Osteopenia refers to bone density that is lower than normal peak density but not low enough to be classified as osteoporosis. Bone density is a measurement of how dense and strong the bones are. If your bone density is low compared to normal peak density, you are said to have osteopenia.steopenia refers to bone density that is lower than normal peak density but not low enough to be classified as osteoporosis. Bone density is a measurement of how dense and strong the bones are. If your bone density is low compared to normal peak density, you are said to have osteopenia.
The Milky Way is the second-largest galaxy in the Local Group, with its stellar disk approximately 100,000 ly (30 kpc) in diameter, and, on average, approximately 1,000 ly (0.3 kpc) thick.
Because of its great distance, we see the galaxy as it was just 700 million years after the Big Bang. At that time galaxies were small because they had yet to grow larger. All the galaxy's stars put together weigh only a billion times more than the Sun, a fraction of the Milky Way's stellar mass. But the galaxy is growing up fast. Its stars have already enriched it with heavy elements.