Last month, scientists announced that they had detected something
never seen before -
two massive neutron stars colliding with each other,
triggering a colossal explosion.
It marks the most dramatic example so far of a new type of astronomy
that focuses on brief transitory events that happen so fast
they're almost impossible to detect.
Welcome to the spectacular world
of astronomy that happens in the blink of an eye.
We're used to thinking that the universe operates on timescales
of millions or even billions of years.
Most change happens with imperceptible slowness.
We have now discovered a whole catalogue of events like the
neutron star collision that happen on much shorter timescales,
seconds or even milliseconds.
Tonight, we explore this world of transitory events.
I'm here at Jodrell Bank to find out the latest theories about the
most mysterious of all transitory events - fast radio bursts.
We'll hear more about the recently detected neutron star collision
and gravitational wave.
Chris joins astronomers attempting to detect gamma ray bursts
- the most powerful short-term event that we know of -
to see just how different this kind of astronomy is.
We could say possible burst if you want.
I don't know what I want. I don't know.
And here it is...
And Lucie Green reveals that some dramatic rapid phenomena
can occur much closer to home.
But we start with Chris, who spent a couple of days with scientists
attempting to detect an elusive gamma ray burst.
Astronomy used to be about staring up at the unchanging heavens,
so the search for transience, things that go bang in the night,
is truly revolutionary.
But it all depends on astronomers' ability to monitor the whole sky.
So I've come to the University of Leicester to see how this is done.
This is the UK base of Swift,
a space-based telescope designed to search for GRBs, gamma ray bursts.
Brilliant flashes of light that last just for a few seconds.
It's thought that some of them are caused by neutron stars
collapsing into black holes.
The problem is that they're rare, and so Swift has to do two things.
First, it has to scan the whole sky to spot when a GRB occurs,
and then second, it has to swerve to get the data before it disappears.
So we're here because you're controlling the spacecraft.
This is not what I thought Mission Control would look like!
So, what's your role?
I am one of a team of observatory duty scientists, ODS for short.
Everything is so well designed now.
As long as you have access to a computer, and you can login
to the relevant computers, we can do everything.
So, how quickly can Swift respond once it's detected something?
Quickly. The maximum speed we can slew at is about a degree a second.
This typically means that, for most gamma ray bursts that we detect,
we'll be on target between one to two minutes.
And that's important for the science?
It is, yes. Gamma ray bursts may be the brightest explosions
in the universe since the Big Bang, but they fade really quickly,
so you have to get on there as fast as you can.
And if you're not swift, you miss it. Exactly.
At 8.33am, there's an alarm.
Swift has spotted something.
Phil Evans, the BA, or burst advocate,
immediately starts to analyse the new data.
And Kim gets on the line to her counterpart at the Goddard Space
Flight Centre in Maryland, to see if they've noticed the same event.
Hi, Amy. It's Kim and the Leicester crowd.
Yes, it's NGC 224 that is the nearby source.
You mean, the one big spike before the...?
Yeah. Yeah.
Could it be an SGR in M31?
I mean, it's less than six Sigma, though.
OK, we've now got a Spernak.
It's got lots of stuff in it, but no point source.
This feels almost like something from science fiction.
Within seconds,
Phil has more information about the location of the source.
Did I hear it is in M31 now, the Andromeda galaxy?
Yeah. So, the thing is M31's full of sources. So we...
It's enormous in the sky as well. It is, which doesn't help.
So we've found an object, which is a known object,
which is that one there in this image.
So there's the core of M31 off here. Right. The issue is, is this
just because that object is there, or has it suddenly got brighter?
And for some reason, I'm not getting a brightness of this new source.
The problem is the signal is very faint, and, what's more,
it's buried in a galaxy chock-full of other sources of radiation.
A sort of vague source. The automatic system
didn't detect anything, but by eye, it looks like there might be.
So they were trying to see if they could figure out what was going on.
I'm assuming the answer was no to that.
I haven't yet managed to get a...
I know why, it's cos... No, that's not what I was asking.
Well, I mean, we could say a possible burst if you want.
I don't know what I want. I don't know.
You're the BA, I'm going to leave this in your hands.
No, give us a second. Let me just think.
After more discussion,
Phil and Kim decide the trigger probably wasn't a GRB,
but instead came from some other source within the Andromeda galaxy.
So, Kim, what just happened?
So, Swift triggered on something. We slewed round rapidly.
We were on target in 74 seconds, so just over a minute.
That's impressive! It then went on and showed us that not only have
we detected one known source, we've detected five known sources.
So it took us about 45 minutes on that telecon.
If it had been a real GRB, yeah, probably more like 15, 20 minutes.
So the satellite is back to its normal job,
and we're back to waiting for a burst? Exactly.
A few hours later, the story changes again,
when Phil and Kim call the American team with their report.
Yeah, Jamie, this is Phil. Can I just mention this morning's event?
Because there's a couple of queries about it.
They've noticed that the same telltale signal was also seen by
a second telescope, called Fermi.
More pressure now on Kim and Phil to come up with an explanation.
Well, that was exciting.
It turns out, while the team here were running about this morning,
the Fermi gamma ray burst-hunting satellite also saw something.
And so the fact that there was something seen by Swift and Fermi
means it's worth going back for another look.
So that's what the spacecraft's doing right now.
For the next few hours,
Kim and Phil are back observing M31, and reconsidering their data.
Continue monitoring this variable AGN
to get a good optical and X-ray... optical to X-ray SED.
And later, they have a new theory.
After running the numbers,
they still believe that what they saw it isn't a gamma ray burst.
They think it's an unusual object, bright in X-rays,
that's actually been seen before.
The object is called Swift J0243.6+6124.
Really sticks in the mind. It's named after the position in the sky.
So this was first detected by Swift on the third of October.
We had a trigger, and we didn't know if it was a new gamma ray burst
or a galactic transient.
So we kept collecting data, and the X-rays stayed bright.
Now, for a GRB, the X-rays, the afterglow and the X-rays will fade,
fairly quickly over time.
The fact that they stayed bright told us it wasn't a GRB,
and it was some kind of transient.
So it's still getting brighter at the moment, so we may trigger again.
We'll just have to wait and see.
Kim's day is over by 7pm.
Any new activity now will come direct to her phone,
and she'll have to deal with it at home.
Which is of course exactly what happened next -
a genuine gamma ray burst was detected at 12.07am.
So, just after midnight, on the early hours of Saturday,
Swift triggered on a GRB. So, what do we know about this burst?
It's a long gamma ray burst,
so this means it was a very massive star originally
- more than 40 times the mass of our sun -
and it just got to the end of its life.
So at that point, it all collapses in on itself.
And, as it does this, stars rotate, generally,
so everything's spiralling round in, and you get jets of material
shot out, and if those jets are pointing towards us,
Swift can detect it, and that's what we see as a GRB.
I can see now just how pressurised observing transient events is.
And it makes sense, because with something that's over so quickly,
decisions have to be made fast,
and often on the basis of incomplete data.
Gamma ray bursts are not the only transitory event in space, though.
Recently, astronomers have observed a new type of phenomena,
shorter, more powerful, and incredibly elusive...
..fast radio bursts.
Unlike anything else known,
these strange chirps of radio waves are only milliseconds long,
and have a unique characteristic sound,
sweeping from high to low frequency, and their wavelength is
at least a billion times longer than gamma ray bursts,
suggesting that they may arise from a different cosmic process.
But what?
I spoke to Ben Stappers at Jodrell Bank,
one of the UK's key research centres for fast radio bursts,
to find out more about this incredibly strange phenomena.
So, Ben, what are the FRBs, these fast radio bursts?
Fast radio bursts are these very short duration,
just a few milliseconds, of radio emission that are detected
from far away by radio telescopes.
So, how many others have been detected?
I think around about 30 so far.
But, you know, we're discovering a few every month now.
So, are there any other variations between them? Yes, so we think
that the vast majority of them so far have never been seen to repeat,
even with observations of many, many hundreds of hours, in fact.
But then, in 2012, the Arecibo telescope in Puerto Rico
observed a fast radio burst that did something totally unexpected.
There was a second FRB from the same source, and then more.
Suddenly, this meant we had a chance to see an FRB happening
in real time.
One of the advantages of something that repeats is that we can
actually go back and do more observing,
and it's been possible for people to localise this burst.
And what I mean by that is you can see exactly where it is in the sky,
and associate it with a host galaxy.
So it brings us to the million-dollar question -
what actually are they?
A lot of people have been having a lot of fun coming up with theories
of what these things are. Presently, there are more theories
than there are bursts. There's two...
If we think that there are now two classes of these objects,
where the repeater is maybe one type and those bursts we have
only detected once are another type,
the single ones might be associated with something cataclysmic,
where the object itself is destroyed or the event is a one-off, so
it could be something like merging neutron stars that are recurring.
And there is also an idea that you have this thing called a blitzar,
which is actually a very rapidly rotating neutron star.
It's very massive, more massive than neutron stars should be,
and eventually, as it slows down, it collapses into a black hole.
And when that happens, it actually ejects its magnetic field,
and these sound very exotic. It does, yes.
In the case of the repeater,
maybe it's a newly-born object called a magnetar.
Now, a magnetar is also a neutron star, something that is spinning,
that has a very large and very strong magnetic field.
And so the idea is that maybe, in the birth event of these things,
something happens that generates these fast radio bursts.
Well, it's fantastic to hear about a genuine astronomical mystery,
and I'd love to come back as you get more information and really find out
what they are. Yes. I hope we can invite you back, and be to tell you
exactly what they are. That's been fascinating.
Thank you so much. Thank you.
What's particularly exciting about this new fast response astronomy
is that these powerful transitory events don't just occur
in deep space. They happen in our solar system, too.
Just think about our sun.
The sun feels as though it hardly changes at all.
But, actually, if we look close enough,
we see a very different story.
Lucie Green explains how the sun is actually a treasure trove
of spectacular transient events.
We all feel familiar with our local star.
At 93 million miles away, the sun is still able to give us
all the heat and the light that we need to survive, and today,
it looks absolutely glorious in this beautiful sunny sky.
But to really see the sun, we actually have to go inside.
Because the best way to see what's happening on the sun
is to look at it from space.
And here it is - the sun as seen by Nasa's Solar Dynamics Observatory.
It's a telescope in orbit around the earth.
These images are just a few minutes old,
and they show, not only an enormous range of structure,
but also just how dynamic the sun is.
And, for example, over here, we see these beautiful
evolving glowing arches of gas in the sun's atmosphere.
And it turns out that these structures are actually key
to understanding the entire sun.
Because they are shaped,
like everything else in the atmosphere of the sun, by magnetism.
The inside of the sun is a swirling mass of electrically charged gas,
and wherever you have moving charged particles,
you have a magnetic field.
And the thing I really love about magnetic fields is that they have
an influence on the material, or the stuff, that's around them.
To show that, I have some iron filings suspended in fluid,
and a bar magnet.
And if I put the magnet on the iron filings, they immediately respond,
and they take on these beautiful, arch-like shapes
as they follow the lines of force of the magnetic field,
running from the north pole to the south pole.
And in the same way that the iron filings responded to my magnet,
the gases in the sun's atmosphere respond to the sun's magnetic field.
So, here you can see these giant arches of gas in the atmosphere.
Oh, look at that, there was a plasma flow shooting along
these magnetic field structures.
Now, underneath this arch-like structure is something that we call
a prominence or a filament - they are exactly the same thing.
This is relatively cooled plasma lofted into the atmosphere
of the sun by its magnetic field.
But just look how it's moving -
it's sort of shimmering and oscillating.
Now, studying these plasma clouds isn't just an academic activity.
They actually mean something for us here on the Earth as well,
because occasionally they will erupt into the solar system.
This is an eruption that happened just a few days ago.
There is a filament structure here,
and it erupts out into the solar system.
Now, to give you...
Here it goes! So there goes the eruption.
And it is an enormous structure.
To give you a sense of scale, the Earth is about as big
as this bright patch in the atmosphere of the sun here.
So this eruption starts off already many times the size of the Earth,
and then expands to become many, many times bigger
actually than the sun itself. And now you can see
that enormous structure heading out into the solar system.
And, if these eruptions are Earth-directed,
they slam into the Earth's magnetic field,
shaking it up and triggering what we call stormy space weather,
affecting our electricity networks, our high-frequency radio
communications, all kinds of ways our modern technologies
are ultimately affected by these eruptions from the sun.
The last transient phenomenon that I want to show you
is something called spicules, and here we are.
All along the edge of the sun are spicules.
You can see these dark, sort of like grass-like features,
or like the spines on a hedgehog, but waving in the wind,
and they are the spicules. They are as tall as the Earth is wide,
and they really are transient features, because they only last
on the sun for around 10 to 15 minutes. Today,
they're viewed as being important in heating the corona of the sun.
They transport gas from the lower layers to the upper atmosphere,
the corona, which has a temperature of millions of degrees Kelvin,
or millions of degrees Celsius.
Ironically, this part of the sun is an area astronomers consider
relatively tranquil, and they call it the quiet sun.
But images like this from the Solar Dynamics Observatory have shown us
that this isn't really the quiet sun at all.
The quiet sun, in a sense, is dominated by all this activity.
Observing this transient solar behaviour
is not just for professionals.
Amateurs can relatively easily spot
many of the phenomena that Lucie saw.
Pete Lawrence explains.
The sun is one of the most rewarding objects in the whole sky.
But first, a word of caution, because looking at the sun
under any circumstances can be extremely dangerous.
It's very bright, and it can permanently damage your eyes
or equipment. So, if you intend to use a telescope,
you need to use a certified solar filter,
because that will reduce the incoming light to a safe level.
And remember to remove or cap your telescope's finder.
Apart from the fact that it too could be damaged, the temptation
to look through it could end with disastrous consequences.
Line the telescope up with the sun
whilst looking at the telescope's shadow.
That way, you won't look into the sun's glare.
So, once you're lined up, you can start viewing,
and the most obvious transit solar phenomenon is sun spots.
These are caused by intense magnetic fields creating localised cooling.
The result is a region that looks darker than its hot surroundings.
Through my white light filter, I can see there is just one tiny sunspot
on view, but other days you can get more sun spots visible.
But to see the really fast-moving action,
I need to switch to a different type of filter - a hydrogen alpha filter.
An H-alpha filter rejects all the wavelengths of visible light,
except those given off by excited hydrogen atoms.
Now I've got the hydrogen alpha filter fitted,
I've got some incredible detail on the sun's disc.
I can see some dark filaments
- that's cool clouds of hydrogen in the sun's atmosphere -
but the really impressive stuff is down at the bottom of the disc
I've got here, because if I go down there and then boost the exposure,
I can see some incredible prominences on the edge of the sun.
So, remember - astronomy can be just as rewarding in the daytime
as at night. But if you're going to get to know the sun,
do make sure you observe it safely.
Observing brief cosmic events isn't only redefining how we do astronomy,
it's also giving us new information about the universe.
Which brings us back to that neutron star collision
that made the headlines last month.
Just as we were preparing to make this programme, news broke of
an exciting new transient of a type that we simply haven't seen before.
Tonight at ten, an international team of scientists has discovered
the effects of a collision between dead stars, called neutron stars,
which happened 130 million years ago.
The first sign was a gravitational wave picked up by the huge detectors
at Ligo in America and Virgo in Italy.
At almost exactly the same time, the Fermi satellite
detected a gamma ray burst coming from the same location.
It's the first time that those two things - gravitational waves
and a burst of light - have been seen coming from the same place.
This detection triggered a secondary flurry of activity of
other telescopes right around the world, including Swift,
all scouring the sky for more information.
All the evidence suggested that what had been seen was the collision of
two neutron stars, the compressed cores of now dead massive stars,
now ripped apart in an event of unimaginable violence.
This turned out to be a kilonova,
one of the biggest and most powerful explosions known.
As well as being burst advocate on Swift,
Phil Evans headed up Swift's observations of the kilanova.
I persuaded him to leave his desk for a moment to explain
what really happened, and how this event helps us understand
how heavy elements are actually created.
So, this is a very exciting event. Yes. So, what did you see?
Well, we didn't see X-rays, which was a surprise.
Because if you have a gamma ray burst, you normally,
not always, but normally get X-rays.
And with this thing being so close, it should have been about
12,000 times brighter than a typical gamma ray burst.
So we were expecting something.
We did see very bright ultraviolet emission.
And that was a real surprise, because if there's no X-rays,
then where did the ultraviolet emission come from?
There's no afterglow.
And this is what led us to the belief that maybe what we'd found
was not a typical gamma ray burst afterglow, but something new.
So, people assume that this thing is what's called a kilanova.
That's right. These two neutron stars merging.
And they have this unusual signature.
Why does two neutron stars colliding produce light anyway?
Why do we see it as a gamma ray burst, and where does
the ultraviolet come from? When you get two neutron stars...
Now, remember, these have got very, very strong gravity.
You've got the mass of the sun, and gravity is proportional to mass,
but crammed down into an area maybe 10km across.
So the size of the city we're standing in right now, for example.
So when you make the radius really small, gravity shoots up.
So you get two neutron stars really close together,
and they start off looking sort of round, and then they start
to distort, almost becoming teardrop shaped, because each one is
pulling really hard on the nearby side of the other one,
and less hard on the other side.
And that changing gravity across the neutron star is enough to start
to distort it, and then eventually, to rip it apart.
So as it falls in, it gives off radiation,
and we think that in a lot of events where you get stuff falling in,
it's spiralling round in a disc, and as it falls in, you launch jets.
So you get material that is blasted out,
the sort of the poles of the event, very close to the speed of light.
But in a kilanova, you're seeing something very special, because
as well as this material that is falling in and coming out in jets,
you've got loads of material swilling round
- very, very dense material - close together, full of neutrons.
So, this is neutron star rubble?
Neutron star rubble, right. And it's neutron rich.
And this makes it a prime site for something that we call
the rapid neutron capture process. And this is basically one of
the ways the universe can create elements heavier than iron.
But when you do that, you make unstable elements, and they decay.
Because, you know, just like your uranium in
your nuclear power station does, it decays, and that glows.
And so that gives us what we call the kilanova, and it's
the signature of the formation of heavy elements in the universe.
So, your bright ultraviolet light that Swift was seeing
from this event might come from the decay of new elements that
are being created. That's right. And now we know when it comes from.
Now we know at least where some of it comes from.
And we only know that because we saw this ultraviolet flash of light.
What all this shows is something very exciting.
We can now actually watch the universe change
in front of our eyes.
And these events that happen in just seconds
can have profound consequences.
That's it for this programme,
from here at Jodrell Bank, and also from Swift.
But do join us again next month, when we're presenting our
Christmas special, getting back to basics to show everybody how
to enjoy the night sky, including how to get started in astronomy,
the best equipment to buy, and also how to enjoy the night sky
with no tech at all. Do go to our website in the meantime,
and check out Pete's star guide,
and also great stuff we couldn't fit into this programme.
In the meantime, of course, get outside, and get looking up.
Goodnight.