What is the largest star in the universe?

About the image. Drawn as a row of stars growing in size, from Sun-like stars to a red supergiant whose edge fills the frame. Sizes are only roughly to scale; the largest stars are far too big to fit in the same picture as the Sun.

The largest stars known are red supergiants and red hypergiants: huge, cool, bloated stars near the end of their lives. The biggest are around 1 500 to 1 800 times wider than the Sun. Put one in the Sun’s place and its surface would reach beyond the orbit of Jupiter.

The leaders

According to the current list of largest stars, the top candidates in our galaxy include Stephenson 2-18 at about 1 840 solar radii, NML Cygni at about 1 590, VX Sagittarii at about 1 460 to 1 560, and VY Canis Majoris at about 1 420. In the Large Magellanic Cloud, WOH G64 measures about 1 540 solar radii.

UY Scuti, often called the largest star, has shrunk in the record books. Earlier estimates put it at about 1 700 solar radii; newer distance measurements bring it down to about 900.

Why the answer keeps changing

Measuring these stars is hard. Most are thousands of light-years away and their sizes are worked out from their brightness and temperature, both of which depend on knowing the distance, which is often uncertain. Their surfaces are not sharp: they fade into thick, dusty winds, so it is not even clear where the star ends. Many also pulse and change size over months or years. Stephenson 2-18 tops the list, but its size depends on the distance to its star cluster, which is uncertain by up to half.

A picture of a giant

In November 2024 a team led by Keiichi Ohnaka used ESO’s Very Large Telescope Interferometer to take the first close-up picture of a star in another galaxy: WOH G64, about 160 000 light-years away. It showed the star inside an egg-shaped cocoon of dust. Some researchers have argued that WOH G64 is now turning into a hotter, smaller yellow hypergiant; others find it is still a red supergiant. The question is open.

How big can a star get?

There appears to be a limit. A red supergiant can only be so cool and so bright and still be stable, and that caps how bloated it can become. One widely cited estimate, by Emily Levesque and colleagues in 2005, puts the limit at around 1 500 solar radii. The largest candidates sit close to it, which is one reason astronomers treat claims of much bigger stars with caution.

Gallery

A row of stars growing in size from a small yellow Sun on the left to a huge, glowing red star on the right, an impression of how the largest stars compare with the Sun. AI-generated painting.

A huge red star seen through a dim reddish haze of dust around it, an impression of one of the largest known stars, the red supergiant WOH G64. AI-generated painting.