STARSET_MirrorFootprints of galactic immigration uncovered in Andromeda galaxy
Astronomers have 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.
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.
在数十亿年的过程中，星系通过锻造新的恒星和与其他星系合并而成长和演化，这一过程被恰当地称为“星系迁移”事件。天文学家试图通过研究星系中单个恒星的运动，以及星系中延伸的恒星晕和暗物质，来揭示这些移民事件的历史。然而，到目前为止，这种宇宙考古学只可能在我们自己的星系——银河系中实现。
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.
一个国际研究小组发现了惊人的新证据，证明银河系最近的大星系邻居仙女座星系发生了大规模的星系移民事件。新的结果是由美国能源部暗能量光谱仪器(DESI)在基特峰国家天文台Nicholas U. Mayall 4米望远镜上获得的，这是美国国家科学基金会NOIRLab的一个项目。
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.
通过测量仙女座星系(也被称为梅西耶31 )内晕中近7500颗恒星的运动，研究小组发现了恒星位置和运动的泄密模式，揭示了这些恒星是如何开始它们的生命的，这些恒星是20亿年前与M31合并的另一个星系的一部分。虽然这种模式早已被理论预测，但它们从未在任何星系中被如此清晰地看到过。
“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. “
“我们对银河系最近的大星系邻居仙女座星系的新观测，详细地揭示了星系移民事件的证据，”美国国家科学基金会NOIRLab的天文学家、发表这项研究论文的主要作者Arjun Dey解释说。“虽然夜空看起来是不变的，但宇宙是一个动态的地方。像M31和我们的银河系这样的星系是由宇宙历史上许多较小星系的积木构成的。”
“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.”
爱丁堡大学的天体物理学家谢尔盖·科波索夫(Sergey Koposov)是这篇论文的合著者，他说:“我们以前从未在恒星的运动中如此清楚地看到这一点，也没有看到这种合并产生的一些结构。”“我们的新发现是，仙女座星系的历史与我们自己的星系银河系的历史相似。两个星系的内部光晕都是由单一的移民事件控制的。”
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.
这项研究不仅揭示了我们银河系邻居的历史，也揭示了我们银河系的历史。银河系光晕中的大多数恒星都是在另一个星系中形成的，后来在80 – 100亿年前的一次星系合并中迁移到我们自己的星系中。研究M31中类似但更近的星系合并的遗迹，为天文学家提供了一个了解银河系过去主要事件之一的窗口。
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.
为了追踪M31的迁徙历史，研究小组求助于DESI。为了测量暗能量对宇宙膨胀的影响，建造DESI是为了绘制附近宇宙中数千万个星系和类星体的地图。它是世界上最强大的多目标巡天摄谱仪，能够在一个晚上测量超过10万个星系的光谱。然而，DESI的世界级能力也可以用于离家更近的地方，并且该仪器对团队对M31的调查至关重要。
“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.”
“这项科学研究在世界上任何其他设施都无法完成。DESI惊人的效率、吞吐量和视野使它成为世界上对仙女座星系进行恒星调查的最佳系统，”Dey说。“在短短几个小时的观测时间里，DESI就能够用更大的望远镜超越十多年的光谱学。”
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.”
尽管梅奥尔望远镜于50年前完工(1973年首次发光)，但由于不断升级和最先进的仪器，它仍然是世界级的天文设施。“50年听起来很长，天真的人们可能会认为这是一个设施的自然寿命，”NOIRLab的合著者Joan R. Najita说。“但随着更新和再利用，像梅奥尔这样古老的望远镜可以继续做出惊人的发现，尽管按照今天的标准，它相对较小。”
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.
这项研究是与哈佛大学的两名本科生加布里埃尔·马克西明和约书亚·约瑟夫-扎克合作进行的，他们通过拉德克利夫高等研究院参与了这个项目。Najita在2021年至2022年期间是拉德克利夫研究员。
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