“The disk in turn is surrounded by hot gas with electrons moving at speeds close to that of light, and when ultraviolet photons encounter these electrons their energy is boosted into the X-rays.” “At the heart of a quasar is a supermassive black hole surrounded by a very hot disk of accreting material that emits in the ultraviolet,” they explained. Bisogni and co-authors propose using quasars as a new standard candle. “However, even supernovae become harder to study in this way as they lie farther away to date the most distant Type Ia supernova with a reliable velocity determination dates from an epoch about 3 billion years after the Big Bang.” “The most reliable supernovae for this purpose, because of their cosmic uniformity, are so-called Type Ia supernovae, which are thought to be ‘standard candles,’ all having the same intrinsic brightness.” “By comparing the observed brightness of a supernova with its intrinsic brightness, based on its classification, astronomers are able to determine its distance comparing that with the host galaxy’s velocity yields the ‘Hubble relation’ relating the galaxy’s velocity to its distance.” “In order to extend the distance scale back to earlier times in cosmic history, astronomers have used supernovae, which can be seen to much greater distances.” “But even today only Cepheid stars in relatively nearby galaxies can be studied in this way,” they said. “She calibrated the effect, and when Hubble compared those calculated values with his observed luminosities he was able to determine their distances.” “Harvard astronomer Henrietta Swan Leavitt had discovered that a Cepheid star varies periodically with a period that is related to its intrinsic luminosity.” Susanna Bisogni from the Harvard-Smithsonian Center for Astrophysics and the INAF – Istituto di Astrofisica Spaziale e Fisica Cosmica Milano and her colleagues. “In 1929, Edwin Hubble published observations that galaxies’ distances and velocities are correlated, with the distances determined using their Cepheid stars,” said Dr. This artist’s impression shows how ULAS J1120+0641, a very distant quasar powered by a black hole with a mass two billion times that of the Sun, may have looked.

Luminosity