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WR 104 Won’t Kill Us After All

WR 104, not so scary (Keck)

WR 104, not so scary (Keck)

Early last year, concern was growing for a Wolf-Rayet star named WR 104 that appeared to be aiming right at Earth (see Looking Down the Barrel of A Gamma Ray Burst). A Wolf-Rayet star is a highly unstable star coming to the end of its life, possibly culminating in a powerful, planet-killing gamma-ray burst (GRB). GRBs are collimated beams of high energy gamma-rays, projected from the poles of a collapsing Wolf-Rayet star. It was little wonder that we were concerned when a dying Wolf-Rayet star was found to be pointing right at us! Today, at the AAS in Long Beach, one scientist working at the Keck Telescope has taken a keen interest in WR 104 and shared new findings that show our Solar System may not be bathed in deadly gamma-rays after all…

Wolf-Rayet stars are evolved massive stars undergoing a suicidal and violent death. They are very hot (up to 50,000K) and losing mass very quickly, generating powerful stellar winds (at velocities of 2000 km/s). WR 104 was imaged using the Keck Telescope in Hawaii last March, and images of the pinwheel spiral star system appeared to show that we were “looking down a rifle barrel”.

So what is causing this spiral structure around WR 104? The star has a binary O-type star partner, so as WD 104 sheds its mass, the stellar winds spiral outward. As we are seeing the full spiral from Earth, it was therefore reasonable to assume the binary system was facing right toward us. As WR 104 probably has its pole pointing 90° from the ecliptic plane, any future GRB could be directed straight at us.

WR 104 is a fascinating object that got a lot of press last spring,” Dr Grant Hill said during the AAS meeting today (Jan 7th). “Since the object is in our galaxy, it could be devastating [for Earth]”

Hill therefore decided to confirm previous Keck observations with spectroscopic data to find out if there could be the possibility of an Earth-directed GRB. His work confirms the system is a binary pair, orbiting each other at an 8 month period. Hill also confirmed the presence of a shock front between the stellar winds of WD 104 and O-type partner. And there is some very good news for Earth. It would appear the original Keck imagry may not have been as straight-forward as it seemed. Spectroscopic emission lines from the binary pair strongly suggest the system is in fact inclined 30°-40° (possibly as much as 45°) away from us.

So, Earth doesn’t appear to be in the firing line of WR 104 after all…

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Hello! My name is Ian O'Neill and I've been writing for the Universe Today since December 2007. I am a solar physics doctor, but my space interests are wide-ranging. Since becoming a science writer I have been drawn to the more extreme astrophysics concepts (like black hole dynamics), high energy physics (getting excited about the LHC!) and general space colonization efforts. I am also heavily involved with the Mars Homestead project (run by the Mars Foundation), an international organization to advance our settlement concepts on Mars. I also run my own space physics blog: Astroengine.com, be sure to check it out!

Comments on this entry are closed.

  • Don Alexander January 7, 2009, 3:47 PM

    So now someone needs to explain why we are seeing what’s basically a perfect spiral, and not ellipses as one would expect for such an inclination.

    Also, it’s “devestating”, as far as I know.

  • Olaf January 7, 2009, 4:18 PM

    A GRB is probably the only thing in the near future that could actually destroy life on Earth.

    Even the Mayans did not see this coming!

  • Mang January 7, 2009, 4:36 PM

    Well I’m relieved!

  • BR January 7, 2009, 4:49 PM

    “As WR 104 probably has its pole pointing 90° from the ecliptic plane”

    Is this a typo? I don’t see what the ecliptic has to do with anything.

  • DH January 7, 2009, 5:33 PM

    It’s “devastating” — the dictionary is your friend.

  • Olaf January 7, 2009, 5:47 PM

    “”As WR 104 probably has its pole pointing 90° from the ecliptic plane”
    Is this a typo? I don’t see what the ecliptic has to do with anything.”

    I agree, and I even would expect 2 angles not one. But what has that to do with the location of our solar system?

  • pmf71 January 7, 2009, 6:07 PM

    They assumed the poles of WR-104 are pointing 90 degrees from the ecliptic plane of the system in which it resides. And they also though they were looking at the system head-on (also 90 degrees) which meant they were looking down the barrel of the GRB shotgun.

  • kenn hammer January 7, 2009, 6:22 PM

    Its so long away that maybe theres something really big blurring our view. So maybe its not pointet near us at all. but what the hell nobody knows.

  • Salacious B. Crumb January 7, 2009, 9:21 PM

    The Wolf-Rayet WR 104 or V 5097 Sgr is placed in Sagittarius, whose position is 18h 02h 04s -23deg 37′ 41″. This is merely 11 arcmin from the Earth’s ecliptic plane, and is occulted by the Sun on 21 December each year. (If it “went off” that the day you wish it would.)
    The best orbital period we know for these stars is about 241.5+/-0.5 days, as published by Tuthill, P.G. et.a; “The prototype colliding-wind oinwheel WR 104.”; Astrophysical Journal, 675, 698-710 (2008), which was determined using the Keck Aperture Masking Experiment. The abstract says the inclination (i) is <16 degrees
    I think what was meant was that the both stars pole was pointing directly at us, and this assumes that the poles are perpendicular to the orbital plane of the binary system. This is evident from the fact that the spiral pattern appears as if we are looking directly down on its disk. If this were not the case, then the pattern overall would look elliptical.
    Also, was the presenter Hill or Tuthill – an amazing coincidence considering they are observing the same telescope in the similar, if not the same year?
    Anyway, it is good news, as this object passes almost overhead everyday from my location. Summer here now is too darn hot already, let alone to be fried by some eminent supernova.
    Thanks for the update.

  • some dumb kid January 7, 2009, 9:31 PM

    phew! one less thing to keep me up at night!

  • Mr.Obvious January 8, 2009, 6:48 AM

    Just because we may be viewing the spiral at an angle, does not mean the spiral should be mis-shapen. First of all, the images we look at are in 2-D; which makes it very difficult to determine depth; distance and the lack of a second object nearby for relationship also make determining angle hard.

    Take any piece of paper, make swirls and then tilt it 20 degrees or so… no distortion.
    Use a 3-d object (like stiff wire), and at a low deflection angle (as long as the swirls are large) you will not notice any great difference either.

  • Mr.1=0 January 8, 2009, 7:48 AM

    Mr Obvious
    Your argument here doesn’t make much sense.
    If the spiral is tilted 0.1 degrees, 20 degrees, or even 30 to 40 degrees, the whole spiral would not be circular, but be shaped like an ellipse not a circle – which is a special condition when the inclination of the pole is exactly zero. I.e. Facing towards us.
    Don Alexander is right. If the tilt of the spiral was inclined at 40 or 50 degrees, as the article says I.e. “…strongly suggest the system is in fact inclined 30°-40° (possibly as much as 45°) away from us.”, the effect would be plainly obvious.

  • jerry January 8, 2009, 12:17 PM

    What should material gravitationally spiraling inward look like? Think of the orbits of the planets, it should get tighter and tighter, ALWAYs, regardless of the angle of observation being somewhat ellipical, as this one is. It is also not necessarly true that the pole of the star is perpendicular to the spiraling accretion flow. Close examination of the minute changes in the spectra are what demonstrate this spiral does not point towards us.

  • Tom January 9, 2009, 11:24 PM

    it probably blew up already by the time the light from the explosion reaches earth

  • Dan January 9, 2009, 11:55 PM

    Hey i got a question and something i really want this website to look into. I want them to look into the rouge planet Niburu. EVERYTHING ABOUT IT. like for example why is it not being announced that it is getting closer. why is it blacked out everywhere on google sky and microsoft telescope. plz look into this!

  • Barak January 10, 2009, 2:42 PM

    I like how so many individuals are assuming that the spiral waves are “circular,” though they don’t state what they mean by that – presumably that the wavelength of the spiral waves is the same measured across the x-axis as across the y-axis for any arbitrary xy coordinate system in the plane of the binary orbits centered at the origin of the spiral. However, most binary objects don’t revolve around each other in circular orbits but in elliptical orbits, and thus the spiral wave itself might be “elliptical.” This leave the odd possibility that the tilt of the orbital plane with respect to Earth is such that the long axis of the spiral wave is foreshortened just enough to make it look circular from the Earth’s point of view.

  • Mr. 1=0 January 11, 2009, 1:02 AM

    Drawing at straws is no basis of science.
    The fact, as given by Salacious B. Crumb, is that;
    “Tuthill, P.G. et.al.; “The prototype colliding-wind pinwheel WR 104.”; Astrophysical Journal, 675, 698-710 (2008), which was determined using the Keck Aperture Masking Experiment. The abstract says the inclination (i) is <16 degrees”
    Therefore, the inclination is less than 16 degrees and is not zero. Then the appearance cannot be, as Don Alexander says in the first post; “basically a perfect spiral.” In addition, as you are talking in xy co-ordinate your admitting the spiral is projected across some flat plane. It is the orientation of that projected plane of the whole spiral that is being questioned here. I.e. It is inclined somewhat to the line of sight.
    As for saying; “This leave the odd possibility that the tilt of the orbital plane with respect to Earth is such that the long axis of the spiral wave is foreshortened just enough to make it look circular from the Earth’s point of view.”
    This is again just paraphrasing Mr.Obvious statement that doesn’t make any sense.
    Well doesn’t this assume “that the spiral does look circular from the Earth’s point of view”, but as already shown by Tuthill’s paper, this is simply not the case. Fact.
    As for the influence of the companion star on the spiralling accretion disk, well yes, there is some influence, but it is inconsequential. Think of satellites orbiting the Earth. How much gravitational influence is exerted on their motion say by the Moon?
    You also state; “However, most binary objects don’t revolve around each other in circular orbits but in elliptical orbits, and thus the spiral wave itself might be “elliptical.” ”
    Well this is only partly true. For close binary systems, whose separations are in the tens of millions of kilometres, most orbits are very close to circular. For wider system binary stars, say like Alpha Centauri, whose semi-major distances are expressed in several to many astronomical units (AU), the orbits tend to be ellipses.
    Also, note the spiral has different densities of brightness following the whole path of the spiral towards the star. Why is that? Note also carefully that the edges around the image the spiral shape is not exactly coherent after about 650 degrees.
    Clearly, this is not a perfect spiral of gas.
    Like Mr. Obvious before you, Barak, your argument isn’t very logical nor is it very convincing.

  • barakn January 11, 2009, 2:16 PM

    Mr. 1=0,

    When they said i<16, they obviously meant 0 <= i < 16. And obviously you missed it but, they stated the best fit was 12 degrees. With an inclination of 12 degrees, we’re looking at a stretching factor of one dimension vs. another of cos 12 degrees = .98, a difference of only 2%. Considering the size of the image, that comes down to a difference of a handful of pixels. But you don’t need to take my word for it. In the words of one of the authors of the paper you quoted, Peter Tuthill:
    “Under the assumption that this should in reality be a pure, planar, Archimedian spiral…[t]he formal best-fit is an inclination of 12 degrees, but this is a hard number to extract. The difficulty lies in that a small tilt in the structure only gives a very small change in the aspect ratio. So values anywhere in the range from exactly face-on to 16 degrees are probably OK. In fact, maybe even a wider margin than that needs to be included, because we are looking through a partly optically-thin strucutre [sic].” http://www.physics.usyd.edu.au/~gekko/pinwheel/tech_faq.html

    In case I need to spell it out for you, “face-on” means 0 degrees.

    You call the spiral an “accretion disk” when it is plainly not a disk, nor is there accretion (the gas and dust are moving outward, not inward). As was stated very clearly in Tuthill’s paper, the companion star is very important, as the opposing stellar winds between the two stars is what compresses the gas to high enough concentrations to form dust. This has very little to do with gravity, meaning your Moon analogy was pointless.

    Nor is your statement about close binary systems relevant. Both of these stars are very massive but their revolution period is 220 days, suggesting they are not very close to each other. Using 25 and 15 solar masses, I calculate a semimajor axis of 2.4 AU, which falls in your category of “wider system binary stars, say like Alpha Centauri, whose semi-major distances are expressed in several to many astronomical units (AU), the orbits tend to be ellipses.”

    “Clearly this is not a perfect spiral of gas.” I never said it was. Naturally there’s going to be a bit of chaos in this system. Also, if the orbits are elliptical, there may be varying amounts of gas created as the distance varies. This adds support to my argument, rather than being evidence against. Knots of dust could also be produced by the gravitational influence of other minor objects in the system.

    I will give you one point though: the best fit was not i=0. So I’ll amend my statement to read thusly: “”This leave the odd possibility that the tilt of the orbital plane with respect to Earth is such that the long axis of the spiral wave is foreshortened just enough to make it look almost circular from the Earth’s point of view.” There – see that extra “almost” in there? That’s thanks to you.

  • Bloviating one April 7, 2009, 6:37 AM

    And here I was wishing my heart out that the GR burst would hit first on Ann Coulters head. Oh, well. Maybe she’ll move on top of a super volcano or something. One can hope.

  • Ana Thomas April 7, 2009, 12:27 PM

    Only God knows when the Earth is going to end!!!

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