Two friendly galaxies, held in sinuous arms that are in fact corridors of stars and gas wrapped in stellar dust, where new stars are born, and planets, and — who knows — perhaps life.
The universe expresses its perfection in exactly these long corridors, which obey the strict mathematics of logarithmic spirals. And if that does not strike you as incredible enough: the universe has gone to the trouble of following one particular logarithmic series, the golden-ratio one of the Fibonacci numbers.
The question is: what we see, measure or calculate — is it the cause or the consequence of the shape of the universe?
A few curiosities
The Whirlpool Galaxy lies in Canes Venatici — the hounds Boötes holds on a leash, snapping at the legs of the Great Bear — and is listed in the Atlas of Peculiar Galaxies. It is between 23 and 32 million light years away and about 75,000 light years across, for some 160 billion solar masses.
It was the first galaxy in which a spiral structure was recognised: Lord Rosse did it in 1845, with a 180-centimetre telescope, when nobody yet knew that those "nebulae" were other island universes.
Its smaller companion, NGC 5195, has been badly deformed by the great whirlpool: which is why it has no canonical shape and is catalogued as lenticular, amorphous or irregular. It is not an innocent encounter — its gravity compresses the gas of M51 and sets its arms alight, which is why they are studded with pink regions, hydrogen clouds where stars are being born en masse. It is the textbook example of how collisions between galaxies, far from rare, are one of the engines of star formation in the universe.
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