How do astronomers see X-rays?

Credit: NASA, ESA, CXC, and JPL-Caltech

Energetic X-rays pass right through lenses and mirrors. To focus them, X-ray telescopes have specially positioned mirrors. Since X-rays from space are absorbed by the atmosphere, they can only be observed from high altitude, above the Earth’s atmosphere.

Luckily for us, the Earth’s atmosphere contains enough matter to absorb harmful X-rays from outer space. As a consequence, X-ray astronomy can only be performed in space. At present, the field is dominated by two large observatories: NASA’s Chandra X-ray Observatory and ESA’s XMM-Newton. To focus the X-ray photons, these telescopes have gold-coated mirrors, positioned so that the photons hit them at a very shallow angle. The same technique is applied by the eROSITA X-ray instrument on board the Russian Spectrum- Roentgen-Gamma satellite.

It’s very difficult to study X-rays coming from space. They are blocked by the Earth’s atmosphere. To see them, you need space telescopes and special equipment.