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ANSWER:

Galaxies are sprawling systems of dust, gas, dark matter, and anywhere from a million to a trillion stars that are held together by gravity. Nearly all large galaxies are thought to also contain supermassive black holes at their centers. In our own galaxy, the Milky Way, the sun is just one of about 100 to 400 billion stars that spin around Sagittarius A*, a supermassive black hole that contains as much mass as four million suns.

TYPES OF GALAXIES:

(Galactic clusters)

-In 1936, Hubble debuted a way to classify galaxies, grouping them into four main types: spiral galaxies, lenticular galaxies, elliptical galaxies, and irregular galaxies.

(Mergers)

-Theoretical models also suggest that in the early universe, vast tendrils of dark matter provided normal matter the gravitational scaffold it needed to coalesce into the first galaxies.

(Supercluster)

-Some galaxies occur alone or in pairs, but they are more often parts of larger associations known as groups, clusters, and superclusters.

(Supermassive)

-Galaxies are sprawling systems of dust, gas, dark matter, and anywhere from a million to a trillion stars that are held together by gravity. Nearly all large galaxies are thought to also contain supermassive black holes at their centers. In our own galaxy, the Milky Way, the sun is just one of about 100 to 400 billion stars that spin around Sagittarius A*, a supermassive black hole that contains as much mass as four million suns.

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