A galaxy is the collection of stars, stellar remnants, gases, dust and dark matter all bound together by gravity. The Earth, the planet in which we live, is in a galaxy called ‘The Milky Way’. Galaxies are of various shapes and sizes. A galaxy which has stars ranging from a hundred million to few billion is called a dwarf galaxy. These galaxies are small as compared to other galaxies. Scientists confirm that the Milky Way galaxy has about four hundred billion stars. The IC 1101 is a super-giant galaxy, which has about hundred trillion stars. These stars orbit around the galaxy’s center of mass, which are thought be massive black holes. A galaxy can be elliptical (ellipse shaped), spiral (disk shaped with arms) or irregular in shape. The Milky Way galaxy is spiral shaped.
The size of a galaxy ranges from 1,000 to 1, 00,000 parsecs in diameter and are separated by millions of parsecs from each other. The Milky Way galaxy is thirty thousand parsecs in diameter. 1 parsec is approximately equal to 31 trillion kilometers. The spaces between galaxies are filled with gases. All the galaxies identified by man are organized into groups, cluster and superclusters.
If you like watching stars at night, you are looking at the stars that belong to the Milky Way galaxy. On dark, cloudless nights especially in the northern hemisphere, you can see bands of the Milky Way galaxy stretch across the sky.
Galaxies are constantly moving, at nearly 600 – 850 kilometers per second. Some are moving away from each other, which in turn mean that they are moving towards other galaxies. The Milky Way galaxy will also collide with other galaxies, but since they are trillions of kilometers apart from the nearest galaxy, this will not happen in the near future.
Astronomers observe galaxies or any heavenly bodies by the use of a very powerful telescope, in observatories. The Hubble telescope is a power space telescope which constantly observes the universe for new discoveries.
Every galaxy has its own magnetic field. They are strong enough to drive mass inflow into the centers of galaxies. They can modify the spiral arm formation of spiral shaped galaxies. Magnetic fields are highly in formation of new stars, as they provide for angular momentum required for collapsing gas clouds.
Spiral galaxies produce new generations of stars, as they have dense molecular clouds of interstellar hydrogen in their spiral arms. Star forming materials are not available in abundance, so once a star is formed, the available supply of hydrogen is reduced and formation is new stars must wait until the level of hydrogen is increased. There is something called as a dark galaxy. These are hypothesized galaxies with none or very few stars. Dragonfly 44 is an ultra-diffuse galaxy with has the same mass of the Milky Way galaxy but with nearly no discernable stars and is completely made of dark matter.
Scientists tell that the universe is constantly expanding; this is hard to observe during one’s lifetime, as it takes millions of years to do so. Hence constant research must made and passed down to future scientists.