A dark star is a kind of star.On December 14, 2008, American scientists said that they had recently found two stars in the Milky Way with the darkest brightness so far, whose brightness is only one millionth of the brightness of the sun.
Chinese name
Dark star
Category
fixed star
Brightness
Only one millionth of the brightness of the sun
Formation
Those halos with the highest concentration of dark matter
According to foreign media reports,Massachusetts Institute of Technology"These two stars are the weakest of all the stars we know. Through this weak feature, we hope to find more brown dwarfs.Therefore, in a sense, these two stars should be the first to be found among the most 'common' brown dwarfs, while the other brown dwarfs have not been found yet, just because their light is too weak.This pair of brown dwarfs was discovered because they broke the upper limit of their luminous power, and their brightness is one millionth of the brightness of the sun. "
Astronomers once thought that this pair of dim "bulbs" was just a single brown dwarf star.However, the use of NASA's "Spitzer" infrared light in BogassellSpace telescopeAfter observing this kind of brown dwarf, scientists finally achieved the first accurate measurement of the weak light and low temperature of the brown dwarf.The observation data of Spitzer Space Telescope shows that this object, which looks like a single brown dwarf, is actually a pair of "Gemini".They are named "2M 0939".Bergacher believes that studying these stars can help astronomers understand the structure and evolution of brown dwarfs.Early research showed that several medium-sized brown dwarfs were surrounded by disks before the formation of planets, but astronomers usedGround-based telescopeIt is difficult to study this dish.Compared with the infrared radiation from brown dwarfs, these disks appear very dim, and the Spitzer infrared space telescope has solved the above problem.The Spitzer telescope is very sensitive to the observation of long wave infrared light.The researchers found that the disk around the brown dwarf was exposed only for 20 seconds, and the disk trace was found.
The observation data shows that the temperature of the atmosphere on the surface of the object is between 560 and 680 degrees Fahrenheit.It is several Baidu higher than Jupiter, but much colder than the star.In fact, these two brown dwarfs are also the coldest brown dwarfs measured so far.In order to calculate the brightness of the star, researchers must first determine its distance from the Earth.After three years of accurate measurement, scientists finally measured the position of "2M 0939".It is about 17 light years away from the constellation "Pump" and is one of the five brown dwarfs closest to the Earth.This measurement data can also be used as an explanation for its low temperature and extremely dim light.However, it is puzzling that, according to its temperature, the brightness of "2M 0939" is twice as bright as expected by ordinary brown dwarfs.How to explain this?Scientists believe that the surface area of this star must be twice that of other brown dwarfs.In other words, it is a "binary star". Each star is responsible for half of the brightness, and each star has a mass 30 to 40 times that of Jupiter.Their brightness is only one millionth of the brightness of the sun.
Brown dwarfs are objects between the smallest star and the largest planet. For this reason, the brightness of brown dwarfs is very dim. It is very complicated to find them, so it is more complicated to determine their size.Recently, however, astronomers have successfully discovered two brown dwarfs that make up a binary system. After determining the parameters of their movement around the common center of gravity, the weight and size of these two brown dwarfs can be calculated.Brown dwarfs are called "failed stars". They cannot become burning stars due to their insufficient mass, but their mass is still far greater than Jupiter, the largest planet in the solar system.Astronomers have found huge planetary storms on these strange planets, which are similar to those on JupiterGreat Red Spot StormComparable.As the brown dwarf will cool down over time, the gaseous iron molecules on the planet will condense into liquid iron clouds and rain.With further cooling, huge storms will sweep through these clouds, allowing bright infrared rays to escape into the universe.
Astronomers have different opinions on the formation mechanism of brown dwarfs, such as the ejection theory, the light induced erosion theory of the former stellar nucleus, the split theory restricted by opacity, and the instability theory of the original stellar disk.According to the ejection theory, brown dwarfs are formed because the low-mass protostellar embryos collide with other celestial bodies before reaching the mass required for hydrogen nuclear fusion and are ejected from the former stellar cores. This theory has been partially confirmed by the double brown dwarfs system.The light induced erosion theory of the former stellar nucleus is based on the light induced erosion of the former stellar nucleus by the radiation of the massive star, which can explain the formation mechanism of the brown dwarf star in the ionized hydrogen region.Brown dwarfs may also be produced by the fragmentation of the massive protostellar disk under the gravitational action of other stars.Each of these theories can only explain part of the formation of brown dwarfs. Studying the star disks around brown dwarfs can effectively test these theories.[1]
The earliest stars
Announce
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For scientists, primitive stars are still a mystery because they cannot be directly observed.Therefore, people can only speculate on the formation process of primitive stars based on known stars.In this blueprint, mysterious dark matter plays a very limited role.Recently, however, an American female astrophysicist put forward a bold hypothesis: dark matter may be the core of the strange brilliance of these giant primitive objects.
Imagine this scene: more than 13 billion years ago, our universe was still in its infancy, and many later galaxies were still dusty nebulae at that time. However, in the center of these nebulae, there were some air masses 1000 times heavier, 2000 times larger, and 1 million times brighter than our sun!These celestial bodies are huge and unheard of. They can be said to be the lighthouses in the breeding world at that time - because they are the light sources in the dark and cold space.Katherine Freese, a female physicist from the University of Michigan, described the magnificent scene of the primitive universe for us.The scientist with equations in his mind has been exploring in the dark corner of the universe in the early years of the universe, and finally found a unique perspective, overturning the previous view of astrophysicists.Her research work convinced her that the first objects to illuminate the universe were these giant stars located in the core of the dust nebula, which appeared 200 million years after the Big Bang.She named these giant stars "dark stars".This name has a reason: the reason why these stars can emit such extraordinary brightness is that they absorb an energy that no star can use later - the energy generated by the decay of dark matter particles inside them.
This is a strange assumption.Because all rigorous astrophysicists believe that stars in the universe emit light because they consume hydrogen through nuclear fusion reaction, rather than dark matter.Secondly, this is an extremely bold hypothesis, because until today, no one has observed any trace of this famous strange matter particle through any detector - which is precisely why it is called dark matter.However, the scientific community can be said to have no choice but to accept the existence of this hypothetical unknown energy material.Because, if it does not exist, physicists (including Einstein's theory of relativity used by them to describe the gravitational effect) cannot explain the rotation of galaxiesSuperclusterAnd the formation of the big structure of the universe.By creating the concept of dark matter and endowing it with some gravitational effects that can explain the great movement of the universe, the above mystery can get an acceptable explanation.Of course, the premise of acceptance is not to overestimate the data: because relevant calculations show that dark matter should account for 85% of the total amount of cosmic matter!However, it is this universal existence of dark matter that prompted Katherine Fritz to propose the idea of "dark stars".In this way, "dark stars" came out in the sky, and they will enter the palace of astrophysics.Although it is hard to imagine what the sky looks like so long ago, astrophysicists still believe that the earliest stars should appear soon, and that it is in their interior that those heavy elements that became the basis of later star formation were generated.However, because it is impossible to directly observe them through telescopes - the most distant pictures collected so far show the appearance of galaxies 600 million years after the Big Bang, that is, 400 million years after the appearance of the first stars - it is difficult for them to speculate on the nature of these primitive objects.According to the now recognized theory, dark matter only plays a passive role in the formation of primitive stars: it is in the regions where such invisible matter is highly concentrated, namely halos, that primitive stars are formed.Ordinary matter, mainly hydrogen, is gradually concentrated by the gravitational attraction toward the center of this halo. This concentration contraction continues until its density is enough to trigger nuclear reaction, and the energy released by the nuclear reaction will light up the star and prevent its collapse accident.
But does dark matter really only play such a catalytic role passively?No one can make it clear.Katherine Fritz explained: "Although we know that the earliest stars were the result of the gravity exerted by dark matter in halos, no one has specifically studied how this dark matter affected the internal mechanical structure of these primitive celestial bodies." However, thanks to this expert in particle astrophysics,This task has been completed... and an unexpected result has been obtained.According to her and her collaborators' theoretical calculations, the collapse of ordinary matter towards the halo center under the action of dark matter gravity, in turn, creates a gravity that can attract more dark matter.Of course, this strange material will not exceed 1% of the mass of the star to be formed, but its density will eventually reach enough to make its particles start to collide with each other.The description of these mysterious particles in the most fashionable model of physicists is the same as that of their antiparticles: when two particles meet, they will inevitably be completely annihilated in a spectacular burst of light energy.The result is that when the star in formation is just a huge, thin hydrogen balloon that cannot yet promote nuclear fusion, the annihilation of dark matter particles is enough to ignite the star and prevent the collapse of the gas cloud.In theory, a dark star was born like this!The characteristics of this dark star are fundamentally different from those of the original star calculated by the existing traditional model, which is hard to imagine... The "dark" of the dark star is just its name.According to the calculation of the American female scientist, its color is between yellow and orange, very similar to the sun, but much brighter than the sun.By attracting more and more material, the dark star soon became a giant with nearly 1000 solar masses, with a radius of almost 3 billion kilometers, which is equivalent to the distance between the sun and Uranus!"In contrast, although the mass of the original stars described by the traditional standard is also quite large, they can not exceed the mass of more than 100 suns at most, and they are much hotter because their color is close to blue." Katherine Fritz emphasized.
Although this discovery, which originated from the imagination of a female scientist, is fascinating, whether these strange stars really existed remains to be assessed.Romain Teyssier of the Astrophysics Division of the French Atomic Energy Commission said: "Obviously, the original stars absorbed dark matter in the formation process. The problem is to find out whether the amount of dark matter is large enough to cause these stars to burn.Katherine Fritz's research is based on the accretion process of dark matter, which is only a theoretical assumption at present.I am not saying that they are wrong, but they have yet to be proved. "Volker Bromm, from the Department of Astronomy at the University of Texas, USA, added: "The idea of this dark star is very interesting and worth taking seriously. However, due to the lack of direct observation, we can not be absolutely sure about the properties of dark matter. Even those properties mentioned by Katherine Fritz are worthy of approval."
Paris Normal UniversityPatrick Hennebelle of the Astronomical Ray Laboratory also held the same view. He further pointed out: "Although we are not very clear about the properties of dark matter, it is still valuable for the study of the entire primordial universe. Now, dark stars have become a subject that can be discussed.You should know that black holes and white dwarfs were once regarded as bizarre theories before they were actually observed! "Pierre Salati of the French Anansi Le Vie particle physics laboratory suggested: "Maybe we should imagine such a primitive universe: there are both dark stars and primitive stars in traditional theory.
