The Milky Way is populated by at least 100 billion stars. Less than 10 of these belong to the WO2 spectral class. These are highly evolved stars that are in the last stages of the nuclear fusion process: they have in fact finished burning all their available hydrogen and, in some cases, even helium.
The most studied star of class WO2 is WR 102, located 9500 light years away from Earth, in the constellation Sagittarius.
Like all other stars in this class, WR 102 is extremely hot and bright. Its brightness is in fact more than 300,000 times greater than that of the Sun and its surface temperature is 210,000 Kelvin, the highest ever recorded in a stellar atmosphere!
The star currently has a mass of 16 solar masses, but this value decreases from year to year as WR 102 ejects a large amount of material into space in the form of stellar wind.
The incredible thing is that this extreme star is smaller than the Sun: its diameter is in fact equal to just 60% of the solar diameter!
A star like WR 102 that has already finished burning hydrogen hasn't long life: it has been calculated that the star will explode and become a supernova in just 1500 years.
Credit: NASA.
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