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The largest known star, UY Scuti, is a red supergiant that has a volume 5,000 million times greater than that of the Sun. But despite being the largest, this
is not, however, the most massive star
.
supergiants
The stars are very diverse.
Their brightness and colors can differ greatly, there are hot and cold, small and large.
The smallest ones have sizes of a few kilometers, like a medium-sized city.
But
what are the biggest stars like?
Can there be stars of unlimited size and mass?
Stars are formed from large clouds of gas and dust that can have millions of solar masses and that collapse under the effect of their own weight.
However, during gravitational collapse processes, the cloud does not shrink monolithically to form a single star, but rather, due to hydrodynamic instabilities,
a large cloud breaks apart to form a group or cluster of stars
.
The most massive stars can exceed 200 times the mass of the Sun, and the diameters of the largest can be more than a thousand times greater than the Sun.
These huge or massive stars are huge balls of gas, are
as luminous as millions of suns, and can have different colors
.
The main types are called hypergiants and supergiants, and they can be more or less evolved, blue or red.
Very massive stars are not very abundant and their lives are very short: due to the high temperatures and densities of their inner regions, they deplete their nuclear fuel "quickly", in just a few million years.
Let us remember that
the life of a star like the Sun is a thousand times longer
: about 10,000 million years.
The biggest
The largest star ever observed is called UY Scuti.
Its diameter is 1,700 times greater than that of the Sun. That is, if we placed it instead of the Sun, in the center of the solar system, it
would cover up to the orbit of Saturn
.
In its enormous volume would fit 5,000 million soles.
This colossal star is located near the center of the Milky Way, about 9,500 light-years away, in the constellation of Sobieski's Shield (Scutum).
Shortly after its discovery, which took place in 1860 from the Bonn Observatory, it was found that
its brightness increased and decreased with a period of 740 days
.
It is therefore a semiregular red supergiant star that will end its life in a violent supernova explosion.
the most massive
Despite being so large, UY Scuti is not the most massive star, as its mass is about 30 times the mass of the Sun. The most massive of all known stars is called R136a1, it has a mass of 215 solar masses and is It is located in the Tarantula Nebula, in the Large Magellanic Cloud (a satellite galaxy of the Milky Way).
However,
its diameter is only 30 times larger than that of our Sun
and, therefore, 57 times smaller than that of UY Scuti.
Illustration of R136a1 compared to Sol.R.
Kelly/RB
Contrary to the latter, R136a1 is not a red supergiant, but belongs to the class of so-called Wolf-Rayet stars, which are much hotter, so they have a bluish glow and emit ultraviolet radiation.
The Wolf-Rayet represent a more advanced evolutionary phase than that of the red supergiants;
they are, therefore,
much closer to undergoing a supernova explosion than the red ones
.
In addition to being the most massive, R136a1 has the honor of being the most luminous star known: its luminosity exceeds the solar luminosity by more than 6 million times.
fuzzy edges
These large or massive stars do not have a well-defined surface like Earth.
They are gigantic balls of gas with atmospheres that are accelerated by the effect of
powerful winds blowing into space
from the outer layers.
Therefore, the diameter of such stars is defined by locating a point of precise physical characteristics in the gas.
The fuzzy boundaries of large stars make size comparisons difficult.
Also, as they vary in brightness, these stars contract and expand.
About 30 stars are known today
that are similar in size to UY Scuti
and that may even exceed it when it is in its phase of greatest contraction.
Of these 30, there are three stars with more than 1,500 times the solar diameter and, like UY Scuti,
all three are red supergiants
: NML Cygni (in the constellation of the Swan), WOH G64 (in the Large Magellanic Cloud), and Westerlund 1 -26 (in the constellation of Ara, the Altar).
Rafael Bachiller
is director of the National Astronomical Observatory (National Geographic Institute) and academic of the Royal Academy of Doctors of Spain.
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