Mass of Stars

by Fraser Cain on February 12, 2009

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Sirius. Image credit: Hubble

Sirius. Image credit: Hubble


Stars can range in mass from the least massive red dwarf stars to the monstrous hypergiant stars. Let’s take a look at the mass of stars at various sizes.

The least massive stars in the Universe are the red dwarf stars. These are stars with less than 50% the mass of the Sun, and they can be as small as 7.5% the mass of the Sun. This tiny mass is the minimum amount of gravitational force you need for a star to be able to raise the temperature in its core to the point that nuclear fusion can begin. If an object is less than this 7.5%, or about 80 times the mass of Jupiter, it can never get going; astronomers call these failed stars brown dwarfs. Instead of having nuclear fusion in their cores, brown dwarfs are heated by the gravitational friction of their ongoing collapse.

Above 50% the mass of the Sun, and you start to get colors other than red. The least massive stars are orange, and then yellow, and then white. Our own Sun is about the least massive example you can have of a white star (it looks yellow, but that’s just because of the Earth’s atmosphere).

The most massive stars are the blue giants, supergiants and hypergiants. Rigel, for example, is the brightest star in the constellation Orion. It has 17 times the mass of the Sun, and gives off 66,000 times the energy of the Sun.

But an even more extreme example is the blue hypergiant Eta Carinae, located about 8,000 light-years away. Eta Carinae is thought to have 150 times the mass of the Sun and puts out 4 million times as much energy. It’s probably less than 3 million years old, and astronomers guess that it will detonate as a supernova within 100,000 years. The most massive stars live the shortest lives.

We have written many articles about stars here on Universe Today. Here’s an article about the upper limits on star mass, and the discovery of a Jupiter-sized star.

If you’d like more information on stars, check out Hubblesite’s News Releases about Stars, and here’s the stars and galaxies homepage.

We have recorded several episodes of Astronomy Cast about stars. Here are two that you might find helpful: Episode 12: Where Do Baby Stars Come From, and Episode 13: Where Do Stars Go When they Die?

About 

Fraser Cain is the publisher of Universe Today. He's also the co-host of Astronomy Cast with Dr. Pamela Gay.

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