The Milky Way’s core doesn’t look like the ancient stellar graveyard many astronomers once thought it was.
At the heart of a massive new survey from NASA‘s Hubble Space Telescope, astronomers are mapping one of the most crowded regions in our galaxy. Early results from the project may help address a long-running debate about the age of the Milky Way’s central bulge — the tightly packed region of space surrounding the galaxy’s core.
For decades, many astronomers treated the bulge as a relic from the Milky Way’s earliest years. Previous studies of star brightness and color placed most of its formation around 10 billion years ago. By comparison, our solar system formed just 4.6 billion years ago.
But newer research has complicated that picture. Some studies suggest a noticeable share of stars near the galactic center may be much younger — perhaps only 5 billion to 8 billion years old. If true, that would mean the Milky Way kept developing its central region far later than some scientists had ever imagined. If astronomers can determine when the bulge’s stars formed, they can reconstruct how the galaxy itself grew and changed over time.
The Hubble survey will build a catalog of 20 to 30 million objects in this dense region, said Sean Terry, an assistant research scientist at the University of Maryland and NASA’s Goddard Space Flight Center. The team has published a paper on the Hubble survey in The Astrophysical Journal Letters.
Researchers designed the Hubble program to support the upcoming Nancy Grace Roman Space Telescope, which will search the same region for planets using gravitational microlensing, a technique that detects distant objects by measuring how their gravity bends and brightens starlight. The Roman mission could launch as early as this fall.
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“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 Jay Anderson, a co-author based at the Space Telescope Science Institute in Maryland, in a statement. “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.'”
But the Hubble survey also stands on its own. It delivers one of the sharpest wide-area views ever captured of the Milky Way’s crowded core, where dust clouds block much of the light and stars are so tightly packed that their images often overlap. By distinguishing those stars more cleanly, the survey allows astronomers to assemble a consistent catalog across 354 fields near the galactic center.
Even so, conditions vary sharply throughout the region. In some fields, astronomers match thousands of stars to measurements from the Gaia spacecraft, a mission that tracked star positions and their motion across the sky. In others, dense dust blots out so much light that only a few hundred stars appear clearly enough for comparison.
The variation itself helps map the inner galaxy. It shows where dust obscures the view and where starlight passes through more easily. While Hubble sharpens the view of crowded stars, it cannot remove the effects of dust. That means there are still some patchy areas of the Milky Way’s interior.
Credit: NASA / ESA / Thomas Brown
Researchers expect future work from the survey to produce detailed maps of the interstellar dust in the galactic center, showing where starlight is blocked and where it shines. That will help astronomers trace how stars are distributed.
The Roman telescope will repeatedly monitor the same region and track changes in how stars move and brighten over time across millions of objects. By collecting Hubble images years earlier, astronomers effectively created a “before” snapshot of the galactic bulge.
That long time gap could help scientists measure how fast stars drift across the sky with unusual precision. It may also help them identify faint or otherwise hidden objects through their gravitational effects.
