Science News for Kids: No Fat Stars (March 16, 2005)

This news article was originally published on March 16, 2005, on sciencenewsforkids.org. It is being reposted for archive purposes.

There's a limit to how big most things can get. Some people are really tall, but no one is as tall as a house. Cats can get really fat, but there's never been a tabby as heavy as a truck. And so on.

Now, astronomer Don Figer of the Space Telescope Science Institute in Baltimore has discovered that the size of a star may have a limit, too. No stars in our galaxy, he estimates, can weigh more than 150 times the mass of our sun.

This conclusion comes from observations of an area near the center of the Milky Way called the Arches cluster. The cluster is between 2 million and 2.5 million years old, and stars are still forming there. It contains about 2,000 stars.

Figer thought that the Arches cluster would be a good place to search for the galaxy's biggest stars because it's still fairly young. Massive stars have short lives, so it wouldn't make sense to look at a cluster that was much older than Arches. It also wouldn't make sense to look at much younger ones because stars in young clusters are still hidden behind gas and dust.

The Arches cluster was also promising because it's big. Its total mass is that of about 10,000 suns. In theory, it could hold at least 18 stars weighing more than 130 times the mass of the sun.

Using the Hubble Space Telescope to gauge the weight of hundreds of stars in the Arches cluster, Figer found no stars this big. This means, he concluded, that there must be an upper limit to the size of a star—perhaps about 150 times the sun's mass.

Astronomers are just beginning to understand the processes behind star birth. No one yet knows what determines the limits on their growth. Figer plans to study clusters of different ages to find out more. —E. Sohn