back to article Worried about the Andromeda galaxy crashing into our Milky Way in four billion years? Too bad, it's quite possibly already happening

Andromeda sports a ginormous halo of gas with a mass greater than 100 billion Suns that stretches from its outer edges up to two million light-years – a distance that reaches more than halfway to our own Milky Way galaxy. If the structure was visible to the naked eye, it would appear three times the width of the Big Dipper, …

  1. The Oncoming Scorn Silver badge

    With Apologies To Ultravox - Hello.

    Halo, halo, halo

    Welcome to this Galaxy

    Halo, halo, halo

    Look at the mess you'll make

    Icon - Midge Ure's raincoat.

  2. Little Mouse Silver badge

    Friday challenge:

    See if you can slip the term "gas band" into one of your meetings today.

    1. Caver_Dave

      Re: Friday challenge:

      I tried "halo gas band". The bod thought that I'd got a new weapon for my first person shooter game.

      I'm not trying "gas band" on my wife who plays in a Brass Band, as she may be offended (for the next month or so!)

  3. Anonymous Coward
    Anonymous Coward

    If the universe is still expanding after the big bang, how can galaxies end up colliding? Surely they'd be moving away from each other?

    1. Anonymous Coward
    2. KittenHuffer Silver badge

      The simple answer is that if you're close enough (and massive enough) that gravity is drawing you closer faster than the Universe expands for the distance apart, then you are 'gravitationally bound' and a collision/merger is inevitable.

      So the Milky Way and Andromeda are massive enough and close enough that gravity has won out over the expansion rate of the Universe.

      Go check out Starts With A Bang (on Medium or Forbes) for plenty of articles on this sort of stuff.

    3. Gob Smacked

      An honest question should not be downvoted... You're correct: on the large scale of the universe, everythings seems to drift apart, like a helium weather balloon floating up in the sky pushing individual heliums atoms further apart as the balloon grows in size. These helium atoms still bounce against eachother though, but that frequency drops as the balloon gets higher up: the internal pressure drops. It's just that individual helium atoms have speeds greater than the speed with which the balloon extends.

      It's the same for stars and star systems: if their individual movement is with higher speed than the speed with which the universe is expanding, that individual movement will prevail.

    4. Brewster's Angle Grinder Silver badge

      Think of a cannon ball on the rubber sheet. We're heating the sheet so it stretches and expanding the outer frame to keep the tension the same. None of which changes the dimple created by the cannon ball. If there was a marble spinning round the cannon ball, the marble would move slightly higher round the well as the sheet was tugged outwards, but providing it didn't break free, it would carry on spinning and return to it's original height.

      More simply: you can model metric expansion as a repulsive force and in the modern universe it's much smaller than the correctional gravitational attraction.

    5. DJO Silver badge

      Galaxies are in clusters which are gravitationally bound to each other.

      The expansion of the universe means that clusters are moving apart from other clusters but movement within the clusters themselves will continue.

      Eventually the clusters will start to spread out and the stars fade away but that is zillions of zillions years in the future.

    6. HildyJ Silver badge

      Life, the Universe, and Everything

      First, the expansion of the universe doesn't affect the movement of galaxies. Space itself is expanding. The perceived movement of galaxies due to space expanding is such that distant galaxies are perceived to be moving at more than the speed of light (which they can't do).

      That said, galaxies (and solar systems, and planets) do move due to gravity. In our galactic neighborhood gravity, electromagnetism, and other forces are much more noticeable than the expansion of space which only becomes noticeable for objects millions of light years away. Thus we have drawn in and will continue to draw in dwarf galaxies which orbit the Milky Way and Andromeda will continue to draw in our smaller galaxy.

      One other correction for a subsequent post - the sun is predicted to start expanding about a billion years after the galactic merger so whatever life is surviving on Earth will see a great show.

      Congrats to the boffins who worked this out and I look forward to an analysis of what the interactions of the halos will do to star formation.

      1. Anonymous Coward
        Anonymous Coward

        Or Gravity isn't a constant

        "Space itself is expanding.... perceived movement of galaxies due to space expanding is such that distant galaxies are perceived to be moving at more than the speed of light (which they can't do)... etc etc etc"

        You assume that the gravitational constant is actually a constant, but there's no real proof of it. Measuring it locally, then extrapolating it universe wide does not work. It needs dark-matter and inflation to fix it up. Yet you cling to the 'constant'!

        A more obvious observation is that gravity cannot be a constant, that gravitational 'constant' must be stronger locally than distantly.

        I can show you why that must be the case quite easily with a thought experiment.

        1) Take a bunch of magnets, shake them together, they will align to clump together. Like-polls push each other apart, opposing-polls pull each other together, add motion and they will order themselves to form a net-attraction force. Lets call this 'magnetic clumping'.

        2) You see the same "attraction only" style forces throughout nature, e.g. water molecules arrange themselves to clump together. Crystals clump together and so on.

        3) This clumping effect does not magically disappear at distance, so it MUST form part of gravity. The overall magic clumping force, gravity, must be the sum of lots of these clumping forces, including our magnetic clumping, water clumping, crystal clumping effects and many many many others.

        4) Our magnets are now stuck together in one place, locally the clumping force is higher, and since the magnets are now concentrated in one place and less spread out across the galaxy, the universe clumping force is slightly lower.

        5) So the act of clumping, causes *local* clumping to be stronger than universe wide clumping.

        6) And since our clumping force forms part of gravity, this also applies to gravity.

        7) Hence local gravity is stronger than distant gravity and "gravitation constant" cannot be an actual constant.

        8) So the internal gravitational 'constant' inside a galaxy is stronger than the gravitational 'constant' between distant galaxies.

        So I haven't gone into the nature of peasoup, the resonant oscillating electric universe, or any kind of deep dive here. It's all very simple and easy to understand and there's nothing in it that isn't logically consistent, yet it shows you why the clumping force, gravity, cannot be a constant and must be locally stronger than at a distance.

        I'm currently asking you (well cosmologists) to find tumbling galaxies, it's really a no-brainer to see why they keep their structure given the above.

        1. Daniel Pfeiffer

          Re: Or Gravity isn't a constant

          1) Take a bunch of magnets, shake them together, they will align to clump together. Like-polls push each other apart, opposing-polls pull each other together

          I see that in the campaign for the Brexit-poll, Farage told you not to like Poles. This has led to your being pushed apart from European like-poles. Meanwhile the hot gas halo drifting out of BoJo's mouth, is magnetically pulling you together into a chlorinated-chicken 51st state of Andromeda fantasy.

    7. herman Silver badge

      It is Eddie's fault

      Surely you know that there are eddies in the space-time continuum?

      1. Spherical Cow

        Re: It is Eddie's fault

        "Eddies in the space-time continuum" he. Is he.

  4. Julz


    About the dark matter? If it is real and is responsible for the unreasonable orbits of stars in galaxies, then a merger like this is going to be an interesting ride.

    1. Pascal Monett Silver badge

      The only problem is the fact that our planet is going to be an roasted husk in about a billion years, due to the Sun's increased activity as it goes through its hydrogen reserves.

      Humanity will have to have migrated from Earth by that time if we want to have a chance of being around when the merger actually becomes visible.

      1. Flocke Kroes Silver badge

        Re: Humanity

        1 billion years ago life was single celled. The Cambrian explosion was 500 million years ago. If humans have descendants a billion years from now evolution will make them very unlike us - and that is ignoring genetic engineering. If anything remotely human exists that far in the future it will be because archaeologists digging up something like a future Jurassic Park get raided by time travellers.

        1. aberglas

          Re: Humanity in 100 years

          Will be robots.

          Ok, so maybe 200 years, but no longer. Once machines are smarter than us why would they want us around?

          So, no need to wait around a billion years.

          1. Yet Another Anonymous coward Silver badge

            Re: Humanity in 100 years

            > Once machines are smarter than us why would they want us around?

            Don't you read on-call ?

      2. KittenHuffer Silver badge

        I would hope that in a billion years humanity would have been able to migrate the Earth a little further out from the Sun, keeping it within the Goldilocks zone.

        1. The Oncoming Scorn Silver badge


          Or simply move it to a new system & wait for a couple of Ancillary Guardians of Enviroment and Life in a starship to turn up.

          All this has happened before & will again (etc).

        2. Sudosu

          Can we load up the B Ark now and send it off ahead?

          1. Proton_badger

            Ark Fleet Ship B

            I'm sure our population of Social Influencers are keen to board Ark B and I see no reason to delay them.

          2. Michael Habel Silver badge
          3. Doctor_Wibble

            Good idea, but needs a change to the passenger selection - as per above the 'influencers' should get priority, and since we know the lesson of it we should keep the telephone sanitisers here because their skills are needed right now.


            And being unable to mention the subject without one of my favoured remarks "social media influenzas are a plague on the internet" as it has that magical combination of both punnage and accuracy on how their infection spreads.

      3. ThatOne Silver badge

        > Humanity

        Will most likely be long extinct. Since this planet appeared, countless very successful or even dominant species have gone extinct after a period, even non-suicidal species without access to nuclear weapons.

        1. David Hicklin

          Will most likely be long extinct

          We have to survive the next supercontinent first as all the land masses move back together.

    2. Brewster's Angle Grinder Silver badge

      Re: What

      I came to post a similar thought. If there really are dark matter halos, then a merger really ought to shed *ahem* light on it.

  5. Anonymous Coward
    Anonymous Coward

    Unwanted neighbors

    Don't let the Orange One learn about this -- he'll build a wall and send the bill to the Andromedans.

    1. Stoneshop Silver badge

      Re: Unwanted neighbors

      Let him lay down[0] the first element, and supervise its building from up close too.

      [0] or up, or sideways, whatever.

    2. Michael Habel Silver badge

      Re: Unwanted neighbors

      Oh HO HO U SO PHUNNY not -_-

  6. Pascal Monett Silver badge

    Just as an aside

    Google "andromeda collision" images. Most of them are breathtaking. I rather like this one.

  7. Magani
    Thumb Up

    As long as...

    ... you know where your towel is, you'll be OK.

    Vale Douglas

  8. Elledan

    Job interview question

    Where do you see yourself in four billion years?

    1. ThatOne Silver badge

      Re: Job interview question

      > Where do you see yourself in four billion years?

      Still waiting for a pay rise?

    2. John R. Macdonald

      Re: Job interview question

      Wondering why the Brexit talks are still dragging on.

      1. Michael Habel Silver badge

        Re: Job interview question

        Knowing how the Goverment works... This wouldn't even be halfway surprising.

  9. Alister

    Worried about the Andromeda galaxy crashing into our Milky Way?

    It's alright we have nice big crumple zones

    1. The Oncoming Scorn Silver badge
      Paris Hilton

      But that's quite enough about Eccentrica Gallumbits.

      Icon - Seems apt.

  10. hagster


    For a split second I misread the article and was horrified to read it was only 4 million years away. But it's actually 4 billion years - phew!

    1. This post has been deleted by its author

      1. The Oncoming Scorn Silver badge

        Re: Billions

        can not fall because in an infinite space there is no up for it to fall down from.

        Icon - Pint to Douglas.

  11. Mystic Megabyte

    mind blown?

    Due to lockdown and also not owning a TV I've watched too many YouTube videos. Unfortunately I've watched a whole load of flat-earth debunking videos. Most of these are amusing but there is something really wrong with these flat-earthers. A complete lack of imagination. I can imagine galaxys colliding, it is sort of mind blowing. But these poor flat-earthers who believe that they live in a snow dome are very sad. Our knowledge of the Universe has expanded exponentially in the last few hundred years. How can people still be so dim?

    1. Stoneshop Silver badge
      Thumb Up

      Re: mind blown?

      How can people still be so dim?

      Probably has to do with not wanting to confront the reality that they're an amazingly primitive ape-descendant life form on an utterly insignificant little blue-green planet some ninety-two million miles out from a small unregarded yellow sun in the uncharted backwaters of the unfashionable end of the western spiral arm of the Galaxy.

      1. Joe W Silver badge

        Re: mind blown?

        And they are always unhappy, especially when it comes to little green bits of paper - which is strange, because it's not the little bits of paper that are unhappy...

        1. aberglas

          Flat earthers just don't swallow propaganda whole

          They think about what they see and read. And they see the fallacies, piled one upon the other. Lots of naive people agreeing with each other, all wrong.

  12. This post has been deleted by its author

    1. bonkers

      Re: 'Big Dipper'

      Erm, it's actually called Ursa Major.

      1. The Oncoming Scorn Silver badge

        Re: 'Big Dipper'

        I've always called it The Plough.

        1. Stoneshop Silver badge

          Re: 'Big Dipper'

          Nothing happens.

          Oh wait, that was 'plugh'. Never mind.

          You're in a maze of twisty little coat racks, all alike.

      2. OldGuit

        Re: 'Big Dipper'

        Ursa Major includes the bear's legs, shoulders and head. The Plough (and the Big Teaspoon) don't

  13. swm Silver badge

    Which is bigger - Andromeda or the Milky Way?

    I've heard both. So who absorbs whom?

    1. ThatOne Silver badge

      Re: Which is bigger - Andromeda or the Milky Way?

      Insurance will decide.

    2. Francis Boyle

      It's a merger

      It'll probably end up being called something like the AnWay Corporation.

  14. Rol

    Clarification required.

    If the light from Andromeda's quasars gives our scientists an understanding of the material it has passed through on its journey to Earth, and they have no means to measure the Milky Way's halo gases, then surely their findings are the sum of both galaxies' halos.

    I guess the only solution is to measure it again after a few million years have passed, and then calculate the influence of our own halo based on the assumption that Andromeda has remained constant, while the distance travelled through the Milky Way to get to us has changed as we orbit our galactic black blob.

    Then again, I'm sure that has already been factored into their findings, and my argument is based solely on the article presenting the juicy information while not getting bogged down in the technical whys and ways.

    Rogue stars! That's the answer. Stars that had slipped their galactic chains long ago, and therefore their light arriving at Earth is far more influenced by our own halo than anything else, give or take the odd intergalactic gas cloud.

  15. DJV Silver badge

    Project AMIGA

    I hope the person in charge isn't called the Commodore...

    1. Spanners Silver badge

      Re: Project AMIGA

      I thought he was called Vic.

    2. Kevin McMurtrie Silver badge

      Re: Project AMIGA

      This isn't about Dylan, Rommie, Beka, Tyr, Seamus, and Trance?

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