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.
These twisted galaxies range from a billion to a trillion times as massive as the sun. The visible disk can be anywhere from 10 to 300 thousand light-years across. The largest known spiral galaxy is NGC 6872, which is 522,000 light-years across from the tips of its outstretched spiral arms, about 5 times the size of the Milky Way. In the early universe, galaxies frequently collided and interacted with one another, so the spiral shape of these ancient giants would have been quickly disrupted.