Astronomers have recently detected in the stellar halo that represents the Milky Way’s outer limits a group of stars more distant from Earth than any known within our own galaxy – almost halfway to a neighboring galaxy.

 

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.