Shaped like a flat disk, it's about 100,000 light years in diameter, and about 10,000 light years thick. What is it?

The description of a celestial object shaped like a flat disk, approximately 100,000 light-years in diameter and about 10,000 light-years thick, accurately describes the Milky Way. This vast cosmic structure is a barred spiral galaxy, meaning it has a central bar-shaped structure composed of stars, from which spiral arms extend outwards. The "flat disk" appearance comes from the concentration of billions of stars, gas, and dust within these spiral arms. While the main disk is about 1,000 light-years thick, the central bulge is thicker, reaching around 10,000 light-years.

Our own solar system, including Earth, is situated within this immense galaxy. We reside in one of its spiral arms, specifically the Orion Arm or Orion Spur, located roughly 25,000 to 27,000 light-years away from the galactic center. The Milky Way is estimated to contain between 100 billion and 400 billion stars, with at least as many planets. At its very heart lies a supermassive black hole known as Sagittarius A*, which has a mass millions of times that of our Sun.

The Milky Way is not a static entity; it is constantly in motion. Our solar system, for instance, orbits the galactic center at an incredible speed, completing one full revolution approximately every 230 to 250 million years. Looking far into the future, the Milky Way is on a collision course with its nearest large galactic neighbor, the Andromeda galaxy. This monumental galactic collision is predicted to occur in about 4.5 billion years, eventually merging the two spiral galaxies into a single, larger elliptical galaxy. Despite the dramatic nature of such an event, the vast distances between stars mean that individual stellar collisions are highly improbable.