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Gamma-2 Velorum

April 5, 2013

Most stars, including the Sun, are celestial nuclear reactors. Deep beneath their surfaces, nuclear reactions generate the energy that heats them and makes them shine.

We normally can’t see the products of these reactions. But in a few cases, hot, bright stars have blown off their outer layers, revealing the secrets of their nuclear activity.

The brightest of these “Wolf-Rayet” stars in Earth’s night sky is in the system known as Gamma-2 Velorum. It’s visible to the unaided eye, but only if you’re in the southern half of the country, where it’s quite low in the south as darkness falls tonight. It’s the brightest star of the constellation Vela, which represents the sail of the ship Argo.

Gamma-2 Velorum is actually a system of two stars - one relatively “normal” star, plus the Wolf-Rayet star. This glowing orb has already passed into a more advanced stage of evolution than the Sun. The Sun generates energy by converting hydrogen, the lightest element, into helium, the second lightest. But the Wolf-Rayet star has moved on to the next step, converting the helium into carbon and oxygen. We know this because the star has blown off its outer layers, exposing the bounty of carbon deep inside it.

Eventually, the star will convert the carbon and oxygen into still-heavier elements. Then it’ll explode as a spectacular supernova - making it not just the brightest Wolf-Rayet star in the night sky, but the brightest star in the entire galaxy.


Script by Ken Croswell, Copyright 2013

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