what is the biggest star in the galaxy?

Answer 1

If by big you meant heaviest, then it is not the Pistol star but Eta Carinae:

(http://en.wikipedia.org/wiki/Eta_Carinae)
"Eta Carinae (η Carinae or η Car) is a very large, very luminous star. Estimates of its mass range from 100–150 times the mass of the Sun, and its luminosity is about four million times that of the Sun.

This object is currently the most massive star that can be studied in great detail. Several other known stars may be more luminous and more massive, but data on them is far less robust. (Caveat: Since examples such as the Pistol Star have been demoted by improved data, one should be skeptical of most available lists of "most massive stars." As of late 2006, Eta Car still has the highest confirmed luminosity, based on data across a broad range of wavelengths.)"

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If you meant largest, then it might be VV Cephei A with a radius 1600 to 1900 larger than our sun:

(http://en.wikipedia.org/wiki/Largest_star)
"VV Cephei A, the supergiant, is one of the largest stars known"

Answer 2

In order to know what the largest star in the universe is we would have had to look at all the stars. We haven't come close to that - we haven't even looked at all the stars in our galaxy. There are about 100 billion stars in our galaxy, and about as many galaxies in the observable universe so you might understand why.

The best I can do is tell you what the largest known star is, but to do that I also need to know what you mean by largest. Do we pick the brightest, or the largest in volume, or the most massive (the one with the most mass)? More massive stars are generally less dense so take up a proportionally bigger volume. The most massive known is generally accepted to be the Pistol Star, which has a mass about 100-150 times that of the Sun, and is about 10 million times brighter . About 100 Suns would provide the same amount of stuff as the star, but we would need more that 100 Suns worth of volume to fill in the space it takes up.

Here's a picture....
http://antwrp.gsfc.nasa.gov/apod/ap971008.html

Answer 3

red giants are the biggest stars in the galaxy

The four largest known red supergiants in the Galaxy are Mu Cephei, KW Sagitarii, V354 Cephei, and KY Cygni, which all have radii about 1500 times that of the sun (about 7 astronomical units, or 7 times as far as the Earth is from the sun)

Answer 4

It used to be Marlon Brando.

Answer 5

The "Pistol Star", named for the pistol shaped nebula surrounding it.