Astrophysics

The road towards precision measurements of H_0 with bright sirens in the Einstein Telescope era

Chiara De Leo, Elsa M. Teixeira, Vivian Poulin

Featured July 27, 2026

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Simply

Using future cosmic ripples (bright sirens) and galaxy patterns (BAO), scientists can measure how fast the universe expands, needing far fewer ripples if they combine both clues to solve a cosmic puzzle.

In depth

The paper forecasts the precision of Hubble constant (

H_{0}

) measurements using future bright sirens (gravitational wave events with electromagnetic counterparts) from the Einstein Telescope. It reveals that while low-redshift bright sirens are crucial for standalone

H_{0}

constraints, combining them with Baryon Acoustic Oscillation (BAO) data significantly reduces the required number of events and extends the informative redshift range by breaking parameter degeneracies.

Key Takeaways

1
Future bright siren catalogues from the Einstein Telescope can provide an independent, distance-ladder-free measurement of the Hubble constant ( $H_{0}$ ).
2
For bright sirens alone, approximately 90 low-redshift events ( $z ≲ 1$ ) are needed to achieve $H_{0}$ precision of $σ_{H_{0}} \sim 1$ km s $^{- 1}$ Mpc $^{- 1}$ , due to degeneracy with $\Omega_m$ at higher redshifts.
3
Including Baryon Acoustic Oscillation (BAO) data dramatically improves precision, requiring only about 20 bright sirens across a broader redshift range ( $z ≲ 2$ ) for the same $σ_{H_{0}} \sim 1$ km s $^{- 1}$ Mpc $^{- 1}$ by breaking the $H_{0} - Ω_{m}$ degeneracy.

Conceptual Flow

HIGH LEVEL

Methodology: Combining Cosmic Clues

The scientists simulated future cosmic ripple signals and galaxy patterns, then combined them to figure out how fast the universe is growing.

Simulated Cosmic Ripples

Simulated Galaxy Patterns

Combine & Analyze

Universe Expansion Rate

Results: Sharper Picture of Expansion

They found that using many cosmic ripples alone gives a fuzzy answer, but combining fewer ripples with galaxy patterns gives a much clearer picture of the universe's expansion.

Many Ripples Alone

Fewer Ripples + Patterns

Compare Precision

Precise Expansion Rate