Despite a century of measurements, astronomers can’t agree on the rate at which the universe is expanding. A technique that relies on measuring distances to a specific type of aging star in other galaxies—called the J-region Asymptotic Giant Branch, or JAGB method—might be able to help.
Astrophysicist and University of Chicago graduate student Abigail Lee is the lead author on a new paper that analyzed observations of light from a nearby galaxy to validate the JAGB method for measuring cosmological distances. This novel technique will allow future independent distance measurements that can help answer one of the biggest outstanding questions in cosmology: how fast is the universe expanding?
“One of the most exciting questions in cosmology today is whether there is new physics that is missing from our current understanding of how the universe is evolving. A current discrepancy in the measurement of the Hubble constant could be signaling a new physical property of the universe or, more mundanely, unrecognized measurement uncertainties,” said Wendy L. Freedman, the John and Marion Sullivan University Professor of Astronomy and Astrophysics and senior author on the paper. “There are very few methods for measuring distances that can deliver the required accuracy. Lee is developing this new JAGB method, which shows early promise for resolving this discrepancy.”
A key to the history of the universe
Back in 1920, Edwin Hubble, PhD’17, first noticed the relationship between a galaxy’s distance and how fast it was moving away from us. This value, now known as the Hubble constant, is a key parameter in cosmological models.
Hubble first measured this constant by comparing galactic distance and velocity measurements derived from a specific kind of star that pulses regularly. Measurements using direct methods like Hubble’s have improved greatly over the decades, but they don’t agree with methods that extrapolate from the Cosmic Microwave Background—light leftover from the very early universe. This disagreement is called the Hubble tension, and is one of the most prominent issues of modern cosmology.