‘
As I sit here in my living room, laptop keeping me warm (and probably irradiating parts of me that are best left unirradiated), the sounds of "South Park" playing in the background, I feel pretty safe.
But it’s a lie, an illusion.
The Universe is a dangerous place. We sit here in the Milky Way, isolated and out of danger… for now. But other galaxies are out there. They can get close, and their immense gravity can distort our Galaxy, fling stars out like a dog shaking off water, rip out long streams of gas and stars, and then eventually merge with us.
What evidence do I have for this chilling scenario? For one thing, we see it happening in the Milky Way. Our Galaxy is actively eating at least one other one, for example. We’re also pretty sure that in 3 billion years, we’ll merge with the Andromeda galaxy too.
And, for the clincher, we just plain old see other galaxies colliding. The image above, just released by the Spitzer Space Telescope, shows two spiral galaxies named NGC 2201 (left) and IC 2163 (right). Each is similar to ours, except that they are in the process of colliding. The red color in the image is actually from infrared light, showing dust warmly glowing (the blue and green parts are from a Hubble image, and added together make the false-color image). See how the dust is all in the spiral arms? When the two galaxies passed each other, the gravity of each disturbed the other, causing clouds of gas and dust to collide, collapse, and form stars. This happens predominantly in the spiral arms, which is why they are so obvious in the image.
The two galaxies will pass each other, swing around due to gravity, and pass again. This will happen multiple times, until, about a half billion years from now, they will merge into one colossal galaxy. It’ll probably be elliptical in shape, like a football, the spiral arms distorted beyond recognition. Probably, the same fate awaits us when we merge with Andromeda.
A thought: In the image above, the two galaxies are superposed on the other. Can you tell which galaxy is in front of the other? No? Maybe this image will help:
That’s the Hubble image of the same galaxies that was used in the Spitzer image above (click on it for a higher-res version). See on the right, how the spiral arm from NGC 2207 cuts across the nucleus of IC 2163? In optical light, dust is dark, absorbing light behind it. Since we see the dark arm in front of IC 2163, NGC 2207 must be in front. If it were behind the smaller galaxy, we wouldn’t see that arm at all, because it would be blocked by dust in the other galaxy.
As usual, it’s the combined might of telescopes that see in different wavelengths of light that reveals clues about the goings-on of our Universe. And if you don’t think knowing this stuff is important, then just wait three billion years. When Andromeda is filling up the whole sky, and the Sun gets tossed out of the Galaxy like you’d flick some noisome goo off your finger, well, you’ll be sorry then! Or maybe you’ll have other things on your mind. Or maybe, realistically, it won’t happen until three billion years from now, so maybe it’s not so pressing.
But it’s cool. Don’t ever underestimate that.’
April 27th, 2006 at 12:45 am
A very thought-provoking late-night entry, Doctor! I can honestly say I’ve felt the same way, that the relative safety we know here on Earth is a fallacy, and that the Universe is a chaotic, dangerous place.
April 27th, 2006 at 12:51 am
Merger: The Motion Picture!
John Dubinski used a supercomputer to model the collision. Here is the one he did in 2001 (this is a big page):
http://www.cita.utoronto.ca/~dubinski/tflops/
And here is a newer one that he did last year that looks nicer and has music (this is a big movie):
http://www.galaxydynamics.org/spiralmetamorphosis.html
I highly recommend downloading one–if you aren’t on dialup anyway.
April 27th, 2006 at 4:09 am
Why merge should be dangerous? Psychically, very few stars will collide. Many things in universe is dangerous, but galaxy merging is not one of them.
April 27th, 2006 at 4:33 am
Agreed; the Universe is mostly a hostile environment. There’s a reason why we’re here, now. It’s because at this particular place & time circumstances don’t *prevent* living things from thriving. It wasn’t always this way, and it won’t always stay this way. We’re enjoying a lengthy summer, but winter will return.
April 27th, 2006 at 5:12 am
Stars aren’t the only things in galaxies, nor are they all that will collide. Collisions of dust clouds will kick off star formation, and I don’t imagine an actively star-forming region is a safe place to be.
At least, such is my understanding.
Also, “you may not think this is important, but just wait three billion years” is now one of my favourite statements.
April 27th, 2006 at 6:42 am
Earth needs the sun to survive, but does it need any of the rest of the galaxy? If the sun were flung in to the most isolated depths of space, with Earth’s orbit intact, would it impact life at all? Other than the sudden lack of constellations.
And speaking of orbits, regardless of whether the sun gets flung from the galaxy or not, how badly would near passing stars perturb our orbit? Could we survive a 1 solar mass star at 1 ly? .5 ly? 5 solar mass?
April 27th, 2006 at 7:06 am
“you may not think this is important, but just wait three billion yearsâ€
There’s a funny anecdote, perhaps apocryphal, in which an astronomer is delivering a public lecture. The lecturer says, “The Sun will probably perish in about five billion years, making life on Earth impossible.”
A layperson from the audience perks up with a question: “Did you say billion, or million?” The astronomer replies, “Billion.”
The audience member gives a sigh of relief and says back, “Oh, thank God. For a moment I thought you said million.”
April 27th, 2006 at 8:16 am
There’s a great Sydney Harris cartoon about the Sun turning into a red giant in about 5 billion years.
It’s about 2/3rds of the way down in the right column. Can’t get the link to the direct image.
April 27th, 2006 at 9:02 am
Oh my gosh! It’s His Noodly Appendage incarnate.
Raman.
http://www.venganza.org/
April 27th, 2006 at 9:02 am
Beautiful, cool, and a little scary. Knowing I’ll be dead billions of years before it happens makes me feel a little better.
But still very cool to see it happening to another pair of glaxies.
April 27th, 2006 at 9:18 am
I like the Hubble images from some time ago here of a
Milky Way & Andromeda Collision.
More galaxy events from Hubble.
I like the Hubble Site’s explanation for the demise of the Sun…umm “noisome goo” sounds like a big, bad galaxy mocking the, “Garden-variety stars like our Sun [who have lived] undistinguished lives in their galactic neighborhoods, churning out heat and light for billions of years. When these stars reach retirement age, however, they become unique and colorful works of art.”
April 27th, 2006 at 9:42 am
The cool thing about astronomy is you get to do what any scientist would truly love to do: Travel back in time.
While we won’t see our galaxy merging with Andromeda, we can look deep into space and see galaxies in the midst of mergers that occured hundreds, thousands, millions of years ago.
By the way, in those photos, is it just me or is there an image of the Virgin Mary in there?
April 27th, 2006 at 10:13 am
Reminds me of the old “No Fear” logo.
http://destickerman.nl/catalog/images/nofear/nofear_met_ogen_3.gif
I know… pareidolia…..
Footballs are round, not elliptical
April 27th, 2006 at 10:42 am
[...] Because I haven’t posted about astronomy (which is one of my favorite things) in a very long time, I’ve decided to link to this story from a blog I dig called Bad Astronomy. [...]
April 27th, 2006 at 11:04 am
I wonder, though. If a star, say our Sun, is ‘flung’ in such an encounter, I should assume that in at least SOME circumstances (MOST circumstances?), it’s planets go with it, yes?
And, in the flinging, I can imagine that would change the constellations, but I assume that would be over centuries. Am I right that such a change might not be known about until centuries after it happened?
I’m just having difficulty imagining the scenario, and whether it would, indeed, actually threaten life our our little blue planet, and if it didn’t, what sort of changes would be perceived and over how long. What would a cosmic ‘flinging’ be like? Would Earth be scoured of all lfe, or due to the vastness of empty space, would the planet’s population even NOTICE such a flinging? Over how long? Centuries? Millenia? The grandness and majesty of it all can sometimes be a little big to get one’s head around.
Any apt descriptions, quite welcome!
Thanks,
Jonathan
April 27th, 2006 at 12:12 pm
Eric says:
April 27, 2006 @ 6:42 am
Earth needs the sun to survive, but does it need any of the rest of the galaxy? If the sun were flung in to the most isolated depths of space, with Earth’s orbit intact, would it impact life at all? Other than the sudden lack of constellations.
Well, I’d predict an awful lot of Astrologers out of a job for a start…
April 27th, 2006 at 12:28 pm
The whole collision would take about a billion years, so no one would notice as it happened. Meteors might be a more frequent, but that’s only relative–those huge dust clouds are thinner than the best vacuums we can make on Earth. However, in the unlikely event of star(s) passing *through* the solar system, all bets are off. Earth could even get separated from the sun then. (Or combined with it!)
The constellations would be different than what we’re used to. If we’d been flung out of the galaxy, there would be fewer bright stars and no “Milky Way” stripe, but instead, the whole new galaxy would be visible from some locations! THAT would be spectacular, but not a lot brighter than the Milky Way now.
Of course all this will be happening as the sun turns into a red giant, so the population (whatever they are) will have other things to worry abount.
April 27th, 2006 at 12:32 pm
Astrologers ignore the stars! The constellations are all a sign and a half off, and they don’t care. We will still have the planets, and that’s enough for them. Sigh.
April 27th, 2006 at 2:07 pm
Galactic collisions are always cool (in my view, anyway).
April 27th, 2006 at 2:15 pm
We need Jupiter to keep space junk ( astroids, meatorites, etc.) out. If everything within the solar system was kept intact. We’d probably be okay. However, if another galaxy comes in and tears through the solar system, we’d have a problem. However, it’s possible to get lucky because we might fit between two stars in the galazy.
April 27th, 2006 at 2:43 pm
Remember that one hubble photo labeled “Eye of God?” This one looks like the eyes of the devil.
April 27th, 2006 at 5:03 pm
I’ve said for years that the only reason anyone thinks the Universe is benevolent is because we don’t live long enough.
Galactic collisions are the grand-daddy of catastrophes, but asteroid impacts are much more common. Irradiation by nearby supernovae is troubling too. The wavefront could already be on it’s way.
The Universe is a very dangerous place, and we live in a small, fragile place. The energy scales involved in “garden-variety” cosmic events are so far beyond our experience that we cannot have any visceral appreciation for them.
The only way to ensure our species long-term survival (assuming you view that as a good thing) is to get off this one little rock and spread far and wide. (Of course, there’s a paradox, in that spreading humanity far and wide is likely to produce speciation among different populations of humanity.)
April 28th, 2006 at 12:18 am
This is a very interesting topic. A pair of galaxies called “The Mice” is another interesting (and more advanced) result of galactic collision.
I suspect that most living worlds in such galaxies would face mass extinctions or eradications from wayward debris stirred up by the collision or the increased density of stars (from new star formation) in the spiral arms (the best part of the galaxy for life) Who knows some might get lucky. Intelligent life has an edge of course, evacuations and evasion then become possible.
April 28th, 2006 at 6:15 am
As my 7-year old would say, “Oooooh, angry eyes!”
April 28th, 2006 at 7:23 am
Let’s see, by my calculations, the human race will have evolved into giant, hugh headed, big eyed homineds living in trillions of 200 km long space structures, scattered thruout the galaxy, controlling the entire energy output of the Milky Way. SO, who’s gonna worry about a little rearrangement of the local environment? It will just give us more STUFF to play with,,,
Gary 7
April 28th, 2006 at 12:28 pm
Am I the only one who thinks that first photo looks uncannily like the Flying Spaghetti Monster Himself? Could this be the proof we’ve been waiting for of His existence?
April 28th, 2006 at 12:36 pm
If the Sun were moved out of the Galaxy intact, there probably wouldn’t be much impact on us. But a gravitational influence powerful enough to move the solar system would likely distort the orbits of the planets. That may not be a big hairy deal for us, depending how it all goes down, or it may spin the Earth into a highly elliptical orbit (or a higher or lower one) that might be destructive of most life on the planet.