History of the Universe eBook. 398 pages, 300 illustrations only $2.99
Looking from above the of a spiral galaxy (like the where we live) a new picture appears. We can see dense spiral arms in the disc of the Galaxy. We think it is gravity which created the spiral pattern, although the details are not clear. The spiral arms are places where the of the disc is squashed together.
Note that we can never see our own Galaxy from outside, since we are embedded within it and it would take millions of years to travel out of it. Thus we are not sure what our Galaxy looks like, but we think it is probably a typical barred spiral galaxy, so-called because it has a small bar across the center, perhaps similar to the one shown in the next image.
Image of barred spiral galaxy NGC 6217 from NASA, ESA, and the Hubble SM4 ERO Team
The disc of our Galaxy measures about 100,000 across and 1000 light-years thick.
New and important stars form in these spiral arms.
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