There are trillions of galaxies out there in the universe.
They come in all shapes and sizes and at different stages of development.
Some are brand-new, some are middle-aged and healthy, some are middle-aged and unstable,
and others are as old as time.
But does our very own galaxy hold a mystery that we’re only just scratching the surface
of?
This is Unveiled, and today we’re answering the extraordinary question; did scientists
just uncover the energy source at the center of the galaxy?
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In May 2021, the astronomer Daniel Wang of the University of Massachusetts Amherst published
a landmark study twenty years in the making about the Milky Way’s galactic center.
With time to pass during the Covid-19 pandemic, Wang had spent months collating two decades’
worth of images from NASA’s Chandra X-ray Observatory.
All those images then coalesced into a stunning collage of the heart of the Milky Way.
A spectacular shot to show us what’s really happening in the middle of the galaxy.
And, among other things, they suggested numerous, previously unknown energy sources.
But what, exactly, was Wang looking for in the first place?
What’s so interesting about the center of any galaxy, let alone our own?
Galactic centers are also known as rotational centers.
They’re the gravitational point in space around which the entire galaxy and all of
its contents orbits.
For example, the Earth may orbit the Sun, but the Sun is orbiting the Milky Way’s
galactic center at an incredible speed of around 500,000 miles per hour.
We move around one thing, that thing moves around something else, and the universe continues
on and on.
We’re dealing with huge distances here, though.
In a billion years, the Sun and all the contents of the solar system complete just four full
circuits of the entire galaxy.
That’s around 250 million years per lap, for a period sometimes known as a cosmic year.
As for what’s powering it all, we look to supermassive black holes.
These are truly immense structures, capable of keeping an entire galaxy on the move…
and often there’s more than one of them.
The high-energy radio source at the center of the Milky Way, for example, is almost certainly
a supermassive black hole – but some believe that there may be two (or perhaps even more
than two) of these cosmic giants lurking there.
Either way, this crucial region of space (from our perspective) is named Sagittarius A-star...
although we’re only just getting to know it.
In 2013, NASA published some of the first images of Sagittarius A-star - specifically,
the cosmic dust and other material circling around it, rather than the black hole itself.
These images were also taken by the Chandra Observatory, with Daniel Wang also heading
up that particular mission.
All in all, Sagittarius A-star is roughly 4.6 million times more massive than our Sun
is, and a genuine colossus in space.
Other galactic centers are even more exciting, though.
Particularly if they have an active galactic nucleus, or an AGN, often known as a quasar.
Quasars are supermassive black holes with a vast accretion disk.
There’s a huge amount of stellar material circling them that the black hole is pulling
in, but not quickly enough to destroy it.
The material swirls around the black hole’s event horizon and all that heat, speed, and
friction generates an enormous amount of light.
So much so that quasars are among the most luminous objects in the entire universe.
They’re brighter than most stars, and are often visible from Earth.
Quasar or not, noisy space dust is one of the main reasons why it’s usually so difficult
to see what’s actually happening at the center of the Milky Way.
Most telescopes, including even the celebrated Hubble, can’t see through all the dust and
debris.
So, although we know there are massive, high energy-emitting objects and powerful radio
sources out there, we can’t usually pick them up.
It’s one reason why Daniel Wang had to use Chandra, the lesser-known, x-ray telescope,
to take his remarkable images.
While machines like the Hubble - as well as the upcoming James Webb Telescope – are
designed to see infrared light… the Chandra sees x-rays.
This means that it is capable of permeating the layer of space dust that would otherwise
have blocked infrared telescopes, and it can therefore open a fresh window into Sagittarius
A-star - allowing us to see it with far greater clarity, and therefore to gain information
about its energy source.
Wang describes that source as a; “violent, energetic ecosystem in our galaxy’s downtown”,
packed with plenty of powerful signals.
Wang’s images include a dazzling pattern of x-ray threads, which are thought to be
a by-product of another cosmic phenomenon called magnetic field reconnection.
According to NASA, magnetic field reconnection is “little understood”, but we did at
least know about it before, and we know roughly what its effects are.
In fact, most of us have almost definitely seen a magnetic reconnection event ourselves,
although perhaps only in photos… because that’s what the northern lights are, over
the Arctic Circle.
They can be caused by coronal mass ejections from the Sun, where the Sun spits out a large
amount of plasma… and when this plasma interacts with the atmosphere of any other celestial
body, not just Earth, it releases immense energy.
In our case, we see this energy take shape in the form of the northern (and southern)
lights.
Something similar, but most probably even more spectacular happens at Sagittarius A-star.
So, to recap what we have: Something, out in the galactic center as yet undiscovered,
is emitting large amounts of energy… that energy is then interacting with nearby magnetospheres
and atmospheres to release a northern lights-like series of x-ray threads shown in Daniel Wang’s
2021 study.
The next question, then, is what is that “something” that’s igniting the display?
Wang’s theories include there being a wide array of relatively normal astronomical objects
in the region.
More, smaller black holes, perhaps… or neutron stars… or the remnants of a supernova that’s
still producing energy.
It may be, then, that whenever we do uncover what the main energy source actually is, the
chances are that it isn’t going to be anything new according to our understanding of the
universe.
But there is another, much stranger theory about what could be hiding in the center of
the galaxy, causing everything that Wang has observed.
This time, it involves arguably the most elusive stuff in all of outer space: dark matter.
According to another team of researchers at the International Center for Relativistic
Astrophysics, Sagittarius A-star could, in fact, be made entirely out of dark matter,
and the same could be true of various other supermassive black holes, too.
Again, our knowledge is in its infancy, but we do know that dark matter makes up the vast
majority of matter in the universe.
We know it’s called dark matter because it’s totally undetectable and doesn’t
interact with light, so we only know it’s there because we can see how it affects gravity.
Galaxies are able to keep their distinct shapes because the normal matter within them is being
shaped by dark matter.
And, while it may seem a little off the wall to propose a theory that black holes could
be made of dark matter, it arises from a very real problem in physics.
Scientists have long pondered how supermassive black holes are able to form so quickly, relative
to the age of the universe and the galaxies they reside in.
But they say that this problem is solved if black holes are made of dark matter.
For now, that isn’t the conclusion that Wang reaches.
But his study has pushed Sagittarius A-star back under the cosmic microscope, as we try
to get a firmer grip on what’s really happening in the Milky Way.
Yes, we’re still trying to work out exactly how Earth itself works, too… and the solar
system.
But, science is also keen to better understand our place in the grander scheme of the universe
as a whole.
Our galaxy is certainly a mysterious place, and there are all kinds of things that we
don’t yet know about it.
It’s also true that we might never be able to travel to our galactic center, seeing as
it resides 26,000 lightyears away from us.
But, still, how it works is vital to how we work, and how our planet carves its path through
space.
Thanks to a twenty-year study, and ever increasing and diversifying technology, we’re now getting
to see it in all new ways… and that’s why scientists may have just uncovered the
true nature of the energy source at the center of our galaxy.
What do you think?
Is there anything we missed?
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