UY Scuti: The Largest Known Star in Universe – Size, Facts, and James Webb Insights

Updated on March 10, 2025 | By Jameswebb Discovery Editorial Team 

Imagine a star so colossal it could swallow the orbit of Jupiter whole, dwarfing our Sun like a grain of sand next to a mountain. Meet UY Scuti, widely regarded as the largest known star in the universe. Located 9,500 light-years away in the Scutum constellation, this red supergiant has captured the imagination of astronomers and stargazers alike. But what makes UY Scuti so extraordinary? How big is it really? And could the James Webb Space Telescope unlock new secrets about this stellar giant? On JamesWebbDiscovery.com, we dive deep into the wonders of UY Scuti—its mind-boggling size, fascinating facts, and its place in the cosmos.

What is UY Scuti?

UY Scuti is a red supergiant star, a rare and massive type of star nearing the end of its life cycle. Found in the Scutum constellation near the Milky Way’s bustling galactic center, it’s a celestial titan that pushes the boundaries of what we believe stars can become. Discovered in 1860 by German astronomers at the Bonn Observatory, UY Scuti has since been studied for its extreme properties. Unlike our Sun, a modest main-sequence star, UY Scuti belongs to the hypergiant class—stars so large and luminous they defy easy comprehension.

As a red supergiant, UY Scuti is in its final evolutionary phase. It has exhausted its core hydrogen, ballooning to an enormous size as it fuses heavier elements like helium and carbon. Soon (in cosmic terms), it will collapse under its own gravity and explode as a supernova, potentially leaving behind a black hole or neutron star. This makes UY Scuti not just a marvel of size but a window into the dramatic life cycles of the universe’s most massive stars.

How Big is UY Scuti? Size Comparison

When we ask, "How big is UY Scuti?" the answer staggers the mind. UY Scuti’s radius is estimated at approximately 1,700 times that of the Sun. To put that in perspective, the Sun’s radius is about 432,000 miles (695,000 kilometers). Multiply that by 1,700, and UY Scuti’s radius stretches to roughly 734 million miles (1.18 billion kilometers). Its diameter? A jaw-dropping 1.5 billion miles (2.4 billion kilometers).

If UY Scuti replaced the Sun at the center of our solar system, its outer edge would extend beyond Jupiter’s orbit, engulfing Mercury, Venus, Earth, Mars, and the asteroid belt. Saturn would be perilously close to its surface. To visualize this, imagine the Sun as a basketball; UY Scuti would be a sphere the size of a small stadium.

UY Scuti’s size isn’t just about raw numbers—it’s a testament to the extremes of stellar physics. Its massive volume comes with a caveat: its density is incredibly low, far less than the Sun’s, because red supergiants expand as they age.

UY Scuti Facts You Need to Know

Let’s explore some key facts about UY Scuti that make it one of the most intriguing objects in the cosmos:

1. Discovery: UY Scuti was first cataloged in 1860 by astronomers at Germany’s Bonn Observatory during a sky survey. Its variability—changes in brightness over time—earned it the "UY" designation, marking it as a variable star.

2. Luminosity: Despite its distance, UY Scuti shines 340,000 times brighter than the Sun. However, much of its light is emitted in the infrared spectrum, obscured by interstellar dust, making it faint to the naked eye.

3. Mass: Estimates suggest UY Scuti is 7–10 times the Sun’s mass, though it once may have been 20–40 solar masses before shedding material as it evolved.

4. Pulsations: Like many red supergiants, UY Scuti pulsates, expanding and contracting over months. This variability complicates precise size measurements, leading to debates about its true dimensions.

5. Temperature: Its surface is relatively cool for a star—around 3,365 Kelvin (5,585°F)—compared to the Sun’s 5,778 Kelvin (9,941°F), giving it a reddish hue.

These facts cement UY Scuti’s status as the largest star in the universe, at least among those we’ve measured so far. But its title isn’t uncontested—stars like VY Canis Majoris and WOH G64 challenge its supremacy, though current data favors UY Scuti.

Where is UY Scuti Located?

UY Scuti resides in the Scutum constellation, a small but star-rich region near the Milky Way’s galactic center. Its coordinates are roughly Right Ascension 18h 27m 36.5s and Declination -12° 27' 58.9". At 9,500 light-years from Earth, it’s far too distant to see without a telescope, even for a star of its brilliance.

Scutum, meaning "shield" in Latin, lies between Sagittarius and Aquila, close to the galaxy’s dense core. This location places UY Scuti in a crowded stellar neighborhood, surrounded by dust clouds and other massive stars. Its distance means the light we see today left UY Scuti 9,500 years ago—when human civilizations were just beginning to farm and build.

For amateur astronomers, spotting UY Scuti is a challenge. Its apparent magnitude hovers around 11, well below the naked-eye limit of 6. A powerful telescope and clear, dark skies are essential, though its infrared glow is best studied by observatories like the James Webb Space Telescope.

UY Scuti and the James Webb Space Telescope

The James Webb Space Telescope (JWST), launched in 2021, is revolutionizing our understanding of the universe’s most distant and enigmatic objects—including red supergiants like UY Scuti. While no specific JWST observations of UY Scuti have been publicly detailed as of March 10, 2025, its infrared capabilities make it an ideal tool to study such stars.

Red supergiants emit much of their energy in infrared wavelengths, obscured by dust and gas. JWST’s advanced instruments, like the Near-Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI), can pierce these veils, offering sharper views of UY Scuti’s outer layers, pulsations, and surrounding environment. Could JWST refine UY Scuti’s size estimate, currently uncertain due to its variability and distance? Might it detect chemical signatures in its atmosphere or hints of its impending supernova?

At JamesWebbDiscovery.com, we’re excited about JWST’s potential to unlock UY Scuti’s mysteries. For instance, its observations of similar red supergiants could reveal how these stars shed mass, forming dust clouds that obscure their light. UY Scuti’s faintness despite its luminosity suggests significant dust interference—JWST could map this in unprecedented detail, enhancing our grasp of its true scale and fate.

Even without direct data, tying UY Scuti to JWST strengthens your site’s niche. As the telescope continues its mission, future updates could spotlight UY Scuti, making this article a go-to resource for astronomy enthusiasts.

UY Scuti vs. Other Giant Stars

Is UY Scuti truly the largest star in the universe? Let’s compare it to other contenders:

• VY Canis Majoris: Once considered the biggest, this red hypergiant has a radius of ~1,420 solar radii. Recent studies suggest it may be smaller than UY Scuti, though its size remains debated.

• Betelgeuse: A well-known red supergiant in Orion, Betelgeuse spans ~700–1,000 solar radii. It’s massive but falls short of UY Scuti’s scale.

• WOH G64: Located in the Large Magellanic Cloud, this star’s radius is estimated at ~1,540 solar radii, rivaling UY Scuti but less studied due to its distance.

The "largest star" title hinges on measurement challenges. Red supergiants are notoriously difficult to size accurately—pulsations, irregular shapes, and dust clouds skew results. UY Scuti’s 1,700 solar radii is an average, with some estimates ranging from 1,500 to 2,000. Still, it holds the crown based on current consensus.

Compared to the Sun, all these giants are behemoths. The Sun’s modest size—1 solar radius—pales beside UY Scuti’s sprawling bulk, a reminder of the diversity among stars.

The Future of UY Scuti

UY Scuti’s days are numbered. As a red supergiant, it’s in its final act, fusing heavy elements in its core. Within the next million years—a blink in cosmic time—it will collapse and detonate as a supernova. This explosion will outshine entire galaxies briefly, scattering elements like carbon, oxygen, and iron into space—raw materials for future stars and planets.

Post-supernova, UY Scuti’s fate depends on its mass. At 7–10 solar masses today, it’s likely below the threshold for a black hole (typically 20+ solar masses at birth). Instead, it may form a neutron star, a dense remnant just 12–19 miles (20–30 kilometers) wide. If its original mass was higher, a black hole remains possible.

Studying UY Scuti offers clues to these explosive endings. Its pulsations and mass loss hint at the processes driving supernovae, a field where JWST’s infrared gaze could shine. For now, UY Scuti stands as a cosmic titan, its future as dramatic as its present.

Conclusion

UY Scuti, the largest known star in the universe, is a testament to the grandeur of the cosmos. Its radius—1,700 times the Sun’s—stretches imagination, while its red supergiant nature promises a spectacular end. From its discovery in 1860 to its potential scrutiny by the James Webb Space Telescope, UY Scuti captivates us with its size, mystery, and scientific value. At JamesWebbDiscovery.com, we’re thrilled to explore such wonders, connecting the dots between cutting-edge astronomy and the universe’s most awe-inspiring objects. Want to learn more about stellar giants or JWST’s discoveries? Dive into our other articles and join the cosmic journey!