HD1 is a proposed high-redshift

galaxy A galaxy is a system of stars, stellar remnants, interstellar gas, dust, 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 System. ...

, and 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-shaped region of the universe comprising all matter that can be observed from Earth or its space-based telescopes and exploratory probes at the present time, because the electromagnetic radiation from these obj ...

. 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 simultaneous increase in f ...

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

Big Bang The Big Bang event is a physical theory that describes how the universe expanded from an initial state of high density and temperature. Various cosmological models of the Big Bang explain the evolution of the observable universe from the ...

, 13.787 billion years ago. It has a light-travel distance (

lookback time Before Present (BP) years, or "years before present", is a time scale used mainly in archaeology, geology and other scientific disciplines to specify when events occurred relative to the origin of practical radiocarbon dating in the 1950s. Becau ...

) of 13.463 billion light-years from

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

, and, due to the

expansion of the universe The expansion of the universe is the increase in distance between any two given gravitationally unbound parts of the observable universe with time. It is an intrinsic expansion whereby the scale of space itself changes. The universe does not exp ...

, 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")

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 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 wo ...

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 gala ...

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 HD 1, also known as HIP 422, is the first star catalogued in the Henry Draper Catalogue. It is located in the northern circumpolar constellation Cephus and has an apparent magnitude of 7.42, making it readily visible in binoculars, ...

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

, having a spectroscopic

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 Proper length or rest length is the length of an object in the object's rest frame. The measurement of lengths is more complicated in the theory of relativity than in classical mechanics. In classical mechanics, lengths are measured based on t ...

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 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 During 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 noticed th ...

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 pronounced , and sometimes known as a quasi-stellar object, abbreviated QSO. This emission from a galaxy nucleus is powered by a supermassive black hole with a m ...

hosting a supermassive 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 the

James Webb Space Telescope The James Webb Space Telescope (JWST) is a space telescope which conducts infrared astronomy. As the largest optical telescope in space, its high resolution and sensitivity allow it to view objects too old, distant, or faint for the Hubble Spa ...

. The previous farthest known galaxy,

GN-z11 GN-z11 is a high-redshift galaxy found in the constellation Ursa Major. It is one of the farthest known galaxies from Earth ever discovered. The 2015 discovery was published in a 2016 paper headed by Pascal Oesch and Gabriel Brammer (Cosmic Dawn ...

, 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.

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, 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 System. ...

, or, possibly as quasars or

black holes A black hole is a region of spacetime where gravity is so strong that nothing, including light or other electromagnetic waves, has enough energy to escape it. The theory of general relativity predicts that a sufficiently compact mass can def ...

, when carefully examined by the

Nancy Grace Roman Space Telescope The Nancy Grace Roman Space Telescope (shortened as Roman or the Roman Space Telescope, and formerly the Wide-Field Infrared Survey Telescope or WFIRST) is a NASA infrared space telescope currently in development and scheduled to launch by Ma ...

, 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. EarliestGalaxyCandidates-20220407

References

External links

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

Discovery

Physical properties

Future considerations

See also

References

External links