How big is WOH G64?

WOH G64 is a star in the Large Magellanic Cloud, a small galaxy that orbits the Milky Way, and has long been classed as a red supergiant. It is about 160,000 light-years from Earth, where a light-year is the distance light travels in a year, about 9.46 trillion kilometers. A 2009 study estimated that it was about 2.1 billion kilometers across its visible surface, some 1,540 times the width of the Sun. The star has changed since, and as of 2026 astronomers disagree about how big it is now.

Size

An arcsecond is 1/3,600 of a degree. At WOH G64's distance, a star 2.1 billion kilometers across looks only about 0.3 thousandths of an arcsecond wide. That is how wide a human hair, about 0.1 millimeters thick, looks from about 70 kilometers away.

The star's width is worked out from its surface temperature and the total light it gives off. That is hard, because WOH G64 is wrapped in a thick cocoon of dust that hides much of its light. In 2008 a team led by Keiichi Ohnaka modeled the dust and estimated a radius of 1,730 times the Sun's, about 2.4 billion kilometers across.

In 2009 a team led by Emily Levesque measured the star's surface temperature: about 3,400 kelvins, on the scale that starts at absolute zero. That is warmer than the 3,200 kelvins the 2008 team had assumed. They found a radius of 1,540 times the Sun's, uncertain by 5%, so the star was 2.0–2.2 billion kilometers across. Both estimates describe the star as it was before about 2014.

Size comparisons

At the 2009 estimate, WOH G64 is about 1,540 times as wide as the Sun, which is about 1.39 million kilometers (865,000 miles) across.
If it took the Sun's place, its surface would reach about 7.2 astronomical units out, past the orbit of Jupiter and three-quarters of the way to the orbit of Saturn. An astronomical unit is Earth's average distance from the Sun, about 150 million kilometers.
It is about a twelfth wider than VY Canis Majoris, one of the widest red supergiants known in the Milky Way as of 2024.
If the Sun were shrunk to the size of a basketball, WOH G64 would be a ball about 370 meters (1,200 feet) across, longer than three American football fields.

The first close-up of a star in another galaxy

In 2024 astronomers released the first zoomed-in picture of a star in another galaxy. They took it with the Very Large Telescope Interferometer, which combines light from several telescopes. It shows an egg-shaped cocoon of dust close around WOH G64, about 200 astronomical units long. That is more than three times the width of Neptune's orbit.

The team suggested that the cocoon's stretched shape comes from material the star has shed, or from an unseen companion star. They also found that the star had grown dimmer over the previous decade.

A star in transition

A study published in 2026 found that WOH G64 brightened in visible light between mid-2013 and mid-2014. Its surface had warmed by more than 1,000 kelvins. That team concluded it had become a yellow hypergiant, a hotter kind of supergiant, with a companion star.

They put its present radius at about 800 times the Sun's, about half its earlier size and close to that of Betelgeuse. They called that figure indicative rather than definitive.

Two astronomers, Jacco van Loon and Keiichi Ohnaka, disagree. They took spectra of the star, spreading its light out by color, from November 2024 to December 2025. These still show the dark bands of titanium oxide gas, a sign of a red supergiant. They argue that WOH G64 is still a red supergiant with a very extended outer atmosphere, and may never have stopped being one.