The Pinwheel Galaxy is a face-on spiral galaxy distanced 21 million light-years away in the constellation Ursa Major. It is a relatively large galaxy compared to the Milky Way. With a diameter of 170,000 light-years it is seventy percent larger than the Milky Way. It has a disk mass on the order of 100 billion solar masses, along with a small bulge of about 3 billion solar masses
On photographs M101 can be seen to be asymmetrical on one side. It is thought that in the recent past (speaking in galactic terms) M101 underwent a near collision with another galaxy and the associated gravitational tidal forces caused the asymmetry.
In addition, this encounter also amplified the density waves in the spiral arms of M101. The amplification of these waves leads to the compression of the interstellar hydrogen gas, which then triggers strong star formation activity. Much like the Orion Nebula in our own galaxy the Milky way.
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| 420min F800mm at F6.5 exposure with a DSLR |