Key Facts and Comparison of Milky Way and Andromeda Galaxies

The Milky Way is the galaxy we live in. It contains the Sun and 100 to 500 billion other stars. It is a barred spiral galaxy as grouped in the Hubble tuning fork diagram. It is located at the  outskirts of the Virgo supercluster. The centre of the Virgo cluster is about 50 million light-years away from Milky Way.

Basic Features of Milkyway

Location of Earth in Milky Way

Earth orbits the Sun, which is situated in the Orion Arm, one of the Milky Way’s spiral arms. Earth and the Sun are about 25,000 light-years away from the galactic center.

Size of Milky Way

The Stellar disk of the Milky Way is about 100,000 light-years across and 1,000 light-years thick. Based on current measurements, at least 90 percent of the mass in the Milky Way’s gravitational field is made up of dark matter, so the luminous stars, gas, and dust of the galaxy are embedded at the center of a huge, roughly spherical dark matter halo more than a million light-years across.

Blackhole at centre of milky way

There is an object at the center of the Milky Way called Sag-A* (Sagittarius A-star) which emits much more X-rays and radio waves than expected for a star-sized body.

After mapping the motions of stars near Sag A* for more than a decade, astronomers concluded that Sag A* is an invisible object that is more than three million times the mass of the Sun. This is a super massive black hole.

Movement of Earth within the Milky Way Galaxy

Earth (and the solar system) is moving through the Milky Way’s disk in a stable, roughly circular orbit around the galactic center. Our orbital velocity around the center of the Milky Way is about 200 kilometers per second. Even so, the Milky Way is so huge that one complete orbit takes about 250 million years.

Can we see the whole Milky Way?

Much of the galaxy is blocked from our view on Earth  due to the barriers created by dusty gas clouds blocking much of the light. Using infrared, microwave, and radio astronomy techniques, it is possible to penetrate much of this dusty fog. However, that too allows us only detect only half of stars and gas.

Neighbours of Milky Way

Milky way galaxy is one of the 54 galaxies in the “Local Group” of galaxies. The Local group itself is a part of a larger group called Virgo Supercluster. Virgo super cluster itself is a part of Laniakea Supercluster.

Within the local group, three largest galaxies viz. Milky Way, Andromeda and Triangulum have their own system of satellite small galaxies and clouds. For example, the satellite galaxies of Milky way include Sagittarius Dwarf Galaxy, Large Magellanic Cloud, Small Magellanic Cloud, Canis Major Dwarf, Ursa Minor Dwarf etc. Some of those galaxies, such as the Sagittarius dwarf galaxy, are almost in physical contact with the Milky Way’s outskirts.

The Andromeda Galaxy (aka. M31) is the closest large galaxy to the Milky Way. It can be seen from earth with naked eyes. This galaxy is considered to be slightly larger than Milky way and largest galaxy of the local group.

Important Facts About Andromeda

• In the local cluster, the Andromeda is largest galaxy but may not be most massive. It is thought that Milky way has indeed more dark matter which makes is more massive.
• Andromeda is nearest spiral galaxy from milky way. Both Andromeda and Milky way are approaching each other and it is thought that 4.5 billion years from this time, the Andromeda Galaxy and the Milky Way would collide and would form a giant elliptical galaxy.

Similarities between Andromeda and Milky Way

Both milkyway and Andromeda are spiral galaxies, both appear to be of same age and both have similar objects including a massive blackhole at the center. However, Andromeda is known to have a crowded double nucleus and its spiral arms are getting distorted by gravitational interactions with two satellite galaxies viz. M32 and M110.

Radio Galaxies

Radio galaxies are those ordinary-looking elliptical galaxies in which the radio wave emission far exceeds that of the galaxy’s visible light emission.

Large / Small Magellanic Clouds

The Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC)  are two dwarf galaxies that are satellite galaxies of Milky way and orbit around Milkyway. Both of them are irregular galaxies. Both of them have forming stars at much faster rates than milkyway and so are important for the astronomers studying the formation and aging of stars and galaxies.

Interstellar medium

The interstellar medium is the matter that exists within, between and among the galaxies. Almost all of the interstellar medium is comprised of gas and microscopic dust particles.

Its density is very less, for example, interstellar medium in our region of the Milky Way galaxy has a density of about one atom of gas per cubic centimetre. By contrast, Earth’s atmosphere at sea level contains about 1019 gas molecules per cubic centimeter.