Free Astronomy Magazine July-August 2023

JULY-AUGUST 2023 A planet orbits a Sun-like star that is nearing the end of its life. As the star expands, it begins to interact with an orbiting planet. bon, and hydrogen fusion migrates to the star’s outer layers, causing them to expand, and changing the Sun-like star into a red giant. Such a transformation, however, is bad news for any inner-system plan- ets. When the star’s surface eventu- ally expands to engulf one of its planets, their interaction would trig- ger a spectacular outburst of energy and material. This process would also put the brakes on the planet’s orbital velocity, causing it to plunge into the star. The first hints of this event were un- covered by optical images from the Zwicky Transient Facility. Archival in- frared coverage from NASA’s Near- Earth Object Wide-field Infrared Sur- vey Explorer (NEOWISE), which is able to peer into dusty environ- ments in search of outbursts and other transient events, then con- firmed the engulfment event, named ZTF SLRN-2020. “Our team’s custom reanalysis of all-sky infrared maps from NEOWISE exemplifies the vast discovery potential of archival sur- vey data sets,” said NOIRLab as- tronomer Aaron Meisner, another co-author on the paper. Distinguishing a planetary-engulf- ment outburst from other types of outbursts, such as solar-flare-type events and coronal-mass ejections, is difficult and requires high-resolu- tion observations to pinpoint the lo- cation of an outburst and long-term measurements of its brightness without contamination from nearby stars. Gemini South provided these essential data thanks to its adaptive- optics capabilities. “Gemini South continues to expand our understanding of the Universe and these new observations support predictions for the future of our own planet,” said NSF Gemini Ob- servatory program director Martin Still. “This discovery is a wonderful example of the feats we can accom- plish when we combine world-class telescope operations and cutting- edge scientific collaboration.” T his illustration shows a Sun-like star transforming into a red giant and engulfing a giant planet. For the first time, NOIRLab astronomers have observed an advanced stage of this process. [International Gemini Observatory/NOIRLab/NSF/AURA/P. Marenfeld]