Free Astronomy Magazine January-February 2023

26 JANUARY-FEBRUARY 2023 ASTRO PUBLISHING The astronomical community cap- tured one of these remarkable kilo- nova events in 2017. Scientists at the National Science Foundation’s Laser Interferometer Gravitational-Wave Observatory (LIGO) detected the col- lision of two neutron stars first with gravitational waves – ripples in space-time. Almost simultaneously, NASA’s Fermi Gamma-ray Space Tel- escope detected high-energy light. NASA quickly pivoted to observe the event with a broader fleet of tele- scopes, and captured the fading glow of the blast’s expanding debris in a series of images. But the players in this example col- lided practically in our “backyard,” at least in astronomical terms. They lie only 130 million light-years away. There must be more kilonovae – and many that are farther flung – dot- ting our ever-active universe. “We don’t yet know the rate of these events,” said Daniel M. Scolnic, an assistant professor of physics at Duke University in Durham, North Carolina. Scolnic led a study that es- timates the number of kilonovae that could be discovered by past, present, and future observatories in- cluding Roman. “Is the single kilo- by NASA/ESA Claire Blome & Christine Pulliam Kilonovae, a target for the Roman Space Telescope W hat happens when the densest, most massive stars – that are also super small – collide? They send out bril- liant explosions known as kilonovae. Think of these events as the uni- verse’s natural fireworks. Theorists suspect they periodically occur all across the cosmos – both near and far. Scientists will soon have an ad- ditional observatory to help follow up on and even scout these remark- able events: NASA’s Nancy Grace Roman Space Telescope, which is set to launch by May 2027. The key actors in kilonovae are neu- tron stars, the central cores of stars that collapsed under gravity during supernova explosions. They each have a mass similar to the Sun, but are only about 6 miles (10 kilome- ters) in diameter. And when they collide, they send out debris moving near the speed of light. These explo- sions are also thought to forge heavy elements, like gold, platinum, and strontium (which gives actual fireworks their stunning reds). Kilo- novae shoot those elements across space, potentially allowing them to end up in rocks forming the crust of terrestrial planets like Earth.