The Lockman Hole is an area of the

sky The sky is an unobstructed view upward from the surface of the Earth. It includes the atmosphere and outer space. It may also be considered a place between the ground and outer space, thus distinct from outer space. In the field of astronomy, ...

in which minimal amounts of neutral

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...

gas Gas is one of the four fundamental states of matter (the others being solid, liquid, and plasma). A pure gas may be made up of individual atoms (e.g. a noble gas like neon), elemental molecules made from one type of atom (e.g. oxygen), or ...

are observed. Clouds of neutral hydrogen glow faintly with

infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...

light and obscure distant views at

extreme ultraviolet Extreme ultraviolet radiation (EUV or XUV) or high-energy ultraviolet radiation is electromagnetic radiation in the part of the electromagnetic spectrum spanning wavelengths from 124 nm down to 10 nm, and therefore (by the Planck– ...

and

soft x-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 Picometre, picometers to 10 Nanometre, nanometers, corresponding to frequency, ...

wavelengths. They interfere with observations at those wavelengths in nearly all other directions since they are common in our galaxy. So the Lockman Hole serves as a relatively clear window on distant objects, which makes it an attractive area of the sky for observational astronomy surveys. It is located near the pointer stars of the

Big Dipper The Big Dipper ( US, Canada) or the Plough ( UK, Ireland) is a large asterism consisting of seven bright stars of the constellation Ursa Major; six of them are of second magnitude and one, Megrez (δ), of third magnitude. Four define a "bowl" ...

in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...

Ursa Major Ursa Major (; also known as the Great Bear) is a constellation in the northern sky, whose associated mythology likely dates back into prehistory. Its Latin name means "greater (or larger) bear," referring to and contrasting it with nearby Ursa ...

and is about 15 square degrees in size. It is named after its discoverer, astronomer Jay Lockman.

Location

The Lockman Hole is located at about RA 10h 45m, Dec. +58° and is defined by a region of low neutral hydrogen gas and dust

column density The area density (also known as areal density, surface density, superficial density, areic density, mass thickness, column density, or density thickness) of a two-dimensional object is calculated as the mass per unit area. The SI derived unit is ...

. Column density is a commonly used measure in astronomy for the quantity of a given

chemical element A chemical element is a species of atoms that have a given number of protons in their nuclei, including the pure substance consisting only of that species. Unlike chemical compounds, chemical elements cannot be broken down into simpler sub ...

molecule A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioch ...

in a certain direction. In this region, the typical column density of neutral hydrogen is ''N''_H = 0.6 x 10²⁰ cm⁻². This column density is moderately lower than typical values near the galactic poles, where ''N''_H

\sim

10²⁰ cm⁻², and H I column densities of ''N''_H > 10²¹ cm⁻² are common at low galactic latitudes and towards H I clouds. The region around B1950.0 RA Dec has a minimum ''N''_H of 4.5 x 10¹⁹ cm⁻². There is a diffuse cloud covering half of the field. The ''Lockman Hole East'' is a subregion of the Lockman Hole centered at J2000.0 RA Dec . The ''Lockman Hole North-west'' (LHNW) is a region that appears about as wide as the moon centered at J2000.0 RA Dec ., with a column density of ''N''_H = 5.72 x 10¹⁹ cm⁻².

Hydrogen gas absorption and emission

Clouds of neutral hydrogen are ubiquitous in the

Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye ...

galaxy, and effectively absorb

photon A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they always ...

s that are energetic enough to

ionize Ionization, or Ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecule i ...

hydrogen, which requires an energy of 13.6

electron volt In physics, an electronvolt (symbol eV, also written electron-volt and electron volt) is the measure of an amount of kinetic energy gained by a single electron accelerating from rest through an electric potential difference of one volt in vacuum. ...

s (in the

range). Even the relatively small amounts of hydrogen in the Lockman Hole absorb most radiation at and just above energies of 13.6 electron volts, but even so it transmits

and

radiation In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes: * ''electromagnetic radiation'', such as radio waves, microwaves, infrared, visi ...

from extragalactic objects to a greater degree than other areas of the sky. Neutral hydrogen is also associated with

diffuse Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical p ...

emission at

wavelengths that can confuse observations of faint infrared sources.

Observations

The relatively clear

field of view The field of view (FoV) is the extent of the observable world that is seen at any given moment. In the case of optical instruments or sensors it is a solid angle through which a detector is sensitive to electromagnetic radiation. Humans a ...

offered by the Lockman Hole has allowed its use to view extremely distant regions of the universe. Observations by the Spectral and Photometric Imaging Receiver (SPIRE) instrument aboard the

Herschel Space Telescope The Herschel Space Observatory was a space observatory built and operated by the European Space Agency (ESA). It was active from 2009 to 2013, and was the largest infrared telescope ever launched until the launch of the James Webb Space Teles ...

of the Lockman Hole have imaged thousands of extremely distant

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. ...

that appear as they did 10–12 billion years ago. This field of view also contains hundreds of

astronomical X-ray source Astrophysical X-ray sources are astronomical objects with physical properties which result in the emission of X-rays. Several types of astrophysical objects emit X-rays. They include galaxy clusters, black holes in active galactic nuclei (AGN), ...

s, some of them supermassive

black hole A black hole is a region of spacetime where gravitation, gravity is so strong that nothing, including light or other Electromagnetic radiation, electromagnetic waves, has enough energy to escape it. The theory of general relativity predicts t ...

s. The

Chandra X-ray Observatory The Chandra X-ray Observatory (CXO), previously known as the Advanced X-ray Astrophysics Facility (AXAF), is a Flagship-class space telescope launched aboard the during STS-93 by NASA on July 23, 1999. Chandra is sensitive to X-ray sources 1 ...

and

ROSAT ROSAT (short for Röntgensatellit; in German X-rays are called Röntgenstrahlen, in honour of Wilhelm Röntgen) was a German Aerospace Center-led satellite X-ray telescope, with instruments built by West Germany, the United Kingdom and the Uni ...

have been used to study X-ray sources from the Lockman Hole. Some 75 X-ray sources are observed with the PSPC of

. Detailed X-ray spectral analysis has been performed on 123 X-ray sources in the Lockman Hole using XMM-Newton. The diffuse X-ray background (XRB) has also been studied in the area. Active galactic nuclei have also been studied in the area, for example MBC2005.

References

External links

Lockman Hole at Chandra

The Lockman Hole by the Herschel Space Observatory

Spitzer Space Telescope and the Lockman Hole

XMM-Newton Observations of the Lockman Hole

The Lockman Hole from the Max-Planck-Institut für extraterrestrische Physik
Interstellar media Observational astronomy Ursa Major (constellation) X-ray astronomy

Location

Hydrogen gas absorption and emission

Observations

See also

References

Further reading

External links