Revelation of the Hidden Cosmos with Full-shell X-ray Optics is a reality

The study of X-ray emission from astral objects reveals secrets about the Cosmos at the smallest and largest spatial scales. Celestial X-rays are produced by black holes consuming proximate stars, emitted by the million-degree gas that fills the space between galaxies, and can be used to predict whether a star is capable of hosting planets hospitable to life. X-ray observations have shown that most of the visible matter in the cosmos exists as hot gas between galaxies and have conclusively established that the presence of “dark matter” is required to explain galaxy cluster dynamics, that dark matter dominates the mass of galaxy clusters, and that expansion of the cosmos is governed by it.

X-ray observations also empower us to probe mysteries of the Cosmos on the smallest scales. X-ray observations of compact objects such as neutron stars, white dwarfs, and black holes let us to use the Cosmos as a physics laboratory to study conditions that are orders of magnitude more immense in terms of density, temperature, pressure, and magnetic field strength than anything that can be produced on Earth. In this astrophysical laboratory, scientists expect to bare new physics at the subatomic scale by carrying out investigations such as examine the neutron star equation of state and testing quantum electrodynamics with observations of neutron star atmospheres. At NASA’s Marshall Space Flight Center, a team of engineers and scientists is building, testing, and flying ground-breaking optics that bring the Cosmos’s X-ray mysteries into sharper focus.

Contrasting optical telescopes that create images by refracting or reflecting light at near-90-degree angles (normal incidence), focusing X-ray optics must be designed to reflect light at extremely small angles (grazing incidence). At normal incidence, X-rays are either absorbed by the surface of a mirror or penetrate it completely. But, at grazing angles of incidence, X-rays reflect very proficiently due to an effect termed total external reflection.  In grazing incidence, X-rays reflect off the surface of a mirror akin to rocks skipping on the surface of a pond.

A typical design for astronomical grazing incidence optics is the Wolter-I prescription, which comprises of two reflecting surfaces, a parabola and hyperbola. This optical prescription is revolved around the optical axis to create a full-shell mirror (i.e., the mirror spans the full circumference) that looks like a gently tapered cone. To increase the light collection area, multiple mirror shells with incrementally bigger diameters and a common focus are fabricated and nested concentrically to comprise a mirror module assembly (MMA).

Focusing optics are crucial to studying the X-ray cosmos because, contrary to other optical systems like collimators or coded masks, they produce high signal-to-noise images with low background noise. Two important metrics that characterize the performance of X-ray optics are angular resolution (which is the capability of an optical system to discriminate between closely spaced objects) and effective area (which is the light collecting area of the telescope, typically quoted in units of cm²).