What is a Galactic halo?

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.