How big are galaxies?
There are around 10 raise to the power 71, atoms and around 10 raise to the power 81, invisible mass forming dark matter in an average galaxy. Galaxies are found in large structures known as superclusters, which themselves are massive filaments with immense voids in between. Each galaxy contains trillion stars. The Eridanus Supervoid, with a diameter of 1 billion light years is about 10,000 times larger than the Milky Way (our own galaxy) and is considered the largest galaxy. In the visible part of the universe, there are about 100 billion galaxies.
The Milky Way has something between 200 to 400 billion stars most of which turn into black holes. If, for instance, a 100 billion individuals surround a star, there would be space enough for 1022 stars, which are more than all the sand grains collectively found on earth’s beaches. A light year is defined as the distance travelled by a ray of light in one year. Our galaxy, the Milky is 100,000 such light year in width and 1000 light years in thickness.
The Andromeda galaxy is about 220,000 light years, in width. A previous estimation suggested that the width was about 80,000 light years but it seems that the galaxy is fast growing in its proportions. The distance of Andromeda galaxy, from the Milky Way is around 2 million light years. Thus, it suggests that not only the galaxies are a huge cluster, they are getting bigger in no time. Thus, it would be awesome to imagine that there are around 100 billion galaxies!
The Milky Way is actually a galactic system (binary) which is gravitationally locked to Andromeda Galaxy, which is a sister galaxy. These two galaxies are members of a cluster of 35 galaxies, which is a Local Group. It is thought that the Milky Way is the second largest, the first one being Andromeda itself. Moreover, this Local group is a small part of ‘Virgo’ supercluster, which has a total number of 100 galaxies. All total, the local group measures 110 million light years in diameter.
Extra terrestrial evidence
Our galaxy is big enough. This argument is further strengthened by the theory that if it was small enough, extra-terrestrial bodies would have already discovered the earth and our universe. But this has not been the case. It is strongly felt that these space faring beings do exist, but either they have evolved recently or the galaxy is too big. The second theory seems more appropriate since nothing can testify their recent emergence. If they had to exist (and they do) then it had to be before earth took its form.
Thus we can conclude by saying that our galaxy is bigger than we can imagine it to be. Moreover, evidence from Andromeda suggests that galaxies can grow very fast and really at an astonishing rate. From the earth, the sun or the space consisting of all the 9 planets seems to be the biggest entities, but they are only a mere fraction of our galaxy.