At the center of the Milky Way galaxy is a super massive black hole and just
like how in the solar system the earth and all the other planets orbit the sun
in the center. The sun and all the hundred billion other stars of the milky way
orbit the black hole in the center. But what would happen if hypothetically speaking we could remove
the black hole from the center of the milky way? If we could just *click* and it would disappear?
Now you're probably expecting me to decry that chaos would ensue and we'd all be doomed but
that is not what would happen at all - in fact the galaxy would barely even notice if the black
hole in the center disappeared. Intrigued? Confused? Keep watching to find out why...
now i am a sucker for a good hypothetical science question and
especially this one because it's about my favorite topic black holes but also
because the answer is so unexpected that you know nothing would really happen if you were
to remove the black hole from the center. Instead, I guess what you would expect is the chaos that
would ensue if, for example, you were to remove the sun from the center of the solar system.
The planets and asteroids and comets and only the detritus of the solar system you know wouldn't
have anything gravitationally holding them in their orbits anymore it'd be like releasing a
lot of discus or hammer throws all at once - they'd all just fly off in whatever direction
they'd been going in at whatever speed as well they'd been going at and it'd all disperse. But
that's not what would happen to the hundreds of millions of stars in the Milky Way if you were
to remove the thing that they're orbiting around, the black hole at the center and it's all to do
with the fraction of mass of the black hole compared to the rest of the galaxy so in the solar
system if we were to add up the total mass of all the stuff in the solar system and compare that to
the mass of the thing they're orbiting around the sun we find that the sun is 99.86 of all the stuff
in the solar system so jupiter saturn earth etc all the asteroids comets they only make up 0.14
of all of the mass in the solar system and jupiter is the majority of that so if you were to remove
the sun you'd remove the majority of the mass in that system you're literally removing the anchor
that holds everything into place but if i were to do the same with the milky way galaxy and i were
to add up the mass of all of the stars in the milky way galaxy maybe the dust and the gas as
well and compare that to the mass of the black hole in the center get a very different answer
we find that the black hole in the center is four million times the mass of the sun
whereas the entire galaxy is more like 60 billion times the mass of the sun meaning that the
supermassive black hole although supermassive is still only 0.01 of the total mass in stars of the
galaxy so it's a tiny fraction and so the impact won't be as great if we could just and remove the
black hole from the center of the galaxy having said that the stars that orbit really close to the
black hole right in the very center of the galaxy the ones that we've been studying for decades
tracing out their orbits and using that to actually measure the mass of the black hole
at the center and work out that it's four million times bigger than the sun those are the ones that
probably would actually feel an impact yes they probably would just fly off in whatever direction
they were going in their orbit at whatever speed as soon as the black hole disappeared you know
just disperse just like we spoke about before saying you know if you could remove the sun
from the center of the solar system the planets would all fly off and disperse as well but the
majority of the stars in the milky way wouldn't even notice a thing the galaxy would just keep on
spinning and that's because of something we call self-gravity yes it's made up of individual stars
that are at these great great distances along with you know gas dust and dark matter and everything
but the sheer scale of it means that it acts like a single system in the same way that if we removed
a big chunk of the earth for example like you know what would all the atoms do that make up
the earth which you know atoms are very very tiny but comparison to their size they're really spread
out but if you just took out this tiny little fraction of the earth this tiny chunk of 0.01
the earth would be fine right it has its own self-gravity holding it together and it's the
same for the milky way the self-gravity of the 60 billion times the mass of the sun mass of all
the stars would hold it together and you might be thinking well what about galaxies that have more
massive black holes that aren't a million times the mass of the sun but a billion times the mass
of the sun surely that's going to be a sizable fraction compared to the galaxy for example like
in messier 87 right this is the galaxy that we've took an image of the supermassive black
hole in the center of with the event horizon telescope and with that image we were able
to work out the mass of the black hole is 6.5 billion times the mass of the sun that's over a
thousand times bigger than the milky way's black hole and you'd think well removing that from the
galaxy would have a much bigger impact surely but no because messier 87 the galaxy that it lives in
is also much more massive it has so many more stars than the milky way you know into
the trillions and this is something we see for all galaxies across the universe the total mass in
stars in a galaxy correlates with the supermassive black hole mass and as the galaxy grows
so too does the black hole so this is something we call co-evolution the galaxy and the black hole
growing and evolving together over cosmic time in the universe what it means is essentially that the
supermassive black hole will always be somewhere in the range of about 0.01 up to about one percent
of the stellar mass of the galaxy the mass in stars and that's just because of you know scatter
around that correlation and this is what i do my research on you know i look into the processes
that are responsible for this simultaneous growth of galaxies and black holes so it's quite close to
my heart so it's so cool to think that this graph this graph that i pretty much stare at nearly
every single day of my life is the reason why if you could just make a black hole in the center of
a galaxy disappear the galaxy of billions if not trillions of stars wouldn't feel a single thing
before we get to the bloopers which i know is everyone's favorite part i just want to say a huge
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science as well we love that here but now roll those bloopers i am on the struggle bus today
i feel like i've come back for my holiday and i just need another holiday in my view
black house gonna do nothing and i believe that gravity will hold in place
that means that the supermassive black hole is only 0.01 percent oh hang on last time i said
no the americans were like what was that um
that means that the supermassive black hole in the center of the milky way is only point zero one
zero it just sounds weird i'm sorry i'm sticking to naught