X-Ray Astronomy

When stars explode, or supernovae burst, or when supermassive black holes feast on galaxy clusters, they emit X-rays – high-energy light particles that are invisible to the human eye. Like the X-rays used by doctors to take pictures of broken bones inside a patient, these radiation beams provide astronomers with valuable information about some of the Universe’s most violent and energetic phenomena.

But observing X-rays isn’t easy, as the rays are too energetic to be captured by telescopes that use lenses or mirrors to focus visible light. Astronomers instead have to make use of X-ray telescopes that employ a grazing incidence design, where the mirrors skim over the source of X-rays, catching them at an angle, rather than perpendicular to their surface.

The X-rays that astronomers detect are classified by their energy, with lower-energy X-rays known as soft X-rays and higher-energy ones called hard X-rays. The amount of energy an X-ray has is measured in keV, where 1 keV equals one billion times the energy of a visible light photon.

X-rays also have very short wavelengths, meaning that X-ray telescopes must be large to cover an adequate area of the sky. This limits the number of X-ray sources astronomers can study, unless they’re very close to Earth. Astronomers use a technique called imaging to get around this constraint. By analyzing data from many overlapping observations, scientists can create a composite picture of an object’s X-ray emission.

Most X-ray observatories are built on satellites, which can carry far more sensitive instruments than the balloons and sounding rockets that were previously used to investigate the cosmic X-ray sky. This allowed for a huge leap in X-ray astronomy starting in the 1970s, with the launch of dedicated satellites such as Japan’s HAKUCHO and TENMA in 1979, India’s Vela 5B in 1983, and Europe’s XMM-Newton and Athena.

The resulting data allows scientists to investigate many new kinds of sources and phenomena. For example, the Chandra X-ray Observatory has helped them discover the bright X-ray emission from celestial bodies such as the debris falling out of an exploding star, and the superheated material swirling around a black hole. The observatory’s images have also revealed other ethereal scenes, such as the Pillars of Creation and the Milky Way’s supermassive black hole.

To get a better understanding of the origin and nature of these phenomena, astronomers must also conduct detailed simulations of their processes. Using the computer software AIPS (Astrophysics Image Processing System), which is designed by ISRO, scientists are able to reproduce in the laboratory what they’ve seen at the astronomical observatories and generate predictions of how these events might behave in different scenarios. The data from these simulations can then be compared to the observational data to help refine models and test theories. In this way, astronomers are able to develop more accurate and complete theories about these exciting and powerful events. This work is essential for understanding the underlying mechanisms that drive our Universe’s most dramatic and high-energy phenomena.