CXC: Deepest X-ray Image Ever Reveals Black Hole Treasure Trove

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bystander
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CXC: Deepest X-ray Image Ever Reveals Black Hole Treasure Trove

Post by bystander » Thu Jan 05, 2017 7:39 pm

CDF-S: Deepest X-ray Image Ever Reveals Black Hole Treasure Trove
NASA | MSFC | SAO | Chandra X-ray Observatory | 2017 Jan 05
This is the deepest X-ray image ever obtained, made with over 7 million seconds of observing time with NASA's Chandra X-ray Observatory. These data give astronomers the best look yet at the growth of black holes over billions of years beginning soon after the Big Bang, as described in our latest press release.

The image is from the Chandra Deep Field-South, or CDF-S. The full CDF-S field covers an approximately circular region on the sky with an area about two-thirds that of the full Moon. However, the outer regions of the image, where the sensitivity to X-ray emission is lower, are not shown here. The colors in this image represent different levels of X-ray energy detected by Chandra. Here the lowest-energy X-rays are red, the medium band is green, and the highest-energy X-rays observed by Chandra are blue.

The central region of this image contains the highest concentration of supermassive black holes ever seen, equivalent to about 5,000 objects that would fit into the area of the full Moon and about a billion over the entire sky.

Researchers used the CDF-S data in combination with data from the Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey (CANDELS) and the Great Observatories Origins Deep Survey (GOODS), both including data from NASA's Hubble Space Telescope to study galaxies and black holes between one and two billion years after the Big Bang. ...

The deepest X-ray view of high-redshift galaxies: Constraints on low-rate black-hole accretion - Fabio Vito et al The Chandra Deep Field-South Survey: 7 Ms Source Catalogs - B. Luo et al
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Re: CXC: Deepest X-ray Image Ever Reveals Black Hole Treasure Trove

Post by neufer » Fri Jan 06, 2017 4:37 pm

https://en.wikipedia.org/wiki/Shoe-fitting_fluoroscope wrote: <<Shoe-fitting fluoroscopes, also sold under the names X-ray Shoe Fitter, Pedoscope and Foot-o-scope, were X-ray fluoroscope machines installed in shoe stores from the 1920s until about the 1970s. An estimated 10,000 machines were sold in the US, 3,000 in the UK, 1,500 in Switzerland, and 1,000 in Canada before authorities began discouraging their use.

A shoe-fitting fluoroscope was a metal construction covered in finished wood with a ledge with an opening where the child would then place his or her feet in the opening provided and while remaining in a standing position, look through a viewing porthole at the top of the fluoroscope down at the x-ray view of the feet and shoes. Two other viewing portholes on either side enabled the parent and a sales assistant to observe the child's toes being wiggled to show how much room for the toes there was inside the shoe. The bones of the feet were clearly visible, as was the outline of the shoe, including the stitching around the edges.

The gimmick changed from decade to decade to suit the market at the time, but the most famous sales pitches were that the fluoroscope allowed salesmen to better fit shoes and that it made it more fun for kids to go to the shoe store. During the Great Depression, a popular sales pitch was that the fluoroscope allowed the best possible fit, which made for longer-lasting shoes and implied that customers would not have to buy as many pairs for themselves or for their children. In reality, the shoe-fitting fluoroscope was nothing more than a way to attract potential customers because the fit also depends on the flesh size, which was difficult to make out in the fluoroscope.

The risk of radiation burns to extremities were known since Wilhelm Röntgen's 1895 experiment, but this was a short-term effect with early warning from erythema. The long-term risks from chronic exposure to radiation began to emerge with Hermann Joseph Muller's 1927 paper showing genetic effects, and the incidence of bone cancer in radium dial painters of the same time period. However, there was not enough data to quantify the level of risk until atomic bomb survivors began to experience the long-term effects of radiation in the late 1940s. The first scientific evaluations of these machines in 1948 immediately sparked concern for radiation protection and electrical safety reasons, and found them ineffective at shoe fitting.

Radiation surveys showed that American machines delivered an average of 13 roentgen (r) (roughly 0.13 sievert (Sv) in modern units) to the customer's feet during a typical 20 second viewing, with one capable of delivering 116 r (~1 Sv) in 20 seconds. British Pedoscopes were about ten times less powerful. Although most of the dose was directed at the feet, a substantial amount would scatter or leak in all directions. Shielding materials were sometimes displaced to improve image quality, to make the machine lighter, or out of carelessness, and this aggravated the leakage. Three shoe salespersons have been identified with rare conditions that might be associated with their chronic occupational exposure: a severe radiation burn requiring amputation in 1950, a case of dermatitis with ulceration in 1957, and a case of basal-cell carcinoma of the sole in 2004.>>
Art Neuendorffer

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