The Universe is home to numerous exotic and beautiful phenomena, some of which can generate almost inconceivable amounts of energy. Supermassive black holes, merging neutron stars, streams of hot gas moving close to the speed of light … these are but a few of the marvels that generate gamma-ray radiation, the most energetic form of radiation, billions of times more energetic than the type of light visible to our eyes. What is happening to produce this much energy? What happens to the surrounding environment near these phenomena? How will studying these energetic objects add to our understanding of the very nature of the Universe and how it behaves?
The Fermi Gamma-ray Space Telescope, formerly GLAST, is opening this high-energy world to exploration and helping us answer these questions. With Fermi, astronomers at long last have a superior tool to study how black holes, notorious for pulling matter in, can accelerate jets of gas outward at fantastic speeds. Physicists are able to study subatomic particles at energies far greater than those seen in ground-based particle accelerators. And cosmologists are gaining valuable information about the birth and early evolution of the Universe.
Here is a list of features that explain the different things Fermi will explore.
Blazars and active galaxies
Cosmic rays and supernova remnants
The Milky Way galaxy
Gamma-ray background radiation
The early universe
Our solar system
Electromagnetic Spectrum Basics
The electromagnetic spectrum is the basis for the observations Fermi undertakes.
Image above: Measuring wavelengths.
To be able to understand how Fermi works, you need to understand the electromagnetic spectrum.
What we call “light” is actually just a tiny fraction of the broad range of radiation on the electromagnetic radiation spectrum. The entire span stretches from very-low-energy radio waves through microwaves, infrared light, visible light, ultraviolet light, X rays, and finally to very-high-energy gamma rays. The processes producing photons (single particles of electromagnetic radiation) of each type of radiation differ, as do their energy, but all of the different forms of radiation are still just part of the electromagnetic spectrum’s family. The only real difference between a gamma-ray photon and a visible-light photon is the energy. Gamma rays can have over a billion times the energy of the type of light visible to our eyes.
In fact, gamma rays are so energetic that they are harmful to life on Earth. Luckily, Earth’s atmosphere absorbs gamma rays, preventing them from affecting life on the ground. But this poses a problem if you want to observe the Universe in gamma-ray light. The very atmosphere that protects us from gamma rays prevents us from directly observing them from the ground. Astronomical observations of gamma-ray sources in the Fermi energy range are therefore done with high-altitude balloons or satellites, above the protective blanket of Earth’s atmosphere.
The high energy of gamma rays poses another problem: they can pass right through any lens or mirror, making it very difficult to focus them in a telescope. Astronomical observations, therefore, must rely on a different technology to view the gamma-ray universe. Scientists must make use of methods developed by particle physicists, who have long understood techniques for measuring high-energy particles. Fermi’s specialized astronomical instruments will therefore employ detectors used and perfected by physicists interested in the interactions of subatomic particles.