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The Twin Quasars — a Cosmic Mirror of Einstein’s Vision

An original essay by Dhinakar Rajaram — image by Dr. Arun K. Shankar (used with permission)

Under truly dark skies and with patient accumulation of photons, an amateur observer may achieve work ordinarily reserved for professional observatories. The photograph below — realised from 1,136 sub-exposures of 20 seconds (totaling c. 6 hours 18 minutes) at a Bortle 3 site — shows the famed twin images of quasar Q0957+561: A and B. The light arrived here from a distance of c. 8.7 billion light-years, and began its voyage long ante the birth of our Solar System.

Image © Dr. Arun K. Shankar — Photon Hunter. Used with permission. Original Facebook post: view post.

Preface

Photons are archivists of cosmic history. When we collect them patiently, summing faint glows across hours, we assemble narratives of epochs long past. The double image of Q0957+561 is not merely an aesthetic curiosity: it is one of the earliest, most striking visual confirmations of Einstein’s General Theory of Relativity, for it manifests the bending of light by gravity — gravitational lensing.

Capturing such remote celestial light requires not merely precision optics but extraordinary patience. Each individual exposure gathers only a minute fraction of the photons arriving from the quasar — remnants of an epoch when the Universe was young. Because these photons are so few and faint, astronomers must accumulate hundreds or even thousands of exposures over several hours, later combining them digitally to enhance the signal while suppressing noise. This meticulous process, known as integration or stacking, enables the invisible to become visible, transforming random specks into coherent cosmic history.

What Is a Quasar?

The term quasar derives from “quasi-stellar radio source”, first used in the 1960s when astronomers found intense radio emissions emerging from points of light resembling stars. In truth, a quasar is the incandescent core of a remote galaxy, its brilliance powered by a supermassive black hole consuming gas and dust at extraordinary rates. The infalling material forms an accretion disc that heats to millions of degrees, radiating energy across the entire electromagnetic spectrum—from radio waves to X-rays.

By contrast, a neutron star is the dense remnant of a massive star’s core, only a few kilometres wide yet containing more mass than the Sun. When such a neutron star rotates rapidly and emits regular beams of radiation, it is termed a pulsar. A black hole, on the other hand, is a gravitational abyss from which nothing—not even light—can escape. Quasars differ in that the light we see comes not from within the black hole, but from matter in the final moments before crossing its event horizon, where gravitational energy is converted into luminous fury.

In essence, a quasar is both a monument to creation and a herald of destruction—gravity’s own paradoxical masterpiece, where annihilation becomes light.