A dense fog, through which only occasional headlight beams pierce. So it was in the early universe: young galaxies were wrapped in clouds of neutral hydrogen, which eagerly absorbed ultraviolet light. But sometimes gaps appeared in this shroud, and ionizing radiation burst out, making the cosmos transparent. Astronomers have long searched for such 'leaking' galaxies to understand how the cosmic fog lifted.
Using the James Webb Space Telescope, scientists examined two candidate galaxies at a distance of about 11.5 billion light-years. The first, LACES-94460, turned out to be a false alarm: its ultraviolet brightness was explained by a neighboring galaxy that happened to be in the frame. The second, LACES-104037, showed a genuine stream of ionizing radiation. It did not come from the galaxy's center but from a long tail formed by the collision of two galaxies. This tail, like a torn sleeve, exposed young stars born only about 5 million years ago — a blink of an eye in cosmic terms.
This discovery convincingly shows for the first time that galaxy mergers can be an important source of ionizing radiation in the early universe. Previously, it was thought that single galaxies with vigorous star formation played the main role. Now it is clear: when galaxies collide, their gas clouds mix and tear apart, opening a path for light. Such 'windows' in the fog may have helped disperse neutral hydrogen, making the universe transparent to the light of distant stars.
The age of the stars in the outflowing region of LACES-104037 is only about 5 million years. For comparison, our Sun is 4.6 billion years old. These stars are so young that, by cosmic standards, they have just been 'born'.
In Arthur C. Clarke's novel '2001: A Space Odyssey', the monolith orbiting Jupiter serves as a window through which the protagonist passes into another dimension. Here, galaxy mergers create literal windows in the gas shroud, through which light escapes into intergalactic space.