- 2830 - CHANDRA - X-ray telescope. From the launch of the Aerobee rocket in 1962, astronomers had known that the X-ray sky wasn’t dark, instead it is teeming with high-energy photons. Chandra telescope sharpened the view, resolving almost all of the background into its individual sources. Data from Chandra and XMM-Newton suggest that most of the sources that remain undetected are shrouded in gas and dust.
--------------------------- 2830 - CHANDRA - X-ray telescope discoveries?
- Infrared to X-ray astronomy gave us new eyes to view the Universe. Various types of celestial objects. Starting with the planets of the solar system, stars, nebulae, and galaxies give off energy at wavelengths in the “infrared region” of the electromagnetic spectrum, from about one micrometer to one millimeter.
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- The techniques of infrared astronomy enable investigators to examine many such objects that cannot otherwise be seen from the Earth because the light of optical wavelengths that they emit is blocked by intervening dust particles.
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- As amazing as this sounds Infrared Astronomy originated in the early 1800s with the work of the British astronomer Sir William Herschel, who discovered the existence of infrared radiation while studying sunlight.
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- Modern infrared techniques, such as the use of cryogenic detector systems to eliminate obstruction by infrared radiation released by the detection equipment and special interference filters for ground-based telescopes, were introduced during the early 1960’s.
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- By the 1970’s astronomers had surveyed the sky at the relatively short infrared wavelength of 2.2 micrometers and identified approximately 20,000 sources in the northern hemispheric sky alone. Since that time, balloons, rockets, and spacecraft have been employed to make observations of infrared wavelengths from 35 to 350 micrometers.
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- Radiation at these wavelengths is absorbed by water vapor in the atmosphere, and so telescopes and spectrographs have to be carried to high altitudes above most of the absorbing molecules. Specially instrumented high-flying aircraft such as the Kuiper Airborne Observatory and the Stratospheric Observatory for Infrared Astronomy have been designed to facilitate infrared observations near microwave frequencies.
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- In January 1983 the United States, in collaboration with the United Kingdom and the Netherlands, launched the Infrared Astronomical Satellite (IRAS), an unmanned orbiting observatory equipped with a 57-centimeter (22-inch) infrared telescope sensitive to wavelengths of 8 to 100 micrometers in the infrared spectrum.
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- At these wavelengths, IRAS made a number of unexpected discoveries in a brief period of service that ended in November 1983. The most significant of these were clouds of solid debris around Vega, Fomalhaut, and several other stars, the presence of which strongly suggests the formation of planetary systems similar to that of the Sun.
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- IRAS was succeeded in 1995–98 by the European Space Agency’s Infrared Space Observatory, which had a 60-centimeter (24-inch) telescope with a camera sensitive to wavelengths in the range of 2.5–17 micrometers and a photometer and a pair of spectrometers that, between them, extended the range to 200 micrometers.
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- IRAS made significant observations of protoplanetary disks of dust and gas around young stars, with results suggesting that individual planets can form over periods as brief as 20 million years. It determined that these disks are rich in silicates, the minerals that form the basis of many common types of rock. It also discovered a large number of brown dwarfs, objects in interstellar space that are too small to become stars but too massive to be considered planets.
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- The most advanced infrared space observatory is a U.S. satellite, the Spitzer Space Telescope, which is built around an all-beryllium 85-centimeter (33-inch) primary mirror that focuses infrared light on three instruments, a general-purpose infrared camera, a spectrograph sensitive to mid-infrared wavelengths, and an imaging photometer taking measurements in three far-infrared bands.
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- Together the instruments cover a wavelength range of 3.6 to 180 micrometers. The most striking results from the Spitzer’s observations concern extrasolar planets. The Spitzer has determined the temperature and the atmospheric structure, composition, and dynamics of several extrasolar planets
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- Photography was an essential tool from the late 19th century until the 1980s, when it was supplanted by charge-coupled devices (CCD). A photograph of a particular celestial object may include the images of many other objects that were not of interest when the picture was taken but that become the focus of study years later.
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- Photographic film converted only a few percent of the incident photons into images, whereas CCD have efficiencies of nearly 100 percent. CCD can be used for a wide range of wavelengths, from the X-ray into the near-infrared.
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- Gamma rays are detectable through their Compton scattering, electron-positron pair production, or “Cerenkov radiation“. For infrared wavelengths longer than a few microns, semiconductor detectors that operate at very low (cryogenic) temperatures are used. Reception of radio waves is based on the production of a small voltage in an antenna rather than on photon counting.
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- Spectroscopy involves measuring the intensity of the radiation as a function of wavelength or frequency. In some detectors, such as those for X-rays and gamma rays, the energy of each photon can be measured directly.
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- To astronomers’ surprise, Chandra’s X-ray image of Cassiopeia A, the bloom of gas left over after a massive star went supernova some 340 years ago, revealed a star turned inside out. While massive stars fuse the heaviest elements in their cores and lighter elements in surrounding, onion-like layers, the Cas A explosion had flung clumps of iron to the outermost regions. The find suggests the star’s contents mixed together right before or after its core collapsed, or both.
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- With Chandra and XMM-Newton, astronomers could for the first time estimate black hole spin. By measuring how a black hole’s strong gravity smears the emissions from iron ions, astronomers can see how close the gas comes to the event horizon, the closer it comes, the faster the black hole is spinning. Astronomers have used this and other X-ray-based methods to gauge the spins of dozens of black holes.
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- Monitoring by Chandra and XMM-Newton has also shed light on the slumbering beast at the center of the Milky Way known as Sgr A*. While Sgr A* doesn’t seem to be devouring gas in the manner of the supermassive black holes that power distant quasars, it’s doing something that sets off roughly daily X-ray flares. Sometimes they’re accompanied by infrared sizzles, but other times the X-rays pop on their own. The flares may originate in snapping magnetic fields, the occasional ingestion of an asteroid, or something else entirely.
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- The combination of X-ray and radio observations of galaxy clusters solved a long-term mystery: The hot gas between galaxies in clusters ought to cool over time, raining down on the clusters’ central galaxies and forming stars by the handful. But in many clusters astronomers haven’t found the expected stellar newborns.
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- It turns out radio-emitting jets from the central galaxies’ supermassive black holes blow bubbles into the surrounding X-ray-emitting gas, sending out pressure waves that pump heat back into the surrounding medium, which prevents it from cooling. Astronomers soon realized that this concept of “black hole feedback” might affect everything from galaxy evolution to cosmology.
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- Galaxy clusters have proven key to testing dark matter and understanding dark energy. X-ray observations first revealed the wildly hot gas within clusters gas that would have drifted away if it weren’t for the cluster’s dark matter, which gravitationally holds it in place.
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- September 14, 2020 2830
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