HD1 is a proposed high-redshift

galaxy A galaxy is a Physical system, system of stars, stellar remnants, interstellar medium, interstellar gas, cosmic dust, dust, and dark matter bound together by gravity. The word is derived from the Ancient Greek, Greek ' (), literally 'milky', ...

, 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 observable universe is a Ball (mathematics), spherical region of the universe consisting of all matter that can be observation, observed from Earth; the electromagnetic radiation from these astronomical object, objects has had time to reach t ...

. The galaxy, with an estimated

redshift In physics, a redshift is an increase in the wavelength, and corresponding decrease in the frequency and photon energy, of electromagnetic radiation (such as light). The opposite change, a decrease in wavelength and increase in frequency and e ...

of approximately z = 13.27, is seen as it was about 324 million years after the

Big Bang The Big Bang is a physical theory that describes how the universe expanded from an initial state of high density and temperature. Various cosmological models based on the Big Bang concept explain a broad range of phenomena, including th ...

, 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 Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

, and, due to the

expansion of the universe The expansion of the universe is the increase in proper length, distance between Gravitational binding energy, gravitationally unbound parts of the observable universe with time. It is an intrinsic and extrinsic properties (philosophy), intrins ...

, a present proper distance of 33.288 billion light-years. KEMP Cosmology Calculator - Set H₀=67.4 and Omega_M=0.315 (see Table/Planck2018 at " Lambda-CDM model#Parameters") 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 Sextans is a faint, minor constellation on the celestial equator which was introduced in 1687 by Polish astronomer Johannes Hevelius. Its name is Latin for the astronomical sextant, an instrument that Hevelius made frequent use of in his obs ...

constellation, along with another high-redshift galaxy, HD2 ( RA:02:18:52.44 DEC:-05:08:36.1) in the

Cetus Cetus () is a constellation, sometimes called 'the whale' in English. The Cetus (mythology), Cetus was a sea monster in Greek mythology which both Perseus and Heracles needed to slay. Cetus is in the region of the sky that contains other water- ...

constellation, was reported by astronomers at the

University of Tokyo The University of Tokyo (, abbreviated as in Japanese and UTokyo in English) is a public research university in Bunkyō, Tokyo, Japan. Founded in 1877 as the nation's first modern university by the merger of several pre-westernisation era ins ...

on 7 April 2022. These two galaxies were found in two patches of sky surveyed by the

Cosmic Evolution Survey The Cosmic Evolution Survey (COSMOS) is a Hubble Space Telescope (HST) Treasury Project to survey a two square degree equatorial field with the Advanced Camera for Surveys (ACS). The largest survey ever undertaken by HST, the project incorpora ...

and by the

Subaru Telescope is the telescope of the National Astronomical Observatory of Japan, located at the Mauna Kea Observatory on Hawaii. It is named after the open star cluster known in English as the Pleiades. It had the largest monolithic primary mirror in the ...

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 Lyman-break galaxies are star-forming galaxies at high redshift that are selected using the differing appearance of the galaxy in several imaging filters due to the position of the Lyman limit. The technique has primarily been used to select g ...

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 The ''Henry Draper Catalogue'' (HD) is an astronomical star catalogue published between 1918 and 1924, giving spectroscopic classifications for 225,300 stars; it was later expanded by the ''Henry Draper Extension'' (HDE), published between 192 ...

Physical properties

HD1 is one of the earliest and most distant known galaxies yet identified in the

, having a

spectroscopic Spectroscopy is the field of study that measures and interprets electromagnetic spectra. In narrower contexts, spectroscopy is the precise study of color as generalized from visible light to all bands of the electromagnetic spectrum. Spectrosc ...

of , meaning that the light from the galaxy travelled for 13.5 billion years on its way to Earth, which due to the

, corresponds to a proper distance of approximately . The observed position of HD1 was determined to be about 330 million years after the

. Another similar high-redshift galaxy, HD2, was determined to be nearly as far away as HD1. 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 active

, or a rather extreme

starburst galaxy A starburst galaxy is one undergoing an exceptionally high rate of star formation, as compared to the long-term average rate of star formation in the galaxy, or the star formation rate observed in most other galaxies. For example, the star format ...

producing stars at a rate far higher than any previously observed. It is also considered that it may have a significant population of

Population III stars In 1944, Walter Baade categorized groups of stars within the Milky Way into stellar populations. In the abstract of the article by Baade, he recognizes that Jan Oort originally conceived this type of classification in 1926. Baade observed tha ...

that are far more massive and luminous than present-day stars. Another scenario is that it may be a

quasar A quasar ( ) is an extremely Luminosity, luminous active galactic nucleus (AGN). It is sometimes known as a quasi-stellar object, abbreviated QSO. The emission from an AGN is powered by accretion onto a supermassive black hole with a mass rangi ...

hosting a

supermassive black hole A supermassive black hole (SMBH or sometimes SBH) is the largest type of black hole, with its mass being on the order of hundreds of thousands, or millions to billions, of times the mass of the Sun (). Black holes are a class of astronomical ...

; 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 the

James Webb Space Telescope The James Webb Space Telescope (JWST) is a space telescope designed to conduct infrared astronomy. As the largest telescope in space, it is equipped with high-resolution and high-sensitivity instruments, allowing it to view objects too old, Lis ...

. 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. EarliestGalaxyCandidates-20220407

Future considerations

According to the discoverers of HD1 and HD2, "If spectroscopically confirmed, these two sources e, HD1 and HD2will represent a remarkable laboratory to study the Universe at previously inaccessible redshifts." The researchers expect even further clarification of the astronomical objects, including better identifying the objects as

galaxies A galaxy is a system of stars, stellar remnants, interstellar gas, dust, and dark matter bound together by gravity. The word is derived from the Greek ' (), literally 'milky', a reference to the Milky Way galaxy that contains the Solar Sys ...

, or, possibly as

quasars A quasar ( ) is an extremely Luminosity, luminous active galactic nucleus (AGN). It is sometimes known as a quasi-stellar object, abbreviated QSO. The emission from an AGN is powered by accretion onto a supermassive black hole with a mass rangi ...

black holes A black hole is a massive, compact astronomical object so dense that its gravity prevents anything from escaping, even light. Albert Einstein's theory of general relativity predicts that a sufficiently compact mass will form a black hole. Th ...

, when carefully examined by the

Nancy Grace Roman Space Telescope The Nancy Grace Roman Space Telescope (shortened as the Roman Space Telescope, Roman, or RST) is a NASA infrared space telescope in development and scheduled to launch to a Sun–Earth L2 orbit by May 2027. It is named after former NASA Chie ...

, and GREX-PLUS space missions. HD1, on close examination, may also reveal the first visible

, due to its very early age. 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.

References

External links

* {{Sky, 10, 01, 51.31, +, 02, 32, 36.1, 33400000000 Astronomical objects discovered in 2022 Cetus Sextans Galaxies discovered in 2022

Discovery

Physical properties

Future considerations

See also

References

External links