The biggest galaxy in the Leo Triplet swaggers in the constellation of Leo, in this new image from the Hubble Space Telescope. Notice those assymetrical arms, which come from a powerful attraction to two neighboring galaxies.
Messier 66 is about 100,000 light years across, much bigger than the other galaxies in the Leo Triplet. According to NASA and the European Space Agency:
Messier 66 is the proud owner of exclusive asymmetric spiral arms which seem to climb above the galaxy's main disc and an apparently displaced nucleus. This asymmetry is unusual; most often, dense waves of gas, dust and newly born stars wind about the galaxy's centre in a symmetric way. Astronomers believe that Messier 66's once orderly shape has most likely been distorted by the gravitational pull of its two neighbours.
Hubble has imaged Messier 66's striking dust lanes and bright star clusters along the spiral arms in fine detail with the Advanced Camera for Surveys. Star clusters - pictured in the blue and pinkish regions of the image - are key tools for astronomers since they are used as indicators of how the parent galaxies assembled over time.
Messier 66 boasts a remarkable record of supernovae explosions. The spiral galaxy has hosted three supernovae since 1989, the latest one occurring in 2009. A supernova is a stellar explosion that may momentarily outshine its entire host galaxy. It then fades away over a period lasting several weeks or months. During its very short life the supernova radiates as much energy as the Sun would radiate over a period of about 10 billion years.
And here's a cool-looking image of the whole triplet: