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his composite image, created out of two different pointings from Hubble,
shows the barred spiral galaxy NGC 1512 (left, previous page) and the dwarf
galaxy NGC 1510 (right). Both galaxies are about 30 million light-years away
from Earth and currently in the process of merging. At the end of this process
NGC 1512 will have cannibalised its smaller companion. [ESA/Hubble, NASA]
ances. The bar in NGC 1512 acts as a
cosmic funnel, channelling the raw
materials required for star formation
from the outer ring into the heart of
the galaxy. This pipeline of gas and
dust in NGC 1512 fuels intense star
birth in the bright, blue, shimmering
inner disc known as a circumnuclear
starburst ring, which spans 2400 light-
years. Both the bar and the starburst
ring are thought to be at least in part
the result of the cosmic scuffle be-
tween the two galaxies — a merger
that has been going on for 400 mil-
lion years. NGC 1512, which has been
observed by Hubble in the past, is also
home to a second, more serene, star-
forming region in its outer ring. This
ring is dotted with dozens of HII re-
gions, where large swathes of hydro-
gen gas are subject to intense radia-
tion from nearby, newly formed stars.
This radiation causes the gas to glow
and creates the bright knots of light
seen throughout the ring. Remark-
ably, NGC 1512 extends even further
than we can see in this image — be-
yond the outer ring — displaying
malformed, tendril-like spiral arms
enveloping NGC 1510. These huge
arms are thought to be warped by
strong gravitational interactions with
NGC 1510 and the accretion of mate-
rial from it. But these interactions are
not just affecting NGC 1512; they
have also taken their toll on the
smaller of the pair. The constant tid-
al tugging from its neighbour has
swirled up the gas and dust in NGC
1510 and kick-started star formation
that is even more intense than in NGC
1512. This causes the galaxy to glow
with the blue hue that is indicative of
hot new stars. NGC 1510 is not the
only galaxy to have experienced the
massive gravitational tidal forces of
NGC 1512. Observations made in
2015 showed that the outer regions
of the spiral arms of NGC 1512 were
indeed once part of a separate, older
galaxy. This galaxy was ripped apart
and absorbed by NGC 1512, just as it
is doing now to NGC 1510. Together,
the pair demonstrate how interac-
tions between galaxies, even if they
are of very different sizes, can have a
significant influence on their struc-
tures, changing the dynamics of their
constituent gas and dust and even
triggering starbursts. Such interac-
tions between galaxies, and galaxy
mergers in particular, play a key role
in galactic evolution.
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