Space & Physics

Hubble Survey Sets Up Roman’s Future Look Near Milky Way’s Center

The Milky Way’s galactic bulge, the bulbous region that surrounds the galactic center, contains a dense collection of stars, planets, and other free-floating objects. This region has been studied for decades with numerous ground-based and space-based telescopes, including NASA’s Hubble and James Webb space telescopes. Soon, NASA’s Nancy Grace Roman Space Telescope will be the […]

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May 11, 2026 - 20:00

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Hubble Survey Sets Up Roman’s Future Look Near Milky Way’s Center

An observation (labeled u201cVISTA V V V Survey, Near-infrared) of the Milky Wayu2019s center pointing toward its supermassive black hole, which is labeled Sagittarius A* (pronounced u201cA staru201d). At 7 ou2019clock from center is a small region, outlined with 5 fields of view from the Nancy Grace Roman Space Telescope that are stacked together in a horizontal rectangle. This region is about a third of the image in length and a fifth of the image in width. Within that same region are diagonal lines that alternate between orange and blue. A legend at the bottom left shows two Hubble instruments. One of them, marked with an orange diamond, is labeled u201cW F C 3 / U V I S.u201d The other, marked with a blue diamond, is labeled u201cA C S / W F C.u201d The background is a field of stars, gas, and dust that appear grey, except the center third that runs from the left to the right of the frame, which is composed of brown filaments of dust and gas. The tiny region surrounding Sagittarius A star appears orange.

This VISTA VVV Survey image shows the galactic bulge near Sagittarius A*, the supermassive black hole at the Milky Way’s center. A region planned for observation by NASA’s Nancy Grace Roman Space Telescope is outlined. This area has been observed by NASA’s Hubble Space Telescope.

Image: NASA, Alyssa Pagan (STScI); Acknowledgment: VISTA, Dante Minniti (UNAB), Ignacio Toledo (ALMA), Martin Kornmesser (ESO)

The Milky Way’s galactic bulge, the bulbous region that surrounds the galactic center, contains a dense collection of stars, planets, and other free-floating objects. This region has been studied for decades with numerous ground-based and space-based telescopes, including NASA’s Hubble and James Webb space telescopes. Soon, NASA’s Nancy Grace Roman Space Telescope will be the first to make studying the galactic bulge a part of its core science objectives, building on the data collected from all observatories before it. Roman’s field of view will cover more area at a far faster cadence than previous space telescopes, allowing it to survey millions of stars and find thousands of new exoplanets.

To support Roman in characterizing numerous stars and planets, astronomers sought to use Hubble to observe many of the same areas of the galactic bulge that Roman will observe in its core Galactic Bulge Time-Domain Survey. By comparing Hubble data taken months or years earlier to new Roman data, astronomers will be better able to interpret Roman’s forthcoming observations. The Roman telescope team is targeting as soon as early September 2026 for launch.

“A top priority of our Hubble survey is to cover as much sky area as possible,” said Sean Terry, project lead and assistant research scientist from the University of Maryland, College Park and NASA’s Goddard Space Flight Center in Greenbelt.

A paper about the team’s work published May 11, 2026 in the Astrophysical Journal.

‘Small’ lenses, large discoveries

Many planetary systems within the Milky Way evolve much like our solar system did, beginning with the collapse of a cosmic gas cloud, the growth of a star, and the formation of surrounding planets. However, in some systems, different events can result in a planet being ejected from the system where it formed. Hundreds of these “rogue planets” will be detected by Roman’s Galactic Bulge Time-Domain Survey, in addition to previously unseen, isolated neutron stars, and even black holes with masses similar to our Sun.

This survey consists of six 72-day observing seasons during which Roman will take a snapshot every 12 minutes of a large portion of the bulge (approximately 1.7 square degrees of the region, or the area of 8.5 full moons). While it will detect a variety of targets, the survey is optimized to look for a specific type of event known as microlensing.

Microlensing events, a type of gravitational lensing event, occur when the light from a more distant object is warped by the mass of a closer object along the line of sight. These events occur on a much smaller scale than larger lensing events (on the order of individual stars instead of galaxies or galaxy clusters) and allow us to search for exoplanets between us and the densely packed stars within the galactic bulge.

“The great thing about microlensing is that we’ll be able to do a complete census of objects as small as Mars that are moving between us and these fields in the bulge, no matter what it is,” said co-author Jay Anderson of the Space Telescope Science Institute in Baltimore.

For Roman, from Hubble

When a telescope observes a lensing object, such as a bright star, aligning with a star in the galactic bulge, it can be difficult for astronomers to decipher which of the two the starlight comes from. Therefore, timing is a key consideration. If astronomers can identify light sources separately before a microlensing event occurs, it becomes far easier to disentangle them.

To collect this pre-Roman data, astronomers used the Hubble Space Telescope to conduct a large-scale survey, which began in the spring of 2025, covering much of the same area that Roman will observe in the Galactic Bulge Time-Domain Survey. The size of this program is even larger than two previous surveys (each around 0.5 square degrees) that led to Hubble’s largest mosaic, that of our neighboring Andromeda galaxy, which took over 10 years to assemble.

“The main goal of these observations is to be able to identify objects that participate in lensing events during the Roman survey, catching them before they undergo the lensing event,” said Anderson. “When, in a couple of years, an event happens during Roman’s long stare at the field, we can go back and say, ‘This was a red star, this was a blue star, and the event happened when the red star went in front of the blue star.’”

The data from Hubble also will help shape the analysis of the lensing objects themselves. The microlensing event itself measures only a ratio of the masses of a host star and its planet. With data from stars before or after their microlensing events, however, scientists would be able to measure the stars’ individual masses, echoing the way Hubble previously determined the mass of a star and its planet in the Milky Way. This method turns a more opaque measurement of the relationship between a star and its planet into one far more certain.

“Instead of estimating a mass ratio of a planet that’s orbiting a star, we can say that we’re confident it’s a Saturn-mass planet orbiting a star that’s 0.8 solar masses, for example,” Terry said. “So with the help of precursor imaging from Hubble you can hope to get direct measurements of the masses as opposed to indirect mass ratios.”

Next leap in magnitude

While exoplanet discovery is a large part of Roman’s Galactic Bulge Time-Domain Survey, observing such a large area with Hubble also can help identify areas of extinction, dense pockets of dust and gas that absorb or scatter light, allowing us to create maps detailing where we can see stars and where we can’t.

Hubble’s survey also has provided the crucial beginning of a brand-new catalog of stars, which will help astronomers characterize the host stars of exoplanets discovered by Roman. The research team predicts Roman will add to Hubble’s star catalog by an order of magnitude.

“This Hubble survey will build a catalog of 20 to 30 million point sources,” said Terry. “But, by the end of the Galactic Bulge Time-Domain Survey, Roman may measure about 200 to 300 million, and it will produce, essentially, some of the deepest images ever taken of any part of the sky.”

The data from the most recent Hubble survey is available in the Mikulski Archive for Space Telescopes.

The Hubble Space Telescope has been operating for over three decades and continues to make ground-breaking discoveries that shape our fundamental understanding of the universe. Hubble is a project of international cooperation between NASA and ESA (European Space Agency). NASA Goddard manages the telescope and mission operations. Lockheed Martin Space, based in Denver, also supports mission operations at Goddard. The Space Telescope Science Institute in Baltimore, which is operated by the Association of Universities for Research in Astronomy, conducts Hubble science operations for NASA.

The Nancy Grace Roman Space Telescope is managed at NASA Goddard with participation by NASA’s Jet Propulsion Laboratory in Southern California; Caltech/IPAC in Pasadena, California; the Space Telescope Science Institute; and a science team comprising scientists from various research institutions. The primary industrial partners are BAE Systems, Inc. in Boulder, Colorado; L3Harris Technologies in Melbourne, Florida; and Teledyne Scientific & Imaging in Thousand Oaks, California.

Related Images & Videos

Hubble/Roman Galactic Bulge Survey Region (VISTA VVV Survey)

A field of stars, which are blue, white, and orange. A small region between the center and the right of the frame is outlined with a square box. Above it is a pullout of the outlined region, labeled u201cOGLE-2013-BLG-0341.u201d The pullout shows two fuzzy red orbs that are very close together, each of which are stars. One of the stars is labeled u201clensu201d, while the other is labeled u201cbackground star.u201d

Microlensing Event at OGLE-2013-BLG-0341 (Hubble Image)

A follow-up observation by NASA’s Hubble Space Telescope shows a region containing a microlensing event captured by the Optical Gravitational Lensing Experiment (OGLE) in 2013. Hubble was able to separate the foreground lens from the background star.

A graphic showing the process of microlensing with three columns indicating different times. Against a star-filled background, a distant yellow background star appears at top of the graphic, while a small red foreground star passes in front of it from left to right in the middle of the graphic. Three panels progress from u201cBefore Lensingu201d to u201cDuring Lensingu201d to u201cAfter Lensing.u201d As the foreground star aligns with the background star in the middle panel, white curved lines show the bending of the background staru2019s light by gravity. Two diverging lines converge again to indicate a magnification of the staru2019s light. Three boxes show the image captured by the Hubble telescope (left) and Roman telescope (middle, right). Underneath these panels is a bell curve (y-axis reads u201cApparent Brightness of the Background Staru201d, x-axis reads u201cTimeu201d). Its lowest points (at left and right) and highest point (middle) connect to the three boxes by a dotted white line.

Microlensing Infographic

This graphic illustrates a microlensing event, which occurs when the light from a distant object warps as a mass, such as a foreground star, precisely aligns in front of that object. This causes the more distant background star to increase in apparent brightness.

The video begins with a title card that says, u201cZoom Into The Milky Wayu2019s Galactic Bulge: Hubble and Roman Survey Regionsu201d laid over a view of the Milky Way from the 2MASS, an all-sky survey taken in near-infrared wavelengths. The video zooms into the center of this survey before transitioning to the VISTA VVV Survey, a survey of the Milky Wayu2019s galactic bulge. At the zoomu2019s deepest point, Sagittarius A star is labeled with a star icon. Several diagonal lines appear, alternating from orange to blue across a small area to the bottom left of the frameu2019s center. This region is outlined with 5 fields of view from the Nancy Grace Roman Space Telescope that are stacked together in a horizontal rectangle. At the bottom left is a legend, which shows two Hubble instruments. One of them, marked with an orange diamond, is labeled u201cW F C 3 / U V I S.u201d The other, marked with a blue diamond, is labeled u201cA C S / W F C.u201d

Zoom Into the Milky Way’s Galactic Bulge – Hubble/Roman Survey Regions

This video shows a zoom into the Milky Way’s galactic bulge near the galactic center. As it zooms in, the view changes from the near-infrared 2MASS survey to the VISTA VVV survey (both ground-based).