Cosmic optical illusions in Ursa Major
Copyright: NASA, ESA and the Hubble Heritage Team (STScI/AURA)
Some of the stunning views we have of the cosmos owe their beauty to a
trick of perspective, as captured in this NASA/ESA Hubble Space
Telescope image.
The galaxies at the top and bottom of the frame
are named PGC 37639 and PGC 101374 respectively.
Although it may look as
if the two are in the middle of a galactic tug-of-war, connected by the
prominent stream of blue through the centre of the image, PGC 37639
lies somewhat closer to Earth than its companion, and the two are not
physically connected.
In another optical trick, this image does
not contain two galaxies, but at least four. The upper left patch
actually hosts two galaxies in the early stages of merging. Their bright
centres can still be seen separately, glowing amid a maelstrom of gas
and dust.
A smaller and relatively intact spiral galaxy, known as
SDSSCGB 19.4, can be seen to the right of the merging duo. This trio of
galaxies comprises Arp 194, a galaxy group just under 600 million
light-years away from Earth in the constellation of Cepheus.
The
blue stream is thought to have formed through the turbulent
gravitational interactions occurring at the top of the frame — the
uppermost galaxy clump is a whirl of flailing once-spiral arms. The
stream is some 100 000 light-years long, and made up of gas, dust and
many millions of newborn stars. These stars, which are clumped together
to form star clusters, which in turn later accumulate as superclusters,
are responsible for the striking blue hue visible here. They are mostly
young, hot and massive, a combination that causes them to emit blue
light.
This image was released in 2009,
to commemorate the Hubble’s 9th year in space. The telescope has gone
on to hit a quarter of a century orbiting Earth, a milestone it reached
this April.
Source: ESA/Space Images
