One of the strangest mysteries of the universe that
continues to baffle astronomers are the phenomena of fast radio bursts or FRBs.
Lasting only a few milliseconds, these highly energetic bursts have only been
known since about 2001. And while we don't yet know much about them, we can
infer from their behavior that the sources of the bursts seem to be very small.
So small in fact that the sources must be less than a few hundred miles across.
This eliminates a lot of possibilities as potential sources of the activity,
including most normal stars, sending us into another tier of explanations, none
of them particularly good so far. One of those potential explanations are the
activities of alien civilizations.
Unexplained radio signals from space are nothing new, the
universe is teeming with natural radio emitting objects. But in the case of
FRBs, they behave very strangely and one research team suggested in 2015 that
they seem to conform to a mathematical pattern, at least as far as the bursts
known at the time were concerned. If present, that pattern doesn't really make
much sense as far as our understanding of cosmology goes. And to add icing to
the cake, they appear to originate invariably, again so far, from only outside
our galaxy. A head-scratcher indeed.
They seem to be distant because of a metric known as the
dispersion measure. The FRB's emit the same thing at many frequencies at once.
Think of it as a radio station that beams out the same radio show on all frequencies
on the dial. But those frequencies do not all travel at the same speed, some of
the waves get delayed by floating electrons in space. This has the effect of
higher frequencies crossing space faster than lower ones. The bigger the
difference in time between the two, the further away the origin of the burst
is.
As it turns out, the origins for the FRBs seems very distant.
And new research suggests they are very common, with thousands happening each
day. The reason we don't see them is because they happen so fast that we can
only catch them by chance. More, just a few days ago research came out that
found one that repeats. This eliminates one of the main natural explanations,
that of colliding neutron stars.
But even stranger, there is another kind of reported pattern
to these bursts. In 2015, researchers Michael Hippke and John Learned
determined that of the 10 or so FRB's known at the time, the delay between the
arrival of the first and last parts of the signals are always multiples of the
number 187.5. No known natural process can do that. But, the pattern may not
actually be real, more on that in a minute.
If that pattern is present, it might imply that the sources
of the bursts line up at regularly spaced distances from earth. This is very
difficult to explain with a natural explanation if we take the data at face value,
so much so that alien activity is the easy explanation in much the same way
that finding distance marker signs on a road would indicate human activity. The
odds are in the alien's favor in this case and are estimated to be 5 in 10,000
that this pattern would just be due to chance.
But don't get excited yet, we could be misinterpreting the
data. And subsequent observations of FRB's since 2015 do not line up with the
pattern, calling the whole thing into question. Why the first ten did and the
subsequent bursts did not is a complete mystery but the current consensus is
that the pattern wasn't really there and that the effect was a statistical flaw
from having too small of a sampling to go on.
It could also be that the sources for the FRBs are in
reality much closer to home. They could have galactic origins and merely
present the appearance of being billions of light-years away by emitting long
frequency waves before emitting short ones on a delay. Or they could be even
closer, it has been suggested that the FRBs are emissions from our own spy
satellites that we're accidentally picking up. This is particularly interesting
because a group of FRB-like signals that had been detected by a single radio
telescope were thought to be originating from space. It turns out, they
weren't. They were coming from the microwave oven in the lunch room.
Another possibility is that superdense stellar remnants
could be the sources, though this explanation is somewhat weak because it's based
on the fact that we really don't know very much about the physics of how those
produce radio waves. Other potential explanations include oddly behaving solar
flares, activity around black holes, and many others. So it's best not to run
to the alien explanation just yet.
There's a good reason for this other than skepticism. While
sending out engineered signals that contain mathematical patterns would be a
logical way to announce your presence to the universe, there are a lot cheaper
ways to do it. FRBs, if they originate outside the Milky Way, would take a huge
amount of energy to produce, about the same amount our sun produces in a month
or more.
In addition to that the signals are pretty ambiguous, they
don't really look like something aliens would intentionally send. If your aim
was to wow other civilizations with your math skills, you'd probably do
something less ambiguous, such as base a message on Pi or simply count out
numbers like they did in the movie "Contact". And you would do it on
selected frequencies as opposed to eating up energy by blasting the signal out
on a wide spectrum of frequencies as is the case with FRBs.
No two frequencies are the same where interstellar
communications are concerned. Certain ones, such as the hydrogen line that SETI
places a high value on are better at tagging your signal as a dead ringer for
being artificial than other frequencies. What you wouldn't do is intentionally
make your communication questionable as in the case of FRBs. You'd want your
signal to be loud and clear and easily understood as artificial. This is not so
with the FRBs.
But that's all based on the assumption that alien signals
would come in the form of communications. But, if we are any indicator, that
would not be true in most cases. The fact is we've only sent out a few intentional
signals and we have a nasty habit of not repeating them, which is one of the
criteria SETI requires to call an alien signal an alien signal, it must repeat
and be independently verifiable by other scientists. In reality most of our
radio signals that aliens might pick up would be random things like radar. So that
begs a question, if artificial, what if the FRBs are not designed for
communications at all?
Enter in a paper released on January 5th of 2017 by Manasvi
Lingham and Abraham Loeb that lays out just such an alien scenario that seems consistent
with the data where a specific type of alien activity would fit. Their idea is
that the FRBs might be extremely powerful for a reason: they are pushing sails.
They have determined that the frequencies where we see the
FRBs just happen to be those perfect for pushing spacecraft connected to huge
sails. They suggest that the beams powering them sweep by very rapidly
explaining the short duration of the bursts and that if they are indeed pushing
spacecraft we should see that in the light curves of the bursts. They also note
that not all FRBs need to be of alien origin, some may be natural or they may
all be natural. Only time and more research will tell.
https://arxiv.org/abs/1701.01109
Hippke and Learned's Paper from 2015
https://arxiv.org/abs/1503.05245
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