Portal:X-ray astronomy

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X-ray astronomy

X-rays start at ~0.008 nm and extend across the electromagnetic spectrum to ~8 nm, over which Earth's atmosphere is opaque.

X-ray astronomy is an observational branch of astronomy which deals with the study of X-ray observation and detection from astronomical objects. X-radiation is absorbed by the Earth's atmosphere, so instruments to detect X-rays must be taken to high altitude by balloons, sounding rockets, and satellites. X-ray astronomy is the space science related to a type of space telescope that can see farther than standard light-absorption telescopes, such as the Mauna Kea Observatories, via x-ray radiation.

X-ray emission is expected from astronomical objects that contain extremely hot gases at temperatures from about a million kelvin (K) to hundreds of millions of kelvin (MK). Although X-rays have been observed emanating from the Sun since the 1940s, the discovery in 1962 of the first cosmic X-ray source was a surprise. This source is called Scorpius X-1 (Sco X-1), the first X-ray source found in the constellation Scorpius. The X-ray emission of Scorpius X-1 is 10,000 times greater than its visual emission, whereas that of the Sun is about a million times less. In addition, the energy output in X-rays is 100,000 times greater than the total emission of the Sun in all wavelengths. Based on discoveries in this new field of X-ray astronomy, starting with Scorpius X-1, Riccardo Giacconi received the Nobel Prize in Physics in 2002. It is now known that such X-ray sources as Sco X-1 are compact stars, such as neutron stars or black holes. Material falling into a black hole may emit X-rays, but the black hole itself does not. The energy source for the X-ray emission is gravity. Infalling gas and dust is heated by the strong gravitational fields of these and other celestial objects.

Many thousands of X-ray sources are known. In addition, the space between galaxies in galaxy clusters is filled with a very hot, but very dilute gas at a temperature between 10 and 100 megakelvins (MK). The total amount of hot gas is five to ten times the total mass in the visible galaxies.

Selected article

A launch of the Black Brant 8 Microcalorimeter at the turn of the century as a part of the joint undertaking by the University of Wisconsin-Madison and NASA's Goddard Space Flight Center known as the X-ray Quantum Calorimeter (XQC) project.

X-ray astronomy by sounding rocket uses a sounding rocket to carry an X-ray detector to high altitudes. The first evidence of X-rays from the Sun and of an X-radiation source from the Milky Way, other than the Sun, was detected by a sounding rocket. These rockets have contributed significantly to our understanding of the Sun, the solar system, and the universe as a whole.

In astronomy, the interstellar medium (or ISM) is the gas and dust that pervade interstellar space: the matter that exists between the star systems within a galaxy. It fills interstellar space and blends smoothly into the surrounding intergalactic space. The interstellar medium consists of an extremely dilute (by terrestrial standards) mixture of ions, atoms, molecules, larger dust grains, cosmic rays, and (galactic) magnetic fields. The energy that occupies the same volume, in the form of electromagnetic radiation, is the interstellar radiation field.

Of interest is the hot ionized medium (HIM) consisting of coronal gas at 106-107 K which emits X-rays. The ISM is turbulent and therefore full of structure on all spatial scales. Stars are born deep inside large complexes of molecular clouds, typically a few parsecs in size. During their lives and deaths, stars interact physically with the ISM. Stellar winds from young clusters of stars (often with giant or supergiant HII regions surrounding them) and shock waves created by supernovae inject enormous amounts of energy into their surroundings, which leads to hypersonic turbulence. The resultant structures – of varying sizes – can be observed, such as stellar wind bubbles and superbubbles of hot gas, seen by X-ray satellite telescopes. The Sun is currently traveling through the Local Interstellar Cloud, a denser region in the low-density Local Bubble.

Selected biography


Riccardo Giacconi received a degree from the University of Milan before moving to the US to pursue a career in astrophysics research.

Giacconi worked on the instrumentation for X-ray astronomy, from rocket-borne detectors in the late 1950s and early 1960s, through to Uhuru, the first orbiting X-ray astronomy satellite, the Einstein Observatory, the first fully imaging X-ray telescope put into space, and the Chandra X-ray Observatory which was launched in 1999 and is still in operation. Giacconi was awarded the Nobel Prize in Physics in 2002 "for pioneering contributions to astrophysics, which have led to the discovery of cosmic X-ray sources".

In the news

The GOES 14 spacecraft carries a Solar X-ray Imager to monitor the Sun's X-rays for the early detection of solar flares, coronal mass ejections (CME), and other phenomena that impact the geospace environment.

GOES 14 was launched into orbit on June 27, 2009 at 22:51 GMT from Space Launch Complex 37B at the Cape Canaveral Air Force Station. GOES 14 is the most recent satellite to be launched with X-ray detection capability. The importance of X-ray astronomy is exemplified in the use of an X-ray imager such as the one on GOES 14 for the early detection of solar flares, CMEs and other X-ray generating phenomena that impact the Earth.

Selected picture


NRL scientists J. D. Purcell, C. Y. Johnson, and Dr. F. S. Johnson among those recovering instruments from a V-2 used for upper atmospheric research above the New Mexico desert. This is V-2 number 54, launched January 18, 1951 (photo by Dr. Richard Tousey, NRL).

Did you know?

...that the first extrasolar X-ray source may have been the diffuse X-ray background. The first Aerobee 150 sounding rocket flight that apparently discovered Scorpius X-1 may have occurred on June 12th or 19th, 1962, and may not have been able to resolve Scorpius X-1 from the Galactic Center as the X-ray detector on board was designed to detect X-rays from the Moon.

...that as the constellation Serpens is actually divided into Serpens Cauda and Serpens Caput, Serpens X-1 is in Serpens Cauda and Serpens Caput was perhaps ignored.

...that Cepheus X-1 is actually in the constellation Cassiopeia.

...that some X-ray sources although initially detected as the first X-ray source in a respective constellation may not have received the designation X-1 as they are diffuse sources, contain several X-ray sources within the celestial object, or occupy area in two constellations. The Large Magellanic Cloud (LMC) is in Dorado and Mensa and contains many X-ray sources. Although established as the first X-ray source in Dorado, the LMC was never designated as Dorado X-1. It was first detected on October 29, 1968.

...that an occasional source such as Triangulum Australe X-1 was designated as the X-1 yet another source in the same constellation had been detected earlier and confirmed prior to its detection. The same may have happened to Orion X-1.

...that Carina X-1 (Car X-1) may have been a misprint for Cir X-1.



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