March 19 – A Gamma-Ray Bursts the World Record!

Posted on March 19, 2017

Do you know about the dreaded GRB?

A gamma-ray burst is the brightest electromagnetic event known to occur in the universe - a super-duper high-energy explosion. We think that most GRBs are caused by supernovas or even bigger-than-that star-explosions, which are called hypernovas. Scientists speculate that the burst might occur just as the exploding star collapses into a neutron star, a quark star, or a black hole. 

Some GRBs might be caused by two neutron stars that had been revolving around each other (in other words, binary stars) finally collapsing together to merge into one star.

Most GRBs are short-lived. Like, really short-lived - just a matter of milliseconds or seconds. After the flash of gamma rays, there is a longer period of "glow," which is made up of less energetic forms of electromagnetic radiation: X-rays, ultraviolet rays, visual light, infrared light, microwaves, and radio waves. A GRB can last as long as several hours.

Gamma rays are very damaging to living things, and a nearby GRB that happened to be pointed at our planet could cause "a mass extinction event." (Think dinosaurs.) But, luckily, GRBs are really rare. Like really, really rare. There may be only two or three in an entire galaxy every MILLION years! The ones we have detected (thanks to our satellites) are billions of light years away.

Today's historical anniversary is for a record-breaking gamma-ray burst that was detected on this date in 2008. What was the record that was broken, you may ask? GRB 080319B is the farthest object that was observable with the naked eye. It had an apparent magnitude of 5.8 and was visible for about 30 seconds. 

(Apparent magnitude means how bright the object seems to us. It is a combination of how bright the object really is - the absolute magnitude - and how far away the object is. It's one of those tricky scales - the smaller the number, the brighter the object is, because ancient Greeks classified the brightest stars in the night sky as 1 and the dimmest stars visible as 6. The Sun is - 26.7 (notice that is a negative number!), the Moon is - 12.6, Venus is -4.4, and the brightest nighttime star, Sirius, is -1.4.) 

Note that the GRB is, at 5.8, only barely visible to the human eye. On a really clear night with no light pollution, there were still thousands - maybe around 4,000! - stars brighter than this gamma-ray burst was, back in 2008. A tiny pebble burning up in our atmosphere (a "falling star") would have been more noticeable that night. 

But that's still amazing - because the GRB was 7.5 BILLION light-years away from us. When the electromagnetic radiation started traveling Earthward, there was no Earth, and there was no Sun. Our solar system wouldn't form until the GRB was about halfway to us!

W - O - W!

Also on this date:

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