How many galaxies are in our Local Group?

How many galaxies are in our Local Group?
Our Milky Way Galaxy wheels within the Local Group of Galaxies in a relatively quiet corner of the cosmos. The Virgo cluster of galaxies, some 50 million light-years away, plays
city center to our boondocks. The Virgo cluster holds an amazing 2,000 "island universes." Our little Local Group, by contrast, contains roughly three dozen galaxies, most of them unimpressive dwarfs.
Many, perhaps most, galaxies exist in such small groups scattered throughout the cosmos. The Local Group spans a mere 6 million light-years, and only three large galaxies lie within it. The most significant, the Andromeda Galaxy (M31), is an expansive spiral whose magnificent disk extends 140,000 light-years.
Next in size is our own Milky Way, with a disk spanning 100,000 light-years. The third spiral in the group,
M33 (sometimes called the Pinwheel Galaxy), measures 55,000 light- years across.
The Local Group's remaining members include irregular, elliptical, and dwarf elliptical galaxies, most of which are quite small. The two big guys on the block, Andromeda and the Milky Way, each have a retinue of satellite galaxies around them. Andromeda hosts ellipticals M32,
NGC 205, NGC 147, and NGC 185, and dwarfs Andromeda I, II, III, V, VI, and VII.
The Milky Way holds the Large and Small Magellanic Clouds, both irregulars, plus many dwarf galaxies. Prominent ones lie in a Carina, Draco, Fornax, Sagittarius, Sculptor,
LLI
| Sextans, and Ursa Minor.
O
| The 40 or so galaxies of the Local Group
originated about 13 billion years ago, when s? the first clumps of matter accreted into protogalaxies.
As these clumps compressed, stars formed and ignited their nuclear-fusion fires. When the first stars and clusters emerged from the billion-year-long Dark Ages that followed the Big Bang, the Local Group stretched only 600,000 light-years across. Being so close together, galaxies merged more often back then. Such mergers may have built the Milky Way out of as many as 100 protogalaxies.
This process continues: Our galaxy is in the process of shredding and devouring the Sagittarius Dwarf Spheroidal Galaxy, and it eventually will absorb the Magellanic Clouds. Several billion years from now, the Andromeda Galaxy and the Milky Way will collide in a dash of fireworks that ultimately will create a single, messy super-spiral.
Observing the Local Group's galaxies gives astronomers a microcosm — a laboratory close at hand that represents the universe at large. A substance astronomers call dark matter accounts for Vs of the universe's mass-energy, but, as yet, no one knows what the stuff is. Using a technique called gravitational lensing, astronomers have scoured the Milky Way's halo and ruled out several suspected candidates.
Likewise, astronomers also use the nearest galaxies to study where black holes form. What they've found in our galactic neighborhood matches up well with observations in more distant galaxies.EG

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