Astronomers have clarified the expansion rate of the Universe
A new large survey of distant supernovae has made it possible to estimate the dark energy content of the universe and to calculate the rate of its expansion. However, these figures have not resolved, but only exacerbated, the old paradox of cosmology. They are even more inconsistent with similarly accurate results, but obtained from observations of the relic background.
To estimate cosmic distances, standard candlesticks, distant objects with precisely known luminosity, are used. These include, for example, Type Ia supernovae, which are associated with thermonuclear explosions of white dwarfs that have pulled too much matter from a nearby nearby star. For a brief time, such explosions can shine brighter than an entire galaxy and become visible at distances of billions of light-years. Since explosions occur when they reach a strictly defined mass, their true brightness is almost the same, and their visible brightness depends on the distance. This allows them to be used as standard candles.
In the late 1990s, it was type Ia supernovae that allowed us to observe the accelerating expansion of our Universe. Since then, new observations have emerged that clarify the speed of this process. Several years ago, as part of the Pantheon survey, astrophysicists analyzed the luminosities of about a thousand distant supernovae. And now they have supplemented and expanded that data: the new Pantheon+ survey already included more than 1,500 supernovae at distances as far as 10.7 billion light-years. It has made it possible to once again estimate the rate of expansion of the Universe, its dark matter and energy content. The report of the work is published in The Astrophysical Journal.
According to these estimates, 33.8 percent of our world is made up of gravitational matter, ordinary and dark matter. The remaining 66.2 percent is dark energy, a mysterious entity that has been linked to the expansion of the universe. The rate of this expansion is described by the Hubble constant, which astronomers have determined to be 45.6 miles per second per megaparsec. In other words, the near Universe is expanding at a rate of nearly 161,500 miles per hour for every megaparsec, which in turn is about 3.26 light-years. This is slightly more than past estimates from supernovae observations.
Unfortunately, these figures have not resolved the well-known cosmological crisis associated with the Hubble constant. The problem is that data from different observations give markedly different results. In particular, studies of the microwave background of the Universe indicate lower values of the constant, 41.5 miles per second per megaparsec. The Pantheon+ results only exacerbated the gap between these values and those obtained from supernovae observations. Moreover, the deviation has reached the proverbial value of five sigmas (σ) – meaning that it is statistically reliable, and the chances of an accident do not exceed one in a million. The problem remains, requiring new models to explain this difference.