Question

Describe the galactic bulge in terms of its shape, size(diameter, thickness), the amount of gas and dust, the types of stars (age, colors), the motion of the stars, and the state of any star formation.

Answer 1

Galactic bulge:

• A galactic bulge is the central region of a galaxy, a swollen structure, which is a tightly packed region of stars and interstellar medium. It resembles the shape of a spheroid and is sometimes bar shaped.

• Their diameter span from several hundred to several tens of thousands of light years, and their thickness spans from few hundred light years depending on the type and size of the galaxy.

• Most of the bulges host a supermassive black hole in their centre. Galactic bulges have a huge number of Population II stars that are old, and hence a reddish hue is observed. They even have some Population I young and intermediate aged stars.

• The motion of these stars is dependent on its chemical composition i.e. its metallicity and hence have orbits random in nature.

• The amount of gas and dust is about only 4-7% of the whole galaxy. The lack of gases and dust makes the bulges to have very less star formation.