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SN Refsdal
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SN Refsdal is the first detected multiply-lensed supernova, visible within the field of the galaxy cluster MACS J1149+2223. It was named after Norwegian astrophysicist Sjur Refsdal, who, in 1964, first proposed using time-delayed images from a lensed supernova to study the expansion of the universe. The observations were made using the Hubble Space Telescope.
SN Refsdal (inset picture) and galaxy cluster MACS J1149.6+2223.
SN Refsdal (inset picture) and galaxy cluster MACS J1149.6+2223.
The image to the left shows a part of the deep field observation of the galaxy cluster MACS J1149.5+2223 from the Frontier Fields programme. The circl
The image to the left shows a part of the deep field observation of the galaxy cluster MACS J1149.5+2223 from the Frontier Fields programme. The circle indicates the predicted position of the newest appearance of the supernova. To the lower right the Einstein cross event from late 2014 is visible. The image on the top right shows observations by Hubble from October 2015, taken at the beginning of the observation programme to detect the newest appearance of the supernova. The image on the lower right shows the discovery of the supernova on 11 December 2015, as predicted by several different models.
Hubble's law
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Hubble's law, also known as the Hubble–Lemaître law, is the observation in physical cosmology that galaxies are moving away from Earth at speeds proportional to their distance. In other words, the farther they are, the faster they are moving away from Earth. The velocity of the galaxies has been determined by their redshift, a shift of the light they emit toward the red end of the visible spectrum. The discovery of Hubble's law is attributed to Edwin Hubble's work published in 1929.
Three steps to the Hubble constant
Three steps to the Hubble constant
Fit of redshift velocities to Hubble's law. Various estimates for the Hubble constant exist. The HST Key H0 Group fitted type Ia supernovae for redshi
Fit of redshift velocities to Hubble's law. Various estimates for the Hubble constant exist. The HST Key H0 Group fitted type Ia supernovae for redshifts between 0.01 and 0.1 to find that H0 = 71 ± 2 (statistical) ± 6 (systematic) km⋅s−1⋅Mpc−1, while Sandage et al. find H0 = 62.3 ± 1.3 (statistical) ± 5 (systematic) km⋅s−1⋅Mpc−1.
A variety of possible recessional velocity vs. redshift functions including the simple linear relation v = cz; a variety of possible shapes from theor
A variety of possible recessional velocity vs. redshift functions including the simple linear relation v = cz; a variety of possible shapes from theories related to general relativity; and a curve that does not permit speeds faster than light in accordance with special relativity. All curves are linear at low redshifts. See Davis and Lineweaver.
The landscape of H0 measurements around 2021, with the Planck (2018) and SH0ES (2020) values highlighted in pink and cyan respectively.
The landscape of H0 measurements around 2021, with the Planck (2018) and SH0ES (2020) values highlighted in pink and cyan respectively.