The Andromeda Galaxy, Messier 31 or M31, is our closest spiral galaxy. The Andromeda Galaxy and the Milky Way is predicted to merge within the next five billion years. In the future, the number of stars in the Milky Way could match the number observed in the Andromeda Galaxy.
The universe is filled with galaxies which looks like enormous star cities – collections of up to a trillion (10 12 ) or more individual stars. Each galaxy belongs to a larger group, and our Milky Way belongs to the Local Group, which consists of the Andromeda Galaxy, the Triangulum Galaxy, and about 30 smaller galaxies.
The Andromeda Galaxy, Messier 31 or M31, is our closest spiral galaxy. The Andromeda Galaxy and the Milky Way is predicted to merge within the next 5 billion years. One unexpected possibility of the merger between the galaxies is that our Sun could switch galaxy and become bound to M31. It is an unlikely event, but whatever happens the galaxies are predicted to have their first close encounter within the next few billion years.
Andromeda is about 2.5 million light years away, but the gap between M31 and the Milky Way is closing at 500 000 km/hour. Calculating the mass of the Andromeda Galaxy is not easy, the error range is high since astronomers do not yet know how much dark matter the galaxy has. The M31 may be less massive than our own galaxy, despite the fact that it contains more stars than our galaxy and has a larger size. The Milky Way may have more dark matter.
The Andromeda appears to have more common stars than the Milky Way, and the estimated luminosity is double that of the Milky Way. There are bright and faint galaxies, and the luminosity is related to the number of stars in the galaxy. The more luminous galaxies are also more massive.
In the future, the number of stars in the Milky Way could match the number observed in the Andromeda Galaxy. The rate of star formation in the Milky Way is much higher. The Milky Way could be in the middle of a star formation phase, while the Andromeda has experienced a great star formation phase. In the future, billions of years from now, the Milky Way may look similar to the Andromeda Galaxy now.
The Andromeda is a spiral galaxy just like the Milky Way. A spiral galaxy consists of a flat rotating disc of stars, gas and dust. In the middle, there is a concentration of stars that are called the bulge. A spiral galaxy has winding arms that are rich in star formation. The arms are brighter than the surrounding disk because of the young and hot stars. Like the Milky Way, the spiral galaxy Andromeda revolves around the central bulge. Scientists believe this centre contains a massive black hole.
The Andromeda Galaxy has a giant ring, and it is possible that the galaxy will be changing into a ring galaxy. Ring galaxies are believed to be formed when a smaller galaxy passes through the centre of a larger galaxy. The intruding galaxy compresses the interstellar gas and dust and causes a wave of star formation. Young blue stars can be seen in the ring shape, indicating a star forming ring, as well as star forming regions further away from the galactic centre. When galaxies collide, their individual stars seldom come into contact. The galaxies pass through each other; however, the galaxies’ gravitational fields may be distorted by the collision.
The Andromeda Galaxy has a double nucleus. A few million densely packed stars are in each nucleus. Astronomers do not know why M31 has two nucleuses. One possible explanation is that the true centre of the galaxy has been divided. Another is that one cluster is the remnant of a galaxy cannibalised by M31. A galaxy can “eat” a smaller galaxy, which has intruded its core. Part of only one core could also be obscured by dark material.
One supernova explosion has so far been observed in the Andromeda Galaxy. The supernova, Supernova 1885 or S Andromedae, was the first one to be observed beyond our galaxy. In 1885, the supernova was observed. A supernova occurs at the end of a star’s lifetime, when the star’s nuclear fuel is exhausted. It is a violent explosive event.
The Andromeda Galaxy is bright enough to be seen without binoculars, it looks like a smudge of light to the naked eye in the constellation Andromeda. It is the most distant object you can see with the naked eye. If you use binoculars, you can clearly see the shape of the galaxy.