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Astronomy

7 Biggest Stars in the Universe

A star-forming region in the Large Magellanic Cloud
A star-forming region in the Large Magellanic Cloud. A star is type of astronomical object consisting of a luminous spheroid of plasma held together by its own gravity. The Large Magellanic Cloud (LMC) is a satellite galaxy of the Milky Way. At a distance of about 50 kiloparsecs (~163,000 light-years), the LMC is the second or third-closest galaxy to the Milky Way, after the Sagittarius Dwarf Spheroidal (~16 kpc) and the possible dwarf irregular galaxy known as the Canis Major Overdensity. Image: Wikipedia. The image is from the European Space Agency. It is listed as the LH 95 star forming region of the Large Magellanic Cloud. The image was taken using the Hubble Space Telescope (ESA/Hubble).

What is the biggest star in the Universe? In fact, it is really hard to give an exact answer to this question since the universe is big, neighboring and the other galaxies are billions of light-years away from us. But, we can give it a try. Here are the top 7 biggest stars in the universe currently known by radius.

Since the Sun is the best-known star for us, solar radius and solar mass are two useful units of measurement to depict how big is a star. A solar radius is approximately 690,000 km (432,000 miles) and 1 solar mass is 2 x 1030 kilograms (4.3 x 1030 pounds).

Please keep in mind that the list below can change at any time with new findings and discoveries.

Biggest stars in the Universe (as far as we know so far)

7. VY Canis Majoris: 1,420 ± 120 Solar Radii

One of the largest known stars, and also one of the most luminous and massive red supergiants (or red hypergiants), VY Canis Majoris has a radius of 1,420 ± 120 solar radii. This red hypergiant star was previously estimated to be 1,800 to 2,200 solar radii, making it even larger than the orbit of Saturn (which is between 1,940-2,169 solar radii), but that size put it outside the bounds of stellar evolutionary theory. New measurements brought it down to size.

But, still, if placed at the center of the Solar System, this red hypergiant’s surface would extend beyond the orbit of Jupiter, which is between 1,064 and 1,173 solar radii. It is big, really big: you can see how far away is Jupiter from the Sun using a scaled model of our solar system.

It is located 1.2 kiloparsecs (3,900 light-years) away from Earth in the constellation of Canis Major. Some sources still list VY Canis Majoris as the largest star in the Universe.

Biggest Stars in the Universe: VY Canis Majoris
Biggest Stars in the Universe: Hubble Space Telescope image showing the asymmetric nebula surrounding VY Canis Majoris, which is the central star. Taken on November 6, 2013. Image source: Wikipedia via Flickr, by the user Judy Schmidt

6. HD 143183: 1,480-1,830 Solar Radii

HD 143183 is a red supergiant or hypergiant star in the constellation Norma, at a distance of over 2 kiloparsecs (over 6,523 light-years). It is one of the most luminous red supergiants and its calculated radius is between 1,480 and 1,830 solar radii.

Biggest Stars in the Universe: HD 143183
Biggest Stars in the Universe: HD 143183 (the brightest star in the image) as seen from the Rutherfurd Observatory, the astronomical facility maintained by Columbia University named after Lewis Morris Rutherfurd (November 25, 1816 – May 30, 1892), the American lawyer and astronomer, and a pioneering astrophotographer. HD 143183 is a red supergiant or hypergiant star in the constellation Norma, at a distance of over 2 kiloparsecs (over 6,523 light-years). It is one of the most luminous red supergiants and its calculated radius is between 1,480 and 1,830 solar radii.

5. Westerlund 1-26: 1,530-1,580 Solar Radii

With a radius between 1,530-2,550 solar radii, Westerlund 1-26 is one of the largest stars discovered so far. This red supergiant or hypergiant is located on the outskirts of the Westerlund 1 super star cluster, a compact young super star cluster in the Milky Way galaxy, about 3.5-5 kiloparsecs (11,415-16,300 light-years) away from Earth. Westerlund 1-26 is located about 11,500 light-years from our planet.

Biggest stars in the Universe: Westerlund-1-26
Biggest Stars in the Universe: NASA’s Hubble Space Telescope reveals the supercluster Westerlund 1, home to one of the largest stars ever discovered, originally named Westerlund 1-26. It is a red supergiant (although sometimes classified as a hypergiant) with a radius over 1500 times that of our Sun. Image: ESA/Hubble.
Most of Westerlund 1’s stars are thought to have formed in the same burst of activity, meaning that they have similar ages and compositions. The cluster is relatively young in astronomical terms – at around three million years old it is a baby compared to our own Sun, which is some 4.6 billion years old.

4. RW Cephei: 1,535 Solar Radii

Estimated at 1,535 solar radii, RW Cephei is an orange hypergiant star in the constellation Cepheus. It is about 4 kiloparsecs (14,000 light-years) away from Earth.

Biggest stars in the Universe: RW Cephei
Biggest Stars in the Universe: RW Cephei is the bright star at the left bottom. Photo: Sloan Digital Sky Survey

3. WOH G64: 1,540-1,730 Solar Radii

163,000 light-years away from Earth and one of the largest known stars, with a radius of 1,540 to 1,730 solar radii, WOH G64 is a red hypergiant star in the Large Magellanic Cloud, a satellite galaxy of our Milky Way. Some estimate it is even bigger: in 2004, Monnier et al. calculated that the star has a radius of around 3,000 radii.

Biggest Stars in the Universe: WOH G64 location
Biggest Stars in the Universe: Location of WOH G64 (circled) in the Large Magellanic Cloud, a satellite galaxy of our Milky Way. Image: NASA’s Spitzer Space Telescope

2. UY Scuti: 1,708 ± 192 Solar Radii

With a radius of 1,708 ± 192 Solar Radii, UY Scuti is probably the biggest known star. It was first cataloged in 1860, by German astronomers at the Bonn Observatory.

In the summer of 2012, astronomers using AMBER interferometry from the Very Large Telescope (VLT) in the Atacama Desert in Chile measured the parameters of three red supergiants near the Galactic Center region: UY Scuti, AH Scorpii, and KW Sagittarii. They determined that all three stars are over 1,000 times bigger than the Sun and over 100,000 times more luminous than the Sun. UY Scuti was found to be the largest and the most luminous of the three stars measured, at 1,708 ± 192 R☉ (Solar radii).

Biggest Stars in the Universe: UY Scuti, the biggest known star in the Universe
Biggest Stars in the Universe: Dense starfield around the red supergiant star UY Scuti as seen from the Rutherfurd Observatory at Columbia University in New York, United States. UY Scuti is the brightest star in the image. The picture was captured in 2011. UY Scuti is one of the largest known stars by radius (and perhaps the largest). Image: Wikipedia, by the user Haktarfone
Biggest star in the Universe: UY Scuti vs Sun size comparison
UY Scuti vs Sun size comparison. The Sun is only 1 pixel in diameter in this image. UY Scuti is the biggest known star in the Universe.
Biggest star in the Universe: UY Scuti vs Sun size comparison
Biggest Stars in the Universe: UY Scuti vs Sun size comparison.

1. Stephenson 2-18 (2,150) Solar Radii, the biggest known star in the Universe

The red hypergiant Stephenson 2-18, also known as Stephenson 2 DFK 1 or RSGC2-18 is the largest known star in the Universe. It is so big that around 10 billion Suns could fit inside it.

Stephenson 2-18 is located 20,000 light-years from Earth in the Scutum-Centaurus Arm of the Milky Way galaxy.

What is the most massive star?

UY Scuti’s large radius doesn’t make it the most massive star – that title goes to R136a1. It lies at a distance of about 50 kiloparsecs (163,000 light-years) in the Large Magellanic Cloud. It has the highest mass and luminosity of any known star, at 315 M☉ (solar mass) and 8.7 million L☉ (solar luminosity), and is also one of the hottest at around 53,000 K. It is much larger than our Sun, but with a radius of between 28.8-35.4 solar radii, it is much smaller than the stars in this list.

UY Scuti has around 10 solar masses.

R136a1 - an artist's impression - the most massive star ever known
Artist’s impression of R136a1, the most massive star ever known. Image: Wikipedia, created by Sephirohq.

Sources

M. Özgür Nevres
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Özgür Nevres

By M. Özgür Nevres

I am a software developer and a science enthusiast. I was graduated from the Istanbul Technical University (ITU), Computer Engineering. In the past, I worked at the Istanbul Technical University Science Center as a science instructor. I write about the planet Earth and science on this website, ourplnt.com. I am also an animal lover! I take care of stray cats & dogs. This website's all income goes directly to our furry friends. Please consider supporting me on Patreon, so I can help more animals!

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