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dark matter is some cosmically strange
stuff we can't see it but it appears to
outnumber all the stuff we can see all
the stars and planets and random dust
floating around by five to one we only
know or think we know it's there because
of the gravitational effect it has and
astronomers have spent decades trying to
figure out what kind of strange stuff
this dark matter could be made of one
candidate is a bunch of regular matter
our equipment just isn't sensitive
enough to detect but the hunt also
includes objects that are a little more
exotic a handful of papers published
within the past couple weeks dive into
that hunt and show that it's far from
over one of these candidates for dark
matter is a group of black holes that
formed long before the first stars ever
shown they're called primordial black
holes or pbhs but there's not much
actual evidence for them yet they're
still hypothetical the black holes we
typically think of form after a really
massive star goes supernova but that
doesn't have to be the only way it's
been theorized that not long after the
big bang small random pockets of space
just happened to have enough matter
stuffed into them that they collapsed
into black holes because they didn't
start out from stars they could come in
an extreme range of masses from
fractions of a gram up to many many
times that of a star and that also means
that unlike black holes that started as
stars they're not likely to be
surrounded by large swaths of gas and
dust which would make them really tough
to spot some scientists including
stephen hawking have suggested that
these so far undetected black holes
could make up at least some of the
universe's dark matter previous research
had already found that they can't
account for all dark matter though so
new research out of japan published this
week in the journal nature astronomy set
out to determine how abundant they might
be to find these black holes the team
searched galactic halos that's the
region beyond the disk which doesn't
have nearly as many stars gas and dust
and is where astronomers suspect
primordial black holes could invisibly
hang out when a star passes between us
and dark matter its light gets bent and
magnified so to hunt for pbhs the team
monitored the change in brightness of
over 10 million stars in the outer
fringes of the andromeda galaxy and the
milky way after controlling for
everything they could think of that
would cause a dip in brightness
including one unwelcome asteroid there
was only one possible event that might
be attributed to a pbh annoyingly even
that one could just be a variable star
that dips in brightness naturally but
they couldn't be sure but running with
the assumption that they were able to
observe a single potential pbh the team
was able to place an upper limit on just
how common these things could possibly
be at least in the range of masses they
looked for if pbhs made up all dark
matter they would have expected to see
about a thousand brightness dips over
the course of their experiment seeing
only one they say means that those pbhs
could only account for a small fraction
of dark matter maybe 0.1 percent rather
than black holes other teams are working
to find an incredibly tiny hypothetical
particle called the axion axions if they
exist are fundamental particles that
means that like electrons they're not
made up of any constituent particles and
like neutrinos they have almost no mass
and don't interact with ordinary matter
very often and even weirder they can
actually bend the rules we expect
electricity and magnetism to play by
at least by a teeny tiny amount because
of that a team based out of mit designed
a laboratory experiment to try and
detect these changes they call it
abracadabra which might have been
appropriate if they could have pulled
dark matter out of it or if it had been
shaped like a top hat but instead it's a
donut shaped magnet roughly the size of
a basketball inside an insulated
refrigerator under the standard laws of
electromagnetism there's no magnetic
field in the donut hole but if an axion
is there there should be it would be
super duper weak though roughly a
trillion times weaker than the earth's
magnetic field so the team had to design
their experiment to block out everything
that could drown out that signal from
the local radio stations to leds on
nearby electronics and they had to keep
the magnet as cold as possible just
above absolute zero after running the
experiment for a month they were unable
to detect evidence of axions at least
none within their target mass range
around a quintillionth the size of a
proton so that either means they don't
exist or their influence on
electromagnetism isn't as strong as
predicted but this experiment was only a
prototype so a larger and better
shielded one will be able to hunt for
smaller axions they just haven't built
it yet but we don't necessarily have to
build contraptions to find axions we can
try to find them in space on an
astronomical scale a large number of
axions together could basically act as
its own field think of it like a cosmic
ball pit made of incomprehensibly tiny
floating balls stuff passing through
would theoretically interact with these
axions at least a little especially
light otherwise known as electromagnetic
waves and passing through the field
would affect its polarization or the
angle of the light waves and that is
something we could potentially observe
so in another recent paper published in
the journal of cosmology and
astroparticle physics one team based in
russia went hunting for that
polarization they looked at objects
called active galactic nuclei which are
dense galactic centers that spew out
tons of polarized electromagnetic
radiation specifically they were looking
to see if the polarization of the light
coming from their targets changed over
time and all in the same way so if they
observe the predicted changes that would
mean that the light from all the
different active galactic nuclei was
being affected by an external field made
up of a very large number of very light
axions but they didn't see that they too
were unable to conclude whether or not
axions exist at least for their studied
mass range which incidentally was way
smaller than the one probed by
abracadabra all of this work helps to
place limits on what masses dark matter
particles can have or what they can even
be it might be primordial black holes as
massive as the earth and it might be as
teeny tiny as the smallest subatomic
particles in existence or something else
entirely our technology just hasn't cut
up with our curiosity yet it just means
that the hunt for dark matter is still
on and i can promise you that when
scientists figure it out you'll hear
about it here thanks for watching this
episode of scishow space news before you
go i have something pretty exciting to
tell you about and no i promise this one
is not an april fool's prank introducing
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