Q&A: Normal Stars, White Dwarf Stars, and Star Clusters

Q:
Do you have a list of the biggest stars?

A:
The adjective "biggest" covers a multitude of sins, when referring to stars. The biggest stars in both size and mass are ones that are producing so much radiation that they are barely able to hold together. Their intense radiation fields are driving mass off the star at such a high rate that it is difficult to tell just how large the star really is. What astronomers can measure is how much energy the star is producing. They can fold this information into theoretical models to get an estimate of the mass of the star. Using this method, the title of heavyweight champion goes to the Pistol star in the constellation Sagittarius, near the center of our Milky Way Galaxy. The Pistol Star shines with the power of 10 million suns, and has a mass estimated to lie between 150 and 200 suns.

Some stars in the Galaxy and the Magellanic Clouds (satellite galaxies of the Milky Way) are almost as powerful. Mk 42 and Sk-67 211 in the Large Magellanic Cloud are of similar luminosity. Eta Carinae in our galaxy and HD 5980 in the Small Magellanic Cloud have the luminosities of several million suns, but they are apparently double stars. AG Carinae and R127 both top a million solar luminosities, and may brighten to equal the Pistol Star from time to time.

All these stars are losing mass so rapidly that, if they continued at their present rate for ten million years, they would be a mere shadow of their former brilliance. Before that happens, however, they will end their life as a supernova, and in all likelihood leave behind a black hole.