2024-12-16 18:01:00
The study co-directed by the Superior Council of Scientific Research (CSIC), an organization dependent on the Ministry of Science, Innovation and Universities, and the Institute of Astrophysics of the Canary Islands (IAC) presents a new method to measure extragalactic distances using type Ia supernovae (SNe Ia) through a purely empirical approach. This method, published in The Astrophysical Journal, allows estimates to be made relative galactic distances with 2% uncertainty.something that until now was 8% or higher than this percentage.
In 1929, astronomer Edwin Hubble discovered that the universe is expanding. Since then, scientific researchers have disagreed on the speed of cosmic expansion, what in the scientific world is known as the Hubble constant (H0).
Research groups have continued for decades taking different references to carry out these measurements, using increasingly advanced technologies that have allowed us to obtain increasingly precise data. But the conclusions they come to show discrepancies with the Hubble constant, this is what is called the Hubble tension.
The Cepheid star method
To determine cosmic expansion, the tricky thing is measuring distances to galaxies throughout the universe. Edwin Hubble himself used Cepheids, a type of variable star that changes both temperature and diameter to produce changes in brightness with a very regular period and amplitude. But some industry experts suspect that measurement errors occur because Cepheid stars are found in young galaxies, where there are many other stars, as well as dust and gas.
The Cepheid method attempts to calibrate the brightness of supernovae in galaxies up to 40 Mpc in which Cepheids whose distance has been determined and supernovae in that intermediate range coincide, which then serves to calibrate the more distant ones. The option chosen by the authors of the published study is to avoid calibrating the SNe Ia in that mid-distance range of 40 Mpc and to focus on supernovae in nearby galaxies, whose distance is well known to more distant galaxies.
Supernova twins
“The key to our approach is based on the ‘SNe Ia twin’. That is, we have a Type Ia supernova nearby and another one that is virtually identical, much further away.” explains Pilar Ruiz-Lapuente, research professor at the Institute of Fundamental Physics (IFF-CSIC), CSIC.. “Because the distant SNe Ia twins are found in galaxies where peculiar velocities are relatively unimportant, their distances allow us to directly obtain the Hubble constant (H0) and help solve the Hubble stress problem.”
The work studied the supernova SN 2013dy (in the galaxy NGC 7250), which is the twin of SN 2017cbv/SN 2013aa (both in NGC 5643, still considered a good galaxy according to the methods based on Cepheid stars and on the cusp of the red giants or TRGB (Tip of the Red Giant Branch). the authors used phases close to maximum brightness of this type of supernovae and also after that maximum for better distance accuracy which can approach the percentage of 2% in relative distances.
“Another 2% error is associated with adding the obtained error in relative distances to the error in anchor distances and thus obtaining the absolute distances. We use, for this accuracy, only nearby galaxies for which distances have been obtained, giving the same result, with various methods”, comments Jonay González Hernández, researcher at the Institute of Astrophysics of the Canary Islands.
The authors of this study have already applied this new method to distant galaxies and intend to publish the result of the value of the Hubble constant (H0) in a new scientific article.
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