over time. This change is particularly interesting for the very smallest and coolest stars. Along with magnetic spots, clouds are also expected on the surface of stars cooler than roughly 2,500 C. As the stars rotate, these features come in and out of view, allowing astronomers to measure their rotation periods. Comparing rotation across many targets can reveal patterns in how these stars change over broad timescales. Yet these stars are quite faint and red, making studying large numbers incredibly difficult with current surveys.

The Transiting Exoplanet Survey Satellite telescope, which has observed almost the entire sky over the past eight years, has revealed rotation periods for hundreds of these tiny stars. But this telescope observes in visible light, where these stars appear relatively faint, and its low spatial resolution makes crowded fields challenging. Roman’s wide-field, high-resolution and near-infrared observations can significantly increase this sample, allowing astronomers to study rotation and activity across a much larger population of these smallest stars. A larger and more diverse sample could reveal how these stars’ environments vary, helping us understand worlds found around them. From supernovae in distant galaxies to the smallest stars in our own, Roman will capture a cosmos that is constantly changing. Look closely, and the seemingly static sky is anything but. Samantha Lambier, PhD Candidate in Astronomy, Western University This article is republished from The Conversation under a Creative Commons license. Read the original article. Expert Insight reflects the perspective and scholarly interest of Western faculty members and is not an articulation of official university policy on issues being addressed.