The nearby universe is not filled with galaxies evenly. Matter forms clusters, sheets and filaments around regions containing far fewer galaxies, producing a cosmic structure often compared with foam.
A vast underdense region called the Local Void extends at least about 150 million light-years beside the Milky Way. Available maps place the galaxy near that void’s edge rather than inside an empty region that surrounds it on all sides.
Gravity builds filaments around emptier regions
Tiny density differences in the early universe grew under gravity. Regions with slightly more matter attracted additional material and eventually formed galaxies and clusters. Regions with less matter lost material relative to their surroundings and became voids, though they are not literally empty.
A NASA map of the nearby universe shows the Milky Way on the edge of the Virgo Cluster environment and next to the Local Void. The map spans more than 600 million light-years and uses observed galaxy motions to infer where mass concentrations and underdensities lie.
The Local Void is large but does not wrap around the galaxy
The Local Void extends for at least about 150 million light-years and contains far fewer obvious galaxies than denser neighboring regions. NASA highlighted galaxy NGC 6503 at its edge, describing the area as a product of the universe’s clumpy large-scale structure.
That Hubble description does not place the Milky Way at the center of a spherical cavity. The galaxy sits amid the Local Group, which includes Andromeda and many dwarf galaxies, and near the larger Virgo Supercluster structure. Dense and sparse directions coexist.
A broader local underdensity is a separate hypothesis
Astronomers have also proposed that the wider region around the Milky Way is less dense than the cosmic average. One influential model, often called the KBC void, used galaxy luminosity data to suggest an underdensity extending hundreds of megaparsecs.
The original KBC analysis describes a large local underdensity, not an empty bubble. Later studies have tested whether such a feature could affect measurements of the universe’s expansion rate. Results depend on survey completeness, dust corrections, galaxy bias and the assumed shape of the structure.
Galaxy motions reveal unseen terrain
Voids influence motion because galaxies fall toward denser regions. From another viewpoint, an expanding underdense region appears to push matter outward, though no repulsive force is required. The Local Void and nearby mass concentrations both contribute to the Milky Way’s motion relative to the cosmic microwave background.
Astronomers map that terrain with redshift surveys, distance indicators and peculiar velocities, which measure motion beyond smooth cosmic expansion. The Milky Way’s dusty disk blocks a portion of the sky, making reconstruction harder in the so-called zone of avoidance.
Scale and wording determine whether the claim holds
A void 150 million light-years wide is immense beside the Milky Way’s roughly 100,000-light-year disk. Yet cosmic maps contain many overlapping definitions. Local Void, Local Sheet and proposed larger underdensity refer to related but distinct features and scales.
The evidence supports a fascinating, precise statement: the galaxy lies near a large region unusually poor in galaxies, and the wider cosmic neighborhood may also be underdense. It does not establish a vast void encircling the Milky Way as a simple shell. The mapped structure is more irregular and less settled than that image suggests.
A local void cannot casually solve the expansion-rate debate
Measurements of cosmic expansion disagree depending on whether researchers infer the rate from the early universe or measure distances to relatively nearby galaxies and exploding stars. A sufficiently large local underdensity could make nearby galaxies recede faster than the global average, shifting the local result.
Models test this possibility by specifying a void’s depth, radius and position, then calculating its effect on distance indicators. The Milky Way would need to occupy a favorable location, and the required structure must remain compatible with galaxy counts, supernova observations and the cosmic microwave background.
Most analyses find that plausible local structure may change the inferred rate modestly but does not automatically remove the full discrepancy. Calling the region a solution before those constraints agree converts a testable hypothesis into a conclusion.
Voids still contain matter and evolve over time
Even the emptiest cosmic voids hold dark matter, diffuse gas and occasional galaxies. They are underdense relative to the universe’s average, not holes cut from space. As surrounding filaments grow, voids can expand and merge, while small voids squeezed by dense environments may collapse.
Their shapes are rarely perfect spheres. Boundaries depend on the galaxy catalog and algorithm used to identify them. That complexity makes the word surround especially misleading for the Milky Way’s position.
Future surveys will map vastly more galaxies across the obscured and faint portions of the sky. Improved distance measurements can turn a qualitative neighborhood map into a sharper three-dimensional density field, testing whether proposed underdensities share one connected structure or result from several adjacent features.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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