The Milky Way
The Milky Way is the galaxy in which we, our sun and the solarsystem reside. Most of the times our galaxy is just referred to as "the galaxy", but the name was originally meant to describe the vast and fuzzy band of stars which spans a substantial part of our night sky.
can easily be seen on a dark night and is a marvellous sight, especially when viewed through a pair of binoculars.
The Milky Way is a spiral galaxy with a mass of 1012 suns, each weighing 1030 kg. It is thought to have a barred core (which is about 25 000 light years long) of the SBb type (since we are located inside the galaxy, we cannot actually see the whole galaxy, but this SBb type has been inferred from observations). It spans about 100 000 light years of space and the sun is located about 25 000 light years from the center,
which is in the direction of the constellation Sagittarius from earth. In the center a supermassive black hole resides, weighing in at about 3 million solar masses.
The distance 25 000 ly indicates that the sun takes about 250 million years to orbit the galactic core. Since the sun and the earth was born, the solar system has orbited the galactic center about 18 times.
The Spiral Arms
Research has shown that the Milky Way has two main arms that are connected to the central bar. They are known as the Perseus and the Scutum - Centaurus arm. These two arms are in turn split into two each.
The arm "inside" the Perseus arm is the Sagittarius arm, and the arm located inside the Scutum-Centaurus arm is the Norma arm. Our sun is located in the Orion arm, which is a small fragment of an arm. It is located between the Sagittarius and the Perseus arm.
Another arm, located outside the Perseus arm is the Outer arm. Finally, on each side of the barred core, there is a small arm called the Near 3 kpc arm and the Far 3 kpc arm, both named after their distance to the center: 3 kiloparsec (1 parsec 3.26 light years), or 10 000 light years.
The speed (210-250 km/s) which the stars orbit the galactic center is surprisingly not in proportion to the mass of the galaxy. This indicates that there is substantial amount of dark matter in the galaxy, which exerts its' influence.
Back to top.
To this date, the Milky Way is known to have atleast 14 satellite galaxies which orbit it from various distances. The most famous are of course the Large and the Small Magellanic Cloud, named after their discoverer, the famous sailor Fernando Magellan. Located at about 160 000 and 190 000 ly respectively, both are irregular galaxies, like many of the satellites. Other satellites have the shapes of ellipses, but are dwarfs.
Back to top.
The Local Group
The Milky Way is part of a galactic cluster called The Local Group, which was named by Edwin Hubble. The cluster consists of atleast 30 known galaxies of which our own Milky Way and the Andromeda Galaxy are members of. The Local Group spans about 10 million light years and is a part of an even larger cluster: The Virgo Supercluster.
This supercluster spans about 110 million light years and is made up of atleast 100 clusters. The Virgo Supercluster is just one of millions of superclusters in the known universe!
Back to top.
As mention on the Formation of Galaxies page, the Milky Way and the Andromeda Galaxy are going to collide with each other (and merge into one large galaxy) in about 3 billion years, according to current theories. Such collisions are common in the universe and is a natural part of some galaxies' evolution.
The Andromeda galaxy and the Milky Way are approaching each other at a speed of 120 km/s and when the galaxies do collide, the chances of collision between individual stars are very, very slim. What will happen is that the gas in both galaxies will collide and thus create new stars. The supermassive black holes located in each of the galactic centers may also collide to make one even larger
black hole. This black hole may even become active again.
Back to top.
Previous: Active Galactic Nuclei.
Above: An illustration of the future collision between the Andromeda galaxy and The Milky Way galaxy.
This illustration is available upon request, as a print (5000x3000 pixels, 300 dpi), and as a PSD-document so that it can be customized according to your own desire.
Above: This painting features the barred nature of the Milky Way galaxy's core. Notice the HII-regions that are part of the ring around the center, which resembles a wreath.