Planetary nebulae. The Cat's Eye Nebula

Nebulae in space - one of the wonders of the universe, amazing with its beauty. Valuables are not only visual attractiveness. The study of nebulae helps scientists to clarify the laws of the functioning of the cosmos and its objects, to correct theories about the evolution of the universe and the life cycle of stars. Today we know a lot about these objects, but not all.

Mixture of gas and dust

For quite a long time, until the middle of the century before last, the nebulae were considered star clusters distant from us for considerable distances. The use of the spectroscope in 1860 made it possible to establish: many of them consist of gas and dust. The English astronomer W. Huggins revealed that light from nebulae is different from radiation coming from ordinary stars. The spectrum of the former contains bright colored lines alternating with dark ones, whereas in the second case such black bands are not observed.

Further studies have established that the nebulae of the Milky Way and other galaxies mainly consist of a hot mixture of gas and dust. Quite often meet and similar cold formations. Such clouds of interstellar gas also belong to nebulae.

Classification

Depending on the properties of the constituent elements of the nebula, several types are distinguished. All of them in large numbers are represented in space and are equally interesting for astronomers. Nebulae that emit light for one reason or another are usually called diffuse or light. The opposite of them in terms of the main parameter, of course, are denoted as dark. Diffuse nebulae are of three types:

• Reflective;

• Emission;

• Supernova remnants.

Emission, in turn, is divided into areas of formation of new stars (H II) and planetary nebulae. All these types are characterized by certain properties, making them unique and worthy of close study.

Areas of star formation

All emission nebulae are clouds of glowing gas of various shapes. The main element constituting them is hydrogen. Under the action of a star located in the center of the nebula, it ionizes and collides with atoms of heavier components of the cloud. The result of these processes is a characteristic pinkish glow.

The Eagle Nebula, or M16 - is a magnificent representative of this type of objects. Here is the region of star formation, many young, as well as massive hot luminaries. The Eagle Nebula is the place where a well-known stretch of cosmos is located, the Pillars of Creation. These gas clusters, formed under the influence of the stellar wind, are a zone of star formation. The formation of luminaries is caused by the compression of gas-dust columns under the action of gravity.

Recently, scientists have learned that we can still admire the Pillars of Creation for only a thousand years. Then they disappear. In fact, the destruction of the Pillars occurred about 6,000 years ago due to a supernova explosion. However, light from this area of space goes to us about seven thousand years, therefore 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-dust clouds was introduced by W. Herschel. The planetary nebula is the last stage of the star's life. Luminous shells form a characteristic pattern. The nebula looks like a disk, usually surrounding the planet when it is observed through a small telescope. To date, more than a thousand such objects are known.

Planetary nebulae are part of the process of turning red giants into white dwarfs. In the center of the formation there is a hot star, similar in its spectrum to class O luminaries. Its temperature reaches 125,000 K. Planetary nebulae generally have relatively small dimensions-0.05 parsecs. Most of them are located in the center of our galaxy.

The mass of the gas shell dropped by the star is small. It is a tenth of the analogous parameter of the Sun. A mixture of gas and dust is removed from the center of the nebula at a speed reaching 20 km / s. The shell exists approximately for 35 thousand years, and then it 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. Nebulae are round, ring-shaped, similar to dumbbells, irregular in shape. The spectra of such cosmic objects include the emission lines of the glowing gas and the central star, and sometimes the absorption lines from the spectrum of the light.

The planetary nebula emits a huge amount of energy. It is much larger than the analogous index for the central star. The nucleus of formation, because of its high temperature, emits ultraviolet rays. They ionize the atoms of the gas. The particles are heated, instead of ultraviolet, they begin to emit visible rays. Their spectrum also contains emission lines characterizing the formation as a whole.

The Cat's Eye Nebula

Nature - a craftsman to create unexpected and beautiful forms. Noteworthy in this respect is the planetary nebula, due to the similarity called the Cat's Eye (NGC 6543). It was discovered in 1786 and was the first that scientists defined as a cloud of glowing gas. The Cat's Eye Nebula is located in the constellation of the Dragon and has a very interesting complex structure.

It was formed about 100 years ago. Then the central star dropped its shells and formed concentric lines of gas and dust, characteristic of the drawing of the object. To date, the mechanism of formation of the most expressive central structure of the nebula remains incomplete. The appearance of such a pattern is well explained by the location in the core of the double-star nebula. However, while there is no evidence to support this state of affairs,

The halo temperature of NGC 6543 is approximately 15,000 K. The nucleus of the nebula is heated to 80,000 K. The central star is several thousand times brighter than the Sun.

A colossal explosion

Massive stars often end their life cycle with impressive "special effects". Huge explosions in its power lead to the loss of the luminary of all external shells. They move away from the center at a speed exceeding 10,000 km / s. The collision of a moving substance with a static 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, and nebulae of a variety of forms. This happens because the substance ejected at a tremendous speed unevenly forms clots and accumulations.

A thousand-year-old trace

Perhaps the most famous remnant of the supernova is the crab nebula. The star that spawned it exploded almost a thousand years ago, in 1054. The exact date was established on the Chinese chronicles, where it is well described its outbreak in the sky.

A characteristic picture of a crab nebula is a gas ejected by a supernova and not yet completely intermingled with interstellar matter. The object is located at a distance of 3300 light years from us and is continuously expanding at a speed of 120 km / s.

In the center, the crab nebula contains a supernova remnant - a neutron star that emits electron fluxes that are sources of continuous polarized radiation.

Reflecting Nebulae

Another type of these space objects consists of a cold mixture of gas and dust that is incapable of independently emitting light. Reflecting nebulae shine due to the nearby objects. It may be stars or similar diffuse formations. The spectrum of scattered light remains the same as that of its sources, but the blue light in it for the observer prevails.

A very interesting nebula of this type is associated with the Merope star. Light from the Pleiades cluster for several million years destroys a molecular cloud passing by. As a result of the action of the star, the particles of the nebula line up in a certain sequence and are stretched toward it. After some time (exact time is unknown) Merope can completely destroy the cloud.

A dark horse

Diffuse formations are often contrasted with the absorbing nebula. The Milky Way Galaxy has a lot of them. These are very dense clouds of dust and gas, absorbing the light of the emission and reflecting nebulae behind them, as well as the stars. These cold cosmic formations mainly consist of hydrogen atoms, although they contain heavier elements.

A magnificent representative of this type is the Horsehead nebula. It is located in the constellation Orion. A nebular form, so similar to the head of a horse, was formed as a result of the action of the stellar wind and radiation. The object is clearly visible due to the fact that the background is a bright emission formation. In this case the Horsehead Nebula is only a small part of the long absorbing cloud of dust and gas, almost invisible.

Thanks to the Hubble telescope nebulae, including planetary ones, are familiar to a wide range of people today. Photographs of areas of space where they are located, impress to the depths of the soul and leave no one indifferent.