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Each of these same-scale images shows the Crab supernova remnant in a different wavelength. Each image will print on one overhead transparency. The purpose is to show the differences in the information conveyed by the image in each wavelength. The transparencies are designed to be superimposed as overlays. Each image is surrounded by small symbols (squares, triangles and circles) that when matched, will orient and align the images to superimpose accurately. These overlays allow superimposition of all four wave lengths simultaneously. Note that the on-line composite provides superimposition of images in selected pairs only. The overlays can be used as a classroom orientation with any of the activites listed below. Students can pursue individual investigations by using the on-line composite option.
These overlays can be used in conjunction with any of the investigations, tasks, or activities on this page which ask students to compare and contrast objects in different wavelengths. These include the Electromagnetic spectrum and CAS Timeline investigations, and the perfomance tasks "Signals from the Cosmos", "Point of View", "The universe Rated R!", "The Crab Through Time", and "Portrait Gallery of the X-Ray Universe".
The Crab Nebula is the remnant of a supernova explosion that was seen on Earth in 1054 AD. It is 6000 light years from Earth. At the center of the bright nebula is a rapidly spinning neutron star, or pulsar that emits pulses of radiation 30 times a second. These images show the Crab as viewed by four different types of telescopes. Comparing the X-ray, optical, infrared, and radio images of the Crab shows that the nebula appears most compact in X-rays and largest in the radio. The X-ray nebula shown in the Chandra image is about 40% as large as the optical nebula, which is in turn about 80% as large as the radio image. This can be understood by following the history of energetic electrons produced by the neutron star. Electrons with very high energies radiate mostly X-rays.
Chandra X-ray
Chandra's X-ray image of the Crab Nebula directly traces the most
energetic particles being produced by the pulsar. This amazing image
reveals an unprecedented level of detail about the highly energetic
particle winds and will allow scientists to probe deep into the dynamics
of this cosmic powerhouse.
Credit: NASA/CXC/SAO)
Optical
As time goes on, and the electrons move outward, they lose energy to
radiation. The diffuse optical light comes from intermediate energy
particles produced by the pulsar. The optical light from the filaments
is due to hot gas at temperatures of tens of thousands of degrees.
(Credit: Palomar Obs.)
Radio
Radio waves come from the lowest energy electrons. They can travel the
greatest distance and define the full extent of the nebula. The Crab's
central pulsar was discovered in 1968 by radio astronomers. The pulsar
was then identified as a source of periodic optical and X-ray radiation.
The periodic flashes of radiation are caused by a beam from the rapidly
rotating neutron star.
(Credit: NRAO/AUI/NSF)
Crab Nebula Composite | Crab Nebula Photo Album
Revised: April 16, 2008