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 means of 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 darkish matter. Such cosmic archaeology, nevertheless, has solely been doable in our personal galaxy, the Milky Method, till now.

A global workforce of researchers has uncovered placing new proof of a big galactic immigration occasion within the Andromeda Galaxy, the Milky Method’s nearest giant galactic neighbor. The brand new outcomes had been made with the DOE’s Darkish Vitality 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 called 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 Method’s nearest giant 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 evening sky could seem unchanging, the Universe is a dynamic place. Galaxies like M31 and our Milky Method are constructed from the constructing blocks of many smaller galaxies over cosmic historical past.”

“We have now by no means earlier than seen this so clearly within the motions of stars, nor had we seen a few of the constructions that consequence from this merger,” mentioned 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 just like that of our personal Galaxy, the Milky Method. The inside halos of each galaxies are dominated by a single immigration occasion.”

This analysis sheds mild on not solely the historical past of our galactic neighbors but in addition the historical past of our personal galaxy. Many of the stars within the Milky Method’s halo had been shaped 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 identical, however more moderen, galaxy merger in M31 offers astronomers a window onto one of many main occasions within the Milky Method’s previous.

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

“This science couldn’t have been completed at some other facility on the earth. DESI’s superb effectivity, throughput, and subject of view make it one of the best system on the earth to hold out a survey of the celebrities within the Andromeda Galaxy,” mentioned Dey. “In only some hours of observing time, DESI was capable of 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 mild in 1973), it stays a world-class astronomical facility due to continued upgrades and state-of-the-art instrumentation. “Fifty years appears like a very long time, and naïvely one may suppose that is the pure lifetime of a facility,” mentioned 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 as we speak’s requirements.”

The analysis was carried out in collaboration with two Harvard College undergraduates, Gabriel Maxemin and Joshua Josephy-Zack, who linked with the undertaking by means of 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 goal 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 at the moment are hoping to conduct a survey of your entire M31 halo with DESI. Who is aware of what new discoveries await.”

The analysis is forthcoming in The Astrophysical Journal.