Mira Variable Stars | 01 Sep 2025

Source: IE

A new study by the Inter-University Centre for Astronomy and Astrophysics (IUCAA), co-authored by Nobel Laureate Adam Riess, uses oxygen-rich Mira variable stars to measure the Hubble constant with 3.7% precision.

Mira Stars (Omicron Ceti)

• About: Mira is a pulsating red giant star whose brightness varies regularly, with periods ranging from 100 to 1,000 days, due to expansion and contraction cycles in its outer layers.
  • It was the first known variable star (a star that doesn't shine with a constant brightness), identified in the 17th century.
  • They are relatively cool, with surface temperatures around 3,000 Kelvin, and are in the late stages of stellar evolution. 
• Significance: They help measure cosmic distances and calibrate the extragalactic distance ladder (a series of methods to determine distances to far-off galaxies).
  • They assist in determining the Hubble constant and resolving the Hubble tension (difference in the Universe’s expansion rate measured from early vs. late-Universe observations) in cosmology.

Hubble Constant (H₀) 

• Formulated by Edwin Hubble in 1929, it measures the current expansion rate of the universe in kilometers per second per megaparsec (km/s/Mpc), indicating how fast galaxies move apart.  H₀ helps estimate the universe’s size and age. 
• Edwin Hubble observed that the farther a galaxy is, the faster it moves away. This is measured using redshift, a shift of light toward the red end of the spectrum, indicating the universe is expanding.