The universe is vast and filled with celestial bodies of incredible scale. Among these, stars stand out as some of the most awe-inspiring objects. Determining the "biggest" star can be interpreted in several ways, primarily by mass or by radius. While the most massive stars are not always the largest in physical size, both categories contain true giants.

UY Scuti: The Current Radius Champion

Currently, the star widely recognized as the largest by radius is UY Scuti. It is a red supergiant located in the constellation Scutum.

• Type: Red Supergiant
• Location: Scutum constellation
• Distance from Earth: Approximately 9,500 light-years
• Radius: Estimated to be around 1,700 times the radius of our Sun. If UY Scuti were placed at the center of our Solar System, its photosphere would extend beyond the orbit of Jupiter, and potentially even Saturn.

Characteristics of UY Scuti

Other Contenders for Largest Star

While UY Scuti holds the record for radius, other stars are also incredibly large and noteworthy.

• Betelgeuse: A well-known red supergiant in the constellation Orion, with a radius estimated between 764 and 1,000 times that of the Sun.
• WOH G64: A red supergiant in the Large Magellanic Cloud, with a radius estimated to be around 1,540 times that of the Sun. This star is a strong contender, though its precise size is subject to ongoing research.
• NML Cygni: Another red hypergiant with an estimated radius of about 1,640 times that of the Sun, also a significant contender for one of the largest.

The Most Massive Stars

The most massive stars are often blue supergiants or hypergiants. These stars, while incredibly luminous and massive, are typically more compact than red supergiants like UY Scuti due to their higher temperatures and different evolutionary stages.

• R136a1: Located in the Large Magellanic Cloud, this star is currently the most massive known, with an estimated mass of 215-250 times that of the Sun. Its radius is relatively small compared to UY Scuti, at about 30-40 times the Sun's radius.
• Pistol Star: Another highly luminous and massive star, estimated to be around 25,000 light-years from Earth.

How Do We Measure Star Sizes?

Measuring the exact size of distant stars is a complex process. Astronomers use several methods:

• Angular Diameter: For nearby, very large stars, astronomers can directly measure their apparent size in the sky using interferometry.
• Stefan-Boltzmann Law: By knowing a star's luminosity and surface temperature, its radius can be inferred.
• Binary Systems: For stars in binary systems, the orbital mechanics can provide clues about their sizes and masses.