(click on image to enlarge)
From NASA/ ESA, July 3, 2026:
In today’s Picture of the Month
from the NASA/ESA/CSA James Webb Space Telescope we are taken on a
visit to a building site of significant scale. The project is a galaxy
cluster named MACS J0553.4-3342, located in the constellation Columba (the Dove).
MACS J0553.4-3342 is situated at a redshift of 0.412. Redshift is a
measure of how much the cluster’s light has been stretched by the
expansion of the Universe over the course of its long journey to Webb’s
mirrors; this unassuming number tells us that we are seeing MACS
J0553.4-3342 as it was 4.4 billion years in the past. But for a galaxy
cluster, this is relatively young. In fact, observations with the
NASA/ESA Hubble Space Telescope and other telescopes show a cluster still in the process of being built.
MACS J0553.4-3342 is composed of two sub-clusters — roughly equal in
mass — that are actively merging. The two subclusters have already
slammed through each other and travelled over one million light-years
apart, but they will eventually come back together again and again until
they finally merge. The construction process is messy, and MACS
J0553.4-3342 is filled with extremely hot gas that radiates powerful
X-rays. Each subcluster is anchored on an immensely bright and massive
elliptical galaxy, which are easily identifiable as the two brightest
points in the centre of this scene with the largest glowing halos around
them. The many smaller white elliptical galaxies are bound to one of
the two subclusters by gravity, and will be incorporated into the final
galaxy cluster. This image also features many foreground galaxies —
spirals and dusty discs that are unrelated to MACS J0553.4-3342 — and
prominent bright stars in our own Milky Way galaxy.
Even mid-way through its construction, the titanic clumps of matter
swirling around in this galaxy cluster have built a device that is
already very useful for us here on Earth: a gravitational lens.
The extreme and concentrated mass in MACS J0553.4-3342 curves light
with its gravity, similar to how a glass lens bends and focuses light.
In this image you can see prominent orange, stretched-out arcs alongside
each of the subclusters. These arcs are images of distant background
galaxies, whose light has been warped by the galaxy cluster’s
gravitational pull. The arc on the left side, three bright spots joined
together, is actually three images of a single background galaxy! A
forest of smaller arcs and lines are scattered across the image too;
such a fantastic view appears in few other places in the Universe.
Look in the right spot, however, and this galaxy cluster turns from a
distorting funhouse mirror into a precision scientific device. The
gravitational lensing focuses light, magnifying objects and enhancing
their brightness so if they lie in exactly the right place, background
galaxies and even individual stars that would have been far too faint
and distant to spot will be made visible. By carefully mapping out the
mass of the cluster, researchers can reconstruct where and how strongly
it distorts light from our point of view, then search for
serendipitously-magnified distant objects to study. The arcs we can see
in MACS J0553.4-3342 already show a few galaxies from less than a
billion years after the Big Bang.
This image, taken with Webb’s Near-Infrared Camera (NIRCam), stems from a survey programme named VENUS (#6882).
Astronomers aimed to create a collection of deep, high-quality images
of massive galaxy clusters like MACS J0553.4-3342 across a wide range of
infrared wavelengths, greatly expanding the area covered by Webb’s
sensitive instruments. Researchers can then scour the clusters for
distant and faint objects that have been brightened through
gravitational lensing, from young galaxies and low-mass black holes to
supernova explosions and individual stars. Gravitational lensing has
been key to many of Webb’s most dramatic discoveries
in recent years, and having many more examples of it allows us to
systematically study the distant past and the evolutionary stages of the
galaxies, stars and black holes we see today.
[Image Description: A galaxy cluster in deep space. It is
filled with elliptical galaxies: small, bright white glowing ovals. The
two largest elliptical galaxies, left and right of center, are bright
cores that radiate light. Unrelated, distant galaxies are scattered
around as red smudges and dots.Many of these are stretched out into red
arcs and lines by the galaxy cluster’s strong gravity, creating multiple
images in places. Numerous spiral galaxies and bright stars appear in
the foreground.]
Credit: ESA/Webb, NASA & CSA, S. Fujimoto
