How Would You Define an X-ray Source? A source of X-rays is something that emits X-rays. In space, astronomers search for X-ray sources. Radiation emitted by objects in space can take many different forms. Astronomers have studied one type of radiation, light, for thousands of years. They have studied radio waves, which have longer wavelengths, much more recently. It’s radio astronomy here. These days, they also examine radiation with shorter wavelengths, such X-rays.
Satellites carrying X-ray telescopes circle the planet. X-rays are produced by very hot gases. Supernovae, or exploding stars, and pulsars are examples of X-ray sources. Cygnus X-1, one X-ray source, may contain a black hole. Any of a group of cosmic objects that generate radiation at the X-ray wavelength is referred to as a “X-ray source” in astronomy. In order to observe objects that emit such electromagnetic radiation, X-ray telescopes and detectors must be lifted well above the Earth’s atmosphere due to the planet’s extremely efficient X-ray absorption.
An increasing number of X-ray sources have been found thanks to improvements in instrumentation and observational methods. Thousands of these items had been found around the universe by the late 20th century.
In 1949, X-ray emissions from the Sun’s corona (outer atmosphere) were measured by rocket-borne radiation detectors, making it the first astronomical object known to emit X rays. However, the Sun is a poor X-ray generator by nature and is only noticeable because it is so close to the Earth. Thirty years later, the orbiting HEAO 2 satellite, also known as the Einstein Observatory, successfully detected X rays from other, farther-off ordinary stars. By using the X-radiation from their coronas, it was able to identify more than 150 common stars. Main sequence stars, red giant stars, and white dwarf stars are all represented by the stars that have been observed.
Only a tiny portion of the energy emitted by most stars is manifested as X-rays. The strongest X-ray emitters are the young, big stars. Their heated coronal gases can expand to form nebulas themselves observable X-ray sources. They typically occur in nebulas.
A supernova remnant, the gaseous shell expelled following the explosive explosion of a dying star, is a more potent type of X-ray source. The Crab Nebula, a byproduct of a supernova explosion whose radiation reached Earth in AD 1054, was the first to be seen. However, because its X rays are synchrotron radiation created by high-speed electrons from a core pulsar, it is a very unusual remnant.
Most other supernova remnants instead emit X-radiation from heated gas. Although the gases released by a supernova explosion are relatively cool, interstellar gas is accumulated as they sweep outward at a speed of several thousand kilometres per second. This gas is heated by the powerful shock wave to a temperature of around 10,000,000 K, which is sufficient for X-ray emission.
Some binary stars are the most potent X-ray emitters in the Milky Way Galaxy. The X-ray emission of these so-called X-ray binaries is 1,000 times more than the Sun’s output overall. Most of the sources found in the early years of X-ray astronomy, notably Scorpius X-1, are X-ray binaries. A typical X-ray binary source is a pair of closely spaced stars, one of which is a very small object.
This object could be a neutron star, which has the mass of two Suns compressed into a sphere barely 20 km (12 mi) across, or it could be an even more compact black hole, a collapsed star whose gravity is so powerful that not even light can escape from it. In order to create an accretion disc, the compact star spins around as gas from the partner star falls towards it. The orbital energy of the gas is converted into heat by viscous processes within the disc, and when sufficiently high temperatures are reached, significant volumes of X-rays are released.
X-ray binaries come in a variety of varieties. A neutron star’s poles receive gas from an X-ray pulsar, which emits radiation in the form of pulses with extremely regular periods. In so-called burster objects, a neutron star’s magnetic field holds the gas in place until the weight of the accumulating gas momentarily crushes the field, causing the falling gas to suddenly release a burst of X rays. In stellar pairings with elongated orbits and sporadic gas transfer (i.e., when the component stars are nearest to one another), a transient happens. The compact object in an X-ray binary is often categorised as a neutron star unless its estimated mass is greater than three solar masses. They classify the item in these situations as a black hole. Cygnus X-1 (nine solar masses) and LMC X-3 (seven solar masses) are two very potent black hole possibilities.
The emission from the X-ray binaries’ constituent galaxies, like the Andromeda Galaxy, allows for the detection of nearby galaxies. When compared to active galaxies, which include quasars, radio galaxies, and Seyfert galaxies, they are comparatively faint sources. All of these galaxy kinds exhibit violent activity at their centres, which is typically attributed to an accretion disc of hot gases surrounding a central black hole with a mass of approximately 1,000,000,000 Suns. These galaxies exhibit a wide range in X-ray energy. For instance, the X-ray output of the quasar OX 169 has been found to change significantly in less than two hours, suggesting that the region generating this radiation is smaller than two “light-hours” across (i.e., smaller than the solar system).
Galaxy clusters are other strong extragalactic X-ray sources. The heated gas held within the cluster by the gravitational pull of the cluster’s constituent galaxies, not the galaxies themselves, is what generates the cluster’s X rays. The gas may have started as hot gas ejected by several supernovas and is typically 100,000,000 K in temperature.
Finally, there is an all-pervasive diffuse background of X-radiation coming from large distances. Despite being discovered in 1962, it wasn’t until 2000 that its nature was finally determined. The majority of the background is made up of X rays from a variety of active galaxies.
Content for this question contributed by Joey Tellas, resident of Greensburg, Decatur County, Indiana, USA
