The Hubble Space Telescope has completed a nearly 30-year cycle of observing cosmic objects known as “standard candles” – cephalopods and Type Ia supernovae. As a result, astronomers now have an unprecedented body of data to calculate the rate at which the universe is expanding.
Hubble constant problem
In 1924, the American astronomer Edwin Hubble discovered that there are many other galaxies besides ours and found that they were at a constant distance from each other. The farther away galaxies are, the faster they move away. Hence Hubble’s Law, where we can calculate the speed of this expansion.
Hubble created a unit that describes how fast the universe is expanding, which is (km/s)/Mpc. At that time, Hubble measured the value at 501 km / sec for 1 Mpc (Megaparsec, equivalent to 3.26 million light-years), that is, galaxies at a distance of 1 Mpc will have a speed of 501 km / sec. This result, however, has been shrouded in skepticism.
When the Hubble telescope was planned, this was a problem. Therefore, astronomers planned to use the new instrument to definitively determine the expansion rate of the universe. This could be done if the telescope could collect accurate data from Cepheid stars and Type Ia supernovae.
That’s exactly what the Hubble Telescope did during its first marathons of observations — thanks to the untold efforts of decades of research by various teams. Despite this, the problem of the Hubble constant has not yet been solved.
The Hubble telescope is searching for a solution
Shortly after the launch of the Hubble Space Telescope in 1990, the first batch of observations of Cephas stars came to calculate the Hubble constant. For this, two teams were needed: the HST Key Project and the team led by Alan Sandage. Cepheids are stars that periodically increase in size, which allows you to calculate their distances with high accuracy.
By knowing and measuring the distances to the Cepheids periodically, astronomers should be able to tell the rate at which the universe is expanding, as they are moving away due to this phenomenon. But in practice, it is not so simple: other methods of equal accuracy for calculating the expansion of the universe yield different results.
In the early 2000s, teams studying the Phaephians through the Hubble telescope declared they had “mission accomplished.” They obtained a value of 72 (km/sec) Mpc and a margin of error of only 10% – for comparison, estimates before the telescope have a margin of error of 50%.
Although giving some confidence to the scientists, the 10% margin is still not as satisfactory as we would like. So in 2005, and then in 2009, new cameras were added to the space telescope, starting a “second generation” search for the Hubble constant. The goal: to get 99% sure results.
The SH0ES project (short for Supernova, H0, for dark energy state equation) was one of the new teams formed to calculate the number by studying the cosmic microwave background radiation (“light” left over from 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) million cubic metres. Other methods have been used to measure the Hubble constant and have reached approximate results. However, the controversy is far from over, and it is causing headaches for physicists.
Unfortunately (or not), measurements from the European Space Agency’s Planck mission (which also monitored microwave background radiation) predicted a lower value of the Hubble constant: 67.5 (km/s) Mpc. Some say this difference would be “no problem,” but the concern remains.
Nearly 30 years after the first scans of the Hubble constant with the telescope of the same name, the SH0ES team measured 42 new standard candles — all Type Ia supernovae, meaning stars that explode at a rate of about once a year.
“We have a complete sample of all the Hubble-accessible supernovae seen in the past 40 years,” said Adam Rees of the Space Telescope Science Institute (STScI) and Johns Hopkins University. He is the leader of a new study that has been accepted for publication in Astrophysical Journal.
“The Hubble constant is a very special number. Our understanding of the universe. This requires an enormous amount of detailed work,” said Dr. Licia Verdi, a cosmologist at ICREA and ICC-University of Barcelona.
Of the estimates that the standard candlestick catalog could provide once complete, with Hubble’s sample count, “there’s only a one in a million chance for unlucky astronomers to be wrong,” Reese said of the estimates. “I don’t really care about the value of scaling specifically, but I like using it to learn about the universe,” he added.
Reese and his colleagues may well be rewarded for 30 years of work expanding the universe with the Hubble telescope. It is, depending on the results that will be obtained with a new group of supernovae, that scientists may arrive at the discovery of completely new physics. This is something worth investing in a career.