UY Scuti- The Unbelievably Massive Star

Can you imagine a star so enormous that if it replaced the Sun in our solar system, it would reach Jupiter’s orbit? UY Scuti is just such an extreme red hypergiant monster. It has one of the largest radii of any known star, approximately 1,700 times that of the Sun.

UY Scuti is essential to astronomy due to its immense size and mass. Astronomers study it to gain insight into supergiant stars’ hugely varying conditions and processes. Understanding this star enhances our understanding of stellar evolution and the life cycles of massive celestial bodies. Furthermore, UY Scuti’s properties and behavior affect scientists’ understanding of galaxies’ dynamics and the universe’s overall structure.

What Is UY Scuti?

UY Scuti is a pulsating variable star with an extreme red supergiant or hypergiant classification.

Image: Wikipedia

Where Is UY Scuti Located?

UY Scuti is a giant star in its relatively small neighborhood in the constellation Scutum. Scutum is one of the 88 International Astronomy Union’s (IAU) 1922-defined constellations. And it lies south of the celestial equator, about 9,500 light-years from Earth.

Size Comparison With Other Stars

While UY Scuti (BD-12°5055) isn’t the brightest star in its constellation, it does have a varying brightness between a magnitude of 8.29 and 10.56 on its lower end. 

But what really sets UY Scuti apart is its immensity. With a volume almost 5 billion times the Sun’s, this monster dwarfs the center of our solar system. Check out the image below to see just how vast and bright UY Scuti is compared to other nearby stars.

This Digitized Sky Survey (DSS) image by the Space Telescope Science Institute shows UY Scuti in all its glory. It is a digital version of the photographic night sky surveys produced between 1983 and 2006.

UY Scuti Size Comparison
Image: Space Telescope Science Institute

Discovery and Observations

German astronomers first cataloged UY Scuti in 1860 at the Bonn Observatory. Originally designated BD-12°5055, UY Scuti was the 5,055th Bonner Durchmusterung Stellar Catalogue star.

Scientists noted that the star’s brightness changed in the second survey, so they called it UY Scuti, the 38th variable star in Scutum. They said its location a few degrees north of Gamma Scuti and northeast of the Eagle Nebula.

UY Scuti sits a few degrees north of the A-type star Gamma Scuti and northeast of the Eagle Nebula. In addition, it is very luminous, but since it is so far from Earth, we see it as only 9th magnitude.

Another thing scientists observe about UY Scuti is that it, like other hypergiant stars, loses its mass due to the intense stellar winds that continually buffet it. And because of its location in the Milky Way disc, astronomers believe the star is metal-rich.

Combining all the knowledge from the original discovery with the observations over the years, it has been made clear that UY Scuti is the biggest star in the universe that we have discovered this far.

Characteristics And Future Of UY Scuti

UY Scuti is a semiregular variable red supergiant star. It pulses about every 740 days. Scientists believe it is in the helium-fusing stage of stellar evolution. It also continues fusing hydrogen around its core.

Stellar Evolution and Life Cycle of UY Scuti

Based on current lifecycle models, UY Scuti will fuse its heavy elements and then produce iron. That will likely offset its gravity balance, causing radiation within the star’s core, resulting in its collapse into a supernova.

Stars like this supergiant often evolve and change back to hotter temperatures. They usually become one of three star types.

  • Wolf-Rayet
  • Yellow hypergiant
  • Luminous blue variable

And once that happens, UY Scuti’s intense stellar winds will increase, stripping the outer layers to expose its core. Finally, at some point, the star will explode into a supernova.

UY Scuti In Context

The constellation Scutum holds several clusters of supergiant stars. And they’ve been the center of much research.

AMBER (Astronomical Multi-BEam combineR), an instrument on the Very Large Telescope Interferometer (VLTI,) is now decommissioned. But it helped scientists study the close environments of stars and other astronomical objects.

Image: European Southern Observatory/Y. Beletsky

For example, in 2012, astronomers used AMBER to measure three red supergiants, including UY Scuti (UY Sct.) The other two giants were AH Scorpii (AH Sco) and KW Sagittarii (KW Sgr.) In addition to finding the approximate sizes of each supergiant, the research also indicated that the stars “exhibit extended atmospheric layers of H2O and CO.”

Comparison With Other Supergiant Stars

All three stars measure more than 1,000 times the Sun’s radius and are about 100,000 times more luminous. UY Scuti is one of the largest and most luminous compared to the other two supergiants.

  • UY Scuti Radius: 1,708 ± 192 R☉
  • UY Scuti Luminosity: 340,000 L☉, effective temperature of ~3,365 K
  • UY Scuti Mass: approximately 25 to 40 M☉ in some studies, while only 7 and 10 M☉ in others.

UY Scuti is so large that if an object could travel around it at the speed of light, it would take seven hours. However, the same hypothetical thing could travel around the Sun in only 14.5 seconds. Now that’s an enormous supergiant!

Of note is that the star continually loses mass due to the extreme stellar winds that encircle it. The gas and dust environment both pull from and add to its mass and radius.

Uy Scuti’s Role in the Milky Way Galaxy

UY Scuti plays a significant role in the Milky Way Galaxy as one of the most massive and luminous stars. Its stellar winds and eventual supernova release vast amounts of matter and energy into interstellar space. So it constantly enriches its surroundings with heavy elements.

That matter influences the formation of new stars and planetary systems. Astronomers study it to better understand the complex interactions between stars and interstellar matter. UY Scuti also helps inform the overall structure and evolution of the Milky Way.

Connection to the Study of Distant Galaxies and the Universe

In addition to its role within our universe, UY Scuti serves as a valuable point of comparison when studying distant galaxies. As scientists better understand the hypergiant’s properties and behaviors, they can use the knowledge to analyze similar objects further from Earth.

Additionally, UY Scuti’s extreme estimated size and nature prompt scientists to question the upper limits of stellar size and mass. And those answers help inform models or theories of the universe’s vast limits and structure.

UY Scuti’s Photosphere

Stars have diffuse edges without ridged surfaces. So it’s hard to know where gases end, and the vacuum begins. As a result, astronomers determine a star’s size by its photosphere.

A star’s photosphere is the deepest layer that is directly observable. For example, the Sun’s photosphere starts at the solar disk’s center surface and extends about 250 miles above it. It’s the area where the giant star is transparent to light, and the photons (or light particles) can escape.

So when you imagine UY Scuti replacing our Sun, it is the star’s photosphere that extends past Jupiter’s orbit. And additionally, the gas nebula ejected from UY Scuti extends past Pluto’s orbit. That’s about 400 times the distance between the Sun and Earth.

James Webb Space Telescope (JWST) And UY Scuti

The JWST will use its Near-Infrared Spectrograph (NIRSpec) and Mid-Infrared Instrument (MIRI) to help scientists analyze UY Scuti’s atmospheric structure and composition. Star observations across various wavelengths let the telescope examine the outer layer elements. So hydrogen, carbon, oxygen, and helium analysis can help explain the star’s evolution and processes.

Star Sizes
Image: Wikipedia and JWST

In addition, the JWST spectroscopic abilities let scientists study the intense stellar winds that stream from UY Scuti’s surface. Astronomers learn how massive stars lose their mass by understanding the wind’s velocity and composition. This particular study looks at shifting spectral lines to understand the reactions of stellar pulsations and radiation pressure. It also looks at other factors causing material ejection from the star’s atmosphere.

Another area of exploration for the JWST and UY Scuti is the detailed monitoring of the hypergiant’s variability. Analyzing its period changes and pulsation patterns helps scientists understand how massive stars evolve and shape the galaxies around them.

But perhaps most exciting are the expected high-resolution images of UY Scuti from the JWST. With them, scientists plan to study stellar evolution’s late stages. They’ll learn what leads to a massive star’s death and explosion into a supernova.

The JWST’s exploration of UY Scuti promises revolutionary insight into the universe. Maybe it will explain some of the mysteries of the universe by helping refine stellar physics models and massive star life cycles.


UY Scuti is a massive red hypergiant pulsating star in the Scutum constellation. It is about 1,700 times the size of the Sun and holds a special place in studying monster stars. The scientific potential that UY Scuti has is almost as enormous as the star itself. Especially now, with the capabilities of the James Webb Space Telescope, scientists hope to unravel the universe’s mysteries by studying UY Scuti.

Information about its evolution, variability, atmosphere, and how it loses mass promises to take astronomy to levels of awareness and possibility.