binary stars, sun, solar system

Artist impression of young binary system. Credit: NASA.

The case of the vanishing Sun: Did our star have a twin?

A recent theory posits that our Sun may have started its life with a binary companion. But what happened to the second Sun, and what does it mean for the Oort Cloud?

binary stars, sun, solar system

Artist impression of young binary system. Credit: NASA.

A recent theory posits that our Sun may have started its life with a binary companion. We live in a one-star system, but if we lived in a binary system (where two stars orbit each other) we would see two Suns. A binary system would also explain the existence of the Oort Cloud.

Binary systems can morph into one-star systems over time and scientists believe that may have been the case with our solar system. A new theory published in Astrophysical Journal Letters explains why it could be possible.

The Oort Cloud

The research team believe that our Sun’s twin would have been roughly the same size, and that it was the binary system theory could even explain the existence of the Oort cloud and ‘Planet Nine’.

The Oort cloud – also known as the Öpik–Oort cloud, is a “theoretical cloud of predominantly icy planetesimals proposed to surround the Sun” at distances ranging from 2 000 to 200 000 astronomical units (au)

Scientists now believe that a binary system would explain the Oort cloud’s density, as “a binary system tends to draw in and capture more material and objects than a single star”.

solar sun binary oort cloud
Solar system and the Oort Cloud

Amir Siraj, the lead author of the study, explains that previous models “have had difficultly producing the expected ratio between scattered disk objects and outer Oort cloud objects”. Siraj adds:

“The binary capture model offers significant improvement and refinement, which is seemingly obvious in retrospect: most sun-like stars are born with binary companions”.

Planet Nine

Then there’s the mythical Planet Nine, a mysterious, yet-to-be-identified object that possibly exists in the far-distant edges of our solar system (not to be confused with Pluto, but let’s not go down that rabbit-hole right now…)

Scientists observed movement in the Kuiper belt – a junkyard stretch of space past Neptune that is 200 times more massive than the asteroid belt – which suggests the gravitational pull of something very large is at play.

The object referred to as Planet Nine exerts its gravitational pull on anything that gets too close. The theory suggests that the Sun and its twin could draw in and “capture” such a large planet.

solar sun binary planet nine
Artist’s concept of the hypothetical Planet Nine orbiting far from the Sun. Credit: Caltech/R. Hurt (IPAC)

However, some scientists believe that Planet Nine is just a mirage.The patterns in orbits of small bodies in the outer solar system “could arise from the gravity of a massive disk of icy debris rather than an undiscovered giant world”.

What happened to the second Sun?

One theory is that the companion star could have been drawn away by other passing objects, perhaps even other star systems during the early formation of our solar system. According to Dr Avi Loeb:

“Passing stars in the birth cluster would have removed the companion from the sun through their gravitational influence.”

Siraj explains that before the theoretical sun was pulled away, the “solar system already would have captured its outer envelope of objects, namely the Oort cloud and the Planet Nine population.”

The “sun’s long-lost companion could now be anywhere in the Milky Way”, Siraj says.


Back in the 1980s, scientists suggested that the Sun had a “Nemesis”, likely a brown dwarf, a dim red dwarf or a white dwarf. Nemesis was believed to be the reason behind periodic mass extinctions that occurred in Earth’s history.

“Every 26 million years or so, some palaeontologists suggest, Nemesis’ motion disturbs asteroids and other space rocks in the cold margins of the solar system, flinging some on a collision course with the Earth. Such an asteroid may have killed all the dinosaurs 65 million years ago”.