Hello, and welcome to the Physics World Weekly
Podcast. I'm Hamish Johnston.
In this episode, we revisit the wow signal.
A curious astronomical
observation
made nearly 50 years ago that has been
described
as one of the most compelling
potential instances
of extraterrestrial
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Back in 1977,
the Big Ear
radio telescope in the US
was scanning the skies
in search for signs of extraterrestrial
intelligent life.
On 15th
August, it detected
a strong
narrow bandwidth
signal
that vanished
24 hours later when Big Ear
again looked at the same patch of sky.
This was exactly the sort of techno signature
that astronomers
were looking for.
Indeed,
one scientist wrote the word wow
next to the signal on a printout of
Big Ear data.
Ever since, the origins of the wow signal
have been debated,
and now a trio of astronomers
believe they have the answer.
Here is Physics World's
Margaret Harris
in conversation
with one of those scientists.
My guest in the virtual studio today is
Abel Mendez, a planetary astrobiologist
and director of the planetary habitability laboratory at
the University of Puerto Rico at Arecibo.
Hello, and welcome to the podcast.
Oh, nice to be here. Thank you for
invitation.
Now, Abel, you and your colleagues have been
doing some research recently
on something called the Wow signal.
What is this wow signal, and how did
it get its strange name?
That's a
amazing story.
A story that I heard from,
from my early childhood,
that famous wow signal, but,
always was not into details. And I never
thought that I was going,
do doing some work with this,
signal.
Well, in 1977,
a Big Air,
Telescope, that's a telescope for the University of
Ohio,
they were doing
a risk radio astronomy research,
exploring
different sources. It's in the early days of
the radio astronomy.
It's a it's a telescope that was contemporary
with the receiver observatory,
which was that started in the both started
in 1963.
So they
have been doing this radio astronomy,
research.
And in that particular year,
they detected an interest in signal. That was
at a
particular project
in what we know today as SETI or
TENOT signatures.
So they were actually,
doing in with that observatory
a search
for extraterrestrial intelligence on purpose.
And,
and they they just got what they were
looking for.
This telescope was scanning the skies, so it
was not targeted at any particular direction. It
was using the movement of Earth
and the rotation of Earth through through through
the stars just to see what's there.
And, for a moment, they got, for actually
72 seconds,
they got a signal that was increased and
decreased,
which was something that we're expecting for a
stationary signal
that they just happened to drift and pass
by.
So we have to make clear that, that
signal was, constant at least during the time
that they were drifting, even that it would
they saw that it changed in intensity because
they were drifting
and moving. So the signal was narrowband,
so it was very particular, and that was
it was
makes interesting the signal. It was a narrowband
frequency.
Usually,
astronomical
events when they,
supernova
or some flares, they emit
radiation
in all frequencies
on all the spectrum. Could be visible or
x rays, gamma rays,
optical, and then radio. So
and they are easy to recognize. And that
was something that they were doing and detecting
for the first time
with the with this, telescope.
But this was just one particular frequency,
and that's the amazing part. Only things that,
transmit in one particular physic frequency
are spectral lines from different molecules. We know
that they,
do that.
But also technology
because,
our technology is much easier to transmit
at one particular
frequency because otherwise you will spreading
spreading your energy,
and it would be a waste of of
communications.
So,
but then why not a a astronomical
spectral line or something like that? Well,
the signal just,
when they came back
through the all their Earth rotation 24 hours
later
and saw and checked it up and checked
the the data,
they
it was not there.
Spectral lines are constant.
They are there, and they stay there.
And, and there are some events like,
masers that produce, so this is the the
same thing as lasers, but but in your
in the video frequencies
that they can emit the signal. But, usually,
they are pretty constant.
So the signal just
lasts
for a a for those second observation
is not there the other day,
and
that was amazing. That was like,
instead of a a
astronomical maser.
It was, more like an artificial maser.
So that was it. That that that was,
the
the the story, and they,
had at that time,
they don't have the computer capacity to save
the data in disk
or tapes
that were that
were available. That was too much
for that time, and they just printed the
information.
Information was printed. That's it. That's all the
data that we had in those in those
days.
And, one of the scientists
of the project just highlight
this strong signal with, wow.
It could be something else. He could write,
wow, or
or what is this? But, wow, as simple
as that.
So do you think that the astronomers working
at the the Big Ear telescope actually thought
that they'd heard something from an alien civilization,
a a technologically advanced alien civilization?
Yes. They they they thought that because that
was exactly what they were looking for, a
very strong signal,
One particular here in the sky with very
strong signal.
And,
and,
it just lasted at least less than 24
hours.
So that they were very intrigued,
and they looked through all the data because
in those days, you save the data and
printer, and it was later after
that you saw the the data. And you
look through the printed and then continue
scanning
that just to see if there's any repetition
and that, and they were actually discussing that.
That's a
a a strong possibility that they detected because
there was no other explanation
for
and there are multiple
people have been proposed on multiples,
at least qualitatively,
multiple explanation,
but they fail at something.
Even the,
saying that this was a a terrestrial communication,
let's say, satellite, we are we're talking in
the seventies.
There were not much, and those frequencies were
already protected.
So for use of astronomy. So it was
not supposed that any radio communications will be
performed and in in those frequencies.
And this was a a target thing. It
was one particular region of the sky
that was otherwise
probably
some radio frequency interference
will be shorter in time and will be
something that could be repeated.
And it's it's very hard to it was
very hard to come, and that's probably what
is was so famous
that,
astronomical
or
terrestrial explanations
or even instrumental
defects,
they were very
something
very hard to come by to for us
as as planet.
But over the intervening years since the late
19 seventies, people have gradually come to the
view that this this wasn't, in fact, a
communication from the alien signal. How has that
consensus come about?
Well, I think
so we tend to everything that we cannot
explain otherwise is evidence.
I see. I think that's that's that's the
general,
public perception
that,
no. It's something well,
we can learn from this, that anything that
we cannot explain is something that need to
be explained. That's it.
And, and, because no astronomical explanation was easy,
then one easy explanation
is assuming,
okay, there are aliens there, and they were,
trying to communicate.
And just to be noticed, they've
constructed
a some maser,
like we we do on Earth. We have
masers in in this particular frequency.
And, and then because it's the easy ways
to to narrow your signal to all your
energy
to be concentrated in something that can be
detected, and then,
you
just shine that
maser everywhere, and it happens that they were
at the right
time observing that location.
But they turn off it is is energy
consuming
for having so much energy in one direction.
So they turn off or they or the
planet is rotating also. So they they they
are,
chiming other targets.
So so so there could be many
possible explanation why it's short lived even easy.
You consider this as as as as an
alien communication.
But let's turn now to your new work,
which I understand you've carried out at Arecibo
even though, as some of our listeners may
remember, the famous 305 meter diameter radio telescope
there suffered a serious structural failure and collapsed
back in 2020.
Is the work you've done all based on
old data from before then?
No.
I I started using the the the observatory
in 2017.
Our objective
was to look at particular stars that we
know that have potentially habitable planets.
It's not it was not to search for
life on those planet,
but for habitable condition for those planets.
Because we were looking on the stars, those
stars emit, flares, and that flares can produce,
can damage the atmospheres of these planets on
the long run.
So we were trying to get the sense
of the space weather
that was affecting those
planets.
But when you have a radio telescope,
it has a a a field view, what
we call a beam size.
So that beam size is is large, and
you will have signals not only from the
stars
but also from the other planets
and some background stars.
So so it so we're getting all the
radio information from that region in particular. So
it's not only the star. So I got
always in my mind, well,
if I'm looking
targets of particular interest for for the search
for actually search for life,
but I'm not doing that. And, maybe sometime
in the future, I look through the data
and and and
so that was my impression. So we have
observations
until,
August
2020
because in August 2020 was the
time that the first cable broke
at the observatory,
and, so they stopped working.
And then by December, they equalized.
So it was a slow process.
And then,
so I looked through our data, and
and this project, what is amazing for me
that I started doing this May.
Okay. Let's so finally, I decided just to
look for 10 signatures.
So that's a big shift. This is a
side project,
and and and I was motivated by the
video of on the
on the WAV signal because probably, like, in
most astronomers,
I dismiss the WAV signal. Even that I
know from my childhood,
I
I never thought the wipe signal as something
real
or something. I thought maybe it was a
glitch.
I I didn't put much attention to that.
Something fun probably, but, and and
the association with aliens, it doesn't help. So
so that's probably but when I saw this
video and, and it tried to dig into
what was the signal about,
this the strain, that's something that I may
see. It was a strong signal for for
for that duration. That's I that's in my
experience, that's very hard
to do as in in astronomy. I've never
seen something like that in in my data.
So, that motivated me to go deeper into
that and expecting that,
in this project, let's search for wow signal.
So I for me, the must fun part
was to get into the history of the
Big Air serve observatory,
compare with a receiver,
know how they did the observation,
try to imitate the exact analysis that they
did,
even going
that retro
to also our,
analysis
converted to to numbers
to text and numbers like they did
at that time just for the fun of
it
because I love it, this this this, part
of history.
And,
and I was expecting that, I was not
expecting to get any signal at all, something
interesting,
but we have to search anyway.
Maybe I write a paper in 1, 2
years that we look at this region,
and they
that we are is is is,
we don't detect anything with this,
sensitivity, and and that and that no result
is important to be published because that's something
that,
other scientists will look and say, okay.
These people did this, and if you want
to look further on that,
then we not increase the sensitivity or your
time or your frequency because it was an
observed before in that. So we we we
build up. So that's one important these node
results. So that was my idea that in
1 or 2 years, I will be talking
about this,
about my node results on that. But it
was amazing that, just
something interesting happened.
Too early.
So what was that interesting thing? Do you
basically see a few sort of miniature versions
of something like the wow signal in the
data?
Yes. Definitely. That was a miniature version. That's
that's the one way to call it. That's
so it was exactly,
the frequencies
that were expected.
We narrowband
a very particular narrowband frequency,
which looks like a a space meter.
And,
but the only difference within that and the
whole signal was the intensity.
That was it. These signals were in the
limit of detection
of the big ear.
So they were not,
in general be able to detect the signal.
So only if they get brighter, much brighter,
they will be detectable.
And they have to be brighter for,
also for a short time. And short time,
if I mean, I mean, minutes, hours.
So
so I I so I start this project
May, and we I analyze
the data using their their procedures, some
some much better procedures.
I immediately saw
these
lines, the signals.
And I look through the signals, and I
say, wow. That well, yeah, wow. No point
intended.
That look exactly like like the wall signal.
And,
they just have to be brighter.
And that got me thinking how we can
make those signal brighter for a moment,
Because they are natural emission for the for
the hydrogen atoms, they are very well known.
So those those signals
I I knew there were clouds
of hydrogen that they are very cold, and
because they are they are very cold, they
emit in narrow band.
But, usually, hydrogen
is a is a is a is a
atom at different speeds everywhere
moving through the galaxy.
So the general when we say the
hydrogen line is in astronomy is actually when
you see it is a profile.
It's a big signal. It's a broad signal.
So that's why one of the reason that
it never
occurred before that it could be a hydrogen
line is a broad line.
But there are pockets
of these,
small clouds
that are are cold enough
for that narrow signal to be and and
bright enough to narrow signal to be detected
if you have the right telescope.
And that's why I saw that that signals,
and I got thinking maybe for a week
or so for different,
methods because I knew that, for example, a
supernova explosion will excitate that gas, and it
will highlight the the the hydrogen line. It
will stimulate
the emission. But also it will move and
compress the the atoms there,
and they will have different speeds and
by the Doppler effect,
that signal will be broadband. It will spread
in the spectrum, and you will recognize, okay,
we have seen this before.
So all the mechanisms
that made those brighter were also make the
signal broad and not narrowband.
So the point was and the only thing
that makes sense was a some kind of
maser effect,
which won't increase the temperature of the system,
but it will stimulate.
And for that, you will need
a background source
of high energy radiation
that could be in any parts of the
spectrum,
but it will include the radio spectrum.
And if if the sign is the
including the frequency of the of the hydrogen
emission, and that will stimulate
for a moment because
that's the big issue here. We know of
many astrophysical measures
by different molecules.
And even for hydrogen,
atomic hydrogen,
it was discovered in is it rare for
the for atomic hydrogen, but it was at
other frequencies.
Never
in this particular frequency
of the 21 centimeters.
Never. And it was thought that it was,
very difficult to impossible
to and that was my perception too.
So so
but this also made sense that this could
be a rare event and you need then
a strong radiation source, and the main effect
won't be able to be sustained anyway.
So it will be a very transient effect.
So that's one that that's one of the
explanations
that makes it makes sense.
There are other options in that line, but
all require
that you have a strong background source
that will stimulate
and that that source are not necessarily visible.
Right. So, I mean, some of our listeners
may hear the words hydrogen maser and think
of, as you said, a laboratory device. We
may people people make mazers, and they use
them for atomic clocks and this sort of
thing.
How does the natural world sort of
duplicate that sort of physical system
out
somewhere light years away from Earth?
Well, I I get an impression
that
everything we do in our lab,
nature does it better
and more magnificent,
bigger.
So we can do a high
foot function of fission in the lab on
nature. We do with stars, fission, marginally. So
I think
so for this, we can do masers in
the lab. So I think the the well,
as as astronomy is doing, masers. So this
kind of masers that we do in the
lab and we haven't seen before,
I think that that's what's happening here. Nature
is doing
that measure of it. But, anyway, it will
be
a rare event because many thing has to
be right also.
Because the you have to have the
strong emission from this,
within the the only things that could be
that a strong emission enough for producing and
stimulate this emission in this cloud are magnetars,
which is a kind of natural
neutral star with a high magnetic field, and
they emit the strongest flare ever compared to
any flare star or so.
So
we think so that has to happen. And
those we know not that many, and we
have detected
the magnetile flares, and they are rare because
it it will hours be directional
also.
So they could be flaring in other direction,
and you will never detect it.
And
that flare has to be in the background
of of one of these clouds
because, these cold clouds will highlight
the and increase,
the
the the signal.
And it it will be a
a a a a a process of
chance and good luck.
And it's amazing,
but,
that,
even the
the air had the
the chance to detect something,
like this.
And the fact that you've now detected more
of them, albeit at a much lower intensity,
what are the implications
of that for future research in this this
area?
Okay. So we detected
a different signal. I have to make clear,
these these signals
are known
because these clouds are are ubiquitous,
are everywhere.
They're
in in in in I mean, in the
whole sky.
And I if you but you need
to recognize those signals a a big telescope.
And,
you need also to analyze the data in
the same way
that they were,
exploring the signal, looking at the exchanges in
the background.
And you need also to have the the
bandwidth that they were using,
which is with everybody call it as a
narrowband. They were looking narrowband saying that, well,
we're looking for SETI right now in much
narrower bands because you usually, for communications,
transmit
in much narrower bands.
But that was narrowband
back then
back then. And for just by coincidence,
our observations
were in that narrowband
because we were not looking at spectral lines.
We were not going for 30. If if
I were looking for spectral lines,
I will be using a much narrower band,
and I will be seeing this.
So so you have to have
looking at the right
sky at the right region of the sky
with this, sensitive telescope
in a and do this type of particular
type of analysis looking for narrowband
that that side just to to to recognize
the signal.
So
we will continue to do so,
observing because now we there's an intriguing possibility.
Okay?
Now that we know that the
corporate,
we believe,
is, one of these clouds,
so these clouds should be in the area
of the web signal. That will be the
first thing to to other people or us
to search for.
And why we haven't seen those clouds in
search? Well, there is not a a
so far, a a
telescope with enough sensitivity had looked at that
region.
A resevo was not able to look at
any way to that region in particular, so
to the region of the WAP signal
because it was outside of the declination.
And all the telescope that were able are
smaller ones.
The
the next that's in the
green bank, for example, a 100 meters, unless
you are using FASS
from China
or the BLA.
BLA is,
it has a a a
a nice
space resolution
to see
in that. It's not that sensitive,
but but but, it compensates that because it
has
a nice space of resolution. So that's the
only one that could could look through the
area
and spot
these small clouds.
And if somebody do that, and we're planning
to do that,
but
now the paper is out, somebody
might might search, probably diagnose.
So
is the good thing is that
we should start trying to falsify this hypothesis,
is to look for these clouds in the
region, which I'm sure you will find those
clouds there because they are everywhere.
And for the first time, you will have
a a a
this idea.
So where the actual if this is true,
where the signal came from. Because we know
the general region, the beam size, as I
told you before, for radio telescope is big,
so it encompass many objects.
And that was true for the big ears
since it was not that big.
So there are 1,000 stars in the in
this field. So we don't know actually which
one was. So the clouds
will discriminate.
So you will see these clouds, and maybe
I expect that there being that that field
file or 6.
That will be, reduction
where to search for.
And,
and once you find that,
so
the responsible
to excite that cloud will be in the
background of those clouds. So these clouds are
transparent. They are visible in their radio spectrum.
So
only you see them in the radio spectrum.
But in any optical telescope, you will you
won't see those. You won't,
you will see the background stars.
And one of the background stars or objects
there will be, we don't know of any
magnetar in that video.
We haven't discovered that. But magnetars have been
randomly been detected
in the sky
because
of luck.
Or maybe we see one of the stars
in in that field, and we see that
and we know already that's it's orbiting something
that we don't see because a magnet are
usually you only see when they they emit
these
flares.
Then and you calculate the mass and they
may it makes sense that this is an
outer star that is orbiting
the object because you see the star moving
or within something that is and that will
keep me a delta that, okay, maybe this
is the the corporate one. But
I know it will also motivate other people
to look in that particular region, now more
sensitive to Telugu for a long time. I
think that would be a long time
just to just to try to to to
even that you know if the the no
magnetars, even that
wait for that to happen,
that will be something you you have to
wait.
We know a few that has been
active and repeat for some time, and they
just stop.
We for weaker signals on only flares.
And, but that,
that will be
something to do anyway. So I I hope
this motivates
people first to look at the wild signal
differently,
more
astronomical
thing. So something interesting, something to test about,
to look for and,
explore.
And, definitely, we will look through our data.
Maybe we have
our data
a similar event recorded somewhere.
Only
I will net it through our analysis to
study
stellar flares.
I will never
will be able to detect to
see this unless I did the right analysis.
So having the the data is not enough.
You have to have the right analysis. Now
we're doing that analysis,
and then we will explore our data. Maybe
we see it,
a random event that looks like that,
and then we will move to the archive
data of the RSC observatory.
So going back,
that the data is
saved from the even from the sixties.
So the data is there, and we we
will have a long project
scanning through all that data for this particular
type of of phenomena.
I guess you can't find what you haven't
been looking for. Yes.
Yes.
Does this discovery that that, in this new
hypothesis, I should say, of, a magnetar
creating a hydrogen maser because of this intervening
cloud of gas and then happening
to be pointed at Earth when it does
it and when some telescope is listening for
it, does Does this tell us anything about
the the search for extraterrestrial intelligence in terms
of what types of signals we need to
rule out and what things we
we need to say in the future? Wow.
That's interesting, but it's definitely not aliens.
Well, now you have an example
of a false positive.
Something that you can tell immediately
now that you know if this is some,
real phenomena.
But we have to be also cautious because
these,
emissions are still
broadband
by the SETI standards or techno signals research.
They're actually searching a much narrow bands.
So
if you are searching a a a a
much narrow bands, which makes sense for more
technological signals,
then you will easily differentiate.
It will still be
a a much narrower,
broader band that than the you are searching
for.
So depending on on on on on the
how you're searching,
you now that you know this, it could
probably,
may you realize that zone events that you're
detecting
be more cautious and say, okay.
Let's rule out
the this astrophysical measure.
And then
but,
tunnel signature also is not searching only in
this, close to the hydrogen line. They're searching
in in other, frequencies, so you don't have
that problem,
other frequencies.
So all sorts of things have moved on
since 19 seventies. What was broad what was
narrowband then is not narrowband anymore for SETI
and the technology and that sort of thing.
It must be quite interesting to sort of
revisit this
this these old observations. Does that happen very
often in astronomy, or is it does everybody
just sort of move on to look at
the new next new thing? Is it is
it common in astronomy to look back at
old data and revisit it and reanalyze it?
Yes. Yes. And that's important.
We can,
for example, the fast radio burst. Fast radio
bursts were detected
in
in house in a telescope in Australia in,
I think, it was 2,007.
And these
these
first signals
that are short duration, very intense,
never seen before
by other telescopes.
So and this telescope detect those signals, and
everybody an astronomer was cautioned. That's probably some,
you know, fluke in the data. Like the
world's Sydney.
There was some fluke in in Sydney.
But scientists decided
that motivates others to look for forward, to
take it seriously,
and they looked through the archive data of
the receiver observatory,
and they found it.
So because they found it in the receiver
observatory, this and publish that, okay, we found
the what now
it make for everybody real. Oh, this is
real.
We have to look for this signal.
So for detecting the signal, you have to
have observations
and and and running
with a time step.
Very small.
So that's that's one of the reason, and
they are random everywhere.
It was something hard to detect and never
realized. And it's amazing that,
because our archive data, we were able to
confirm
and then
and and then, other people. And now it's
it's a hot it's a hot topic of
exploration.
What are the what was the source? And,
actually,
sure after that, people thought, well, maybe this
is aliens again because we don't know what
this emitting from random places in the in
the the customers,
these strong signals.
They're broadband,
but they are very strong
and for a short time, and we don't
know any phenomena that could do that. So
people were thinking about aliens again.
And
but,
eventually,
astronomers pinpoint those signals to galaxies.
Oh, so the earth is coming from far
away
from this galaxy and this galaxy,
but still what phenomena is is doing that?
And
then what happened was
the, in our own galaxy why
not in our own galaxy?
There is a magnetar,
and that magnet we detect the fast radio
bursts from that magnetar.
And, now we think,
so, probably, this is our magnetors are the
ones that are emitting these 5 effect of
and that's now a stronger
hypothesis that
fast radio inverters are due to magnetars and
among many other explanation. So
and that's
quite recently in the few years that we
are
starting to realize this.
And, that's
so so there are many other examples of
of
looking through archive data
because you have to analyze the data in
different ways.
Look.
As you said, if you're not looking you're
looking for something,
you don't not looking for something you won't
fight in.
Well, Abel Mendez, thank you very much for
the coming in the podcast. I hope you
find more interesting things as you look through
the data. Yes. Thank you.
I appreciate that. Bye.
That was Abel Mendez in conversation with Margaret
Harris.
You can find a preprint of Abel and
colleagues' paper on the archive server.
Just look for the title,
Arecibo
Wow 1,
an astrophysical
explanation
for the Wow signal.
CERN is one of Europe's premier research facilities.
And this year, the lab is celebrating
its 70th
anniversary.
In the August episode of the Physics World
Stories podcast,
2 former
public relations
gurus at CERN,
James Gillies and Achinche Rao,
look back on some of the highlights of
their careers.
These include welcoming Hollywood royalty to the lab
for the launch of the film Angels and
Demons
and the announcement of the discovery
of the Higgs boson
at the lab.
That episode is hosted by Andrew Glester, and
it's called
CERN at 70.
How the Higgs Hunt Elevated Particle Physics
to Hollywood Status.
You can find it on the Physics World
website or at your favorite podcast provider.
And the CERN celebrations
continue here at Physics World.
On Thursday, 26th
September,
we present
the future of particle physics,
a Physics World live event
produced in partnership with the journal Reports on
Progress in Physics.
The live panel discussion will feature
Tara Shears
of the University of Liverpool,
Phil Burrows at the University of Oxford,
and Talika Bowes of the University of Wisconsin
Madison.
They will explore what the future holds for
high energy physics
and where the next particle collider
should be built.
You can register now for this free event
on the Physics World website.
Just click on the Physics World live tab
at the top right of the homepage.
I'm afraid that's all the time we have
for this week's podcast.
Thanks to Abel Mendez and Margaret Harris for
a fascinating discussion
about the Wow signal.
And a special thanks to our producer, Fred
Ailes.
We'll be back again next week. See you
then.