The existence of our Universe is dependent
upon interactions — from the tiniest sub-
atomic particles to the largest clusters of gal-
axies. At galactic scales, interactions can take
millions of years to unfold. This new image
released in December captures a moment
in the slow and intimate dance of a pair of
galaxies some 160 million light years distant
and reveals the sparkle of subsequent star
formation fueled by the pair’s interactions.
As in all galactic collisions, these galaxies are
engaged in a ghostly dance. Astronomers
have concluded that the two partners have
already “collided” at least once, though the
distances between the stars in each galaxy
preclude actual stellar collisions. Neverthe-
less, galactic collisions can be a lengthy pro-
cess of successive gravitational encounters,
with each galaxy’s gravity deforming the
other’s overall shape. Over time the galax-
ies can morph into exotic forms that bear no
resemblance as to how we see them today.
One by-product of the pair’s turbulent in-
teractions is that hydrogen gas coalesces
into regions of star formation. In this image,
these stellar nurseries appear as reddish
clumps scattered in a ring-like fashion in the
January 2020 / 2019 Year in Review
larger galaxy (and a few in the smaller gal-
axy). Also visible is a dusty ring seen in sil-
houette against the backdrop of the larger
galaxy. A similar ring structure appears in
this previous image from the Gemini Obser-
vatory, likely the result of another interact-
ing galaxy pair.
A well-known target for amateur astrono-
mers, the light from NGC 5394/5 first piqued
humanity’s interest in 1787, when William
Herschel used his giant 20-foot-long tele-
scope to discover the two galaxies in the
same year that he discovered two moons of
Uranus. Many stargazers today imagine the
two galaxies as a heron. In this interpreta-
tion, the larger galaxy is the bird’s body and
the smaller one is its head — with its beak
preying upon a fish-like background galaxy!
NGC 5394 and NGC 5395, also known col-
lectively as Arp 84 or the Heron Galaxy, are
interacting spiral galaxies 160 million light
years from Earth in the constellation of
Canes Venatici. The larger galaxy, NGC 5395,
is 140,000 light years across, and the smaller
one, NGC 5394, is 90,000 light years across.
See the full image release here.
GeminiFocus
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