Until recently, the Pistol Star in the constellation of Sagittarius was the largest star known to astronomers. The star, hiding deep within the dust of the galactic core and named for the shape of the huge nebula in which it was born, was discovered in 1997 by the Hubble Space Telescope. It is big enough that if it replaced the sun, the Earth would orbit inside it, and it radiates heat and light at a prodigious rate, blasting the sun's annual energy production into space in just six seconds.
But Mr. Big is no longer Mr. Biggest. On 2004 January 6, it was announced by University of Florida explorer Stephen Eikenberry that a star known somewhat romantically as LBV 1806-20 has usurped the Pistol Star's heavyweight crown. Where the Pistol Star is ten million times as luminous as the sun, LBV is more than forty. It also outmasses the sun by more than 150 times, and occupies at least a million times its volume. To put this in some kind of perspective, if the sun were the size of a basketball, the Earth would be about the size of a smallish BB, and would orbit at a distance of roughly 30 metres/30 yards. on this same scale, LBV 1806-20 would be a sphere entirely filling a football field, and the difference in size between it and the sun would compare to the size difference between the sun and the Earth.
Imagine North America (or your local continent) painted on the BB. If you can, visualize the relative size of your state or province. If you live in a major urban area, it would be about dust-speck size at this scale. And you? Well… Imagine this teensy little micro-speck of a you looking at the thing in the middle of the football field.
Hubris is dangerous among humans, and it is no less dangerous for our large friends. While the sun, a bit of a dwarf as stars go, will sail on pretty much unchanged for another four or five billion years barring unforseen circumstances, profligate stars like the Pistol Star and LBV 1806-20 will meet their ends in unimagineably titanic explosions in somewhere between one and three million years, all things being equal. In other words, for all their powerhouse behavior now, they will live only a thousandth as long as the sun. Life imitates rock 'n' roll.
Donald Figer, a researcher with the Space Telescope Science Institute, cautions that not all the data are in yet, and that LBV 1806-20 may simply be two or three stars masquerading as one. Nonetheless, the discovery of at least two such supergiant stars in less than ten years means there must surely be other such monsters lurking within the depths of our galaxy.
Sources:
Science News 2004 January 24
http://hubblesite.org/newscenter/newsdesk/archive/releases/1997/33/text/
http://nemesis.stsci.edu/~figer/web/LBV1806-20/NYT.htm