The Hubble Space Telescope has made a new discovery – a star that is 250 times larger than the Earth’s sun. It is so large that it is leaving scientists without an explanation as to how it could have gotten that big.
Astronomers had previously thought they knew how big stars could be, but those beliefs were nowhere near the size of the star known as R136a1. Eight other stars in the same cluster have masses more than 100 times larger than our sun, and astronomers can’t figure out how so many ultra-massive stars could be so close together.
The explanation to the unexplained mystery lies in how stars form. They start from a swirling gas cloud that begins to accumulate more gas by gravity generated by denser regions of the cloud that are formed by gas and dust. Once there is enough gas, the pressure becomes great enough for the gas to ignite, forming a star.
Once the gas ignites, a stellar wind is created that blows back outside gas, which stops further accumulation and should stop the star from getting any bigger at that point. The question is how nature can form a star so much bigger than our sun.
Scientists think it might be possible for two stars to merge, but they would have to get close enough and pass in exactly the right configuration. Otherwise they would just be caught in each other’s gravity and orbit each other in which is called a binary system. Approximately half of all known stars are in such a situation.
Another theoretical model has the stars in a binary system merging. Still, many such mergers would be needed to explain the size of R136a1.
The question would not even have been possible before the advent of the Hubble, which is the best detecter of ultraviolet light that present day scientists have. Massive stars burn very hot through nuclear fusion – the bigger the star, the more pressure at its center and the more nuclei fusing together. These hotter temperatures cause the massive stars to emit excessive amounts of ultraviolet light, which the Hubble’s imaging spectrograph can see.
R136a1 is 165,000 light years away from earth, and is the largest star ever discovered. It is located in the Large Magellanic Cloud, which is a nearby dwarf galaxy orbiting the Milky Way. The stars in this cluster are fairly young – only about 2 million years, compared to earth’s sun at 4.5 billion years. It is an exceptionally hot star, with estimated surface temperatures of around 95,000F, almost 10 times hotter than our sun.