What is the biggest star in the universe?

The largest star observed to date is called UY Scuti and is about 9500 light years away from Earth in the Shield constellation.
It is a red supergiant 1,700 times the size of the sun and has a diameter of 2.4 billion kilometres, the largest star in our galaxy.

With a volume about 5 billion times that occupied by our Sun, if it were at the centre of our solar system, UY Scuti would envelop the planets Mercury, Venus, Earth, Mars and Jupiter.
To make a comparison: if the star were the size of a basketball, the Sun would be smaller than a dust mite and the Earth would be the size of a bacterium.

The star measures a radius 1708 times larger than that of the Sun, which is equivalent to more than a billion km or, in terms of astronomical units, 8 UA (one unit of this measurement corresponds to the distance Earth-Sun).

UY Scuti is composed of hydrogen, helium and heavier elements.
The star has a density of 7 x 10-6 kg/m3 (more than a billion times less dense than water).
According to this data, UY Scuti is only 20-40 times heavier than our Sun.

The heaviest star, on the other hand, is called R136a1, a blue hypergiant located in the Great Magellanic Cloud, about 165 thousand light years from the solar system, smaller than UY Scuti but 10 times heavier.
R163a1 also holds another record as the brightest star, a beacon 94,000 times brighter than the Sun.

A short but intense life

The Sun may seem insignificant compared to these giants, but it can count on a much longer life.
In fact, the more massive the stars are, the shorter their life cycle will be.

In particular, a star with a mass between 10 and 70 solar masses, after a few tens of millions of years, leaves the main sequence and can evolve into a supergiant: this is the last stage of its life and the explosion generally occurs after a few million years.
This is a very short period of time if we consider that our star has already been radiating the solar system for 5 billion years, and is barely a “middle-aged” star.

UY Scuti is one of the stars characterized by a short, though very intense, life, which will culminate in what astrophysicists consider one of the most energetic events in the Universe, a supernova: a violent explosion that touches temperatures of the order of hundreds of billions of Kelvin and for brief moments brighter than a galaxy.