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04宇宙的大尺度结构.pdf
1 星系集团
2星系间的相互作用
第四章宇宙的大尺度结构
1
3星系的演化
(Chapter 24)
本章的教学目标
l掌握星系成团的层次性
l了解星系间相互作用的基本情况
l掌握宇宙的大尺度结构特征
l了解星系的演化*
§4.1 星系集团
Galaxies are not distributed uniformly throughout space --
most are evidently held together by gravity due to dark
matter between the galaxies.
Systems of galaxies
Binary galaxies(双重星系 )
Multiple galaxies(多重星系 )
Groups of galaxies(星系群 )
Clusters of galaxies(星系团 )
Superclusters of galaxies(超星系团 )
The larger a given system, the less its density exceeds the
mean density of the Universe.
1. The Local Group(本星系群 )
The galaxy cluster includes the Milky
Way galaxy, with size of ~1.2 Mpc.
There are at least 40 galaxies in the
Local Group, three of them are spirals,
four irregulars and more than 20
ellipticals.
The Milky Way galaxy and Andromeda (M31) are the largest
members, and most of the smaller galaxies are gravitationally
bound to one or the other of them.
Spatial Distribution of the Local Group
Spatial Distribution of the Local Group
(1) The Magellanic Clouds(麦哲伦云)
The Large and Small Magellanic Clouds
(大、小麦哲伦云 )
First recorded by F. Magellan in 1519.
Physical parameters
LMC: D = 50 kpc, M = 2×1010M⊙,
d = 10 kpc.
SMC: D = 60 kpc, M = 4×109M⊙ ,
d = 6 kpc.
Both are irregular galaxies, orbiting our
Milky Way galaxy.
Abundant young stars and neutral
hydrogen gas.
SN1987A occurred in LMC.
The Magellanic Stream
A 180º long thin stream of
neutral hydrogen clouds
connecting the Galaxy and
the Magellanic clouds.
Canis Major Dwarf: A New Closest Galaxy
D = 42,000
light years
(2) The Andromeda galaxy (M31)
The largest galaxy in
the Local group, with
distance of ~770 kpc
and diameter of ~60
kpc.
Type Sb spiral galaxy
It has seven satellites,
all are ellipticals. The Andromeda Galaxy and two of its
satellite galaxies, M32 (left) and M110
(bottom right).
X-ray Census in Andromeda
Supermassive BH X-ray binaries
(3) The M33 galaxy
The third largest galaxy in the Local Group, with distance of ~720
kpc and diameter of ~18 kpc.
Type Sc spir
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