|Spiral galaxy NGC 4651 is a mere 35 million light-years distant,
toward the well-groomed constellation
About 50 thousand light-years across, this galaxy is seen to have
a faint umbrella-shaped structure (right) that
seems to extend some 50 thousand light-years farther,
beyond the bright galactic disk.
giant cosmic umbrella is now known to be composed of
tidal star streams.
The streams themselves are
extensive trails of stars
from a smaller satellite galaxy that was eventually
Recent work by a remarkable collaboration of amateur and professional
astronomers to image faint structures around bright galaxies suggests that even in nearby galaxies, such tidal star streams are common. The result is predicted by models of galaxy formation, including the formation of our Milky Way.
R Jay Gabany
David Martinez-Delgado (MPIA, IAC), et al.