Mysterious objects peering out from the depths of space have long attracted the interest of sky watchers. Even the ancient Greek scientist Hipparchus noted in his catalog the presence of several foggy objects in the night sky. His colleague Ptolemy added five more nebulae to the list. In the 17th century, Galileo invented a telescope and with its help was able to see the Orion and Andromeda nebulae. Since then, as telescopes and other instruments have improved, new discoveries in outer space have begun. And nebulae are classified as a separate class of stellar objects.
Over time, there were a lot of known nebulae. They began to interfere with scientists and astronomers in their search for new objects. IN late XVIII century, while studying certain objects - comets, Charles Messier compiled a “catalog of diffuse stationary objects” that were similar to comets. But due to the lack of sufficient technical support, this catalog included both nebulae and galaxies, along with globular star clusters.
Just as telescopes improved, so did astronomy itself. The concept of “nebula” acquired new colors and was constantly refined. Some types of nebulae were identified as star clusters, some were classified as absorbing ones, and in the 20s of the last century Hubble was able to establish the nature of nebulae and identify regions of galaxies.
The portal site will tell about the theories of the origin of nebulae, their approximate quantity, types and distance from our planet. The portal operates purely on scientifically verified facts and the most popular ideas.
Classification and types of nebulae on the portal website
The primary principle by which nebulae are classified is whether they absorb or scatter (emit) light. This criterion divides nebulae into light and dark. The emission of light colors depends on their origin. And the energy sources that excite their radiation depend on their own nature. Very often, not one, but two radiation mechanisms can operate in a nebula. Dark ones can only be seen due to the absorption of radiation sources located behind them.
But if the first principle of classification is accurate, then the second (dividing nebulae into dust and gas) is a conditional principle. Each nebula contains dust and gas. This division is due by different mechanisms radiation and observation methods. The presence of dust is best observed during the absorption of radiation by dark nebulae, which are located behind the sources. The intrinsic emission of the gaseous components of the nebula is visible when it is ionized by ultraviolet light or when the interstellar medium is heated. Last process possible after being hit by a wave that formed after the explosion above nova.
The dark nebula appears as a dense, most often molecular cloud of interstellar dust and gas. Absorbing light, the cloud becomes opaque. Most often, dark nebulae are visible against a background of light ones. It is extremely rare for scientists to notice them against the background of the Milky Way. They are called giant globules.
Light absorption Av in dark individuals varies widely. Can reach values: from 1–10 m to 10–100 m. The structure of nebulae with high absorption can only be studied using the methods of submillimeter astronomy and radio astronomy, with observations from infrared radiation and molecular radio lines. Often, in the nebula itself, individual compactions are found with an Av value of up to 10,000 m. According to the theories of advanced astrophysicists, stars are formed there.
In the translucent parts of nebulae, the fibrous structure is clearly visible in the optical range. The overall elongation and fibers are associated with the presence of magnetic fields, which make it difficult for matter to move across magnetohydrodynamic instabilities and lines of force. This connection occurs because the dust particles are charged with electricity.
Another bright type of nebula is the reflection nebula. These are gas and dust clouds illuminated by stars. If the stars are located in or near an interstellar cloud, but are not too hot to reduce the amount of hydrogen around them, then the main source of optical radiation from the nebula itself becomes the star light scattered by interstellar dust. A striking example of this phenomenon is found around the Pleiades stars.
Most reflection nebulae are located near the plane of the Milky Way. In some cases, the presence of such nebulae is observed at high galactic latitudes. These molecular clouds have different sizes, shape, density and mass and are illuminated by the combined radiation of the stars of the Milky Way. They are difficult to study because the surface brightness is very low. Sometimes, appearing in images of galaxies, non-existent details are visible in the photographs - jumpers, tails, etc.
A small portion of reflection nebulae have a comet-like appearance. They are called cometary. At the head of such a nebula, as a rule, there is a variable star of the Taurus type. It illuminates the nebula. They vary in brightness and are small in size, about hundredths of a parsec.
A light echo is the rarest type of reflection nebula. A striking example is the formation of a Novaya outbreak in the constellation Perseus. This flash illuminated the dust, causing the resulting nebula to be visible for several years. And at the same time in space she moved at the speed of light. In addition to the light echo, gas nebulae are formed after such incidents.
Most reflection nebulae have a fine-fibrous structure, that is, a system of almost parallel filaments. Their thickness can reach several hundredths of a parsec. These filaments occur as a result of the magnetic field penetrating the flute instability of the nebula. Fibers of dust and gas push apart the lines of force in the magnetic field and leak between them.
Dust properties such as albedo, shape, grain orientation, scatter indicator, and size have given scientists and astronauts the opportunity to study the distribution of light polarization and brightness across the surface of reflection nebulae.
Radiation-ionized nebulae are regions of interstellar gas that are highly ionized by radiation from stars. This radiation can also appear from other sources. Most of all, such nebulae are studied in regions of ionized hydrogen, as a rule, this is the H II zone. In such zones, the substance is completely ionized. Its temperature is about 104 K. Heats up due to internal ultraviolet radiation. Inside the H II zones, stellar radiation in the Lyman continuum turns into subordinate-serial radiation (corresponding to Rosseland's theorem). Because of this, the spectrum of nebulae contains bright lines of the Bellmer series and Lyman-alpha lines.
Such nebulae also include zones of ionized carbon - C II. The carbon in them is completely ionized by starlight. C II zones are usually located around H II zones. They are obtained due to the low ionization potential of carbon compared to hydrogen. They can also form around stars with a high spectral type in the densities of the interstellar medium. Nebulae ionized by radiation also appear around strong X-ray sources. They have higher temperatures than in H II zones and a relatively higher degree of ionization.
The most common type of emission nebulae are planetary nebulae. They are created to expire top layers atmospheres of stars. Such a nebula glows and expands in the optical range. They were first discovered in the 17th century by Herschel and called them that because of their external resemblance to the disks of planets. But not all planetary nebulae are disk-shaped; some have rounded shape rings. Inside such nebulae there is a fine structure in the form of spirals, jets and small globules. Such nebulae are expanding at a speed of 20 km/s, and their mass is 0.1 solar masses. They live for about 10 thousand years.
The portal site provides only verified and up-to-date information. We will take you to the mysterious world of space. And thanks to astronomers and astrophysicists, nebulae are no longer such a huge mystery as they once were.
In addition to the usual, long-lived, foggy formations, there are short-term ones created by shock waves. They disappear when the kinetic energy of the moving gas disappears. There are several sources for the generation of such shock waves. Most often, this is the result of a star explosion. Less often - stellar wind, outbursts of novae and supernovae. In any case, there is one source of emission of such matter - a star. Nebulae of this origin have the shape of an expanding shell or the shape of a sphere. The substance ejected as a result of the explosion can have different speeds from hundreds to thousands of km/s, because of this the temperature of the gas behind the shock wave reaches not millions, but billions of degrees.
Gas heated to enormous temperatures is emitted in the X-ray range both in spectral lines and in the continuous spectrum. In spectral optical lines it glows faintly. When encountering the inhomogeneity of the interstellar medium, the shock wave bends around the densities. Inside the seal itself, its own shock wave propagates. It also causes radiation in the spectrum lines of the optical range. The result is bright fibers that are clearly visible in photographs.
The brightest nebulae that arise after shock waves are created by supernova explosions. They are called stellar flare remnants. They play an important role in shaping the shape of interstellar gas. They are characterized by small size, weakness and fragility.
There is another type of nebula. This type is also created after the occurrence of a shock wave. But the main reason is the stellar wind from the Wolf–Rayet stars. Wolf stars have a fairly powerful wind mass flow and outflow velocity. They form medium-sized nebulae with very bright filaments. Comparing them with the remnants of supernova explosions, scientists argue that the radio emission from such nebulae is of a thermal nature. Nebulae that are located around Wolf stars do not live long. Their existence directly depends on the duration of the star’s presence in the Wolf–Rayet star stage.
Absolutely similar nebulae are found around O stars. These are very bright hot stars that belong to spectral type O. They have a strong stellar wind. Unlike the nebulae located around Wolf-Rayet stars, the nebulae of O stars are less bright, but have a much larger size and lifetime.
The most common nebulae are found in star-forming regions. Low-velocity shock waves are created in regions of the interstellar medium. It is in them that star formation occurs. This process entails heating the gas to hundreds and even thousands of degrees, partial destruction of molecules, heating of the dust itself, and excitation of molecular levels. Such shock waves have the appearance of elongated nebulae and, as a rule, glow in the infrared range. A striking example of such a phenomenon can be seen in the constellation Orion.
Some examples of such use still exist today. For example, the Andromeda Galaxy is often called the "Andromeda Nebula."
As astronomy and the resolution of telescopes developed, the concept of “nebula” became more and more refined: some of the “nebulae” were identified as star clusters, dark (absorbing) gas-dust nebulae were discovered, and, finally, in the 1920s, first Lundmark, and then and Hubble, managed to resolve the peripheral regions of a number of galaxies into stars and thereby establish their nature. Since that time, the term “nebula” has been used in the above sense.
Types of nebulae
The primary feature used in the classification of nebulae is the absorption or emission (scattering) of light by them, that is, according to this criterion, nebulae are divided into dark and light. The former are observed due to the absorption of radiation from sources located behind them, the latter - due to their own radiation or reflection (scattering) of light from nearby stars. The nature of the radiation of light nebulae, the energy sources that excite their radiation, depend on their origin and can be of a diverse nature; Often several radiation mechanisms operate in one nebula.
The division of nebulae into gas and dust is largely arbitrary: all nebulae contain both dust and gas. This division is historically determined different ways observations and radiation mechanisms: the presence of dust is most clearly observed when radiation is absorbed by dark nebulae of sources located behind them and when radiation from nearby stars or in the nebula itself is reflected, scattered, or re-emitted by dust contained in the nebula; the intrinsic emission of the gas component of a nebula is observed when it is ionized by ultraviolet radiation from a hot star located in the nebula (emission regions of H II ionized hydrogen around stellar associations or planetary nebulae) or when the interstellar medium is heated by a shock wave due to a supernova explosion or the influence of a powerful stellar wind of Wolf-Rayet type stars .
Dark nebulae
Dark nebulae are dense (usually molecular) clouds of interstellar gas and interstellar dust that are opaque due to interstellar absorption of light by the dust. They are usually visible against the background of bright nebulae. Less often, dark nebulae are visible directly against the background of the Milky Way. These are the Coalsack Nebula and many smaller ones called giant globules.
Interstellar absorption of light A v in dark nebulae varies widely, from 1-10 m to 10-100 m in the densest ones. The structure of nebulae with large A v can only be studied by methods of radio astronomy and submillimeter astronomy, mainly from observations of molecular radio lines and infrared radiation from dust. Often, individual densities with A v up to 10,000 m are found inside dark nebulae, in which stars apparently form.
In those parts of nebulae that are translucent in the optical range, the fibrous structure is clearly visible. The filaments and general elongation of nebulae are associated with the presence of magnetic fields in them, which impede the movement of matter across the lines of force and lead to the development of a number of types of magnetohydrodynamic instabilities. The dust component of nebula matter is associated with magnetic fields due to the fact that dust grains are electrically charged.
Reflection nebulae
Reflection nebulae are clouds of gas and dust illuminated by stars. If the star(s) are in or near an interstellar cloud, but are not hot enough to ionize a significant amount of interstellar hydrogen around it, then the main source of optical radiation from the nebula is starlight scattered by interstellar dust. An example of such nebulae are the nebulae around bright stars in the Pleiades cluster.
Most reflection nebulae are located near the plane of the Milky Way. In a number of cases, reflection nebulae are observed at high galactic latitudes. These are gas-dust (often molecular) clouds various sizes, shapes, densities and masses, illuminated by the combined radiation of the stars in the Milky Way disk. They are difficult to study because of their very low surface brightness (usually much fainter than the sky background). Sometimes, when projected on images of galaxies, they lead to the appearance in photographs of galaxies of details that do not exist in reality - tails, bridges, etc.
The Angel reflection nebula is located at an altitude of 300 pc above the galactic plane
Some reflection nebulae have a comet-like appearance and are called cometary nebulae. In the “head” of such a nebula there is usually a variable star of the type T Tauri, illuminating the nebula. Such nebulae often have variable brightness, tracking (with a delay during the propagation of light) the variability of the radiation of the stars illuminating them. The sizes of cometary nebulae are usually small - hundredths of a parsec.
A rare type of reflection nebula is the so-called light echo, observed after the 1901 nova explosion in the constellation Perseus. The bright flare of the new star illuminated the dust, and for several years a faint nebula was observed, spreading in all directions at the speed of light. In addition to the light echo, after the outbursts of new stars, gaseous nebulae are formed, similar to the remnants of supernova explosions.
Many reflection nebulae have a fine-fibrous structure—a system of nearly parallel filaments several hundredths or thousandths of a parsec thick. The origin of the filaments is related to flute or permutation instability in a nebula permeated by a magnetic field. Fibers of gas and dust push the lines of force apart magnetic field and are embedded between them, forming thin threads.
Studying the distribution of brightness and polarization of light over the surface of reflection nebulae, as well as measuring the dependence of these parameters on wavelength, makes it possible to establish such properties of interstellar dust as albedo, scattering indicatrix, size, shape and orientation of dust grains.
Nebulae ionized by radiation
Radiation-ionized nebulae are areas of interstellar gas that have been highly ionized by radiation from stars or other sources of ionizing radiation. The brightest and most widespread, as well as the most studied representatives of such nebulae are regions of ionized hydrogen (H II zones). In H II zones, the matter is almost completely ionized and heated to a temperature of ~10 4 K by ultraviolet radiation from the stars located inside them. Inside the HII zones, all the star's radiation in the Lyman continuum is processed into radiation in the lines of subordinate series, in accordance with Rosseland's theorem. Therefore, in the spectrum of diffuse nebulae there are very bright lines of the Balmer series, as well as the Lyman-alpha line. Only rarefied low-density H II zones are ionized by stellar radiation, in the so-called. coronal gas.
Nebulae ionized by radiation also include the so-called zones of ionized carbon (zones C II), in which carbon is almost completely ionized by the light of the central stars. C II zones are typically located around H II zones in neutral hydrogen (H I) regions and manifest themselves via carbon recombination radio lines similar to those of hydrogen and helium. C II zones are also observed in the C II infrared line (λ = 156 μm). Zones C II are characterized by low temperature 30-100 K and low degree of ionization of the environment as a whole: N e /N< 10 −3 , где N e и N концентрации электронов и атомов. Зоны C II возникают из-за того, что потенциал ионизации углерода (11,8 эВ) меньше, чем у водорода (13,6 эВ). Излучение звёзд с энергией E фотонов 11,8 эВ E 13,6 эВ (Å) выходит за пределы зоны H II в область H I, сжатую ионизационным фронтом зоны H II, и ионизует там углерод. Зоны C II возникают также вокруг звёзд спектральных классов B1-B5, находящихся в плотных участках межзвёздной среды. Такие звёзды практически не способны ионизовать водород и не создают заметных зон H II.
Radiation-ionized nebulae also occur around powerful X-ray sources in the Milky Way and other galaxies (including active galactic nuclei and quasars). They are often characterized by higher temperatures than in H II zones and a higher degree of ionization of heavy elements.
Planetary nebulae
A type of emission nebulae are planetary nebulae, formed by the upper outflowing layers of stellar atmospheres; usually this is a shell ejected by a giant star. The nebula expands and glows in the optical range. The first planetary nebulae were discovered by W. Herschel around 1783 and were named so for their external resemblance to the disks of planets. However, not all planetary nebulae are disk-shaped: many are ring-shaped or symmetrically elongated along a certain direction (bipolar nebulae). A fine structure in the form of jets, spirals, and small globules is noticeable inside them. The expansion rate of planetary nebulae is 20-40 km/s, diameter is 0.01-0.1 pc, typical mass is about 0.1 solar masses, lifetime is about 10 thousand years.
Nebulae created by shock waves
The variety and multiplicity of sources of supersonic motion of matter in the interstellar medium lead to a large number and variety of nebulae created by shock waves. Typically, such nebulae are short-lived, since they disappear after the kinetic energy of the moving gas is exhausted.
The main sources of strong shock waves in the interstellar medium are stellar explosions - ejections of shells during explosions of supernovae and novae, as well as stellar wind (as a result of the latter, so-called stellar wind bubbles are formed). In all these cases, there is a point source of ejection of matter (a star). The nebulae created in this way have the appearance of an expanding shell, close to spherical in shape.
The ejected substance has speeds of the order of hundreds and thousands of km/s, so the temperature of the gas behind the shock wave front can reach many millions and even billions of degrees.
Gas heated to a temperature of several million degrees emits mainly in the X-ray range, both in the continuous spectrum and in spectral lines. In optical spectral lines it glows very weakly. When the shock wave encounters inhomogeneities in the interstellar medium, it bends around the densities. A slower shock wave propagates inside the seals, causing radiation in the spectral lines of the optical range. The result is bright fibers that are clearly visible in photographs. The main shock front, compressing a clump of interstellar gas, sets it in motion in the direction of its propagation, but at a speed lower than that of the shock wave.
Remnants of supernovae and novae
The brightest nebulae created by shock waves are caused by supernova explosions and are called supernova remnants. They play a very important role in shaping the structure of interstellar gas. Along with the described features, they are characterized by non-thermal radio emission with a power-law spectrum, caused by relativistic electrons accelerated both during the supernova explosion and later by the pulsar that usually remains after the explosion. Nebulae associated with nova explosions are small, faint, and short-lived.
Nebulae around Wolf-Rayet stars
Thor's Helmet - Nebula around the Wolf-Rayet Star
Another type of nebula created by shock waves is associated with the stellar wind from Wolf-Rayet stars. These stars are characterized by a very powerful stellar wind with a mass flux per year and an outflow velocity of 1·10 3 -3·10 3 km/s. They create nebulae several parsecs in size with bright filaments at the edge of the astrosphere of such a star. Unlike the remnants of supernova explosions, the radio emission of these nebulae is of a thermal nature. The lifetime of such nebulae is limited by the duration of the stars' stay in the Wolf-Rayet star stage and is close to 10 5 years.
Nebulae around O stars
The nebulae around Wolf-Rayet stars are similar in properties, but are formed around the brightest hot stars of the O-O spectral class, which have a strong stellar wind. They differ from nebulae associated with Wolf-Rayet stars in their lower brightness, larger size and, apparently, longer lifespan.
Nebulae in star-forming regions
The Orion A Nebula is a giant star-forming region
Shock waves of lower speeds arise in regions of the interstellar medium in which star formation occurs. They lead to heating of gas to hundreds and thousands of degrees, excitation of molecular levels, partial destruction of molecules, and heating of dust. Such shock waves are visible in the form of elongated nebulae that glow primarily in the infrared. A number of such nebulae have been discovered, for example, in the star formation center associated with the Orion Nebula.
In the Universe, in addition to stars, planets and galaxies, there are also diffuse nebulae. Their role in the development of outer space is enormous: it is in the depths of nebulae that stars are born. Nebulae consist of two components - gas and dust. The gas is of prehistoric origin, i.e. it was formed at the dawn of the Universe, it was at this time that hydrogen and helium were formed - the main components of the first stars. Heavier elements appeared later, when stellar flares and ejections into the interstellar medium began to occur.
The dust that is part of the nebulae consists of a mixture of carbon in various stages of cohesion and silicates; there are also traces of other organic matter. The gas is mainly hydrogen.
In principle, nebulae are regions of gravitationally compacted interstellar medium in which clouds have formed. Increasing in size, they attracted part of the matter from environment. Sometimes these clouds become visible because the relatively young stars that make up them excite atoms. As a result, the nebula becomes brighter.
Nebula classification
There are many nebulae in the sky. They are divided into three types: emission nebulae, light (they glow by reflected light) and dark. This division is based on appearance nebulae and phenomena characteristic of them. Emission nebulae are bright because atoms are excited by ultraviolet radiation from nearby young stars. The nebulae themselves also become a source of radiation.
Light nebulae do not emit radiation, but reflect the light of nearby stars. Classic example light nebula - a bluish nebula surrounding the open star cluster of the Pleiades. Dark nebulae are dense concentrations of dust that actively absorb light. They become visible only if there is a source of shine behind them.
Many nebulae are easily visible, sometimes even with the naked eye. It is enough to use binoculars or a small amateur telescope. Such nebulae are recorded in the famous Messier catalogue. This French astronomer compiled it in the second half of the 18th century.
The brightest nebula in our hemisphere is the Orion Nebula; in the catalog it is designated M42. This is perhaps the first celestial object that sky lovers aim their astronomical instruments at on long winter nights.
There are many other very beautiful nebulae. Here are some examples.
Nebula in the constellation Sagittarius
The Lagoon Nebula, M8, is located in the constellation Sagittarius. There are many nebulae in this area of the sky. This is a very “populated” region of the Milky Way, with many gas clouds.
M8 is located next to an open star cluster - this combination is not uncommon. As already noted, nebulae are star formation zones and often clusters of young and bright stars are located within them or nearby. Even with the help of small binoculars you can see some details of the M8, and with more powerful binoculars you can see characteristics, for example a dark stripe inside a cloud.
In the open star cluster NGC 6530, approximately 40 stars are visible, ranging in magnitude from 8 to 13. Their light excites the nebula's atoms, causing it to become visible.
M8 also contains Bok globules, dark zones whose diameter is tens of thousands of AU. The distance to M8 is 3000-4000 light years. In the constellation Sagittarius there is also M20, a typical emission nebula. This refers to the Trifida Nebula (“divided into three parts”). The name reflects its shape.
This nebula was discovered by the astronomer Le Gentil in 1750, but its first description appeared only in 1764. Messier did it. William Herschel identified three lines that divide this nebula into three triangular sectors. With binoculars you can see the brightest part of the nebula. It looks like a round spot with a diameter of up to 10’. The existence of dark zones that divide the cloud into three parts is associated with the presence of dust and cold gases in its composition.
The distance to M20 is approximately 3200 light years. In the constellation Sagittarius, in the middle of the Milky Way, there is also the M24 nebula, visible to the naked eye. It was discovered earlier, even before Messier included it in his catalogue. This astronomer believed that its diameter was about 1.5°.
Eagle Nebula in the constellation Serpens
M16, the Eagle Nebula, was discovered by De Chaizeau in 1746. Messier recorded it two years later. This nebula is located on the border of the constellations Scutum and Serpens. Inside it there is a dark area that extends from the northern to the central part of the cloud.
The star cluster contains several dozen stars, some of them very faint and red in color. The magnitude of the brightest stars ranges from 8 to 11, they belong to spectral classes O and B, i.e. these are classic hot and young stars. M16 is an emission nebula, but it also has an element of reflection nebula. Its distance ranges from 5,000 to 11,000 light years, with an average of about 7,500.
Planetary nebulae
In addition to diffuse ones, there are also planetary nebulae. Their name stems from the fact that in the beginning, observers often confused them with planets, since they are round in shape.
These nebulae are formed from emissions from the gas envelope of stars in the later stages of their evolution.
The most famous planetary nebula, M57, is located in the constellation Lyra. It is difficult to identify due to low surface illumination. There is also the M27 nebula - the Dumbbell, it is located in the constellation Vixen. This nebula was discovered by Messier in 1764. He, observing it through a telescope, determined the formation to be oval in shape. In small amateur telescopes, this nebula appears in the form of “ hourglass" M27 is located at a distance of 500-1000 light years from Earth. Its diameter at maximum is about 2.5 light years
- This types of nebulae. They are beautiful, majestic, fascinating, and despite the fact that they are difficult to detect through a telescope, observation enthusiasts devote a lot of time to searching for them. They are unique, each one is different from the other. The dimensions in space are relatively small and are located at short distances from us (from the point of view of astronomical values). They consist predominantly of hydrogen - 90% and helium - 9.9%. We will not consider whether each nebula belongs to one or another within the framework of this article; our task is different. And let me stop ranting and get straight to the point.
1. Diffuse nebula
Diffuse Lagoon Nebula
Diffuse nebulae, unlike stars, do not have their own source of energy. The glow inside them comes from hot stars that are inside or near it. Such nebulae are found to a greater extent on the “branches” of galaxies, where active star formation occurs and are substances that are not included in the composition of the star.
Diffuse nebulae are predominantly red in color - this is due to the abundance of hydrogen inside them. Green and blue colors tell us about others chemical elements, such as helium, nitrogen, heavy metals.
These nebulae include the most popular and accessible for observation with devices with low magnification - Orion Nebula in the constellation Orion, which I mentioned in the article.
Diffuse nebulae are also often called emission.
2. Reflection nebula
Witch's Head Reflection Nebula
A reflection nebula does not emit any light of its own. This is a cloud of gas and dust that reflects light from nearby stars. Just like diffuse nebulae, reflection nebulae are found in regions of active star formation. They have a bluish tint to a greater extent, because... it dissipates better than others.
Not many nebulae of this type are known today—about 500.
Some sources do not distinguish reflection nebula separately, but classify it as a diffuse nebula.
3. Dark Nebula
Dark Horsehead Nebula
Such a nebula occurs due to the blocking of light from objects located behind it. This is a cloud. The composition is almost identical to the previous reflection nebula, differing only in the location of the light source.
As a rule, a dark nebula is observed together with a reflection or diffuse nebula. Great example in the photo above. "Horse head"- here the dark region blocks the light from the diffuse nebula behind it much bigger size. With an amateur telescope, such nebulae will be extremely difficult or almost impossible to see. However, in the radio range, such nebulae actively emit electromagnetic waves.
4. Planetary nebula
Planetary nebula M 57
Perhaps the most beautiful type of nebula. As a rule, such a nebula is the result of the end of a star’s life, i.e. its explosion and scattering of gas into outer space. Despite the fact that the star explodes, it is called planetary. This is due to the fact that when observed, such nebulae look like planets. Most of them are round or oval in shape. The shell of gas located inside is illuminated by the remains of the star itself.
In total, about two thousand planetary nebulae have been discovered, although in our Milky Way galaxy alone there are more than 20,000 of them.
5. Supernova Remnant
Crab Nebula M 1
Supernova- this is a sharp increase in the brightness of a star as a result of its explosion and the release of a huge amount of energy into the outer space environment.
The photo above shows great example explosion of a star in which the ejected gas has not yet mixed with interstellar matter. Based on Chinese chronicles, this explosion was recorded in 1054. But we must understand that the distance to the Crab Nebula is about 3300 light years.
That's all. There are only 5 types of nebulae that you need to know and be able to recognize. I hope I was able to convey information to you in an accessible form and in simple language. If you have questions, ask, write in the comments. Thank you.
Previously, the definition of “nebula” meant any static phenomenon in space that has an extended shape. Then this concept was specified by studying the mysterious object in more detail. Let's try to figure out what such a section of the interstellar medium is like.
Nebula concept in space
A nebula is a gas cloud containing a huge number of stars inside. The radiance of these celestial bodies allows the cloud to glow different colors. Through special telescopes such space formations look like peculiar spots with a bright base.
Some interstellar regions have fairly clear contours. Many known gas accumulations are wisps of fog that spread into different sides jets and has a diffuse form of origin.
The space that lies between the stars of the nebula is not empty substance. Particles of a diverse nature are concentrated here in fairly small quantities, which include atoms of some substances.
They distinguish between the origin of diffuse and planetary formations in space. The nature of their formation differs significantly from one another, so it is necessary to carefully understand the structure of the formation of different nebulae. Planetary objects are the product of the activity of the main stars, and diffuse ones represent the consistency after the formation of stars.
Nebulae of diffuse origin are located in the spiral arms of galaxies. Such a cosmic compound of gas and dust is in most cases associated with large and cold clouds. Stars form in this region, making the diffuse nebula very bright.
Education of this kind does not have its own source of nutrition. It exists energetically due to the stars elevated temperature, which are located next to it or inside. The color of such nebulae is predominantly red. This factor is due to the fact that they contain a large number of hydrogen. Shades of green and blue indicate the presence of nitrogen, helium and some heavy metals.
In the stellar region of Orion, very small nebulae of diffuse formation can be observed. These formations are very small against the background of a giant cloud, which occupies almost the entire described object. In the constellation Taurus, it is realistic to detect only a few nebulae near fairly young T-type stars. This variety indicates that there is a disk that appears around bright celestial bodies.
A planetary nebula in space is a shell whose energy is final stage formation is ejected by a star without hydrogen reserves in the core. After such changes, the celestial body turns into a red giant, capable of tearing off its surface layer. As a result of the incident, the interior of the object sometimes has a temperature exceeding 100 degrees Celsius. As a result, the star is deformed in such a way that it becomes a white dwarf without a source of energy and heat.
In the 20s of the last century, there was a demarcation between the definitions of “nebula” and “galaxy”. The division that occurred is examined using the example of formation in the Andromeda region, which is a vast galaxy of a trillion stars.
Main types of nebulae
Space education is classified according to various parameters. The following types of nebulae are distinguished: reflection nebulae, dark nebulae, emission nebulae, planetary gas clusters and the residual product after the activity of supernovae. The division also concerns the composition of nebulae: there is gas and dust cosmic matter. First of all, attention is paid to the ability of such objects to absorb or scatter light.
Dark Nebula
Dark nebulae are fairly dense compounds of interstellar gas and dust, the structure of which is opaque due to the influence of dust. Clusters of this kind can occasionally be observed against the background of the Milky Way.
The study of such objects depends on the AV indicator. If the data is quite high, then experiments are carried out exclusively using submillimeter and radio wave astronomy technologies.
An example of such a formation is the Horsehead, formed in the constellation Orion.
Such concentrations scatter the light carried by nearby stars. This object is not a source of radiation, but only reflects radiance.
A gas-dust cloud of this type depends on the location of the stars. At close range, there is a loss of interstellar hydrogen, which leads to a gain of energy from scattered galactic dust. The Pleiades cluster is the best example of the described cosmic phenomenon. In most cases, such gas and dust clumps are located near the Milky Way.
Light nebulae have the following subtypes:
- Cometary. Variable star lies at the basis of such education. It illuminates the described region of the interstellar medium, but has a varying brightness. The sizes of the objects amount to hundreds of fractions of a parsec, which indicates the possibility of a detailed study of such concentrations of gas and dust in space.
- Light echo. This phenomenon is quite rare and has been studied since the beginning of the last century. The constellation Perseus after the supernova explosion in 2001 made it possible to observe a similar change in the cosmic sphere. High-intensity flares activated dust, which formed a moderate nebula over several years.
- Reflective substance with a fibrous structure. Hundreds or thousands of fractions of a parsec are the dimensions of this variety. The forces of the magnetic field of a star cluster are pushed apart under external pressure, after which gas-dust objects are introduced into these fields and a kind of shell filament is formed.
Gas nebula
Such manifestations of space activity have different shapes, and their types can be indicated by the following points:
- Planetary substances in the form of a ring. In this case, such a type of nebula is observed as a planetary one. The arrangement of its components is very simple: the main star is visible in the center, around which all external changes occur.
- Fibers of gas that release their energy separately. These luminous gaseous substances are formed in the most unexpected way in the form of scattered sparkling weaves of gas.
- Crab Nebula. It is a residual phenomenon after the explosion of a star of a new format. Such an event was recorded during the study of celestial bodies that reflect their energy. At the very center of the cluster is a pulsating neutron star, which by some measures is one of the most productive sources of galactic energy.
Dust nebula
This type of nebula looks like a kind of failure, standing out against the background of a bright cosmic clump. This fragment can be observed in the constellation Orion, where a similar trail divides a single cloud into two distinct zones. Against the background of the Milky Way, there are also dusty areas that are clearly expressed in the Ophiuchus region (the Serpent Nebula).
It is possible to study such dust accumulation only with the help of a telescope of fairly high power (diameter from 150 mm). If a dust nebula is located near a bright star, then it begins to reflect the light of this celestial body and becomes a visible phenomenon. Only in special photographs will it be possible to see this ability, which is close to diffuse nebulae.
The main indicator of such a cosmic cloud is its heat. It consists of ionized gas, which is formed due to the activity of the closest hot star. Its effect is that it activates and illuminates the atoms of the nebula using ultraviolet radiation.
The phenomenon is interesting because, according to the principle of formation and visual indicators, it resembles neon light. As a rule, emission-type objects are red in color due to large cluster hydrogen in its composition. There may be additional tones in the form of green and blue, which were formed due to atoms of other substances. The most striking example of such a star cluster is the famous Orion Nebula.
The most famous nebulae
The most popular nebulae in terms of study are the Orion Nebula, the Triple Nebula, the Ring Nebula and the Dumbbell Nebula.
Orion Nebula
This phenomenon is remarkable in that it can be observed even with the naked eye. The Orion Nebula is classified as an emission-type formation, which is located below the belt part of Orion.
The area of the cloud is impressive because it is almost four times the size of the Moon at full phase. In the northeastern part there is a dark dust cluster, which is cataloged as M43.
In the cloud itself there are almost seven hundred stars, which are this moment are still being formed. The diffuse nature of the Orion Nebula formation makes the object very bright and colorful. Red zones indicate the presence of hot hydrogen, while blue zones indicate the presence of dust, reflecting the glow of bluish hot stars.
M42 is the closest place to Earth where stars form. Such a cradle of celestial objects is located at a distance of one and a half thousand light years from our planet and delights outside observers.
Trifid Nebula
The Triple Nebula is located in the constellation Sagittarius and looks like three separated petals. It is difficult to accurately calculate the distance from the Earth to the cloud, but scientists are guided by parameters of two to nine thousand light years.
The uniqueness of this formation lies in the fact that it is represented by three types of nebulae at once: dark, light and emission.
M20 is a cradle for the development of young stars. Such large celestial bodies are predominantly blue color, which was formed due to the ionization of gas accumulated in that area. When observing with a telescope, two things immediately catch your eye: bright stars right in the center of the nebula.
Upon closer examination, it becomes clear that the object seems to be torn into two parts by a black hole. Then, above this gap, you can see a crossbar that gives the nebula the shape of three petals.
Ring
The ring, located in the constellation Lyra, is one of the most famous planetary substances. It is located at a distance of two thousand light years from our planet and is considered a fairly recognizable cosmic cloud.
The Ring glows due to the white dwarf present nearby, and the gases included in its composition act as remnants of the ejected consistency of the central star. The inside of the cloud flickers greenish color, which is explained by the presence of emission lines in that area. They were formed after double ionization of oxygen, which led to the formation of a similar shade.
The central star was originally a red giant, but later became a white dwarf. It can only be viewed through powerful telescopes, because its dimensions are extremely small. Thanks to the activity of this celestial body, the Ring Nebula arose, which in the form of a slightly elongated circle envelops the central source of energy.
The ring is one of the most popular observation objects among both scientists and ordinary space enthusiasts. This interest is due to the excellent visibility of the cloud at any time of the year and even in urban lighting conditions.
Dumbbell
This cloud is the territory between stars of planetary origin, which is located in the constellation Chanterelle. Dumbbell is located at a distance of about 1200 light years from Earth and is considered a very popular object for amateur study.
Even with the help of binoculars, the formation can be easily recognized if you focus on the constellation Sagittarius in the northern hemisphere of the starry sky.
The shape of M27 is very unusual and looks like a dumbbell, which is why the cloud got its name. It is sometimes called the “stub” because the nebula’s outline resembles a bitten apple. Several stars shine through the gaseous structure of the Dumbbell, and when using a powerful telescope, small “ears” can be seen in the bright part of the object.
The study of the nebula in the constellation Vulpecula has not yet been completed and suggests many discoveries in this direction.
There is a rather bold hypothesis that gas-dust nebulae can influence human consciousness. Pavel Globa believes that such education can completely change the lives of some people. According to experts in the field of astrology, nebulae have a destructive effect on the senses and change the consciousness of the inhabitants of the Earth. Star clusters, according to this version, are capable of controlling the duration of human existence, shortening the life cycle or making it longer. It is believed that nebulae have a greater influence on people than stars. Famous astrologers explain all this by saying that there is a certain program for which a certain cosmic cloud is responsible. Its mechanism begins to act instantly, and a person is not able to influence it.
What the nebula looks like - look at the video:
Nebulae are a magnificent phenomenon of extraterrestrial origin that needs to be studied in detail. But it is difficult to judge the reliability of the voiced assumption about the influence of star clusters on human consciousness!
