Wr-104

[shadron]

In my pursuit of catastrophe stories, I just viewed the recently released the video: The Universe - Death Stars. It was done by the History channel and seems to have an unusual amount of "gloom-doom -repent now and buy our insurance" sort of urgency, not to speak of the breathless errors the narrative/narrator interject. "Igniting the ozone layer", with the repeated imagery of an recurve archer with a flaming arrow either hitting or missing an NAA-approved Olympic competition 70 meter target face at the range of perhaps 20 meters, forsooth. Far out.

The first of several problems discussed was that of WR-104, a binary star pair about 8000 LY form here. Both of the stars are at about 20x sun mass, and so have great potential for going nova soon. One of the two is a Wolf-Rayet (W-R) star, which continuously throws off an exterme amount of its mass as solar wind. The speculation is that the W-R star is capable of causing a gamma ray burst (GRB). WR-104 was described in a set of papers by Peter Tuthill in 2009. Of particular interest is that the two stars interact to focus the WR stars emissions into a spiral that moves outwards. The spiral seems to be face onto us (Tuthill estimates that we are no more than 16 degrees from the axis) which potentially brings us into the GRB focus if/when the WR goes nova. At the range of 8000ly the results may be pretty bad for us. Phil wrote this up on his Bad Astronomy blog; another recent paper brings the exact angle that we are viewing the spiral into question: http://www.universetoday.com/2009/01/07/wr-104-wont-kill-us-after-all/

For those who have astronomy backgrounds, I'd like to ask the following questions:

1. Is a W-R star particularly prone, theoretically, to cause a GRB? I see a lot of equivocation about this in the papers I've read.
2. Is the assumption that the W-R star's spin equator (which defines the axis of the GRB, as I understand it) equates to the spiral's "equator", which I presume matches the ecliptic of the binary star system, a good assumption? Out of suriosity, what about the other star?
3. I understand that trying to measure a presumed major and minor axis of the spiral, in order to see if we are face onto it or not is going to be frought with large error estimates, but is the difference between Tuthill's "0-16 degrees" vs the later "30-40, perhaps 45 degrees" a reasonable observational difference?
4. Are there other considerations which may make the spiral appear space-front when it actually isn't? I understand that the spiral is an observational phenomenon, that the actual particles making it up are travelling outwards radially; could they be excited in an unusual manner or some such so that the spiral itself is not indicative of the ecliptic/axis of the two stars?

[Perpetual Student]

Could a stellar event 8,000 light years away really effect the earth? I have no idea, but I do find that astonishing!

[shadron]

Could a stellar event 8,000 light years away really effect the earth? I have no idea, but I do find that astonishing!

Yes, I believe it could, if the event was a GRB and we were in its crosshairs.

There is an hypothesis (from scientists at Kansas U and NASA) that the second greatest extinction event in the history of Earth, the Silurian-Ordovician event 444 MYA, was caused by such an event; it was used in an episode of Animal Armageddon (associated with Animal Kingdom). There is no smoking gun; the hypothesis will probably not be proven until gamma ray exposures of the moon are measured.

It is interesting that if such an event occurred, it would have lasted here on Earth for all of 10 seconds, but would have destroyed about 50% of the ozone in the atmosphere, allowing up to a 50x increase in ultraviolet radiation. Recovery would take around 5 years. There would also be cooling from nitogen oxide (smog) in the air, and acid rains for quite a while.

[Perpetual Student]

There is an hypothesis (from scientists at Kansas U and NASA) that the second greatest extinction event in the history of Earth, the Silurian-Ordovician event 444 MYA, was caused by such an event
OK, "GRBs are collimated beams of high energy gamma-rays, projected from the poles of a collapsing Wolf-Rayet star," according to the link you provided.
At 8,000 light years, would not the beam become spread out considerably before it reached the earth? We have a star only 8 light minutes away, producing solar gamma ray bursts, that we can tolerate quite easily.
I have absolutely no way of understanding how it is possible for such a distant object to be a threat. Could you or anyone else elaborate?

[iMaGiNaTioN]

I saw this same show. As if I didn't have enough to worry about; now, I lay awake at night waiting for stars in distant galaxies to nova. Thanks History.

[BenBurch]

I'm not sure we have EVER sourced a GRB to a particular star. I believe that unlikely as they are observed at cosmological distances. Now, a WR star THEORETICALLY could cause a "hypernova" in which there is an asymmetrical collapse and a GRB is formed, but I do not believe we have ever observed that, and the belief is the result of simulation.

[shadron]

OK, "GRBs are collimated beams of high energy gamma-rays, projected from the poles of a collapsing Wolf-Rayet star," according to the link you provided.
At 8,000 light years, would not the beam become spread out considerably before it reached the earth? We have a star only 8 light minutes away, producing solar gamma ray bursts, that we can tolerate quite easily.
I have absolutely no way of understanding how it is possible for such a distant object to be a threat. Could you or anyone else elaborate?

Read further:
Gamma-ray bursts are very bright as observed from Earth despite typical immense distances. An average long GRB has comparable bolometric (http://en.wikipedia.org/wiki/Bolometric_magnitude) flux to a bright Galactic star despite a distance of billions of light years (compared to a few tens of light years for most stars). Most of this energy is released in gamma rays, although some GRBs have extremely luminous optical counterparts as well. GRB 080319B (http://en.wikipedia.org/wiki/GRB_080319B), for example, was accompanied by an optical counterpart that peaked at a visible magnitude (http://en.wikipedia.org/wiki/Visible_magnitude) of 5.8,[44] (http://en.wikipedia.org/wiki/Gamma-ray_burst#cite_note-Racusin-46) comparable to that of the dimmest naked-eye stars despite the burst's distance of 7.5 billion light years. This combination of brightness and distance requires an extremely energetic source. Assuming the gamma-ray explosion to be spherical, the energy output of GRB 080319B would be within a factor of two of the rest-mass energy (http://en.wikipedia.org/wiki/Mass-energy_equivalence) of the Sun (the energy which would be released were the Sun to be converted entirely into radiation.) [26] (http://en.wikipedia.org/wiki/Gamma-ray_burst#cite_note-Bloom-27)[Shad Note: that is about as big as any short-term explosion imaginable. Larger explosions would have to take longer due to interactions which must proceed at the speed of light, at best.]

No known process in the Universe can produce this much energy in such a short time. However, gamma-ray bursts are thought to be highly focused explosions, with most of the explosion energy collimated into a narrow jet (http://en.wikipedia.org/wiki/Relativistic_jet) traveling at speeds exceeding 99.995% of the speed of light (http://en.wikipedia.org/wiki/Speed_of_light).[45] (http://en.wikipedia.org/wiki/Gamma-ray_burst#cite_note-47)[46] (http://en.wikipedia.org/wiki/Gamma-ray_burst#cite_note-48) The approximate angular width of the jet (that is, the degree of beaming) can be estimated ... from between 2 and 20 degrees.
So, at 8000 ly, it would destroy ozone layers in an area at least 40 ly in diameter.

Whatever it is the sun is doing, it is not creating a GRB. Surely, it does emit some gamma rays. But the difference betwee the flux of a GRB and what the sun does is at least 12 to 15 orders of magnitude.