Journey to Center of Milky Way With Upcoming NASA Roman Core Survey

At the heart of our own galaxy lies a thick thicket of stars with a supermassive black hole at its center. NASA’s Nancy Grace Roman Space Telescope will provide the deepest view yet of this area, revealing unique stars, planets and objects that resist definition.

Drawing on contributions from astronomers around the world, the Roman Space Telescope will devote three-quarters of its five-year primary mission to conducting three groundbreaking surveys of unprecedented scale. Their combined results will transform all areas of astronomy and answer long-standing questions about dark matter, dark energy and planets outside our solar system, called exoplanets.

The latter theme will be addressed by the Galactic Bulge Time-Domain Survey, which will peer into the center of our galaxy to study the stars and exoplanets that make up the densely populated region around the center of the Milky Way, known as the galactic bulge.

The survey will observe six areas of the galactic bulge, one located at the center and five nearby, every 12 minutes for 438 days of total observation time. The observations will be divided into six “seasons” spread over five years.

By spending a lot of time focusing on a relatively small area of ​​the sky, the mission will be able to track changes in the motion and light of hundreds of millions of stars, as well as any planets orbiting them, over long periods of time – the “time” aspect of the survey.

“This survey will be the highest precision, highest cadence and longest continuous observational baseline survey of our Galactic bulge, where the highest density of stars in our galaxy resides,” said Jessie Christiansen of Caltech/IPAC, who served as co-chair of the committee that defined the time-domain survey of the Galactic bulge.

Exoplanet microlensing

Roman will use a method called microlensing to search for exoplanets, a technique that has so far identified just over 200 exoplanets, compared to more than 4,000 discovered with the transit method, out of more than 6,000 currently confirmed.

With this study, scientists expect to see more than 1,000 new planets orbiting other stars using microlensing alone. This would increase the number of exoplanets identified using this method by more than five times.

A microlensing event occurs when light from a distant star in the background is slightly distorted by a foreground object, such as a star and its planet. This distortion of light is called gravitational lensing, with the gravity of the star and planet bending the fabric of space the light passes through and focusing it like a magnifying glass.

While the transit method is very effective in identifying exoplanets that orbit close to their star, the microlensing method can discover exoplanets that orbit farther from their star and in planetary systems further from Earth than ever studied before. Roman will be versatile enough to observe inhabiting exoplanets from the inner edge of the habitable zone to great distances from their stars, with a wide range of masses from planets smaller than Mars to the size of gas giants like Jupiter and Saturn. It could even discover “rogue planets” without host stars, which formed on their own or were ejected from their host systems long ago.

“For the first time, we will have a comprehensive view of Earth and our solar system in the broader context of the Milky Way exoplanet population,” Christiansen said. “We still don’t know how common Earth-like planets are, and the Roman investigation of the Galactic Bulge time domain will provide us with that answer.”

This survey will create a census of exoplanets on which scientists can draw statistical conclusions, revealing common patterns found in exoplanets and deepening our understanding of planet formation and habitability.

An investigation; lots of science

Due to the immense amount of observation time and subsequent data produced, the Galactic Bulge Time-Domain Survey will advance not only the field of exoplanet microlensing, but also other areas of astronomy.

“There is an incredibly rich diversity of science that can be accomplished with a high-precision, high-throughput survey like this,” said Dan Huber of the University of Hawaii, the survey’s other co-chair.

The main survey was optimized not only for microlensing, but also to observe changes in brightness, from small, quick flashes to long-term trends. This property allows astronomers to discover and characterize transiting planets, red giant stars, stellar-mass black holes and other stellar remnants, as well as binary eclipses, and can lead to a deeper understanding of the physics of star formation and evolution.

“Stars in the bulge and center of our galaxy are unique and not yet well understood,” Huber said. “The data from this survey will allow us to measure the age of these stars and their place in the history of the formation of our galaxy, the Milky Way.”

Roman’s observing strategy as part of the Galactic Bulge Time-Domain Survey, as well as the High-Latitude Time-Domain Survey and the High-Latitude Wide-Area Survey, will allow astronomers to maximize their scientific results, all with a single telescope.

Abundance of data to explore

Roman will observe hundreds of millions of stars every 12 minutes during the survey period, providing an unprecedented volume of data to astronomers.

The Caltech/IPAC Roman Science Support Center in Pasadena, California, will be responsible for processing high-level science data for the time domain investigation of the Galactic Bulge, including microlensing of exoplanets and general community outreach to Roman exoplanet science. The Science Support Center’s monitoring of these stars has been automated to detect microlensing and variable events in the data. This helps scientists understand features such as how often a star’s brightness changes, or whether there are hidden planets near the lensing stars, or other sources of variability. The number of stars and the frequency of observations make the Roman data an ideal dataset for finding such sources.

All Roman sightings will be made public after a short processing period. The mission is scheduled to launch no later than May 2027, and the team is on track for a fall 2026 launch.

The Nancy Grace Roman Space Telescope is operated at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, with participation from NASA’s Jet Propulsion Laboratory in Southern California; Caltech/IPAC in Pasadena, California; the Baltimore Space Telescope Science Institute; and a scientific team composed of scientists from various research institutions. Key industry partners include BAE Systems Inc. in Boulder, Colorado; L3Harris Technologies in Rochester, New York; and Teledyne Scientific & Imaging in Thousand Oaks, California.

By Isabelle Swafford
Caltech/IPAC, Pasadena, California.

Media contact:

Claire Andreoli
NASA Goddard Space Flight CenterGreenbelt, Maryland.
301-286-1940