A peculiar galactic clash

Arp 256 is a stunning system of two spiral galaxies, about
350 million light-years away, in an early stage of merging.
The image, taken with the NASA/ESA Hubble Space Telescope,
displays two galaxies with strongly distorted shapes and an
astonishing number of blue knots of star formation that
look like exploding fireworks. The star formation was
triggered by the close interaction between the two
galaxies. Credit: ESA/Hubble, NASA

Galaxies are not static islands of stars—they are dynamic and
ever-changing, constantly on the move through the darkness of
the Universe. Sometimes, as seen in this spectacular Hubble
image of Arp 256, galaxies can collide in a crash of cosmic

350 million light-years away in the constellation of Cetus (the
Sea Monster), a pair of barred spiral have just begun a magnificent merger.
This image suspends them in a single moment, freezing the
chaotic spray of gas, dust and stars kicked up by the
gravitational forces pulling the two galaxies together.

Though their nuclei are still separated by a large distance,
the shapes of the galaxies in Arp 256 are impressively
distorted. The galaxy in the upper part of the image contains
very pronounced tidal tails—long, extended ribbons of gas, dust
and stars.

The galaxies are ablaze with dazzling regions of star
formation: the bright blue fireworks are stellar nurseries,
churning out hot infant stars. These vigorous bursts of new
life are triggered by the massive gravitational interactions,
which stir up interstellar gas and dust out of which stars are

Arp 256 was first catalogued by Halton Arp in 1966, as one of
338 galaxies presented in the aptly-named Atlas of Peculiar
Galaxies. The goal of the catalogue was to image examples of
the weird and wonderful structures found among , to provide snapshots of
different stages of galactic evolution. These peculiar galaxies
are like a natural experiment played out on a cosmic scale and
by cataloguing them, astronomers can better understand the
physical processes that warp spiral and into new shapes.

Many galaxies in this catalogue are with indistinct structures, or
generating powerful
jets—but a large number of the galaxies are interacting, such
as Messier 51, the Antennae Galaxies, and Arp 256. Such
interactions often form streamer-like tidal tails as seen in
Arp 256, as well as bridges of gas, dust and between the galaxies.

Long ago, when our expanding Universe was much smaller,
interactions and mergers were more common; in fact, they are
thought to drive galactic evolution to this day. The galaxies
in the Arp 256 system will continue their gravitational dance
over the next millions of years, at first flirtatious, and then
intimate, before finally morphing into a single galaxy.

This spectacular image was taken by Hubble’s Advanced Camera
for Surveys (ACS) and the Wide Field Camera 3 (WFC3). It is a
new version of an image already released in 2008
that was part a large collection of 59 images of merging
taken for Hubble’s 18th anniversary.

Explore further:
frenzy of stars

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