What is the difference between the Galactic bulge and disk What are the main differences in stellar populations there and why do those differences exist?

The disk population inhabits the rotating, flattened region of our Galaxy. The disk contains all the gas and young stars, although old stars are also found there. The bulge is dominated by old stars and a violent core. The halo contains very old stars and globular clusters.

Which of these galactic objects are only or mostly found in the disk or spiral arms?

Type II supernovae will only be found in the disk (especially in the spiral arms and galactic bulge). The reason for this is that Type II supernovae are the result of the explosion of massive stars and that massive stars only live for very short periods of time.

What types of stars are found in spiral galaxies?

The bulge of a spiral galaxy is composed primarily of old, red stars.

What is the density wave theory for spiral arm galaxies?

One of the more successful models developed to explain the origin of spiral arms in galaxies is the density wave model. In this model, spiral arms are regions of the thin disk that are denser than average, and move around the galaxy more slowly than the individual stars and interstellar material.

How many stars does the galactic bulge have?

There are around 10 million stars within one parsec of the Galactic Center, dominated by red giants, with a significant population of massive supergiants and Wolf-Rayet stars from star formation in the region around 1 million years ago. The core stars are a small part within the much wider galactic bulge.

Why do older stars have less metal?

Older stars generally have lower metallicity because they formed when the universe was younger and less metal rich. Old stars are also typically lower mass, because the high mass ones already evolved to end of life.

Why are high mass stars only seen in spiral arms?

Stars are found with equal density everywhere in the disk. Young type O and B stars, however, are only found in the spiral shaped arms. Type O stars are about 10,000 times more luminous than the Sun, so the light from these stars dominates the picture of a spiral galaxy, making it look like a spiral.

Do galaxies evolve from one type to another?

Alas, normal galaxies do not likely evolve directly from one type to another. Spirals don’t seem to be ellipticals with arms, nor do ellipticals appear to be spirals without arms. The answer for astronomical galaxies, as for biological life, is probably both.

How many arms can a spiral galaxy have?

But most spiral galaxies have only two to four main arms. Spiral arms show the same structure whether composed of billion-year-old stars or million-year-old stars. This indicates that the arms are the result of a persistent pattern of stars rather than particular stars causing the structures.

What causes spiral density waves?

The first is that spiral arms are really indications of density waves (slowly moving regions of higher density) in the disk of the galaxy. The second is that the spiral structure is generated by self-sustaining star formation, coupled with the differential rotation of the galaxy.

Why are spiral arms brighter than the rest of the Galaxy?

More young stars in spiral arms. Spiral arms appear visually brighter because they contain both young stars and more massive and luminous stars than the rest of the galaxy. As massive stars evolve far more quickly, their demise tends to leave a darker background of fainter stars immediately behind the density waves.

What are the characteristics of a star-bearing Galaxy?

A flat, rotating disc of stars and interstellar matter of which spiral arms are prominent components A central stellar bulge of mainly older stars, which resembles an elliptical galaxy A bar-shaped distribution of stars A near-spherical halo of stars, including many in globular clusters

What type of stars make up the bulge of a galaxy?

Using the Hubble classification, the bulge of Sa galaxies is usually composed of Population II stars, which are old, red stars with low metal content. Further, the bulge of Sa and SBa galaxies tends to be large. In contrast, the bulges of Sc and SBc galaxies are much smaller and are composed of young, blue Population I stars.

Where are the Stars in a spiral galaxy located?

The bulk of the stars in a spiral galaxy are located either close to a single plane (the galactic plane) in more or less conventional circular orbits around the center of the galaxy (the Galactic Center), or in a spheroidal galactic bulge around the galactic core.