Is the Sun from another galaxy?

The entire universe in blog form
June 27 2007 8:59 PM

Is the Sun from another galaxy?

Note: I generally don't do a thorough debunking of pseudoscientific nonsense on the blog, and instead relegate that to the main site. But I decided to do this on the blog, knowing that more people would read it than if I put it on the main site and linked to it from the blog. So here it is. Bon appetit.

We've always assumed the Sun was born in the Milky Way, and has been here its whole life. Is it possible it was actually born in a different galaxy, and the Milky Way stole it?

Phil Plait Phil Plait

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death from the Skies! Follow him on Twitter.

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Do we have (cue evil music)... an alien Sun?

No.

Oh, you want more info? Alrighty then, sit back. This'll be fun.

Introduction

A website called Viewzone recently posted an article claiming that scientists have determined the Sun is not native to the Milky Way Galaxy, but instead was absorbed by the Milky Way while eating a smaller dwarf galaxy.

There's just one eensy weensy problem with this: it's totally wrong.

Here's how the writer from Viewzone sets this up; I have synopsized but kept his argument intact:

1) The Milky Way is eating a smaller galaxy, called the Sagittarius Dwarf galaxy.

2) Because this galaxy has far less mass than our own, the Milky Way has far stronger gravity. This has destroyed the other galaxy, turning it into a long stream of stars.

3) This stream is at an angle to the plane of the Milky Way's disk, and intersects that disk.

4) The Sun is very near the position of this intersection. The odds of this happening are very low.

5) Therefore, the Sun originally came from the dwarf galaxy, and is not originally from the Milky Way.

I'm not exaggerating their claim at all. They make it very clear, saying:

We actually belong to the Sagittarius Dwarf galaxy.

As with most pseudoscientific claims, this one has some truth to it. The Milky Way is indeed cannibalizing another, smaller galaxy. The MW is bigger, and so its gravity did rip the smaller galaxy up, turning into a long ribbon or stream of stars. It does intersect the MW, and the Sun is in fact near this intersection point.

But their conclusion -- that we come from the Sagittarius Dwarf -- is complete nonsense. Here's why.

The Plane Truth

First: look at the illustration created by the scientists who discovered the dwarf (click for higher res).

The Milky Way is the blue spiral, the dwarf galaxy is the red stream, and the Sun's position is marked by the yellow dot. See how the dwarf galaxy is tilted with respect to the Milky Way? That means that all the stars from that galaxy are orbiting the Milky Way at that angle. So if the Sun came from the dwarf, we'd be orbiting the Milky Way at that angle ourselves!

We're not. Studies of the Sun's motion relative to the plane of the Milky Way (using the stars, globular clusters, other galaxies, and many other sources) make it a rock-solid certainty that the Sun's orbit is in fact in the plane of the Milky Way. It's not plunging through the disk at a high angle at all. So right away we see that the claim that the Sun is alien to the Milky Way is complete rubbish.

Seriously, we're done here. You can stop.

Oh, you want more? OK. Let's continue the smackdown.

If you read the Viewzone article (or the original claim from a site called, interestingly, CureZone) you can see they don't understand this angle issue at all! They do seem to get that the stream is at an angle to the Milky Way, but they also claim that this is why the plane of our solar system is at an angle to the Milky Way's plane, which is a bizarre (and totally incorrect) idea.

First, the plane of the solar system (defined, really, by the plane of the Earth's orbit) is tilted with respect to the Milky Way's plane by about 60 degrees or so. But this is not a big deal; the Sun formed from a gas cloud 4.6 billion years ago, and any number of forces would have caused that cloud to collapse such that the plane of our solar system could be pointed any which way. There's no reason to assume the two planes would align.

Second, the articles never actually make the case that the solar system is aligned with the angle of the Sagittarius dwarf stream! If the Sun came from that galaxy, and they make these claims about angles and planes, don't you think they'd actually see if our solar system aligns with the dwarf galaxy? That should set off alarm bells in your head.

Anyway, by looking at the illustration I can see right away that the tilt of the solar system is not aligned with the dwarf galaxy's star stream either. Note: this next part of the paragraph is difficult to describe, so feel free to skip it and go to the next paragraph. It's incidental to the main point anyway. The plane of the dwarf stream is perpendicular to the direction toward the center of the Milky Way, while the solar system's plane is pointed at the center of the Galaxy. In other words, at one point in Earth's orbit, you can draw a line from the Earth through the Sun and it will pass very near the center of the Milky Way (if you were at the Galactic center, you'd see our solar system "edge-on"). If our solar system were aligned with the dwarf stream, that wouldn't happen (from the Milky Way's center, the solar system would appear to be "face-on"). That means we're not aligned with either galaxy, and their claims about angles are bogus.

Look: the important thing to see here is that the angle of the Milky Way in the sky is not important at all. What counts is the Sun's orbit around the center of the Milky Way. And the Sun's orbit is aligned perfectly with the plane of the Milky Way, and not at all in the plane of the Sagittarius dwarf.

So again, we're done.

But of course, I can always add more.

It does seem a coincidence that the Sun happens to be near the intersection point of the two galaxies. But look at the drawing: the stream from the dwarf galaxy is far, far larger than the Milky Way. If we belong to the dwarf galaxy, what are the odds that at this point in time we'd be almost exactly in the center of the plane of the Milky Way? A star in the dwarf stream would spend billions of years, going around the Milky Way, but only spend about a million years plunging through the Milky Way's disk, and a fraction of that right at the midplane. The odds of us being precisely at the halfway point through the Milky Way's disk just as this discovery is made are incredibly, ridiculously low. It makes a lot more sense if we are instead part of the Milky Way, and happen to be near where the two galaxies meet.

Conclusion: we're native to the Milky Way.

Heavy Metal

One way to try to figure out if a star belongs to one population or another is to look at the chemical compositions involved. The Sun, for example, is known to have an above-average amount of iron in it, indicating that it's a third-generation star. Most stars in the Milky Way have lower iron abundances, but some have more. However according to a paper on the composition of stars in the dwarf galaxy, the dwarf stars are much lower in iron than the Sun. If I am reading this paper correctly (it's tough going, I'll admit!) then it's very unlikely just from this that the Sun came from the dwarf galaxy. It's far more likely it was born right where we always thought: in the Milky Way.

Conclusion: we're native to the Milky Way.

Artful Dodger

Also, I want to point out that the article on Viewzone is artfully constructed such that it sounds like the astronomers who wrote the original (and scientifically accurate) paper on the galaxy are agreeing (or at least supporting) with Viewzone's (erroneous) conclusions. Quotations from real astronomers are interspersed with totally incorrect conclusions by the Viewzone article author.

Look at this from the Viewzone article:

On the other hand, Majewski and his colleagues have been surprised by the Earth's proximity to a portion of the Sagittarius debris.

"For only a few percent of its 240 million-year orbit around the Milky Way galaxy does our Solar System pass through the path of Sagittarius debris," Majewski said. "Remarkably, stars from Sagittarius are now raining down onto our present position in the Milky Way. Stars from an alien galaxy are relatively near us. We have to re-think our assumptions about the Milky Way galaxy to account for this contamination."

Wow, that sounds like Majewski, the lead author of the scientific paper, agrees that the Sun must come from the dwarf galaxy, doesn't it? Especially that last sentence. But he's not really saying that at all. If you remove that last sentence about rethinking assumptions, he's just commenting that it's remarkable that we're near the intersection point. Remarkable, but not mind-blowing. But the important part is that the last sentence is on another topic, the idea that we can't assume that all nearby stars are native to the Milky Way. The vast majority are, to be sure (or else we would have discovered the interloping galaxy a long time ago), and astronomers will have to be careful when looking at individual stars. But he's not commenting on the Sun at all.

To be fair, this is from the original press release. But the way it's placed in the Viewzone article is misleading. It doesn't support the Viewzone article's premise at all.

Conclusion: don't trust what the article says. But that's true for anything.

Weird Stuff

I'm not a fan of attacking the messenger, but sometimes it pays to look at someone's pedigree when they are making a huge claim like this. If they say the Sun comes from another galaxy, and also that Napolean talks to them through their houseplant, then you have to take the Sun claim with at least a modicum of salt.

Which brings me to this from the Viewzone article:

It has been postulated that this is the real reason for both global warming since higher energy levels of the Milky Way are almost certain to cause our Sun to burn hotter and emit higher energies. Indeed, temperatures have been seen to rise on virtually all the planets in our system. This seems quite apart from any local phenomenon like greenhouse gases etc.

Sigh. The warming of the outer planets is another bad idea. First, not every planet is warming -- and saying "virtually all" is dead wrong -- and the ones that are, if they are (it's hard to tell), all have good reasons for doing so.

At least the ViewZone article author is in the good company of bonehead Fred Thompson.

Also, what are "higher energy levels of the Milky Way"? This vague term is never explained... and I know why: it's meaningless. What energy levels? Kinetic energy? Gravitational energy? I suspect they mean "energy" in the meaningless New Age sense, given the very next paragraph:

This grand turning is possibly the root cause for the discontinuation of the Mayan calendar (the most accurate on the planet) because the 'read-point' of the Pleiades star cluster, which many believe the calendar was based upon, can no longer be a constant as we begin to steer away from the earlier predictable movements.

The Mayan calendar is the most accurate on the planet? That will surprise most astronomers, who have things timed to fractions of a millisecond.

Invoking the Mayans when discussing galactic interactions is a little, um, odd. The term "non-sequitur" seems inadequate. "Goofy" might be a better word.

Incidentally, the original article on CureZone, on which the Viewazone article is based, is a total mishmash of gobbledygook. The opening headline is:

New Discovery Evidencing Solar System Traveling Different Direction To Milky Way Substantiates Astounding New Theories -- Coming To Be Called The 3 Most Pivotal Discoveries Of Our Time...

Anyone who says their idea is ONE OF THE MOST PIVOTAL OF ALL TIME, well, they'll score pretty high on the crackpot index. That doesn't mean they are a crank, of course. But it sure helps.

And the headline is certainly wrong -- the solar system is traveling quite nicely around the center of the Milky Way in the plane of the disk, as I hammered home above.

Conclusion: The article is strongly suspect as to its accuracy.

Wrap Up

This kind of stuff comes and goes. Mostly goes, which is good. It's silly pseudoscience of the highest order: all of the evidence points to the Sun being a native of the Milky Way (a native Sun! Bwahahahahahaha!). But someone sees a scientific article, doesn't do any real research, jumps to any number of bad conclusions, ignores obvious refuting evidence, and then wraps up the nonsense in scientific-sounding jargon.

This particular silliness got a degree of success because it did well at Digg.com. But it'll go away, just like all other silly claims. Well, not all others; more's the pity. But I'll keep at 'em.

So if you hear someone claim that the Sun is not from around here, you know where to point them. There's a reason I gave my website the name I did.

Tip o' the sun visor to the bazillion folks who kindly sent me emails about this stuff!