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Gamma Ray Telescope Senses High-Energy Radiation

Resource for Grades 9-12
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Gamma Ray Telescope Senses High-Energy Radiation

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Running Time: 2m 15s
Size: 13.1 MB

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This media asset is from "What are Gamma Rays" NASA/Goddard Space Flight Center.

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WNET

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WGBH Educational Foundation WNET

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NASA

In this video adapted from NASA, NASA astronomers describe what gamma rays are (highest form of energy along the EM spectrum), describe the GLAST satellite (which is equipped with a gamma-ray telescope), and share some background about the kinds of extreme universal phenomena indicated by the presence of gamma rays. The video also includes a brief description about why gamma-ray observations must be done from space rather on the ground.
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open Background Essay

The light we can see with our eyes is just a tiny portion of the radiation along the electromagnetic spectrum. What makes it a spectrum is that it spans a wide range of energy, from very low-energy radio waves to very high-energy gamma rays. The bands of the spectrum, in order of increasing energy, are: radio, microwaves, infrared, visible, ultraviolet, X rays, and gamma rays. Though each type of light differs in its energy (and therefore frequency), they share some basic properties. They are transverse waves and, unlike sound waves, don’t need a medium. It can travel through a vacuum – and can travel through the “emptiness” of space. Sound can’t, because it requires a medium. It’s true what they say: In space, no one can hear you scream.

The highest-energy light, gamma rays, can have about a billion times the energy of the light we can see with our eyes. That level of energy could cause great harm. Our atmosphere absorbs high-energy radiation, so we’re protected. One downside of our atmosphere absorbing gamma rays is that, in order to see the universe in the gamma ray section of the spectrum, we need to get above the atmosphere. NASA’s GLAST (Gamma-ray Large Area Space Telescope) satellite does just that.

Renamed the Fermi Gamma Ray Space Telescope after launch, the satellite loops in orbit around Earth and views the entire sky every day in the gamma ray band of the spectrum. Since gamma rays have the most energy of any type of electromagnetic radiation, the natural phenomena that create them must be very powerful. These include black holes, exploding stars, and other extreme phenomena.

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open Discussion Questions

Before Viewing

  • What’s different – and what’s the same – about radio waves, microwaves, infrared, visible light, ultraviolet, X rays, and gamma rays?
  • Would it be more harmful to be exposed to low-intensity gamma rays or high-intensity infrared radiation? Why?
  • Our atmosphere blocks certain types of radiation. Why do you think those tend to be the types of EM light with the highest energies?

    • While Viewing

  • How does the energy of gamma rays compare with the energy of light elsewhere along the EM spectrum? What exactly is it that changes from one type of light to another?
  • Why are NASA scientists interested in gamma rays to begin with? What’s interesting about the universe as seen through the gamma ray band?
  • What’s an example of an important question the GLAST satellite is helping scientists unravel?
  • Our atmosphere blocks gamma rays – a problem overcome by GLAST. Is there, however, a benefit to this atmospheric effect?

    • After Viewing

  • Why does shorter-wavelength light have higher energy than longer-wavelength light?
  • What exactly is a black hole, and why would it give off gamma rays?
  • Besides black holes or exploding stars, what else might produce gamma rays? Why would gamma rays be created by only the most energetic cosmological events?
  • Bonus Question: If gamma rays have a billion times the energy of visible light, what do you think the ratio is between visible light and radio waves? How could you find out?
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open Teaching Tips

Classroom Activity: Energy Spectrum Ratios

Students work in small groups to calculate the energy ratios between selected spots on the EM spectrum. (The instructor selects several EM-energy pairs for each group, perhaps three or four.) Then, the student groups conduct some quick research to come up with other scenarios that match the scaling difference. An example might relating the ratio of two energy bands to the different heights of, say, an ant and Mt Everest.

Discussion Questions

  • Do you think energy changes along the spectrum are linear? Can you describe or prove why that would or would not be the case?
  • What exactly is changing as you move up and down the spectrum?
  • How are energy and wavelength related?
  • What about energy and frequency?
  • Is there something physically different or significant about crossing from one EM band to another? If so, what?
  • If you could “see” in another band beside visible light, which one would you pick – and why?
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open Transcript

Phil Plait: GLAST is designed to look at gamma rays. And gamma rays are the highest energy form of light.

Dave Thompson: There’s the light we see with our eyes but there are lots of other types of light. Gamma rays are the most energetic form of light, the most powerful.

Valerie Connaughton: Gamma rays are the part of what we call the electromagnetic spectrum which starts in radio at very long wavelengths, goes through optical, then through x-rays, and then gamma rays are the very highest energy form of that type of radiation.

Neil Gehrels: The reason it’s important to look at the high-energy gamma rays is that many objects, the most violent and some of the most interesting objects in the universe, emit most of their light in this high energy gamma ray part.

Phil Plait: and the only things that can generate gamma rays are incredibly violent events, incredibly energetic events. We’re talking stars exploding, and neutron stars with really strong magnetic fields, and really exotic and strange objects like that.

Isabelle Grenier: It’s like a Christmas tree, shining and it’s flaring, and there are eruptions every day.

Peter Michaelson: Gamma ray bursts being an example, something that for a brief instant of time outshines the entire rest of the universe.

Chip Meegan: These are the biggest explosions in the universe.

Neil Gehrels: We think that they’re the signals that happen when a black hole is born but we don’t know in detail how it works. And by looking with GLAST, we’ll be able to study the physics of what causes a gamma ray burst.

Martin Pohl: The thing is that most of the gamma rays we look at in terms of gamma ray astronomy, never reach people and the atmosphere essentially absorbs all of those gamma rays, which is the reason why GLAST has to fly on a satellite. None of the gamma rays we want to see actually make it to the ground.

Neil Gehrels: GLAST is going to open-up that part of the electromagnetic spectrum to better understand the universe.

Valerie Connaughton: It provides the widest energy coverage for gamma ray bursts that has ever been put into space.

Isabelle Grenier: It’s going to see the frontiers of many objects, high-energy objects.

Steve Ritz: And history shows that when you open-up a new band in the electromagnetic spectrum, you can expect some surprises, some great surprises.

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