Science & Technology

Wolf-Rayet Stars Are Ridiculously Hot, Bright, and Massive

What's the brightest star in the sky? Trick question: it's the sun. The brightest star in the night sky, though, is Sirius, known as the "Dog Star." But what about the brightest star ever? That honor goes to a really, really massive celestial object called a Wolf-Rayet star. Our sun may be bright, but it's got nothing on these things.

Hungry Like The Wolf-Rayet

Wolf-Rayet stars don't start their lives as the universe's brightest, but they are born big. They start out at least 20 times as massive as our sun, and that's where the trouble begins. See, just like you need to digest food for energy, stars need to fuse elements to keep on shining. For our sun, that means fusing hydrogen, the lightest element, into helium, the second lightest. Bigger stars fuse those into even heavier elements, from carbon to oxygen all the way to iron. Ideally, all the energy blasted outward from that fusion is balanced by the star's gravity pulling inward, and the star can happily survive for billions of years.

But if a star is big enough, that process goes a lot faster. As a Wolf-Rayet star runs from heavier element to heavier element, the energy it creates starts to exceed the gravity it takes to keep everything together. This energy is what makes Wolf-Rayet stars so hot and bright: they burn at 50,000 kelvins and shine millions of times brighter than our sun. But that energy-gravity imbalance leads to winds that blow at up to 5.4 million miles per hour (9 million kilometers per hour) and strip away the star's outer layers.

As the star loses elements to the universe, it starts to run out of stuff to fuse. Once it (or any star) fuses iron, it's done — fusion stops, there's no more outward pressure, and the only force left is the squeeze of gravity. At that point, one of two things happen: if the star is small, it explodes as a supernova. If it's big, its gravity warps to the point that not even light can escape, and it becomes a black hole.

You Are Star Stuff

But there's a happy ending to this story. The high-energy winds that blow off the star's outer layers? They carry newly fused elements out into the universe, where they can play a role in the formation of everything from new celestial objects to life itself, yours included. Every element in your body was fused in the core of a star. As Carl Sagan famously said, we're made of star stuff. Cosmic, isn't it?

For more poetic words about our place in the universe, check out Carl Sagan's timeless tome "Cosmos." We handpick reading recommendations we think you may like. If you choose to make a purchase through that link, Curiosity will get a share of the sale.

What Are Wolf-Rayet Stars?

Written by Ashley Hamer January 31, 2018

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