Universe's expansion rate refined using supernova 'twins' express

Original: ""SNe Ia twins" in the Hubble flow, and the determination of H0"
arXiv:2512.02391 · 2025-12-02 · CC BY 4.0 · 1 min
The 'twin' method refined the universe's expansion rate and deepened the mystery of the 'Hubble tension'.

Type Ia supernovae are like light bulbs of a fixed wattage: the dimmer the light, the farther the source. Such supernovae serve as distance markers to remote galaxies. But cosmic dust, like a dirty window, dims and reddens the light, messing up the calculations. Astronomers led by Adam Riess sidestepped the problem: they compared only 'twins'—supernovae with identical properties, whose light traveled through similarly dusty regions. It's like gauging distance by lamps hidden in identical lampshades. The new data yield a universe expansion rate of about 72.4 km/s per megaparsec (that's 3.26 million light-years). That's noticeably faster than the ancient light from the Big Bang predicts. The discrepancy, known as the 'Hubble tension', has now grown even stronger.

The more carefully scientists rule out errors, the more stubborn the Hubble tension becomes. Perhaps the infant universe expanded under different rules, and our physics textbook is incomplete.

It was precisely with type Ia supernovae that the accelerating expansion of the universe was discovered in 1998—a Nobel Prize-winning breakthrough.

Confirmation of the Hubble tension makes sci-fi scenarios where physical laws evolve just a little less fictional.

H_0 \approx 72.4 \ \text{km/s/Mpc}
The Hubble constant indicates how fast the recession velocity of galaxies increases with distance.
Scientists
Adam RiessBrian SchmidtEdwin HubbleGeorges LemaîtreMaarten SchmidtSaul Perlmutter
Concepts
hubble tension type ia supernova supernova cosmology hubble constant five sigma intermediate mass black hole Hubble's law pantheon plus