Astronomers find a quadruple star system where four stars are 'birthing' one planet

Meet HD 98800, a nearby quadruple‑star system in the constellation Crater. It sits about 150 light‑years away and is approximately 10 million years old.

That age places it in a formative phase when stars finish settling and nearby material can still glow in infrared light.

The system belongs to the TW Hydrae association, a group of about twenty very young stars located 160 light‑years from Earth. HD 98800 contains four stars arranged as two close binaries that orbit each other as a wider pair.

One of those close pairs, called HD 98800B, hosts a dust disk; the other pair does not. The two binaries remain gravitationally bound, yet sit apart by about 50 astronomical units – roughly 4.65 billion miles.

“Typically, when astronomers see gaps like this in a debris disk, they suspect that a planet has cleared the path, noted Dr. Elise Furlan, who led the study from University of California at Los Angeles (UCLA).

“However, given the presence of the diskless pair of stars sitting 50 AU away, the inward-migrating dust particles are likely subject to complex, time-varying forces, so at this point the existence of a planet is just speculation.”

Orbits that tug and stretch

Each close pair completes an orbit in a few hundred days. Their paths are not perfect circles; they are “eccentric,” so the stars swing closer together at one point and farther apart at another.

That detail matters because changing distances can heat and stir nearby dust.

The two binaries orbit each other on a far wider track with a period of a few hundred years. Astronomers observed only a single moment in that cycle; the configuration seen here will slowly change as the wide orbit advances.

Distance and brightness of HD 98800

Precise distance measurements for HD 98800 came from a satellite that gauged tiny position shifts as Earth moved around the Sun.

With the distance known, astronomers could compute intrinsic brightness rather than the apparent brightness we see from Earth.

Imaging measured their colors in blue, optical, and near‑infrared light. With color and brightness together, the stars fell on the Hertzsprung–Russell diagram above the “main sequence,” where mature stars like the Sun spend most of their lives.

They no longer sit in the very earliest “baby star” phase and instead line up with the pre‑main‑sequence tracks that lead toward maturity. Astronomers often call this in‑between stage “post–T Tauri.”

Age and mass estimates agree

Teams compared each star’s temperature and luminosity to evolutionary models for young stars. They considered several assumptions, including the effects of dust that can redden starlight.

The results clustered tightly: the four stars lined up with ages between seven and twelve million years.

Mass estimates matched that picture. One star lies near the Sun’s mass, another is a bit lighter, and at least one is roughly half the Sun’s mass. Those values make sense for stars still contracting toward the main sequence yet shining strongly.

Two belts in the HD 98800 disk

Using NASA’s Spitzer Space Telescope, scientists obtained a detailed look at the potential planet‑forming disk around HD 98800B.

Spitzer’s infrared spectrometer revealed two dust belts. One belt sits approximately 5.9 AU from the central binary (about 549 million miles) and likely contains asteroids and comets.

The other belt lies at 1.5 to 2 AU (about 139.5 to 186 million miles) and consists of fine dust grains. Together they mark a structured environment where collisions grind solids and heat radiates efficiently.

HD 98800 shines strongly at infrared wavelengths, indicating abundant warm dust. Earlier work suggested relatively large grains in a compact disk rather than a vast cloud.

Optical images did not resolve the disk clearly, which points to a small or faint structure in visible light. The infrared “excess” is large, and the most consistent picture keeps the disk with the B pair, possibly influenced by the gravity of the other binary.

Dust under the influence

The wider orbit between the two binaries likely nudges the disk around HD 98800B. Gravitational tugs can reshape dust belts, herd particles into rings, or warp the disk.

When the wide orbit brings the binaries closer, the disk may intercept more starlight, heating and brightening at infrared wavelengths.

These interactions can also stir collisional cascades that grind larger bodies into smaller grains, consistent with the fine dust seen in the inner belt.

“Planets are like cosmic vacuums. They clear up all the dirt that is in their path around the central stars,” explained Dr. Furlan.

A compact disk with two distinct belts hints at regions with different kinds of solids and different collision rates.

The outer belt, with larger material, behaves more like a storehouse for comets and asteroids. The inner belt, dominated by fine grains, points to active grinding and rapid heating closer to the stars.

Origins and neighborhood

Kinematics – how the system moves through space – traces back to a familiar nursery.

When astronomers ran the motion backward, the path likely crossed the Scorpius-Centaurus association, a large star‑forming complex not far from our part of the galaxy.

The timing of that crossing fits the age estimates and supports the idea that HD 98800 formed in or near that region before drifting to its current position.

Membership in the TW Hydrae association adds another clue. Its age estimates align with the youth seen in HD 98800. Clustering in both space and time strengthens the case for a shared origin.

Lessons from HD 98800

The “cosmic house” discovered at HD 98800 offers a nearby, rare case of a young multi‑star system with a structured disk around one pair.

The communal nature of this system’s layout is both rare and “eccentric,” giving astronomers a perfect case study to examine stars during their early years and how multi-star systems influence planet formation.

The presence of two dust belts in a system with four stars sets useful constraints for models of planet formation in complex gravitational settings. It also shows that significant solid material can persist while stars finish contracting.

All of these characteristics combine to make HD 98800 a strong testbed for how long protoplanetary disks last, how they evolve under multiple stars, and how those conditions may shape future planets.

The full study was published in the journal Astronomy and Astrophysics.

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