The Pinwheel Galaxy, also known as M101, is estimated to be about 200 million years old.
This age is based on the understanding of the galaxy’s formation and its characteristics. Being a spiral galaxy, M101 has gone through a long process of evolution, with the current structures, like its beautiful spiral arms, shaped by gravitational interactions and star formation over millions of years.
When we say that the Pinwheel Galaxy is around 200 million years old, we are primarily referring to the age of its current spiral structure and the stars within it. However, the interstellar medium and the underlying dark matter that contributes to its mass and shape have existed far longer, dating back to the early universe.
In summary, while the Pinwheel Galaxy has matured into its current form over the last 200 million years, the materials that constitute the galaxy are much older, stretching back to the era of the universe’s formation.