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NASA’s Roman Space Telescope could reveal millions of invisible neutron stars

Date:

May 15, 2026

Source:

NASA

Summary:

NASA’s Roman Space Telescope could expose a vast hidden population of neutron stars lurking unseen across the Milky Way. By detecting subtle shifts in starlight caused by gravity, the mission may identify and even weigh isolated neutron stars that are otherwise impossible to see. Scientists hope the discoveries will reveal how these extreme objects are born and why they are blasted through space at incredible speeds.

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NASA’s Roman Telescope could finally uncover the Milky Way’s hidden neutron stars by spotting the tiny gravitational fingerprints they leave on starlight. Credit: NASA

Astronomers have long believed the Milky Way is filled with neutron stars, the ultra dense remnants left behind when massive stars explode. The problem is that most of these objects are nearly impossible to see. A new study published in Astronomy and Astrophysics suggests NASA's upcoming Nancy Grace Roman Space Telescope may finally be able to uncover some of them.

Using advanced simulations of the Milky Way and predictions of Roman's future observations, researchers found the space telescope could detect and study dozens of isolated neutron stars through a phenomenon known as gravitational microlensing.

"Most neutron stars are relatively dim and on their own," said Zofia Kaczmarek of Heidelberg University in Germany, who led the study. "They are incredibly hard to spot without some sort of help."

How Roman Could Detect Invisible Neutron Stars

Neutron stars contain more mass than the Sun packed into an object roughly the size of a city. Scientists study them to better understand how stars evolve, explode, and distribute heavy elements throughout the cosmos. They also offer a rare opportunity to investigate matter under the most extreme conditions (pressures and densities) imaginable.

Most neutron stars remain hidden unless they appear as pulsars that emit radio waves or shine brightly in X-rays. Even the most powerful telescopes can miss isolated neutron stars that produce little or no detectable light.

The Roman Space Telescope could find them indirectly. When a massive object such as a neutron star passes in front of a more distant star, its gravity bends and magnifies the background star's light. This effect, called microlensing, temporarily makes the distant star appear brighter and slightly shifted in the sky.

Many telescopes can detect the brief brightening caused by microlensing, but Roman is expected to do much more. The observatory will precisely measure both the increase in brightness (photometry) and the tiny positional movement (astrometry) of the background star.

Because neutron stars are relatively heavy, they create a stronger astrometric signal than smaller objects. That means Roman may not only detect hidden neutron stars, but also measure their masses, something extremely difficult to achieve using photometry alone.

"What's really cool about using microlensing is that you can get direct mass measurements," said paper co-author Peter McGill of Lawrence Livermore National Laboratory. "Photometry tells us that something passed in front of the star, but it's the amount the star's position shifts that tells us how massive that object is. By measuring that tiny deflection on the sky, we can directly weigh something that is otherwise unseen."

Solving Neutron Star Mysteries

Roman's observations could help scientists answer major questions about neutron stars and black holes, including whether there is a true gap between their masses. The mission may also reveal how quickly neutron stars travel through the galaxy.

Researchers are especially interested in the powerful "kicks" neutron stars receive during supernova explosions. These violent events can launch them through space at hundreds of miles per second.

The team plans to use Roman's future Galactic Bulge Time Domain Survey, which will repeatedly observe millions of stars in enormous sections of the sky.

"We're going to get to work as soon as the data start coming in," said McGill. "Even in the first months after commissioning, we expect to start identifying promising events."

Even a modest number of confirmed discoveries could significantly improve models of stellar explosions and the behavior of matter under extreme conditions.

"We don't know the mass distribution of neutron stars, black holes, or where one ends and the other begins with any certainty," McGill said. "Roman will really be a breakthrough in that."

A Hidden Population Waiting To Be Found

So far, astronomers have identified only a few thousand neutron stars, most of them detected as pulsars. However, scientists estimate the Milky Way could contain anywhere from tens of millions to hundreds of millions of neutron stars. Researchers have also only been ab