Earlier this month astronomers turned their telescopes on the heart of our galaxy, as
they have done for years- yet tonight would be different.
Invisible to any wavelength of light, a monster lurks at the very center of our Milky Way-
the single most destructive force in the known universe.
Spinning silently in space, a supermassive black hole over 44 million kilometers in diameter
swallows all matter that strays too close.
Known as Sagittarius A, this black hole has a mass of more than 4 million of our suns,
and has held our entire galaxy in its tight grip for untold eons.
For most of that time scientists have believed that Sagittarius A has been relatively quiet,
with our galaxy carefully spinning in its gravitational embrace, and the innermost stars
playing a constant and very dangerous game as they orbited near the terminal limits of
its deadly embrace, just out of reach.
Earlier this year however, the monster awoke, and now scientists are scrambling to understand
what this means.
Working from the European Southern Observatory's Very Large Telescope in Chile, and the W.M.
Keck Observatory in Hawaii, astronomers observed Sagittarius A, probing the secrets of the
leviathan at the heart of our galaxy.
Because of thick dust clouds between us and Sagittarius A though, scientists often observe
the black hole in the infrared spectrum, which can cut through most of that dusty haze that
blocks out regular light.
Now, black holes obviously can't be directly observed due to the fact that their massive
gravity sucks in even light itself, so there's no photons left to travel across space and
deliver their information to a computer sensor or your eye.
What scientists can do however is observe their effects on space around them, specially
the effects of their massive gravity.
This is how new black holes are very often discovered- scientists will find a region
of space with stars moving at peculiarly fast speeds, and long-term observations will reveal
that they seem to be orbiting a patch of empty space.
Bingo, you got yourself an invisible monster there, a tear in the fabric of space-time
that's completely camouflaged from detection- save for the incredible influence it has on
other nearby bodies.
But not only can scientists detect black holes by watching their effects on clouds of gas,
dust, or stars, but they can even calculate how massive the black hole is by calculating
the velocity of the objects orbiting around them.
This is how scientists were able to discover the monstrous size of Sagittarius A.
Sometimes though, black holes have much more dramatic displays of their terrible power,
and earlier this month Sagittarius A reminded us of its presence in a dramatic way- one
that has scientists fearing the implications.
Black holes, much the same as stars, can display changes in their output across the electromagnetic
spectrum.
Stars can brighten and dim over time, or show other changes across the EM spectrum.
Black holes can also do the same, and by observing them over the course of years scientists can
measure their variability and develop a good model for each individual celestial body.
This year though Sagittarius A bucked the trend in pretty major ways.
Observing the massive black hole in the infrared spectrum, scientists picked up what they called
“unprecedented” changes in its variability.
Twice Sagittarius A exceeded historical peaks in its output of infrared radiation, with
scientists describing the event as eruptions.
Having observed the black hole for the last twenty years, astronomers were shocked to
discover bursts of infrared radiation stronger than the average variability by a factor of
75!
To make matters even more strange though, over two nights this May huge drops in brightness
were observed, each occurring over the course of a few minutes.
Something was happening- and if it was affecting a black hole 44 million kilometers in diameter
then this something was big.
Really, really big.
Just what that something was though is something that has left scientists scratching their
heads.
Some have proposed that these changes in variability could be perfectly normal for Sagittarius
A. Given the fact that it has existed for an unimaginably long time and we've only been
observing it for the last two decades, it very well could be that we simply don't have
an accurate model of Sagittarius A's variability yet.
Its cycles could stretch far outside of the 20 year observation period we've logged so
far.
Others however point to a possible change in the accretion state of this supermassive
black hole as a cause for the unexplained flashes of infrared light, and subsequent
dimming.
In layman terms, this means that Sagittarius A could have just had a lunch, and we were
lucky enough to observe it, only this would have had to have been a very, very big lunch.
Despite popular opinion, black holes don't constantly 'suck in' all material in the universe
like some sort of galactic drain.
If this were true then our universe would have been emptied of all matter billions of
years ago.
Black holes do have massive gravity, and typically this gravity is so powerful that as they form
they pull in all local material and... well to be honest we're not exactly sure what happens
to material inside a black hole because mathematics turns to gibberish at the heart of these monsters,
but 'destroy it' is definitely a pretty safe assumption.
However, just like any object with mass, the extent of their gravity is wholly dependent
on their mass.
So every black hole has a limit on just how far its ability to pull in material extends,
and after initially clearing everything in its orbit, or caught within its own gravitational
pull, black holes tend to quiet down and just sort of sit there doing not much of anything.
That's because any matter that's survived around it is all matter that is now safely
orbiting the monster outside of its event horizon, in exactly the same way that we orbit
our giant sun without actually plunging into it.
Our sun loves us.
It loves us so much that it wants nothing more than to give us a giant hug.
It tries to do this by exerting an attractive force on the earth, constantly pulling it
down towards it where it can obliterate us in a fatal fiery embrace.
However, like someone caught in a relationship with an overly clingy individual, the earth
exerts sideways momentum that is perpendicular to our direction towards the sun.
Our sideways movement is fast enough that as we fall towards the sun, we manage to miss
it and zip by its side instead, only for the sun to pull us back down towards itself and
our sideways speed once more making us sidestep it.
This in essence is all it means to orbit an object- you maintain a large enough sideways
velocity to constantly miss falling directly into the object pulling you down.
When Sagittarius A first formed, it swallowed up all material orbiting it that lacked sufficient
momentum to sidestep its fatal attractive force.
Billions of years later though, the center of the galaxy has been pretty sufficiently
cleared of material, leaving behind an accretion disk where friction and collisions between
particles gradually, but very slowly, continues to feed material into the black hole.
Some scientists suspect though that this year, something big- really big- managed to stray
into Sagittarius A's gravitational pull.
This could have been a rogue gas giant, propelled into a fatal flight through the galaxy by
the gravitational effect of other stars around it, until it eventually intersected paths
with Sagittarius A. Or it could have been a huge cloud of dust and gas, who's slowly
decaying orbit around Sagittarius A finally led it into the maw of the beast itself.
Either of these two occurrences would by now be pretty rare events given Sagittarius A's
age and the fact that it should have swallowed up most things not in a stable orbit around
it, and we would have been very fortunate to be looking in the right direction in time
to spot this rare galactic event.
However, a third, terrifying possibility may be that Sagittarius A is actually growing
by some unknown mechanism, and as it grows so does its gravitational force, pulling in
material and stars once safe from its grasp.
Scientists do not think this is likely, but if it were true then we may be witnessing
the awakening of a galactic behemoth, and maybe one day soon the Earth will be on the
menu...
What do you think the strange bright flashes of radiation were?
Are we all going to die horrible deaths as we're swallowed up into a black hole?
Why didn't we mention aliens once for a change in this entire episode?
Let us know in the comments!
And as always if you enjoyed this video don't forget to Like, Share, and Subscribe for more
great content!