2023-05-14 20:00:00
Imagine a star. Not like the Sun, but much smaller. And dark in color, pulling garnet. Also, it is not very hot and does not manage to radiate much light. Nor can it emit almost energy, because it is not capable of unleashing the fusion process characteristic of stars. Actually, it is very similar to the large planets, called gaseous, like Jupiter and, in fact, the factors that differentiate them are a matter of debate because, externally, they are very similar.
Would you then say that the description closer to star or planet? How would you characterize it? This is the dilemma astronomers face with brown dwarfs, stellar objects that do not fully identify with either definition.
RIDING BETWEEN STARS AND PLANETS
Brown dwarfs are one of the most curious stellar bodies today. These are “stars” with a composition similar to stars but whose mass and temperature are not sufficient to trigger the internal processes of nuclear fusion from hydrogen to helium. However, they are capable of fusing deuterium and, in the case of the larger ones, lithium, which generates much lower energy and luminosity than the “real” stars.
In order to develop a mental idea of the situation the mass of Jupiter is used as a unit of measurement, since, in most cases, brown dwarfs are very similar in size to this planet, only with greater weight and, therefore, greater density. Thus, it is usually stipulated that a body with a composition similar to the Sun and with a mass 75 times greater than that of Jupiter is a star, while with a lower mass, it is identified as a brown dwarf.
In addition, the temperature inside it is much lower than that of common stars, which is why it is believed that it never fuses hydrogen, which requires a temperature of approximately 15 million degrees Celsius to carry out the fusion process. For its part, the brown dwarf has a core temperature of about 100 thousand degrees Celsiusthat is to say, much smaller and coinciding with the one necessary for the deuterium fusion process to take place.
According to what is known so far, deuterium is consumed especially during their youth, but it is a fuel that it ends very quickly, so it is a reaction that can lead to the collapse of the dwarf. Once there is no deuterium left for the fusion, the dwarf can keep shining dimly a time thanks to the residual heat of the reactions and the slow contraction of matter. In fact, it will continue to contract and cool until it reaches a dormant equilibrium in which it takes on very planet-like characteristics.
WHY BROWN DWARFS?
Although its discovery is considerably recent, since it dates from 1995, already in the 60s its existence was intuited, although no dwarf had been detected. the indian astrophysicist Shiv Kumar He was the first to theoretically study the evolution and characteristics of stars with masses lower than those known, which would correspond to current brown dwarfs. However, at that first moment, Shiv Kumar called them black dwarfs.
A few years later, in 1975, the astrophysicist Jill Tarterspokesperson for SETI projectnicknamed them, even without having observed them, brown dwarfs, alluding that the name assigned by Kurmar could confuse them with other cosmological phenomena. Even so, despite relying solely on theoretical studies, Tarter was not wrong to nickname them “browns”, although it is not the most accurate.
What color is the sun? The answer is not what you imagine
In the spectral classification of stars, we find that the hottest stars are blue in color, becoming more yellow, orange, or reddish tones as they cool. It is in this way that brown dwarfs with the highest temperatures can reach certain reddish tones, but normally they remain in colors closer to purple or dark golds. However, it is true that it would be very rare for them to reach a brown hue, due to the characteristics of their emission peak, centered on long wavelengths, as well as their luminosity and low surface temperatures. Even so, the name was maintained due to the ease it entails, since it is the one that has been attributed to them since Tarter stipulated it.
HOW TO DETECT THEM?
One of the great unknowns around these bodies is his formation, since it is unknown if its beginning is similar to that of the planets, that is, inside a disk of material and from a solid nucleus, or as stars, from a stellar nebula. Therefore, this lack of information makes more difficult to detectsince it does not know when or under what conditions they will form and it is reduced only to observation during its useful life.
The process, up to now, most used for its detection is llithium proof. It is based on the fact that “common” stars destroy all the lithium inside them during the hydrogen fusion process, while brown dwarfs, by not producing this fusion, keep it intact. Thus, the lithium contained in dwarfs can be detected through their emission spectra by astronomers. To date, through this system, up to 2,000 different brown dwarfs have been detected, and the number is on the rise.
IAC
Image of the brown dwarf Teide 1 located in the Open Cluster of the Pleiades
The first detection occurred in the year 1995with the use of IAC-80 telescope of the Teide Observatory, in Tenerife. The discovery of the brown dwarf, nicknamed Teide 1, was carried out by a Spanish group of astrophysicists belonging to the Institute of Astrophysics of the Canary Islands, IACled by Rafael Rebolo Lopez.
possible HABITABILITY
Characteristics very similar to those of brown dwarfs have been found in the disks surrounding brown dwarfs. the rocky discs that surround most of the stars and that, for example in the case of the Sun, gave rise to the planets of the Solar System. Therefore, it is expected that there are planets formed by accretion of this material around brown dwarfs, which will adapt more to the characteristics of a terrestrial planet (such as Earth or Mars), than to those of a gas giant (such as Jupiter or Saturn).
So it has been studied possible habitability of planets that orbit around brown dwarfs, resulting in conditions that would be extremely strict, since the habitable zone would be very narrow. Besides, I would go narrowing as time goes by, since the dwarf would suffer a cooling and the zone of ideal luminosity would be smaller and closer to the “star”. Therefore, the possibilities are remote.
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