Alien Sun followup

By Phil Plait | June 28, 2007 2:34 pm

There has been some interesting fallout from the Alien Sun debunking I wrote last night.

I talked to Steve Majewski, the lead author on the horribly maligned scientific paper about the Sagittarius Dwarf galaxy. He thanks me for saving him the trouble of having to debunk the claim himself. :-) He has updated his original page about all this with a disclaimer saying the Viewzone article is wrong, too.

But while we were talking, he pointed out that I made a mistake!

Before I go into details, let me add that the error I made does not in any way negate the facts that

1) The claim that the Sun came from a different galaxy is wrong, wrong, wrong, and
2) The Sun orbits the Milky Way smack dab along the MW’s disk plane. That one fact alone kills the alien Sun claim.

What I said was that the plane of Sag Dwarf stream was perpendicular to the Galactic center. Turns out that’s not right. I was basing this on a still frame from an animation based on the original data, showing the stream, the Milky Way, and the position of the Sun.

The problem was, I was seeing all that from one angle. I didn’t realize it was from an animation! Dr. Majewski pointed this out, so I looked at it. If, in fact, you freeze the movie at a different spot, you get another angle on the issue:


Interestingly, from this angle, you can see that coincidentally, the stream’s plane does, more or less, cut across the Galactic center. Also — though you can’t tell from the video — the plane of the solar system, while not aligned with the stream, isn’t hugely far off either from the plane of the stream, either (though not exact, of course).

However, and this is a big but, it doesn’t matter. It’s irrelevant. The key issue is that the Sun is well-known to orbit the MW center in the plane of the Galaxy’s disk, and therefore cannot be from the dwarf.

And I have to add: while looking at the animation, it’s also clear that where the stream intersects the MW disk is not right next to the Sun; it’s displaced a bit. Remember, that point of intersection is what started this whole thing.

AND, something I totally forgot to add in yesterday’s entry: the Sun is near that intersection point… now. But 50 million years ago (yesterday in terms of the Sun’s lifetime) the Sun was 90 degrees around the Milky Way from the stream! The Sun orbits the Galactic center every 200 million years or so. That means that right now, at this particular slice of time, we’re near the intersection of the dwarf’s stream and the Milky Way. but in a few million years we’ll be plenty far away. And over the 4.6 billion year lifetime of the Sun, we’ve passed in and out of that stream probably many times as the Sun has orbited the Milky Way.

So that’s another reason the Viewzone claim of the alien Sun is wrong. You can’t say, "Look at how close the stream is the Sun; we must be from that galaxy!" when 50 million years ago the Sun was tens of thousands of light years from the stream.

Fail.

So I will happily admit I made a mistake. It was a small one, and irrelevant (though if it were a big one I’d still admit it; that’s just the way I am). But in finding my own error I found two more reasons Viewzone is wrong. I wonder: will that article get retracted? Anyone wanna take bets?

Incidentally, this silliness has gotten national attention. Even Amanda Cogsdon was fooled by it (4:45 into that video). I left her a comment; we’ll see if she gets back to me. :-)

Comments (19)

  1. Geraint Lewis

    Two points of interest:

    1) The intersection of the orbit with the Sun is interesting from the fact that DM is streaming along the stream and so there is an enhanced chance of detection.

    2) Yes – the Sun does not come from Saggy, but that does not mean it was not made outside the MilkyWay and brought in on a different merger event.

  2. Geraint

    If the Sun came from a “different merger event” how did it manage to get its galactic orbit in the plane of the Milky Way?

    As anybody familiar with astronautics surely knows, changes in the orbital plane are very expensive indeed

  3. Stark

    Geraint, since the sun orbits directly in the plane of the rest of the galaxy it actually does mean it was most likely born here. It is highly unlikely to have a wandering object drop into orbit in the exact same plane as the rest the galaxy. Were the sun a captured item it would almost certainly be on a different plane and quite likely have a much more eccentric orbit than the rest of the MW’s stars – much like comets tend to have eccentric orbits through the solar system. As it is, Sol’s orbit in the galaxy is wholly unremarkable in the galactic population.

  4. Geraint Lewis

    Nope – Approximately in-plane accretions are pulled into the plane even more, and orbits are circularized. I am very familiar with dwarf galaxy orbits.

  5. Brent

    Phil said:

    “AND, something I totally forgot to add in yesterday’s entry: the Sun is near that intersection point… now. But 50 million years ago (yesterday in terms of the Sun’s lifetime) the Sun was 90 degrees around the Milky Way from the stream!…So that’s another reason the Viewzone claim of the alien Sun is wrong. You can’t say, “Look at how close the stream is the Sun; we must be from that galaxy!” when 50 million years ago the Sun was tens of thousands of light years from the stream.”

    Playing devil’s advocate, isn’t this reasoning kind of circular? (pun intended). You’re assuming that the Sun is part of the Milky Way (and not the dwarf), and was therefore in a different part of its galactic orbit 50 million years ago. You can make that assumption, but you can’t use it to prove that the Sun is part of the Milky Way and not the dwarf.

  6. Scott G.

    Brent,

    That would only be circular if he were assuming that the Sun orbited the center of the MW. As stated, the Sun’s path is already known to follow the galactic plane, so it can be stated with reasonable accuracy where the Sun was positioned 50 million years ago, which was nowhere near the Sag. dwarf galaxy’s path.

  7. Geraint

    Orbits can be circularized indeed, but on what timescales? We are talking about the Sun born in another galaxy, this galaxy getting “eaten up” by the Milky Way, our orbit changing its plane to within the MW’s average thickness, and then even made “almost circular” to the point of obliterating all signs of the previous galaxy. What mechanism do we know that allows that in around 20 or 25 orbits? What has driven all those giant changes in the Solar momentum, and angular momentum?

    How unlikely!!!

  8. Does the sun not bob up and down in the galactic plane as it orbits the Milky Way (like horses on the carnival merri-go-round)? I recall hearing an interview on CBC’s Quirks and Quarks with Dr. Adrian Melott, relating this theoretical periodicity with a cyclical series of extinction events. Link to interview: http://www.cbc.ca/quirks/archives/06-07/may05.html#5

    What has this got to do with saggy? I doubt we’d have been able to do the math on this if we were a part of it, and not the Milky Way.

  9. slang

    Geraint Lewis said: “Yes – the Sun does not come from Saggy, but that does not mean it was not made outside the MilkyWay and brought in on a different merger event.”

    That’s not the point. The original website made a sweeping claim based on ridiculous arguments that they alledged proved that the Sun *was* from Sag. D. and BA’s long debunking post exposed that idiocy. When BA writes “The claim that the Sun came from a different galaxy is wrong, wrong, wrong” I am pretty confident that he refers to that specific, ridiculous claim.

    Other than that all we can say is that the evidence we see is compelling for the sun to have originated in the Milky Way or to be absorbed a long time ago from another galaxy with similar iron content. Other studies might give more evidence for either possibility, maybe some already have, I don’t know.

  10. Geraint Lewis

    Perhaps you should have a read of papers such as

    Accretion relicts in the solar neighbourhood: debris from omegaCen’s parent galaxy
    Authors: Andres Meza, Julio F. Navarro, Mario G. Abadi, Matthias Steinmetz

    Pieces of the puzzle: Ancient substructure in the Galactic disk
    Authors: Amina Helmi, J.F.Navarro, B. Nordstrom, J. Holmberg, M.G. Abadi, M. Steinmetz

    and similar articles, including the extensive discussion on the canis major dwarf and (possibly) associated Monoceros stream? Accreted dwarfs can be pulled into the disk in a couple of orbits and the kinematic signatures of their origins lost quite quickly.

    I agree that it is more likely that an accerted star ends up in the thick disk, but it is clear that a couple of GYrs is all that is needed for a star to end up in the disk on a circular orbit. Once they are there, they are hard to see.

  11. I could not find the link to BA’s comment on the ABC blog, can anyone post it here (Link or comment)

    I prefer this sort of Milky Way drool :)

  12. PK

    Geraint, you may well be right about relaxation into circular orbits in the galactic plane. You probably know more about stellar orbital dynamics than I do. However, what you seem to be saying is that “we have no solid evidence for a very unlikely scenario A, but we should not rule out another, equally unlikely scenario B, for which we also do not have supporting evidence.”

    Technically, you are correct of course. But it is not really relevant to this discussion.

  13. heng

    hmm… a question to the video fly-around:
    why isn`t the milkyway distorted?

    any quasi-simulations and depictions of collision events _both_ systems tend to be distorted… is in the video “our” galaxy deliberately left untouched in a more-or-less generic perfect spiral form?
    i know, e.g. that we don`t know the layout of a pretty large part of the plane (beyond the hub)…

  14. heng

    sorry for doubleposting, but another thing i didn`t get with the original article linked here is:

    [quote]“If people had infrared-sensitive eyes, the entrails of Sagittarius would be a prominent fixture sweeping across our sky,” Majewski said.[/quote]
    so far so good. but on the image on the bottom of the same page there is a [quote]2MASS view of the entire sky[/quote]… meaning: a full(!) sky mosaic in 2micron infrared… yet i don`t see _any_ of the structures depicted in the video…

    something doesn`t add up in my head without further explanation…
    could you provide some?

  15. Sergeant Zim

    [quote]”If people had infrared-sensitive eyes, the entrails of Sagittarius would be a prominent fixture sweeping across our sky,” Majewski said.[/quote]

    Pardon me, but isn’t infrared the portion of the EM spectrum that is most efficiently filtered out by our atmosphere?(Thus the Spitzer telescope) Ergo, if we were to see in IR, we still wouldn’t see Saggy at all…

  16. CS

    Heng:

    The reason the Milky Way is not distorted is that it is far more massive than the Sagittarius dwarf galaxy. Think of a comet and the Sun: the comet’s orbit is highly dependent upon the Sun, but the Sun’s motion is hardly perturbed by a passing comet. The number of particles used for each of the two galaxies in the simulation is not indicative of the masses involved (i.e. 1 MW particle does not equal 1 Sgr particle).

  17. Irishman

    Nice followup, with the link to the University of Virginia page. That animation was interesting to rotate.

    That page also answered my other question, why is the Sag Dwarf galaxy stretched into a Q shape around the MW? The other animation on that page shows the dwarf galaxy as it rotates while orbiting the MW. The gravitic and inertia forces stretch and elongate the galaxy, swinging some parts wider than other parts, and creating the long streamer swirls that don’t follow in a neat circle. Cool!

    I still think you might be begging the question with that comment about the Sun being on the other side of the MW 50 Mya.

  18. Geraint, you have made a legitimate point, so I posted again about this.

  19. Mapnut

    It seems to me that Dr. Majewski has been somewhat victimized by his tendency to use colorful language, such as “who’s the bully” “eating its smaller neighbors”, “stars are now raining down on our present position”, and “debris trail”, which implies massive destruction. This might attract people looking to create a sensation, and help fool the gullible by distorting the time frame. If a star from Saggitarius was passing near us at a large angle to the galactic plane, we could hardly see the change in its position in our lifetime, if I’m not mistaken (speaking of amateur observers, of course).

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