Brown dwarfs - stars in the solar system: temperature, photo, spectral classes

The more extensive the theoretical knowledge and technical capabilities of scientists become, the more discoveries they make. It would seem that all objects of the cosmos are already known and it is only necessary to explain their features. However, every time the astrophysicists come up with such a thought, the Universe presents them with another surprise. Often, however, such innovations can be predicted theoretically. Such objects include brown dwarfs. Until 1995, they existed only "on the tip of the pen."

let's get acquainted

Brown dwarfs are rather unusual stars. All their main parameters are very different from the characteristics of the luminaries that are familiar to us, however, there are similarities. Strictly speaking, the brown dwarf is a substar object, it occupies an intermediate position between the luminaries and planets proper. These cosmic bodies have a relatively small mass - from 12.57 to 80.35 of the same parameter of Jupiter. In their bowels, as in the centers of other stars, thermonuclear reactions are carried out. The difference between brown dwarfs in the extremely insignificant role of hydrogen in this process. As a fuel, such stars use deuterium, boron, lithium and beryllium. "Fuel" comparatively quickly ends, and the brown dwarf begins to cool down. After the completion of this process, it becomes a planet-like object. Thus, brown dwarfs are stars that never fall on the main sequence of the Hertzsprung-Russell diagram.

Invisible Wanderers

These interesting objects are distinguished by several more noteworthy characteristics. They are wandering stars not associated with any galaxy. Theoretically, such cosmic bodies can plow the expanse of space for many millions of years. However, one of their most significant properties is the almost complete absence of radiation. It is impossible to notice such an object without the use of special equipment. Appropriate equipment for astrophysicists was not for a sufficiently long period.

First discoveries

The strongest emission of brown dwarfs occurs in the infrared spectral region. The search for such tracks was successful in 1995, when the first such object, Teide 1, was discovered. It belongs to the spectral class M8 and is located in the Pleiades cluster. In the same year at a distance of 20 light years from the Sun, another such star was discovered, Gliese 229B. It rotates around the red dwarf Gliese 229A. Discoveries began to follow one after another. To date, there are more than a hundred brown dwarfs.

Differences

Brown dwarfs are not easy to identify because of their similarity in different parameters with planets and light stars. By their radius, they approach, to varying degrees, Jupiter. Approximately the same value of this parameter is preserved for the whole range of masses of brown dwarfs. In such conditions it becomes extremely difficult to distinguish them from the planets.

In addition, not all dwarfs of this type are capable of supporting thermonuclear reactions. The lightest of them (up to 13 masses of Jupiter) are so cold that even deuterium-based processes are impossible in their depths. The most massive are very fast (on a space scale - for 10 million years) cool down and also become incapable of maintaining thermonuclear reactions. Scientists distinguish between brown dwarfs and two main methods. The first of these is the density measurement. Brown dwarfs are characterized by approximately the same values of radius and volume, and therefore a cosmic body with a mass of 10 Jupiter and above, most likely refers to this type of objects.

The second method is the detection of X-ray and infrared radiation. The presence of such a noticeable characteristic can not boast of brown dwarfs, the temperature of which has fallen to a planetary level (up to 1000 K).

Way of distinction from light stars

The light with a small mass is another object from which it is not easy to distinguish a brown dwarf. What is a star? It is a thermonuclear boiler, where all the light elements are gradually burned. One of them is lithium. On the one hand, in the depths of most of the stars, it quickly ends. On the other hand, a relatively low temperature is required for the reaction with its participation. It turns out that the object with lithium lines in the spectrum probably belongs to the class of brown dwarfs. This method has its limitations. Lithium is often present in the spectrum of young stars. In addition, brown dwarfs can, over a period of half a billion years, exhaust all the reserves of this element.

A distinctive feature can be methane. At the final stages of the life cycle, a brown dwarf is a star whose temperature allows one to accumulate an impressive amount of it. Other luminaries can not cool to such a state.

For the difference between brown dwarfs and stars, their brightness is measured. The luminaries grow dim at the end of their existence. Dwarfs are cooling down the whole "life". At the final stages, they become so dark that it is impossible to confuse them with the stars.

Brown dwarfs: the spectral class

The temperature of the surface of the objects described varies depending on the mass and age. The possible values are in the range from planetary to characteristic for the coolest stars of class M. For these reasons, for the brown dwarfs, two additional spectral types, L and T, were initially identified. In addition to them, the class Y existed in theory. To date, its reality has been confirmed . Let us dwell on the characteristics of objects of each of the classes.

Class L

Stars belonging to the first type of the named ones differ from representatives of the previous class M by the presence of absorption bands not only of titanium and vanadium oxide, but also of metal hydrides. It was this feature that made it possible to single out a new class L. Also, in the spectrum of some brown dwarfs related to it, lines of alkali metals and iodine were found. By 2005, 400 such facilities were opened.

Class T

T-dwarfs are characterized by the presence of methane bands in the near infrared range. Similar properties were previously found only in the gas giants of the solar system, as well as the satellite of Saturn Titan. In place of hydrides FeH and CrH, characteristic for L-dwarfs, alkali metals such as sodium and potassium come in the T-class.

Under the assumptions of scientists, such objects should have a relatively small mass - no more than 70 masses of Jupiter. Brown T-dwarfs are similar in many respects to gas giants. The typical temperature of the surface varies in the range from 700 to 1300 K. If once such brown dwarfs get into the camera lens, the photo will show objects of a pinkish-blue color. This effect is associated with the influence of spectra of sodium and potassium, as well as molecular compounds.

Class Y

The last spectral class existed for a long time only in theory. The surface temperature of such objects should be below 700 K, that is 400 ° C. In the visible range, such brown dwarfs are not found (the photo can not be made at all).

However, in 2011, American astrophysicists announced the discovery of several similar cold objects with a temperature of 300 to 500 K. One of them, WISE 1541-2250, is located at a distance of 13.7 light years from the Sun. Another, WISE J1828 + 2650, is characterized by a surface temperature of 25 ° C.

The double of the sun is a brown dwarf

The story of such interesting space objects will be incomplete, if not to mention the "Death Star". This is how the hypothetically existing twin of the Sun is called, according to the assumptions of some scientists, located at a distance of 50-100 astronomical units from it, outside the Oort cloud. According to astrophysicists, the proposed object is a pair of our luminary and passes the Earth every 26 million years.

The hypothesis is connected with the assumption of paleontologists David Raup and Jack Sepkowski about the periodic mass extinction of biological species on our planet. It was expressed in 1984. In general, the theory is rather controversial, but there are also arguments in its favor.

The Death Star is one of the likely explanations for such extinctions. A similar assumption has simultaneously arisen in two different groups of astronomers. According to their calculations, the Sun's twin must move along a strongly elongated orbit. When approaching our luminary, it revolts comets, in large numbers "inhabiting" the Oort cloud. As a result, the number of their collisions with the Earth increases, which leads to the death of organisms.

The "death star", or Nemesis, as it is called, can be a brown, white or red dwarf. To date, however, there were no suitable objects for this role. It has been suggested that in the Oort cloud zone there is still an unknown giant planet that affects the orbits of comets. It draws ice blocks to itself, preventing thereby their possible collision with the Earth, that is, it does not work at all like the hypothetical "Death Star". However, there is no evidence of the existence of the planet Tycho (that is, sister of Nemesis).

Brown dwarfs for astronomers are relatively new objects. A lot more information about them is to be obtained and analyzed. Already today it is assumed that such objects can be the companions of many famous stars. The difficulties of research and detection of dwarfs of this type set a new high bar for scientific equipment and theoretical comprehension.