A new study, consuming data collected over nearly 30 years by the Hubble Space Telescope, may well be the venerable satellite’s greatest contribution to human understanding of the Universe: it shows that, in essence, pieces are missing from our most established model of evolution. of the cosmos, started with the Big Bang, 13.8 billion years ago.
The whole thing revolves around the so-called Hubble constant, a term named after not the telescope, but the astronomer who lent it its name, the American Edwin Hubble. In the 1920s and 1930s, the researcher was part of the first consolidated estimates of the relationship between distance and speed of retreat of galaxies, demonstrating that the universe is expanding. At what pace? That’s what the Hubble constant says, and increasingly accurate measurements of it have been made over the last century. The one that is now presented, in a special article to appear in the Astrophysical Journal, is the most accurate to be taken by a method similar to that adopted by the ancient astronomer.
The work is part of the SH0ES project and is led by Adam Riess, one of the cosmologists awarded the Nobel Prize for the discovery, in 1998, of dark energy, a force that supposedly took over the Universe in the last 5 billion years and made the expansion accelerated cosmic. Using images produced by the space telescope practically since its launch, the researchers focused on Cepheid variables and type Ia supernovae located in 42 different galaxies. Cepheids are a class of pulsating giant stars, and supernovae Ia consist of white dwarf explosions stealing enough material from a companion star. In both cases, they allow a reliable estimate of the distance from their brightness.
The speed of withdrawal, in turn, can be extracted from the redness (redshift) measured in the light of galaxies. It’s the fact that objects moving away from us get redder in light the faster they retreat (as well as bluer if they’re getting closer instead).
With the two data, it is possible to estimate the Hubble constant, known as H0. Riess’ group arrived at a very precise number: 73 km/s/megaparsec, with a margin of error of 1 km/s/Mpc. Translation: with each passing second, each megaparsec of space (3.26 million light-years) expands by another 73 km.
And now comes the mystery: according to the standard cosmological model, applied to data from the European Planck satellite, that number should be 67.5 km/s/Mpc, with a margin of error of half a km/s/Mpc. “There is no indication that the discrepancy arises from measurement uncertainties or analysis variations considered to date,” write Riess and his colleagues. What possibly needs revision, therefore, to bring everything back into line, is the standard cosmological model.
This column is published on Mondays, in Folha Corrida.
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