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The galaxy's disk is a fundamental component of many galaxies, including our own Milky Way. Imagine the disk as a giant, flat, pancake-like structure that spins through space. Within this disk, we find a rich mixture of stars, gas, and dust.

This structure is particularly vibrant as it hosts regions of active star formation. Most notably, these regions appear as majestic spiral arms threading through the disk. The spiral arms are packed with young and hot stars, nebulae, and star clusters. These stars shine brightly and come to life relatively close to our cosmic backyard where new stars are continuously born.

Key features of the galaxy's disk include:

• Flattened, rotating shape.
• Presence of spiral arms filled with young stars and nebulas.
• Active regions of star formation.

Sitting just beyond the disk is the galaxy's halo. While it's not easily visible, this part of the galaxy is vast and ethereal. The halo is like a giant, spherical cushion encompassing the disk and extends far out into space.

The galaxy's halo is much less dense than the disk and is populated by older stars and globular clusters. These are clusters of stars that move together through the galaxy in a manner distinct from the younger, ferociously burning stars we observe in the disk. The halo also includes some faint interstellar gas, providing a faint, ghostly light.

Characteristics of the galaxy's halo:

• Spherical and diffuse structure.
• Contains older stars and globular clusters.
• Extends beyond the visible parts of the galaxy.

Dark matter remains one of the universe's greatest mysteries. It doesn’t shine or absorb light like regular matter, which makes it completely invisible to telescopes. We know dark matter exists because of its gravitational effects on objects we can see, like stars and galaxies. It affects the rotation speeds of galaxies, including our Milky Way, particularly at the edges.

Dark matter forms a massive, invisible halo enveloping galaxies. This halo is far more extensive than the galaxy's visible boundaries, significantly impacting how galaxies rotate. Without dark matter, the outer regions of galaxies would rotate far slower than observed.

Some essential facts about dark matter include:

• Invisible to all forms of electromagnetic radiation (light).
• Detected through gravitational effects on visible matter.
• Constitutes a large part of the galaxy's halo.