Naked-Eye Visible GRB!

Bad Astronomy
The entire universe in blog form
March 20 2008 9:41 AM

Naked-Eye Visible GRB!

Holy Haleakala! Yesterday, a gamma-ray burst went off that was so bright that had you been looking at the right spot in the sky you could have seen it with just your own eyes!

It's difficult to put this into the proper context. GRBs are monumental explosions, the exploding of a massive star where most of the energy of the catastrophe is channeled into twin beams of energy. These beams scream out from the explosion like cosmic blowtorches, and for thousands of light years anything they touch is destroyed. Happily for us, GRBs always appear hundreds of millions or billions of light years away.

Let me put this in perspective for you. Imagine a one megaton nuclear weapon detonating. That's roughly 50 times the explosive yield of the bomb dropped on Nagasaki. Devastating.

The Sun, every second of every day of every year, gives off 100 billion times this much energy. That's every second. A star is a terrifying object.

In the few seconds that a gamma-ray burst lasts, it packs a million million million times that much energy into its beams. In other words, for those few ticks of a clock the GRB is sending out more energy than the Sun will in its entire lifetime.

There is, quite simply, no way to exaggerate the devastation of a gamma-ray burst.

Yet for all that, they are optically faint due to their terrible distance. At billions of light years away, even the Universe's second biggest bangs are difficult to see.

So that's what makes GRB 080319B (the second GRB seen on 2008 March 19) so incredible: distance measurements put it at 7.5 billion light years away, yet it was visible to the unaided eye had you just happened to be looking up at the sky at that moment.

Whoa.

This is the single brightest GRB ever seen in optical light, so as you can imagine reports are pouring in from observatories all over the world right now. Anything this bright must be extraordinary, and you can bet that astronomers will be falling over themselves to observe this incredible event. We still don't know enough about GRBS; just what mechanisms focus those beams? We know black holes are at their core, powering these events, but how do the gravity and magnetic fields come together to generate forces like this? How tightly focused are the beams? Do they open at a one degree angle? 5? 10? Why does every GRB behave somewhat differently, with some lasting for seconds and others for minutes?

And why was this one so frakkin' bright? Was it a more energetic explosion itself, or were we, by coincidence, looking precisely down the center of the beam? If the beam of a GRB is pointed ever-so-slightly away from us, so that the edge nicks us, the GRB will look fainter. By staring down the throat of a GRB we'd see it as bright as it could possibly be. Maybe GRB080319B had us dead in its sights.

Watching the extremes of GRB behavior can help us constrain the more normal aspects of them... if you can even use the word "normal" when it comes to such titanic explosions on these scales. There is a fascination we humans have with such terrible events, an atavistic thrill even when our puny brains can't comprehend the size and scale of them.

I wrote about GRBs extensively for my book Death from the Skies!, and spent a lot of time working through the math and thinking about the destruction they can wreak. If you want to know what my nightmares look like, then GRBs are a good place to start. I'm just glad there (most likely) aren't any stars nearby that can do this. I like GRBs... when they're far, far away.


Two notes to follow-up: according to the GRB Real Time Skymap (which I used to work on), there were 5 GRBs seen yesterday. That needs to be confirmed, but if true that's a record! Second, I've written quite a bit about GRBs on this blog, so feel free to go back and check out more on these incredible objects.

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