gas and dust in interstellar nebulae can form -
stars
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stars, while others are so diffuse they can only be detected with long exposures and special filters. Some nebulae are variably illuminated by T Tauri variable stars. Nebulae are often star-forming regions, such as in the "Pillars of Creation" in the Eagle Nebula. In these regions the formations of gas, dust, and other materials "clump" together to form denser regions, which attract further matter, and eventually will become dense enough to form stars. The remaining material is then believed to form planets and other planetary system objects. Around 150 AD, Claudius Ptolemaeus (Ptolemy) recorded, in books VII–VIII of his "Almagest",
Nebula
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400–450 light years distant in the ρ Ophiuchi cloud complex. A more compact site of star formation is the opaque clouds of dense gas and dust known as Bok globules, so named after the astronomer Bart Bok. These can form in association with collapsing molecular clouds or possibly independently. The Bok globules are typically up to a light year across and contain a few solar masses. They can be observed as dark clouds silhouetted against bright emission nebulae or background stars. Over half the known Bok globules have been found to contain newly forming stars. An interstellar cloud of gas
Star formation
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that the emission spectrum nebulae are nearly always associated with stars having spectral classifications of B or hotter (including all O-type main sequence stars), while nebulae with continuous spectra appear with cooler stars. Both Hubble and Henry Norris Russell concluded that the nebulae surrounding the hotter stars are transfomed in some manner. There are a variety of formation mechanisms for the different types of nebulae. Some nebulae form from gas that is already in the interstellar medium while others are produced by stars. Examples of the former case are giant molecular clouds, the coldest, densest phase of interstellar gas, which
Nebula
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Reflection nebula 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
Reflection nebula
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Dark nebula A dark nebula or absorption nebula is a type of interstellar cloud that is so dense that it obscures the light from objects behind it, such as background stars and emission or reflection nebulae. The extinction of the light is caused by interstellar dust grains located in the coldest, densest parts of larger molecular clouds. Clusters and large complexes of dark nebulae are associated with Giant Molecular Clouds. Isolated small dark nebulae are called Bok globules. Like other interstellar dust or material, things it obscures are only visible using radio waves in radio astronomy or infrared in infrared
Dark nebula
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of two smaller galaxies that were rotating in opposite directions to each other. Bright stars in galaxies can also help determine the distance to a galaxy, which may be a more accurate method than parallax or standard candles. The interstellar medium is matter that occupies the space between star systems in a galaxy. 99% of this matter is gaseous - hydrogen, helium, and smaller quantities of other ionized elements such as oxygen. The other 1% is dust particles, thought to be mainly graphite, silicates, and ices. Clouds of the dust and gas are referred to as nebulae. There are three
Astronomical spectroscopy
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interstellar gas, pulsars, and active galactic nuclei. Infrared astronomy is founded on the detection and analysis of infrared radiation, wavelengths longer than red light and outside the range of our vision. The infrared spectrum is useful for studying objects that are too cold to radiate visible light, such as planets, circumstellar disks or nebulae whose light is blocked by dust. The longer wavelengths of infrared can penetrate clouds of dust that block visible light, allowing the observation of young stars embedded in molecular clouds and the cores of galaxies. Observations from the Wide-field Infrared Survey Explorer (WISE) have been particularly
Astronomy
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formation. 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: where "k" is a constant that depends on the sensitivity of the measurement. Reflection nebula 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
Reflection nebula
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Sun, a black hole. Closely orbiting binary stars can follow more complex evolutionary paths, such as mass transfer onto a white dwarf companion that can potentially cause a supernova. Planetary nebulae and supernovae distribute the "metals" produced in the star by fusion to the interstellar medium; without them, all new stars (and their planetary systems) would be formed from hydrogen and helium alone. Our solar system orbits within the Milky Way, a barred spiral galaxy that is a prominent member of the Local Group of galaxies. It is a rotating mass of gas, dust, stars and other objects, held together
Astronomy
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stars, while others are so diffuse they can only be detected with long exposures and special filters. Some nebulae are variably illuminated by T Tauri variable stars. Nebulae are often star-forming regions, such as in the "Pillars of Creation" in the Eagle Nebula. In these regions the formations of gas, dust, and other materials "clump" together to form denser regions, which attract further matter, and eventually will become dense enough to form stars. The remaining material is then believed to form planets and other planetary system objects. Around 150 AD, Claudius Ptolemaeus (Ptolemy) recorded, in books VII–VIII of his "Almagest",
Nebula
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born although only massive, hot stars can release sufficient energy to ionize a significant part of a cloud. In many emission nebulae, an entire cluster of young stars is doing the work. The nebula's color depends on its chemical composition and degree of ionization. Due to the prevalence of hydrogen in interstellar gas, and its relatively low energy of ionization, many emission nebulae appear red due to the strong emissions of the Balmer series. If more energy is available, other elements will be ionized and green and blue nebulae become possible. By examining the spectra of nebulae, astronomers infer their
Emission nebula
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be possible. The arguments are that: given an observed typical grain diameter "a", the time for a grain to attain "a", and given the temperature of interstellar gas, it would take considerably longer than the age of the Universe for interstellar grains to form. On the other hand, grains are seen to have recently formed in the vicinity of nearby stars, in nova and supernova ejecta, and in R Coronae Borealis variable stars which seem to eject discrete clouds containing both gas and dust. So mass loss from stars is unquestionably where the refractory cores of grains formed. Most dust
Cosmic dust
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cool stars where molecules can form. The vibrational and rotational signatures of molecules such as titanium oxide, cyanide, and carbon monoxide can be seen in this wavelength range and can give a clue towards the star's spectral type. It is also used for studying molecules in other astronomical contexts, such as in molecular clouds where new stars are formed. The astronomical phenomenon known as reddening means that near-infrared wavelengths are less affected by dust in the interstellar medium, such that regions inaccessible by optical spectroscopy can be studied in the near-infrared. Since dust and gas are strongly associated, these dusty
Near-infrared spectroscopy
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Dwingeloo 1 and Dwingeloo 2, discovered in 1994 and 1996 respectively. Zone of Avoidance The Zone of Avoidance (ZOA) is the area of the sky that is obscured by the Milky Way. From the galactic plane of the Milky Way, the Zone of Avoidance spans roughly 10° on either side. The Zone of Avoidance was originally called the Zone of Few Nebulae in an 1878 paper by English astronomer Richard Proctor that referred to the distribution of "nebulae" in John Herschel's "General Catalogue of Nebulae". When viewing space from Earth, the attenuation, interstellar dust, and stars in the plane of
Zone of Avoidance
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Zone of Avoidance The Zone of Avoidance (ZOA) is the area of the sky that is obscured by the Milky Way. From the galactic plane of the Milky Way, the Zone of Avoidance spans roughly 10° on either side. The Zone of Avoidance was originally called the Zone of Few Nebulae in an 1878 paper by English astronomer Richard Proctor that referred to the distribution of "nebulae" in John Herschel's "General Catalogue of Nebulae". When viewing space from Earth, the attenuation, interstellar dust, and stars in the plane of the Milky Way (the galactic plane) obstruct the view of around
Zone of Avoidance
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hole. Because new stars and planets form from gases, the cosmic winds that push the gases away are preventing new stars from forming. Cosmic wind Cosmic wind is a powerful cosmic force that can push interstellar dust clouds of low density into intergalactic space. Although it easily pushes low density gas and dust clouds, it can not easily push high density clouds. As the cosmic winds start to push the clouds, they start to separate and start looking like taffy being pulled apart. It has a primary composition of photons ejected from large stars and sometimes thermal energy from exploding
Cosmic wind
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stars in the star cluster are two stars with late-O or early-B spectral types, but the cluster also contains hundreds of lower-mass stars. This region is also home to objects with Herbig–Haro jets, HH 1042 and HH 1043. Like most star-forming regions, the interstellar medium around RCW 36 contains both the gas from which stars form and some newly formed young stars. Here, young stellar clusters form in giant molecular clouds. Molecular clouds are the coldest, densest form of interstellar gas and are composed mostly of molecular hydrogen (H), but also include more complex molecules, cosmic dust, and atomic helium.
RCW 36
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form clouds, or "diffuse nebulae", where star formation takes place. In contrast to spirals, an elliptical galaxy loses the cold component of its interstellar medium within roughly a billion years, which hinders the galaxy from forming diffuse nebulae except through mergers with other galaxies. In the dense nebulae where stars are produced, much of the hydrogen is in the molecular (H) form, so these nebulae are called molecular clouds. Observations indicate that the coldest clouds tend to form low-mass stars, observed first in the infrared inside the clouds, then in visible light at their surface when the clouds dissipate, while
Star formation
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. In addition to the stars, there is also interstellar gas, comprising 90% hydrogen and 10% helium by mass, with two thirds of the hydrogen found in the atomic form and the remaining one-third as molecular hydrogen. The mass of this gas is equal to between 10% and 15% of the total mass of the galaxy's stars. Interstellar dust accounts for an additional 1% of the total mass of the gas. The Milky Way contains between 200 and 400 billion stars and at least 100 billion planets. The exact figure depends on the number of very-low-mass stars, which are hard
Milky Way
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NGC 1232 NGC 1232 is an intermediate spiral galaxy about 60 million light-years away in the constellation Eridanus. It was discovered by German-British astronomer William Herschel on 20 October 1784. It is dominated by millions of bright stars and dark dust, in spiral arms rotating about the center. Open clusters containing bright blue stars are sprinkled along these spiral arms, with dark lanes of dense interstellar dust between. Less visible are dim normal stars and interstellar gas, producing such high mass that they dominate the dynamics of the inner galaxy. Not visible is matter of unknown form called dark matter,
NGC 1232
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Cosmic wind Cosmic wind is a powerful cosmic force that can push interstellar dust clouds of low density into intergalactic space. Although it easily pushes low density gas and dust clouds, it can not easily push high density clouds. As the cosmic winds start to push the clouds, they start to separate and start looking like taffy being pulled apart. It has a primary composition of photons ejected from large stars and sometimes thermal energy from exploding stars. It can be caused by orbital motion of gas in the cluster of a galaxy, or can be ejected from a black
Cosmic wind
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Photodissociation region Photodissociation regions (or photon-dominated regions, or PDRs) are predominantly neutral regions of the interstellar medium in which far ultraviolet photons strongly influence the gas chemistry and act as the most important source of heat. They occur in any region of interstellar gas that is dense and cold enough to remain neutral, but that has too low a column density to prevent the penetration of far-UV photons from distant, massive stars. A typical and well-studied example is the gas at the boundary of a giant molecular cloud. PDRs are also associated with HII regions, reflection nebulae, active galactic nuclei,
Photodissociation region
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main types of nebula: absorption, reflection, and emission nebulae. Absorption (or dark) nebulae are made of dust and gas in such quantities that they obscure the starlight behind them, making photometry difficult. Reflection nebulae, as their name suggest, reflect the light of nearby stars. Their spectra are the same as the stars surrounding them, though the light is bluer; shorter wavelengths scatter better than longer wavelengths. Emission nebulae emit light at specific wavelengths depending on their chemical composition. In the early years of astronomical spectroscopy, scientists were puzzled by the spectrum of gaseous nebulae. In 1864 William Huggins noticed that
Astronomical spectroscopy
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of a galaxy. Because of their dimension (typically smaller than a few tenths of a micron), they are very effective in absorbing and scattering the radiation emitted by stars in the ultraviolet, optical and near-infrared. Although the interstellar regions are more devoid of matter than any vacuum artificially created on earth, there is matter in space. These regions have very low densities and consist mainly of gas (99%) and dust. In total, approximately 15% of the visible matter in the Milky Way is composed of interstellar gas and dust. The study of dust in galaxies is interesting for many reasons.
Galaxy Zoo
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Interstellar ice Interstellar ice consists of grains of volatiles in the ice phase that form in the interstellar medium. Ice and dust grains form the primary material out of which the Solar System was formed. Grains of ice are found in the dense regions of molecular clouds, where new stars are formed. Temperatures in these regions can be as low as , allowing molecules that collide with grains to form an icy mantle. Thereafter, atoms undergo thermal motion across the surface, eventually forming bonds with other atoms. This results in the formation of water and methanol. Indeed, the ices are
Interstellar ice
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are parts of the same interstellar cloud of ionized hydrogen (H II region). Between the Earth and the nebula complex lies a band of interstellar dust that absorbs the light of stars and nebulae behind it, and thereby determines the shape as we see it. The distance of the nebula complex is not precisely known, nor is the star responsible for ionizing the hydrogen so that it emits light. If the star inducing the ionization is Deneb, as some sources say, the nebula complex would be about 1,800 light-years' distance, and its absolute size (6° apparent diameter on the sky)
North America Nebula
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surfaces where life then emerged (abiogenesis). From the early 1970s, it started to become evident that interstellar dust included a large component of organic molecules. Interstellar molecules are formed by chemical reactions within very sparse interstellar or circumstellar clouds of dust and gas. The dust plays a critical role in shielding the molecules from the ionizing effect of ultraviolet radiation emitted by stars. The chemistry leading to life may have begun shortly after the Big Bang, 13.8 billion years ago, during a habitable epoch when the Universe was only 10 to 17 million years old. Though the presence of life
Panspermia
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cloud incorporates two prominent dark nebulae which are vast clouds of dense, obscuring interstellar dust. This dust blocks light from the more distant stars, which keeps them from being seen from Earth. Lying on the northwestern side is Barnard 92, which is the darkest out of the two. Inside the field filled with stars, the nebula appears as an immense round hole that is devoid of any stars. American astronomer Edward Emerson Barnard discovered this dark nebula in 1913. Along the northeast side contains Barnard 93, which is less obvious and large as the other dark nebula. There are also
Sagittarius Star Cloud
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stars known as globular clusters. Between the stars lies the interstellar medium, a region of sparse matter. In the densest regions, molecular clouds of molecular hydrogen and other elements create star-forming regions. These begin as a compact pre-stellar core or dark nebulae, which concentrate and collapse (in volumes determined by the Jeans length) to form compact protostars. As the more massive stars appear, they transform the cloud into an H II region (ionized atomic hydrogen) of glowing gas and plasma. The stellar wind and supernova explosions from these stars eventually cause the cloud to disperse, often leaving behind one or
Astronomy
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of carbon isotopes in stars and studied the structure of nebulae, attempting to determine their size and the role of dust and gas in formation of the nebulae. She discovered around 150 "new galactic emission nebulae by recording their light in the red H-alpha (Hα) emission". In 1952 Gaze and Shajn published a book together entitled, "Some results of the study of diffuse gaseous nebulae and their attitude to cosmogony". Gaze died on 3 October 1954 in Leningrad and was buried at the memorial cemetery for astronomers, near the Pulkovo Observatory outside Saint Petersburg. Posthumously, a planet, 2388 Gase, discovered
Vera Fedorovna Gaze
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Pinwheel nebula A pinwheel nebula is a "nebulous region" in the shape of a pinwheel. The term 'Pinwheel nebula' is an antiquated misnomer used by observers before Edwin Hubble realized that many of these spiral shaped nebulae were actually 'island universes' or what we now call galaxies. Some Wolf-Rayet stars are surrounded by pinwheel nebulae. These nebulae are formed from the dust that is spewed out of a binary star system. The stellar winds of the two stars collide and form two dust lanes that spiral outward with the rotation of the system. An example of this is WR 104.
Pinwheel nebula
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Pinwheel nebula A pinwheel nebula is a "nebulous region" in the shape of a pinwheel. The term 'Pinwheel nebula' is an antiquated misnomer used by observers before Edwin Hubble realized that many of these spiral shaped nebulae were actually 'island universes' or what we now call galaxies. Some Wolf-Rayet stars are surrounded by pinwheel nebulae. These nebulae are formed from the dust that is spewed out of a binary star system. The stellar winds of the two stars collide and form two dust lanes that spiral outward with the rotation of the system. An example of this is WR 104.
Pinwheel nebula
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Superbubble A superbubble or supershell is a cavity which is hundreds of light years across as is populated with hot (10 K) gas atoms, less dense than the surrounding interstellar medium, blown against that medium and carved out by multiple supernovae and stellar winds. The winds, passage and gravity of newly born stars strip superbubbles of any other dust or gas. The Solar System lies near the center of an old superbubble, known as the Local Bubble, whose boundaries can be traced by a sudden rise in dust extinction of exterior stars at distances greater than a few hundred light
Superbubble
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strengthened rigidity or sealant to vulnerable edges and joins. Cosmic dust is widely present in space, where gas and dust clouds are primary precursors for planetary systems. The zodiacal light, as seen in a dark night sky, is produced by sunlight reflected from particles of dust in orbit around the Sun. The tails of comets are produced by emissions of dust and ionized gas from the body of the comet. Dust also covers solid planetary bodies, and vast dust storms occur on Mars that cover almost the entire planet. Interstellar dust is found between the stars, and high concentrations produce
Dust
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nebulae meant there could not be stars within them, as these would have emitted abundant infrared light. In 1975 American astronomer R. D. Schwartz theorized that winds from T Tauri stars produce shocks in ambient medium on encounter, resulting in generation of visible light. With discovery of collimated jet in HH 46/47, it became clear that HH objects are indeed shock induced phenomenon with shocks being driven by collimated jet from protostars. Stars form by gravitational collapse of interstellar gas clouds. As the collapse increases the density, radiative energy loss decreases due to increased opacity. This raises the temperature of
Herbig–Haro object
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general in the interstellar medium of galaxies, as molecular hydrogen can only be detected using ultraviolet light, which requires space telescopes. Carbon monoxide observations provide much of the information about the molecular clouds in which most stars form. Beta Pictoris, the second brightest star in the constellation Pictor, shows an excess of infrared emission compared to normal stars of its type, which is caused by large quantities of dust and gas (including carbon monoxide) near the star. Solid carbon monoxide is a component of comets. Halley's Comet is about 15% carbon monoxide. It has also been identified spectroscopy on the
Carbon monoxide
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"Spitzer Space Telescope" observations in 2005, which showed that the Milky Way's central bar is larger than was previously suspected. Spiral 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. Spiral galaxies are named by their
Spiral galaxy
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Spiral 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. Spiral galaxies are named by their spiral structures that extend from the center into the galactic disc. The spiral arms are sites of ongoing star formation
Spiral galaxy
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Once most of the red giant's atmosphere is dissipated, ultraviolet radiation from the hot luminous core, called a planetary nebula nucleus (PNN), ionizes the ejected material. Absorbed ultraviolet light then energises the shell of nebulous gas around the central star, causing it to appear as a brightly coloured planetary nebula. Planetary nebulae likely play a crucial role in the chemical evolution of the Milky Way by expelling elements to the interstellar medium from stars where those elements were created. Planetary nebulae are observed in more distant galaxies, yielding useful information about their chemical abundances. Starting from the 1990s, Hubble Space
Planetary nebula
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to the line of sight. For a typical G8 star, the rotation velocity is about . The relatively low rotational velocity measurements may indicate that Tau Ceti is being viewed from nearly the direction of its pole. The chemical composition of a star provides important clues to its evolutionary history, including the age at which it formed. The interstellar medium of dust and gas from which stars form is primarily composed of hydrogen and helium with trace amounts of heavier elements. As nearby stars continually evolve and die, they seed the interstellar medium with an increasing portion of heavier elements.
Tau Ceti
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of contraction from a gas nebula to a veritable star. Most protostars exhibit irregular brightness variations. Variability of more massive (2–8 solar mass) Herbig Ae/Be stars is thought to be due to gas-dust clumps, orbiting in the circumstellar disks. Orion variables are young, hot pre–main-sequence stars usually embedded in nebulosity. They have irregular periods with amplitudes of several magnitudes. A well-known subtype of Orion variables are the T Tauri variables. Variability of T Tauri stars is due to spots on the stellar surface and gas-dust clumps, orbiting in the circumstellar disks. These stars reside in reflection nebulae and show gradual
Variable star
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be detected as opaque clouds blocking light from luminous objects behind them; they are called "dark nebulae". Although these nebulae have different visibility at optical wavelengths, they are all bright sources of infrared emission, chiefly from dust within the nebulae. Planetary nebulae are the remnants of the final stages of stellar evolution for lower-mass stars. Evolved asymptotic giant branch stars expel their outer layers outwards due to strong stellar winds, thus forming gaseous shells, while leaving behind the star's core in the form of a white dwarf. The hot white dwarf illuminates the expelled gases producing emission nebulae with spectra
Nebula
11569910
Extraterrestrial materials Most atoms on Earth came from the interstellar dust and gas from which the Sun and Solar System formed. However, in the space science community, "extraterrestrial materials" generally refers to objects now on Earth that were solidified prior to arriving on Earth. In October 2011, scientists reported that one form of extraterrestrial material, cosmic dust, contains complex organic matter ("amorphous organic solids with a mixed aromatic-aliphatic structure") that could be created naturally, and rapidly, by stars. In February 2014, NASA announced a greatly upgraded database for tracking polycyclic aromatic hydrocarbons (PAHs) in the universe. According to scientists, more
Extraterrestrial materials
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is carbon because its formation from He is a bottleneck in the entire process. Carbon is produced by the triple-alpha process in all stars. Carbon is also the main element that causes the release of free neutrons within stars, giving rise to the s-process, in which the slow absorption of neutrons converts iron into elements heavier than iron and nickel. The products of stellar nucleosynthesis are generally dispersed into the interstellar gas through mass loss episodes and the stellar winds of low mass stars. The mass loss events can be witnessed today in the planetary nebulae phase of low-mass star
Nucleosynthesis
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found within these lanes, mix together and combine to form stars and planets. Dust lane A dust lane is a relatively dense obscuring band of interstellar dust, observed as a dark swath against the background of a brighter object, especially a galaxy. These dust lanes can usually be seen in spiral galaxies (e.g., the Milky Way) when viewed from the edge. Due to the dense and relatively thick nature of this dust, light from the galaxy is reduced by several magnitudes. In the Milky Way, this reduction of light makes it impossible to see the light from the central bulge
Dust lane
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denser region that is heated and forms the visible infrared shape. The term "dust wave" is applied when the dust piles up but the gas is largely unaffected, as opposed to a "bow wave" where both dust and gas are stopped. Dust waves occur when the interstellar medium is sufficiently dense and the stellar wind sufficiently weak that the dust stand-off distance is larger than the stand-off distance of a bow shock. This would clearly be more likely for slow-moving stars, but slow-moving luminous stars may not have lifetimes long enough to produce a bow wave. Low luminosity late class
Sigma Orionis
542107
must also account for the statistics of binary stars and the initial mass function. A spiral galaxy like the Milky Way contains stars, stellar remnants, and a diffuse interstellar medium (ISM) of gas and dust. The interstellar medium consists of 10 to 10 particles per cm and is typically composed of roughly 70% hydrogen by mass, with most of the remaining gas consisting of helium. This medium has been chemically enriched by trace amounts of heavier elements that were ejected from stars as they passed beyond the end of their main sequence lifetime. Higher density regions of the interstellar medium
Star formation
161490
can observe highly energetic galactic phenomena. Ultraviolet flares are sometimes observed when a star in a distant galaxy is torn apart from the tidal forces of a nearby black hole. The distribution of hot gas in galactic clusters can be mapped by X-rays. The existence of supermassive black holes at the cores of galaxies was confirmed through X-ray astronomy. Galaxy A galaxy is a gravitationally bound system of stars, stellar remnants, interstellar gas, dust, and dark matter. The word galaxy is derived from the Greek "" (), literally "milky", a reference to the Milky Way. Galaxies range in size from
Galaxy
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regions are several times that distance from Earth. Secondly, the formation of these stars is deeply obscured by dust, and visible light observations are impossible. Radio and infrared light can penetrate the dust, but the youngest stars may not emit much light at these wavelengths. H II region An H II region or HII region is a region of interstellar atomic hydrogen that is ionized. It is typically a 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
H II region
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but would have become an extinct radionuclide (specifically Ca) after the time required for mixing with the interstellar gas. Its discovery proved the prediction from 1975 that it might be possible to identify SUNOCONs in this way. The SiC SUNOCONs (from supernovae) are only about 1% as numerous as are SiC stardust from AGB stars. Stardust itself (SUNOCONs and AGB grains that come from specific stars) is but a modest fraction of the condensed cosmic dust, forming less than 0.1% of the mass of total interstellar solids. The high interest in stardust derives from new information that it has brought
Cosmic dust
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upper atmosphere or from space. Ultraviolet astronomy is best suited to the study of thermal radiation and spectral emission lines from hot blue stars (OB stars) that are very bright in this wave band. This includes the blue stars in other galaxies, which have been the targets of several ultraviolet surveys. Other objects commonly observed in ultraviolet light include planetary nebulae, supernova remnants, and active galactic nuclei. However, as ultraviolet light is easily absorbed by interstellar dust, an adjustment of ultraviolet measurements is necessary. X-ray astronomy uses X-ray wavelengths. Typically, X-ray radiation is produced by synchrotron emission (the result of
Astronomy
4815390
being tracked on a ladder (ranking) system. Players can also form up or join squadrons in "SquadWar", an online persistent galaxy hosted by Volition on PXO, where squadrons fight each other for territories. "FreeSpace 2" takes place entirely in outer space. The playing area is vast when compared to the small starfighters piloted by the player and the effective range they have. This space is populated with interstellar bodies such as stars, planets, asteroids, etc. The implementation of nebulae as an interactive environment is one of the most distinctive and crowning aspects of "FreeSpace 2". Flying through a nebula involves
FreeSpace 2
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they are extended and contain no well-defined boundaries. Diffuse nebulae can be divided into emission nebula, reflection nebulae and "dark nebulae." Visible light nebulae may be divided into emission nebulae that emit spectral line radiation from excited or ionized gas (mostly ionized hydrogen); they are often called HII regions (the term "HII" refers to ionized hydrogen). Reflection nebulae are visible primarily due to the light they reflect. Reflection nebulae themselves do not emit significant amounts of visible light, but are near stars and reflect light from them. Similar nebulae not illuminated by stars do not exhibit visible radiation, but may
Nebula
285823
can form by the cooling and condensation of more diffuse gas. Examples of the latter case are planetary nebulae formed from material shed by a star in late stages of its stellar evolution. Star-forming regions are a class of emission nebula associated with giant molecular clouds. These form as a molecular cloud collapses under its own weight, proceeding stars. Massive stars may form in the center, and their ultraviolet radiation ionizes the surrounding gas, making it visible at optical wavelengths. The region of ionized hydrogen surrounding the massive stars is known as an H II region while the shells of
Nebula
5929249
a record-breaker, from Sagittarius A*. The unusual event may have been caused by the breaking apart of an asteroid falling into the black hole or by the entanglement of magnetic field lines within gas flowing into Sagittarius A*. Outside the gravitational influence of the Galactic bars, the structure of the interstellar medium and stars in the disk of the Milky Way is organized into four spiral arms. Spiral arms typically contain a higher density of interstellar gas and dust than the Galactic average as well as a greater concentration of star formation, as traced by H II regions and molecular
Milky Way
378779
Stellar evolution Stellar evolution is the process by which a star changes over the course of time. Depending on the mass of the star, its lifetime can range from a few million years for the most massive to trillions of years for the least massive, which is considerably longer than the age of the universe. The table shows the lifetimes of stars as a function of their masses. All stars are born from collapsing clouds of gas and dust, often called nebulae or molecular clouds. Over the course of millions of years, these protostars settle down into a state of
Stellar evolution
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Elephant trunk (astronomy) Elephant trunk is a term used to describe certain formations of interstellar matter found in space. More formally, scientists refer to them as cold molecular pillars, referring to their existence in molecular clouds. They are located in the neighborhood of massive O type and B type stars, which, through their intense radiation, can create expanding regions of ionized gas known as H II regions. Elephant trunks resemble massive pillars or columns of gas and dust, but they come in various shapes, lengths, and colors. Astronomers study elephant trunks because of their unique formation process and use 2-D
Elephant trunk (astronomy)
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the nebulae: they were far too distant to be part of the Milky Way. In 1936 Hubble produced a classification of galactic morphology that is used to this day. In 1944, Hendrik van de Hulst predicted that microwave radiation with wavelength of 21 cm would be detectable from interstellar atomic hydrogen gas; and in 1951 it was observed. This radiation is not affected by dust absorption, and so its Doppler shift can be used to map the motion of the gas in our galaxy. These observations led to the hypothesis of a rotating bar structure in the center of our
Galaxy
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pyrimidine, found in meteorites. Pyrimidine, like polycyclic aromatic hydrocarbons (PAHs), the most carbon-rich chemical found in the Universe, may have been formed in red giants or in interstellar dust and gas clouds, according to the scientists. The Solar System has its own interplanetary dust cloud, as do extrasolar systems. There are different types of nebulae with different physical causes and processes: diffuse nebula, infrared (IR) reflection nebula, supernova remnant, molecular cloud, HII regions, photodissociation regions, and dark nebula. Distinctions between those types of nebula are that different radiation processes are at work. For example, H II regions, like the Orion
Cosmic dust
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much of the optical and X-ray emission from supernova remnants originates from ionized gas, a great amount of the radio emission is a form of non-thermal emission called synchrotron emission. This emission originates from high-velocity electrons oscillating within magnetic fields. Nebula A nebula (Latin for "cloud" or "fog"; pl. nebulae, nebulæ, or nebulas) is an interstellar cloud of dust, hydrogen, helium and other ionized gases. Originally, the term was used to describe any diffuse astronomical object, including galaxies beyond the Milky Way. The Andromeda Galaxy, for instance, was once referred to as the "Andromeda Nebula" (and spiral galaxies in general
Nebula
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carbon and an oxygen to sulfur. In molecular clouds, simple carbon molecules are formed, including carbon monoxide and dicarbon. Reactions with the trihydrogen cation of the simple carbon molecules yield carbon containing ions that readily react to form larger organic molecules. Carbon compounds that exist as ions, or isolated gas molecules in the interstellar medium, can condense onto dust grains. Carbonaceous dust grains consist mostly of carbon. Grains can stick together to form larger aggregates. Meteorites and interplanetary dust shows the composition of solid material at the start of the Solar System, as they have not been modified since its
Geochemistry of carbon
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diameter. The scattering of light from dust grains in long exposure visible photographs is quite noticeable in reflection nebulae, and gives clues about the individual particle's light-scattering properties. In X-ray wavelengths, many scientists are investigating the scattering of X-rays by interstellar dust, and some have suggested that astronomical X-ray sources would possess diffuse haloes, due to the dust. Stardust grains (also called presolar grains by meteoriticists) are contained within meteorites, from which they are extracted in terrestrial laboratories. Stardust was a component of the dust in the interstellar medium before its incorporation into meteorites. The meteorites have stored those stardust
Cosmic dust
780039
Interstellar medium In astronomy, the interstellar medium (ISM) is the matter and radiation that exists in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, as well as dust and cosmic rays. It fills interstellar space and blends smoothly into the surrounding intergalactic space. The energy that occupies the same volume, in the form of electromagnetic radiation, is the interstellar radiation field. The interstellar medium is composed of multiple phases, distinguished by whether matter is ionic, atomic, or molecular, and the temperature and density of the matter. The interstellar medium
Interstellar medium
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clouds (especially at high densities). Far infrared radiation penetrates deeply due to the low optical depth. Dust grains are heated via this radiation and can transfer thermal energy during collisions with the gas. A measure of efficiency in the heating is given by the accommodation coefficient: where "T" is the gas temperature, "T" the dust temperature, and "T" the post-collision temperature of the gas atom or molecule. This coefficient was measured by as "α" = 0.35. Radio waves from ≈10 kHz (very low frequency) to ≈300 GHz (extremely high frequency) propagate differently in interstellar space than on the Earth's surface.
Interstellar medium
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Nebula A nebula (Latin for "cloud" or "fog"; pl. nebulae, nebulæ, or nebulas) is an interstellar cloud of dust, hydrogen, helium and other ionized gases. Originally, the term was used to describe any diffuse astronomical object, including galaxies beyond the Milky Way. The Andromeda Galaxy, for instance, was once referred to as the "Andromeda Nebula" (and spiral galaxies in general as "spiral nebulae") before the true nature of galaxies was confirmed in the early 20th century by Vesto Slipher, Edwin Hubble and others. Most nebulae are of vast size; some are hundreds of light years in diameter. A nebula that
Nebula
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that other galaxies apart from the Milky Way therefore existed. By 1925, Edwin Hubble had confirmed that many objects previously thought to be clouds of dust and gas and classified as "nebulae" were actually galaxies beyond the Milky Way. When astronomers realized that starlight can be absorbed by clouds of gas and dust, infrared radiation was used to penetrate the dust clouds. Estimates dating after 2000 locate our solar system within the range from the Galactic Center of the Milky Way galaxy. Galactocentrism In astronomy, Galactocentrism is the theory that the Milky Way Galaxy, home of Earths Solar System, is
Galactocentrism
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and Planetary nebulae. All the atomic gas and most of the molecular gas in the galaxy is found in PDRs. The study of photodissociation regions began from early observations of the star-forming regions Orion A and M17 which showed neutral areas bright in infrared radiation lying outside ionised HII regions. Photodissociation region Photodissociation regions (or photon-dominated regions, or PDRs) are predominantly neutral regions of the interstellar medium in which far ultraviolet photons strongly influence the gas chemistry and act as the most important source of heat. They occur in any region of interstellar gas that is dense and cold enough
Photodissociation region
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the propulsion mechanism. This energy has to be generated onboard from stored fuel, harvested from the interstellar medium, or projected over immense distances. A knowledge of the properties of the interstellar gas and dust through which the vehicle must pass is essential for the design of any interstellar space mission. A major issue with traveling at extremely high speeds is that interstellar dust may cause considerable damage to the craft, due to the high relative speeds and large kinetic energies involved. Various shielding methods to mitigate this problem have been proposed. Larger objects (such as macroscopic dust grains) are far
Interstellar travel
268781
this assumption in observations of some other galaxies. Within molecular clouds are regions with higher density, where lots of dust and gas cores reside, called clumps. These clumps are the beginning of star formation, if gravity can overcome the high density and force the dust and gas to collapse. Within the Milky Way, molecular gas clouds account for less than one percent of the volume of the interstellar medium (ISM), yet it is also the densest part of the medium, comprising roughly half of the total gas mass interior to the Sun's galactic orbit. The bulk of the molecular gas
Molecular cloud
198565
Interstellar cloud An interstellar cloud is generally an accumulation of gas, plasma, and dust in our and other galaxies. Put differently, an interstellar cloud is a denser-than-average region of the interstellar medium, (ISM), the matter and radiation that exists in the space between the star systems in a galaxy. Depending on the density, size, and temperature of a given cloud, its hydrogen can be neutral, making an H I region; ionized, or plasma making it an H II region; or molecular, which are referred to simply as molecular clouds, or sometimetimes dense clouds. Neutral and ionized clouds are sometimes also
Interstellar cloud
198571
metallicity is needed. High-velocity clouds are identified with an HVC prefix, as with HVC 127-41-330. Interstellar cloud An interstellar cloud is generally an accumulation of gas, plasma, and dust in our and other galaxies. Put differently, an interstellar cloud is a denser-than-average region of the interstellar medium, (ISM), the matter and radiation that exists in the space between the star systems in a galaxy. Depending on the density, size, and temperature of a given cloud, its hydrogen can be neutral, making an H I region; ionized, or plasma making it an H II region; or molecular, which are referred to
Interstellar cloud
319439
organic molecules. The first suggestion came from Chandra Wickramasinghe, who proposed a polymeric composition based on the molecule formaldehyde (CHO). Interstellar molecules are formed by chemical reactions within very sparse interstellar or circumstellar clouds of dust and gas. Usually this occurs when a molecule becomes ionized, often as the result of an interaction with cosmic rays. This positively charged molecule then draws in a nearby reactant by electrostatic attraction of the neutral molecule's electrons. Molecules can also be generated by reactions between neutral atoms and molecules, although this process is generally slower. The dust plays a critical role of shielding
Panspermia
878750
226868 but not overflowing, so the material at the stellar surface is not being stripped away by its companion. However, a significant proportion of the stellar wind emitted by the star is being drawn onto the compact object's accretion disk after passing beyond this lobe. The gas and dust between the Sun and HDE 226868 results in a reduction in the apparent magnitude of the star as well as a reddening of the hue—red light can more effectively penetrate the dust in the interstellar medium. The estimated value of the interstellar extinction (A) is 3.3 magnitudes. Without the intervening matter,
Cygnus X-1
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and (ii) the products of stellar and explosive nucleosynthesis found in almost undiluted form in presolar grains. The latter are providing astronomers with up-close information on the state of the whole periodic table in exotic environments scattered all across the early Milky Way. Extraterrestrial materials Most atoms on Earth came from the interstellar dust and gas from which the Sun and Solar System formed. However, in the space science community, "extraterrestrial materials" generally refers to objects now on Earth that were solidified prior to arriving on Earth. In October 2011, scientists reported that one form of extraterrestrial material, cosmic dust,
Extraterrestrial materials
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dominated by water and methanol, as well as ammonia, carbon monoxide and carbon dioxide. Frozen formaldehyde and molecular hydrogen may also be present. Found in lower abundances are nitriles, ketones, esters and carbonyl sulfide. The mantles of interstellar ice grains are generally amorphous, only becoming crystalline in the presence of a star. The composition of interstellar ice can be determined through its infrared spectrum. As starlight passes through a molecular cloud containing ice, molecules in the cloud absorb energy. This adsorption occurs at the characteristic frequencies of vibration of the gas and dust. Ice features in the cloud are relatively
Interstellar ice
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interstellar dust. Though many hypotheses regarding this dust had been postulated by various astronomers since the middle of the 19th century, all were found to be wanting as and when new data on the gas and dust clouds became available. probably polymers. Chandra Wickramasinghe proposed the existence of polymeric composition based on the molecule formaldehyde (HCO). In 1974 Wickramasinghe first proposed the hypothesis that some dust in interstellar space was largely organic (containing carbon and nitrogen), and followed this up with other research confirming the hypothesis. Wickramasinghe also proposed and confirmed the existence of polymeric compounds based on the molecule
Diseases from Space
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Comet dust Comet dust refers to cosmic dust that originates from a comet. Comet dust can provide clues to comets' origin. When the Earth passes through a comet dust trail, it can produce a meteor shower. The models for the origin of comets are: Bulk properties of the comet dust such as density as well as the chemical composition can distinguish between the models. For example, the isotopic ratios of comet and of interstellar dust are very similar, indicating a common origin. The 1) interstellar model says that ices formed on dust grains in the dense cloud that preceded the
Comet dust
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40,000 years to diffuse to the outer layers of the Sun, neutrinos generated in stellar fusion reactions at the core cross this distance practically unimpeded at nearly the speed of light. Neutrinos are also useful for probing astrophysical sources beyond the Solar System because they are the only known particles that are not significantly attenuated by their travel through the interstellar medium. Optical photons can be obscured or diffused by dust, gas, and background radiation. High-energy cosmic rays, in the form of swift protons and atomic nuclei, are unable to travel more than about 100 megaparsecs due to the Greisen–Zatsepin–Kuzmin
Neutrino
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Sun. The mix of ice and dust then aggregated into a comet without appreciable chemical modification. J. Mayo Greenberg first proposed this idea in 1986. In the 2) Solar System model, the ices that formed in the interstellar cloud first vaporized as part of the accretion disk of gas and dust around the protosun. The vaporized ices later resolidified and assembled into comets. So the comets in this model would have a different composition than those comets that were made directly from interstellar ice. The 3) primordial rubble pile model for comet formation says that comets agglomerate in the region
Comet dust
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time of eclipses. A change in day length of milliseconds per century shows up as a change of hours and thousands of kilometers in eclipse observations. The ancient data are consistent with a shorter day, meaning the Earth was turning faster throughout the past. The Earth's original rotation was a vestige of the original angular momentum of the cloud of dust, rocks, and gas that coalesced to form the Solar System. This primordial cloud was composed of hydrogen and helium produced in the Big Bang, as well as heavier elements ejected by supernovas. As this interstellar dust is heterogeneous, any
Earth's rotation
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drives attached. Ekti is harvested from gas giants as their atmosphere is mostly Hydrogen. Hydrogen being the most abundant element in the universe can also be found in interstellar nebulae as well as planets close to and farthest away from the Sun. To extract the Hydrogen which in turn is converted to Ekti large Skymines are used. These plants are usually manned by Roamers, nomadic breakaway Earthers, but occasionally by Ildirans and the Hansa. In extracting Hydrogen from nebula large Nebular Skimmers slowly collect the Hydrogen for transport to be converted into Ekti, where it is shipped off. Harvesting of
Technology of The Saga of Seven Suns
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thing we’re imagining [is that] as the galaxy moves into a denser environment, there’s lot of gas in clusters as well as galaxies, and it’s possible the gas from the galaxy just gets stripped off by the denser medium it’s plowing into." The properties of Galactic Dust have been examined in several Galaxy Zoo papers. The interstellar medium of spiral galaxies is filled by gas and small solid particles called dust grains. Despite constituting only a minor fraction of the galactic mass (between 0.1% and 0.01% for the Milky Way), dust grains have a major role in shaping the appearance
Galaxy Zoo
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of the Rho Ophiuchi cloud complex. It is a nebula of gas and dust, which the Rho Ophiuchi system is embedded in. It is one of the easiest star forming regions to observe, as it is one of the nearest, and it is visible from both hemispheres. The interstellar extinction (A) of Rho Ophiuchi is measured to be 1.45 magnitudes, meaning the dust and gas in front of Rho Ophiuchi absorbs light from the system, making it appear 1.45 magnitudes dimmer than it should be. Additionally, gas and dust also scatters more higher-frequency light, leaving the light appearing more reddish.
Rho Ophiuchi
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Cosmic dust Cosmic dust, also called extraterrestrial dust or space dust, is dust which exists in outer space, or has fallen on Earth. Most cosmic dust particles are between a few molecules to 0.1 µm in size. Cosmic dust can be further distinguished by its astronomical location: intergalactic dust, interstellar dust, interplanetary dust (such as in the zodiacal cloud) and circumplanetary dust (such as in a planetary ring). In the Solar System, interplanetary dust causes the zodiacal light. Solar System dust includes comet dust, asteroidal dust, dust from the Kuiper belt, and interstellar dust passing through the Solar System. Thousands
Cosmic dust
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in the initial composition of the interstellar medium and hence the star. Interstellar gas therefore contains declining abundances of these light elements, which are present only by virtue of their nucleosynthesis during the Big Bang. Larger quantities of these lighter elements in the present universe are therefore thought to have been restored through billions of years of cosmic ray (mostly high-energy proton) mediated breakup of heavier elements in interstellar gas and dust. The fragments of these cosmic-ray collisions include the light elements Li, Be and B. The first ideas on nucleosynthesis were simply that the chemical elements were created at
Nucleosynthesis
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at least 10 gas vents were active. The comet itself has a diameter of 5 kilometres. "Stardust"s "sample return canister" was reported to be in excellent condition when it landed in Utah, on January 15, 2006. A NASA team analyzed the particle capture cells and removed individual grains of comet and interstellar dust, then sent them to about 150 scientists around the globe. NASA is collaborating with The Planetary Society who will run a project called "Stardust@Home", using volunteers to help locate particles on the Stardust Interstellar Dust Collector (SIDC). As of 2006, the composition of the dust has contained
81P/Wild
550775
or both, are far below our ability to measure with any certainty. Since the effective temperature is merely a number that represents the temperature of a black body that would reproduce the luminosity, it obviously cannot be measured directly, but it can be estimated from the spectrum. An alternative way to measure stellar luminosity is to measure the star's apparent brightness and distance. A third component needed to derive the luminosity is the degree of interstellar extinction that is present, a condition that usually arises because of gas and dust present in the interstellar medium (ISM), the Earth's atmosphere, and
Luminosity
780041
matter is primarily ionized, and the density may be as low as 10 ions per cm. Compare this with a number density of roughly 10 molecules per cm for air at sea level, and 10 molecules per cm (10 billion molecules per cm) for a laboratory high-vacuum chamber. By mass, 99% of the ISM is gas in any form, and 1% is dust. Of the gas in the ISM, by number 91% of atoms are hydrogen and 8.9% are helium, with 0.1% being atoms of elements heavier than hydrogen or helium, known as "metals" in astronomical parlance. By mass this
Interstellar medium
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board the Hubble Space Telescope. The star has a current mass of around 0.64 solar masses. It is surrounded by a particularly dense equatorial disc composed of gas and dust. This dense disc is postulated to have caused the star's outflows to form a bipolar structure similar to an hour-glass. This bipolar structure shows many interesting features seen in planetary nebulae such as ionization walls, knots and sharp edges to the lobes. As it is included in the New General Catalogue, this object has been known since at least 1888. The earliest known study of NGC 6302 is by Edward
NGC 6302
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found, and conversely, a compositional analysis of a dust particle can reveal much about the dust particle's origin. General diffuse interstellar medium dust, dust grains in dense clouds, planetary rings dust, and circumstellar dust, are each different in their characteristics. For example, grains in dense clouds have acquired a mantle of ice and on average are larger than dust particles in the diffuse interstellar medium. "Interplanetary dust particles" (IDPs) are generally larger still. Most of the influx of extraterrestrial matter that falls onto the Earth is dominated by meteoroids with diameters in the range 50 to 500 micrometers, of average
Cosmic dust
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frequencies accessible to this telescope range from which includes rotational transitions of dozens of molecular species as well as continuum emission from interstellar dust grains. Although the array is capable of operating both day and night, most of the observations take place at nighttime when the atmospheric phase stability is best. The SMA is jointly operated by the Smithsonian Astrophysical Observatory and the Academia Sinica Institute of Astronomy and Astrophysics. The SMA is a multi-purpose instrument which can be used to observe diverse celestial phenomena. The SMA excels at observations of dust and gas with temperatures only a few tens
Submillimeter Array
578505
a singular planet. A hypothesis to the asteroid belt creation is that in general, in the Solar System, a planetary formation is thought to have occurred via a process comparable to the long-standing nebular hypothesis: a cloud of interstellar dust and gas collapsed under the influence of gravity to form a rotating disc of material that then further condensed to form the Sun and planets. During the first few million years of the Solar System's history, an accretion process of sticky collisions caused the clumping of small particles, which gradually increased in size. Once the clumps reached sufficient mass, they
Asteroid belt
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the Milky Way. Messier 86 is linked by several filaments of ionized gas to the severely disrupted spiral galaxy NGC 4438 and shows some gas and interstellar dust that may have been stripped of it like the one present in those filaments. It is also suffering ram-pressure stripping as it moves at high speed through Virgo's intracluster medium, losing its interstellar medium and leaving behind a very long trail of X ray-emitting hot gas that has been detected with the help of the Chandra space telescope. Messier 86 has a rich system of globular clusters, with a total number of
Messier 86
198566
called "diffuse clouds". An interstellar cloud is formed by the gas and dust particles from a red giant in its later life. The chemical composition of interstellar clouds is determined by studying electromagnetic radiation or EM radiation that they emanate, and we receive – from radio waves through visible light, to gamma rays on the electromagnetic spectrum – that we receive from them. Large radio telescopes scan the intensity in the sky of particular frequencies of electromagnetic radiation which are characteristic of certain molecules' spectra. Some interstellar clouds are cold and tend to give out EM radiation of large wavelengths.
Interstellar cloud
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density 2.0 g/cm³ (with porosity about 40%). The total influx rate of meteoritic sities of most IDPs captured in the Earth's stratosphere range between 1 and 3 g/cm³, with an average density at about 2.0 g/cm³. Other specific dust properties: in "circumstellar dust", astronomers have found molecular signatures of CO, silicon carbide, amorphous silicate, polycyclic aromatic hydrocarbons, water ice, and polyformaldehyde, among others (in the diffuse interstellar medium, there is evidence for silicate and carbon grains). "Cometary dust" is generally different (with overlap) from "asteroidal dust". Asteroidal dust resembles carbonaceous chondritic meteorites. Cometary dust resembles interstellar grains which can include
Cosmic dust
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and is mostly composed of ionized helium. A faint halo of interstellar dust surrounds the nebula. Lemon Slice Nebula IC 3568 is a planetary nebula that is 1.3 kiloparsecs (4500 ly) away from Earth in the constellation of Camelopardalis (just 7.5 degrees from Polaris). It is a relatively young nebula and has a core diameter of only about 0.4 light years. It was dubbed the Lemon Slice Nebula by Jim Kaler, due to its appearance in one false-colour image from the Hubble Space Telescope. The Lemon slice nebula is one of the most simple nebulae known, with an almost perfectly
Lemon Slice Nebula
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Sharpless 2-88 Sharpless 2-88, also known as Sh 2-88, is a region of diffuse nebulae northwest of the nebula knots Sh 2-88A, Sh 2-88B1, and Sh 2-88B2, which are all associated with Vulpecula OB1. This nebula is a HII type diffuse nebula excited by the type O8 star BD +26°3952. Both neutral and ionized gases in Sh 2-88 are between 150 and 410 Msolar and the dust mass is about 2 to 9 Msolar. The nebula is ionized by an O8.5 to 9.5V star. The structure been interacting with a HI interstellar bubble shaped by the stellar winds of BD
Sharpless 2-88
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the light from the background source and so its composition and velocity can be studied. One of IUE's early discoveries was that the Milky Way is surrounded by a vast halo of hot gas, known as a galactic corona. The hot gas, heated by cosmic rays and supernovae, extends several thousand light years above and below the plane of the Milky Way. IUE data was also crucial in determining how the light from distant sources is affected by dust along the line of sight. Almost all astronomical observations are affected by this interstellar extinction, and correcting for it is the
International Ultraviolet Explorer
3395084
Boris Vorontsov-Velyaminov Boris Aleksandrovich Vorontsov-Velyaminov (Борис Александрович Воронцов-Вельяминов) (February 14, 1904 – January 27, 1994) was a Soviet/Russian astrophysicist. His name is sometimes given as Vorontsov-Vel'yaminov. He independently discovered the absorption of light by interstellar dust, which was also discovered by Robert Julius Trumpler. He compiled a catalogue of what are now known as Vorontsov-Velyaminov galaxies (the "Atlas of Interacting Galaxies"), as well as a larger and more general catalogue of galaxies (the "Morphological Catalogue of Galaxies"). He also studied and classified planetary nebulae. He is also the author of the standard Russian astronomy textbook for high schools as well
Boris Vorontsov-Velyaminov
5473593
Nebula, where a lot of star-formation is taking place, are characterized as thermal emission nebulae. Supernova remnants, on the other hand, like the Crab Nebula, are characterized as nonthermal emission (synchrotron radiation). Some of the better known dusty regions in the Universe are the diffuse nebulae in the Messier catalog, for example: M1, M8, M16, M17, M20, M42, M43. Some larger dust catalogs are Sharpless (1959) A Catalogue of HII Regions, Lynds (1965) Catalogue of Bright Nebulae, Lynds (1962) Catalogue of Dark Nebulae, van den Bergh (1966) Catalogue of Reflection Nebulae, Green (1988) Rev. Reference Cat. of Galactic SNRs, [The
Cosmic dust
1414922
diffuse nebulae and reflection nebulae. Dust is widely present in the galaxy. Ambient radiation heats dust and re-emits radiation into the microwave band, which may distort the cosmic microwave background power spectrum. Dust in this regime has a complicated emission spectrum, and includes both thermal dust emission and spinning dust emission. Dust samples returned from outer space may provide information about conditions in the early solar system. Several spacecraft have sought to gather samples of dust and other materials. Among these craft was Stardust, which flew past Comet Wild 2 in 2004, and returned a capsule of the comet's remains
Dust