Astronomers observe companion star orbiting stellar giant Betelgeuse

By Will Dunham

WASHINGTON, July 29 (Reuters) - Betelgeuse is a superstar among the stars — one of the brightest in the night sky, a massive red supergiant in the constellation Orion that sometimes brightens and dims, and adds to its allure with ‌the fact that it may be on the brink of exploding.

It has been observed for millennia, but astronomers have now ‌nailed down a crucial detail about this star: Betelgeuse is not alone. Researchers using the European Southern Observatory's Chile-based Very Large Telescope have directly imaged a star that orbits ​with Betelgeuse — pronounced "beetle juice" — in what is called a binary system.

Betelgeuse's mass is about 16.5 to 19 times greater than our sun's, and its physical size is 750 to 850 times larger than the sun. Its newly identified companion is big in its own right, 2.6 to 3.1 times more massive than the sun, with a diameter 1.8 to two times greater. Betelgeuse shines about 100,000 times brighter than the sun. Its companion's luminosity is ‌up to 92 times that of the sun.

The ⁠two stars are located around 500 to 600 light-years from Earth. A light-year is the distance light travels in a year, 5.9 trillion miles (9.5 trillion km).

Scientists have suspected for a century that Betelgeuse may have a companion, ⁠and some studies in recent years have provided strong evidence. The new research represented the first unambiguous detection, according to astronomer Miguel Montargès of the Laboratory of Instrumentation and Research in Astrophysics, or LIRA, at the Paris Observatory, lead author of the study published in the journal Astronomy & Astrophysics.

"Betelgeuse has been ​observed throughout ​history. It is even depicted in prehistoric paintings. Still, we discover one of ​its fundamental characteristics only now: it has a companion, ‌and we obtained a direct image of this," Montargès said.

Betelgeuse and its companion are gravitationally bound and orbit each other at a distance roughly equivalent to Saturn's orbital span from the sun, or about 8.8 times greater than Earth's distance from the sun.

Massive stars like Betelgeuse typically reside in binary systems or systems with even more other stars.

"According to various models, massive stars should never form as a single," Montargès said.

Previous research indicated that Betelgeuse's variable luminosity was driven by a hot and dense cloud of material that the star expelled into space that cooled ‌to form dust and sometimes obstructs the starlight.

The largest stars in the cosmos live ​relatively short lives, rapidly burning through their material. Betelgeuse is roughly 10 million years ​old, far younger than the sun, which is about 4.5 ​billion years into an estimated 10 billion year lifespan. Betelgeuse is believed to be in the final stages ‌of its life, having expanded immensely as a prelude to ​a supernova explosion.

Betelgeuse is so colossal ​that if it were in the sun's place in our solar system, its surface would reach past the orbit of Jupiter.

"When it was considered a single star, it was believed that it would explode between 10,000 and 100,000 years from now. Now that ​we know that it has a companion that ‌could be interacting with it, I must say that I don't know when it will explode," Montargès said.

"If the two ​stars have interacted or will interact, it could delay or accelerate the supernova. We cannot be sure of anything anymore ​regarding this star," Montargès said.

(Reporting by Will Dunham, Editing by Rosalba O'Brien)