NASA released a huge report, which astronomers called magnum opus of Hubble. An analysis of 30 years of space telescope gives the most accurate idea of how fast the universe is expanding.
For most of this century, scientists knew that the universe was expanding. Observing galaxies moving away from us has helped with this. The greater the distance to them, the faster they travel. The speed of their movement relative to the distance from the Earth is called the Hubble constant. Measuring its value was one of the main tasks of the telescope.
To measure the Hubble constant, astronomers have studied distances to objects whose brightness is well known. Thus, the more they fade, the further they are. For relatively close objects within our galaxy, the role of such objects was played by the Cepheids, a class of stars that pulsate in a predictable rhythm. For greater distances, supernovae of type Ia are used – space explosions, whose peak brightness is well studied.
The study of these objects in recent decades has allowed astronomers to count Hubble constant is about 70 km per second per megaparsec. That is, a galaxy one megaparsec from Earth (about 3.3 million light-years) is drifting 70 km away from us every second. Its speed increases by 70 km/s for each additional megaparsec.
For a new study, a team of scientists compiled and analyzed the most complete catalog of these objects to measure the Hubble constant as accurately as possible. To do this, they studied 42 galaxies that had both Cepheids and type Ia supernovae in their composition, filmed by Hubble over the past 30 years.
“This is what the Hubble Space Telescope was built to do, using the best techniques we know to do it. This is likely Hubble’s magnum opus, because it would take another 30 years of Hubble’s life to even double this sample size,” said Adam Riess, Nobel Laureate in Physics and Leading Scientist on the team.
Scientists have calculated that the Hubble constant is 73 (km/s)/Mpc. This is much more accurate than previous measurements. The new data will allow astronomers to improve cosmological models, including a better estimate of the age of the universe and its possible future.
“The Hubble constant is a very special number. It can be used to thread a needle from the past to the present for an end-to-end test of our understanding of the universe. This took a phenomenal amount of detailed work,” says cosmologist Licia Verde.
However, another mystery remains unsolved. The standard model of cosmology assumes that the Hubble constant should be much slower – about 67.5 (km/s)/Mpc. This was even confirmed by observations of the background radiation left over from the Big Bang. The discrepancy seems to depend on the part of the universe that scientists are studying. In the nearest part of it, the constant is faster, while in the distant universe it is slower, even though expansion is accelerating.
The simplest explanation for this would be someone’s mistake, but both cases were measured very reliably. Instead, astronomers speculate that new physics may be at work here. To unravel this mystery, scientists will continue to work with the Webb Telescope, which will be able to measure the same markers even more accurately.