Reflection nebula

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The Witch Head reflection nebula (IC2118), about 900 light years from earth, is associated with the bright star Rigel in the constellation Orion. The nebula glows primarily by light reflected from Rigel, located just outside the top right corner of the image. Fine dust in the nebula reflects the light. The blue color is caused not only by Rigel's blue color but because the dust grains reflect blue light more efficiently than red. Reflection.nebula.arp.750pix.jpg
The Witch Head reflection nebula (IC2118), about 900 light years from earth, is associated with the bright star Rigel in the constellation Orion. The nebula glows primarily by light reflected from Rigel, located just outside the top right corner of the image. Fine dust in the nebula reflects the light. The blue color is caused not only by Rigel's blue color but because the dust grains reflect blue light more efficiently than red.

In astronomy, reflection nebulae are clouds of interstellar dust which might reflect the light of a nearby star or stars. The energy from the nearby stars is insufficient to ionize the gas of the nebula to create an emission nebula, but is enough to give sufficient scattering to make the dust visible. Thus, the frequency spectrum shown by reflection nebulae is similar to that of the illuminating stars. Among the microscopic particles responsible for the scattering are carbon compounds (e. g. diamond dust) and compounds of other elements such as iron and nickel. The latter two are often aligned with the galactic magnetic field and cause the scattered light to be slightly polarized. [1]

Contents

Discovery

Reflection nebula IC 2631. Young star lights up reflection nebula IC 2631.jpg
Reflection nebula IC 2631.
Reflection Nebula vdB1 VdB1.jpg
Reflection Nebula vdB1

Analyzing the spectrum of the nebula associated with the star Merope in the Pleiades, Vesto Slipher concluded in 1912 that the source of its light is most likely the star itself, and that the nebula reflects light from the star (and that of the star Alcyone). [3] Calculations by Ejnar Hertzsprung in 1913 lend credence to that hypothesis. [4] Edwin Hubble further distinguished between the emission and reflection nebulae in 1922. [5]

Reflection nebulae are usually blue because the scattering is more efficient for blue light than red (this is the same scattering process that gives us blue skies and red sunsets).

Reflection nebulae and emission nebulae are often seen together and are sometimes both referred to as diffuse nebulae.

Some 500 reflection nebulae are known. A blue reflection nebula can also be seen in the same area of the sky as the Trifid Nebula. The supergiant star Antares, which is very red (spectral class M1), is surrounded by a large, red reflection nebula.

Reflection nebulae may also be the site of star formation.

Luminosity law

Cosmic dust clouds in Messier 78. Cosmic dust clouds in reflection nebula Messier 78.jpg
Cosmic dust clouds in Messier 78.

In 1922, Edwin Hubble published the result of his investigations on bright nebulae. One part of this work is the Hubble luminosity law for reflection nebulae, which makes a relationship between the angular size (R) of the nebula and the apparent magnitude (m) of the associated star:

5 log(R) = -m + k

where k is a constant that depends on the sensitivity of the measurement.

See also

Related Research Articles

Galaxy Astronomical structure

A galaxy is a gravitationally bound system of stars, stellar remnants, interstellar gas, dust, and dark matter. The word is derived from the Greek galaxias (γαλαξίας), literally "milky", a reference to the Milky Way. Galaxies range in size from dwarfs with just a few hundred million stars to giants with one hundred trillion stars, each orbiting its galaxy's center of mass.

Nebula Body of interstellar clouds

A nebula is a distinct body of interstellar clouds. Originally, the term was used to describe any diffused astronomical object, including galaxies beyond the Milky Way. The Andromeda Galaxy, for instance, was once referred to as the Andromeda Nebula before the true nature of galaxies was confirmed in the early 20th century by Vesto Slipher, Edwin Hubble and others. Edwin Hubble discovered that most nebulae are associated with stars and illuminated by starlight. He also helped categorize nebulae based on the type of light spectra they produced.

Redshift Eventual increase of wavelength in radiation during travel

In physics, a redshift is an increase in the wavelength, and corresponding decrease in the frequency and photon energy, of electromagnetic radiation. The opposite change, a decrease in wavelength and simultaneous increase in frequency and energy, is known as a negative redshift, or blueshift. The terms derive from the colours red and blue which form the extremes of the visible light spectrum.

Planetary nebula Type of emission nebula

A planetary nebula, is a type of emission nebula consisting of an expanding, glowing shell of ionized gas ejected from red giant stars late in their lives.

Pleiades Open cluster in the constellation of Taurus

The Pleiades, also known as The Seven Sisters,Messier 45, and other names by different cultures, is an asterism and an open star cluster containing middle-aged, hot B-type stars in the north-west of the constellation Taurus. At a distance of about 444 light years, it is among the nearest star clusters to Earth. It is the nearest Messier object to Earth, and is the most obvious cluster to the naked eye in the night sky.

Andromeda Galaxy Barred spiral galaxy within the Local Group

The Andromeda Galaxy, also known as Messier 31, M31, or NGC 224 and originally the Andromeda Nebula, is a barred spiral galaxy approximately 2.5 million light-years from Earth and the nearest large galaxy to the Milky Way. The galaxy's name stems from the area of Earth's sky in which it appears, the constellation of Andromeda, which itself is named after the Ethiopian princess who was the wife of Perseus in Greek mythology.

Emission nebula Nebula formed of ionized gas that emit light of various wavelengths

An emission nebula is a nebula formed of ionized gases that emit light of various wavelengths. The most common source of ionization is high-energy ultraviolet photons emitted from a nearby hot star. Among the several different types of emission nebulae are H II regions, in which star formation is taking place and young, massive stars are the source of the ionizing photons; and planetary nebulae, in which a dying star has thrown off its outer layers, with the exposed hot core then ionizing them.

An active galactic nucleus (AGN) is a compact region at the center of a galaxy that has a much-higher-than-normal luminosity over at least some portion of the electromagnetic spectrum with characteristics indicating that the luminosity is not produced by stars. Such excess non-stellar emission has been observed in the radio, microwave, infrared, optical, ultra-violet, X-ray and gamma ray wavebands. A galaxy hosting an AGN is called an "active galaxy". The non-stellar radiation from an AGN is theorized to result from the accretion of matter by a supermassive black hole at the center of its host galaxy.

Seyfert galaxy Class of active galaxies with very bright nuclei

Seyfert galaxies are one of the two largest groups of active galaxies, along with quasars. They have quasar-like nuclei with very high surface brightnesses whose spectra reveal strong, high-ionisation emission lines, but unlike quasars, their host galaxies are clearly detectable.

H II region Large, low-density interstellar cloud of partially ionized gas

An H II region or HII region is a region of interstellar atomic hydrogen that is ionized. It is typically a cloud in a molecular cloud of partially ionized gas in which star formation has recently taken place, with a size ranging from one to hundreds of light years, and density from a few to about a million particles per cubic cm. The Orion Nebula, now known to be an H II region, was observed in 1610 by Nicolas-Claude Fabri de Peiresc by telescope, the first such object discovered.

Spiral galaxy Class of galaxy

Spiral galaxies form a class of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae and, as such, form part of the Hubble sequence. Most spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as the bulge. These are often surrounded by a much fainter halo of stars, many of which reside in globular clusters.

Trifid Nebula Emission nebula in the constellation Sagittarius

The Trifid Nebula is an H II region in the north-west of Sagittarius in a star-forming region in the Milky Way's Scutum-Centaurus Arm. It was discovered by Charles Messier on June 5, 1764. Its name means 'three-lobe'. The object is an unusual combination of an open cluster of stars, an emission nebula, a reflection nebula, and a dark nebula. Viewed through a small telescope, the Trifid Nebula is a bright and peculiar object, and is thus a perennial favorite of amateur astronomers.

Cats Eye Nebula Planetary nebula in the constellation Draco

The Cat's Eye Nebula is a planetary nebula in the northern constellation of Draco, discovered by William Herschel on February 15, 1786. It was the first planetary nebula whose spectrum was investigated by the English amateur astronomer William Huggins, demonstrating that planetary nebulae were gaseous and not stellar in nature. Structurally, the object has had high-resolution images by the Hubble Space Telescope revealing knots, jets, bubbles and complex arcs, being illuminated by the central hot planetary nebula nucleus (PNN). It is a well-studied object that has been observed from radio to X-ray wavelengths.

Astronomical spectroscopy Study of astronomy using spectroscopy to measure the spectrum of electromagnetic radiation

Astronomical spectroscopy is the study of astronomy using the techniques of spectroscopy to measure the spectrum of electromagnetic radiation, including visible light, ultraviolet, X-ray, infrared and radio waves that radiate from stars and other celestial objects. A stellar spectrum can reveal many properties of stars, such as their chemical composition, temperature, density, mass, distance and luminosity. Spectroscopy can show the velocity of motion towards or away from the observer by measuring the Doppler shift. Spectroscopy is also used to study the physical properties of many other types of celestial objects such as planets, nebulae, galaxies, and active galactic nuclei.

Pistol Star One of the most luminous and massive and hypergiant stars located in the Milky Way galaxy

The Pistol Star is an extremely luminous blue hypergiant star, one of the most luminous and massive known in the Milky Way. It is one of many massive young stars in the Quintuplet cluster in the Galactic Center region. The star owes its name to the shape of the Pistol Nebula, which it illuminates. It is located approximately 25,000 light-years from Earth in the direction of Sagittarius. The star has a large mass comparable to the V4998 Sagittarii and a luminosity 3.3 million times the Sun (L). It would be visible to the naked eye as a 4th-magnitude star if it were not for the interstellar dust that completely hides it from view in visible light.

Vesto Slipher American astronomer (1875–1969)

Vesto Melvin Slipher was an American astronomer who performed the first measurements of radial velocities for galaxies. He was the first to discover that distant galaxies are redshifted, thus providing the first empirical basis for the expansion of the universe. He was also the first to relate these redshifts to velocity.

NGC 7027 Planetary nebula in the constellation Cygnus

NGC 7027, Also known as the Jewel Bug Nebula, is a very young and dense planetary nebula located around 3,000 light-years from Earth in the constellation Cygnus. Discovered in 1878 by Édouard Stephan using the 800 mm (31 in) reflector at Marseille Observatory, it is one of the smallest planetary nebulae and by far the most extensively studied.

A protoplanetary nebula or preplanetary nebula is an astronomical object which is at the short-lived episode during a star's rapid evolution between the late asymptotic giant branch (LAGB) phase and the subsequent planetary nebula (PN) phase. A PPN emits strongly in infrared radiation, and is a kind of reflection nebula. It is the second-from-the-last high-luminosity evolution phase in the life cycle of intermediate-mass stars.

IC 349 Nebula in the constellation of Taurus

IC 349, also known as Barnard's Merope Nebula, is a nebula which lies 3500 AUs from the star Merope in the Pleiades cluster.

WR 31a Wolf Rayet star in the constellation Carina

WR 31a, commonly referred to as Hen 3-519, is a Wolf–Rayet (WR) star in the southern constellation of Carina that is surrounded by an expanding Wolf–Rayet nebula. It is not a classical old stripped-envelope WR star, but a young massive star which still has some hydrogen left in its atmosphere.

References

  1. Kaler, 1997.
  2. "A Star's Moment in the Spotlight" . Retrieved 10 February 2016.
  3. Slipher, Vesto M. (1922). "On the spectrum of the nebula in the Pleiades". Lowell Observatory Bulletin. 2: 26–27. Bibcode:1912LowOB...2...26S.
  4. Hertzsprung, E. (1913). "Über die Helligkeit der Plejadennebel". Astronomische Nachrichten. 195 (23): 449–452. Bibcode:1913AN....195..449H. doi:10.1002/asna.19131952302.
  5. Hubble, E. P. (1922). "The source of luminosity in galactic nebulae". Astrophysical Journal. 56: 400. Bibcode:1922ApJ....56..400H. doi:10.1086/142713.
  6. "Sifting through Dust near Orion's Belt". ESO Press Release. Retrieved 2 May 2012.

Bibliography