Astronomy Picture of the Day 3-25-03

Explanation: Why would a gamma ray burst fade so slowly? This behavior, recorded last October, is considered a new clue into the cause of gamma-ray bursts, the most powerful explosions known in the universe. The burst, first detected by the orbiting HETE satellite and later tracked by numerous ground-based telescopes, showed an unusually slow and tumultuous decay in visible light. Speculations on the cause of the unusual light curve include a blast wave striking a windy circumburst medium, a blast wave energetically refreshed by a faster outgoing shock, and non-uniformity in a fast moving jet. Pictured above is the massive Wolf-Rayet star WR124, a star itself undergoing a slow explosion by producing a very powerful but tumultuous wind. Popular candidate progenitor sources for GRBs include supernova or hypernova explosions from massive stars, possibly ones with similarities to Wolf-Rayet stars.

This article is a bit ambiguous as to the image shown, until it finally identifies it as a Wolf-Rayet star.

Gamma-ray bursts are one of the universe's most intriguing and energetic events. The very first link in the article (marked "gamma ray burst") will describe these mysterious events insofar as we understand them.

I highly recommend the Imagine the Universe NASA website to adults and teens for its fascinating topics. Even those who know little of astronomy will enjoy the site.

If you have grade-school-age children, there is a NASA site for them too. It's called StarChild.

You may wonder why I'm recommending these sites. I don't work for NASA. I was doing some research for a detail for APOD recently and came across several astronomy-subject websites which were full of bad information; outdated, erroneous, misconceived, you name it. One site even named Titan as a moon of Jupiter!

Wolf-Rayet stars are bright, hot, luminous, and rare. Only about 200 are known to exist in the Milky Way. The brightest one is Gamma Velorum, magnitude 1.74. It is the only prominent one; all others are fainter than magnitude 5. It's fairly nearby at approximately 840 light years. It's too far south to see from most of the Northern Hemisphere.

A most peculiar Wolf-Rayet star

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