Red dwarf refers to low surface temperature and reddish colordwarf star, especiallyMain sequence starM and K stars, which are relatively "cold"Stellar massNot more thanSolar massThe surface temperature is 2500 to 5000K.The star closest to the earth except the sunAdjacent star(Proxima Centauri) is a red dwarf star.
Red dwarf, according toHerotu, among manyfixed starIts size and temperature are relatively small and low.They are abundant in stars. The diameter and mass of most red dwarfs are less than one-third of the sun, and the surface temperature is less than 3500 K.The light released is also much weaker than the sun, sometimes less than one thousandth of the sun's luminosity.
oursGalaxy(This may be true of all galaxies) 70% of the stars are red dwarfs, which are more dim than the sun.Because the light emitted is too weakAstronomical telescopeWe can't see any red dwarf.
Flares of red dwarfs
Low mass means that the nuclear reaction inside the star is weak, so the radiation emitted by the red dwarf is very weak, lower thanSolar radiation intensity5%, some even less than one thousandth of the solar radiation intensity.The radiation of a star includes all the bands from infrared to ultraviolet, but with the change of star temperature, the band with concentrated radiation energy will change.Generally speaking, the radiant energy of stars with high temperature is concentrated in the bluish band, while those with low temperature are reddish, so red dwarfs look reddish.However, red dwarfs that should emit weak red light sometimes exhibit abnormal phenomena under the action of their own magnetic field, and they will emit strongX-rayAnd ultraviolet radiation, and flare activity often occurs.
Due to the slow nuclear fusion of hydrogen in red dwarfs, they also have a long life span.In addition, because red dwarfs are small in size and have relatively small gravity, the pressure and temperature generated inside are not enough to combine helium into heavier elements, so it is impossible to expand into red giants, but gradually shrink until hydrogen is exhausted.For this reason, a red dwarf can live for tens of billions of years, almost as long as the age of the universe.
Cradle of life
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For a long time, few astronomers have devoted themselves to the scientific research of red dwarfs due to their size and brightness.For decades, scientists believed that there could be no intelligent life near red dwarfs.If there are red dwarfs aroundplanetAround them, the planets will be completely "locked" by the red dwarf, just as the moon is locked by the earth, because they are too close.There will be only one planet facing its "sun", that is, a red dwarf star.The other side is always in darkness.Therefore, the planet will have an extremely harsh environment. On the dark side, any atmospheric gas will be frozen, while on the day side, it will be completely exposed to the starsradialUnder the irradiation of.It is hard to imagine that there will be life in such a planetary environment, so red dwarfs are almost indisputably excluded from theExtraterrestrial life explorationThe target is out of the list.
But recently, another American scientist suggested that red dwarfs might be more suitable for breeding life.U.S.AVillanova University's scientists recentlyAmerican Astronomical SocietyThey calculated the radiation of 20 red dwarfs and found that if the atmosphere and magnetic field of a planet are enough to scatter and reflect harmful rays, its environment is suitable for life.In addition, although gravity will gradually make the planet face the red dwarf with a fixed side, and the other half will not get light, air flow can transfer heat, making the planet's back and shade warm as summer night.The nuclear fusion on red dwarfs is very slow, which makes them have a very long life span and can maintain a stable state for billions of years or even longer, which is beneficial to the development of life.In contrast, the sun can only support the life of the earth for 1.5 billion years (the sun is getting bigger and hotter at the rate of 1% per 100 million years), and then it will expand into a red giant star, scorching and devouring the earth.
Because life on the earth cannot be separated from liquid water, if a galaxy wants to have the same life form as people and other advanced animals and plants on the earth, it must first have a region that is neither too cold nor too hot and may have liquid water, which we call "habitable zone".For red dwarfs, their light is too weak, so their habitable zone is very close to the stars themselves. Only in this way can we get more heat from red dwarfs.For most red dwarfs, the habitable distance to the star is closer than the distance from Mercury to the sun.
Red dwarf
But a close distance will lead to a serious consequence.As we all know, the period and rotation of the moonEarth revolutionThe period of is the same, so it always faces the earth, which is the result of the long-term effect of the earth's tidal force.Similarly, planets that are very close to the stars will also be "fixed" by the tide force, resulting in the phenomenon that the "yin and yang faces" will never change.Therefore, the planets in the habitable zone near the red dwarf are always facing the star on one side, one hemisphere is always in the day, and the other half is always in the night.
At first, scientists worried that the temperature of the hemisphere always dark night was too low, which would freeze the atmosphere of the planet, so that there was not much air left for living things to breathe even on the side facing the light of the star.However, later studies have shown that atmospheric flow can effectively disperse heat, thus preventing global air freezing.Although there is no need to worry about the freezing of the atmosphere, there are other difficulties for life to survive on the red dwarf planet.When the flares of red dwarfs appear several times a day, the ultraviolet radiation will instantly increase hundreds to tens of thousands of times.In those few minutes, the stars changed from red to blue, and such strong ultraviolet rays would kill all life on the planet.The only chance of survival is to hide in the dark hemisphere, or the area where night meets day.
Moreover, even without considering flares, the ultraviolet radiation and high-energy charged particles emitted by red dwarfs at ordinary times will blow away the planet's atmosphere.IfPlanetary atmosphereWithout effective protection or supplement, it will disappear sooner or later.
For these reasons, astronomers in the past often skipped these bleakSmall starBecause they think the planets around such stars are not suitable for life.
However, there have been some changes in this concept.Astronomers have noticed that strong high-energy radiation is mainly emitted by young stars. As red dwarfs grow older, their magnetic activity will become weaker and weaker, and they will start to emit radiation in the visible light band steadily.Such a stable stage can last for tens of billions of years or even longer.
Therefore, if a planet can survive the wild young age of the red dwarf and maintain its own atmosphere, then when the red dwarf enters a stable middle age, the planet will be reborn and may become a suitable place for life to live.
Red dwarf
NASA announced on April 17, 2014 that astronomers have discovered the planet most similar to the Earth so far. ①It orbits a red dwarf star about 500 light-years away from the Earth ② located in the outer layer of the habitable zone where liquid water can be preserved ③ with a volume about 1.1 times that of the Earth.Researchers believe that the new discovery is the first time to confirm the existence of planets close to the Earth in the habitable zone of stars, and may find signs of extraterrestrial life.
According to the Science News website, currently, NASA GoddardSpaceVladimir Airapetian, a scientist at the flight center, said that a newly developed computer model can evaluate the escape speed of exoplanets around red dwarfs, which plays an important role in detecting the habitability of exoplanets.This latest research report was published in the recently published Astrophysical Journal Letters.
Dr. Elapetian said that if we want to find a star that can form and maintainlifeWe must calculate and analyze their parent stars, and we must go furtherGeographyUnderstand the parent stars we need.In order to detect the habitable zone of a starAstronomyScientists analyze the heat and light emitted by the star.
Stars with more mass than the sun will produce more heat and light, so the habitable zone of stars will be farther, and the habitable zone of cold stars with less mass than the sun will be smaller.The release of heat and visible light from stars, the release of X-ray and ultraviolet radiation, and the creation of flares and coronal mass ejections are collectively referred to as space meteorology.[1]
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Red dwarf
People can infer the approximate age of a star cluster based on the long life span of red dwarfs.Because the sameclusterThe formation time of the stars inside is the same. An older star cluster, separated fromMain sequence starThere are many stars in the stage, and the mass of the remaining main sequence stars is also low, but people can not find any red dwarf stars out of the main sequence star stage, which indirectly proves thatCosmic ageThe exists of.It is believed that among the stars in the universe, red dwarfs account for the majority, about 75%.For example, the star closest to the sun,CentaurOfAlpha Bilin star is a red dwarf star whose spectrum is classified as M5,Apparent magnitude11.0。
Red dwarf
Around the planet
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By 2005, people had discovered for the first time that there wereExtrasolar planetsRotating around, the mass of the first planetNeptuneAlmost, the daily distance is about 6 million km (0.04 AU), and its surface degree is about 150 ° C.In 2006, another planet similar to the Earth was found to revolve around another red dwarf star, with a daily distance of 390 million kilometers (2.6 AU) and a surface temperature of minus 220 ° C.
In April 2007,European Southern Observatory80% of astronomers have announced that they found the most similarExtrasolar planets。The mass of this planet is about five times that of the Earth, and its surface temperature may be between 0 ℃ and 40 ℃, just allowing liquid water to exist on its surface.This is the first time that scientists have found a planet outside the solar system that may be suitable for human habitation.
Research plan
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Scientists will observe about 2000 red dwarfs in the northern celestial sphere.By analyzing the degree of variation of the brightness of these celestial bodies, researchers will be able to calculate whether there are "transit planets" with a mass between two and seven times that of the Earth in the so-called "living area" (the area is moderately distant from the central star, which may create an environment similar to that on the Earth).Although there are many observation objects, experts estimate that the probability of observing "transit planets" near the above-mentioned red dwarfs is only about one percent.
Scientists hope to find it nearbyTransit planet, refers to a kind of planet that will periodically block the light of some stars from the earth.Normally, the phenomenon like solar eclipse caused by the "transit planet" will block about half of the light emitted by the star.As a resultStellar brightnessThe changes can be recorded by observers on Earth.In the process of implementing the MEArth plan, scientists plan to use eightLarge optical telescopeFive sets have been put into use for observation activities.
