Nebulae in space - one of the wonders of the universe, striking in its beauty. They are valuable not only visual appeal. The study of nebulae helps scientists clarify the laws of the functioning of the cosmos and its objects, correct theories about the development of the Universe and the life cycle of stars. Today, we know a lot about these objects, but far from everything.
Mixture of gas and dust
For quite a long time, until the middle of the century before last, nebulae were considered star clusters, distant from us at considerable distances. The use of a spectroscope in 1860 made it possible to establish that many of them are composed of gas and dust. The English astronomer W. Heggins found that the light from nebulae is different from the radiation coming from ordinary stars. The spectrum of the former contains bright colored lines interspersed with dark ones, while in the latter case no such black bands are observed.
Further research has established that the nebulae of the Milky Way and other galaxies inmainly composed of a hot mixture of gas and dust. Similar cold formations are often encountered. Such clouds of interstellar gas are also referred to as nebulae.
Classification
Depending on the properties of the elements that make up the nebula, there are several types of them. All of them are presented in large numbers in the vastness of space and are equally interesting for astronomers. Nebulae that emit light for one reason or another are usually called diffuse or bright. Opposite to them in the main parameter, of course, are designated as dark. There are three types of diffuse nebulae:
- reflective;
- issue;
- supernova remnants.
Emission, in turn, are divided into regions of formation of new stars (H II) and planetary nebulae. All of these types are characterized by certain properties that make them unique and worthy of close study.
Star formation regions
All emission nebulae are clouds of luminous gas of various shapes. Their main element is hydrogen. Under the influence of a star located in the center of the nebula, it ionizes and collides with the atoms of the heavier components of the cloud. The result of these processes is a characteristic pinkish glow.
The Eagle Nebula, or M16, is a great example of this type of object. Here is a region of star formation, many young, as well as massive hot stars. The Eagle Nebula is wherehosts a well-known region of space, the Pillars of Creation. These gas clumps, formed under the influence of the stellar wind, are the zone of star formation. The formation of luminaries here is caused by the compression of gas and dust columns under the action of gravity.
Recently, scientists have learned that we will only be able to admire the Pillars of Creation for another thousand years. Then they will disappear. In fact, the destruction of the Pillars occurred approximately 6,000 years ago due to a supernova explosion. However, light from this region of space has been coming to us for about seven thousand years, so the event calculated by astronomers for us is only a matter of the future.
Planetary Nebulae
The name of the next type of luminous gas and dust clouds was introduced by W. Herschel. A planetary nebula is the last stage in a star's life. The shells shed by the luminary form a characteristic pattern. The nebula resembles a disk that usually surrounds a planet when viewed through a small telescope. To date, more than a thousand such objects are known.
Planetary nebulae are part of the transformation of red giants into white dwarfs. At the center of the formation is a hot star, similar in its spectrum to class O luminaries. Its temperature reaches 125,000 K. Planetary nebulae are mostly relatively small in size - 0.05 parsec. Most of them are located in the center of our galaxy.
The mass of the gas envelope thrown off by the star is small. It is tenths of a similar parameter of the Sun. The mixture of gas and dust is removed fromthe center of the nebula at a speed of up to 20 km/s. The shell exists for about 35 thousand years, and then becomes very rarefied and indistinguishable.
Features
The planetary nebula can be of various shapes. Basically, one way or another, it is close to the ball. There are round, ring-shaped, dumbbell-shaped nebulae of irregular shape. The spectra of such space objects include the emission lines of the luminous gas and the central star, and sometimes the absorption lines from the spectrum of the star.
The planetary nebula emits a huge amount of energy. It is much larger than that for the central star. The core of the formation emits ultraviolet rays due to its high temperature. They ionize gas atoms. The particles are heated, instead of ultraviolet, they begin to emit visible rays. Their spectrum contains emission lines that characterize the formation as a whole.
Cat's Eye Nebula
Nature is a craftswoman for creating unexpected and beautiful forms. Noteworthy in this respect is the planetary nebula, because of the similarity called the Cat's Eye (NGC 6543). It was discovered in 1786 and was the first to be identified by scientists as a cloud of luminous gas. The Cat's Eye Nebula is located in the constellation Draco and has a very interesting complex structure.
It was formed about 100 years ago. Then the central star shed its shells and formed concentric lines of gas and dust, characteristic of the pattern of the object. On theToday, the mechanism of formation of the most expressive central structure of the nebula remains unclear. The appearance of such a pattern is well explained by the location of a double star in the core of the nebula. However, so far there is no evidence to support this state of affairs.
The temperature of the halo of NGC 6543 is approximately 15,000 K. The core of the nebula is heated to 80,000 K. At the same time, the central star is several thousand times brighter than the Sun.
Colossal explosion
Massive stars often end their life cycle with spectacular "special effects". Huge in their power explosions lead to the loss of all external shells by the luminary. They move away from the center at a speed exceeding 10,000 km/s. The collision of a moving substance with a static one causes a strong increase in the temperature of the gas. As a result, its particles begin to glow. Often, supernova remnants are not spherical formations, which seems logical, but nebulae of various shapes. This happens because the substance ejected at high speed irregularly forms clots and clusters.
Trace of a thousand years ago
Perhaps the most famous supernova remnant is the Crab Nebula. The star that gave birth to her exploded almost a thousand years ago, in 1054. The exact date was established according to Chinese chronicles, where its flash in the sky is well described.
The characteristic pattern of the crab nebula is gas ejected by a supernova and not yet completely mixed with interstellar matter. The object is located at a distance of 3300 light years fromus and is continuously expanding at a speed of 120 km/s.
At the center, the Crab Nebula contains a supernova remnant - a neutron star that emits streams of electrons that are sources of continuous polarized radiation.
Reflection Nebulae
Another type of these space objects consists of a cold mixture of gas and dust, unable to emit light on its own. Reflection nebulae glow due to nearby objects. These may be stars or similar diffuse formations. The spectrum of scattered light remains the same as that of its sources, but blue light dominates for the observer.
A very interesting nebula of this type is associated with the star Merope. A luminary from the Pleiades cluster has been destroying a passing molecular cloud for several million years. As a result of the influence of the star, the particles of the nebula line up in a certain sequence and are pulled towards it. After some time (the exact time is unknown), Merope can completely destroy the cloud.
Dark horse
Diffuse formations are often contrasted with an absorbing nebula. The Milky Way galaxy has many of them. These are very dense clouds of dust and gas that absorb light from the emission and reflection nebulae and stars behind them. These cold cosmic formations are mostly made up of hydrogen atoms, although they also contain heavier elements.
An excellent representative of this type is the Horsehead Nebula. It is located in the constellation Orion. The characteristic shape of the nebula, so similar to the head of a horse, was formed as a result of the influence of stellar wind and radiation. The object is clearly visible due to the fact that a bright emission formation serves as its background. At the same time, the Horsehead Nebula is only a small part of an extended, almost invisible, absorbing cloud of dust and gas.
Thanks to the Hubble telescope, nebulae, including planetary ones, are familiar to a wide range of people today. Photographs of the areas of space where they are located impress to the depths of the soul and leave no one indifferent.
