Thursday, April 21, 2022

The Most distant galaxy yet discovered

13.5 billion light-years (z=13.3): is the distance of Hd1, which is the most distant astronomical object discovered.

Hd1 is an extremely bright galaxy in ultraviolet light and scientists are already making assumptions about its nature. Initially it was believed to be a starbust galaxy, characterized by a high rate of star formation, but observations have shown that Hd1 is forming more than 100 stars each year, a rate that is ten times higher than that of normal starbust galaxies.

To explain their observations, the researchers made two main assumptions. The first assumes that the stars that the galaxy is forming are of Population III. These stars, theorized but never observed, are the very first stars formed just after the Big Bang. Of zero metallicity, the stars of Population III are more massive, warm and bright than normal stars and emit much of their radiation in ultraviolet light, which would explain the luminosity of Hd1 in these wavelengths.

The characteristics of Hd1 could otherwise be explained by assuming that it hosts a supermassive black hole. This second hypothesis is also revolutionary, as supermassive black holes that are so close to the Big Bang have never been observed (or even believed to exist).

To discover Hd1, it took over 1200 hours of joint observation with the Subaru, Spitzer, Vista and Ukirt telescopes, as well as follow-up observations with ALMA, which observed over 700,000 remote objects in space time. The researchers went through all these objects one by one, until they came across Hd1 and its remoteness.

Credit: Harikane et al.

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