A ‘bizzare star’, an incomplete explanation

NASA just announced the discovery of a previously unnoticed astronomical phenomenon, a star exhibiting ‘comet-like’ behavior (H/T Personal Demon). This can be read about both on NASA’s web page as well as through CNN.

A large star in its death throes is leaving a huge, turbulent tail of oxygen, carbon and nitrogen in its wake that makes it look like an immense comet hurtling through space, astronomers said on Wednesday.

Rocketing through our Milky Way galaxy at 80 miles per second — literally faster than a speeding bullet — the star is spewing material that scientists believe may be recycled into new stars, planets and maybe even life.

“We believe that the tail is made up of material that is being shed by the star which is heating up and then spiraling back into this turbulent wake,” said astronomer Christopher Martin of California Institute of Technology, one of the researchers in the study published in the journal Nature.

There’s something about the explanation, at least as presented, which seems to me to be highly misleading, and possibly wrong.

According to the well-established principles of Einstein’s special relativity, a solitary object streaking through ‘open space’ can’t possibly have a tail. Special relativity asserts that there is in fact no such thing as absolute motion, only relative motion between objects. This means that a person in a spaceship moving at a constant velocity will be unable to detect physically any motion of himself or the ship. From his/her point of view, the spaceship is stationary, and everything else around is moving. There is no direction of motion according to the spaceship pilot, and therefore can’t be a tail ‘behind’ the ship.

One possibility is that the star is ejecting material asymmetrically, more in one direction than another (in the same way a flashlight radiates light more in one direction than others), but this would cause the motion of the star, not be a consequence of motion.

Why, then, does a comet have a tail? The tenuous material surrounding a comet is pushed away from the sun by radiation pressure and solar wind. In other words, the sun is constantly radiating stuff (photons and ions) and that stuff pushes material off the comet and away from the sun. And this is what seems to be missing from the star-tail explanation: in order for the tail to be produced by the relative motion of objects, either the star has to be traveling through something (some sort of gas cloud, probably) or interacting with some other large object, probably gravitationally.

This is sort of hinted at on the NASA page, in the images in which one sees a ‘bow shock’ in front of the star, like a bullet passing through air at supersonic speeds. You can’t have a bow shock without passing through a medium. However, neither the NASA page nor the CNN page mention this explicitly, though I’m sure NASA’s physicists are certainly aware of it.

This concludes my nitpicking of NASA’s press release. Having done a couple of these regarding my own research, however, I can tell you that it’s often hard to get material out that both comprehensible and scientifically correct.

I’ll probably start doing some elementary relativity posts for kicks in the near future…

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2 Responses to A ‘bizzare star’, an incomplete explanation

  1. Personal Demon says:

    So, the interesting thing here is that this star is inexplicably leaving a trail of potential star material in its wake (sort of like Prince in the early 80’s), not just that it’s moving? I guess that makes sense. I mean, everything in the universe is moving. Even Earth is orbiting at nineteen miles a second, so it’s reckoned, a sun that is the source of all our power.

    [My apologies. I’m just learning HTML, and I’m going through the obligatory hyper-hyperlinking phase. I also use movie/TV quotes as a substitute for a personal sense of humor. Pity me.]

  2. skullsinthestars says:

    PD wrote: “So, the interesting thing here is that this star is inexplicably leaving a trail of potential star material in its wake…not just that it’s moving?”

    I would say so. Especially in our own galaxy, we wouldn’t expect everything to be moving directly away from us; some objects would certainly have some transverse motion relative to us.

    I wouldn’t say it’s ‘inexplicably leaving a trail’; I’m sure the scientists have a perfectly good idea why it’s happening (I hope). I just found it interesting and a bit maddening that this wasn’t addressed in the press releases.

    (Sorry about the delay in replying. The comment got held up in the moderation queue for some reason, even though it shouldn’t.)

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