The picture itself is breathtaking. But what we learn is truly eye-opening.
Galaxy clusters, like the massive one captured here by Hubble,
PLCK G004.5–19.5, impress not just for their looks, but for their science.
In this Hubble Space Telescope image, the many red galaxies are members of the massive MACS J1149.6+2223 cluster, which creates distorted and highly magnified images of the galaxies behind it. A large cluster galaxy (centre of the box) has split the light from an exploding supernova in a magnified background galaxy into four yellow images (arrows), whose arrival time was delayed relative to one another owing to the bending of spacetime by mass. (Hubble Space Telescope / ESA and NASA)
Out there in the depths of space, collections of thousands of galaxies have formed over billions of years from gravity’s relentless pull.
The Laniakea supercluster, containing the Milky Way (red dot), on the outskirts of the Virgo Cluster (large white collection near the Milky Way). Despite the deceptive looks of the image, this isn’t a real structure, as dark energy will drive most of these clumps apart, fragmenting them as time goes on. (Tully, R. B., Courtois, H., Hoffman, Y & Pomarède, D. Nature 513, 71–73 (2014))
These are the largest bound structures of all, as dark energy
will drive the apparently larger “superclusters” apart.
Our local supercluster, Laniakea, contains the Milky Way, our local group, the Virgo cluster, and many smaller groups and clusters on the outskirts. However, each group and cluster is bound only to itself, and will be driven apart from the others due to dark energy and our expanding Universe. (Andrew Z. Colvin / Wikimedia Commons)
If you map out the motions of the galaxies inside the cluster, you can derive the total cluster mass.
The mass distribution of cluster Abell 370. reconstructed through gravitational lensing, shows two large, diffuse halos of mass, consistent with dark matter with two merging clusters to create what we see here. Around and through every galaxy, cluster, and massive collection of normal matter exists 5 times as much dark matter, overall. (NASA, ESA, D. Harvey (École Polytechnique Fédérale de Lausanne, Switzerland), R. Massey (Durham University, UK), the Hubble SM4 ERO Team and ST-ECF)
Most of the mass is in between the galaxies, proving that there’s unseen matter in the cluster.
A galaxy cluster can have its mass reconstructed from the gravitational lensing data available. Most of the mass is found not inside the individual galaxies, shown as peaks here, but from the intergalactic medium within the cluster, where dark matter appears to reside. (A. E. Evrard. Nature 394, 122–123 (09 July 1998))
We find these clusters from the hot, intergalactic gas that
shifted the background light left over from the Big Bang.
Shown here at frequencies above 220 GHz, the light from the cosmic microwave background gets shifted to higher energies from the presence of heated gas. This gas is found in galaxy clusters, and allows us to infer how much normal matter is present: about 15% of the total mass needed from gravitational lensing. (ESA/Planck Collaboration)
There’s more gravity than the gas can provide, showing the presence of non-baryonic dark matter.
The smallest, faintest, most distant galaxies identified in the deepest Hubble image ever taken. A 2017 study, by Livermore et al., has them beat, by perhaps two orders of magnitude, thanks to stronger gravitational lenses. The RELICS collaboration hopes to identify even better targets for James Webb. (Credit: NASA, ESA, R. Bouwens and G. Illingworth (UC, Santa Cruz))
But all the mass, combined, contributes to gravitational lensing.
An illustration of gravitational lensing showcases how background galaxies — or any light path — is distorted by the presence of an intervening mass, such as a foreground galaxy cluster. (NASA/ESA)
The bending of space stretches and magnifies the light from galaxies behind the cluster.
The streaks and arcs present in Abell 370, a distant galaxy cluster some 5–6 billion light years away, are some of the strongest evidence for gravitational lensing and dark matter that we have. The lensed galaxies are even more distant, with some of them making up the most distant galaxies ever seen. (NASA, ESA/Hubble, HST Frontier Fields)
This is the whole purpose of
the joint Hubble/Spitzer RELICS program, highlighted by this galaxy cluster.
From the distant Universe, light has traveled for some 10.7 billion years from distant galaxy MACSJ2129–1, lensed, distorted and magnified by the foreground clusters imaged here. The most distant galaxies appear redder because their light is redshifted by the expansion of the Universe, which helps explain what we measure as Hubble’s law. (NASA, ESA, and S. Toft (University of Copenhagen) Acknowledgment: NASA, ESA, M. Postman (STScI), and the CLASH team)
Gravitationally lensed galaxies are the most distant ever identified.
The galaxy cluster MACS 0416 from the Hubble Frontier Fields, with the mass shown in cyan and the magnification from lensing shown in magenta. Mapping out the cluster mass allows us to identify which locations should be probed for the greatest magnifications and ultra-distant candidates of all. (STScI/NASA/CATS Team/R. Livermore (UT Austin))
Through this process, RELICS can reveal the perfect observing targets for the James Webb Space Telescope.
The GOODS-N field, with galaxy GN-z11 highlighted: the presently most-distant galaxy ever discovered. With the power of gravitational lensing and its advanced equipment, the James Webb Space Telescope will break this record. (NASA, ESA, P. Oesch (Yale University), G. Brammer (STScI), P. van Dokkum (Yale University), and G. Illingworth (University of California, Santa Cruz))
Mostly Mute Monday tells the astrophysical story of an object, picture, or phenomenon in images, visuals, and no more than 200 words. Ethan Siegel is the author of
Beyond the Galaxy and Treknology. You can pre-order his third book, currently in development: the Encyclopaedia Cosmologica.