Watch out! Andromeda, the giant spiral galaxy colliding with our own Milky Way, has devoured several galaxies before Andromeda, a massive spiral galaxy, has swallowed several galaxies within the last few billion years before setting its sights on the Milky Way. "The Milky Way is on a collision course with Andromeda in about four billion years,” said Dougal Mackey, co-author of a new study published in Nature and a research fellow at the …
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Hmm, now it seems as if to ensure mankind's survival just getting off this planet isn't enough - we really need to spread our wings beyond this galaxy.
After that, well this universe is obviously doomed in the medium term, so we should be working on a way out.
I'd say things aren't changing slowly enough.
"Hmm, now it seems as if to ensure mankind's survival just getting off this planet isn't enough - we really need to spread our wings beyond this galaxy"
^ This. It's time to migrate to the M33 Triangulum spiral galaxy because when the Milky Way and Andromeda galaxies collide and merge, there'll be an enormous starburst of new stars using up pretty much all of star forming gas in one huge go...meaning that you'll end up with a massive elliptical galaxy which is basically like a retirement home for old and ageing stars waiting to die.
That's like moving from one volcanic island to another. Same problems, different real estate.
The thing to do is go out to sea well away from all the issues of nebulae, novas, colliosions, etc
Now what is lurking in intergalactic space is still to be determined mind you.
Hmm, now it seems as if to ensure mankind's survival just getting off this planet isn't enough - we really need to spread our wings beyond this galaxy.
Not really, at least not in this context of two galaxies colliding.
Galaxies are mostly empty space. When (if) the two galaxies collide, there will be little to no direct affect on 99% of the stellar systems. Stars and their associated stellar systems will mostly (99%) just pass each other in the empty vastness of inter-planetary space between the systems, like two ships passing in the night (although if there are icebergs we're in trouble). Sure, entire star systems will change their orbit around the new galaxy, but within the systems themselves there will be no to little change as the system as a whole will still be intact, the same as before. Therefore any life on those planets will carry on as before, except with different (over galactic timescales) stellar arrangements in the sky (i.e. new constellations), a lot of new stars being formed (starburst galaxy) from the colliding gas clouds, more supernovae, etc.
So as long as life has spread itself across even just a few systems spread across a few dozen light-years or so, then the chance of that life surviving the foreseen galaxy merger and any highly unlikely stellar system-affecting 'collisions' would be 99.99(many recurring)%.
Well, unless the galaxy merger brings with it a vicious, implacable, xenophobic species that is strong enough to destroy all opposing life that our Milky Way brings into the new union that is.
When the time comes, Grand Marshall Galaxy will issue the order for the defense against Andromeda to begin.
General Milky Way and his aide, Lieutenant Mars, will begin putting the battle plan into action. gobstoppers will be their shells, M&Ms will be their bullets, all fired using Boosts as propellant.
Curly Wurlies used as trenching ladders by the Freddo mounted infantry, riding atop those Lindt Bunnies.
Hundreds and Thousands will be called into service in defense of the clusters.
Even though science has already simulated this a number of times, it is obvious that more data can only yield better understanding and more precise simulations.
So go for it, boffins !
By the same physics that cause comets to occasionally come into the inner solar system, just on a much larger scale.
Andromeda and the Milky Way have been dancing around each other along with several satellite galaxies as part of the Local Group. It's probable that one big galaxy won't be the only outcome of the collision. Further smaller galaxies will be formed.
It's also likely that no-one will even notice a thing - even if (as is hypothesised) our star gets flung out of the Milky Way.
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I thought it wasn't matter that was expanding, but space which the matter occupies. So things appear (at least on the small scales of galaxies) to remain the same size relatively. We only notice it for really far objects in that we notice the distances increasing so much that light wavelengths get greater.
Space is expanding (at evidently an increasing rate) but it's expanding in all directions at the same time, and at the same rate. In the case of the Milky Way and Andromeda, the forces of gravity and any existing momentum and direction they were already travelling in overcome the rate of space expansion between them.
I'm going to take a really hypothetical punt that if space is expanding at greater rates, in the extremely far future gravity for the most part won't be able to overcome that expansion and eventually strong forces like magnetism and atomic forces won't be strong enough. Wavelengths for light will get longer, energy more diluted across the universe and eventually even subatomic particles will get "pulled" apart.
Apparently (on some really rudimentary searching) that space is expanding at 68km/s per 3.2 million light-years (or 1 mega parsec). The more space the faster the speed and acceleration relative to us.
Andromeda is 2.5 million light years away and travelling toward us at 111km/s relative (250,000 mph)... the space inbetween is expanding at roughly 45km/s (due to less than 1Mparsec)... and this will reduce as Andromeda gets closer. Also as Andromeda gets closer the acceleration due to gravity will increase.
All information just from https://phys.org/news/2015-02-fast-universe.html
There are three possible final states for the Universe. Expand at a steady constant rate, expand at an ever increasing rate, or the rate of expansion eventually slows down and once it stops, the Universe collapses in on itself. The models require large quantities of dark matter and dark energy to replicate what is being observed and are further complicate by the fact that the relative proportions of dark matter and energy to 'normal' matter and energy have varied over the life of the Universe. So although the rate of expansion is currently increasing it may not always continue to do so depending upon how these ratios change.
I think your theory (ever increasing rate) is known as the entropic heat death of the Universe (while the contraction is the big crunch).
"I'm going to take a really hypothetical punt that if space is expanding at greater rates, in the extremely far future gravity for the most part won't be able to overcome that expansion..."
That idea is called the Big Rip. And, on balance, the evidence is probably against it.
I've always like a mental model of space being like a balloon that is being slowly inflated, with the universe (in 2D) on the surface of the balloon. This assumes that our universe is part of some larger construct which we probably can't ever prove or disprove. If there's nothing to stop the inflation, perhaps like a balloon someday it simply bursts? If that happens, I'm sure it will happen on a Monday.
Well, you see, the balloon is space (in the cosmological and empty area on a desk sense), so it's not that there's nothing outside the balloon, it's that there is no space outside the balloon for there to be nothing in.
I'm probably a bit off with that decription, but then the universe is under no obligation to make sense to me.
If you subscribe to a religion... then its God who is driving this ship.
And of course this confirms the theory that God must be a woman. An elderly Asian Woman to be precise... ;-P
(Note: This is an old joke that anyone who's driven down the 101 in SFO or on an LA freeway knows. )
Don't be a hater, it was said in jest. :-)
All matter in the universe is expanding, at an ever incresing rate i.e. getting further apart.So how do 2 very big lumps of matter end up on a collision course?
To be technically accurate, you should say:
AllOn average the matter in the universe is expanding, at an ever increasing rate i.e. getting further apart.
It's not an absolute 'all' statement. Like with any other average, there are elements above and below the average that don't behave like the average. There are some regions were matter is moving apart faster than the average, some where it is moving more slowly than the average, and some where it is the opposite of that average, that is, it is moving together.
Designations like 'galaxy cluster', whether it's local group or cluster or supercluster refer to groupings of galaxies (or groups of groups) where, within that group, the gravitational attraction between the galaxies is stronger than the rate of the expansion of the universe. They are gravitationally bound to each other, therefore they are travelling along as a single group (on large scales), including orbiting each other, or towards each other and merging. As space stretches apart at <whatever the number is>km/s2, the gravitational attraction between the galaxies is equal to or greater than that expansion rate, keeping galaxies at the same approximate distance, or reducing the distance thus allowing for mergers.
You know those pictures of active galaxies firing matter out of their poles, but in bursts toggling in opposing directions?
We've got plenty of time to develop interstellar travel and get to the core, then we divert matter into the central black hole to make it active.
But we only let it fire matter in one direction.
The ejected matter goes one way, the black hole goes the other way and drags the Milky Way galaxy with it. So we simply fly the galaxy away from Andromeda.
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Easy peasy. You simply tow in another smaller supermassive black hole to sit in position to suck in the matter being fired in one direction so only the other direction can be used as thrust.
To prevent this second black hole from moving towards the first you have to remember to set its brakes, and put chocks under its wheels just to be safe.
Didn't the Time Lords create an artificial singularity? They maybe moved a few planets around but I'm not sure even they would be up to the job of moving a million solar mass black hole around.
Come to think of it, instead of moving another black hole in place you'd only need to fit a Shkadov Thruster to one 'end' of the black hole. It would be held in place by a neutral balance of the black hole's gravity and the outward thrust of the polar jet. Then the thrust is only coming out of one side and it will (slowly) move, and take the entire galaxy (even more slowly) with it.
Unlike my previous tongue in cheek suggestion this could actually work, assuming you could manufacture a material strong enough to survive a matter/radiation jet hitting it at a good chunk of light speed, in some pretty significant quantities. Neutronium ought to be fairly durable, but perhaps you must assume it will be ablative, let it be eroded away, and you continually add onto it on the other side? But hey, if you wake in the morning and your boss tells you "OK we have a new project which is to move this entire galaxy out of the way of Andromeda before it hits in 4 billion years" you are probably used to solving such problems. Maybe the Milky Way's central government is already on it, but it has hit cost overruns of a few quintillion credits as the schedule lagged out to 400 million years until completion.
You could put this second black hole with its spin axis at right angles to the 'propulsion' black hole, directly under the stream from the propulsion black hole that you don't want to provide any propulsive force. Then this 'attitude thruster' black hole would send the jet from the propulsion black hole out as two new jets emanating from this attitude thruster at right angles to the direction of movement, providing no (or counterbalanced) lateral thrust.
Of course, this would mean sending those additional streams out, most likely, into the plane of the galaxy, thus destroying all life for thousands, tens of thousands, of light years through the plane.
However the stars have been around a significantly longer period of time than 50,000 years so if gravity does travel, it would already be at those stars and they would already be attracted to the 'black hole'. As Andromeda and The Milky Way are being attracted towards each other gravity must already exist between them. In fact Astrophysicists recognise structures called galaxy clusters which contain thousands of galaxies all of which are gravitationally bound to each other. 50,000 light years is quite insignificant in terms of those distances.
You also get superclusters in which the galaxy clusters are not gravitationally bound so that suggests there is a limit to how far gravity can impact something. However as we can observe these superclusters from a greater distance than their component clusters then gravity, if it travels either loses most of its strength in that distance, or travels a lot slower than the speed of light.
Evil_Tom actually has a good point. We need to start now.
Gravity does travel at the speed of light (see gravity waves). While our galaxy is gravitationally bound and behaves as if the core is located and moving where and how it is, a change caused by acceleration can only propagate at the speed of light (otherwise FTL communication would be possible). The same phenomenon is seen for charged particles in motion. If they are moving with constant speed then their apparent field at a distance is consistent with that, but change their direction (e.g. accelerate or stop them) and the observer only notices the difference in their local field after enough time has passed for the signal to reach them. Charged particles at a distance find themselves attracted to where the accelerating charge was.
On the other hand, while Sagittarius A* is really massive, it's actually only around a millionth of the total mass of the Milky Way, which is really really massive.
that suggests there is a limit to how far gravity can impact something
No, gravity's range is infinite. The effect is just incredibly weak at great distances.
gravity, if it travels either loses most of its strength in that distance, or travels a lot slower than the speed of light.
The first item. Definitely the first. Have you heard of the inverse-square law?
So Andromeda is guilty of galaxy-cide, by consuming smaller neighboring galaxies, and now it's coming for us. Isn't the Milky Way equally culpable? It was only a year or so ago that I was reading about how the Milky Way had hoovered up five or seven smaller galaxies.
In any event, we personally and humanity in general will be long gone before that happens.
That's easy to answer. When two trucks collide, which one "wins"? Neither of them; nobody "wins" in a collision.
But galaxies aren't solid, and the individual stars will only very rarely collide. What's likely to happen is that they will fold in upon themselves like water splashing from the collision of two bucket-fulls of water. Most of the combined mass will be in the consolidated "MilkyDromeda" galaxy, and some of the star systems will be whipped out into intergalactic space. And there will likely be a frenzy of star formation as the combined gas clouds are blended together.
The spearhead of the invasion force began to cross the 5,000 light years of intergalactic space in an attempt to form a bridgehead for the main force. Their forecasts of chaotic stellar trajectories updated in real time and fed into a matrix of plans and contingencies a million years in the making.
"Conquer... or be conquered!" had been the rallying cry which had brought together a galaxy in turmoil. Thousands of star systems had been sacrificed, converted into materiel for the conflict ahead. And there would be conflict, because they could see similar preparations being made on the other side of the gulf. They could surmise the strategies behind the out-of-sequence supernovae, stars perceptibly changing course and so on, but were more concerned about what they couldn't see.
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