Here's how NASA's future telescope will determine ages of stars

NASA's upcoming space-based observatory, the Nancy Grace Roman Space Telescope, is poised to dramatically transform our understanding of stars after it launches by May 2027.

With a field of view at least 100 times greater than Hubble, Roman will focus on thousands of millions of stars in our Milky Way galaxy to determine their ages and subsequently help study the origin and evolution of our galaxy.

In order to determine the age of a star, scientists need to find out its mass and rotation rate. To measure the rotation rate of a distant star, they observe changes in the brightness of the star caused by starspots. Starspots are cooler and darker patches that appear on the surface of a star, similar to sunspots. When a starspot is visible on the star, it appears slightly dimmer than when it is on the other side of the star.

When a star has only one large spot on it, it experiences a regular pattern of dimming and brightening as the spot rotates in and out of view. However, it is much more challenging to identify the star's rotation when it has multiple spots scattered across its surface, which vary over time. This is because the periodic signals of dimming caused by the star's rotation are more difficult to tease out periodic signals of dimming from the star’s rotation.

To address this issue, a team of astronomers at the University of Florida is developing new techniques to extract a rotation period from measurements of a star’s brightness over time, through a program funded by NASA’s Nancy Grace Roman Space Telescope project.

The AI technique, known as a convolutional neural network, will analyze light curves, or plots of a star’s brightness over time, which requires the neural network to be trained on simulated light curves. University of Florida postdoctoral associate Zachary Claytor, the science principal investigator on the project, wrote a program to generate such light curves.

The approach has been successfully applied to data from NASA's TESS (Transiting Exoplanet Survey Satellite). Systematic effects make it more challenging to accurately measure longer stellar rotation periods, yet the team’s trained neural network was able to accurately measure these longer rotation periods using the TESS data, NASA said in a statement on Friday.

The upcoming Roman Space Telescope will perform three core community surveys, one of which is the Galactic Bulge Time Domain Survey. The telescope will be aimed towards the center of our galaxy, which is home to a large number of stars, to study the changes in their brightness over time. This data will be used to conduct various scientific investigations, such as the discovery of distant exoplanets and determining the rotation rates of stars.

"We have a lot of the tools already, and we think they can be adapted to Roman," said Jamie Tayar, assistant professor of astronomy at the University of Florida and the program’s principal investigator.