Refining the Expansion Rate of the Universe with 'Twins' Among Type Ia Supernovae express

Type Ia supernovae are the 'standard candles' of cosmology: their peak luminosity is nearly identical, allowing distances to be determined from apparent brightness — the fainter the object, the farther away it is. Such supernovae serve as markers for measuring distances to distant galaxies. However, on their way to us, light inevitably encounters cosmic dust — microscopic solid particles that scatter and absorb radiation. Like a dirty windowpane, dust dims brightness and slightly alters color, introducing a systematic error into calculations. To circumvent this problem, a team of astronomers led by Adam Riess employed an elegant method: they selected only pairs of 'twins'—supernovae with nearly identical spectral characteristics and light curves, whose light passed through regions with the same degree of dustiness. The analogy of lamps hidden in identical shades is apt, though it simplifies the picture: in reality, many parameters were considered, including spectral reddening. This approach significantly reduced the influence of the dust factor. The new, more precise data yielded a value for the rate of expansion of the Universe, the Hubble constant, of about 72.4 km/s per megaparsec (a megaparsec is 3.26 million light-years). This value is notably higher than that derived from analysis of the cosmic microwave background — ancient light left over from the Big Bang that carries information about the early Universe. The discrepancy, known as the 'Hubble tension', became even more statistically significant after this work.