UY Scuti is the largest star in the observable Universe with a mass coming in at around 1,700 times larger than the mass of the sun. UY Scuti is a specific type of star known as a hypergiant which are usually short lived and extremely rare because of the fact that they lose a large portion of their mass extremely quickly due to stellar winds.To give some perspective, UY Scuti is around 6.5 Quadrillion times larger than Earth, 738.4 million miles in radius, and is 9,500 light years away from our solar system.It really makes you think as to how something so large can exist in our universe.

What is the Largest Star in our Universe?

<figcaption itemprop="caption description" dir="ltr">
The radius of UY Scuti is about 1,700 times larger than the sun's radius.
(Image credit: Philip Park)
</figcaption>The sun may appear to be the largest star in the sky but that's just because it's the closest. On a stellar scale, it's really quite average — about half of the known stars are larger; half are smaller. The largest known star in the universe is UY Scuti, a hypergiant with a radius around 1,700 times larger than the sun. And it's not alone in dwarfing Earth's dominant star.&nbsp;&nbsp;<h2>The largest of all</h2>In 1860, German astronomers at the Bonn Observatory first cataloged UY Scuti, naming it BD -12 5055. During a second detection, the astronomers realized it grows brighter and dimmer over a 740-day period, leading astronomers to classify it as a variable star. The star lies near the center of the Milky Way, roughly 9,500 light-years away.Located in the constellation Scutum, UY Scuti is a hypergiant, the classification that comes after supergiant, which itself comes after giant. Hypergiants are rare stars that shine very brightly. They lose much of their mass through fast-moving stellar winds.Of course, all stellar sizes are estimates, based on measurements taken from far away.<div>RECOMMENDED VIDEOS FOR YOU...</div>"The complication with stars is that they have diffuse edges," <a href="https://theconversation.com/how-big-is-the-biggest-star-we-have-ever-found-37304" data-url="https://theconversation.com/how-big-is-the-biggest-star-we-have-ever-found-37304" data-component-tracked="1" dir="ltr">wrote astronomer Jillian Scudder</a> of the University of Sussex. "Most stars don't have a rigid surface where the gas ends and vacuum begins, which would have served as a harsh dividing line and easy marker of the end of the star."Instead, astronomers rely on a star's <a href="https://www.space.com/17160-sun-atmosphere.html" data-url="/17160-sun-atmosphere.html" data-component-tracked="1" dir="ltr">photosphere</a>, where the star becomes transparent to light and the particles of light, or photons, can escape the star."As far as an astrophysicist is concerned, this is the surface of the star, as this is the point at which photons can leave the star," Scudder said.If UY Scuti replaced the sun in the center of the solar system, its photosphere would extend just beyond the orbit of Jupiter. The nebula of gas stripped from the star extends even farther out, beyond the orbit of Pluto to 400 times time the Earth-sun distance.But UY Scuti doesn't remain stagnant. Scudder pointed out that the star <a href="https://www.space.com/15396-variable-stars.html" data-url="/15396-variable-stars.html" data-component-tracked="1" dir="ltr">varies in brightness</a> as it varies in radius, with a margin of error of about 192 solar radii. These errors could allow other stars to beat out UY Scuti in the race for size. In fact, there are as many as 30 stars whose radii fit within UY Scuti's smallest estimated size, so it shouldn't sit too securely on its throne.Nor does UY Scuti's large radius make it the most massive star. That honor goes to R136a1, which weighs in at about 300 times the mass of the sun but only about 30 solar radii. UY Scuti, in comparison, is only about 30 times more massive than the sun.<figure><picture><source type="image/webp" alt="NASA's Hubble Space Telescope reveals the supercluster Westerlund 1, home of one of the largest known stars. Westerlund 1-26, a red supergiant, has a radius more than 1,500 times that of the sun." class="pull- expandable lazy-image-van optional-image" onerror="if(this.src &amp;&amp; this.src.indexOf('missing-image.svg') !== -1){return true;};this.parentNode.replaceChild(window.missingImage(),this)" sizes="(min-width: 1000px) 970px, calc(100vw - 40px)" data-normal="https://vanilla.futurecdn.net/space/media/img/missing-image.svg" data-srcset="https://cdn.mos.cms.futurecdn.net/wCbcoHCxRpdYXTRQUb5sDi-320-80.jpg.webp 320w, https://cdn.mos.cms.futurecdn.net/wCbcoHCxRpdYXTRQUb5sDi-650-80.jpg.webp 650w, https://cdn.mos.cms.futurecdn.net/wCbcoHCxRpdYXTRQUb5sDi-970-80.jpg.webp 970w" data-original-mos="https://cdn.mos.cms.futurecdn.net/wCbcoHCxRpdYXTRQUb5sDi.jpg" data-pin-media="https://cdn.mos.cms.futurecdn.net/wCbcoHCxRpdYXTRQUb5sDi.jpg" srcset="https://cdn.mos.cms.futurecdn.net/wCbcoHCxRpdYXTRQUb5sDi-320-80.jpg.webp 320w, https://cdn.mos.cms.futurecdn.net/wCbcoHCxRpdYXTRQUb5sDi-650-80.jpg.webp 650w, https://cdn.mos.cms.futurecdn.net/wCbcoHCxRpdYXTRQUb5sDi-970-80.jpg.webp 970w"><source type="image/jpeg" alt="NASA's Hubble Space Telescope reveals the supercluster Westerlund 1, home of one of the largest known stars. Westerlund 1-26, a red supergiant, has a radius more than 1,500 times that of the sun." class="pull- expandable lazy-image-van optional-image" onerror="if(this.src &amp;&amp; this.src.indexOf('missing-image.svg') !== -1){return true;};this.parentNode.replaceChild(window.missingImage(),this)" sizes="(min-width: 1000px) 970px, calc(100vw - 40px)" data-normal="https://vanilla.futurecdn.net/space/media/img/missing-image.svg" data-srcset="https://cdn.mos.cms.futurecdn.net/wCbcoHCxRpdYXTRQUb5sDi-320-80.jpg 320w, https://cdn.mos.cms.futurecdn.net/wCbcoHCxRpdYXTRQUb5sDi-650-80.jpg 650w, https://cdn.mos.cms.futurecdn.net/wCbcoHCxRpdYXTRQUb5sDi-970-80.jpg 970w" data-original-mos="https://cdn.mos.cms.futurecdn.net/wCbcoHCxRpdYXTRQUb5sDi.jpg" data-pin-media="https://cdn.mos.cms.futurecdn.net/wCbcoHCxRpdYXTRQUb5sDi.jpg" srcset="https://cdn.mos.cms.futurecdn.net/wCbcoHCxRpdYXTRQUb5sDi-320-80.jpg 320w, https://cdn.mos.cms.futurecdn.net/wCbcoHCxRpdYXTRQUb5sDi-650-80.jpg 650w, https://cdn.mos.cms.futurecdn.net/wCbcoHCxRpdYXTRQUb5sDi-970-80.jpg 970w"><figure class="expandable-image"><img src="https://vanilla.futurecdn.net/space/media/img/missing-image.svg" alt="NASA's Hubble Space Telescope reveals the supercluster Westerlund 1, home of one of the largest known stars. Westerlund 1-26, a red supergiant, has a radius more than 1,500 times that of the sun." srcset="https://cdn.mos.cms.futurecdn.net/wCbcoHCxRpdYXTRQUb5sDi-320-80.jpg 320w, https://cdn.mos.cms.futurecdn.net/wCbcoHCxRpdYXTRQUb5sDi-650-80.jpg 650w, https://cdn.mos.cms.futurecdn.net/wCbcoHCxRpdYXTRQUb5sDi-970-80.jpg 970w" width="745" height="419"><div class="expand icon icon-expand-image"></div></figure></picture><figcaption dir="auto">NASA's Hubble Space Telescope reveals the supercluster Westerlund 1, home of one of the largest known stars. Westerlund 1-26, a red supergiant, has a radius more than 1,500 times that of the sun. (Image credit: ESA/Hubble &amp; NASA)</figcaption></figure><h2>Title contenders</h2>So which star would take UY Scuti's place if it weren't exactly 1,708 solar radii? Here are a few of the stars that might dominate:<UL><LI>WOH G64, measuring 1,504 to 1,730 solar radii. It is a red hypergiant star in the Large Magellanic Cloud (a satellite galaxy to the Milky Way). Like UY Scuti, it varies in brightness. Some estimates have placed its radius as high as <a href="http://iopscience.iop.org/article/10.1086/382218/meta" data-url="http://iopscience.iop.org/article/10.1086/382218/meta" data-component-tracked="1" dir="ltr">3,000 solar radii.</a> Variations are due in part to the presence of dust, which affects the brightness of the star and its related radius.</LI><LI>RW Cephei, at 1,535 solar radii. This star is an orange hypergiant in the constellation of Cepheus, and also a variable star.</LI><LI>Westerlund 1-26, which comes in at 1,530 to 2,550 solar radii. If the upper estimate is correct, its photosphere would engulf the orbit of Saturn if the star were placed at the center of the solar system. The star changes its temperature but not its brightness.</LI><LI>KY Cygni, at 1,420 to 2,850 solar radii. It's a red supergiant in the constellation Cygnus. The upper estimate is considered by astronomers to be dubious due to an observational error, while the lower estimate is consistent with other stars from the same survey, as well as theoretical models of stellar evolution.</LI><LI>VY Canis Majoris, ranging from 1,300 to 1,540 solar radii. This red hypergiant star was previously estimated to be 1,800 to 2,200 solar radii, but that size put it outside the bounds of stellar evolutionary theory. New measurements brought it down to size. (Some sources still list it as the largest star.)</LI></UL>Follow Nola Taylor Redd at <a href="https://twitter.com/nolatredd" data-url="https://twitter.com/nolatredd" data-component-tracked="1" dir="ltr">@NolaTRedd</a>, <a href="https://www.facebook.com/astrowriter/" data-url="https://www.facebook.com/astrowriter/" data-component-tracked="1" dir="ltr">Facebook</a> or <a href="https://plus.google.com/112799861620975032900" data-url="https://plus.google.com/112799861620975032900" data-component-tracked="1" dir="ltr">Google+</a>. Follow us at <a href="https://twitter.com/spacedotcom" data-url="https://twitter.com/spacedotcom" data-component-tracked="1" dir="ltr">@Spacedotcom</a>, <a href="http://www.facebook.com/spacecom" data-url="http://www.facebook.com/spacecom" data-component-tracked="1" dir="ltr">Facebook</a> or <a href="https://plus.google.com/+SPACEcom/" data-url="https://plus.google.com/+SPACEcom/" data-component-tracked="1" dir="ltr">Google+</a>.<a href="https://forums.space.com/" dir="ltr">Join our Space Forums</a> to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: <a href="mailto:community@space.com" dir="ltr">community@space.com.</a><picture><source type="image/webp" alt="Nola Taylor Redd" class="lazy-image-van optional-image manual-image-sizes" onerror="if(this.src &amp;&amp; this.src.indexOf('missing-image.svg') !== -1){return true;};this.parentNode.replaceChild(window.missingImage(),this)" sizes="100px" data-normal="https://vanilla.futurecdn.net/space/media/img/missing-image.svg" data-srcset="https://cdn.mos.cms.futurecdn.net/vsJ4bwDNLZekj5W2X6a6Xm-300-80.jpg.webp 300w" data-original-mos="https://cdn.mos.cms.futurecdn.net/vsJ4bwDNLZekj5W2X6a6Xm.jpg" data-pin-media="https://cdn.mos.cms.futurecdn.net/vsJ4bwDNLZekj5W2X6a6Xm.jpg" data-pin-nopin="true" srcset="https://cdn.mos.cms.futurecdn.net/vsJ4bwDNLZekj5W2X6a6Xm-300-80.jpg.webp 300w"><source type="image/jpeg" alt="Nola Taylor Redd" class="lazy-image-van optional-image manual-image-sizes" onerror="if(this.src &amp;&amp; this.src.indexOf('missing-image.svg') !== -1){return true;};this.parentNode.replaceChild(window.missingImage(),this)" sizes="100px" data-normal="https://vanilla.futurecdn.net/space/media/img/missing-image.svg" data-srcset="https://cdn.mos.cms.futurecdn.net/vsJ4bwDNLZekj5W2X6a6Xm-300-80.jpg 300w" data-original-mos="https://cdn.mos.cms.futurecdn.net/vsJ4bwDNLZekj5W2X6a6Xm.jpg" data-pin-media="https://cdn.mos.cms.futurecdn.net/vsJ4bwDNLZekj5W2X6a6Xm.jpg" data-pin-nopin="true" srcset="https://cdn.mos.cms.futurecdn.net/vsJ4bwDNLZekj5W2X6a6Xm-300-80.jpg 300w"><img src="https://vanilla.futurecdn.net/space/media/img/missing-image.svg" alt="Nola Taylor Redd" srcset="https://cdn.mos.cms.futurecdn.net/vsJ4bwDNLZekj5W2X6a6Xm-300-80.jpg 300w" width="100" height="100"></picture><div>Nola Taylor Redd is a contributing writer for Space.com. She loves all things space and astronomy-related, and enjoys the opportunity to learn more. She has a Bachelor’s degree in English and Astrophysics from Agnes Scott college and served as an intern at Sky &amp; Telescope magazine. In her free time, she homeschools her four children. Follow her on Twitter at @NolaTRedd</div>

The largest known star in the universe is UY Scuti, a hypergiant with a radius around 1,700 times larger than the sun.

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The sun may appear to be the largest star in the sky but that's just because it's the closest. On a stellar scale, it's really quite average — about half of the known stars are larger; half are smaller. The largest known star in the universe is UY Scuti, a hypergiant with a radius around 1,700 times larger than the sun. And it's not alone in dwarfing Earth's dominant star.

In 1860, German astronomers at the Bonn Observatory first cataloged UY Scuti, naming it BD -12 5055. During a second detection, the astronomers realized it grows brighter and dimmer over a 740-day period, leading astronomers to classify it as a variable star. The star lies near the center of the Milky Way, roughly 9,500 light-years away.

Located in the constellation Scutum, UY Scuti is a hypergiant, the classification that comes after supergiant, which itself comes after giant. Hypergiants are rare stars that shine very brightly. They lose much of their mass through fast-moving stellar winds.

Of course, all stellar sizes are estimates, based on measurements taken from far away.

"The complication with stars is that they have diffuse edges," <a href="https://theconversation.com/how-big-is-the-biggest-star-we-have-ever-found-37304">wrote astronomer Jillian Scudder </a>of the University of Sussex. "Most stars don't have a rigid surface where the gas ends and vacuum begins, which would have served as a harsh dividing line and easy marker of the end of the star."

Instead, astronomers rely on a star's <a href="https://www.space.com/17160-sun-atmosphere.html">photosphere </a>, where the star becomes transparent to light and the particles of light, or photons, can escape the star.

"As far as an astrophysicist is concerned, this is the surface of the star, as this is the point at which photons can leave the star," Scudder said.

If UY Scuti replaced the sun in the center of the solar system, its photosphere would extend just beyond the orbit of Jupiter. The nebula of gas stripped from the star extends even farther out, beyond the orbit of Pluto to 400 times time the Earth-sun distance.

But UY Scuti doesn't remain stagnant. Scudder pointed out that the star <a href="https://www.space.com/15396-variable-stars.html">varies in brightness </a>as it varies in radius, with a margin of error of about 192 solar radii. These errors could allow other stars to beat out UY Scuti in the race for size. In fact, there are as many as 30 stars whose radii fit within UY Scuti's smallest estimated size, so it shouldn't sit too securely on its throne.

Nor does UY Scuti's large radius make it the most massive star. That honor goes to R136a1, which weighs in at about 300 times the mass of the sun but only about 30 solar radii. UY Scuti, in comparison, is only about 30 times more massive than the sun.

So which star would take UY Scuti's place if it weren't exactly 1,708 solar radii? Here are a few of the stars that might dominate:

<ul><li>WOH G64, measuring 1,504 to 1,730 solar radii. It is a red hypergiant star in the Large Magellanic Cloud (a satellite galaxy to the Milky Way). Like UY Scuti, it varies in brightness. Some estimates have placed its radius as high as <a href="http://iopscience.iop.org/article/10.1086/382218/meta">3,000 solar radii. </a>Variations are due in part to the presence of dust, which affects the brightness of the star and its related radius. </li><li>RW Cephei, at 1,535 solar radii. This star is an orange hypergiant in the constellation of Cepheus, and also a variable star. </li><li>Westerlund 1-26, which comes in at 1,530 to 2,550 solar radii. If the upper estimate is correct, its photosphere would engulf the orbit of Saturn if the star were placed at the center of the solar system. The star changes its temperature but not its brightness. </li><li>KY Cygni, at 1,420 to 2,850 solar radii. It's a red supergiant in the constellation Cygnus. The upper estimate is considered by astronomers to be dubious due to an observational error, while the lower estimate is consistent with other stars from the same survey, as well as theoretical models of stellar evolution. </li><li>VY Canis Majoris, ranging from 1,300 to 1,540 solar radii. This red hypergiant star was previously estimated to be 1,800 to 2,200 solar radii, but that size put it outside the bounds of stellar evolutionary theory. New measurements brought it down to size. (Some sources still list it as the largest star.) </li> </ul>

Follow Nola Taylor Redd at <a href="https://twitter.com/nolatredd">@NolaTRedd </a>, <a href="https://www.facebook.com/astrowriter/">Facebook </a>or <a href="https://plus.google.com/112799861620975032900">Google+ </a>. Follow us at <a href="https://twitter.com/spacedotcom">@Spacedotcom </a>, <a href="http://www.facebook.com/spacecom">Facebook </a>or <a href="https://plus.google.com/+SPACEcom/">Google+ </a>.

<a href="https://forums.space.com/">Join our Space Forums </a>to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: <a href="mailto:community@space.com">community@space.com. </a>

What Is the Biggest Star?

What is the Largest Star in our Universe?

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