One hour of light: How a single event may reveal secrets of the early universe

Astronomers have identified a space object that may be a primordial black hole dating back to the early universe. The discovery was made using gravitational microlensing, a phenomenon where a massive object briefly amplifies the light of a distant star. While the data suggests the object's nature, its status as a primordial black hole remains an unconfirmed hypothesis. The event was recorded on December 18, 2019, during observations of a star in the Large Magellanic Cloud, a satellite galaxy of the Milky Way. The object, named Phoebe, caused a symmetrical increase and subsequent decrease in the star's brightness over approximately one hour before the luminosity returned to normal levels. Researchers from Swinburne University in Melbourne applied the method of gravitational microlensing, based on Einstein's general theory of relativity. In this process, the gravity of a massive compact object acts as a lens, focusing and magnifying the light from a background star. The specific pattern of brightness change observed in this case allowed the team to rule out flares, asteroids, or variable stars.