Footprints of ‘galactic immigration’ uncovered in Andromeda galaxy

Over the course of billions of years, galaxies develop and evolve by forging new stars and merging with different galaxies by aptly named “galactic immigration” occasions. Astronomers attempt to uncover the histories of those immigration occasions by finding out the motions of particular person stars all through a galaxy and its prolonged halo of stars and dark matter. Such cosmic archaeology, nevertheless, has solely been potential in our personal galaxy, the Milky Way, till now.

A world workforce of researchers has uncovered putting new proof of a giant galactic immigration occasion within the Andromeda Galaxy, the Milky Way’s nearest massive galactic neighbor. The brand new outcomes have been made with the DOE’s Darkish Power Spectroscopic Instrument (DESI) on the Nicholas U. Mayall 4-meter Telescope at Kitt Peak Nationwide Observatory, a Program of NSF’s NOIRLab.

By measuring the motions of almost 7500 stars within the inside halo of the Andromeda Galaxy, also referred to as Messier 31 (M31), the workforce found telltale patterns within the positions and motions of stars that exposed how these stars started their lives as a part of one other galaxy that merged with M31 about 2 billion years in the past. Whereas such patterns have lengthy been predicted by principle, they’ve by no means been seen with such readability in any galaxy.

“Our new observations of the Milky Way’s nearest massive galactic neighbor, the Andromeda Galaxy, reveal proof of a galactic immigration occasion in beautiful element,” defined Arjun Dey, astronomer at NSF’s NOIRLab and the lead creator of the paper presenting this analysis. “Though the night time sky could seem unchanging, the Universe is a dynamic place. Galaxies like M31 and our Milky Way are constructed from the constructing blocks of many smaller galaxies over cosmic historical past.”

“We’ve got by no means earlier than seen this so clearly within the motions of stars, nor had we seen among the constructions that outcome from this merger,” stated Sergey Koposov, an astrophysicist on the College of Edinburgh and co-author of the paper. “Our rising image is that the historical past of the Andromeda Galaxy is much like that of our personal Galaxy, the Milky Way. The inside halos of each galaxies are dominated by a single immigration occasion.”

This analysis sheds gentle on not solely the historical past of our galactic neighbors but in addition the historical past of our personal galaxy. A lot of the stars within the Milky Way’s halo have been fashioned in one other galaxy and later migrated into our personal in a galactic merger 8–10 billion years in the past. Finding out the relics of an analogous, however newer, galaxy merger in M31 offers astronomers a window onto one of many main occasions within the Milky Way’s previous.

To hint the historical past of migration in M31, the workforce turned to DESI. DESI was constructed to map tens of tens of millions of galaxies and quasars within the close by Universe as a way to measure the impact of darkish vitality on the enlargement of the Universe. It’s the strongest multi-object survey spectrograph on the planet, and is able to measuring the spectra of greater than 100,000 galaxies an evening. DESI’s world-class capabilities will also be put to make use of nearer to dwelling, nevertheless, and the instrument was essential to the workforce’s survey of M31.

“This science couldn’t have been accomplished at another facility on the planet. DESI’s superb effectivity, throughput, and area of view make it the perfect system on the planet to hold out a survey of the celebs within the Andromeda Galaxy,” stated Dey. “In just a few hours of observing time, DESI was in a position to surpass greater than a decade of spectroscopy with a lot bigger telescopes.”

Regardless that the Mayall Telescope was accomplished 50 years in the past (it achieved first gentle in 1973), it stays a world-class astronomical facility due to continued upgrades and state-of-the-art instrumentation. “Fifty years feels like a very long time, and naïvely one would possibly assume that is the pure lifetime of a facility,” stated co-author Joan R. Najita, additionally at NOIRLab. “However with renewal and reuse, a venerable telescope just like the Mayall can proceed to make superb discoveries regardless of being comparatively small by right now’s requirements.”

The analysis was carried out in collaboration with two Harvard College undergraduates, Gabriel Maxemin and Joshua Josephy-Zack, who linked with the mission by the Radcliffe Institute for Superior Examine. Najita was a Radcliffe Fellow from 2021 to 2022.

The workforce now plans to make use of the unparalleled capabilities of DESI and the Mayall Telescope to discover extra of M31’s outlying stars, with the intention of showing its construction and immigration historical past in unprecedented element.

“It is superb that we will look out on the sky and skim billions of years of one other galaxy’s historical past as written within the motions of its stars—every star tells a part of the story,” concluded Najita. “Our preliminary observations exceeded our wildest expectations and we are actually hoping to conduct a survey of the complete M31 halo with DESI. Who is aware of what new discoveries await.”

The analysis is forthcoming in The Astrophysical Journal.