HD1: The oldest and farthest galaxy

HD1 HD1 is a proposed high-redshift galaxy, which is considered (as of April 2022) to be one of the earliest and most distant known galaxies yet identified in the observable universe. The galaxy, with an estimated redshift of approximately z = 13. 27, is seen as it was about 324 million years after the Big Bang, which was according to scientists around 13. 787 billion years ago. It has a light-travel distance (lookback time) of 13. 463 billion light-years from Earth, and, due to the expansion of the universe, a present proper distance of 33. 288 billion light-years. According to the latest (2024) spectroscopic studies, HD1 is a passive galaxy with redshift z = 4. 0. Discovery The discovery of the proposed high-redshift galaxy HD1 (RA:10:01:51. 31 DEC:+02:32:50. 0) in the Sextans constellation, along with another high-redshift galaxy, HD2 (RA:02:18:52. 44 DEC:-05:08:36. 1) in the Cetus constellation, was reported by astronomers at the University of Tokyo on 7 April 2022. These two galaxies were found in two patches of sky surveyed by the Cosmic Evolution Survey and by the Subaru Telescope in the Subaru/XMM-Newton Deep Survey Field respectively. They were found by looking for objects that are much brighter in the so-called K band of infrared than in the H band (around 1. 6 microns), which could indicate a Lyman-break galaxy red-shifted by a factor of around 13. For this reason they were named "HD 1" and "HD 2" (for "H band dropout", not to be confused with stars HD 1 and HD 2 in the Henry Draper Catalog. Physical properties HD1 is one of the earliest and most distant known galaxies yet identified in the observable universe, having a spectroscopic redshift of z = 13. 27, meaning that the light from the galaxy travelled for 13. 5 billion years on its way to Earth, which due to the expansion of the universe, corresponds to a proper distance of approximately 33. 4 billion light-years (10. 2 billion parsecs). The observed position of HD1 was determined to be about 330 million years afte