Aligned orbits found in double M dwarf system and trends across planets, brown dwarfs, and binaries

Star system: TOI 5375 A | Distance from the Sun: 397 light years

A new study has measured the alignment between the spin of an M dwarf star and the orbit of its very-low-mass stellar companion, marking the first such measurement for a double M dwarf system. Using the Rossiter-McLaughlin effect, researchers found that the two stars are well aligned, meaning the companion orbits in the same direction as the primary star spins. This suggests the system either formed aligned or was later realigned by tidal forces.

The study also compared the alignment, or obliquity, of orbits across different types of systems, including giant planets, brown dwarfs, and binary stars. It found that well-aligned orbits are more common around cooler stars and that companions with wide orbits tend to be aligned. There was no clear link between orbital alignment and how stretched out the orbits are. The analysis showed that binary stars and brown dwarfs have more tightly aligned orbits than giant planets, but more data are needed to confirm trends for high-obliquity systems.

These findings help scientists understand how different types of systems form and evolve, showing that alignment patterns seen in planets may also apply to more massive companions like brown dwarfs and other stars.

Key findings
- First obliquity measurement for a double M dwarf system shows strong alignment
- Well-aligned orbits are common around cooler stars
- Wide-orbit companions tend to be aligned
- No link found between alignment and orbital eccentricity
- Binary stars and brown dwarfs have more tightly aligned orbits than giant planets

Scientific study

An Aligned Very-Low-Mass Star Orbiting an M dwarf and Obliquity Patterns Across Giant Planets, Brown Dwarfs, and Binary Stars (external link)