Hubble bubble (astronomy)

Lore & Background

In 1998, Zehavi et al. reported evidence supporting a Hubble bubble based on observations of 44 Type Ia supernovae, suggesting Earth lies inside a relative void of roughly 20% underdensity surrounded by a dense shell. This idea challenged the Copernican principle that Earth is not in a specially favored position, as it would imply a local deviation from the globally averaged Hubble constant.

Later testing produced mixed results. In 2007, Conley et al. examined supernova color data accounting for cosmic dust and concluded the data did not support a local Hubble bubble. In 2010, Moss et al. analyzed void models without using the term 'Hubble bubble,' finding them in severe tension with data from supernovae, the cosmic microwave background, and Big Bang nucleosynthesis, predicting a very low local Hubble rate and an 'old age problem.'

Despite these challenges, some evidence has been interpreted as consistent with a local void. Data from the Two Micron All Sky Survey (2003) suggested a local underdensity approximately 200 megaparsecs in diameter, and larger voids like the KBC Void out to 600 Mpc have been proposed based on galaxy luminosity density studies.

Reader's Guide

The Hubble bubble hypothesis is significant because it offers a potential alternative to dark energy for explaining the apparent acceleration of the universe, and it may help resolve the Hubble tension—the persistent discrepancy between measurements of the Hubble constant from the cosmic microwave background (lower values) and from local methods like the cosmic distance ladder (higher values). If Earth is near the center of a large, low-density void, the local expansion rate would be faster, potentially accounting for the higher local measurements. However, the hypothesis remains disputed: studies in 2007 and 2010 found it inconsistent with supernova and cosmic microwave background data, while later galaxy surveys have provided some support for a local underdensity. The debate underscores the challenge of determining whether Earth occupies a special position in the universe, and the Hubble bubble remains an active area of research in cosmology, particularly in relation to the Hubble tension.

Did You Know?

• The term 'Hubble bubble' refers to a local departure of the Hubble constant from its globally averaged value, possibly caused by a local void in mass density.
• In 1998, Zehavi et al. reported evidence for a Hubble bubble based on 44 Type Ia supernovae, suggesting Earth is inside a 20% underdense region.
• In 2010, Moss et al. concluded that void models are in severe tension with data, predicting a very low local Hubble rate and an 'old age problem'.
• Data from the Two Micron All Sky Survey (2003) suggested a local underdensity approximately 200 megaparsecs in diameter.