The Biggest Star in the Universe
The biggest star in the universe is UY Scuti, a red supergiant star that is estimated to be over 1,700 times larger than our Sun. It is located in the constellation Scutum and has a diameter of approximately 2.4 billion kilometers.
UY Scuti’s size is due to its massive core, rapid expansion, and short lifespan. By studying stars like UY Scuti, astronomers can learn about the properties and behavior of these massive objects and gain a better understanding of the universe as a whole.
A zoomed-in picture of the luminous red supergiant star UY Scuti. (DSS2 survey, Wikipedia Commons).
The Biggest Star in the Universe
As an astrophotographer, I’ve always been fascinated by the sheer size and complexity of the universe. And when it comes to size, there’s nothing quite like UY Scuti, the biggest star that we know of. UY Scuti is a red supergiant star located in the constellation Scutum and is estimated to be over 1,700 times larger than our Sun.
In this article, we’ll take a closer look at UY Scuti, exploring what makes it so massive, how astronomers study stars like it, and what its existence can teach us about the universe as a whole.
One of the most remarkable things about UY Scuti is its sheer size. With a diameter of approximately 2.4 billion kilometers, UY Scuti is so large that it’s difficult to even comprehend.
To put it in perspective, if UY Scuti were placed at the centre of our Solar System, its outer layers might extend nearly to the orbit of Jupiter, based on the higher radius estimate. However, given newer measurements, the extent may be somewhat less. The key point is its sheer scale, dwarfing the Sun.
In the amazing illustration below, you can see just how massive UY Scuti is. Arcturus is a very large star compared to our Sun, and UY Scuti absolutely dwarfs this giant star by comparison. Sirius and our Sun are nowhere near as large!
Comparison of UY Scuti to other stars (Sun, Sirius, Pollux, Arcturus) by S. Clester (Astronomy Trek).
So how do astronomers study stars like UY Scuti, which are located millions of light-years away? One of the most important tools we have is spectroscopy, the analysis of the light emitted by a star. By studying the spectrum of light that a star emits, astronomers can learn a great deal about its chemical composition, temperature, and other properties.
Another key tool for studying stars like UY Scuti is computer modeling. Using complex simulations, astronomers can model the life cycles of stars and predict their behavior. By comparing these predictions to observations of real stars, we can refine our models and gain a better understanding of how these massive objects form and evolve.
Despite our best efforts, there’s still much we don’t know about UY Scuti and the universe as a whole. However, by continuing to study and explore the cosmos, we’re sure to make new and exciting discoveries in the years to come. In the next section, we’ll take a closer look at what makes UY Scuti so massive and how it compares to other stars in the universe.
Size comparison between UY Scuti and our Sun. Philip Park (Wikipedia Commons).
The Largest Stars in the Known Universe: A Comparison
Here is a table showing the largest stars in the universe, their average size (in Solar Radius), and what type of star they are:
| Star Name | Type | Approx. Radius (× Sun) | Constellation | Distance (light-years) |
|---|---|---|---|---|
| UY Scuti | Red Supergiant | ~900 – 1,700 R☉ | Scutum | ≈ 5,900 |
| Stephenson 2-18 | Red Hypergiant | ~1,500 – 2,150 R☉ | Scutum | ≈ 19,500 |
| VY Canis Majoris | Red Hypergiant | ~1,400 R☉ | Canis Major | ≈ 3,900 |
| NML Cygni | Red Hypergiant | ~1,650 R☉ | Cygnus | ≈ 5,250 |
| WOH G64 | Red Supergiant | ~1,500 R☉ | Doradus (LMC) | ≈ 163,000 |
Note: Stellar radii are approximate and subject to revision as new distance and luminosity data become available.
These stars are all truly massive, with sizes that are difficult to comprehend. Red supergiants and red hypergiants are the largest types of stars that we know of, and they can have diameters that are thousands of times larger than that of our Sun.
UY Scuti is currently believed to be the largest star we know of, but new discoveries are constantly being made in astronomy, and there may even be larger stars waiting to be discovered.
Related Article: 13 Amazing Facts about Space
Mass vs. Size: What’s the Difference?
When people ask “What’s the biggest star?”, they usually mean largest by radius (how physically wide the star is). Astronomers, however, also talk about the most massive stars (how much matter they contain). These are not the same thing, and the record-holders are often different objects.
Largest by size (radius):
Red supergiants and hypergiants (like UY Scuti, VY Canis Majoris, or Stephenson 2-18) can swell to hundreds or even over a thousand times the Sun’s radius. Their outer layers are very diffuse and cool (low surface temperatures), which allows the star to puff up to an enormous volume while remaining relatively “fluffy.”
Most massive:
The heaviest stars (often hot, blue O-type or Wolf-Rayet stars) pack tens to well over a hundred times the Sun’s mass into a much tighter radius than red supergiants.
A classic example is R136a1 in the Tarantula Nebula. It’s extraordinarily massive and luminous, but not physically as “wide” as the largest red supergiants. These stars burn through fuel at extreme rates and have intense stellar winds that can strip their outer layers.
The R136 super star cluster, near the center of the Tarantula Nebula (NGC 2070). Hubble Space Telescope.
Why the confusion happens
- Temperature vs. volume: Cooler surfaces in red supergiants allow a giant, extended atmosphere; hotter massive stars are more compact.
- Density: Giant radius does not mean high density—red supergiants have very low-density envelopes.
- Different extremes: “Largest” highlights radius; “most massive” highlights mass. A star can be a radius champion without being anywhere near the mass champion.
- Evolving targets: As stars age, especially massive ones, they can expand dramatically—so the same star may be compact and ultra-massive early on, then become enormous in radius later.
Red supergiants can look huge but relatively low-density, while ultra-massive blue stars may be smaller in radius yet far heavier and more energetic.
What Makes UY Scuti So Big?
- Massive Core: UY Scuti has an extremely dense core that generates enormous amounts of energy through nuclear fusion.
- Rapid Expansion: The energy released by the core causes the outer layers of the star to expand rapidly, creating its massive size.
- Short Lifespan: While UY Scuti is incredibly large, it won’t live for very long due to its high rate of energy consumption.
How Do We Study Stars Like UY Scuti?
- Spectroscopy: By analyzing the light emitted by a star, we can learn about its chemical composition, temperature, and other properties.
- Stellar Evolution Models: Using computer models, scientists can simulate the life cycles of stars like UY Scuti and make predictions about their behavior.
- Telescopes: Ground-based and space-based telescopes allow astronomers to observe and study stars like UY Scuti in great detail.
The Role of Massive Stars in the Universe
- Heavy Elements: Massive stars like UY Scuti are responsible for producing many of the heavy elements in the universe, including gold, silver, and uranium.
- Supernovae: When massive stars run out of fuel, they explode in a spectacular event known as a supernova, scattering their material across the galaxy.
- Black Holes: Some massive stars can collapse inward, forming black holes, among the most mysterious and powerful objects in the universe.
Video: The Biggest Stars in the Universe
Enormous Stars You Can See with a Telescope
While most of the contenders for “largest known star” are thousands of light-years away and invisible to the naked eye, a few of these enormous red supergiants can still be spotted through backyard telescopes or even binoculars under dark skies. Observing them adds a thrilling perspective. Here are some of the most massive, luminous, and short-lived stars in the Milky Way, and you can see them from your own backyard.
VY Canis Majoris
One of the most famous red hypergiants, VY Canis Majoris, resides in the constellation Canis Major, the “Great Dog.” It lies about 3,900 light-years away and is estimated to span roughly 1,400 times the radius of the Sun.
Observing VY Canis Majoris: One of the largest known stars, VY Canis Majoris lies in the constellation Canis Major — the “Great Dog.” You can find it by looking diagonally down and to the left of Orion’s Belt. Though too faint to see with the naked eye, it’s visible through binoculars or a small telescope under dark skies.
Rho Cassiopeiae
A rare yellow hypergiant, Rho Cassiopeiae, sits in the distinctive “W”-shaped constellation Cassiopeia. It’s located about 8,200 light-years away and measures roughly 500 times the Sun’s radius, yet shines tens of thousands of times brighter than the Sun.
Unlike the red supergiants above, its golden hue comes from a hotter surface temperature (~6,000 K). Rho Cassiopeiae is visible to the naked eye under dark skies (around magnitude 4.5) and shows its soft yellow tint through even modest backyard telescopes.
I recommend using a telescope with an aperture of at least 8 inches to observe the stars listed. (Apertura AD8 Dobsonian Telescope pictured).
Final Thoughts
Studying stars like UY Scuti is a challenging and rewarding task for professional astronomers. Through spectroscopy, computer modeling, and telescopes, we can learn a great deal about these massive objects and gain a better understanding of the universe as a whole.
The incredible scale and complexity of the universe continue to amaze me, which is one of the reasons I believe astronomy is a lifelong journey.
When studying stars like UY Scuti, astronomers are only scratching the surface of what we know about them. There is still a lot to learn, and new discoveries are being made all the time. At the end of the day, studying stars like UY Scuti is not just about gaining knowledge, but also about appreciating the beauty and wonder of the cosmos.
From the smallest particles to the largest stars, the universe is full of mysteries waiting to be uncovered. By exploring these mysteries, we can deepen our connection to the universe and the night sky and gain a greater appreciation for the incredible world around us.
Helpful Resources:
“The Hertzsprung-Russell Diagram” by Edward L. Robinson – This article provides an in-depth introduction to the Hertzsprung-Russell Diagram, which is a valuable tool for understanding the properties and behavior of stars like UY Scuti. The article is published on the website of the American Association of Variable Star Observers (AAVSO).
“Stellar Evolution” by Kip Thorne and Roger Blandford – This book provides a comprehensive overview of the processes that govern the formation and evolution of stars, including red supergiants and red hypergiants like UY Scuti. The book is published by Princeton University Press and is available in both print and electronic formats.