NGC 6397

NGC 6397
	哈伯太空望远镜(HST)拍摄的NGC 6397。; 创建者： HST/NASA/ESA.
观测数据(J2000 历元)
分类	IX
星座	天坛座
赤经	17h 40m 42.09s
赤纬	–53° 40′ 27.6″
距离	7.8 kly（2.4 kpc）
视星等 (V)	+6.68
视直径(V)	32′.0
物理性质
Mass	1.2×105 M☉
半径	34 ly
VHB	14.2
金属量	–1.76 dex
估计年龄	13.4 ± 0.8 Gyr
值得注意的特色	第二接近的球状星团
其它名称	GCl 74, Lacaille III.11, Dunlop 366, Bennett 98, 科德韦尔 86
	参见：球状星团，球状星团表

NGC 6397(也称为科德韦尔86)是在天坛座的球状星团。它距离地球大约7,800光年^[3]，使它成为离地球最近的两个球状星团之一（另一个是 M4）。这个星团大约有400,000颗恒星^[8]，在良好的观察条件下可以用肉眼看到^[9]。

NGC 6397是银河系中至少20个经历了核心坍塌的球状星团之一^[8]，这意味着核心收缩而有着非常致密的恒星。 .

天文学研究

估计银河系的年龄

在2004年，一组天文学家^[8]聚焦在星团，用它来估计银河系的年龄。这组的成员包括卢卡·帕斯奎尼、皮尔卡洛·博尼法西奥、索菲亚·兰迪奇、丹尼尔·加利和拉斐尔·G·格拉顿。他们使用帕瑞纳山甚大望远镜的紫外-可见光的光栅摄谱仪测量星团中两颗恒星的铍含量。这使他们能够推断整个银河系中第一代恒星的诞生到星团中第一代恒星诞生之间所经过的时间。再加上对星团中恒星估计的年龄，就可以估计银河系的年龄：136亿年，这年龄几乎和宇宙本身一样老。这一估计假设NGC 6397不会比银河系古老。

恒星质量的下限

在2006年，发表了使用哈伯太空望远镜对NGC 6397的一项研究，显示星丸中黯淡恒星的亮度明显的有一个下限。作者推断，这表明恒星的核心要能够进行核聚变有一个质量下限：大约是太阳质量的0.83倍^[10]。

黑洞

在2021年2月据报导，根据哈伯太空望远镜和欧洲航天局盖亚任务收集的数据得出核心附近恒星的运动：NGC 6397的核心含有相对密集的致密天体（白矮星、中子星和黑洞）^[5]^[11]。这个中心区域的黑洞总质量上限约为1,000个太阳质量，来自许多颗，估计平均大小为20个太阳质量的较小黑洞^[12]。然而，也有人认为，由于动力相互作用，这些黑洞中的许多都会从星团核心喷出，这导致这种看不见的浓缩物主要由白矮星和中子星组成，只有极少数的黑洞^[13]。

图集

哈伯观察所见的球状星团NGC 6397^[14]

参考资料

^ Shapley, Harlow; Sawyer, Helen B., A Classification of Globular Clusters, Harvard College Observatory Bulletin, August 1927, 849 (849): 11–14, Bibcode:1927BHarO.849...11S.
^ ^2.0 ^2.1 Goldsbury, Ryan; et al, The ACS Survey of Galactic Globular Clusters. X. New Determinations of Centers for 65 Clusters, The Astronomical Journal, December 2010, 140 (6): 1830–1837, Bibcode:2010AJ....140.1830G, S2CID 119183070, arXiv:1008.2755 , doi:10.1088/0004-6256/140/6/1830.
^ ^3.0 ^3.1 Salazar, Doris Elen. Cosmic 'Yardstick' Measures Distance to One of Universe's Oldest Objects. Space.com. [5 April 2018]. （原始内容存档于2021-07-19）.
^ ^4.0 ^4.1 [
http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=NGC+6397
NGC 6397] 请检查|url=值 (帮助). SIMBAD. 斯特拉斯堡天文资料中心.
^ ^5.0 ^5.1 Vitral, Eduardo; Mamon, Gary A., Does NGC 6397 contain an intermediate-mass black hole or a more diffuse inner subcluster?, A&A, 2021, 646 (A63): A63, Bibcode:2021A&A...646A..63V, doi:10.1051/0004-6361/202039650 
^ distance × sin( diameter_angle / 2 ) = ~34 ly. radius
^ Forbes, Duncan A.; Bridges, Terry, Accreted versus in situ Milky Way globular clusters, Monthly Notices of the Royal Astronomical Society, May 2010, 404 (3): 1203–1214, Bibcode:2010MNRAS.404.1203F, S2CID 51825384, arXiv:1001.4289 , doi:10.1111/j.1365-2966.2010.16373.x.
^ ^8.0 ^8.1 ^8.2 ^8.3 How Old is the Milky Way ?. Results for NGC 6397. [2006-09-26]. （原始内容存档于2008-09-05）.
^ Dunlop, Storm. Atlas of the Night Sky. Collins. 2005. ISBN 978-0-00-717223-8.
^ HST analysis of faint stars in NGC6397. Results for NGC 6397. [2006-09-26]. （原始内容存档于2008-07-08）.
^ Hubble Uncovers Concentration of Small Black Holes. ESA. 11 February 2021 [21 February 2021]. （原始内容存档于2021-04-27）.
^ Overbye, Dennis. Hunting for a Giant Black Hole, Astronomers Found a Nest of Darkness - No Gargantua dwells at the heart of stellar cluster NGC 6397. Instead, a few dozen smaller black holes seem to be swarming around in there, throwing their considerable masses around.. The New York Times. 26 February 2021 [27 February 021]. （原始内容存档于2021-07-28）.
^ Weatherford, Newlin C.; Sourav, Chatterjee; Kremer, Kyle; Rasio, Frederic A., A Dynamical Survey of Stellar-mass Black Holes in 50 Milky Way Globular Clusters, The Astrophysical Journal, 2020, 898 (162): 162, Bibcode:2020ApJ...898..162W, S2CID 208202116, arXiv:1911.09125 , doi:10.3847/1538-4357/ab9f98
^ Hubble's view of dazzling globular cluster NGC 6397. www.spacetelescope.org. [13 April 2018]. （原始内容存档于2018-08-16）.

外部链接

WikiSky上关于NGC 6397的内容：DSS2, SDSS, GALEX, IRAS, 氢α, X射线, 天文照片, 天图, 文章和图片
NASA Astronomy Picture of the Day: Blue Stragglers in NGC 6397 (8 August 2003)
NASA Astronomy Picture of the Day: Oddities of Star Cluster NGC 6397 (20 February 2002)

[hcob849_11-1] Shapley, Harlow; Sawyer, Helen B., A Classification of Globular Clusters, Harvard College Observatory Bulletin, August 1927, 849 (849): 11–14, Bibcode:1927BHarO.849...11S.

[aj140_6_1830-2] 2.0 ^2.1 Goldsbury, Ryan; et al, The ACS Survey of Galactic Globular Clusters. X. New Determinations of Centers for 65 Clusters, The Astronomical Journal, December 2010, 140 (6): 1830–1837, Bibcode:2010AJ....140.1830G, S2CID 119183070, arXiv:1008.2755 , doi:10.1088/0004-6256/140/6/1830.

[Salazar-3] 3.0 ^3.1 Salazar, Doris Elen. Cosmic 'Yardstick' Measures Distance to One of Universe's Oldest Objects. Space.com. [5 April 2018]. （原始内容存档于2021-07-19）.

[simbad-4] 4.0 ^4.1 [
http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=NGC+6397
NGC 6397] 请检查|url=值 (帮助). SIMBAD. 斯特拉斯堡天文资料中心.

[VitralMamon21-5] 5.0 ^5.1 Vitral, Eduardo; Mamon, Gary A., Does NGC 6397 contain an intermediate-mass black hole or a more diffuse inner subcluster?, A&A, 2021, 646 (A63): A63, Bibcode:2021A&A...646A..63V, doi:10.1051/0004-6361/202039650 

[6] stance × sin( diameter_angle / 2 ) = ~34 ly. radius

[mnras404_3_1203-7] Forbes, Duncan A.; Bridges, Terry, Accreted versus in situ Milky Way globular clusters, Monthly Notices of the Royal Astronomical Society, May 2010, 404 (3): 1203–1214, Bibcode:2010MNRAS.404.1203F, S2CID 51825384, arXiv:1001.4289 , doi:10.1111/j.1365-2966.2010.16373.x.

[eso-8] 8.0 ^8.1 ^8.2 ^8.3 How Old is the Milky Way ?. Results for NGC 6397. [2006-09-26]. （原始内容存档于2008-09-05）.

[nightsky-9] Dunlop, Storm. Atlas of the Night Sky. Collins. 2005. ISBN 978-0-00-717223-8.

[HST-10] HST analysis of faint stars in NGC6397. Results for NGC 6397. [2006-09-26]. （原始内容存档于2008-07-08）.

[11] Hubble Uncovers Concentration of Small Black Holes. ESA. 11 February 2021 [21 February 2021]. （原始内容存档于2021-04-27）.

[NYT-20210226-12] Overbye, Dennis. Hunting for a Giant Black Hole, Astronomers Found a Nest of Darkness - No Gargantua dwells at the heart of stellar cluster NGC 6397. Instead, a few dozen smaller black holes seem to be swarming around in there, throwing their considerable masses around.. The New York Times. 26 February 2021 [27 February 021]. （原始内容存档于2021-07-28）.

[13] Weatherford, Newlin C.; Sourav, Chatterjee; Kremer, Kyle; Rasio, Frederic A., A Dynamical Survey of Stellar-mass Black Holes in 50 Milky Way Globular Clusters, The Astrophysical Journal, 2020, 898 (162): 162, Bibcode:2020ApJ...898..162W, S2CID 208202116, arXiv:1911.09125 , doi:10.3847/1538-4357/ab9f98

[14] Hubble's view of dazzling globular cluster NGC 6397. www.spacetelescope.org. [13 April 2018]. （原始内容存档于2018-08-16）.

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