Astronomy, Astrophysics & Astrobiology

X-rays are a form of light, but much more energetic than the light detected by our eyes. The energy of an X-ray photon (light particle) is ~1000 times that of a photon of visible light. They are part of the electromagnetic spectrum which includes visible light, radio waves, microwaves and infrared radiation. X-rays are so energetic that they pass straight through many materials, which is why they are used in hospitals to image bones to check for breaks and fractures. They are absorbed better by materials which are dense, and so, when used in hospitals, they are stopped more by the bone and any metal (e.g. dental fillings) then the fleshy parts of the body. The X-rays cause the film to be exposed, and so if they are blocked, the film remains dark, hence producing a shadow of the denser parts of the body.

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,. Scientists hypothesized that X-rays from stellar sources in our galaxy were primarily from a so-called "X-ray binaries." The X-ray binaries consist of a neutron star in a binary system with a normal star. The X-rays in these systems originate from material traveling from the normal star to the neutron star in a process called acceleration. The binary nature of the system allowed astronomers to measure the mass of the neutron star. For other systems, the inferred mass of the X-ray emitting object supported the idea of the existence of black holes, because they were too massive to be neutron stars. Other systems displayed a characteristic X-ray pulse, just as pulsars had been found to do in the radio regime, which allowed a determination of the spin rate of the neutron star. Finally, some of these galactic X-ray sources were found to be highly variable. In fact, some sources would appear in the sky, remain bright for a few weeks, and then fade again from view. Such sources are called X-ray transients.