The heaviest star in the universe, by mass, is R136a1. Image: Joannie Dennis.
In terms of radius, the largest star known today is UY Scuti, a colossal, crimson entity located in the Scutum constellation. Situated 9,500 light-years away from Earth, UY Scuti consists of hydrogen, helium, and heavier elements similar in chemical composition to the Sun. However, this star boasts a diameter that is 1,708 times greater than that of the Sun.
According to the Epoch Times, the diameter of UY Scuti is nearly 1.2 billion kilometers, with a circumference length of 7.5 billion kilometers. It would take a commercial airliner approximately 950 years to circumnavigate this star. Even light itself takes 6 hours and 55 minutes to travel around UY Scuti. If UY Scuti were to replace the Sun, its surface would extend between the orbits of Mercury and Venus, and Earth would be engulfed by the star.
With its immense size and a mass 20 to 40 times that of the Sun, UY Scuti has a molecular gas density of 7×10⁻⁶ kg/m³, making it less dense than water by a factor of over a billion. In theory, if placed in a large enough body of water, this planet would float.
While UY Scuti may possess the largest size in the universe, it doesn’t hold the top spot in terms of mass. The heavyweight champion in the universe is the star R136a1, located in the Large Magellanic Cloud, which is 165,000 light-years away from Earth.
R136a1 also consists of hydrogen, helium, and heavier elements in its atmosphere. It has a radius 35 times that of the Sun but a mass over 265 times greater. Scientists believe that this star lost an equivalent of 55 Suns’ worth of mass during its 1.5 million years of existence. R136a1 belongs to the category of unstable stars, with a blueish atmosphere and the ability to emit incredibly strong solar winds, moving at speeds of 2,600 km/s.