Galaxies
A galaxy is a huge group of single stars, star
systems, star clusters, dust, and gas. Bound together by only gravity, many
galaxies appear to have black holes – objects/ with a gravitational
pull so strong that even light cannot escape it – at their center. Billions of galaxies exist in the universe, and each galaxy contains
billions of stars. Galaxies still appear to group into clusters –
our galaxy, the Milky Way, is part of a cluster of galaxies called the Local
Group, which is part of the Virgo Supercluster, a group that contains hundreds
of galaxies.
Quasars
In the 1960s, astronomers discovered star-like objects that
were very bright, yet very distant.
Naming these objects quasars, astronomers concluded that these objects
were over 10 million light years away,
and some of the most distant objects in the universe. They believed that
quasars are young galaxies, with massive black holes in their centers. As gas
drifts towards the black hole, the gas heats and shines incandescently.
Types of Galaxies:
There are three main types of galaxies: Spiral, Elliptical, and Irregular
Spiral Galaxies
![Picture](/uploads/2/8/6/3/28635231/600874250.jpg?358)
Spiral galaxies contain a bulge in the middle and arms that spiral outwards. The spiral arms are composed of many bright, young stars, and gas and dust. The higher density in the arms causes new stars to form in the spiral arms.
Some spiral galaxies contained a huge bar-shaped region of stars, dust, ad gas that passes through their center. These galaxies are called barred-spiral galaxies, and their arms extend outward from the bar rather than from the bulge.
The Milky Way (left) is an example of a barred-spiral galaxy, with a central bulge with a bar crossing through it, and spiral arms that extend outward from the bar.
Some spiral galaxies contained a huge bar-shaped region of stars, dust, ad gas that passes through their center. These galaxies are called barred-spiral galaxies, and their arms extend outward from the bar rather than from the bulge.
The Milky Way (left) is an example of a barred-spiral galaxy, with a central bulge with a bar crossing through it, and spiral arms that extend outward from the bar.
Elliptical Galaxies
![Picture](/uploads/2/8/6/3/28635231/781218751.jpg?264)
Elliptical galaxies, however, are rounded, like balls, or elliptical, like eggs, These galaxies have billions of stars within them, but very little gas and dust between them. Because there is little gas and dust, stars can no longer form. Therefore, elliptical galaxies contain mostly old stars. Maffei 1 is an example of an elliptical galaxy.
Irregular galaxies
![Center](/uploads/2/8/6/3/28635231/180697715.jpg?317)
Unlike elliptical and spiral galaxies, some galaxies have no regular shape. These galaxies are called irregular galaxies. Typically smaller than other types of galaxies, irregular galaxies generally have many bright, young stars and lots of gas and dust, which make it easy to form new stars. Also, irregular galaxies are often situated close to other galaxies, and the gravitational pull of these galaxies can distort the shape of the irregular galaxies. An example of an irregular galaxy is the Large Magellanic Cloud, about 180,000 light years away.
The Milky way
Our solar system is located in the Milky Way galaxy. The Milky Way, as mentioned above, is a barred-spiral galaxy, and our solar system is located on one of the spiral arms, about 25,000 light years away from the center. The Milky Way is approximately 100,000 light years in diameter.