CDG-2

CDG-2
CDG-2
	哈勃太空望远镜拍摄的CDG-2图像，其中突显了该星系内的四个球状星团
观测资料
星座	英仙座
赤经	03h 17m 12.61s
赤纬	+41° 20′ 52.64″
距离	约2.45亿ly
属于	英仙座星系团
其他	为暗星系
	参考: https://science.nasa.gov/asset/hubble/dark-galaxy-cdg-2-near-perseus-cluster/
	参见：星系、星系列表

候选暗星系2号（英语：Candidate Dark Galaxy 2，CDG-2）位于英仙座星系团，主要由暗物质构成，另有四个球状星团。^[1]它是迄今发现暗物质占比最高的星系之一，估计暗物质逾99%。^[2]

发现

CDG-2由哈勃太空望远镜英仙座星系团巡天项目PIPER发现。该项目原为寻找球状星团密度异常偏高的区域，因为这类区域可能对应超稀疏星系。2025年3月，研究人员采用一种新统计方法，即泊松簇过程（由内曼—斯科特过程改造而来）展开搜寻，并将CDG-2识别为一颗可能存在的星系。^[3]2025年6月，研究人员检视哈勃太空望远镜、欧几里得太空观察站与昴星团望远镜图像后^[4]，在CDG-2球状星团周围发现弥散辐射，因而有力证明其为星系。它也是首个凭借球状星团踪迹发现的星系。^[5]

概述

与迄今发现的大多数超弥漫星系不同，CDG-2据信只有最初识别出的四个球状星团，另有少数可能的球状星团仍待进一步查证。其暗物质晕质量估计约为 $5.7\times 10^{10}M_{\odot }$ ，可见这是一座暗物质占绝对优势的星系，晕质量占比达99.94%至99.98%。^[5]这座星系的存在，或可成为检验多种星系形成理论的有力例证。^[6]暗星系是ΛCDM模型所预言的一类天体，其多寡因而成为检验这一理论的重要依据。相关丰度模拟也常以CDG-2和Cloud-9为参照。^[7]

参考文献

^ Dark Galaxy CDG-2 Near Perseus Cluster - NASA Science. 2026-02-18 [2026-02-21] （美国英语）.
^ Lea, Robert. Hubble telescope discovers rare galaxy that is 99% dark matter. Space. 2026-02-19 [2026-02-21] （英语）.
^ Li, Dayi; Stringer, Alex; Eadie, Gwendolyn; Abraham, Roberto. Poisson cluster process models for detecting ultra-diffuse galaxies. Annals of Applied Statistics. March 2025, 19 (1): 261–285. doi:10.1214/24-AOAS1958 –通过Project Euclid.
^ information@eso.org. Hubble identifies one of darkest known galaxies - The elusive object dubbed CDG-2 may be composed of 99% dark matter. www.esahubble.org. [2026-02-21] （英语）.
^ ^5.0 ^5.1 Li 李, Dayi (David) 大一; Liu 刘, Qing 青; Eadie, Gwendolyn M.; Abraham, Roberto G.; Marleau, Francine R.; Harris, William E.; van Dokkum, Pieter; Romanowsky, Aaron J.; Danieli, Shany; Brown, Patrick E.; Stringer, Alex. Candidate Dark Galaxy-2: Validation and Analysis of an Almost Dark Galaxy in the Perseus Cluster. The Astrophysical Journal Letters. 2025-06-16, 986 (2): L18. Bibcode:2025ApJ...986L..18L. ISSN 2041-8205. arXiv:2506.15644 . doi:10.3847/2041-8213/adddab .
^ Garay, Jorge. A Galaxy Composed Almost Entirely of Dark Matter Has Been Confirmed. Wired. [2026-02-21]. ISSN 1059-1028 （美国英语）.
^ García-Bethencourt, Guacimara; Cintio, Arianna Di; Comerón, Sébastien; Arjona-Gálvez, Elena; Contreras-Santos, Ana; Cardona-Barrero, Salvador; Brook, Chris B. A.; Negri, Andrea; Libeskind, Noam I. HI-bearing dark galaxies predictions from constrained Local Group simulations: how many and where to find them. 2026-01-07. arXiv:2601.04024  [astro-ph.GA].

[1] Dark Galaxy CDG-2 Near Perseus Cluster - NASA Science. 2026-02-18 [2026-02-21] （美国英语）.

[2] Lea, Robert. Hubble telescope discovers rare galaxy that is 99% dark matter. Space. 2026-02-19 [2026-02-21] （英语）.

[3] Li, Dayi; Stringer, Alex; Eadie, Gwendolyn; Abraham, Roberto. Poisson cluster process models for detecting ultra-diffuse galaxies. Annals of Applied Statistics. March 2025, 19 (1): 261–285. doi:10.1214/24-AOAS1958 –通过Project Euclid.

[4] rmation@eso.org. Hubble identifies one of darkest known galaxies - The elusive object dubbed CDG-2 may be composed of 99% dark matter. www.esahubble.org. [2026-02-21] （英语）.

[:0-5] 5.0 ^5.1 Li 李, Dayi (David) 大一; Liu 刘, Qing 青; Eadie, Gwendolyn M.; Abraham, Roberto G.; Marleau, Francine R.; Harris, William E.; van Dokkum, Pieter; Romanowsky, Aaron J.; Danieli, Shany; Brown, Patrick E.; Stringer, Alex. Candidate Dark Galaxy-2: Validation and Analysis of an Almost Dark Galaxy in the Perseus Cluster. The Astrophysical Journal Letters. 2025-06-16, 986 (2): L18. Bibcode:2025ApJ...986L..18L. ISSN 2041-8205. arXiv:2506.15644 . doi:10.3847/2041-8213/adddab .

[6] Garay, Jorge. A Galaxy Composed Almost Entirely of Dark Matter Has Been Confirmed. Wired. [2026-02-21]. ISSN 1059-1028 （美国英语）.

[7] García-Bethencourt, Guacimara; Cintio, Arianna Di; Comerón, Sébastien; Arjona-Gálvez, Elena; Contreras-Santos, Ana; Cardona-Barrero, Salvador; Brook, Chris B. A.; Negri, Andrea; Libeskind, Noam I. HI-bearing dark galaxies predictions from constrained Local Group simulations: how many and where to find them. 2026-01-07. arXiv:2601.04024  [astro-ph.GA].

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