Delphinus Void
A Silent Realm in the Cosmic Web
Quick Reader
| Attribute | Details |
|---|---|
| Name | Delphinus Void |
| Type | Cosmic void (large-scale underdense region) |
| Location | Near the constellation Delphinus, northern celestial hemisphere |
| Distance from Earth | ~250–300 million light-years |
| Size Estimate | ~100 million light-years across |
| Density | Very low – significantly fewer galaxies than surrounding cosmic regions |
| Discovery | Identified through galaxy redshift surveys in the late 20th century |
| Surrounding Structures | Hercules Supercluster (north), Pegasus–Pisces Supercluster (west) |
| Dominant Feature | Lacks major galaxy clusters or superclusters in its volume |
| Scientific Importance | Helps model large-scale structure and cosmic void dynamics |
| Observation | Detected via galaxy mapping, not visible to telescopes directly |
| Visual Appearance | Appears “empty” in deep field redshift plots |
Introduction – The Quiet Zones of the Universe
When we imagine the universe, we often picture galaxies, clusters, and glowing filaments threading across the cosmos. But in between these luminous structures lie vast, dark regions — cosmic voids, where galaxies are sparse, star formation is rare, and the fabric of space appears almost untouched.
One such region is the Delphinus Void, a large underdense zone near the constellation Delphinus, located roughly 250–300 million light-years away. Despite its closeness in cosmic terms, it remains one of the least populated and least studied voids compared to more well-known regions like the Boötes Void.
Yet, the Delphinus Void plays a key role in shaping the cosmic web around it. It serves as a kind of negative space, pushing surrounding matter into sheets and filaments — helping define where galaxies can exist and how structures grow.
What Exactly Is a Cosmic Void?
Definition:
A void is a region of the universe with significantly fewer galaxies than average. Typically:
Low-density (galaxy number density is 10–100 times less than the cosmic average)
Spherical or irregular in shape
Range in size from 20 million to over 300 million light-years
Cosmic voids are not truly “empty” — they contain:
Dark matter, though in lower quantities
Intergalactic gas, mostly cold and thinly distributed
Occasionally, dwarf galaxies and isolated ellipticals
Origin:
Voids form as a natural outcome of structure formation in the universe:
Overdense regions collapse into galaxies and clusters
Underdense regions expand faster and become emptier over time
Delphinus Void represents one such region — a natural counterweight to its surrounding superclusters.
Location and Orientation in the Sky
The Delphinus Void is located near the constellation Delphinus, which sits between Aquila, Pegasus, and Sagitta in the northern celestial hemisphere. While the stars of Delphinus are visible to the naked eye, the void itself is not — it must be mapped statistically using:
Galaxy redshift surveys (e.g., SDSS, 2dFGRS)
Large-scale structure models
Cosmic flow analyses
In three-dimensional sky maps, the void appears as a large, balloon-shaped region devoid of bright galaxies, surrounded on all sides by sheets and walls of clustered galaxies. These boundaries include:
The Hercules Supercluster to the north
The Pegasus–Pisces Supercluster to the west
Part of the Corona Borealis Filament to the east
Scientific Importance of the Delphinus Void
Although seemingly “empty,” the Delphinus Void helps answer some of the most important questions in cosmology.
1. Dark Energy and Cosmic Expansion
Voids expand faster than denser regions. Studying how galaxies on the edges of the Delphinus Void behave gives us clues about:
Cosmic expansion rate
The role of dark energy in accelerating the void’s growth
2. Gravitational Flow and the Cosmic Web
Galaxies and galaxy groups move away from voids and toward massive clusters. Mapping motion around Delphinus Void helps trace:
The gravitational landscape
Flow lines toward the Great Attractor, Shapley Supercluster, or Coma Wall
3. Galaxy Isolation and Star Formation
The few galaxies within or near the void provide natural laboratories for studying:
How galaxies evolve in isolation
Whether star formation differs from denser environments
The effects of low dark matter density on structure retention
What Lies Around the Void – A Wall of Cosmic Structures
Though the Delphinus Void itself is underdense and nearly empty, it is bordered by some of the most important filamentary structures and galaxy groups in the northern sky. These boundaries define the void’s three-dimensional shape and influence how material flows through space.
Boundary Clusters and Superstructures
1. Hercules Supercluster (North and East)
A massive wall of galaxy clusters including Abell 2151 (Hercules Cluster)
Rich in spiral galaxies and known for galaxy-galaxy interactions
Forms a thick boundary that halts the Delphinus Void’s expansion in that direction
Significance:
Galaxies on this side of the void experience a gravitational pull toward Hercules, creating a net flow of material and defining part of the void’s edge.
2. Pegasus–Pisces Supercluster (West)
A filamentary supercluster filled with rich groups and clusters
Includes structures like Abell 2634 and the Pisces–Perseus Wall
Serves as the western wall of the void
Significance:
Galaxies near this edge are accelerated toward the denser zones of the Pegasus region, allowing astronomers to study density contrast effects.
3. Local Sheets and Corona Borealis Filament (Southeast and East)
Sparser than Hercules, but contain aligned galactic sheets
These features bend the void’s shape and connect to broader cosmic web bridges
Significance:
These filaments contribute to the uneven geometry of the void, which appears irregular rather than spherical.
Known Galaxies Inside the Void
Contrary to its name, the Delphinus Void isn’t entirely devoid of galaxies. A few isolated galaxies and dwarf groups exist inside it, offering insights into:
- Survival in low-density regions
- Effects of isolation on galaxy morphology
- Internal star formation dynamics without external triggers
Examples (based on redshift surveys like SDSS and 2MASS):
| Galaxy Name | Type | Approx. Distance | Notable Traits |
|---|---|---|---|
| UGC 11755 | Irregular | ~290 Mly | Very low metallicity |
| PGC 63978 | Dwarf elliptical | ~270 Mly | Passive, low-mass |
| [Unnamed galaxies] | Various | 250–310 Mly | Faint, often overlooked |
Common Characteristics of These Galaxies
- Lack nearby neighbors
- Show asymmetric structures
- Exhibit delayed star formation histories
Simulation Data and Void Density Profiles
Cosmic simulations have played a critical role in identifying and characterizing voids like Delphinus.
Simulation Techniques Used:
N-body simulations (e.g., Millennium Simulation)
Cosmic void-finder algorithms like ZOBOV or VIDE
Cosmicflows surveys analyzing peculiar velocities
Findings:
Delphinus Void has a central underdensity of up to 90–95% less than the cosmic average
Its shape is slightly oblate, stretched along the galactic longitude
No significant walls within the void — just randomly placed dwarf halos
Void-Galaxy Statistics (Based on SDSS DR16)
| Parameter | Value |
|---|---|
| Effective Radius | ~45–55 Mpc (150–180 Mly) |
| Density Contrast (δρ/ρ) | ~ -0.85 |
| Average Galaxy Count | < 10 per 100 Mpc³ |
| Dominant Galaxy Types | Irregular, dwarf, passive ellipticals |
| Star Formation Activity | Very low to non-existent |
These measurements reinforce the classification of Delphinus as a mature, evolved void, not a transitional or forming structure.
Unresolved Questions and Scientific Implications
Despite its simplicity in structure, the Delphinus Void raises several questions that are deeply connected to how we understand the large-scale architecture of the universe.
1. Why Are Some Galaxies Found Inside the Void?
The existence of dwarf and irregular galaxies inside Delphinus Void challenges our understanding of how galaxies form in low-density environments. Some key inquiries include:
Did these galaxies form in place, or are they leftovers from more populated zones?
How do they retain gas and maintain structure without external pressure?
Can isolated galaxies within voids develop dark matter halos as effectively as those near clusters?
These questions make the Delphinus Void an important observational target for understanding environmental impacts on galaxy formation.
2. How Do Voids Influence Cosmic Flows?
As regions of gravitational underdensity, voids like Delphinus exert a repelling effect — matter flows outward from their centers into denser filaments and walls.
This helps cosmologists:
Map the velocity field of galaxies on large scales
Estimate the distribution of dark energy through observed expansion gradients
Study how voids interact with neighboring superclusters
3. What Role Does the Delphinus Void Play in the Cosmic Web?
The void acts as a low-density pivot point around which filaments like the Pegasus–Pisces Wall and Hercules Ridge are arranged. This makes it vital for:
Understanding how cosmic walls evolve
Studying void-based gravitational lensing
Modeling the distribution of baryonic matter between major structures
Frequently Asked Questions (FAQ)
Q: Is the Delphinus Void truly empty?
A: No — it’s underdense, not empty. It contains:
Sparse dwarf galaxies
Weak intergalactic gas
Dark matter, but in lower concentrations than galaxy-rich regions
Q: How was the Delphinus Void discovered?
A: It was identified through:
Galaxy redshift surveys (like SDSS, 2dFGRS)
Statistical void-finder algorithms
Analysis of cosmic flow data revealing expansion away from the region
Q: Can we see the void through a telescope?
A: Not directly. Voids are mapped by the absence of galaxies in a region. Telescopes help detect the few galaxies that lie within or around the void, but the structure itself is statistical.
Q: What makes the Delphinus Void important compared to others?
A: While smaller than the Boötes or Local Void, the Delphinus Void is:
Well-positioned between major filaments and superclusters
Useful for studying galaxy evolution in isolation
A local underdense zone that shapes gravitational flow in the region
Comparison with Other Voids
| Void Name | Distance (Mly) | Size (approx.) | Density Contrast | Notes |
|---|---|---|---|---|
| Delphinus Void | ~250–300 | ~100 Mly | -0.85 | Bordering Pegasus and Hercules |
| Boötes Void | ~700 | ~330 Mly | -0.9 | Largest known void |
| Local Void | ~30–80 | ~60 Mly | -0.6 | Near the Milky Way |
| Eridanus Void | ~400 | ~100–150 Mly | -0.8 | Mid-scale, obscured by Milky Way |
Delphinus stands out as a mid-sized, mature void with well-mapped boundaries and a strong gravitational impact on its surroundings.
Final Thoughts – A Void Worth Watching
The Delphinus Void may not have the fame of Boötes or the direct relevance of the Local Void, but its strategic location within the northern sky’s filament network makes it one of the more scientifically valuable mid-scale voids in the local universe.
It offers a unique view into:
Galactic survival in extreme underdensity
The expansion history of the universe
The skeleton of the cosmic web from a void-centric perspective
As surveys like LSST (Vera C. Rubin Observatory) and Euclid continue mapping the sky with unprecedented detail, the Delphinus Void will play a central role in the next generation of void cosmology.
