Hello Space Fans and welcome to another edition
of Space Fan News.
In this episode, astronomers from Harvard
are proposing a new model of dark matter that
help explain some observations taken with
radio telescopes as part of the EDGES project:
the Experiment to Detect the Global Epoch
of Reionization Signature.
The observations were strange and astronomers
are proposing that, to help explain them,
perhaps a fraction of dark matter has an electric
charge.
I wish I had time to tell you about all the
amazing collaborations and projects going
on in astronomy from all over the world, here
are just so many of them.
Oh wait, I do, that’s why we have SFN…
Anyway, there is this really cool experiment
going on right now that I just found out about
called EDGES, the Experiment to Detect the
Global Epoch of Reionization Signature.
It’s primary instrument is a radio telescope
located in a radio quiet zone at the Murchison
Radio Astronomy Observatory in Western Australia
and is a collaboration between Arizona State
University and MIT’s Haystack Observatory.
A radio quiet zone is an area where radio
transmissions are restricted in order to protect
a radio telescope or a communications station
from radio frequency interference.
Kind of like a dark-sky initiative for radio
telescopes and are usually in sparsely populated
areas..
This radio telescope is looking at a time
in cosmic history when neutral hydrogen gas
from the early universe became ionized for
the first time due to ultraviolet radiation
from the first stars.
Back in February, scientists from this project
said they had detected the radio signature
from the first generation of stars, and possible
evidence for interaction between dark matter
and normal matter.
Some astronomers quickly challenged the EDGES
claim, but other astronomers immediately began
looking at the theoretical basis of these
observations and did what astronomers do,
started constructing mathematical models to
explain the observations.
To understand the EDGES observations, let’s
start with some basics.
The very first stars in the universe were
very massive, hot, and bright in the ultraviolet.
These stars only lived a few tens of millions
of years or so.
According to the commonly accepted early universe
scenario, this UV light interacted with the
cold hydrogen atoms lying between these first
star which enabled them to absorb the leftovers
from the Big Bang, the Cosmic Microwave Background
(CMB).
This absorption should have led to a drop
in brightness in the CMB during this period,
which was around 200 million years after the
Big Bang.
The EDGES observation did show this absorption,
although it has to be confirmed, but the temperature
of the hydrogen gas during this period was
half of what was expected, making the absorption
twice what is should have been.  Again, a conundrum
Now if it’s true that what EDGES measured
was in fact the absorption of the CMB by the
first stars in the universe, then why are
these stars absorbing so much?
At the time when CMB radiation is being absorbed,
any free electrons or protons associated with
ordinary matter would have been moving at
their slowest possible speeds (since later
on they were heated by X-rays from the first
black holes).
Scattering of charged particles is most effective
at low speeds.
So, any interactions between normal matter
and dark matter during this time would have
been the strongest if some of the dark matter
particles are charged.
This interaction would cause the hydrogen
gas to cool because the dark matter is cold,
potentially leaving an observational signature
like that claimed by the EDGES project.
Only small amounts of dark matter with weak
electrical charge can both explain the EDGES
data 
and avoid disagreement with other observations.
If most of the dark matter is charged, then
these particles would have been deflected
away from regions close to the disk of our
own Galaxy, and prevented from re-entering.
Something that conflicts with observations
showing that large amounts of dark matter
are located close to 
the disk of the Milky Way.
It’s possible that in the early universe,
when free electrons and protons were recombining
into neutral Hydrogen, at time just prior
to reionization, maybe the same thing was
happening to dark matter.
Maybe whatever makes up neutral dark matter
came together from an as yet unknown charged
dark matter particle but not all of it recombined.
So as you can imagine, there’s a lot of
checking, confirming, arguing and reconfirming
going on right now, but some astronomers are
excited about the idea that the elusive dark
matter, whatever it is, some of it anyway,
might actually carry a charge.
I’ll keep you posted.
That’s it for this episode Space Fans, thanks
to all Patreon Patrons who keep SFN on the
intertubes.
These guys in particular, they’ve been with
me for a while.
Thanks to all of you for watching and as always,
Keep Looking Up!
