UY Scuti Facts

UY Scuti is the biggest known star in the universe. It Is a hypergiant with a radius around 1,700 times larger than the Sun.

UY Scuti is a red supergiant star located in the constellation Scutum. It is one of the largest known stars, discovered since 1860. 

Key Facts & Summary

  •  UY Scuti was discovered by German astronomers at the Bonn Observatory in 1860. However, the star was better documented in 2012 with the help of greater technological equipment.
  • Data revealed that UY Scuti was around 7 to 10 times more massive than our Sun, and had a radius approximately 1.700 times larger.
  • It has a radius of 1.1883 billion km / 0.7383 billion mi, and an enormous diameter of 2.3765 billion km / 1.4766 billion mi or around 7 AU across.
  • UY Scuti is located in or galaxy the Milky Way, at about 5.219 light-years away from Earth.
  • UY Scuti changes its brightness but it can be viewed from Earth as it is a pulsating star.
  • It has an absolute magnitude of -6.2, UY Scuti is thus 340.000 times more luminous than our Sun.
  • Because of its distance, its brightness is only ranked 9th in magnitude.
  • It is not known if there are planets orbiting around UY Scuti, but even if they were, radiation from UY Scuti would quickly make them uninhabitable.
  • The pulsation of UY Scuti has a period of about 740 days.
  • Because of this pulsation, its exact size also varies, making an exact estimation difficult.
  • The temperature on UY Scuti is estimated to be around 3,365 K.
  • It is believed that UY Scuti has begun to fuse helium and will eventually go supernova.

Astronomers at the Bonn Observatory in Germany were the first to catalog UY Scuti in 1860 however, due to the technology at the time they couldn’t really grasp what they really did discover – the biggest star in the Milky Way galaxy, at least it held that title for a period of time.

The true size of UY Scuti was later revealed by observations conducted in 2012 through the Very Large Telescope located in Chile’s Atacama Desert.

This discovery was quite overwhelming, and for a period of time UY Scuti held the title of the biggest known star in the Milky Way. Its size surpassed previous records held by other large stars such as Betelgeuse, VY Canis Major, and NML Cygni.


UY Scuti is a red supergiant star, which is usually an aging star. Stars with a big enough mass transform into red supergiant stars. They are the largest known type of stars. They usually form when a star runs out of hydrogen fuel in their core and begins collapsing.

The outer shells of hydrogen around the core get hot enough to begin fusion. The shells then expand, and the now cooler star takes on the red color.


Situated in the Milky Way galaxy in the Scutum constellation, UY Scuti is 5.100 light-years away from us. It is situated just northeast of the famous Eagle Nebula (Messier 16).

Also home to the famous Delta Scuti variable star, the Scutum constellation contains many relatively bright deep-sky objects that are quite popular targets among stargazers.

Size, and Mass

UY Scuti’s exact size is difficult to determine due to its pulsation. However, recent estimates in 2019 have made the planet a bit smaller due to its change in temperature.  The radius has dropped – it now has 1708 times the radius of our Sun.

Even so, it is still enormous but no longer considered the biggest known star. 

If now it has a radius of approximately 999.9 radii ( that corresponds to a diameter of 1.3 million km / 0.864 million mi) then that means stars such as V450 Persei, KW Sagittarrii, U Lacertae, HV 2331, and many more have surpassed it.

Even before these new estimations, UY Scuti was already surpassed by R136a1in mass at least. 

Regardless, UY Scuti is still one of the biggest known stars and if UY Scuti were placed in the Solar System, replacing our sun, its photosphere would reach the orbit of Saturn.

To get a better sense of the scale of UY Scuti, more than 4 quadrillion Earth’s could fit into it.


Current models based on stellar evolution suggest that UY Scuti has begun to fuse helium. It continues to fuse hydrogen in a shell around the core. 

When the star will finish fusing the heavy elements, the core will start to produce iron thus disrupting the balance of gravity, and radiation in its core will result in its collapse thus explode into a supernova.

Scientists believe that UY Scuti will evolve back to hotter temperatures and become a yellow hypergiant, luminous blue variable, or a Wolf-Rayet star.

This will create a strong stellar wind ejecting its outer layers and exposing its core, before exploding as a type llb, lln, or type lb/lc supernova.

This will not affect us since the necessary distance in order for a supernova to do so, would require it to be around 50 light-years away from us.

Life habitability

Currently, we do not know if there are planets orbiting around UY Scuti. Even if it has a habitable zone the radiations emitted by the enormous star will sterilize everything. It may have been possible for life to evolve around these hypothetical planets before the star grew to such sizes.

Future plans for UY Scuti

When UY Scuti goes supernova, it will definitely be a sight to see. However, estimates are not precise when this will happen. The star will continue to be monitored and studied regardless. 

Did you know?

  • If a hypothetical object would travel at the speed of light along UY Scuti’s great circle, it would take it 7 hours to make a circle around it, whereas it would take 14.5 seconds to circle the Sun.
  • Scutum, the constellation where UY Scuti is located, is one of the smallest constellations in the sky.
  • The location of  UY Scuti, deep within the Milky Way galaxy disc suggests that it is a metal-rich star.
  • Even if UY Scuti is located in the Zone of Avoidance, which is an area of space obscured by the Milky Way’s disk, it is so large and bright that it can be seen from Earth even with a pair of binoculars.
  • When UY Scuti was discovered, its name was originally ” BD-12 0 55.”
  • Around 3.69 billion Suns could fit inside UY Scuti.


  1. Wikipedia

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