26,000 light years away, a supermassive black hole is spinning at the center of our galaxy.
A black hole as wide as the orbit of Mercury.
A black hole more than 4,000,000 times as massive as the sun.
And everything in the galaxy is swirling around it.
So, does that mean that the black hole is dragging everything into it until there is nothing left
like a cosmic drain in the great space bath tub that we call the Milky Way?
In short, no. Black holes have gotten a bad rap so lets set some things straight.
A black hole is just an object so dense that as you approach it the velocity you'd need to break free
of its gravitation, known as escape velocity, exceeds the speed of light.
This means that within a certain distance from the center of the black hole, not even light
travels fast enough to escape. And nothing can travel faster than light, so nothing can escape.
And while that might sound a little bit terrifying to you, the first thing you should know about our
resident black hole, which is named Sagittarius A*, is that it's not terribly big... for its kind.
Black holes are generally divided into two classes that are hugely different in size.
First there are stellar-mass black holes, which have the mass of several to maybe a few dozen suns.
These are formed from super nova explosions of giant stars at the end of their lifetimes.
Then, there are supermassive black holes which include the one at the center of our galaxy.
Astronomers don't know for sure how supermassive black holes form, but ours is actually
pretty small, with just 4,000,000 times the mass of the sun. Compared to those at the centers of
some other galaxies, which are more than 100,000,000 times the mass of the sun.
So that makes our black hole sound nice and non-threatening, right? But the much more
important fact is a black hole's gravity doesn't just suck things in like some sort of
cosmic vacuum cleaner. Most things in our galaxy are so far away from it that they barely
even feel the black hole's gravitation. In fact, here on earth the gravitational pull between a person standing
30 feet away from you is 10,000 times stronger than the gravitational pull of our galaxy's distant
supermassive black hole. And even objects that are a lot closer to it will most often just fall into an
elliptical orbit around it. The fact is, our galaxy is orbiting Sagittarius A* just like we are orbiting
the sun, but we are not getting drawn into it. But... I'm not saying that hanging out near a black hole is
gonna be pleasant or even comfortable. In fact, I don't recommend it at all.
This is partly because of the effect
created by clouds of gas that form
around black holes called accretion
disks these lists of gas becomes
superheated producing strong emissions
at x-ray and radio wavelengths so in the
immediate area of a typical supermassive
black hole there is a lot of rather
unfriendly high-energy radiation flying
around. And another concern if you happen
to find yourself in the metro area of a
black hole, is tidal forces. These forces
are exerted because one side of a body
like a planet or moon is closer to the
massive object than the other side. That
closer side feels a stronger
gravitational pull than the far one does
and the closer that body gets to the
massive object the bigger the difference
becomes. Eventually this difference
becomes so great that it causes the body
to start stretching out. Now, the boundary
that stakes out the maximum danger zone
around any black hole is its event horizon.
This is the distance from the center
where the escape velocity equals the
speed of light for our black hole the
event horizon is about thirty percent
the average distance between the Earth
and the Sun. So outside that range an
object orbiting the black hole would be
far enough away that the tidal forces
wouldn't do too much harm but if the
object manages to cross the event
horizon then basically all bets are off.
The side that's closer to the black hole
would begin to accelerate faster than
the farther side creating an inescapable
stretching force that physicists rather
delightfully refer to as
spaghettification. So yes if you found
yourself inside the event horizon, your
noodle would essentially be cooked.
Nonetheless,
you don't have to worry your
intelligent little head about any of
that because our galaxy is orbiting
Sagittarius A*
you can rest assured that the Sun the
earth and everything else is going to
keep on turning blissfully unaware of the
supermassive black hole at the heart of
our galaxy.
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