TL;DR: Astronomers found a red dwarf star 300 light-years away steadily pulling gas off an orbiting brown dwarf every 86.65 minutes, the first seen case of stable mass transfer between two such low-mass objects.

A first: slow feeding instead of fast swallowing

In a paper appearing Oct. 5, 2026 in Nature Astronomy, scientists at MIT and elsewhere reported the direct observation of stable mass transfer from a substellar object onto a main-sequence star, according to Nature Astronomy.

The system is named ZTF J0440+2325, is within the Milky Way galaxy, and is roughly 300 light-years from Earth, according to MIT News.

It represents the first observation of a low-mass object that is slowly and steadily consuming material from another low-mass object, according to MIT News.

The discovery reveals a new way that stars and planetary companions can interact, according to MIT News.

Like Earth, most planetary bodies circle their star in stable, detached orbits, according to MIT News.

These companionable systems can suddenly change when a planet comes too close to its star, according to MIT News.

In such a close encounter, a star can pull the planet in and swallow it whole, according to MIT News.

Across the galaxy, astronomers have seen plenty of stable, detached planetary systems, according to MIT News.

They have also observed a handful of stars quickly engulfing their planet, according to MIT News.

Now, for the first time, scientists have spotted a system that is striking a curious balance between the two extremes, according to MIT News.

In the new system, a star is leisurely snacking on a closely orbiting brown dwarf — a planet-like object that is more massive than a planet yet not quite as big as a star, according to MIT News.

The rate at which the star is feeding from the brown dwarf suggests that this slow stellar cannibalism could carry on for hundreds of thousands, or even billions of years, according to MIT News.

The Nature Astronomy abstract states the same conclusion: the fate of some substellar objects is not rapid engulfment and destruction, but instead gradual consumption for potentially billions of years.

Meet ZTF J0440+2325, 300 light-years away in the Milky Way

ZTF J0440+2325 is an 87-minute binary in which a brown dwarf stably transfers mass onto an M dwarf, according to Nature Astronomy.

The precise orbital period measured from the survey data is 86.65 minutes, according to the study preprint and MIT News reporting.

The two objects orbit each other every 86.65 minutes, with the brown dwarf overflowing onto its companion, according to MIT News.

The stream of material strikes the surface of the red dwarf, heating a large hot spot at the point of impact, according to the MIT illustration caption for the system.

The star and brown dwarf are extremely close, with the brown dwarf circling the star every 87 minutes, in an orbit that could fit within the diameter of the sun, according to MIT News.

Both objects are small by stellar standards, according to MIT News.

The star is around 85 times as massive as Jupiter, while the brown dwarf is around 25 times as massive, according to MIT News.

The new system was located within the Milky Way galaxy, around 300 light-years from Earth, as determined from the original ZTF signal and follow-up observations, according to MIT News.

Substellar objects such as brown dwarfs and planets are generally expected to remain detached from their main-sequence host stars unless orbital decay or stellar expansion brings them into contact, leading to rapid engulfment and destruction, according to Nature Astronomy.

Such a fate is predicted for the Earth and other rocky planets in our Solar System, according to Nature Astronomy and MIT News.

In certain cases, however, theory also allows for stable long-lived mass transfer from a substellar object onto its main-sequence host, although such accretion had not been observed before this system, according to Nature Astronomy.

How a repeating triangle in ZTF data gave it away

The new system was spotted initially by the Zwicky Transient Facility, according to MIT News.

The ZTF uses a camera as part of a telescope at the Palomar Observatory, in California, to scan the sky for rapid changes in brightness, which could signal the presence of a supernova, a gamma-ray burst, or colliding neutron stars, according to MIT News.

The team identified ZTF J0440+2325 in a systematic search for short-period variables in data from the Zwicky Transient Facility, according to the preprint.

The system had a highly significant periodic signal at an orbital period of 86.65 minutes, which motivated ground-based follow-up, according to the preprint.

Several years ago, Kevin Burdge was looking through ZTF data when he noticed a strange light curve, or pattern in brightness, according to MIT News.

Light curves for supernovae resemble a bell curve, signaling the gradual brightening and then fading of a star as it bursts, according to MIT News.

What Burdge picked out looked more like a triangle, that didn't appear once, but again and again, according to MIT News.

“I remember first looking at this and thinking: Stars don’t make triangular waveforms like this,” Burdge recalls, according to MIT News.

At the time, he and his colleagues were focused on a different signal, which they identified as a “black widow binary” — a system in which an extremely dense, spinning neutron star is slowly consuming a much smaller companion star, similar to how its arachnid namesake plays with its prey, according to MIT News.

Burdge wondered whether the triangle signal might also be from a black widow, according to MIT News.

But the light from the signal was puzzling, according to MIT News.

In black widow binaries, the light appears to wobble, as a result of a very light, low-mass object, such as a small companion star, whipping around a much heavier object, such as a neutron star, according to MIT News.

“We weren’t seeing that whipping back and forth here,” Burdge says, according to MIT News.

“It didn’t make any sense. We couldn’t explain what this was,” Burdge says, according to MIT News.

But they had a hunch: the signal could be coming not from a wobbly, David-and-Goliath system, but from a more balanced pair of objects, each with a similarly low mass, according to MIT News.

“If you have less mass in the system overall, things can gently orbit each other without whipping back and forth,” Burdge says, according to MIT News.

“That was the idea. But we never had any proof. And this weird triangle just sat for years,” Burdge says, according to MIT News.

Confirming a low-mass star fed by a brown dwarf

Recently, Burdge and Aaron Householder, a graduate student in MIT’s Department of Earth, Atmospheric and Planetary Sciences, decided to revisit the triangle mystery, according to MIT News.

From the original ZTF signal, they determined the location of its source to be within the Milky Way galaxy, around 300 light-years from Earth, according to MIT News.

They focused multiple telescopes on the source, named ZTF J0440+2325, according to MIT News.

From these observations, they measured various properties of the source, including its wobble, according to MIT News.

Compared to black widows and other similar binaries, the wobbling from ZTF J0440+2325 was much smaller — but not insignificant, according to MIT News.

“That was the real clincher for this system,” Householder says, according to MIT News.

“When we measured that wobble, we found we were not seeing a black widow. This was a low-mass star that’s orbited by a brown dwarf. The wobble was too small in amplitude to be anything else,” Householder says, according to MIT News.

On UT 2023 October 18, the team obtained high-speed simultaneous five-band photometry of ZTF J0440+2325 with HiPERCAM on the 10.4-meter Gran Telescopio Canarias, according to the preprint.

The light curves showed extreme chromatic variability, with amplitudes that increased toward shorter wavelengths, according to the preprint.

In particular, ZTF J0440+2325 brightened by more than a factor of 30 in the u band relative to minimum brightness, according to the preprint.

With two low-mass objects circling at such close range, the scientists examined whether one object could be transferring material to the other, according to MIT News reporting on the follow-up analysis.

Their determination was that the star and brown dwarf are in stable mass transfer, with the brown dwarf stably transferring mass onto the M dwarf companion, according to Nature Astronomy.

Why gradual eating can last billions of years

“When we think of stars interacting with planets or brown dwarfs, the picture is always that the star eventually swallows the other thing,” says Kevin Burdge, assistant professor of physics at MIT, according to MIT News.

“This is what will happen to the Earth when the sun becomes a red giant,” Burdge says, according to MIT News.

“But here, we’ve found an alternative: Instead of swallowing the thing up, the star can gradually eat it, for billions of years,” Burdge says, according to MIT News.

The study’s MIT co-authors include Aaron Householder, Kaitlyn Shin, Saul Rappaport, Joheen Chakraborty, and Emma Chickles, according to MIT News.

Collaborators are from Caltech, the University of Hawaii, the Instituto de Astrofísica de Canarias and the Universidad de La Laguna in Spain, and the Harvard and Smithsonian Center for Astrophysics, according to MIT News.

The full Nature Astronomy author list names Aaron Householder, Kaitlyn Shin, Kevin B. Burdge, Thomas R. Marsh, Saul A. Rappaport, Kareem El-Badry, Joheen Chakraborty, Emma Chickles, Fei Dai, Matthew J. Graham, S. R. Kulkarni, Pablo Rodríguez-Gil, Andrew Vanderburg and Samuel Whitebook, according to Nature Astronomy.

A second candidate: ZTF J1444+4820 at 67 minutes

The paper does not report only one object, according to Nature Astronomy.

The authors present ZTF J1444+4820, with an orbital period of 67 minutes, as a strong candidate low-mass mass-transferring system in a hierarchical triple, according to Nature Astronomy.

The preprint describes the pair together as two binaries, ZTF J0440+2325 and ZTF J1444+4820, with orbital periods of just 87 and 67 minutes, respectively, in which a brown dwarf stably transfers mass onto an M dwarf companion, according to the preprint.

Together, these systems demonstrate that the fate of some substellar objects is not rapid engulfment and destruction, but instead gradual consumption for potentially billions of years, according to Nature Astronomy.

ZTF imaging data are available via the Zwicky Transient Facility public data release, according to Nature Astronomy.

The analysis used custom Python code and publicly available software packages, with custom analysis code publicly available via GitHub and Zenodo, according to Nature Astronomy.

Sources referenced