74 ASTRONOMY • FEBRUARY 2018
A galactic
dogfight
A burst of star formation
wracks the Cocoon Galaxy
(NGC 4490). High-energy
radiation from these new
suns excites the clouds of
hydrogen surrounding
them to glow with a
characteristic pinkish hue.
A collision between the
Cocoon and its neighbor,
NGC 4485 (which lies
out of this Hubble Space
Telescope image), sparked
the starburst. The galaxies
already have passed
through each other and
are now separating. But
gravity’s pull is relentless
— eventually the couple
will collide again and
ultimately merge. The two
lie about 25 million light-
years from Earth in Canes
Venatici the Hunting
Dogs. ESA/HUBBLE AND NASABREAK
THROUGH