- 4129 - DARK MATTER EXISTS - Even though scientists are certain that dark matter exists because as all our universe's normal matter simply can't account for the way galaxies are held together. Still we don't know what it is. We also don't really know where it is (though they have some ideas). And we definitely don't know what it looks like.
-------------------------- 4129 - DARK MATTER EXISTS
- We still don't know what dark matter is,
but here's what it's not. Two views
from Hubble of the massive galaxy cluster Cl 0024+17 (ZwCl 0024+1652) show a blue shading that has been added to
indicate the location of invisible material called “dark matter” that is
mathematically required to account for the nature and placement of the
gravitationally lensed galaxies that are seen.
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- The dark side of our cosmos accounts for an
unsettling 95% of our universe when taking into account dark energy, the unseen
force accelerating space's expansion.
But, how does we analyze something without truly knowing what to
analyze?
-
- Scientists are sifting through data captured
with a detector buried deep within a mine in Minnesota. While they did not find
evidence of dark matter, they say they've created one of the tightest-ever
limits for detecting it.
-
- A null result can be as impactful as a
positive result. Scientists have managed
to rule out a new slice of dark matter parameter space. Using this “SuperCDMS's” experimental
detector, they can now rule out dark matter particles down to about about a
fifth of a proton's mass.
-
- This SuperCDMS experiment basically
harnesses the power of detectors that can identify if and when a dark matter
particle (whatever that is) collides with the atomic nuclei of materials built
into the detectors themselves, specifically either germanium or silicon.
-
- SuperCDMS can pick out whether those dark
matter particles partake in what are known as "elastic collisions."
If they do, what would happen is any energy a dark matter particle loses upon
its crash would get transferred to the motion of the impacted atomic nucleus.
In turn, the two bits would recoil.
SuperCDMS clearly hasn't found any elastic collisions yet.
-
- What if SuperCDMS had been capturing some
other type of collision no one's been looking for all this time? Particularly,
inelastic collisions. Searching for
elastic collisions is still the main thrust of SuperCDMS, but considering
inelastic collisions opened an avenue to dark matter parameter space that the
experiment was not previously sensitive to.
-
- There are two ways a potential
dark-matter-inelastic collision may work. The first, has to do with something called
“Bremsstrahlung radiation”. In the
detector, if this type of inelastic collision happened, the dark matter particle
would transfer some of its energy to a light particle, or photon, rather than
just recoiling.
-
- Though on the other hand, an inelastic
collision may occur through something called the “Midgal effect”. If this
version happened, the dark matter particle slamming into the nucleus would
cause the nucleus itself to get knocked out of position, messing up its
electron cloud distribution. Upon getting back into its original spot, some of
those jostled electrons would get ejected.
-
- This means the team was searching for
SuperCDMS signals of either a flying photon or lonely electron straggler. This analysis used spectral shapes to model
the energy profile of the signal as well as the many known background sources.
-
- They used statistics to answer the question
'what is the probability that we see the signal over the known background? That question is repeated hundreds of
thousands of times and we rule out the parameter space where we should've been
able to see the signal and didn't.
-
- There are roughly 1 billion dark matter
particles passing through you every second, but they interact so rarely that
you can't tell. We're looking for a 1
in a billion billion billion billion chance of interaction. Their conclusion about dark matter particles
is the likely lower mass limits.
-
- The entire Earth's position in space can
affect these dark matter signals. If
dark matter interacts strongly enough with stuff, it'd likely interact with
literally everything in its path on the way to our little Earth-based detectors
underground. One of those things ripe for interaction is our planet's
atmosphere.
-
- And if a dark matter particle did interact
with our atmosphere, this planetary shield would take away some of the
particle's energy by the time we captured its signals. Our solar system is in a spiral arm of the
Milky Way that is spinning, the Earth is orbiting the sun and the Earth rotates
on its axis.
-
- This astronomical motion means the Earth is
passing through the sea of dark matter particles, but from our perspective,
that looks like dark matter particles are constantly bombarding the Earth and
our detectors.
-
- By modeling things like Earth's atmospheric
density, working with geologists to figure out what types of rocks are above
the Minnesotan mine where SuperCDMS is buried and tons of other variables, they
indeed figured out those upper dark matter energy limits.
-
- When you fit a line to some data, there are
2 parameters: Slope and intercept. In
this analysis, we had over 50 parameters being fit simultaneously. These dark matter hunters surely reached for
the stars and managed to softly land on the moon.
-
-
August 28, 2023 DARK
MATTER EXISTS 4129
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