| HD1 | |
|---|---|
 Three-color image of HD1, the most distant galaxy candidate to date, created using data from theVISTA telescope inParanal Observatory. The red object in the center of the zoom-in image is HD1.[1] | |
| Observation data (J2000epoch) | |
| Constellation | Sextans[2][3] |
| Right ascension | 10h 01m 51.31s[2] |
| Declination | 02° 32′ 50.0″[2] |
| Redshift | 13.27[2] |
| Distance |
|
−13 — – −12 — – −11 — – −10 — – −9 — – −8 — – −7 — – −6 — – −5 — – −4 — – −3 — – −2 — – −1 — – 0 — |
| |||||||||||||||||||||||||||||||||||||||
HD1 is a proposedhigh-redshiftgalaxy, which is considered (as of April 2022) to be one of the earliest and mostdistant known galaxies yet identified in theobservable universe. The galaxy, with an estimatedredshift of approximately z = 13.27, is seen as it was about 324 million years after theBig Bang, which was according to scientists around13.787 billion years ago.[6] It has a light-travel distance (lookback time) of 13.463 billion light-years fromEarth, and, due to theexpansion of the universe, apresent proper distance of 33.288 billion light-years.[5]
According to the last spectroscopic studies (cf.https://arxiv.org/abs/2406.18352, 2024), the new redshift of HD1 is z = 4.0.
The discovery of the proposedhigh-redshift galaxy HD1 (RA:10:01:51.31DEC:+02:32:50.0) in theSextans constellation,[2][3] along with another high-redshift galaxy, HD2 (RA:02:18:52.44DEC:-05:08:36.1) in theCetus constellation,[2][3] was reported by astronomers at theUniversity of Tokyo on 7 April 2022. These two galaxies were found in two patches of sky surveyed by theCosmic Evolution Survey and by theSubaru Telescope in theSubaru/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 theH band (around 1.6 microns), which could indicate aLyman-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 starsHD 1 andHD 2 in theHenry Draper Catalog.[2]
HD1 is one of the earliest and mostdistant known galaxies yet identified in theobservable universe, having aspectroscopicredshift ofz = 13.27, meaning that the light from the galaxy travelled for 13.5 billion years on its way to Earth, which due to theexpansion of the universe, corresponds to aproper distance of approximately 33.4 billionlight-years (10.2 billionparsecs).[1][2][4][7][8][9] The observed position of HD1 was determined to be about 330 million years after theBig Bang.[10] Another similar high-redshift galaxy, HD2, was determined to be nearly as far away as HD1.[11]
HD1's unusually high brightness has been an open question for its discoverers; it has a significantly more luminous ultraviolet emission than similar galaxies at its redshift range. Possible explanations have been proposed, one being that it is an activeLyman-break galaxy, or a rather extremestarburst galaxy producing stars at a rate far higher than any previously observed. It is also considered that it may have a significant population ofPopulation III stars that are far more massive and luminous than present-day stars.[12] Another scenario is that it may be aquasar hosting asupermassive black hole; such a scenario would put constraints on models of black hole growth in such an early stage of the universe. A resolution to the true nature of the galaxy would likely await confirmations from theJames Webb Space Telescope.[13]
The previous farthest known galaxy,GN-z11, discovered in 2015, had a redshift of 11, suggesting that the observed position of the galaxy is about 420 million years after the Big Bang.[11]
According to the discoverers of HD1 and HD2, "If spectroscopically confirmed, these two sources [ie, HD1 and HD2] will represent a remarkable laboratory to study the Universe at previously inaccessible redshifts."[7] The researchers expect even further clarification of the astronomical objects, including better identifying the objects asgalaxies, or, possibly asquasars orblack holes, when carefully examined by theJames Webb Space Telescope,Nancy Grace Roman Space Telescope, and GREX-PLUS space missions.[2] HD1, on close examination, may also reveal the first visiblePopulation III stars, due to its very early age.[13] In addition, the researchers claim that the use of the new upcoming space telescopes could help discover over 10,000 galaxies at this early epoch of the Universe.[11]
2022 in space | |||||
|---|---|---|---|---|---|
Space probe launches |
|   | |||
| Impact events | |||||
| SelectedNEOs | |||||
| Discoveries |
| ||||
| Comets | |||||
| Space exploration | |||||
