Last October, as the James Webb Space Telescope beamed down its first long exposures of the sky near the constellation Eridanus, astronomers began to piece together the story of a dim, flickering point of light that seemed to emerge from the deepest recesses of the universe.
Whatever it was, it glimmered for too long to be a supernova; a single star, too, was off the table. “It feels like you’re probably in one of these CSI movies, that you’re a detective,” said José María Diego, an astrophysicist at the Institute of Physics of Cantabria in Spain who worked to decipher the signal. “You have a lot of suspects on the table, and you have to eliminate [them] one by one.”
Diego and his colleagues recently reported that the faint smudge of light appears to come from an extreme star system they nicknamed Mothra — a pair of supergiant stars that, in their heyday, a full 10 billion years ago, outshone nearly everything else in their galaxy.
At that time, the entire universe was younger than the Earth is now; our planet only started to coalesce after the Mothra photons had reached the halfway mark in their cosmic journey to a world that would develop a giant infrared-sensitive space telescope just in time to catch their light. Detecting light emitted by individual star systems that long ago used to be impossible. But Mothra, named after a kaiju monster inspired by silk moths, is just the latest in a recent string of oldest-ever, farthest-ever, just generally superlative star systems astronomers have found in images from JWST and the Hubble Space Telescope. And in a twist, while Mothra and its beastly brethren are intriguing astrophysical objects in their own right, what excites Diego the most is that the monster stars’ light seems to reveal a very different class of object floating between it and Earth: an otherwise invisible clod of dark matter that he and his colleagues calculated weighs between 10,000 and 2.5 million times the mass of the sun.
If such an object really exists — a preliminary conclusion for now — it could help physicists narrow down their theories about dark matter and maybe, just maybe, solve the mystery of the universe’s unexplained mass.
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