Our galaxy also contain a number of elements that are not found in the disk or the central bulge, they're given the collective name of spherical components. The spherical components of our galaxy make up an area called the halo which extends evenly in all directions from the centre of the galaxy. The Milky Way galaxy has many satellite companions mainly clusters of stars, some in the form of dense globular cluster(as shown below) with a million tightly packed stars. These globular clusters orbit the centre of the galaxy in polar orbits and move through the plane of the disk or galactic centre; however most of their time is spent in the halo away form the disk. If our Sun was in a globular cluster the night sky would be lit up with at least five times as many stars with many twenty times as bright as the stars we see.
The stars in the halo and globular clusters are generally very old, some as old as 12 billion years. The age of a globular clusters can give us an estimate of the age of the galaxy itself.
The above picture from the Hubble Space Telescope shows a globular cluster. Nearly 100 such clusters of stars are found around the Milky Way.
There is a great puzzle about the galaxy. Calculations of the mass of our Milky Way galaxy from the mass that is needed to gravitationally attract the outer parts of the of the Milky Way galaxy and keep them spinning around the centre gives a figure for the mass of the galaxy that is much greater than all the matter that we can find in our galaxy including the black hole at the centre. There must be a lot more matter than we can see; About fifty times as much. Looking at the rate that the inner parts of the galaxy rotate tells us that this matter must be distributed throughout the galaxy halo and in an expanded spherical halo. As this matter is invisible, it is often referred to as dark matter.
Hubble Space Telescope image of two overlapping Galaxies, that although millions of miles apart appear in the same alignment with Earth. This image allows us the unique chance to see some of the dust and other components that would normally not be visible. In this image they are silhouetted against its companion.