Milky Way Versus Andromeda Collision As Seen from Earth

[Quixote1818]

[vkkv]

1. But if the universe is expanding as proven by Red Shift

then aren't ALL stars, galaxies, nebulas, etc. moving away from each other?

[Salviati]

3. not systems that are gravitationally bound to each other

Like the milky way and Andromeda, or the sun and earth for that matter. Unless the big rip is our ultimate fate, but I'll let you google that...

[vkkv]

22. A separate galaxy such as M31. is not local and in our gravtational bond, or how is that?

Aren't other galaxies STILL going to be moving away from us?

Starlight will be so far away, the skies will be black at night, I understand.

[Salviati]

31. So one has to think about the total energy of the system of two objects...

Every two objects in the visible universe are gravitationally interacting with each other. If we consider a simple system where we're just looking at the two object in question, say the Milky Way and Andromeda the way we can determine whether they are gravitationally bound to each other is to consider the total energy of the system.

Gravitational potential energy (when treating it in the universal sense, as opposed to just near the surface of the Earth for all you folks remembering past physics classes) is always negative. It's considered to be zero when two objects are infinitely far apart, and how negative it is, reflects how "deep" one of the objects is in the "gravitational well" of the other.

The kinetic energy, on the other hand, is always positive, the translational kinetic energy of an object is related to the mass and speed of an object, and those can never be negative.

As two gravitaionally interacting objects move apart, the gravitational potential energy increases (becomes less negative) and the translational kinetic energy decreases (becomes less positive). If the two objects can get infinitely far apart while still maintaining zero or greater kinetic energy, they they are said to be not gravitationaly bound. There is enough energy in the system to "lift" one of the objects out of the others gravitational well. In this case the total energy of the system is positive.

If the kinetic energy hits zero before the objects are infinitely far apart, then there is not enough energy in the system to lift one of the objects out of the gravitational well of the other. In this case we'd call them gravitationally bound, and the total energy would be negative.

Cosmologically speaking, as you get farther from the Milky way two things happen - 1) The gravitational potential energy gets smaller, since those galaxies are further away, and 2) the kinetic energies get larger due to the hubble expansion. So far away galaxies are going to not be bound, but close by ones can be, as long as they're going slow enough relative to us.

[DRoseDARs]

4. No, what you have is a misconception about the expansion of the universe.

Someone more literate than I will probably come along to explain better than I could. Simply, local units like stars within a galaxy will remain in said galaxy because their mutual gravitation binds them (unless ejected by galactic collisions like the coming one between the Milky Way and Andromeda). Local galactic clusters likewise will tend to stick together. It is only on much vaster scales, the distances between super clusters, does the redshifting become more prevalent. The gravity exerted over such distances isn't enough to overcome or even much slow down the changing super-structures of the visible universe.

[longship]

2. By then, the sun will be a red giant.

So...

[Warpy]

6. We might find Mars a bit toasty as the sun hits Earth's orbit

Titan might be a better bet, warmed up enough by that point to support water, if we still need water in 4 billion years or so. A lot of the gas making up the gas giants will be blown off by a nearer sun pushing out solar winds closer to them.

However, given the rambunctious history of life on this planet with frequent massive dieoffs, we will most likely either not be around or will be completely unrecognizable as ever having been bipedal naked apes with a wasteful technological society.

[longship]

7. Yup, it could go that way, too.

Myself, I am waiting for either the zombie plague, or....

DUN-DUN-DUNNNNNN!

Cthulhu rising from R'lyeh.

ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn

I am not sure which I would prefer.

[Jack Rabbit]

21. There are other problems with Mars

Mars doesn't have the kind of magnetic field that Earth does. This means that when the Sun emits a super solar flair, the Earth protects itself. On Mars, not so. Anything out wandering the Martian plains is toast. Scratch that; it would more like microwave cheese melts.

Once anybody who wants to colonize Mars gets past that problem, then we can talk about the absence of surface water on the planet or the incredibly thin and oxygen-poor atmosphere.

[TRoN33]

26. Actually no.

When our sun become red giant stage, the environment around it will become absolute hostile. New evidence pointed out that red giant stars would spit out more flares, spew out more radiation, and planet-killing solar waves. Red giant stars isn't calm and smooth as previously believed.

[Warpy]

38. That's true

and survivability is based on something that doesn't seem to exist anywhere else. Then agian, just about everything is against life developing here on Earth, too, and required an astonishing series of improbable events, like the collision with another planet that made the core much heavier while much of the crust was blown off to form a large moon that stabilized our rotation.

The universe is an incredibly bizarre place but likely if we stay bipedal naked apes, we won't be around by the time the sun uses up its hydrogen and starts blowing the rest of its fuel off as it expands.

[D Gary Grady]

32. Or build a shell around Saturn

Surprisingly enough, the gravitational attraction at the visible surface of Saturn (its cloud tops) is about the same as at the surface of the Earth. If we were to construct a thin shell around Saturn, supported by the pressure of its atmosphere, we could have a planet with vastly greater surface area than the Earth. Of course, we'd need raw materials, and since Mercury and Venus would be eaten by the Sun anyway, we could use them. Oceans we could import from comets in the Kuiper Belt or Oort Cloud. A couple of billion years hence we might very well have the technology to do all that.

Of course, it would likely be easier to relocate the Earth to a more distant orbit. We'd probably want to do that anyway for sentimental reasons, but it might be nice to have the extra room available on Saturn. Alas, by then the rings would probably be gone unless we regenerated them for old time's sake. For that matter, several-billion-year-advanced technology might give us some way to restock Sun's hydrogen supply and prevent it Sun from entering its red giant phase.

All this assumes, of course, that the don't do destroy ourselves in the meantime or get dragged back to the Dark Ages by those so inclined.

[jimlup]

9. On the time scales given in the video I believe that the Sun will be well past its red giant phase

It will have shed a planetary nebula and will be a cooling white drawf. If Earth some how manages to survive the Sun's ejection of the planetary nebula, the view would be quite spectacular.

http://www.universetoday.com/25669/the-sun-as-a-white-dwarf-star/

[link:|

[SheilaT]

5. According to my son, the astrophysicist, who is currently doing research

on the intersection of galaxies -- what we on earth would call the collision of galaxies -- yes it is true that Andromeda and Milky Way will collide in about 4 billion years. The first couple of things in the video that show two galaxies intersecting and pulling apart is weirdly nothing like what is going to happen. We'll intersect and become one large galaxy.

And there's a lot of evidence, according to my son the astrophysicist, that Milky Way has in the past intersected with other galaxies. The indicators are things like strings of stars lined up in certain ways that look like leftover suns from some other, very ancient, galaxy. Over very long periods of time, galaxies will intersect, resulting in fewer, but larger, galaxies. All of this is incredibly fascinating to me, and I'm fortunate in that I can call up my son and ask him various questions and learn all sorts of amazing things. In fact, every single time I talk to him I learn new stuff. The most recent conversation, just a few days ago, had to do with the Goldilocks Zone, that special place not too far and not too close to the sun (the Goldilocks Zone!) where life as we know it can exist. It's possible, according to my son, that a similar sort of Goldilocks Zone exists within the Galaxy. Too close to the Galactic Center and all sorts of complicated things take place, many of which aren't terribly conducive to the evolution of intelligent life. Farther out seems to be better. Guess what? We're (meaning our solar system) are farther out! Isn't that special?!

[exboyfil]

8. Your last observation is another reason

technological life is probably very rare. Combine that with the fact that it was not a foregone conclusion that evolution would lead to technological life (look how long it took on Earth - we used up over half of our star's life getting to this point and underwent many keyhole events to get to that point). The dinosaurs were present for 160 million years and never developed even rudimentary technology (the closest being some simple tool use by avians their descendants).

[still_one]

13. but, but, I thought the earth was only 5000 years old? (note sarcasm)

[exboyfil]

14. Interesting article on this point

http://www.slate.com/articles/health_and_science/human_nature/2014/12/creationism_poll_how_many_americans_believe_the_bible_is_literal_inerrant.html

My church did something called The Truth Project about five years ago. I went in and tried to reason with a large group of highly educated individuals about most aspects of the presentation (if you could imagine taking nearly everything in science and history and turning it on its head - you would have the Truth Project). I have not been back to a Bible study in that church since, and I barely attend anymore (it is the church my wife grew up in, we were married in, and my kids were baptized in).

[still_one]

16. You are quite courageous what you did.

[exboyfil]

17. Not really

An easy forum to confront authority with little consequence to me. The truth is the truth and this is an easy one. The protestors pointing out the increasingly militarization of our LEOs and the unequal treatment under the law of certain groups in our society are the truly courageous ones.

[SheilaT]

18. The eventual life span of any intelligent species

probably isn't all that long on a cosmic scale, either. I think I've read that a million years is a good run for any individual species. So even if intelligent species arise rather readily, it takes a very long time and the possibility of any two actually overlapping in time is small. Then, of course, there are the incredibly large distances between stars, let along between galaxies. So while it may well be that intelligent species happen frequently, given the right conditions and enough time, each one is for all practical purposes, alone in the Universe.

[exboyfil]

19. Yes

Any intelligence outside of the galaxy for all intents and purposes is probably never discoverable (you would have to imagine huge engineering feats such as harnessing the energy of the galactic center black holes that would allow observation of such intelligence in other galaxies).

As far as our galaxy we should be looking for signs of massive engineering (partial Dyson spheres, high energy propulsion, etc). My guess is the upward limit of four technological civilizations observable at this time in our galaxy - because of the speed of light we may be observing such intelligences 10s of thousands of years in the past. Of course four is just pulled out of my behind. It is sufficiently close to one to indicate we are alone.

Still it does not cost a lot to keep looking.

Back to Fermi. It would take no longer than 10 million years to fully spread through the galaxy using self replicating machines. Such machines have never been observed. That is 1/15th the time that dinosaurs ruled our planet.

http://io9.com/how-self-replicating-spacecraft-could-take-over-the-gal-1463732482

[SheilaT]

23. But dinosaurs were many, many different species.

Any one species has a limited, and relatively short, lifespan. And another species out there looking for massive engineering won't be finding us any time soon.

As you pointed out, the sheer distances between stars is a very limiting feature.

I also don't get the point of colonizing the galaxy with self-replicating machines, if for no other reason than ten million years on the species that develop them won't be around.

[TRoN33]

27. Nope. Many astrophysicists has agreed that there are

Otherworldly intelligence that are capable of living for thousand of years.

[SheilaT]

28. I have to say I hadn't come across that bit of information before.

But even if individual members of a species might live thousands of years -- kind of like a giant sequoia tree? -- the lifespan of the species itself is still going to have a limit. Maybe on earth a given species only lasts a million years, but in some totally different ecosystem where lifespans are many times longer than lifespans on Earth, a species would last comparably longer.

But I'm having trouble picturing this. Such a very long lifespan will have its own problems and issues. Evolution would happen more slowly, since a cohort of individuals will take very much longer to replace. Reproduction would be an interesting problem, because overpopulation would happen far more readily if the individuals are living a whole lot longer.

Very, very interesting idea.

[TRoN33]

29. You're correct

I'm sorry if I didn't add something in first place. Astrophysicists has also agreed that the civilizations with much higher intelligence than ours would be more likely to use nanotechnology or better to help them prolong their longevity of living.

Some would quip that some extraterrestrials would be capable of solve quantum mathematics on their own right after they were born and focus on much more complex mathematics and numeric-based language. I wouldn't argue with that because we came very long way from the point of evolving yet we are considered very slow in term of technological evolutions due to religion and theoretical groups in Dark Age era. Extraterrestrials would just simply done it all in lot less time than we do. If we were 2-5% smarter, we'd be riding in faster than light spaceships by now. We wouldn't have to worry about over populations, political bullshit, and fossil fuel shits. Our own government in America is somehow hindering our technological evolution and focus more on plutocracy and oligarchy.

I would be willing to bet that extraterrestrials would fly past Earth for short observations on us and some would think we are one of the stupidest they have ever seen.

[SheilaT]

30. Oh, I'm not so sure it makes sense to assume

that extraterrestrials would necessarily be a lot smarter than we are. Obviously, we have no way of knowing for sure at this point and can only speculate.

And a mere 2-5% smarter wouldn't be enough. Given the normal range of IQ (however you want to define or measure it) is already far, far greater than 2-5%. Solving quantum math right after birth involves an order or magnitude of brain development I have trouble imagining. Which of course may just prove I don't imagine very well.

I am someone who reads a lot of science fiction, and so I've read lots of speculation about extraterrestrials. That speculation includes the possibility that we have developed technology a whole lot faster than at least one science-fictional ET out there.

Anyway, I'm enjoying our little conversation here.

[D Gary Grady]

37. I'm not sure about that, but...

... given that the Cosmos is almost certainly vastly bigger than the observable part of it and very possibly infinite, anything that's possible probably exists.

Unfortunately, almost all the universe is forever undiscoverable by us at least based on our current understanding of physics. Worse, as time goes on more and more of the universe will expand beyond our cosmic horizon. Billions of years hence astronomers will have no evidence of other galaxies beyond our own big blob of one (by then made up of all the galaxies in the local group). The discoveries of Hubble et al will no longer be possible, and astronomy we have a limited 19th-century-like view of the Cosmos.

More relevant to this thread, I think what you're talking about lies more in the very young field of astrobiology rather than astrophysics. And in any case, the lifetime of a single species isn't necessarily relevant. We have tools made by previous species of humans. They didn't build them for us to look at, but we representatives of H sapiens make things for posterity all the time. We have built structures intended to last long after our deaths (e.g. the pyramids). We even start construction projects we know won't be completed in the lifetimes of those who start them (various cathedrals). We have launched space probes that still work after the deaths of some of their builders. We might well start launching more ambitious ones in the hope our descendants, whether of our species or another, might find the results useful.

Incidentally, I once read a proposal for a laser launch system based in solar orbit that could propel solar sails far out into the galaxy. It would be expensive to build. But it would cost far less than the Iraq war. And that reminds me of this (link to my blog, though I wasn't the person who compiled the figures):

http://dgarygrady.com/2012/11/26/corrected-science-vs-defense/

The bottom line: the grand total of all spending on NASA, including sending humans to the Moon, and adjusted for inflation, over the space agency's entire existence from 1958 through 2011, was *less* than U.S. military/defense spending in the one fiscal year 2011 alone.

[jeff47]

20. We'll become one large galaxy in the end, but the two galaxies are going to overshoot each other

in the process. That's what the video shows - the galaxies accelerate towards each other, and then momentum carries them past each other. Then gravity overcomes the momentum, and they get pulled together again, resulting in another overshoot. This repeats until eventually we settle into a single, merged galaxy.

We're (meaning our solar system) are farther out! Isn't that special?!

Not really. There's several billion stars in the Milky Way that are "farther out".

[SheilaT]

36. Oh. I thought we'd collide and then merge.

There's a lot I don't know.

[D Gary Grady]

33. One big elliptical galaxy eventually, but lots of contortions in the meantime

I'm pretty sure the simulation in the video is reasonably accurate. From what I've read, the Milky Way and Andromeda galaxies will likely collide multiple times with lots of resulting gravitational distortions for both until they settle down into a relatively dull-looking rugby ball of an elliptical galaxy. Ask your son about the intermediate development as well as the final result.

Re the galactic goldilocks zone: Your son is probably speaking in part about what astronomers call "metallicity," which in astronomer-speak means the quantity of elements heavier than hydrogen and helium. The Big Bang gave us lots of the first two elements (and probably some lithium as well, but I'm not sure of that -- this isn't my field, just an area of interest), but heavier ones have to be made in stars and the really heavy ones in supernovas. Hence you need solar systems that formed late enough that they could condense from clouds containing lots of heavier elements, and those tend to be available in certain bands of disk galaxies such as ours.

The Sun, the Earth, and the other planets of our solar system are about a third the age of the universe and formed in the right part of the galaxy, so we had the heavier elements we need. It may be that sigificant'y older solar systems aren't as well-provided with necessities. If our development time is average -- nearly four billion years to develop complex multicellular life and a bit over half a billion to get from there to us -- then maybe we're among the first civilizations around. I hope we don't screw it up. It would be nice to be the Elder Statesmen of the galaxy, or even the crotchety old pharts. You kids get off our spiral arm!

[Derek V]

10. Yeah, but OUR galaxy will be on top: even The Church agrees with that!

[Hoppy]

11. The Milky Way's gonna win. We're #1. U.S.A. .. U.S.A. .. U.S.A. (You get the idea).

[exboyfil]

15. Andromeda's bigger

Going to be tough going.

[belzabubba333]

12. we have to attack it there so we dont have to fight it here

[vkkv]

24. The Orion Nebula is very cool and visible to nearly all of us.

The Men In Black movie said that "the galaxy is in Orion's belt" - not quite true.

The "nebula is in Orion's sword blade"!

We can all see the brightest middle star in the hanging sword within the Orion constellation.
It's the blurry one, blurry because it's not a single star, it's the Orion Nebula.

Less than powerful binoculars or even the naked eye will show the blurriness of a nebula.. M42 is the number.

[D Gary Grady]

35. And nebulae in the belt as well; all around Orion in fact

By far the easiest one to see is the one you're talking about, and in even a small telescope it's spectacular.

(I once showed it to a girlfriend in a small refractor and she was in awe and became downright emotional. I suavely informed her that I was all about giving her new experiences and she grabbed me and kissed me with remarkable enthusiasm. Maybe being a nerd isn't as big a turnoff as one might think.) (Also, maybe that's not his sword.)

Anyway, as I'm sure you know, that whole region of the sky is full of unimaginably humongous molecular clouds, though it takes long-exposure astrophotography to see it.

[WhoIsNumberNone]

25. So, 4 billion years from now, eh?

Think enough time will have passed by then that the Republicans won't blame Obama for it?

[D Gary Grady]

34. You can see both galaxies now with your naked eyes

... provided you go somewhere dark enough and know where to look. I've seen the central bulge of the Andromeda galaxy from inside a city. It looks like a very faint small fuzzy patch.

The full disk stretches about 2.5 to 3 degrees in its long dimension (we see it tilted), about five or six times the size of the full Moon. That may seem hard to believe, but it's true. Look up their respective angular size in an astronomical reference. The Andromeda galaxy would be spectacular if it weren't so dim, and ours would be even more so.

Our ancestors easily saw the Milky Way but today those of us who live in cities rarely do, because we waste so much electricity lighting up the night sky. If you ever go somewhere really dark and give your eyes time to adapt, you'll see a sky that will amaze you. (Take care you aren't driven bananas like the characters in Asimov's "Nightfall.&quot