Early Wednesday (Nov. 4), NASA's Neil Gehrels Swift Observatory fell out of space, burning up in the sky over Sumatra. It was a fitting, fiery end for a telescope that spent 22 years studying the most powerful explosions in the universe — and, even with Swift gone, its observations will continue to feed scientific curiosity for years to come.
Swift's most important contributions to astronomy are not exactly eye candy. Designed to swivel toward deep-space explosions at a moment's notice, Swift excelled at capturing bright, fleeting and faraway specks of light. The multiwavelength observatory was equipped with optical, ultraviolet (UV) and X-ray instruments, allowing it to catch cosmic bursts of energy across the electromagnetic spectrum, zeroing in on flares of light that other telescopes might miss.
One of its most significant detections was a gamma-ray burst — an incredibly bright blast, likely emitted by a giant star as it exploded in a supernova before collapsing into a black hole. Swift's famous image of GRB 221009A, or the BOAT — short for "brightest of all time" — looks like a speckled orange bull's-eye, caused by waves from the explosion rippling across space.
But Swift also took millions of observations of the nearby universe, including galaxies in our backyard. One of its most jaw-dropping images is this 24-hour exposure of the Andromeda galaxy (M31), located about 2.5 million light-years from Earth.
Andromeda is the closest major galaxy to ours, and it may be destined for a shared fate. Scientists suspect that Andromeda and the Milky Way are drawing closer together and might eventually collide. The merger would add Andromeda's roughly 1 trillion stars to our sky, though there probably wouldn't be any life left on Earth to appreciate it.
In Swift's view of our encroaching neighbor, captured with the observatory's ultraviolet instrument, tens of thousands of Andromeda's stars shine like sapphires set in a sparkling ring.
According to NASA, the observatory detected some 20,000 ultraviolet light sources in this image, captured over two months from May to July 2008. These sources include thousands of dense, hot star clusters scattered across Andromeda's 150,000-light-year-wide ring, as well as the distant galaxy M32 (seen as a bright orb of light to the bottom right of Andromeda's center).
In visible-light images of Andromeda taken with ground-based telescopes, the galaxy's bright center bleaches out many of the fiery young stars that emerge in Swift's view. While Swift likely won't be remembered best for shimmering starscapes like this one, it's a powerful reminder that looking at familiar structures in a new light can change everything.
