Astronomers are leveraging data from the Hubble Space Telescope to prepare for upcoming groundbreaking observations by the Nancy Grace Roman Space Telescope. A recent Hubble survey focused on the Milky Way’s galactic bulge, a densely populated region surrounding the galactic center, has provided crucial precursor data. This initiative aims to enhance the scientific return of Roman’s ambitious Galactic Bulge Time-Domain Survey, which is set to commence as early as September 2026.

The Galactic Bulge Time-Domain Survey, a core science objective for the Roman telescope, will scan millions of stars and identify thousands of new exoplanets. By comparing extensive historical data from Hubble with Roman’s future observations, scientists will be better equipped to interpret the new findings. This comparative approach is essential for understanding the complex celestial phenomena within the galactic bulge, including the potential detection of “rogue planets”—those ejected from their original solar systems—isolated neutron stars, and even Sun-like black holes.

Sean Terry, project lead and assistant research scientist, emphasized the survey’s goal: “A top priority of our Hubble survey is to cover as much sky area as possible.” This extensive Hubble data collection is designed to identify objects that will later undergo microlensing events, a phenomenon where the gravity of a foreground object warps the light from a background object. By capturing these objects before they are affected by microlensing, astronomers can more accurately analyze the subsequent events, distinguishing individual stars and their properties. This pre-event data is vital for measuring the masses of host stars and their planets, moving beyond mere mass ratios to more precise determinations.

The Hubble survey, initiated in spring 2025, has already amassed a significant dataset, paving the way for Roman’s even more ambitious observations. While Hubble’s previous large-scale mosaic of the Andromeda galaxy took over a decade, this new survey is expected to contribute to a catalog of tens of millions of stars. Roman’s survey, in turn, is anticipated to expand this catalog by an order of magnitude, potentially cataloging hundreds of millions of stars and producing some of the deepest images of the sky ever captured. The data from this Hubble survey is publicly available through the Mikulski Archive for Space Telescopes.