Astronomy: Galactic left-overs

Journal name:
Nature Physics
6 ,
Year published:

This is Messier 63, also known as the sunflower galaxy. First observed in 1779, by the mid 1800s its spiral structure had been resolved, making it one of the first spiral galaxies identified. This image — positive at the centre, negative around the edges, and published by David Martínez-Delgado and colleagues in the Astronomical Journal (doi:10.1088/0004-6256/140/4/962; 2010) — shows fresh detail in the galaxy's outermost regions, revealing wispy tendrils that are all that remain of another satellite galaxy, swallowed up by M63.


Similar evidence of galactic guzzling had been seen for the three spiral galaxies that are members of the 'local group' of nearby galaxies (which includes the Milky Way). But Martínez-Delgado et al. have probed deeper into space, building a wider sample of galaxies that are up to 50 million light years away.

Their data support current thinking on galaxy evolution, particularly on the likely chain of events when a dwarf galaxy has the misfortune to get too close to a spiral giant: typically, the uneven gravitational pull of the larger galaxy disrupts the smaller one, dragging its stars into a tidal stream that will eventually — over billions of years — be completely assimilated.

The team collected the data using small-aperture, robotic telescopes at privately run observatories in the USA and Australia, and are already extending their survey to enable more quantitative tests of galaxy-evolution models.

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