Exploring the Invisible Universe - Chandra X-ray Telescope

The Chandra X-ray Observatory represents a scientific leap in ability over previous X-ray observatories like NASA’s Einstein, which orbited the Earth from 1978 to 1981. With its combination of large mirror area, accurate alignment and efficient X-ray detectors, the Chandra X-ray Observatory has eight times greater resolution and is 20-to-50 times more sensitive than any previous X-ray telescope.

Science Instruments

Within the instrument section of the observatory, two instruments at the narrow end of the telescope cylinder will collect X-rays and study them in various ways. Each of the instruments can serve as an imager or spectrometer.

A High-Resolution Camera will record X-ray images, giving scientists an unequaled look at violent, high-temperature occurrences like the death of stars or colliding galaxies. The High-Resolution Camera is composed of two clusters of 69 million tiny lead-oxide glass tubes. The tubes are only one-twentieth of an inch long and just one-eighth the thickness of a human hair. When X-rays strike the tubes, particles called electrons are released. As the electrons are accelerated down the tubes by high voltage, they cause an avalanche of about 30 million more electrons. A grid of electrically charged wires at the end of the tube detects this flood of particles and allows the position of the original X-ray to be precisely determined. The High-Resolution Camera also complements the Charge-Coupled Device Imaging Spectrometer, described below.

Chandra Science Center/NASA The Imaging Spectrometer shows the remnant of a supernova

The Chandra X-ray Observatory’s Imaging Spectrometer is also located at the narrow end of the observatory. This detector is capable of recording not only the position, but also the color (energy) of the X-rays. The imaging spectrometer is made up of 10 charge-coupled device arrays. These detectors are similar to those used in home video recorders and digital cameras but are designed to detect X-rays. Commands from the ground allow astronomers to select which of the various detectors to use. The imaging spectrometer can distinguish up to 50 different energies within the range the observatory operates. In order to gain even more energy information, two screen-like instruments, called diffraction gratings, can be inserted into the path of the X-rays between the telescope and the detectors. The gratings change the path of the X-ray depending on its color (energy) and the X-ray cameras record the color and position. One grating concentrates on the higher and medium energies and uses the imaging spectrometer as a detector – the other grating disperses low energies and is used in conjunction with the High Resolution Camera.

By studying these X-ray rainbows, or spectra, and recognizing signatures of known elements, scientists can determine the composition of the X-ray producing objects, and learn how the X-rays are produced.

Observatory Operations

The Smithsonian Astrophysical Observatory controls science and flight operations of the Chandra X-ray Observatory for NASA from Cambridge, Mass. The Smithsonian manages two electronically linked facilities – the Operations Control Center and the Science Center.