Previously, astronomers had detected only three ultracool short-period binary dwarf systems. They were relatively young – up to 40 million years old. In a recent study, astrophysicists at Northwestern University and the University of California San Diego (UC San Diego) discovered an extreme system: the sleekest ultracool dwarf binary system ever observed.

This newly discovered system is known as LP 413-53AB. It consists of a few ultra-cool dwarves. The system is estimated to be billions of years old. Surprisingly, its orbital period is at least three times shorter than any ultracool dwarf double star discovered to date.

The proximity between the two stars is as follows: they take less than one Earth day to orbit each other. Each star’s “year” is only 17 hours long.

Chih-Chun “Dino” Hsu, a Northwestern astrophysicist who led the study, said: “It’s exciting to discover such an extreme system. We knew that in principle these systems should exist, but such systems had not yet been identified.”

The system was first discovered on Jan. 10 as part of a session on stars and their activity. The team found this while exploring archival data.

Hsu created an algorithm that uses a star’s spectral data to simulate it. Astrophysicists can determine a star’s chemical composition, temperature, gravity, and rotation by analyzing the light the star emits. This analysis demonstrates the star’s radial velocity, or the speed at which it moves toward and away from the observer.

Hsu discovered an oddity when he looked at the spectral data of the LP 413-53AB. Hsu thought there was only one star in the system because early observations noted when the stars were close together and their spectral lines overlapped. But as the stars migrated in their orbits, the spectral lines separated into pairs and shifted in opposite directions. Hsu discovered that two stars were entangled in a binary star.

Hsu used powerful telescopes at the WM Keck Observatory to observe the phenomenon himself. On March 13, 2022, the team aimed the telescopes at the constellation of Taurus, where the binary system resides, and observed it for two hours. They then followed with more sightings in July, October and December, as well as January 2023.

Professor Adam Burgasser said: “While making this measurement, we could see things change during a few minutes of observation. Most of the binary stars that we track have an orbital period of years, so you get a measurement every few months. Then after a while you can put the puzzle together With this system, we could see the spectral lines moving apart in real time. It’s amazing to see something happening on a human time scale in the universe.”

“The observations confirmed what Hsu’s model predicted. The distance between the two stars is about 1% of the distance between the Earth and the Sun. This is remarkable, because when they were young, about 1 million years old, these stars would have been on top of each other.”

The team thinks the stars either migrated towards each other as they evolved, or could have come together after the ejection of a third – now lost – stellar member. More observations are needed to test these ideas.

Hsu said so too “By studying similar galaxies, researchers can learn more about potentially habitable planets beyond Earth. Ultracool dwarfs are much fainter and fainter than the sun, so any worlds with liquid water on their surface — a critical ingredient for forming and sustaining life — must be much closer to the star. However, for LP 413-53AB, the distance from the habitable zone is the same as the orbit of the star, making it impossible to form habitable planets in this system.”

“These ultra-cool dwarfs are neighbors of our sun. To identify potentially habitable hosts, it’s helpful to start with our near neighbors. But if nearby binaries are common among ultracool dwarfs, there may be few habitable worlds to be found.”

Magazine reference:

  1. Chih-Chun Hsu, Adam Burgasser, and Christopher A. Theissen. Discovery of the Exceptionally Short Period Ultracool Dwarf Binary LP 413-53AB. The Astrophysical Journal Letters. DOI 10.3847/2041-8213/acba8c