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Gamma Ray Bursts: Flashes in the Sky

Video transcript
The video is 6 minutes and 30 seconds long.
Produced by the American Museum of Natural History, June 2006.

Video begins here.

Visual: Montage of black-and-white historical footage of 1960's naval ships and aircraft.

Speaker: David Burrows, Department of Astronomy and Astrophysics, Pennsylvania State University

Visual: David Burrows in office.

Gamma-ray bursts were first detected back in the 1960’s using a series of satellites that were built to monitor the nuclear test ban treaty.

Visual: Black-and-white historical footage of a nuclear explosion in the ocean. Military men observe with binoculars from a ship.

When a nuclear bomb explodes, it makes gamma rays.

Visual: A large column of water from the explosion rises from the sea.

So the purpose of the satellites was to look for flashes of gamma rays coming from the Earth.

Visual: David Burrows in office

And they saw flashes of gamma rays, but they were coming from the sky.

Visual: A galaxy, speckled with flashes of light from gamma-ray bursts.

People couldn’t imagine what could possibly be making these bright flashes of gamma rays.

Title: Gamma-Ray Bursts: Flashes in the Sky

Speaker: Neil Gehrels, Principal Investigator, Swift Mission

Visual: Neil Gehrels in office

Gamma rays are the shortest frequency end of the electromagnetic spectrum.

Visual: A radio dial with an animated wave above it. The radio dial fades. The wave, undulating, is labeled "Visible", "X-Rays", and "Gamma-rays".

If you could take a radio and then continue tuning it to higher and higher frequencies, you go through the visible band to X-rays and then end up in gamma rays. Those wavelengths are really important because they’re the ones that tell us the most about very energetic things in the Universe.

Visual: A large explosion of light in space. David Burrows in office.

Speaker: David Burrows

Gamma-ray bursts have been probably one of the leading astrophysical mysteries since the early 1970’s, when they were first announced. The biggest challenge in studying gamma-ray bursts is the fact that they last for such a short amount of time. The burst is sometimes over in a second. At best it might last a minute or two.

Visual: A short burst of light in space.

And so that makes it very challenging to point a telescope at it that quickly and be able to study it before it fades away.

Visual: The Swift satellite in space.

Speaker: Neil Gehrels

Swift is a NASA satellite built specifically to study gamma-ray bursts.

Visual: A gamma-ray burst occurs in space, Swift orients itself to face it with its observing instruments.

When Swift detects a gamma-ray burst, the computer on board gets the position. It reorients the satellite.

Visual: Swift relays its data to a receiving satellite in Earth's orbit. The data is then transmitted to ground-based stations.

The data from the burst immediately flow down to the ground, and they’re distributed on the Internet.

Visual: Researchers in an office frantically respond to phone calls regarding a newly discovered gamma-ray burst.

Speaker: Researcher at ground station

Guys, there’s a burst.

Speaker: David Burrows

That allows ground-based telescopes to point at the direction of the burst quickly.

Visual: Observatory domes pivot and open to reveal their telescopes inside. Scientists at a conference table discuss Swift's findings.

Speaker: Joshua Bloom, Department of Astronomy, University of California, Berkeley

What we’ve known now for a decade is that when a gamma-ray burst goes off, it leaves behind this dying ember, this afterglow light.

Visual: Joshua Bloom in office.

And we can use the traditional telescopes, those that are sensitive at optical and infrared wavelengths, to be able to study the details of how the light is changing, how the colors of that light is changing.

Visual: Observatories on mountaintops. Scientists peck away at laptop keyboards and examine data.

And in those details we can uncover some of the physics of the explosions.

Visual: Images of gamma-ray bursts from the Palomar Sky Survey, Chandra X-Ray Observatory, Danish Optical Observation, and Hubble Space Telescope. Joshua Bloom, with another scientist in a lab examine astronomical images on laptops.

This is the afterglow 58 seconds after the gamma-ray burst triggered the Swift satellite.

Speaker: The other researcher

Uhmm.

Speaker: Joshua Bloom

And you can see in this inverse color here that it’s fading from black all the way down to nothing. We start off 58 seconds and then 30 minutes later we really don’t see anything.

Speaker: The other researcher

It fades really fast.

Speaker: Joshua Bloom

Oh yeah, it fades very quickly. It’s a good thing that we got on so early.

Speaker: The other researcher

Yeah, a quick response.

Visual: Scientists at a conference table examine Swift data on a large screen at the front of the room.

Speaker: Joshua Bloom

When you look at each gamma-ray burst in detail, you see very, very different things.

Visual: A scientist points out details of a gamma-ray burst on the screen.

And it’s turning out that as we’re learning more about gamma-ray bursts, we believe that those differences actually amount to differences in what makes the gamma-ray burst.

Speaker: Peter Mesaroz, Department of Astronomy and Astrophysics, Pennsylvania State University

Visual: Peter Mesaroz in office, in front of whiteboard

Based on observations and what we know from physics, there are two types of models that have come to be representative of gamma-ray bursts.

Visual: Peter Mesaroz illustrates on whiteboard.

We think that they originate in a massive star which collapses to a black hole.

Visual: Computer animation of rotating star and jet of stellar matter.

The star is rotating so that the material that falls in forms an accretion disk. And that produces a lot of energy, which creates a relativistic fireball resulting in a jet being ejected along the rotation axis, creating gamma rays, and those gamma rays are thought to give rise to the gamma-ray burst.

Visual: Computer animation of gamma-ray burst.

There is a second model.

Visual: Computer animation of two neutron stars spiraling around and toward each other.

Here it is thought that there are a pair of neutron stars and they spiral in, and as they spiral in eventually they coalesce into a central black hole.

Visual: Peter Mesaroz illustrates on whiteboard.

And as matter is swallowed, a jet forms and that produces gamma rays.

Visual: Peter Mesaroz in office.

We have some issues with this model. It doesn’t seem to explain everything to our satisfaction, but there is continued work going on on these. It may be that eventually we’ll have to dismiss this model and go for another one, but for the moment it seems the best bet in town.

Visual: David Burrows in office

Speaker: David Burrows

Gamma-ray bursts have been mysterious for 30 years.

Visual: Black and white historical-themed fictional footage of UFOs descending upon a city.

And the explanations people have suggested for gamma-ray bursts range all the way from comets falling into the Sun to interstellar warfare.

Visual: David Burrows in office.

We’re always discovering new things about the Universe, things we didn’t understand, things that are different from our expectations, things that we never even imagined.

Visual: Joshua Bloom in office.

We study gamma-ray bursts because they’re out there. It’s a phenomenon that we now know are basically the brightest things that nature knows how to throw at us.

Visual: A computer animation of a gamma-ray burst in space, with Earth in the foreground.

It’s where the most dense objects smash into each other.

Visual: A collage of animated neutron stars, a gamma-ray burst, and the Swift satellite.

It’s where black holes are formed. And if we want to understand some of the most exotic types of phenomenon out there, then we’d better understand gamma-ray bursts.

 

 

Video ends here.

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