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Journey to Center of Milky Way With Upcoming NASA Roman Core SurveyAshley Balzer
Jan 23, 2026 ArticleAt the heart of our own galaxy, there is a dense thicket of stars with a supermassive black hole at the very center. NASA’s Nancy Grace Roman Space Telescope will provide the deepest-ever view of this zone, revealing stars, planets, and unique objects that resist definition.
Based on the input of astronomers from across the globe, the Roman Space Telescope will spend three-quarters of its five-year primary mission conducting This infographic describes the Galactic Bulge Time-Domain Survey that will be conducted by NASA’s Nancy Grace Roman Space Telescope. The smallest of Roman’s core surveys, this observation program will consist of repeat visits to six fields covering 1.7 square degrees total. One field will pierce the very center of the galaxy, and the others will be nearby — all in a region of the sky that will be visible to Roman for two 72-day stretches each spring and fall. The survey will mainly consist of six seasons (three early on, and three toward the end of Roman’s primary mission), during which Roman will view each field every 12 minutes. Roman will also view the six fields with less intensity at other times throughout the mission, allowing astronomers to detect microlensing events that can last for years, signaling the presence of isolated, stellar-mass black holes. Credit: NASA’s Goddard Space Flight Center
The survey will observe six patches of the galactic bulge, one pinpointing the center and five nearby, every 12 minutes during 438 days of total observing time. The observations will be separated into six “seasons” spread out over five years.
Spending so much 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, and any planets that orbit them, over long periods — the “time-domain” aspect of the survey.
“This survey will be the highest precision, highest cadence, longest continuous observing baseline survey of our galactic bulge, where the highest density of stars in our galaxy reside,” said Jessie Christiansen of Caltech/IPAC, who served as co-chair of the committee that defined the Galactic Bulge Time-Domain Survey.
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 the greater than 6,000 currently confirmed.
With this survey, scientists expect to see over 1,000 new planets orbiting other stars just using microlensing alone. This would increase the number of exoplanets identified using this method by more than fivefold.
A microlensing event is when light from a distant star in the background is warped slightly by a foreground object, like a star and its planet. This warping of light is called gravitational lensing, with the gravity from the star and planet bending the fabric of space that light is traveling through and focusing it like a magnifying glass.
This animation illustrates the concept of gravitational microlensing. When one star in the sky appears to pass nearly in front of another, the light rays of the background source star become bent due to the warped space-time around the foreground star. This star is then a virtual magnifying glass, amplifying the brightness of the background source star, so we refer to the foreground star as the lens star. If the lens star harbors a planetary system, then those planets can also act as lenses, each one producing a short deviation in the brightness of the source. Thus we discover the presence of exoplanets, and measure its mass and separation from its star.Credit: NASA’s Goddard Space Flight Center/CI Lab
While the transit method is very good at identifying exoplanets that orbit close to their star, the microlensing method can discover exoplanets that orbit farther away from their star, and in planetary systems farther from Earth than ever studied before. Roman will be versatile enough to see exoplanets dwelling from the inner edge of the habitable zone out 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 may even discover “rogue planets” without host stars that either formed alone or were ejected from their host systems long ago.
“For the first time, we will have a big picture understanding of Earth and our solar system within the broader context of the exoplanet population of the Milky Way galaxy,” Christiansen said. “We still don’t know how common Earth-like planets are, and the Roman Galactic Bulge Time-Domain Survey will provide us with this answer.”
This survey will create a census of exoplanets for scientists to draw statistical conclusions from, revealing common patterns found in exoplanets and furthering our understanding of planetary formation and habitability.
One survey; lots of science
Because of the immense amount of observing time and subsequent data produced, the Galactic Bulge Time-Domain Survey will advance not only the field of exoplanet microlensing, but other areas of astronomy, too.
“There is an incredibly rich diversity of science that can be done with a high-precision, high-cadence survey like this one,” said Dan Huber of the University of Hawaii, the other survey co-chair.
The core survey was optimized not only for microlensing, but also to observe changes in brightness from small, fast blips 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, and eclipsing binaries, and can lead to a deeper understanding about the physics of star formation and evolution.
A simulated image of Roman’s observations toward the center of our galaxy, spanning only less than 1 percent of the total area of Roman’s galactic bulge time-domain survey. The simulated stars were drawn from the Besançon Galactic Model. Credit: Matthew Penny (Louisiana State University)“The 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 how old these stars are and how they fit into the formation history of our Milky Way galaxy.”
Roman’s observing strategy in the Galactic Bulge Time-Domain Survey, as well as the NASA’s Goddard Space Flight Center, Greenbelt, Md.
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Last Updated Jan 23, 2026 EditorAshley BalzerContactAshley Balzerashley.m.balzer@nasa.govLocationGoddard Space Flight CenterRelated Terms
- Nancy Grace Roman Space Telescope
- Exoplanet Detection Methods
- Exoplanets
- Galaxies
- Goddard Space Flight Center
- Gravitational Microlensing
- Stars
- The Milky Way
- The Universe