[BRIEF NOTE] Death from above

[rfmcdonald]

Browsing Wikipedia in the aftermath of Saturday's linkage to articles on the brightest gamma-ray burst ever discovered, I came across an interesting link to the star WR 104, located about eight thousand light years away from the Earth. WR 104 is a binary star, both components of which are Wolf-Rayet stars, relatively evolved, quite hot, and quite massive stars that shed their mass quickly though not always quickly enough to avoid going supernova. As it turns out, WR 104 might actually threaten Earth with a nearby gamma-ray burst--Bad Astronomer has more on WR 104's specialness.

GRBs are a special type of supernova. When a very massive star explodes, the inner core collapses, forming a black hole, while the outer layers explode outwards. Due to a complex and fierce collusion of forces in the core, two beams of raw fury can erupt out of the star, mind-numbing in their power. Composed mostly of high-energy gamma rays, they can carry more energy in them than the Sun will put out in its entire lifetime. They are so energetic we can see them clear across the Universe, and having one too close would be bad.

Enter WR 104. The brighter of the two stars might, just maybe kinda possibly, be ready to go GRB on us. It’s not at all clear if it can, and there is reason to believe it can’t (young stars like this one tend to have characteristics that make it very hard for them to form an actual GRB). Also, even if it does blow up that way, the beams are a double-edged sword; yes, they pack an unbelievable punch, but they’re narrow. A GRB would have to be aimed precisely at us to damage us, and the odds of that are pretty low.

Except that for WR 104, it’s possible the star does have us in its sights.

The only way to know which direction a potential GRB’s beams will blast out is to look for some signs in the system of symmetry; a disk of gas, for example, would orbit the star’s equator, so the poles of that disk would be the direction the beams would follow. WR 104 does have a feature that allows us to determine its orientation — a vast spiral of material being ejected from the system.

[. . .]

The thing to note is that we really are looking at this spiral almost face-on, more-or-less down the pole of the system (it appears to be tilted by about 12 degrees from face-on, but it’s difficult to measure, and could be tilted by anything from 0 - 16 degrees — [Dr Peter] Tuthill’s technical paper has details). It’s hard to say exactly, but it’s close enough to make me wonder.

If the brighter of WR 104's stars were to explode and if its axis points towards the Earth, it could well irradiate the Earth. The impact wouldn't be planet-destroying so much as mass extinction-causing, between the high-energy radiation that would bathe the Earth and the muons that would impact the Earth at relativistic speeds and do something (we're not entirely sure what; the computer models aren't complex enough). We have, in short, a reasonably plausible cosmic apocalypse in WR 104 A.

Tuthill's page on WR 104 is here, while the abstract and pre-print of Tuthill et al.'s "The prototype colliding-wind pinwheel WR 104", available in the 1 March 2008 issue of Astrophysical Journal, is available here. He also is kind enough to provide a page linking to some of the press coverage of WR 104.