M81 and M82. Photo: Dietmar Hager and Torsten Grossmann.
M81, M82 and NGC 3077 in radio waves.
Radio waves are shown as blue. Read about it here.
I always think of M81 and M82 as two members of a galactic triplet, which includes galaxy NGC 3077. The picture at right shows how the three galaxies are connected with streams of neutral hydrogen.
You can really see how the tidal forces between M81 and NGC 3077 (far left) help create the sleek, two-armed spiral shape of M81.
M81 and the famous Whirlpool galaxy, M51, are both grand design galaxies, which is to say that they have two all-dominant spiral arms. Interestingly, it is probable that they got their grand design spiral shapes by interacting with other galaxies, M51 with NGC 5195, and M82 with both NGC 3077 and M82.
Note how different M81 and M51 are as spiral galaxies. The arms of M51 are long, thick, bright, convoluted and full of star formation, while the arms of M81 are short, rather thin, sleek, not so bright and not very rich in star formation. Also note that M51 has a small yellow bulge, whereas the bulge of M81 is really large. But a similarity between these two galaxies is that both are unbarred.
No Hα filter was used for the Hubble image of M81, so the red emission nebulas of M81 don't stand out. They are however much smaller and fewer than the emission nebulas of M51. Check out a Hubble closeup of a part of M81 here
Finally, let's take a look at the too rarely photographed galaxy NGC 3077, which interacts with M81 and helps give it its grand design shape. Outwardly, NGC 3077 looks like a typical all yellow dwarf elliptical galaxy. But it's got a fiery heart, burning blue from raging star formation.
There are some interesting similarities between NGC 3077 and M82, the famous "red-gas-spitting" neighboring galaxy of M81
. Both M82 and NGC 3077 have stopped forming stars almost everywhere except in their cores, which, however, are ablaze with brilliant star formation. Clearly interactions with M81 have forced almost all the gas of NGC 3077 and M82 into the cores of these two galaxies, causing a wildfire of star formation there.
Call the fire brigade!
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