When viewed from Earth, the universe can feel as though it should be quite a tranquil place.
This incredible expanse stretches out seemingly forever, and we’re just one small part of it
on this blue and green world we call home. But really, the universe is also a place of
total turmoil, where entire galaxies face off against one another… fighting and colliding, in
a dramatic cosmic dance into the future. And our galaxy, the Milky Way, has its own role to play.
This is Unveiled, and today we’re exploring the
extraordinary prediction that our galaxy could be heading for a triple collision.
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On a crystal clear night, were you to look up at the sky and gaze at the stars, you might see the
tail of our home galaxy, the Milky Way, stretching out before you. But whether you can pick it up
with the naked eye or not - and sometimes you can - we also know there’s another bright object right
next to the Milky Way… and that it will eventually cause us big problems. That object is Andromeda,
the closest major galaxy to our own. And, though for now it may seem like nothing more than an
inconsequential streak across the sky, it is in fact speeding towards us at a rate of seventy
miles per second… and one day, in the distant future, it will collide with the Milky Way.
So, how concerned should we be? Right now, as we live and breathe and watch YouTube
videos all about it, not very. We are still dealing with truly epic time periods here,
with the collision not set to happen for another 4.5 billion years or so… but, also, this isn’t new
ground for our galaxy, anyway, as the Milky Way already has a history of major collisions… meaning
that many of the billions of stars that now reside within it aren’t permanent residents. It’s thought
that, in total, the Milky Way has been party to at least ten collisions with neighbouring galaxies
over the course of its history… and, according to one multi-authored, August 2020 study,
at least five of those were large-scale, involving at least 100 million stars. With each
of these past events, then, our galaxy has grown. But can we expect more of the same going forwards?
What, for example, is the collision between the Milky Way and Andromeda
actually going to look like? Scientists have been able to learn much more about it thanks to a 2021
image obtained by the Hubble Space Telescope of the Arp 195 galaxy cluster… which is a galactic
group located in the Lynx constellation, some 760 million lightyears away from Earth.
Arp 195 is a cluster that NASA describes as being made up of three different galaxies in a three-way
tug-of-war. The Hubble image, further described by NASA as showing three “squabbling galactic
siblings”, shows how the galaxies are inescapably attracted to each other, gravitationally bound,
and seemingly headed for impact. It’s a cosmic episode of genuine chaos, then,
although there is still some structure to be found. Among the three galaxies in Arp 195,
the largest galaxy is predictably shown to exert the greatest influence over the others…
and it’s therefore thought that it will come out on top. The shapes seen in the Hubble
image - which is a whoosh of dust, gas, and bright light - look as though they should be random,
but actually there’s a reason why they are as they are. Ultimately, in this case,
scientists expect the three individual galaxies to merge into one single galaxy… so that when
astronomers of the future look in the direction of what’s now Arp 195, it won’t be immediately
obvious to them all that has happened. So, Arp 195’s fate is now inevitable,
but why should we care about it? One reason is that what’s happening there provides an early
glimpse into what will happen here, with the Milky Way and Andromeda... and one other galaxy
(which we’ll get to shortly). First, we need to fully chart the rise of Milkdromeda - the
name that’s already been given to the galaxy that will exist once the Milky Way and Andromeda meet.
First things first, while there is some potential for all out carnage, scientists don’t believe
that we’ll see endless explosions amid literal collisions of stars and planets taking place.
This is because space is just too big… and the sometimes lightyears-wide gaps between the stars
inside individual galaxies mean that, even when those galaxies are crashing through one another,
it’s still very rare that any physical thing would smash together. What’s much more likely
is that most objects will just idly pass by one another… and, indeed, it’s been shown that
galactic mergers can actually increase the rate at which new stars are created in the long term,
rather than causing more stars than usual to crash, explode and disappear. The collision will
certainly redistribute the stars and planets, though, of both the Milky Way and Andromeda…
with both galaxies losing their spiral shape in favour of an elliptical structure in Milkdromeda.
This means stars and planets flying off into different orbits (after billions of prior years
undisturbed) as both structures try to make sense of their changing conditions of gravity.
The fates of the supermassive black holes at the core of each galaxy are a little
more difficult to map, although there are predictions for a binary structure at first…
before an eventual, colossal merger emitting a gravitational wave so strong that it will travel
across the universe. An extremely bright quasar is then predicted to form, with an incredible
mass billions of times greater than the sun, to anchor this new galaxy to the rest of the cosmos.
The Milky Way is no more, then. Andromeda is no more. And Milkdromeda is here. But, what of Earth?
And what of that third galaxy we mentioned before? Our planet could well be flung out into
interstellar space… or it could remain unmoved. It’s almost impossible to tell with certainty,
although it’s thought unlikely that it’ll be outright destroyed… at least, not by the
merger. What will almost certainly destroy Earth before any of the rest of this stuff happens
is the sun running to schedule and evolving into a red giant at roughly the same time.
For this reason, any hypothetical human astronomers of the future
will have had to have relocated to some other part of space… so, really,
our vantage point at the creation of Milkdromeda could be very different to what we have now.
But finally, why again are scientists so interested in that recent image of the Arp 195,
three-fold cluster? It’s because, ultimately, the fate of the Milky Way does involve a third galaxy,
too - the M33 (or Triangulum Galaxy). M33 is the third largest galaxy of the Local Group…
and predictions for its fate have somewhat divided the scientific community. What currently seems
most likely is that it won’t be actively involved in the initial collision between the Milky Way and
Andromeda, but that it will become involved at a later date. Once Milkdromeda is formed, it could
be that M33 spends a few million years orbiting around it, before eventually merging into it,
as well. So, we could also pitch the Milky Way’s position as a three-way tug-of-war, kind of… it’s
just that, as the third galaxy involved, M33 really has very little say in the matter.
Nevertheless, astronomers can’t yet rule out another possibility, that the Milky
Way may collide with M33 before it collides with Andromeda… which is a scenario that maybe, when we
think about it on Earth, feels like it shouldn’t make much of a difference. But, actually,
on the grand and majestic scale of space, it would involve redirecting the future paths of
whole worlds and entire planetary groups. It’s little wonder then that any image,
showcasing anything that’s even similar to what we’re expecting for the Milky Way, should cause
scientists and astronomers to take note. For now, the pictures of Arp 195 act something like
a guide… revealing to us just a tiny glimpse of what the future holds. And, when you consider that
all of this is but a warm-up act for another, even further off time when Milkdromeda, too,
will inevitably merge with other nearby galaxies… the sheer immensity of the universe as a whole
comes into even sharper focus. There’s just so much going on here, and there’s seemingly
no end to it. It’s perhaps a little terrifying… but it’s also pretty amazing, don’t you think?
What do you think? Is there anything we missed? Let us know in the comments, check out these other
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