美国国家航空航天局NASA每日一图-2017年7月15日

Discovered by British astronomer William Herschel over 200 years ago, NGC 2500 lies about 30 million light-years away in the northern constellation of Lynx. As this NASA/ESA Hubble Space Telescope image shows, NGC 2500 is a particular kind of spiral galaxy known as a barred spiral, its wispy arms swirling out from a bright, elongated core.

Barred spirals are actually more common than was once thought. Around two-thirds of all spiral galaxies — including the Milky Way — exhibit these straight bars cutting through their centers. These cosmic structures act as glowing nurseries for newborn stars, and funnel material towards the active core of a galaxy. NGC 2500 is still actively forming new stars, although this process appears to be occurring very unevenly. The upper half of the galaxy — where the spiral arms are slightly better defined — hosts many more star-forming regions than the lower half, as indicated by the bright, dotted islands of light.

There is another similarity between NGC 2500 and our home galaxy. Together with Andromeda, Triangulum and many smaller natural satellites, the Milky Way is part of the Local Group of galaxies, a gathering of over 50 galaxies all loosely held together by gravity. NGC 2500 forms a similar group with some of its nearby neighbors, including NGC 2541, NGC 2552, NGC 2537 and the bright, Andromeda-like spiral NGC 2481 (known collectively as the NGC 2841 group).

Image Credit: ESA/Hubble/NASA

Last Updated: July 15, 2017
Editor: Sara Blumberg

在200多年前,由英国天文学家威廉·赫歇尔(William Herschel)发现,NGC 2500在北极星座的天猫大约有三千万光年。随着NASA / ESA哈勃太空望远镜的形象显示,NGC 2500是一种特殊的螺旋星系,被称为禁止的螺旋,其轻柔的手臂从明亮细长的核心旋转出来。

禁止螺​​旋其实比曾经想到的更为常见。大约三分之二的螺旋星系 - 包括银河系 - 显示这些直线穿过他们的中心。这些宇宙结构作为新生星的发光托儿所,并向着星系的活跃核心漏斗。 NGC 2500仍在积极形成新星,虽然这个过程似乎发生非常不均衡。星系的上半部分,其中螺旋臂略微更好地定义 - 比下半部分拥有更多的星形成区域,如明亮的虚线光点所示。

NGC 2500和我们的家庭星系之间有另一个相似之处。与仙女座,三角形和许多较小的天然卫星一起,银河系是当地星系集团的一部分,这是一个超过50个星系的聚会,所有这些都是通过重力松散地聚集在一起的。 NGC 2500与其附近的一些邻居形成了类似的组织,包括NGC 2541,NGC 2552,NGC 2537和明亮的Andromeda样螺旋NGC 2481(统称为NGC 2841组)。

图片来源:欧空局/哈勃/美国航空航天局

最后更新:2017年7月15日
编辑:Sara Blumberg

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