List of Most Luminous Stars

List Of Most Luminous Stars

Below is a list of stars arranged in order of decreasing luminosity (increasing bolometric magnitude). Accurate measurement of stellar luminosities is quite difficult in practice, even when the apparent magnitude is measured accurately, for four reasons:

1. The distance d to the star must be known, to convert apparent to absolute magnitude. Absolute magnitude is the apparent magnitude a star would have if it were 10 parsecs away from the viewer. Since apparent brightness decreases as the square of the distance (i.e. as 1/d2), a small error (e.g. 10%) in determining d implies an error ~2× as large (thus 20%) in luminosity. Stellar distances are only directly measured accurately out to d ~1000 lt-yrs.
2. The magnitudes at the wavelengths measured must be corrected for those not observed. "Absolute bolometric magnitude" (which term is redundant, practically speaking, since bolometric magnitudes are nearly always "absolute", i.e., corrected for distance) is a measure of the star's luminosity, summing over its emission at all wavelengths, and thus the total amount of energy radiated by a star every second. Bolometric magnitudes can only be estimated by correcting for unobserved portions of the spectrum that have to be modeled, which is always an issue, and often a large correction. The list is dominated by hot blue stars which produce the majority of their energy output in the ultraviolet, but these may not necessarily be the brightest stars at visual wavelengths.
3. Even the observed magnitudes must be corrected for the absorption or extinction of intervening interstellar or circumstellar dust and gas. This correction can be enormous and difficult to determine precisely. For example, until accurate infrared observations became possible ~50 years ago, the Galactic Center region of The Milky Way was totally obscured to stellar observations, which had to be made in the optical.
4. A large proportion of stellar systems discovered with very high luminosity have later been found to be binary. Usually this results in the total system luminosity being reduced and then that lower luminosity is spread among several components. These binaries are common both because the conditions that produce high mass high luminosity stars also favour multiple star systems, but also because searches for highly luminous stars are inevitably biased towards detecting systems with multiple more normal stars combining to appear luminous.

Because of all these problems, other references may give very different lists of the most luminous stars (different ordering or different stars altogether). Data on different stars can be of somewhat different reliability, depending on the attention one particular star has received as well as largely differing physical difficulties in analysis (see the Pistol Star for an example). The last stars in the list are familiar nearby stars put there for comparison, and not among the most luminous known. It may also interest the reader to know that the Sun is more luminous than approximately 95% of all known stars in the local neighborhood (out to, say, a few hundred light years), due to enormous numbers of somewhat less massive stars that are cooler and often much less luminous. For perspective, the overall range of stellar luminosities runs from dwarfs less than 1/10,000th as luminous as the Sun, to supergiants over 1,000,000 times more luminous.