Free Astronomy Magazine January-February 2023

28 JANUARY-FEBRUARY 2023 ASTRO PUBLISHING years to reach Earth,” explained Eve Chase, a postdoctoral researcher at Los Alamos National Laboratory in Los Alamos, New Mexico. Chase led a more recent study that simulated how differences in kilono- vae ejecta can vary what we expect to observe from observatories in- cluding Roman. There’s a second benefit to near-in- frared light: It provides more time to observe these short-lived bursts. Shorter wavelengths of light, like ul- traviolet and visible, disappear from view in a day or two. Near-infrared light can be gathered for a week or more. Researchers have been simu- lating the data to see how this will work. “For a subset of simulated kilonovae, Roman would be able to observe some more than two weeks after the neutron star merger oc- curred,” Chase added. “It will be an excellent tool for looking at kilono- vae that are very far away.” Soon, researchers will know far more about where kilonovae occur, and how often these explosions occur in the history of the universe. Were those that occurred earlier dif- ferent in some way? “ Roman will allow the astronomy community to begin conducting population studies along with a slew of new analyses on the physics of these explosions,” Scolnic said. A survey telescope offers enormous possibility – and also a ton of data that will require precise machine learning. Astronomers are meeting this challenge by writing code to au- tomate these searches. Ultimately, Roman’s massive data sets will help researchers unravel perhaps the greatest mysteries about kilonovae to date: What happens after two neutron stars collide? Does it pro- duce a single neutron star, a black hole, or something else entirely? With Roman, we will gather the sta- tistics researchers need to make sub- stantial breakthroughs. O n 17 August 2017, the Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Virgo Interferometerboth detected gravitational waves from the collision between two neutron stars. Within 12 hours observatories had iden- tified the source of the event within the lenticular galaxy NGC 4993, shown in this image gathered with the NASA/ESA Hubble Space Telescope. The associated stel- lar flare, a kilonova, is clearly visible in the Hubble observations. Hubble observed the kilonova gradually fading over the course of six days. [NASA and ESA. Ack.: N. Tanvir (U. Leicester), A. Levan (U. Warwick), and A. Fruchter and O. Fox (STScI)] nova we identified typical? How bright are these explosions? What types of galaxies do they occur in?” Existing telescopes can’t cover wide enough areas or observe deeply enough to find more distant ex- amples, but that will change with Roman. At this stage, LIGO leads the pack in identifying neutron star mergers. It can detect gravitational waves in all areas of the sky, but some of the most distant collisions may be too weak to be identified. Roman is set to join LIGO’s search, offering com- plementary qualities that help “fill out” the team. Roman is a survey telescope that will repeatedly scan the same areas of the sky. Plus, Roman’s field of view is 200 times larger than the Hubble Space Tele- scope’s infrared view – not as vast as LIGO’s, but huge for a telescope that takes images. Its cadence will allow researchers to spot when objects on the sky brighten or dim, whether nearby or very far away. Roman will provide researchers a powerful tool for observing ex- tremely distant kilonovae. This is due to the expansion of space. Light that left stars billions of years ago is stretched into longer, redder wave- lengths, known as infrared light, over time. Since Roman specializes in capturing near-infrared light, it will detect light from very distant ob- jects. How distant? “Roman will be able to see some kilonovae whose light has traveled about 7 billion !