What is a Galactic halo?
- Galactic halo is a nearly spherical volume of thinly scattered stars, globular clusters of stars, and tenuous gas observed surrounding spiral galaxies, including the Milky Way.
- Galactic halo is dominated by invisible dark matter, whose presence is only measurable through the gravity that it exerts.
- Only about 1% of a galaxy’s stellar mass resides in its halo, and due to this low luminosity, the observation of halos in other galaxies is extremely difficult.
What is Stellar halo?
- It is the visible portion of a galactic halo.
- It is composed of globular clusters and field stars which have high space velocities that can take them far out of the galactic disk.
- Stellar halos may hold some of the best preserved fossils of the formation history of galaxies.
What are Globular clusters?
- They are stable, tightly bound clusters of tens of thousands to millions of stars.
- They are associated with all types of galaxies.
- They are more densely populated, with populations ranging from tens of thousands to millions of stars.
- The intense gravitational attraction between the closely packed stars gives globular clusters their regular, spherical shape.
What is meant by a field star?
- Stars that are not connected with an astronomical object being studied but which happen to appear in the same field of view when the object is observed through a telescope. Typical examples of field stars are those that appear in the foreground of a telescopic image of a distant galaxy.
- A field star is not part of any stellar cluster such as a globular cluster or open cluster.
