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Starts With A Bang

This is the loneliest galaxy in the known Universe

With no other galaxies in its vicinity for ~100 million light-years in all directions, it’s as isolated and lonely as a galaxy can be.
Loneliest galaxy MCG+01–02–015
This Hubble Space Telescope image showcases the isolated void galaxy MCG+01-02-015, located near the center of an otherwise galaxy-free void. With no other galaxies known within 100 million light-years of it, it's the loneliest galaxy in the known Universe.
Credit: ESA/Hubble & NASA and N. Grogin (STScI); Acknowledgement: Judy Schmidt
Key Takeaways
  • Galaxy MCG+01-02-015, located about 293 million light-years away, appears to be a relatively typical, evolved spiral galaxy, with dusty arms and a gas-rich disk.
  • However, looking at its neighborhood, it’s immediately clear that something is amiss: there are no other detectable galaxies to be found within 100 million light-years of it.
  • Rather than being located along a cosmic filament or on the outskirts of a massive cluster, this galaxy is found in a great cosmic void: the most isolated location of all.

All throughout the cosmos, stars and galaxies appear everywhere.

astronomy new era
The main galaxies of Stephan’s Quintet, as revealed by JWST on July 12, 2022. The galaxy on the left is only about ~15% as distant as the other galaxies, and the background galaxies are many scores of times farther away. And yet, they’re all equally sharp to JWST’s eyes, demonstrating that the Universe is full of stars and galaxies practically everywhere we look.
Credit: NASA, ESA, CSA, and STScI

In our own backyard, we inhabit the Local Group of galaxies.

local group galaxies
This three-dimensional view of the Local Group showcases the three largest galaxies and their relative positions in space: Andromeda (M31), the Milky Way, and Triangulum (M33). Both Andromeda and Triangulum are visible with the naked human eye, as are the Large and Small Magellanic clouds. Over the next few billion years, these galaxies will interact and merge, as our entire Local Group is gravitationally bound.
Credit: Antonio Ciccolella/Wikimedia Commons

We’re one of many groups on the outskirts of a large galaxy cluster.

virgo supercluster
The various galaxies of our local supercluster, dominated by the dense Virgo Cluster of galaxies. Here, all galaxies appear grouped and clustered together. On the largest scales, the Universe is uniform, but as you look to galaxy or cluster scales, overdense and underdense regions dominate. Each galaxy group and cluster within this larger structure will remain gravitationally bound, individually, but the groups making up the apparent, larger structure are not bound together. As the Universe expands, they will disappear from one another’s reach.
Credit: Andrew Z. Colvin/Wikimedia Commons

On grander cosmic scales, our Universe clusters into a great filamentary network.

dark matter
This snippet from a medium-resolution structure-formation simulation, with the expansion of the Universe scaled out, represents billions of years of gravitational growth in a dark matter-rich Universe. Note that filaments and rich clusters, which form at the intersection of filaments, arise primarily due to dark matter; normal matter plays only a minor role. The larger-scale your simulation is, however, the more that smaller-scale structure is intrinsically underestimated and “smoothed-out.”
Credit: Ralf Kaehler and Tom Abel (KIPAC)/Oliver Hahn

Galaxies inhabit these filaments, with clusters forming at their nexuses.

coma cluster zwicky dark matter
The Coma Cluster of galaxies, as seen with a composite of modern space and ground-based telescopes. The Coma Cluster, the largest galaxy cluster in our nearby Universe, is dominated by two giant elliptical galaxies, with over 1000 other spirals and ellipticals inside. The speed of the individual galaxies within the Coma Cluster is too great for the cluster to remain a bound entity based on its normal matter content alone. It can only remain a bound object under Einstein’s laws of General Relativity if a substantial amount of additional matter, i.e., a source of dark matter, exists throughout this cluster. The total mass of the cluster comes in at a few quadrillion solar masses.
Credit: NASA / JPL-Caltech / L. Jenkins (GSFC)

But the matter-poor space between these filaments creates great cosmic voids.

Lockman hole galaxy cluster herschel
A region of space devoid of matter in our galaxy reveals the Universe beyond, where every point is a distant galaxy. The cluster/void structure can be seen very clearly, demonstrating that our Universe is not of exactly uniform density on all scales. While there are many galaxy-rich regions, galaxy-poor or even galaxy-free regions are also abundant, like holes within a cosmic Swiss cheese.
Credit: ESA/Herschel/SPIRE/HerMES

These underdense regions lose their matter to the surrounding denser areas.

large scale structure growth
Over time, gravitational interactions will turn a mostly uniform, equal-density Universe into one with large concentrations of matter and huge voids separating them. Because simulations are limited in the number of particles they can handle at once, the largest-scale cosmic simulations are inherently limited in their ability to resolve individual, early galaxies. However, the great underdense regions, the cosmic voids within our Universe, are well-understood.
Credit: Volker Springel/MPE

They typically have fewer, smaller, and fainter galaxies than the richer clustered regions.

supervoid dipole repeller underdense
The relative attractive and repulsive effects of overdense and underdense regions on the Milky Way are mapped out here on distance scales of hundreds of millions of light-years. Overdense and underdense regions both pull and push on matter, giving it speeds of hundreds or even thousands of kilometers in excess of what we’d expect from redshift measurements and the Hubble flow alone. These giant collections of galaxies can be divided up into superclusters, but their underdense counterparts, the great cosmic voids, play an equally important role on cosmic scales.
Credit: Y. Hoffman et al., Nature Astronomy, 2017

However, one relatively deep void possesses the remarkable galaxy MCG+01-02-015.

Loneliest galaxy MCG+01–02–015 Hubble
The galaxy MCG+01–02–015, shown here, lies in the center of a void in the direction of the constellation Pisces. The galaxy, located some 293 million light-years away, is the only known galaxy within 100 million light-years of its position.
Credit: ESA/Hubble & NASA and N. Grogin (STScI); Acknowledgement: Judy Schmidt

This impressive, Milky-Way like spiral has many classic features.

NGC 6384 similar milky way galaxy
The spiral arms of galaxy NGC 6384 are where new stars primarily form in this galaxy. Under normal circumstances, spiral arms in the disk of a spiral galaxy are where the majority of new stars form. With many features in common with our own Milky Way, NGC 6384 is one of the best candidates for a near-twin of the Milky Way. Its similarities to MCG+01-02-015 are also striking.
Credit: ESA/Hubble & NASA

It has a gas-rich disk, dusty arms, central bar and bulge, and abundant heavy elements.

void cluster structure universe
In between the great clusters and filaments of the Universe are great cosmic voids, some of which can span hundreds of millions of light-years in diameter. While some voids are larger in extent than others, spanning a billion light-years or more, they all contain matter at some level. Even the void that houses MCG+01–02–015, the loneliest galaxy in the Universe, likely contains small, low surface brightness galaxies that are below the present detection limit of telescopes like Hubble.
Credit: Andrew Z. Colvin and Zeryphex/Astronom5109; Wikimedia Commons

But it’s centrally located within a particularly sparse, underdense “void” region.

Loneliest galaxy MCG+01–02–015 Hubble
Despite the visual appearance of other galaxies near MCG+01-02-015, none of these galaxies are actually located in the same region of space. With only one or two notable exceptions of nearby, small, faint galaxies, almost all of the galaxies shown in this image lie behind MCG+01-02-015; they are background galaxies simply found along the same line-of-sight.
Credit: ESA/Hubble & NASA and N. Grogin (STScI); Acknowledgement: Judy Schmidt

Our best telescopes identify no other substantial galaxies within ~100 million light-years.

large and small magellanic cloud
The Large (top right) and Small (lower left) Magellanic Clouds are visible in the southern skies, and helped guide Magellan on his famous voyage some 500 years ago. In reality, the LMC is located some 160-165,000 light-years away, with the SMC slightly farther at 198,000 light-years. Both galaxies, along with Triangulum and Andromeda, are visible to the naked human eye.
Credit: ESO/S. Brunier

Contrariwise, four galaxies beyond the Milky Way are visible to naked human eyes.

Hubble discovery cepheid andromeda
Hubble’s discovery of a Cepheid variable in the Andromeda galaxy, M31, opened up the Universe to us, giving us the observational evidence we needed for galaxies beyond the Milky Way and leading us, in short order, to the discovery of the expanding Universe.
Credits: NASA, ESA and the Hubble Heritage Team (STScI/AURA); Illustration via NASA, ESA, and Z. Levay (STScI)

Their extragalactic nature was confirmed with 1920s technology.

hubble plot expanding universe
Edwin Hubble’s original plot of galaxy distances versus redshift (left), establishing the expanding Universe, versus a more modern counterpart from approximately 70 years later (right). In agreement with both observation and theory, the Universe is expanding, and the slope of the line relating distance to recession speed is a constant.
Credit: E. Hubble; R. Kirshner, PNAS, 2004

This cosmic companionship first revealed the expanding Universe.

maffei 1 2 infrared galaxies
Italian astronomer Paolo Maffei’s promising work on infrared astronomy culminated in the discovery of galaxies — like Maffei 1 and 2, shown here — in the plane of the Milky Way itself. Maffei 1, the giant elliptical galaxy at the lower left, is the closest giant elliptical to the Milky Way, yet went undiscovered until 1967. For more than 40 years after the Great Debate, no spirals in the plane of the Milky Way were known, due to light-blocking dust that’s very effective at visible wavelengths.
Credit: NASA/JPL-Caltech/UCLA

But uncovering another galaxy, from within MCG+01-02-015, requires 1960s-level telescopes.

x-ray emission 3c 295 cluster
Galaxy 3C 295, at the center of the galaxy cluster ClG J1411+5211, is shown with a composite X-ray/optical view in purple, with the X-rays blown up to reveal the central radio and X-ray loud core. At 5.6 billion light-years away, this was the most distant object known in the Universe from 1960-1964. Only with X-ray or radio telescopes, or with an enormous optical telescope, would the first extragalactic objects from MCG+01-02-015’s perspective be detectable.
Credit: X-ray: NASA/CXC/Cambridge/S.Allen et al; Optical: NASA/STScI

From this isolated perspective, discovering our cosmic origins would’ve been far more challenging.

penzias wilson cmb holmdel horn antenna
According to the original observations of Penzias and Wilson, the galactic plane emitted some astrophysical sources of radiation (center), but above and below, all that remained was a near-perfect, uniform background of radiation. The temperature and spectrum of this radiation has now been measured, and the agreement with the Big Bang’s predictions are extraordinary. If we could see microwave light with our eyes, the entire night sky would look like the green oval shown.
Credit: NASA/WMAP Science Team

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