Free Astronomy Magazine May-June 2023

35 MAY-JUNE 2023 ASTRO PUBLISHING To trace the history of migration in M31, the team turned to DESI. DESI was constructed to map tens of mil- lions of galaxies and quasars in the nearby Universe in order to measure the effect of dark energy on the ex- pansion of the Universe. It is the most powerful multi-object survey spectrograph in the world, and is ca- pable of measuring the spectra of more than 100,000 galaxies a night. DESI’s world-class capabilities can also be put to use closer to home, however, and the instrument was crucial to the team’s survey of M31. “This science could not have been done at any other facility in the world. DESI’s amazing efficiency, throughput, and field of view make it the best system in the world to carry out a survey of the stars in the Andromeda Galaxy,” said Dey. “In only a few hours of observing time, DESI was able to surpass more than a decade of spectroscopy with much larger telescopes.” Even though the Mayall Telescope was completed 50 years ago (it achieved first light in 1973), it re- mains a world-class astronomical fa- cility thanks to continued upgrades and state-of-the-art instrumenta- tion. “Fifty years sounds like a long time, and naïvely one might think that’s the natural lifetime of a facil- ity,” said co-author Joan R. Najita, also at NOIRLab. “But with renewal and reuse, a venerable telescope like the Mayall can continue to make amazing discoveries despite being relatively small by today’s stan- dards.” The research was carried out in col- laboration with two Harvard Univer- sity undergraduates, Gabriel Maxemin and Joshua Josephy-Zack, who connected with the project through the Radcliffe Institute for Advanced Study. Najita was a Rad- cliffe Fellow from 2021 to 2022. The team now plans to use the un- paralleled capabilities of DESI and S triking new evidence for a mass immigration of stars into the Andromeda Galaxy has been uncovered by researchers led by astronomers at NSF’s NOIR- Lab. The team used the DOE’s Dark Energy Spectroscopic Instrument on the Nicholas U. Mayall 4-meter Telescope at Kitt Peak National Observatory, a Pro- gram of NSF’s NOIRLab, to reveal intricate structures in this galaxy with unprece- dented detail and clarity. Each of the dots on this image represents an individual star in the Andromeda Galaxy, with the motion of the star (relative to the galaxy) color-coded from blue (moving toward us) to red (moving away from us). [KPNO/NOIRLab/AURA/NSF/E. Slawik/D. de Martin/M. Zamani] the Mayall Telescope to explore more of M31’s outlying stars, with the aim of revealing its structure and immigration history in unprece- dented detail. “It’s amazing that we can look out at the sky and read billions of years of another galaxy’s history as writ- ten in the motions of its stars — each star tells part of the story,” concluded Najita. “Our initial obser- vations exceeded our wildest expec- tations and we are now hoping to conduct a survey of the entire M31 halo with DESI. Who knows what new discoveries await!” !