A monster version of our sun has been found, the largest known member of the family of yellow stars to which our sun belongs.
The whopper sun emits light in similar
wavelengths as our sun but its diameter is over 1300 times larger. That
means it would engulf all the planets between Mercury and Jupiter if
placed at the centre of our solar system. The star's size also means it
is touching its smaller, companion star.
Dubbed HR 5171 A, the star is located in the
constellation Centaurus around 12,000 light years from Earth. It was
already known to be a hypergiant, the largest class of stars, but its
exact size hadn't been well studied.
Now a team led by Oliver Chesneau of the Côte d'Azur Observatory in Nice, France, has taken a closer look with the Very Large Telescope in Atacama, Chile. They report that it is twice as large as expected.
It still isn't the largest star we know
about – that crown goes to UY Scuti, which is around 1700 times larger
than our sun. But UY Scuti is in a different stage of stellar evolution
and so belongs to a different family of stars called red stars.
Both red and yellow stars can be hypergiants, but
yellow hypergiants were previously thought to be at most 700 times the
size of the sun. The new measurement of HR 5171 A shows they can be much
bigger. HR 5171 A is 50 per cent larger than the red hypergiant Betelgeuse, which is located in the constellation Orion and is the ninth brightest star in the night sky.
Another surprise for Chesneau's team was
the discovery that HR 5171 A has a little brother. Previous observations
suggested the star varied in brightness. Now the team has shown that
this is due to a companion star that is around one third its size.
The two stars orbit each other, forming a binary system.
However, though their centres are separated by more than the distance
between our sun and Saturn, HR 5171 A is so large that the two are
touching, forming a continuous peanut-shaped structure. Guess this star
system ain't big enough for two.
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