Galaxy clusters are some of the most massive structures
that can be found in the Universe — large groups of galaxies bound
together by gravity. This image from the NASA/ESA Hubble Space Telescope
reveals one of these clusters, known as MACS J0454.1-0300. Each of the
bright spots seen here is a galaxy, and each is home to many millions,
or even billions, of stars.
Astronomers have determined the mass of MACS J0454.1-0300
to be around 180 trillion times the mass of the sun. Clusters like this
are so massive that their gravity can even change the behavior of space
around them, bending the path of light as it travels through them,
sometimes amplifying it and acting like a cosmic magnifying glass.
Thanks to this effect, it is possible to see objects that are so far
away from us that they would otherwise be too faint to be detected.
In this case, several objects appear to be dramatically
elongated and are seen as sweeping arcs to the left of this image. These
are galaxies located at vast distances behind the cluster — their image
has been amplified, but also distorted, as their light passes through
MACS J0454.1-0300. This process, known as gravitational lensing, is an
extremely valuable tool for astronomers as they peer at very distant
objects.
This effect will be put to good use with the start of
Hubble's Frontier Fields program over the next few years, which aims to
explore very distant objects located behind lensing clusters, similar to
MACS J0454.1-0300, to investigate how stars and galaxies formed and
evolved in the early Universe.
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