galaxies, the universe contains

very dim galaxies that until

Line recently went unnoticed by

(5) astronomers. Possibly as

numerous as conventional gal-

axies, these galaxies have the

same general shape and even

the same approximate number

(10) of stars as a common type of

conventional galaxy, the spiral,

but tend to be much larger.

Because these galaxies’

mass is spread out over

(15) larger areas, they have far

fewer stars per unit volume

than do conventional galaxies.

Apparently these low-surface-

brightness galaxies, as they

(20) are called, take much longer

than conventional galaxies to

condense their primordial gas

and convert it to stars—that is,

they evolve much more slowly.

(25) These galaxies may

constitute an answer to the long-

standing puzzle of the missing

baryonic mass in the universe.

Baryons—subatomic particles

(30) that are generally protons or

neutrons—are the source of

stellar, and therefore galactic,

luminosity, and so their numbers

can be estimated based on how

(35) luminous galaxies are. How-

ever, the amount of helium

in the universe, as measured

by spectroscopy, suggests

that there are far more baryons

(40) in the universe than estimates

based on galactic luminosity

indicate. Astronomers have

long speculated that the missing

baryonic mass might eventually

(45) be discovered in intergalactic

space or as some large popu-

lation of galaxies that are difficult

to detect

請大家幫忙

紅色的那段話

我看不是很了解

所以後來第二段都很模糊

請哪位幫我解釋一下

我不懂位什麼突然跑出了Baryon are the source of stellar

, and thereofore...

therefore後面跟Baryon又有什麼關係??

這跟後來的However又有什麼關係呢???

唉唷~~~真暈

划红线部分就是解释baryonic mass 是个什么东东的.therefore就是说，因为它是个 source,所以它如何如何.后面是几个形容词,其中包括galactic,
luminosity.however就转折过来说,这个东东实际比通过galactic luminosity预测的多.

逻辑关系就是,因为该东东是什么什么source,所以该东东是galactic的.但是，它的数量又比根据galactic预测出来的数量多。