Videos
Cosmoview Episode 62: Footprints of Galactic Immigration Uncovered in Andromeda Galaxy
Cosmoview Episodio 62: Descubren las huellas de inmigración galáctica en la galaxia de Adrómeda
The Dark Energy Spectroscopic Instrument reveals compelling evidence of a mass migration of stars into a galaxy other than the Milky Way
A team of researchers led by astronomers
at NSF’s NOIRLab has uncovered striking new evidence for a mass
migration of stars into the Andromeda Galaxy. Intricate patterns in the
motions of stars reveal an immigration history very similar to that of
the Milky Way. The new results were obtained with the DOE’s Dark Energy
Spectroscopic Instrument on the Nicholas U. Mayall 4-meter Telescope at
Kitt Peak National Observatory, a Program of NSF’s NOIRLab.
Over the course of billions of years, galaxies grow and evolve by
forging new stars and merging with other galaxies through aptly named
“galactic immigration” events. Astronomers try to uncover the histories
of these immigration events by studying the motions of individual stars
throughout a galaxy and its extended halo of stars and dark matter. Such
cosmic archaeology, however, has only been possible in our own galaxy,
the Milky Way, until now.
An international team of researchers has uncovered striking new
evidence of a large galactic immigration event in the Andromeda Galaxy,
the Milky Way’s nearest large galactic neighbor. The new results were
made with the DOE’s Dark Energy Spectroscopic Instrument (DESI) on the Nicholas U. Mayall 4-meter Telescope at Kitt Peak National Observatory, a Program of NSF’s NOIRLab.
By measuring the motions of nearly 7500 stars in the inner halo of
the Andromeda Galaxy, also known as Messier 31 (M31), the team
discovered telltale patterns in the positions and motions of stars that
revealed how these stars began their lives as part of another galaxy
that merged with M31 about 2 billion years ago. While such patterns have
long been predicted by theory, they have never been seen with such
clarity in any galaxy.
“Our new observations of the Milky Way’s nearest large galactic
neighbor, the Andromeda Galaxy, reveal evidence of a galactic
immigration event in exquisite detail,” explained Arjun Dey, astronomer at NSF’s NOIRLab and the lead author of the paper presenting this research. “Although
the night sky may seem unchanging, the Universe is a dynamic place.
Galaxies like M31 and our Milky Way are constructed from the building
blocks of many smaller galaxies over cosmic history. ”
“We have never before seen this so clearly in the motions of
stars, nor had we seen some of the structures that result from this
merger,” said Sergey Koposov, an astrophysicist at the University of Edinburgh and coauthor of the paper. “Our
emerging picture is that the history of the Andromeda Galaxy is similar
to that of our own Galaxy, the Milky Way. The inner halos of both
galaxies are dominated by a single immigration event.”
This research sheds light on not only the history of our galactic
neighbors but also the history of our own 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 M31 gives
astronomers a window onto one of the major events in the Milky Way’s
past.
To trace the history of migration in M31, the team turned to DESI.
DESI was constructed to map tens of millions of galaxies and quasars in
the nearby Universe in order to measure the effect of dark energy on
the expansion of the Universe. It is the most powerful multi-object
survey spectrograph in the world, and is capable 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 remains a world-class astronomical
facility thanks to continued upgrades and state-of-the-art
instrumentation. “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, 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 standards.”
The research was carried out in collaboration with two Harvard
University undergraduates, Gabriel Maxemin and Joshua Josephy-Zack, who
connected with the project through the Radcliffe Institute for Advanced
Study. Najita was a Radcliffe Fellow from 2021 to 2022.
The team 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.
“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!”
More Information:
The Dark Energy Spectroscopic Instrument reveals compelling evidence of a mass migration of stars into a galaxy other than the Milky Way
A Dey, A. et al., (2023) “DESI Observations of
the Andromeda Galaxy: Revealing the Immigration History of our Nearest
Neighbor” to appear in The Astrophysical Journal.
NSF’s NOIRLab (National
Optical-Infrared Astronomy Research Laboratory), the US center for
ground-based optical-infrared astronomy, operates the international Gemini Observatory (a facility of NSF, NRC–Canada, ANID–Chile, MCTIC–Brazil, MINCyT–Argentina, and KASI–Republic of Korea), Kitt Peak National Observatory (KPNO), Cerro Tololo Inter-American Observatory (CTIO), the Community Science and Data Center (CSDC), and Vera C. Rubin Observatory (operated in cooperation with the Department of Energy’s SLAC National Accelerator Laboratory). It is managed by the Association of Universities for Research in Astronomy (AURA)
under a cooperative agreement with NSF and is headquartered in Tucson,
Arizona. The astronomical community is honored to have the opportunity
to conduct astronomical research on Iolkam Du’ag (Kitt Peak) in Arizona,
on Maunakea in Hawai‘i, and on Cerro Tololo and Cerro Pachón in Chile.
We recognize and acknowledge the very significant cultural role and
reverence that these sites have to the Tohono O’odham Nation, to the
Native Hawaiian community, and to the local communities in Chile,
respectively.
Links
- Research paper
- Images of the Nicholas U. Mayall 4-meter Telescope
- Videos of the Nicholas U. Mayall 4-meter Telescope
Contacts:
Arjun Dey
Astronomer
NSF’s NOIRLab
Email: arjun.dey@noirlab.edu
Joan R. Najita
Astronomer
NSF’s NOIRLab
Email: joan.najita@noirlab.edu
Charles Blue
Public Information Officer
NSF’s NOIRLab
Tel: +1 202-236-6324
Email: charles.blue@noirlab.edu
