The Hubble Space Telescope has completed a nearly 30-year cycle of observing cosmic objects known as “patterned candles” – Cepheid stars and type Ia supernovae. As a result, astronomers now have an unprecedented set of data to calculate the expansion rate of the universe.
Hubble’s constant problem
In 1924, American astronomer Edwin Hubble discovered that there were many other galaxies besides our own and found that they were at a constant distance from each other. The further away the galaxies were, the faster they moved away. Hence Hubble’s law, in which we can calculate the speed of this expansion.
Hubble has created a unit that describes the expansion rate of the universe, which is in (km/s)/Mpc. At the time, Hubble measured the value at 501 km/s for 1 Mpc (Megaparsec, equivalent to 3.26 million light years), i.e. galaxies 1 Mpc apart would have a speed of 501 km/s. However, this result was surrounded by uncertainties.
When the Hubble telescope was planned, this was still a problem. Therefore, astronomers planned to use the new instrument to determine once and for all the expansion rate of the universe. This could be done if the telescope could collect accurate data on Cepheid stars and Type Ia supernovae.
This is exactly what the Hubble Telescope did during its first marathons of observations, thanks to the untold efforts of decades of research carried out by different teams. Despite this, the constant Hubble problem has not yet been solved.
The Hubble telescope is looking for a solution
Shortly after the launch of the Hubble Space Telescope in 1990 came the first batch of Cepheid star observations to calculate the Hubble constant. For this, two teams were needed: the HST Key Project and the team led by Allan Sandage. Cepheids are stars that periodically increase in size, which allows you to calculate their distances with great accuracy.
Knowing the distances to the Cepheids and measuring them periodically, astronomers should be able to tell how fast the universe is expanding, as they are moving away due to this phenomenon. But in practice, it is not so simple: other equally precise methods of calculating the expansion of the universe give different results.
In the early 2000s, teams studying Cepheids through the Hubble telescope declared it “mission accomplished”. They obtained a value of 72 (km/s)Mpc and a margin of error of only 10% – for comparison, the estimates before the telescope had a margin of error of 50%.
Despite some confidence in scientists, the 10% margin is still not as satisfactory as we would like. Thus, in 2005, then in 2009, new cameras were added to the space telescope, which inaugurated the “Generation 2” search for the Hubble constant. The objective: to obtain results with 99% certainty.
Project SH0ES (acronym for Supernova, H0, for Dark Energy Equation of State) was one of several new teams formed to calculate the number by studying cosmic microwave background radiation (the “light”) left by the Big Bang, like a fossil from the beginning of the universe).
Several teams participated in the effort and the data indicated a value of 73 (km/s)Mpc. Other approaches have been used to measure the Hubble constant and have arrived at approximate results. However, the debate is far from over and gives physicists a hard time.
Unfortunately (or not), measurements from the European Space Agency’s Planck mission (which also observed the microwave background radiation) predict a lower value for the Hubble constant: 67.5 (km/s)Mpc . there are those who say that this discrepancy would be a “non-issue”but the turmoil remains.
Almost 30 years after Hubble’s first constant readings with the eponymous telescope, the SH0ES team has measured 42 new standard candles – all Type Ia supernovae, i.e. stars exploding at a rate of about once a year.
“We have a complete sample of all Hubble-accessible supernovae observed over the past 40 years,” said Adam Riess of the Space Telescope Science Institute (STScI) and Johns Hopkins University. He is the leader of the new study, accepted for publication in The Astrophysical Journal.
“The Hubble constant is a very special number,” said Dr Licia Verde, a cosmologist at ICREA and ICC-University of Barcelona. our understanding of the universe. It took a tremendous amount of detailed work.”
With Hubble’s sample count, “there’s only a one-in-a-million chance that astronomers are unlucky enough to be wrong,” Riess said of the estimates the standard candlestick catalog can once provide. finished. “I don’t care specifically about the expansion value, but I like to use it to learn more about the universe,” he added.
Perhaps Riess and his colleagues are well rewarded for their 30 years of work expanding the universe with the Hubble Telescope. It is that, depending on the results to be obtained with a new set of supernovae, scientists may arrive at the discovery of completely new physics. It’s something worth investing a career in.