Image Credit: UC Berkeley / Keck Observatory
Last year, I blogged about the "Pinwheel Star", a pair of massive stars that looked like they might one day (in the next few million years) explode as gamma-ray bursts, bathing the Earth with a lethal dose of radiation and killing all life. Based on results from a new study, it looks like we will all live to see another day.
The study was presented by astronomer Grant Hill of Keck Observatory, who is also quite a fine fellow and has helped me out of many sticky spots while I've been observing at Keck. I also really like the findings because they are quite simple, which makes them all the easier to believe.
The idea behind the deadliness of the Pinwheel was that we seemed to be looking straight down on top of the two stars, and that gamma ray bursts tend to come out the tops of stars. What Grant discovered is that we are not looking straight down the barrel, but are actually quite a ways off to one side.
Grant measured this be measuring how fast the stars are moving toward and away from the Earth. The two stars orbit each other in a flat disk. Think of a vinyl LP (or a compact disc or a frisbee) spinning around. Now, pretend you are looking down on the top of the spinning disk. While you can see the spinning motion, no part of the disk is moving toward you or away from you. It's just going around in a circle, always at the same distance away. Now, think of looking at the spinning disk from its edge. Now, parts of the disk are getting closer to you, and parts are moving away.
In the case of the Pinwheel system, if we are looking straight down on the orbits of the stars, then, just like with the face-on spinning disk, we shouldn't measure any movement toward or away from us. We'll still see the stars moving around each other, but they aren't changing how far away they are from us.
Grant Hill's measurements found that the stars are actually moving toward and away from us. This means we aren't looking straight down on them. Grant's analysis suggests that we are actually seeing the orbits from about a 45 degree angle (halfway between edge-on and face-on). Should the stars blow up and send a gamma ray burst out along their poles (tops and bottoms), it won't be coming toward us. We're safe!
Well, maybe. Perhaps the poles of the stars are not aligned with their orbit. For the Earth, it's pole is 23 degrees away from the pole of its orbit. There's no reason that the stars can't be misaligned. In this case, there is still a very tiny chance that if one of the stars explodes, it could send a gamma ray burst toward us. But there are also reasons to think that the poles of the stars should be close to that of the orbit, in which case our viewing angle is far enough away that we are safe.
As always, we'll need to study more. But now we Earthlings can breathe a tiny bit easier!