Fermi Overview
The Fermi Mission
A considerable improvement over its successful predecessor – the Compton Gamma Ray Observatory – Fermi has the ability to detect gamma rays in a range of energies from thousands to hundreds of billions of times more energetic than the light visible to the human eye. Radiation of such a magnitude can only be generated under the most extreme conditions; therefore Fermi will focus on studying the most energetic objects and phenomena in the Universe.
Because of their tremendous energy, gamma rays travel through the Universe largely unobstructed. This means Fermi will be able to observe gamma-ray sources near the edge of the visible Universe. Gamma rays detected by Fermi will originate near the otherwise obscured central regions of exotic objects like supermassive black holes, pulsars, and gamma-ray bursts. Fermi will study mechanisms of particle acceleration in extreme astrophysical environments. Among topics of cosmological interest will be the information obtained about the periods of star and galaxy formation in the early Universe and on dark matter.
Studying these high-energy objects and events with the advanced technologies of Fermi could give us an entirely new understanding of our Universe, revealing unanticipated phenomena. Historically, such new knowledge has eventually given rise to altogether new technologies.
Fermi was launched on June 11, 2008. General Dynamics was responsible for the design and manufacture of the spacecraft, integration of the scientific instruments with the spacecraft, and integration of the complete observatory with the Delta 2920H-10 launch vehicle. Fermi resides in a low-earth circular orbit (550 km altitude), at a 28.5 degree inclination. The mission was designed for a lifetime of 5 years, with a goal of 10 years of operations.
What Are Gamma Rays?
What we call light is really just a tiny fraction of the broad range of the electromagnetic radiation spectrum. The entire span stretches from very low-energy radio waves through microwaves, infrared radiation, 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 emitted 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 thetype of light visible to our eyes.
In fact, gamma rays are so energetic that they are harmful to life on Earth. Luckily, the Earth's atmosphere absorbs gamma rays, preventing them from affecting life on the ground. However, if you want to observe the Universe in gamma-ray light, this poses a problem. The very atmosphere that protects us from gamma rays prevents us from 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 launched into space, above the protective blanket of the 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 in the world of particle physics, where techniques for measuring high-energy particles have long been understood. Fermi's specialized astronomical instruments will therefore employ detectors used and perfected by physicists interested in the interactions of subatomic particles.