Did we lose our Sun's twin star? New astronomic theory suggests Red Star was created with matching pair

Many stars in the galaxy exist in pairs, but our Sun stands out as a notable exception. However, new clues suggest that it might once have had a stellar companion. The high frequency of binary systems being discovered has led astronomers to wonder if all stars, including the Sun, were born with companions. If so, what happened to it?

Our Sun is something of a lone wanderer. Orbiting one of the Milky Way’s spiral arms, it completes a journey around the galaxy every 230 million years. An article by the BBC, reviewing the proposed hypotheses regarding our solar system's centerpiece, notes, that Proxima Centauri is the nearest other star to us. It is 4.2 light-years away—so distant that even the fastest spacecraft would take over 7,000 years to reach it. Yet, binary stars—pairs of stars gravitationally bound to one another—are common in the galaxy. Some have even been observed near the Milky Way’s supermassive black hole, a location where gravitational forces might be expected to pull them apart.

Fortunately, the Sun does not have a companion today. If it did, its gravitational pull might have destabilized the orbits of Earth and other planets, creating extreme conditions inhospitable to life. The closest binary stars to Earth, Alpha Centauri A and B, orbit each other at about 5.8 billion kilometres apart. While earlier hypotheses suggested the Sun might have a faint companion star—nicknamed Nemesis—none has been found despite extensive surveys.

Stars form within massive clouds of gas and dust, known as nebulae, which collapse under gravity. This process creates protostars surrounded by spinning debris that eventually forms planets. In 2017, Sarah Sadavoy, an astrophysicist at Queen’s University in Canada, studied data from the Perseus molecular cloud, a stellar nursery filled with young binary systems. According to the BBC, her team concluded that star formation might naturally favor binary or multi-star systems.“You get little density spikes within those cocoons, and those are able to collapse and form multiple stars, which we call a fragmentation process,” explains Sadavoy. 

Close companions are more likely to remain gravitationally bound, while distant ones may drift apart. Her findings suggest that many, if not all, stars may start as binaries. Some remain together for billions of years, while others part ways early in their evolution—possibly within a million years, a brief period in the lifespan of a star. This raises the intriguing possibility that the Sun once had a companion. “If we did form with a companion, we lost it,” Sadavoy says.

Clues in the Solar System

Evidence of a lost stellar sibling might lie in the Oort Cloud, a vast shell of icy objects encircling the Solar System far beyond Pluto. In 2020, Amir Siraj, an astrophysicist at Harvard University, proposed that a binary companion could have influenced the distribution of objects in this region. A companion might have resulted in a larger number of dwarf planets like Pluto—or even a Neptune-sized planet such as the hypothesized Planet Nine, which some astronomers believe remains undiscovered in the Solar System’s outer reaches.

Another potential clue is the Sun’s tilt. The star is inclined by about seven degrees relative to the plane of the Solar System. Konstantin Batygin, a planetary scientist, told the British publication that this tilt could have been caused by the gravitational influence of a companion star early in the Sun’s history. Similar effects are seen in binary systems across the galaxy, lending credence to this idea.

Difficult Search for long-lost sibiling

Even if the Sun did have a companion, finding it today poses a significant challenge. Over billions of years, any stellar sibling would likely have drifted into the galaxy’s vast star fields. Sadavoy describes it as being “lost among the sea of stars” visible in the night sky. However, stars formed in the same nebula as the Sun would share a similar chemical composition, making them potential "solar siblings." In 2018, scientists identified a star with a composition and size like the Sun, located less than 200 light-years away. But the nebula that birthed the Sun likely produced hundreds or thousands of stars with similar characteristics, making it impossible to confirm whether this star—or any other—was the Sun’s true companion.

Implications for Exoplanets and Life

If the Sun was once part of a binary system, it did not hinder the emergence of life on Earth. This raises intriguing possibilities for exoplanets in other star systems. The article suggests that the presence of a companion star might not preclude planetary stability or habitability, even if the gravitational dynamics are more complex.

As researchers continue to explore the Solar System’s furthest reaches, they may uncover more evidence of a long-lost companion. For now, the idea that the Sun began as a binary star remains an open question, adding a layer of complexity to our understanding of star formation and evolution. A companion, if it existed, would have left behind subtle traces—a signature waiting to be discovered in the vastness of space.

By Nazrin Sadigova