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!
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