Gamma-ray bursts, called GRBs for short,

are one of the biggest mysteries in modern astronomy.

They're explosions that release tons of highly energetic gamma radiation,

but although we know they come from outside the Milky Way,

scientists aren't exactly sure how they happen.

They are trying to figure it out, though, especially since these bursts

are energetic enough to interfere with satellites and astronauts in space.

But there's a long way to go.

We've spent more than 50 years trying to understand GRBs.

And what's especially surprising is that this mystery began on accident,

thanks to, of all things, the Cold War.

The story starts in 1963, when the U.S., U.K., and Soviet Union

all got together and agreed they wouldn't set off any nuclear bombs

in the atmosphere or in space.

Of course, since this was right in the middle of the Cold War,

it wasn't like everyone was super trusting of each other.

So that same year, the U.S. Air Force started launching

a bunch of monitoring satellites, collectively called Vela,

to help make sure everyone was following the new rules.

Vela carried instruments to detect X-rays, gamma radiation,

and energetic neutrons.

All things that could be released by a nuclear test.

The satellites also always orbited in pairs,

so there was never an unobserved hemisphere.

Over the years, they gathered tons of data,

and some of it was pretty unexpected.

In 1967, the Vela 4 satellites picked up two big peaks of gamma radiation:

first, a tall, sharp one, and then a lower, broader one.

The good news is, they at least didn't seem to be coming from Earth.

Since the satellites operated in pairs, whichever one was closer to a signal

would detect it first, and that would help pinpoint its origin.

But this time, both satellites got basically the same signal at the same time.

Still, that wasn't anything to stop the presses about.

It was just one event, so maybe the detectors malfunctioned.

But then it happened again.

And again.

In fact, by 1973, Velas 5 and 6 had detected 16 more

of these mysterious gamma ray bursts,

and scientists knew this was a new phenomenon.

But that was about all they knew.

Besides “somewhere in space”,

it still wasn't clear where these GRBs were coming from.

We didn't know if they were from inside or outside the galaxy,

and researchers certainly didn't know what was causing them:

Hypotheses covered everything from supernovas to black holes.

Only in 1996, almost 30 years after the first GRB detection,

did we finally make some serious progress in figuring things out.

That year, the Italian and Dutch space agencies launched BeppoSAX,

an Earth-orbiting spacecraft that monitored the skies for objects like GRBs.

Specifically, it was equipped to detect something called afterglows.

After an object like a star releases a big burst of energy,

there's kind of a cool-down period,

where you can see a sort of glow in lower wavelengths.

After a GRB, you'd expect an afterglow with X-rays and visible light,

which could take about a week to fade.

BeppoSAX had wide-field cameras that could pinpoint the location of a burst

and send that data to Earth really quickly.

Fast enough that ground-based telescopes could observe the afterglow.

And that technology finally let us pin down the location of a GRB.

Less than a year after launch, BeppoSAX detected a burst

from some 8 billion light-years away.

So, definitely outside the galaxy.

And in the years since, we've found plenty of others,

all far outside the Milky Way.

So we know these bursts aren't from around here.

Now, we just need to answer the dozens of other questions.

Based on the observations we've made since 1967, we think there are actually

several types of GRBs out there, varying in intensity and duration.

And that suggests there may not be a single,

universal explanation for how they work.

It's possible that some might involve supernovas or merging neutron stars

the dense cores leftover after a supernova.

But there's a lot of gray area, and a lot we have left to learn.

To make things more complicated, we'll also never be able to predict GRBs,

because we can't know when something like a star is going to die,

or when two stars are going to merge together.

Plus, the events that might lead to one of these bursts take place on

cosmological time scales.

Our lives are within the margins of error for these processes.

If nothing else, though, we do know a decent amount about what happens

when gamma rays interact with Earth.

All our detections of GRBs let us know the kinds of energies we can expect

from them, which lets us take any necessary precautions to protect our

satellites and astronauts.

And we can extrapolate from those detections and model what might happen if

Earth were closer to a burst

all of which informs how we understand habitability in the universe.

Realistically, we're a long way from solving this Cold War discovery,

but we've learned a lot from the journey, too.

Thanks for watching this episode of SciShow Space

especially to our amazing patrons on Patreon!

Thanks for helping us explore the mysteries of the universe.

If you'd like to support the show and help us keep making episodes like this,

you can go to patreon.com/scishow.

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