The Universe is a dynamic place where galaxies grow and evolve through „galactic immigration” events that see them merge with other galaxies to form new stars. However, until recently, astronomers have only been able to study these events in our own Milky Way galaxy. Now, an international team of researchers has uncovered striking new evidence of a large galactic immigration event in the Andromeda Galaxy.

The team used the Dark Energy Spectroscopic Instrument (DESI) on the Nicholas U. Mayall 4-meter Telescope at Kitt Peak National Observatory to measure the motions of nearly 7,500 stars in the inner halo of the Andromeda Galaxy. They discovered patterns in the positions and motions of the stars that reveal how they began life as part of another galaxy that merged with Andromeda about 2 billion years ago.

„Although the night sky may seem unchanging, the Universe is a dynamic place. Galaxies like Andromeda and our Milky Way are constructed from the building blocks of many smaller galaxies over cosmic history,” explains Arjun Dey, astronomer at NSF’s NOIRLab and the lead author of the research paper.

This research sheds light on the history not only of Andromeda but also of our own Milky Way galaxy. Most of the stars in the Milky Way’s halo were formed in another galaxy and later migrated into our own in a galactic merger 8-10 billion years ago. Studying the relics of a similar but more recent galaxy merger in Andromeda gives astronomers a window into one of the major events in the Milky Way’s past.

Exploring the Power of DESI

The team turned to DESI to trace the history of migration in Andromeda. DESI is the most powerful multi-object survey spectrograph in the world, capable of measuring the spectra of more than 100,000 galaxies a night. In only a few hours of observing time, DESI was able to surpass more than a decade of spectroscopy with much larger telescopes.

„This science could not have been done at any other facility in the world,” says Dey. „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.”

Continued Innovation at the Mayall Telescope

Even though the Mayall Telescope was completed 50 years ago, it remains a world-class astronomical facility, thanks to continued upgrades and state-of-the-art instrumentation. The team behind the recent discovery of the „Footprints of ‘galactic immigration’ uncovered in Andromeda galaxy” relied on the Mayall Telescope to carry out their observations, and the results exceeded their wildest expectations.

The telescope, along with the DOE’s Dark Energy Spectroscopic Instrument (DESI), was crucial in uncovering the evidence of a large galactic immigration event in the Andromeda Galaxy.

„Fifty years sounds like a long time, and naïvely one might think that’s the natural lifetime of a facility,” said co-author Joan R. Najita. „But with renewal and reuse, a venerable telescope like the Mayall can continue to make amazing discoveries despite being relatively small by today’s standards.”

The Mayall Telescope, located at Kitt Peak National Observatory, has been instrumental in a wide range of astronomical studies, including mapping the large-scale structure of the universe, measuring the expansion rate of the universe, and detecting distant quasars and galaxies.

The Mayall Telescope’s continued upgrades and state-of-the-art instrumentation ensure that it remains a premier astronomical facility, capable of making groundbreaking discoveries for decades to come.

The team behind the recent discovery in the Andromeda Galaxy now plans to use the unparalleled capabilities of DESI and the Mayall Telescope to explore more of M31’s outlying stars. With the aim of revealing its structure and immigration history in unprecedented detail, the team is eager to see what new discoveries await.

„It’s amazing that we can look out at the sky and read billions of years of another galaxy’s history as written in the motions of its stars—each star tells part of the story,” concluded Najita. „Our initial observations exceeded our wildest expectations and we are now hoping to conduct a survey of the entire M31 halo with DESI. Who knows what new discoveries await.”

In conclusion, the recent discovery of the „Footprints of ‘galactic immigration’ uncovered in Andromeda galaxy” is a testament to the continued innovation and cutting-edge capabilities of the Mayall Telescope.

With its ability to make groundbreaking discoveries and reveal the secrets of the universe, the Mayall Telescope remains a shining example of the power of scientific exploration and discovery.



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