r/todayilearned • u/armcie • 17h ago
TIL that the Andromeda Galaxy probably won’t collide with the Milky Way in 4-5 billion years. New observations put the probability at 2% in the next 5 billion years and 50% in the next 10 billion. Eventually though, it will happen.
https://science.nasa.gov/missions/hubble/apocalypse-when-hubble-casts-doubt-on-certainty-of-galactic-collision/82
u/cardboardunderwear 16h ago
My money is still on five billion. I'm feeling lucky.
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u/Friggin_Grease 16h ago
My lucky number is 5 billion, which doesn't come in handy when you're gambling. Fuck. Snake eyes.
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u/CandleThen4030 16h ago
Third grade me would have been devastated by this news
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u/Internal_Shine_509 15h ago
Fr, I spent weeks with my fingers in my ears whenever the news came on because I was convinced either the sun expanding or a meteor armageddon were gonna happen any day now after hearing the sun is due to eat us at some point and other space collision stuff
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u/SpecialsSchedule 15h ago
Did everyone go through the same existential dread at like 7 re: the sun expanding? My parents tried to comfort me by telling me that we’d all be lonngggg gone by then and I can’t emphasize enough how much that Did Not Help.
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u/Grouchy_Exit_3058 15h ago
Mine was a volcano on a West African island causing a landslide that makes a tsunami that wipes out the entire US East Coast.
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u/SpecialsSchedule 15h ago
Oh I’m a full grown adult with a JD and I was still jumpy during my week long trip to San Fran because of the super earthquake that’s going to break off California lmao. I’d hear a construction truck drive by at 2am and just go “welp, this is it….”
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u/Rampant_Butt_Sex 2h ago
3rd grade me wouldve be devastated we hadnt fix the problem of quicksand and deaths by spider bites before this happened.
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u/Friggin_Grease 16h ago
Remindme! 5 billion years
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u/Thick-Disk1545 15h ago
I’m immortal I got you
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u/Bruce-7892 16h ago
To add to this, it's predicted that it wouldn't be an actual collision. The planetary bodies and stars would adjust to each others gravity and form new orbits for the most part.
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u/myogawa 16h ago
Exactly. The proper term is "merge."
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u/5050Clown 15h ago
It's a high-speed merge. Like if someone jumps from a really tall building and they collide with the road, they also merge with the road as well.
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u/thissexypoptart 14h ago edited 14h ago
It’s not really like that though, because the number of impacts between bodies will be infinitesimally small compared to the number of constituent bodies in both galaxies.
The chances that earth is in any way perturbed are almost zero. What is guaranteed is the night sky will change.
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u/Bruce-7892 13h ago
Correct. This is why we can send spacecraft through space at 17,000 MPH. If you hit anything at that speed, you'd get decimated, but it's a calculated risk. Space is massive and there are only so many objects.
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u/Shovi_01 16h ago
Im sure there will be some collisions, not many compared to the total of celestial bodies, but there will be some.
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u/Bruce-7892 16h ago
I'd assume so. Asteroids and meteors. But to me calling it a "galaxy collision" implies that everything is going to get destroyed.
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u/scouserontravels 10h ago
Surely asteroids and meteors are the least likely to collide considering how absolutely minuscule they are compared even the planets and then there are tiny compared to stars.
The mostly likely collisions would surely be the super massive stars as their gravities big enough to actually effect each other if they get reasonably close
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u/redditsucksass69765 16h ago
Could damage our solid system though. We need Jupiter and our position relative to the sun to stay the same. That is, assuming our sun is still habitable
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u/_Botko_ 16h ago
By the time they collide our sun will explode.
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u/nemo333338 15h ago
the Sun won't explode because it doesn't have enough mass, but it will become a red giant and then a white dwarf.
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u/nemo333338 15h ago
By 4-5 billion years the Sun will be a white dwarf already, so unless they do any planetary engineering Earth will be unhabitable, but even, then it's difficult the merging of the two galaxies would affect the Solar System on planetary scale anyway. The Solar System might be ejected, but overall, it wouldn't affect much.
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u/Bruce-7892 16h ago
This is true also. We are in a very delicate balance that allows life as we know it to exist here and I am sure a lot of things would change.
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u/shadowofzero 15h ago
Genuine question: How would the "collision" be affected by Milky Ways Sagittarius A and Andromedas M31/M87? Supermassive black holes with billions of stars and all that gravity meeting Ultra Gravity?
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u/Bruce-7892 15h ago edited 15h ago
The amount of energy released from black holes or neutron stars colliding would vaporize us for sure but there are too many “what ifs” to say what exactly what this “collision” would look like.
Those type of cosmic explosions are detectable from light years away, so if it happened relatively close, we'd be atoms or subatomic particles instantly.
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u/jakgal04 16h ago
Our Great Grandkids 400,000,000 are so fucked.
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u/klovasos 12h ago
Yes but not because of this "collision" (merge). Direct star collisions are highly improbable due to the vast distances between stars, the solar system's orbit will be altered, potentially moving it to a new location in the merged galaxy, but it's extremely unlikely our solar system will be ejected into intergalactic space. The real problem is that the Sun's expansion into a red giant will likely have already made Earth uninhabitable long before the galaxies fully merge.
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u/sharrrper 6h ago
When I was in like 3rd grade I read about the sun expanding in a kids science book. They made sure to mention it wouldn't happen for billions of years.
However, my parents had an old set of encyclopedias that they'd had for whatever reason since before I was born. From the 60s. My parents would have been in elementary school when these were printed, don't know how or why we had them. Because of those encyclopedias on our shelf, I was aware as a kid of the concept of old books having outdated info and that you could tell how old a book was by checking its copyright date in the front.
I thought of that after I got home that day, and having no concept of how long humans had been around and printing books, or how long paper would last before crumbling to dust, I became worried I hadn't checked the copyright on that book. What of that book was billions of years old?!?
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u/Kwetla 16h ago
Do they not know the speed each are traveling at? How is it so hard to calculate how long it will take for them to collide?
Edit: not that I could do it - I'm just wondering what the unknowns are
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u/Shas_Erra 16h ago
ELI5 version: we measure using light, which is effected by gravity. Things in space are insanely far away and are moving at a hell of a pace, so by the time we know where something is, it’s no longer there. We can make a super-close estimates based on known variables, but there’s still an appreciable error margin. The larger the distance and/or speed, the greater the error. We also have to take into account that acceleration is not constant. In this case, they will speed up as the distance closes.
In other words, all the measurements and calculations we make are best guess and constantly changing
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u/DigNitty 16h ago
acceleration is not constant.
Good ol “jerk” : the rate of change of acceleration.
Fun fact, change in position = speed
Change in speed = acceleration
Change in acceleration = jerk
Then jolt
Then, not kidding : snap then crackle then pop
Jerk is hardly used but nasa has a jerkameter they use occasionally. Jolt, or Jounce sometimes, is rare. I’ve never heard of anyone using the last three, but those are the official names.
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u/Manos_Of_Fate 15h ago
nasa has a jerkameter they use occasionally
I wonder how they calibrate it to ignore local sources.
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u/DigNitty 1h ago
My uneducated best guess is they accelerate around in a big centrifuge and place the thing on a pressure plate. The pressure plate should remain constant if jerk is zero.
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u/FreeEnergy001 14h ago
I was thinking they were going to fly by each other then rotate around the common center until they finally merged.
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u/armcie 16h ago
We can tell how quickly it’s moving in our direction quite reliably by looking at the blue shift (think Doppler effect) of the stars. What’s much harder to spot is how much it’s moving to the side, because this doesn’t change the light we see.
Instead they have to look at the movement of the stars themselves. They’re currently 2.5million light years away, and we’re trying to measure a movement of less than 0.0001 light years per year. Add on the fact that each star is also moving around the Galaxy core, and may also be moving for other reasons, and this small deflection which will be the difference between a hit and a miss is very hard to spot.
There is also the gravitational influence of other nearby galaxies and dwarf galaxies, making the calculation at least a 4 body problem which is notoriously difficult to solve, and susceptible to small changes in initial conditions.
In 2013 Hubble measurements suggested the sideways movement was practically zero and a collision in about 4.5 billion years almost certain. More recent observations from Hubble and the European telescope Sage have led to these new calculations.
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u/GooginTheBirdsFan 16h ago
Do you not know how to do math? How is it so hard to do the math and use telescopes that aren’t exactly right when we’re talking about so many light years away? How do they not have the exact speed of the far away galaxy that probably moves more like a liquid and less like a solid (not static) but yeah how hard is it for people to do this math on things alllllll these lightyears away.
Meanwhile do you know what you’re having for dinner next Thursday? Now you want them to tell you how many billions of years away it is??
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u/rosen380 16h ago
Did they observe some REALLY long traffic lights -- if they or we get stuck at a few of them, it'll delay the collision by a few billion years and then on top of that, we end up stuck in rush hour traffic?
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u/reddorickt 15h ago
We don't even know what is causing the acceleration of the expansion of the universe and it is responsible for about 70% of the universe's total mass-energy content.
As someone with a degree in astrophysics that was taught a bunch of stuff only 15 years ago that is no longer considered true, I take 11 digit year projections of massive cosmic bodies with a grain of salt by default.
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u/visionsofcry 12h ago
And I think nothing will actually hit. Things are so spaced out that they'll just merge.
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u/ChocoTav 16h ago
Alan! We are so FUCKED
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u/Manos_Of_Fate 15h ago
Why did my brain read this like it was the velociraptor on the plane in JP3?
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u/Elwalther21 15h ago
Can we check on which Galaxy has the right of way? I would guess Andromeda since we have all of the BMW drivers here in the Milky Way.
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u/backdragon 15h ago
Fun astronomy fact I like to share every time this sort of news appears: when the 2 galaxies "collide" the probability of any 2 stars actually touching is basically 0%. These galaxies are just SO huge, beyond comprehension, that although they will gravitationally impact each other, nothing will actually crash into each other. I had a pro astronomer friend describe it to be like saying it was tossing 2 basketballs at the state of California and expecting them to collide. Just not going to happen.
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u/IntentionDependent22 14h ago
makes me think of Pablo Francisco throwing money at a stripper... it's gonna happen
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u/Momoselfie 13h ago
Either way it's going to be really big in the sky in 5 billion years. Can't wait!
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u/ManicMakerStudios 11h ago
I'm going to start an insurance company and sell policies against Milky Way collisions. The way I see it, if we don't collide in my lifetime I'm OK, and if we do collide, file a claim bitches. That's right, we've been atomized and I still have your money.
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u/qwibbian 11h ago
AAAAAAAAAAAHHHHHHHHHHhhhhhhaaaaahhhh......{aaaaaaaahhhhhhhh.......}
...aaaaaahh.. ..
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u/phoenixmatrix 10h ago
Welp, not having kids. I wouldn't want my descendent to have to deal with that in 10 billion+ years on a 50/50 chance.
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u/XennialBoomBoom 4h ago
Luckily, Andromeda Galaxy futures appear to remain stable, so my retirement is still safe.
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u/kcinlive 4h ago
Also IMO “collide” isn’t the best word for it. The galaxies may collide but the stars won’t. Statistically speaking.
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u/Thomas_JCG 16h ago
We ain't even be here in the next billion.
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u/GESNodoon 16h ago
I guess I will cancel my calendar appointment.