The Pinwheel Galaxy and What's Inside

Spring is Galaxy season. This year I decided to start an imaging project that would reveal (hopefully) some of the non-stellar objects inside of the brighter galaxies. There was no better place to start than Messier 101, the Pinwheel Galaxy. 

This galaxy is in Ursa Major. It is a lovely face on spiral galaxy. I count 4 spiral arms, with one on the left being somewhat distorted and stretched. This is most likely due to tidal affects from a close encounter with another galaxy, but more on that later.

M101 lies about 21 million light years from us. To put that in perspective, the Andromeda galaxy is about 2 million lightyears away. M101's diameter is about 200,000 lightyears, twice that of our own galaxy and it has about 4 times the number of stars as our own galaxy. 

A strange thing about M101 is that it does not have a single massive central black hole like most spirals but has several 3 - 30 solar mass black holes. Our own galaxy has a central black hole of well over 4 million solar masses.

Face on spiral galaxies like M101 make ideal targets for astrophotography and allow us to examine the structure more closely. The image above was transformed into a black and white image and then inverted. This gives a high contrast image below that makes it easier to spot some of the structures. 

You can see "clumps" within the spiral arms. These are hydrogen II regions, areas where the interstellar hydrogen gas is reflecting light of massive young stars, forming reflection nebulas similar to our own Orion Nebula, pictured here. 

The large HII regions are an indication that there is a lot of star formation occurring. Why so much? The clue is that arm on the left of the image above, seems to be stretched out and separated from the other arms. This is a result of an interaction with a nearby galaxy, most probably NGC 5477, the galaxy identified by the red cross on the far left. This galaxy is actually a dwarf galaxy, meaning that most of its stellar mass has been stripped off, most likely by M101. The gravitation interaction by these two galaxies has resulted in the collapse of gas within M101 to form new stars.

M101 is great object both visually and photographically. Many of the HII regions can be visually identified through telescopes of 8" apertures. The M101 image above is about 2 hours of 30 sec sub exposures taken through an Astro Tech 80mm telescope with a ZWO533 MC Pro from a Bortle 4.5 sky. 

Next up will be a spiral galaxy in Coma Berenices, NGC 4559.

Clear skies!