Milky Way is going to collide with Andromeda… over the course of millions of years, and due to the distance between stars and other objects the two galaxies are just going to merge with each other and very few things will actually make physical contact.
Well, if they collide (and merge), they’ll also fling a lot of stars into the void, but we aren’t too sure anymore that’s actually gonna happen. NASA explains why (YT, 2:30min).
Thank you very much for posting the video length. I wasn’t gonna watch a 10 minute video but 2 was short enough.
Nobody liked those stars anyway…
Ah, you mean the void were nearly in the center of?
Humans in 200 years be like: ha ha warp drive go brr.
We’ve only got two billion years. RUN FOR YOUR LIVES
So blue is moving toward you?
I was always a bit confused with the explanations in high school. But I also got a D in physics so maybe I’m just dumb.
Blue shift, it’s moving towards you, the photons are being “compressed” to a higher, bluer frequency. Redshift, the light is being “stretched” to a lower, redder frequency. Both only noticeable at significant fractions of the spped of light, relativistic speed.
Something ominous about the post is that a cosmic object that is moving towards you at a steady rate is consided “blueshifted” in the past tense, it’s velocity is steady. If a galaxy is “Blueshifting” in the present tense, then that galzy is somehow accelerating at you, which is impossible unless it’s under direct control by an entity, presumably a kardeshev level 3 civilization.
Isn’t the rate of expansion in the universe increasing, and at an uneven rate at that? Meaning it could just as easily be an as of yet unknown natural phenomenon?
The expansion is supposed to be happening everywhere at the same time, not just at the edges.
For example, tomorrow there should be more space between the Sol and Alpha Centauri systems than there was yesterday.
Our present understanding suggests that ‘normal’ universal expansion should not (in and of itself) result in anything moving towards us.Aren’t the milky way and andromeda on a collision course with each other?
Milky way and Andromeda are close enough that expansion is too small to overpower gravity
Our local group is racing toward The Great Attractor but will never reach it as expansion is pulling it away faster than we’re falling toward it
Yep. Space is expanding everywhere at once, but the effect is minuscule at the scales we’re used to. And even at galactic scales the “speed” of expansion might seem like a lot to us, but it still isn’t enough to overcome the motion of objects. I looked up some rough numbers to give you an idea:
The rate of expansion of space is 73 km/s/Mpc. So for every 3.26 million light-years between you and a distant galaxy, the space between you and that galaxy is expanding by 73 kilometers per second.
Andromeda’s blue shift indicates it’s headed towards us at 110 km/s. And in my non-expert head I’m thinking that blueshifted light must have already been redshifted by the millions of years traveling through space to reach us. So the galaxy’s speed through space towards us when the light was emitted was considerably higher.
Andromeda is 2.5 Million light-years away, btw. So the cumulative distance of space between here and there is expanding at something like 73 km/s/Mpc * 2.5 Mly * 1Mpc/3.26Mly = 57 km/s.
But when talking about relativistic distances and speeds, basic terms regarding time and location don’t always make sense.
Yes, but not because of universal expansion really, they’re just headed in a direction that is going to intersect at some point, likely combining the two galaxies together. This’ll be so far in the future we’ll all be long dead though, on top of it being unlikely that anything is going to even come close to our solar system
That’s the other part I find fascinating; these two galaxies are gonna intersect, but our solar system probably won’t hit anything. That’s so gnar.
It’s not just that, but it is unlikely that any star in our galaxy will collide with any star in Andromeda.
I think it’s easy to think of galaxies as individual things, like these nodes in the universe where all the stuff is stored. But galaxies are incredibly vast and incredibly empty.
I love the video this guy did on the subject: https://www.youtube.com/watch?v=VsRmyY3Db1Y
The part that stuck with me is that if you made the Milky Way the size of the United States, our gigantic sun holding 99.86% of the matter in the solar system would be microscopic – the size of a red blood cell. And iirc, the planet earth would be all the way down to the size of a virus.
For example, tomorrow there should be more space between the Sol and Alpha Centauri systems than there was yesterday.
Galaxies are gravitationally bound, they do not expand in the same way as the universe.
Fair enough, I should have been thinking bigger.
Expansion red-shifts light.
Yes which would be very odd for a far away object
No, it’s just depressed and that makes us feel sad and worried for it.
I’m blue shifting-daba-dee-di
It’s the doppler effect, but with light instead of sound, and for the same reason.
Thing emits sound/light waves at a constant rate: sound/light waves hit you at a constant rate.
Thing continues to emit the same sound/light at the same rate, but starts to move toward you: sound/light waves hit you at a faster rate, causing the sound/light to turn higher-pitched/bluer.
Thing continues to emit the same sound/light at the same rate, but starts to move away from you: sound/light waves hit you at a slower rate, causing the sound/light to turn lower-pitched/redder.
Eh, the odds of actually colliding with anything is low enough. Plus the night sky would probably be even more breathtaking. I’m in
and lose the character of the spiral arm configuration? For what? A blob??
I think there’s maybe more risk with the solar system being thrown off balance with other gravitational forces pulling things out of orbit. Even if earth just gets pulled away from the sun a little we are screwed. Or even the moon pulled away from earth somewhat.
Even if earth just gets pulled away from the sun a little we are screwed.
I get what you’re saying, but had to laugh at the use of “a little” here. The goldilocks zone in the solar system is roughly the between the orbits of Venus and Mars, and we’re almost right in the middle of it, so “a little” is like 150 million km.
I would imagine that the first issue we would experience would be that the moon would be pulled out of Earth’s orbit first and then we lose the ocean tides and the stable tilt of the earth. It would probably get worse from there.
Goldilocks zone is basically just where life can survive.
Even if we stay within the Goldilocks zone doesn’t mean that most of the species alive today won’t go extinct because it fucks up the seasons or the magnetic poles or tilt of the earth, etc.
Maybe we’ll get lucky and it’ll counter global warming
“Thank god global warming never happened.”
“Actually, it did, but thank god for nuclear winter.”
Just keep scooting away a little every year, problem solved
Could the other galaxy please pull us just the correct distance away from the sun to cancel the effect of global warming?
Given the vastness of space, this is a lot less likely than you might think, and the process itself would likely take millenia anyway.
It’s even safer. The odds that it’s coming directly at us to “collide” is low. Moving towards us doesn’t mean it’s moving directly at us. If you’re driving down the road, all cars going in the other direction get doppler shifted. They’re coming towards you, they pass beside you (hopefully), and then they’re moving away from you.
Might be a dumb question, but if it’s blue-shifting surely we wouldn’t know it’s far away in the first place? I thought the amount of redshift is broadly how we determine cosmic distances?
Armchair expert here
From my understanding blue and red shifting is mostly related to movement. Like when a firetruck run past you with sirens on, you can hear change in pitch when compared it moving towards you vs away from you.
It’s a similar effect with galaxies, red shifting means that after the light was emitted the space between us has increased and the light kind of stretched out to longer wave.Now anyone with more knowledge on the subject, please correct me.
You’re missing the point that the universe is expanding uniformly. That means two points acceleration away from each other is dependent on their distance apart. The further they are from each other the faster they accelerate from each other.
So GP is right. We measure red shift and infer distance.
Yes, but everything red shifts “naturally” as well as the light travels because of the expansion of the universe. So something traveling towards us will still red shift, just slightly less so. To determine distance you have to use something called the cosmic distance ladder. It consists of known properties of stellar objects that we can measure to determine the distance of objects.
Now imagine if it did blue shift.
https://www.youtube.com/watch?v=opvuEVpl_PM&list=RDopvuEVpl_PM&start_radio=1
Yeah, I’m pretty sure red shift is our best method for getting distances on billions of light year distant objects, no idea of it’s the only one at that range
If it’s blue shifting from that distance, then it’s likely some advanced technology is moving it in our direction.
There’s not many other explanations for that.
Let’s suppose that for some reason it’s completely normal, and it’s just simply speeding toward us.
OP says it’s billions of light years away. Doesn’t that mean that we still have a few billion years?
Since they didn’t note extreme blue shift, probably several billions of years
Could it potentially be an object orbiting around the cosmic center that just so happens to have an orbital path that crosses us?
I have to admit that astronomy is what caused me to change majors, but that’s because I stopped going to class when the lesson was, “This is a terrestrial planet, it’s rocky,” and my first exam was like, “If it’s 5:45pm in Tanzina on October 15th, how many degrees is the moon above the horizon?”
Had to do AM because it’s below the horizon in the PM.
I really want you to know that I appreciate this.
Since the speed something is moving away is dependent on the distance, something billions of light years away is absolutely not going to be moving towards us, regardless of its local orbits.
Oh no! We might not survive the collision to hundred fifty thousand years from now!
If it’s billions of light years away it might be just a little longer than that.
might take a little bit o’ while. you got plenty of time to start that pot roast in the slow cooker.
check on it around 100,000 and give it a stir.
*must be
I’m blueshidding
Blue
wafbrownies?
ELI5?
If something is red shifting, it’s accelerating away from you. If something is blue shifting, it’s accelerating towards you. An entire galaxy accelerating towards you is somewhat concerning.
Redshift comes from relative velocity (and other effects), not acceleration. Andromeda’s light is blueshifted as it’s moving towards us, but it’s not accelerating.
I was going to argue with this too, but the meme says blueshifting, not blueshifted. They’re right, but mostly because the meme is probably written poorly. Maybe they meant it’s accelerating toward us though. Idk.
On top of that, we’ve found that basically everything is redshifting as the universe expands. So to see a blueshifting galaxy would mean something potentially unnatural.
Right, but I don’t get why this thread is full of people talking about collisions. Even if it was moving at the speed of light (it’s not) it’s still billions of years away.
It would just prove our theory of universe inflation to be incorrect.
You know how the sound of things moving from you changes? Towards you the pitch is higher, away from you it is lower. The same happens with light. We know how some things should look like, so if they are more toward red or blue, we know their speed relative to us. Blue = towards us = “we will collide” (you also do not collide with every car with a siren where you hear that effect).
Great explanation, thanks!
I know you can’t see this comment but maybe someone else will find it useful
Just like how a siren changes pitch when it’s coming from a vehicle passing by due to the Doppler effect, the same thing happens to moving light sources due to relativistic effects.
Usually astronomical objects are redshifting because the universe is expanding and are thus receding away from Earth’s frame of reference. Most of them are forever unreachable even if we could travel at the speed of light.
Something blueshifting means it’s coming closer from Earth’s frame of reference. In some cases, this could result in the galaxy colliding with ours, such as the hypothesized collision between the Andromeda Galaxy and the Milky Way
isnt andromeda gigantic in the night sky but weve got too much light pollution to see it normally?
anyway retvrn to alien
It is gigantic & very luminous but it’s also just too far away to be really noticeable - on its own is just on the limit of the best of human eyes if there would be no other star in the sky (very dim, with the visible/luminous core being only about the size of the Moon or smaller - the full galaxy is 5× larger on the sky compared to Moon, but that’s not comparable in luminosity).
Disregarding human pollution there are just too many starts from Milfky Way way closer to us.
You see an hughe comet in the sky…but which stand still and it gets bigger and bigger.
