There’s a wall of gas out there twice the
length of the entire Milky Way galaxy and
five times hotter than the core of the Sun.
Thankfully, it’s not headed right for us.
It’s about two hundred and forty million
light-years away, in the Perseus galaxy cluster.
For a while, astronomers didn’t know what
this wall of gas was doing there.
But in a new study published in the Monthly
Notices of the Royal Astronomical Society,
a group of researchers discovered that this
wall-looking thing is actually a gigantic
wave.
And it started rippling because a smaller
galaxy cluster ripped through Perseus two
and a half billion years ago.
Galaxy clusters are some of the largest structures
in the universe, often with more than a thousand
galaxies in them.
But most of a cluster’s mass isn’t in
the galaxies themselves — it’s in the
light-years-big clouds of superheated gas
sitting between the galaxies.
The Perseus cluster has relatively cool gas
in the center surrounded by swirling masses
of much warmer gas.
Back in 2006, astronomers studying Perseus’s
gas clouds with the Chandra X-Ray space telescope
noticed what looked like a wall of gas that
was much hotter and denser than anything nearby.
It’s around two hundred thousand light-years
long, with temperatures as high as eighty
million degrees Celsius.
At first, researchers thought it might be
caused by a black hole swallowing up the gas
behind the wall.
But other telescopes didn’t see any signs
of black hole activity.
So then they checked to see if the extra heat
and density could be from the gas cloud sloshing
around naturally.
And yes, sloshing is the technical term for
it.
But that didn’t really fit the observations,
either.
Now it seems like we finally have an answer.
In this new paper, a team of astronomers used
computer simulations to show that what looked
like a wall is actually more of a /wave/,
caused by the gravitational tug of a smaller
galaxy cluster passing near Perseus’s center
a couple billion years ago.
The simulations showed that the smaller cluster’s
gravity would’ve started the colder and
warmer gases swirling together.
After about 2.3 billion years, the swirling
gas started sort of tripping over itself,
heating and bunching up in the process.
And whenever two fluids with different densities
or temperatures or velocities rub against
each other, it makes waves — whether it’s
two types of gas swirling together or wind
over the ocean.
So this wall we’ve known about for a decade
is actually a type of wave.
The team also thinks that at least two other
clusters, Centaurus and Abell 1795, have waves
that formed in the same way, but they’re
not as easy to see as the one in Perseus.
Matching simulations with observations like
these helps astronomers figure out which factors
are most important when gigantic structures
like galaxy clusters interact with each other.
For example, they know from the simulations
that if Perseus’s magnetic fields were a
lot stronger, the wave would have never formed.
And now that we know what to look for, it’ll
be easier to find evidence of galaxy clusters
ramming into each other in other places in
the universe.
Anyone else up for some extreme galactic surfing?
Or maybe you’re more interested in visiting
a Moon base.
Because yeah, that’s a thing the European
Space Agency wants to build.
And now they have a 3D printer that can build
bricks out of just Moon dust.
The hard part about building on the Moon -- well,
okay, there are /lots/ of hard parts.
There’s a ton of solar radiation, there’s
practically no atmosphere, Moon dust — aka
regolith — can damage your lungs...
The list is pretty long.
But /one/ reason there’s still no Moon base
is that launching building materials like
bricks all the way to the Moon takes a /lot/
of expensive rocket power.
So sending astronauts up with bags of bricks
and mortar isn’t exactly feasible.
Instead, the ESA wants to invent 3D printers
that can use the regolith itself as a building
material.
In theory, basically all you’d need to do
is send up a bunch of those printers and let
them turn lunar soil into all the bricks you
need.
The ESA’s newest printer is at the DLR German
Aerospace Center in Cologne, and last week,
it printed its first bricks out of volcanic
soil that’s processed in a way that makes
it a good substitute for the Moon’s regolith.
If you think the bricks look kinda like some
soil smushed together, well, that’s pretty
much what they are.
The brick printer focuses sunlight to melt
layers of regolith into bricks that stay solid
on their /own/, without the need for any sort
of extra material from Earth.
The process isn’t totally practical yet:
the printers make bricks a 0.1-millimeter-thick
layer at a time, so it can take as much as
five hours to build a hand-sized brick.
They still have to test the strength of the
bricks, and a related project called RegoLight
is still working on making the process better
for the Moon’s harsh conditions.
But this is early proof that we can build
a Moon base out of the Moon itself.
So maybe someday the ESA will have a team
of robotic regolith masons ready to build
humanity’s first extraterrestrial outpost.
Thanks for watching this episode of SciShow
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