Taurus Void
A Subtle Gap in the Galactic Foreground
Quick Reader
| Attribute | Details |
|---|---|
| Name | Taurus Void |
| Type | Cosmic void (underdense region) |
| Location | Near the Taurus constellation, overlapping the Zone of Avoidance |
| Distance from Earth | ~100–160 million light-years |
| Size Estimate | ~50–70 million light-years across |
| Density | Low to very low |
| Discovery | Identified via gaps in galaxy redshift surveys |
| Surrounding Structures | Perseus–Pisces Supercluster (north), Local Sheet (southwest), Eridanus Filament (east) |
| Dominant Feature | Obscured void close to the galactic plane |
| Scientific Importance | Helps understand underdensities in the near-field cosmic web |
| Observation | Inferred from galaxy surveys; partially hidden by Milky Way dust |
| Visibility | Poor in optical; best traced in HI (21 cm) and IR surveys |
Introduction – A Quiet Hole Behind the Bull
The Taurus constellation may be known for its bright stars and clusters like the Hyades and Pleiades, but beyond these stellar sights lies a quiet and underpopulated region of space — the Taurus Void.
This void doesn’t grab headlines like Boötes or Local Void, but its position near the galactic plane makes it a cosmologically interesting blind spot. Though small in comparison to major voids, Taurus Void’s presence:
Contributes to local flow patterns
Defines gaps between larger cosmic filaments
Offers a natural lab for studying structure growth suppression
The Zone of Avoidance Challenge
The Zone of Avoidance (ZoA) refers to the region of the sky that is heavily obscured by our Milky Way galaxy. In this area, dust and foreground stars block light from galaxies beyond, making optical surveys nearly useless.
Taurus Void lies directly within or behind this region, making it:
Difficult to observe in visible light
Dependent on radio (HI) and infrared for detection
Surveys like:
2MASS
ALFALFA
HI4PI have contributed to mapping galaxy absence in this area, confirming a genuine underdensity in redshift space.
Placement in the Cosmic Web
Though modest in size, the Taurus Void is part of the complex local filament network, bordered by:
The Local Sheet, where the Milky Way and other nearby galaxies reside
The Perseus–Pisces Supercluster, a major wall-like structure north of the void
The Eridanus and Orion Filaments, which frame it from the east
This places Taurus Void in a transitional position — not truly deep space, but not densely packed either. It may represent a partially collapsed region, or an extension of the Local Void in some models.
Discovery and Definition
First Recognition:
Voids in the Taurus region were hinted at in IRAS galaxy maps in the 1980s
Later refined using 2MASS redshift surveys
Tully et al. (2008–2014) included it in local velocity flow reconstructions
Redshift Surveys Helped Define:
Gaps in galaxy count between cz = 3000–5000 km/s
Absence of significant clusters in the Taurus direction
Isolation from strong gravitational sources
How Large Is the Taurus Void?
Its size depends on where boundaries are drawn:
Core region: ~50 million light-years across
Extended underdensity (including adjacent gaps): ~70 million light-years
Depth: ~60–100 million light-years from Earth
Because of the Zone of Avoidance, its true three-dimensional shape is still uncertain, and some astronomers treat it as a sub-void of the larger Local Void complex.
Inside the Void – What Galaxies (Barely) Exist
The Taurus Void, like most voids, is defined not by what’s in it—but by what’s missing. Yet even here, astronomers have identified a few galaxies either within or along the boundary of the void using non-optical methods.
Candidate Galaxies Inside or Near the Taurus Void
| Galaxy Name | Type | Distance | Detection Method | Notes |
|---|---|---|---|---|
| UGC 3371 | Dwarf irregular | ~110 Mly | Radio (HI) | Near the void edge, low metallicity |
| WISEA J0503+1911 | Faint elliptical | ~120 Mly | Infrared | Possible embedded galaxy |
| ALFA ZOA J0510+20 | Irregular (undesignated) | ~130 Mly | ALFALFA HI | Hidden behind Milky Way dust |
| 2MASX J0449+2101 | Dwarf spiral | ~105 Mly | IR + HI | Low star formation, boundary object |
Common Traits
- Low surface brightness
- HI-rich but optically faint
- Weak or no cluster membership
- Minimal environmental influence
They are not centrally located but are found in the outer shell or interface zones of the void.
Mapping the Void – Detection Strategies
Given the severe optical obstruction in the Taurus region, mapping relies on multi-wavelength approaches:
1. Radio Surveys (21-cm HI Line)
ALFALFA Survey (Arecibo): Detected gas-rich galaxies obscured in optical
HI4PI Survey: All-sky HI map helping to constrain low-density regions
📌 Key Insight: Many void galaxies are HI-rich, even when not optically luminous. These are best revealed in deep blind HI surveys.
2. Infrared Surveys
2MASS: Penetrates Milky Way dust, used for redshift survey cross-matching
WISE (Wide-field Infrared Survey Explorer): Helped identify faint IR-bright galaxies
📌 Key Insight: IR helps fill in redshift gaps across the Zone of Avoidance, which often aligns with voids like Taurus.
3. Peculiar Velocity Analysis
Tully and collaborators use galaxy motions to infer the presence of voids
Galaxies accelerate away from underdensities, leaving observable motion signatures
📌 Key Insight: The Local Sheet’s motion away from Taurus confirms its role in local velocity divergence.
Taurus Void’s Role in Cosmic Flow
Though not massive, the Taurus Void contributes to anisotropy in local galaxy velocities. It sits near several important flow features:
Milky Way and Local Group show modest outward motion from the Taurus direction
The void helps define the boundary between the Local Sheet and the Perseus–Pisces attraction zone
It may also interface with the edge of the Local Void, adding to the “push” effect from underdense regions
Visualizing the Flow
Simulations from the Cosmicflows-3 project visualize the Taurus Void as:
A modest cavity in an otherwise busy local web
With galaxies streaming away at ~150–250 km/s
Framed by Perseus–Pisces inflow zones and Leo Spur expansion
This makes it part of a balanced system, where dense regions pull and voids push — collectively shaping how galaxies like the Milky Way navigate the cosmic web.
Void-Galaxy Statistics in the Taurus Region
| Parameter | Approximate Value |
|---|---|
| Effective Radius | ~25–35 Mpc (80–115 Mly) |
| Central Underdensity | ~–0.7 to –0.85 (δρ/ρ) |
| Galaxy Number Density | < 10% of surrounding filaments |
| Dominant Galaxy Types | HI-rich dwarfs and irregulars |
| Star Formation | Very low to sporadic bursts |
Cosmological Implications of the Taurus Void
Though relatively small and partially hidden, the Taurus Void provides valuable clues about:
Underdense zone interactions in the local universe
How voids modulate galaxy flow in their surroundings
The transition zone between dense filaments and quiet gaps
The impact of observational limits (Zone of Avoidance) on our view of cosmic structure
1. A Void at the Interface
Taurus Void is not an isolated spherical cavity — rather, it lies at the junction of multiple gravitational domains, including:
The Local Sheet and Leo Spur
The edge of the Local Void
The Perseus–Pisces inflow zone
This places Taurus Void in a dynamically sensitive area, helping define:
Where galaxies accelerate away from the void
How mass concentrations shape local flow fields
It also contributes to the peculiar motion of nearby groups, albeit on a smaller scale than the Local or Delphinus Voids.
2. A Case Study for Void Evolution
In simulations (e.g., Illustris, EAGLE), voids like Taurus often:
Begin as low-density ripples in the early universe
Expand faster than the background Hubble flow
Push neighboring material into filaments and knots
Taurus is likely a secondary void, having developed alongside the more dominant Local Void. It may serve as a testbed for understanding:
Void substructure
Minor expansion dynamics
Feedback-free galaxy evolution
3. Observational Blind Spots and Bias Correction
Because Taurus Void is largely behind the Milky Way’s dusty disk, it reminds astronomers how observational bias can distort our view of the large-scale universe.
This void encourages:
Better multi-wavelength survey strategies
Zone of Avoidance gap-filling efforts
More accurate density field reconstructions
Its very obscuration makes it a necessary void to study — ensuring we’re not missing key components of the cosmic web.
Frequently Asked Questions (FAQ)
Q: Where is the Taurus Void located?
A: The Taurus Void lies behind the Taurus constellation, overlapping with the Zone of Avoidance, at a distance of approximately 100–160 million light-years.
Q: How was the Taurus Void discovered?
A: It was detected through:
Gaps in galaxy redshift surveys
Infrared and radio detections of HI-rich dwarf galaxies
Cosmicflows and peculiar velocity field analyses
Q: Are there galaxies inside the Taurus Void?
A: Yes, but very few. These are mostly:
HI-rich dwarfs or irregulars
Faint infrared galaxies
Found near the outer shell, not the core
Q: Can the Taurus Void be seen through telescopes?
A: No, not directly. Due to the Zone of Avoidance, it’s obscured in visible light. It is instead traced using:
Radio telescopes (21 cm line)
Infrared surveys like 2MASS and WISE
Q: What is the scientific importance of the Taurus Void?
A: It helps:
Define local cosmic flows
Illustrate galaxy evolution in quiet zones
Address gaps in our observational coverage
Complement studies of the Local Void and nearby filaments
Comparison with Other Nearby Voids
| Void Name | Distance | Size | Density | Notes |
|---|---|---|---|---|
| Taurus Void | ~100–160 Mly | ~50–70 Mly | Low | Near ZoA; partially hidden |
| Local Void | ~10–150 Mly | ~100–150 Mly | Very low | Strong influence on Milky Way |
| Delphinus Void | ~250–300 Mly | ~100 Mly | Very low | Northern sky; infrared-revealed |
| Eridanus Void | ~400 Mly | ~150 Mly | Moderate | Southern filament junction |
Final Thoughts – A Modest but Mighty Underdensity
The Taurus Void may not be vast, and it may not be visible—but its presence is felt. From shaping local galaxy flow to challenging our survey strategies, it stands as a reminder that:
What we cannot see often still shapes what we do.
As HI and infrared mapping efforts grow, this quiet corner of the cosmos will become clearer—filling in one more piece of the cosmic puzzle surrounding the Milky Way.
