Betelgeuse, namely, Alpha Orionis, whose unique astronomical name isBetelgeuse[14]，It is a M1-2 typeRed supergiant, onOrionInside.Its radius is about 887 to 955 times that of the sunBinocularsOne of the largest stars that can also be seen.Betelgeuse is 640 to 724 light years away from the earth, and its apparent magnitude varies from 0.0 to 1.3. It is usually the second brightest star in Orion and the tenth brightest star in the whole day.
Most of the time, BetelgeuseEridanaOfWater Commission IA little darker thanCentaurOfAgena Lighter.In the infrared band, Betelgeuse is brighter than other stars in the sky.Although it is only 8 million to 8.5 million years old, it is aevolutionFast massive stars are approaching the end of their life cycle.At some point in the next million years, it will become aSupernova。At that time, it will release the materials needed to form a new generation of stars.[15]
Betelgeuse, that isBayer designation The famous Orionis (α Orionis or α Ori) in is the ninth bright star in the sky and the second bright star in Orion, which is only slightly dimmer than the neighboring Rigel (Orion β).It's obviously redSemiregular variable starThe apparent magnitude varies from 0.0 to+1.3, which is the first class star with the largest dimming amplitude.This star marksWinter TriangleAnd the center of the winter hexagon.
Betelgeuse is in theRed supergiantAnd is one of the largest and brightest stars known.If it is located insolar systemIts surface will surpass the center ofAsteroid beltAnd may reach and surpass the orbit of Jupiter, completely sweeping over Mercury, Venus, Earth and Mars.However, in the last century, the distance estimates of Betelgeuse ranged from 180 ly to 1300 ly, so it is difficult to confirm the estimates of its radius, luminosity and mass.At present, it is thought that the distance of Betelgeuse is about 724 ly, and the average absolute magnitude is -5.85.
In fact, the quality of Betelgeuse has always been controversial. Some data show that its quality is no more than 14~15 M ⊙, but some data believe that its quality reaches 18~19 M ⊙, even 20 M ⊙. The uncertainty of this quality is caused by the uncertainty of the measurement distance.
In 1920, Betelgeuse was the first star (except the sun) whose angular diameter was measured.Since then, researchers have constantly used different technical parameters and telescopes to measure the size of this giant star, and often produce conflicting results.At present, it is estimated that the apparent diameter of this star is 0.043~0.056 angular seconds. As a moving target, Betelgeuse seems to change its shape periodically.Due to the surrounding darkness and luminosity change（Variable star pulsation theory）The diameters of,, and angles change with the wavelength, and the star is still full of puzzling mysteries.Betelgeuse has some complex and asymmetric cladding, which causes huge mass loss. It involves the huge crown plume gas discharged from the surface, making things more complicated.There is even evidence that its gas envelope is surrounded by companion stars, which may aggravate the strange behavior of this star[1]。
Astronomers believe that Betelgeuse is only tens of millions of years old, but it evolves quickly because of its mass.It is considered to be a runaway star from the Orion OB1 star association, and also includes the group of late O and B stars such as Betelgeuse I, Betelgeuse II, and Betelgeuse III in Orion's belt.It is expected that Betelgeuse will explode into a type II supernova and become aneutron star。
Betelgeuse (Orion α, meaning armpit, from Arabic) is the tenth bright star in the whole day (because of its brightness change, sometimes the apparent star magnitude will exceed that of Water Commissar Eridani to become the ninth bright star in the whole day), with brightness varying from 0.0 to+1.3, and the light changing period is 5.5 years, belonging toveinMoving stars.It is a M1-M2 red supergiant with a radius varying from 684 to 1172 R ⊙, and its luminosity changes with the change of the radius (varying from 0.0 to+1.3).The absolute magnitude is -5.85, about 724 ly from the earth, the mass is about 11.6 M ⊙, the surface temperature is 3590 K, and the luminosity is about 90000~1.5 × 10 ^ 5 L ⊙, which is the largest volume found by human beings so farfixed starone of.For these reasons, it is the first time that human beings can resolve the surface size stars except the sun.
Betelgeuse is the first direct useStellar interferometerdeterminationAngular diameterThe stars of.It was discovered in 1966 that BetelgeuseRadio star。The radio spectrum observation shows that Betelgeuse has both atmospheric radio and stellar circular radio.Through the observation of the 2.1 meter telescope television spectroscope, it is found that an extremely thick gas shell has formed around Betelgeuse, which extends to at least 600 times the radius of the star, indicating that the starInterstellar spaceA lot of material was thrown out.It is also believed that Betelgeuse has at least two peristellar shells, which are about 50 and hundreds of radii away from the star respectively, and their expansion velocities are about 11 and 17 km per second, respectively.The distance of Betelgeuse is so far difficult to measure accurately (about 222 pc), so there is no reliable data about its true radius, luminosity, etc.U.S.AKitt Peak Observatory The photos of the four circles of Betelgeuse were obtained with the 4m telescope and the star image processing technology.
Astronomically, Betelgeuse is very interesting.It is one of the first ones to use celestial interferometer to measure the diameterfixed starone of.Astronomers found that its diameter is variable, from the smallest 684 R ⊙ to the largest 1172 R ⊙, which is larger than the diameter of Jupiter's orbit around the sun.
Observation history
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Herschel's discovery
John HerschelSir first described the luminosity change of Betelgeuse in 1836, and he published this discovery in the Astronomical Outline（Outlines of Astronomy）: He noticed that Betelgeuse changed greatly in October 1837 and November 1839[6]。The next is a 10-year standstill period;Then in 1849, he noticed a shorter cycle of changes, and reached a peak in 1852.Subsequent observations recorded an unusual peak every few years, but there was only a small change from 1957 to 1967.
The American Association of Variable Star Observers (AAVSO) records thatApparent magnitude(Brightness) 0.2 in 1933 and 1942, and 1.2 in 1927 and 1941[5]。Such photometric changes are often incorrectly used to explain why Bayer published it in 1603《Geodetic chart》Name BetelgeuseOrion alphaThe brighter opponent Rigel is justOrion beta。[4]
Modern discovery
In 1920, Albert Michelson and Francis PeaseMount Wilson ObservatoryA 6-meter (20 foot) interferometer was installed in front of the 2.5 meter (100 inch) telescope. With the help of John Anderson, the three of them measured theAngular diameterIs 0.047 ", based on the then parallax is 0.018", the diameter is 3.84 × 10eightKm (2.58Astronomical unit）Results.[7]
The two stratospheric telescope projects and the《Structure and evolution of stars》, the main workers work closely togetherMartin Schwarzschild And Richard Harling of Princeton University.This book teaches a new generation of astrophysicists how to use early computer technology to create star models. When the stratospheric telescope plans to use balloons to bring the instrument above the atmosphere, overcome the turbulence of the earth's atmosphere, and produce some previously unseen fine images of rice grains and sunspots, thus confirming the existence of convection in the solar atmosphere.These two developments have proved that they have a significant impact on our understanding of the structure of red giant stars such as Betelgeuse.[8]
Research at the beginning of the 21st century
Betelgeuse photographed by ALMA in June 2017
In a study published in December 2000, infrared spatial interferometer (ISI) was used to measure with mid infrared, and it was estimated that the darkness around Betelgeuse was 55.2 ± 0.5 mas, which was completely consistent with the figure discovered by Michelson 80 years ago.[9]At the time of his publication, the estimated parallax from the Ebague mission was 7.63 ± 1.64 mas, so the estimated radius of Betelgeuse was 3.6Astronomical unit。However, an infrared interferometry study published in 2009 announced that since 1993, this star has shrunk by 15% at a faster and faster rate, but its apparent magnitude has not significantly darkened.[10]Subsequent observations indicate that this apparent contraction may be caused by the shell activity in the extended atmosphere of stars.[11]
The bubbles in Betelgeuse's atmosphere extend from the sun to Neptune
In addition to the diameter of the star, the complex dynamics of Betelgeuse extending the atmosphere also raises questions.The mass of a galaxy will cycle with the formation and destruction of stars. Red supergiant is the main contributor, but the process of mass loss is still a mystery.[12]InterferometryWith the latest progress in methods, astronomers may have approached the solution to this problem.In July 2009, the European Southern Observatory released an image obtained by the Very Large Telescope Interferometer (VLTI), which showed that the distance from the huge plume gas jet to the surrounding area was almost 30 astronomical units.[13]This is equivalent tosunlightAndNeptuneBut this kind of mass ejection is only one of the many dynamics in the surrounding atmosphere.Astronomers have found that there are at least six different shell activities around Betelgeuse.At the beginning of this century, solving the mystery of mass loss in the stage of star evolution may reveal the factors that caused the sudden explosion of these super giants.[10]
Culture
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Betelgeuse on the Dunhuang star map, about 700 A.D
In the constellation system of China, all belong to ginseng. First, introduce the position, structure and related allusions of ginseng in the sky.Betelgeuse isStarry sky in winterOne of the most beautiful and bright stars in China.To the north of it isFive car Star Officer, in the westNet Big star, the brightest star in the sky in the southeast——Sirius。Among the seven main stars of Betelgeuse, there are two stars of order 0, namely, the protagonist of this article, Betelgeuse andRigel(Orion β);Five second-class stars, namelyAlnitak (Orion ζ)Betelgeuse(Orion ε)Betelgeuse(Orion δ)Betelgeuse(Orion gamma)saiph (Orion κ).
According to the Records of the Historian, the Book of Heavenly Palaces, "The reference is a white tiger. Three stars are straight, which is a weight stone. There are three stars below, which are called exchange, which is called punishment, and which is called cutting Ai. The outer four stars are also left and right shoulder shares. The small three stars are placed in the corner, which is called mouth, which is the head of the tiger."
This passage means that there are three stars horizontally arranged in the sky, almost exactly on the equator. It is called Hengshi, that is, a stone playing the role of balance. Therefore, Hengshi means the middle waist of the equator and the middle waist of the white tiger.These three stars are the symbol stars of Betelgeuse, from which the name of Betelgeuse comes.
visibility
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Position 4 of Betelgeuse
Betelgeuse is easy to find in the night sky. It appears in the famousOrionOn the right shoulder, and the naked eye can see its orange red light.In the northern hemisphere, it can be seen rising from the east at sunset from January every year.In the middle of March every year, this star is already in the southern sky at dusk, and can be seen by residents all over the world. Only a few remote research stations in Antarctica that are located further south of 82 ° south latitude can not see it.In the big cities in the southern hemisphere (likesnow pear、Buenos Aires, andCape Down）The height angle of Betelgeuse can almost reach 49 ° above the horizon.Once it comes to May, you can only catch a glimpse of the western horizon just as the sun sets.
The apparent magnitude of Betelgeuse is+0.50, and its average brightness is the tenth bright star in the sky, just behind Shuiwei I.However, because Betelgeuse is a variable star, its luminosity varies from 0.0 to+1.3, so sometimes its luminosity will surpass that of Water Commission I and become the ninth bright star in the whole day.The same is true of Rigel, its usual apparent magnitude is+0.13, but the report points out that the luminosity fluctuates from+0.03 to+0.18, which may make it occasionally compareRigelBright and become the ninth bright star in the sky.When it is darkest, it will be brighter than the 19thTianjin IVAlso dark, and withCross IIICompete for the twentieth place.
The images from ESO's Very Large Telescope show not only the disk of stars, but also the previously unknown smoke plume surrounded by gas accompanied by the expanding atmosphere.
The B-V color index of Betelgeuse is+1.85, indicating that it is a very red object.Its photosphere has an expanding atmosphere, and the spectrum shows strong emission lines rather than absorption lines, which is a phenomenon when a star has a thick gas envelope outside.Depending on the fluctuation of the radial velocity of the photosphere, these expanding gases have been observed moving away from and towards Betelgeuse.Only 13% of the star's radiation energy is emitted through visible light, and most of the radiation is in the infrared band.If the eye can sense all the wavelengths of radiation, Betelgeuse may become the brightest star in the sky.
parallax
Since Bessel successfully measured the parallax in 1838, astronomers have been extremely confused about the distance of Betelgeuse. The uncertainty makes it difficult to estimate the parameters of many stars correctly.The accurate distance and angular diameter will reveal the radius and effective temperature of stars, and derive the luminosity of clear interpretation of thermal radiation;Photometric andIsotope abundanceThe combination can provide estimates of the age and mass of stars.In 1920, when the diameter of a star was first studied with an interferometer, the parallax was assumed to be 0.18 angular seconds.This is equivalent to a distance of 56 pc, or 180 light-years. In this way, not only the star radius obtained is incorrect, but also the star characteristics are different.After that, some investigations suggested that the mysterious actual distance could be as high as 400 pc, or 1300 ly.
stayHipparcos catalogue Before the publication (1997), there were two respected publications with the latest parallax information of Betelgeuse 4.The first one isYale UniversityThe parallax published by the Observatory (1991) is π=9.8 ± 4.7 mas, equivalent to a distance of about 102 pc, or 330 ly.The second is the Ebague Input Catalogue (1993), whose trigonometric parallax is π=5 ± 4 mas, equivalent to 200 pc or 680ly, almost twice the Yale estimate.This uncertainty makes researchers use a loose range for distance estimation. This phenomenon has triggered many disputes, not only on the distance of stars, but also on other stellar parameters.
The National Radio Observatory's Very Large Array in Socolo, New Mexico
The picture shows the National Radio Observatory in Socolo, New MexicoVery large antenna array(Very Large Array, VLA). Each of the 27 antennas weighs 230 t, and can be moved on the track in the array when necessary to conduct a detailed study using an aperture synthesis interferometer.
The long-awaited results of the Ibaku mission were finally released in 1997.This problem is solved. The new parallax value is π=7.63 ± 1.64 mas, which is equivalent to 131 pc, or 430 ly.Because variable stars such as Betelgeuse will cause specific problems affecting the quantification of their distances.Therefore, the large scale error is likely to be caused by stars, which may be related to the movement of the light center at the 3.4 mA level of the Hibakos luminosity HP band.
In this debate, the latest developments in radio astronomy seem to have prevailed.Graham and colleagues used the very large antenna array (VLA) of the National Radio Astronomical Observatory (NRAO) of the United States to obtain more accurate estimates with new high spatial resolution and multi wavelength radio guidance to the position of Betelgeuse 4. In addition to the information of Ebague, they provided new astronomical measurement solutions: π=5.07 ± 1.10 mas,The distance obtained under the rigorous error factor is 197 ± 45 pc or 643 ± 146 ly.
The next breakthrough in computing will probably come from the upcoming Gaia mission of the European Space Agency, which will undertake a detailed analysis of the physical properties of each observed star, revealing brightness, temperature, gravity and composition.Gaia will repeatedly measure the position of each celestial body whose brightness is as dark as 20 stars and brighter than 15 stars, with an accuracy of 24 microseconds, which is equivalent to the diameter of human hair measured from 1000 km away.The detection equipment carried will ensure that the limit of variable stars such as Betelgeuse in the darkest time can be measured, which will solve most of the limitations of the location of the early Ebague mission.In fact, the nearest stars will be able to measure their distance with an error factor of less than 0.001%.Even if the distance of stars near the center of the Milky Way is about 3 × 10 ^ 4 ly, the error in distance measurement will be less than 20%.
Photometric change
Ultraviolet images of Betelgeuse show asymmetric pulsation, expansion and contraction of stars
As a subcategory of the expanding shrinking star "SRc", the researchers provided different hypotheses to try to explain the erratic dance of Betelgeuse, which led to the oscillation of its apparent magnitude between 0.0 and+1.3.According to the stellar structure we know, it is believed that the outer layer of this super giant star gradually expands and contracts, resulting in the alternate increase and decrease of surface area (photosphere), and the rise and decrease of temperature - so it is measured that the brightness of this star changes rhythmically between the darkest+1.3 and the brightest 0.0.
Like BetelgeuseRed supergiantBecause the atmosphere is inherently unstable, it will pass through the method of pulsation.When the star shrinks, it absorbs more and more energy passing through, causing the atmosphere to be heated and expanded.Conversely, when a star expands, its atmosphere becomes thin, allowing more energy to escape and lowering the temperature, thus starting a new contraction phase.It seems that there are several staggered periods when it is difficult to calculate the pulsation and model of stars.In the 1930s, Stebbins and Sanford's research paper pointed out that there was a regular cyclic change period of about 5.7 years modulated by a short period of 150~300 days.
The solar structure shows the rice spots of the photosphere
The illustrated solar structure shows the rice grains of the photosphere:
1. Core
2. Radiation layer
3. Troposphere
4. Photosphere layer
5. Color ball layer
6. Corona
7. Sunspot
8. Rice spot
9. Prominence
In fact, supergiant stars always show irregular changes in luminosity, polarization and spectrum, which indicates that there are complex activities on the surface of stars and the expanding atmosphere.Compared with most monitored stars, they have reasonable regular periodsLong-period variable starRed giant stars are usually semi regular or irregular variable stars with pulsating characteristics.In 1975, Martin Schwarzschild published a landmark paper, which believed that the fluctuation of luminosity was caused by some huge convective cells (the pattern of rice spots) covering the surface of stars.In the sun, these convection cells, or solar rice grains, represent an important mode of heat conduction because those convection elements dominate the brightness changes of the solar photosphere.The typical diameter of the solar rice grain tissue is about 2000 km (about the surface area of India), and the depth is about 700 km.
There are about 2 × 10 ^ 6 such rice spots covering the photosphere on the solar surface, and such a huge number produces relatively constant flux.Under these rice spots, there are 5000~10000 super rice spots with an average diameter of 30000 km and a depth of 10000 km.In contrast, Schwardschild believes that stars like Betelgeuse may have only about a dozen monster like rice spots, with a diameter of 1.8 × 10 ^ 8 km or more, which is enough to dominate the surface of the star, and a depth of 6 × 10 ^ 6 km. This is because the envelope temperature and density of red giant stars are very low, resulting in extremely low convection efficiency.Therefore, if only one third of the convective cells can be seen at any time, their observed luminosity changes with time may reflect the luminosity changes of the whole star.
Schwarzschild's hypothesis that giant convective cells dominate the surface of giant stars and red giant stars seems to have been posted in the astronomical discussion community. When the Hubble Space Telescope directly captured the mysterious hot spot on the surface of Betelgeuse in 1995, astronomers attributed it to convection.Two years later, astronomers revealed that at least three bright spots had caused the observed star's intricate brightness distribution to be asymmetrical, and its amplitude "matched the convection hot spot on the surface".Then in 2000, another group led by Alex Lobel of the Harvard Smithsonian Center for Astrophysics (Cfa) noticed that the cold and hot air currents in the turbulent atmosphere of Betelgeuse showed a raging storm.The team speculated thatStellar atmosphereLarge areas of energetic gas in the middle expand in different directions at the same time, ejecting long warm gas plumes into the cold dust envelope.Another explanation is that warm gas creates shock waves as it crosses the cooler regions of the star.The team has studied the atmosphere of Betelgeuse for more than five years, using data from the Hubble Space Telescope image spectrograph from 1998 to 2003.They found that the bubbles moving on the chromosphere threw gas on one side of the star, and when they fell on the other side, they looked like slow moving billowing lava lamps.
Angular diameter
The third challenge for astronomers is to measure the angular diameter of stars.On December 13, 1920, Betelgeuse became the first celestial body whose diameter had been measured outside the sun.Although the interferometer is still in the early stage of development, experiments have successfully proved that Betelgeuse has a 0.047 "uniform disk. Astronomers' views on the surrounding darkness are worth noting. In addition to 10% of the measurement error, the team concluded that the disk may be 17% larger due to the strong attenuation of the luminosity along the edge of the star, so the angular diameter is about 0.055".Since then, other studies have been carried out, and the obtained range is from 0.042 to 0.069.Combined with the estimated distance in history, from 180 to 815 ly, and these data, it is obtained that the diameter of the star disk is 2.4 to 17.8 AU wherever it is, so the radius is 1.2 to 8.9 AU, which is similar to the standard of the solar system. The orbit of Mars is about 1.5 AU, Ceres in the asteroid belt is 2.7 AU, and Jupiter is 5.5 AU.Therefore, depending on the actual distance between Betelgeuse and the Earth, the photosphere can extend to miles beyond the orbit of Jupiter, but it is uncertain whether it will reach as far as 9.5 AU of Saturn.
The radio image shows the size (circle) of Betelgeuse's photosphere and the convective effect that makes the star's asymmetric atmosphere expand beyond the orbit of Saturn.
There are several reasons why precise diameters are difficult to define:
one
The rhythm of the contraction and expansion of the photosphere, as suggested by the theory, means that the diameter is not always the same;
two
The color change and radiation attenuation of the farther beam extending outward from the center are more due to the surrounding dimness, and there is no clearly defined "boundary";
three
Betelgeuse is surrounded by a peristellar envelope of material ejected from the star.These substances absorb and radiate light, which makes it difficult to define the boundary of the photosphere;
four
The electromagnetic spectrum is measured at different wavelengths, and each wavelength reveals something different.The research shows that the wavelength of visible light has a large angular diameter, which decreases to the minimum in the near infrared ray, but increases again in the mid infrared ray.The reported diameter difference can be as much as 30~35%, but because different wavelengths measure different things, it is problematic to compare one conclusion with another;
five
The scintillation of the atmosphere makes the telescope on the ground reduce the limit angle value of understanding image force due to the influence of atmospheric turbulence.
In order to overcome these limitations, researchers have adopted various solutions.The concept of astronomical interferometer was first proposed by Hippolyte Fizeau in 1868.He proposed that observing the interference of stars through two holes would provide information on the spatial intensity distribution of stars.Since then, scientific interferometers have developed multi aperture interferometers, which can overlap images at multiple locations.The images of these "spots" useFourier analysisSynthesis - a method widely used to examine celestial bodies, including the study of conjoined stars, quasars, asteroids and galactic nuclei.Since 1990adaptive optics Has revolutionized high-resolution astronomy, and at the same time, such as Ebague, Harper, and SpitzerSpace ObservatoryAnd other major breakthroughs.Another instrument, the astronomical multi beam contactor (AMBER), provides a new perspective.the mostVery large telescopeAs part of AMBER, AMBER has the ability to combine three telescopes at the same time, enabling researchers to achieve spatial resolution of microseconds.In addition, by combining three interferometers # astronomical interferometers instead of two, which is a conventional interferometry, AMBER enables astronomers to calculate the closed phase - an important part of astronomical imaging.
Comparison between Betelgeuse and other stars
The current discussion revolves around wavelength - visible light, near infrared (NIR) or medium infrared (MIR) - to obtain the most accurate angle measurement.The most widely accepted solution, its emergence, is the ISI carried out by astronomers at the University of California Berkeley Space Laboratory in the mid infrared band.In the year 2000, this group, under the leadership of John Weiner, published a paper, which ignored any possible hot spots with the generally unnoticed mid infrared ray, showing that the diameter of the uniform disk of Betelgeuse is 54.7 ± 0.3 mas.This paper also includes the theoretically recognized peripheral dim diameter of 55.2 ± 0.5 mas - assuming that the distance from the earth is 197.0 ± 45 pc, which is equivalent to the appearance of a radius of about 5.5 AU (1180 R ⊙).However, since the error of the angular diameter is ± 0.5 mas, combined with the error of ± 45 pc of the Harper value, the radius of the photosphere can actually be as small as 4.2 AU, or as large as 6.9 AU.
CrossingAtlanticAnother group of astronomers led by Guy Perrin of the Paris Observatory made an accurate measurement of 43.33 ± 0.04 mas of the radius of the controversial Betelgeuse photosphere with infrared ray in 2004."Perrin's report gives a reasonable scenario that can consistently explain observations from visible light to mid infrared light." The star's seemingly thick and warm atmosphere slightly increases the diameter of short wave light scattering, and the scattering of wavelengths above 1.3 μ m can be ignored.In the K and L bands, the upper atmosphere is almost transparent.What you see at these wavelengths is a traditional photosphere, so the diameter is the smallest.In the mid infrared, thermal radiation warms the atmosphere and increases the apparent diameter of stars."These parameters have not been widely supported by astronomers.
The research on near-infrared ray using IOTA and VLTI strongly supports Perrin's analysis. The diameter ranges from 42.57 to 44.28 mas, and the minimum error factor is less than 0.04 mas.The focus of this discussion was the second paper in 2009 by the Berkeley team led by Charles Tang, which reported that the diameter of Betelgeuse had decreased by 15% from 1993 to 2009, and the angular diameter measured in 2008 was 47.0 mas, not far from Perrin's estimate.Unlike most of the previously published papers, this research focuses on a 15 year vision of a specific wavelength. Early research usually lasts only 1 to 2 years, and often produces different results on multiple wavelengths.From the perspective of reduction, it is equivalent to 56.0 ± 0.1 mas seen in 1993 to 47.0 ± 0.1 mas seen in 2008, almost 0.9 AU reduced in 15 years, or about 1000 km/h.
Astronomers all think that we don't know the rhythm of the star's expansion and contraction at all. If so, what is the cycle period? Although Tang believes that there is no such cycle, it may also last for decades. Other possible explanations are that the photosphere is slightly asymmetric due to convection or because it is not a sphere,This causes the apparent expansion and contraction of the star as it rotates around its axis.Of course, unless we collect complete data on the period, we will not know whether 56.0 mas in 1993 represents the maximum or average value of star expansion, or 47.0 mas in 2008 is actually a minimum value.Before we know the exact value, we may continue to observe for 15 years or more (2025), that is, 5.5 AU, which is equivalent to the orbital radius of Jupiter, may continue to be regarded as its average radius for a long time.
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Late stage of evolution
Now Betelgeuse has reached the end of its life. It is speculated that it may become type II in the next millions of yearsSupernova。Astronomers predict that Betelgeuse will eventuallyType II supernovaBurst to end its life, or its mass is only enough to become a small black hole.However, there is no consensus on how long it will last: some people believe that the constant change of its diameter means that Betelgeuse is fusing its carbon atoms and will become a supernova within thousands of years;Those who disagree with this view believe that it can survive longer.If a supernova explosion does occur, its luminosity will increase to hundreds of thousands of times, aboutCrescent moonThere are also some predictions that the maximum luminosity can even reach three times of the full moon.
The light of supernovae will last for several months, and can also be seen in the daytime. Then it will gradually darken, disappear in the naked eye night sky, and the hunter's arm will disappear. In a few centuries, it will become a nebula.But if this oneneutron starOfAutorotation shaftIt is toward the earth, which is more troublesome. The high-energy gamma rays and cosmic particles released by it will reach the earth like rain, and will weaken the ozone layer, which will appear in many places in the skyaurora。(Note: It is confirmed that the included angle between the rotation axis of Betelgeuse IV and the earth is about 20 °)
January 22, 2011, AustraliaUniversity of South QueenslandDr. Brad Carter, a senior lecturer in physics, predicted that, from now on, within tens of thousands of years at the latest, human beings on the earth will also be able to see bright stars of about - 12 degrees, although this strange scene will only last for a few weeks.Dr. Carter said that the size of Betelgeuse, the red supergiant star of Orion, has been shrinking and its mass has dropped sharply in recent yearsRed supergiantA typical sign of gravity collapse, Betelgeuse may occur at any timeSupernova explosion, then BetelgeuseAbsolute magnitudeIt will be at least - 17, etc.
In brief, type II supernovae are the violent explosions caused by the extrusion of a supergiant during the collapse of its core.
"This agingfixed starThe core of Betelgeuse has exhausted its fuel. It is these fuels that make Betelgeuse emit light and heat. When the fuel is exhausted, the star will collapse inward, triggering a huge supernova explosion. "When all this happens, the absolute magnitude of Betelgeuse will be at least - 17. When the light of the supernova explosion reaches the earth, it will be like a "second Venus" appearing over the earth in human eyes.However, this "second Venus" will only last for a few months, and then it will gradually fade and disappear in the next few years.Dr. Carter said: "This will become the last brilliant of a star. When Betelgeuse explodes, it will shine in the night sky. We will see its incredible brightness in a few weeks. In the next few years, it will gradually fade, and finally it will be difficult to observe.
Light curve of supernova (type Ⅱ b of four genera of Betelgeuse)
Dr. Carter said that although Betelgeuse might explode as a supernova, it could explode any day in a million years.Even if Betelgeuse explodes, its performance in the sky cannot be the "second sun".What "Star Wars fans" expected from Luke Skywalker on the distant planet Tatooine would not appear.
The most significant difference between the sun and the stars is that it looks larger - the sun is not a light spot, but hangs in the sky like a golden plate.In astronomy, the "size" of such a celestial body is often described by the angular diameter, that is, the included angle formed by the diameter of the celestial body at the observation point is calculated.The closer or larger the celestial body is to us, the larger its angular diameter is. Conversely, the distant or small celestial body has smaller angular diameter.Although Betelgeuse is one of the stars with the largest angular diameter, and its diameter will increase sharply when a supernova explodes, because Betelgeuse is too far away from us, its angular diameter cannot be compared with that of the sun.It is speculated that the maximum angular diameter of Betelgeuse at the time of its explosion may be 0.416 '(calculated according to the diameter of the supernova after the explosion, which is three times the diameter of the solar system and 643 light years away from the Earth), which is less than 1/4500 of the sun. Even Neptune, the planet with the smallest angular diameter in the solar system, is more than 5 times of it.Even if Betelgeuse broke out, it was only a small point.
Effect picture of Betelgeuse supernova explosion
According to astronomers' calculations, when Betelgeuse eruptsApparent magnitudeIt is about - 12, that is, it can reach the brightness of the full moon and can be seen in the daytime.New simulation results show that its brightness may even exceed three times the brightness of the full moon.This is absolutely amazing for a star, but there is still a big gap compared with the sun - the apparent magnitude of the sun is as high as - 26.74.According to the relationship between magnitude and brightness, we can calculate that the brightness of Betelgeuse is less than one half of the sun's brightness.At night, Betelgeuse may leave us a long shadow, but if we want it to shine the night as bright as day, it's really hard.
Explosion is harmless to the earth
The prediction that Betelgeuse may have a supernova explosion at any time has caused a heated discussion on the Internet, and some people even compared the supernova explosion withMayan Calendar The 2012 "end of the world" conspiracy theory in the Chinese version of the Chinese version of the Chinese version of the Chinese version of the Chinese version of the Chinese version of the Chinese version of the Chinese version of the Chinese version of the Chinese version of the Chinese version of the Chinese version of the Chinese version of the Chinese version of the Chinese version of the Chinese version of the Chinese version of the Chinese version of the Chinese version of the Chinese version of the Chinese version of.
However, Dr. Carter said that the supernova explosion could not bring any destructive results to the earth, because the tiny particles released by the supernova explosion——neutrinoIt is harmless to human body.
Dr. Carter said, "When afixed starWhen exploding, we will first observe a rain of particles called 'neutrinos', which will pass through the earth. Even though the supernova explosion will illuminate our night sky, even though 99% of the energy of the supernova will be released into these particles, these tiny particles will never cause any harm to us when they pass through the earth and our bodies. "
Some experts speculate that once Betelgeuse happensSupernova explosion, will become aNeutron star,Or form ablack hole。Dr. Carter said, "It has an equal probability of forming a neutron star or a black hole. If I make a prediction, I think it is more likely to form an eight foldSolar mass"
Volume reduction
Betelgeuse shrinks by nearly 15%
Charles Townes In a statement on the same day, he said: "New measurements have found that the diameter of 'Betelgeuse' has shrunk by 15% in the past 15 years, which is gentle but accelerating year by year." The radius of 'Betelgeuse' is 5.5 AU, which is 5.5 times the distance from the earth to the sun.If it is placed in the center of the solar system, its surface will almost reach the orbit of Jupiter.This means that Betelgeuse has reduced the distance from Venus to the sun in the past 15 years.Today, Betelgeuse is still hugeSpace telescopeObserved, it still belongs to a small number of discs rather than dotsfixed star。But asRed supergiant, it has almost come to the end of life.
Edward Weichner said that they did not know why Betelgeuse shrankRed supergiantPeople still have too many unknowns.
The researchers said that they would continue to study Betelgeuse to see whether it continued to shrink or expand.The researchers also pointed out that although the size of Betelgeuse is shrinking, its brightness has not significantly darkened in the past 15 years[2]。
Unknown bow shock
Betelgeuse
In the direction of motion of Betelgeuse, scientists observed some signs of mass loss, such as a series of dust and material chaos. The closer the region is to the star, the more asymmetric the structure is.Although some earlier theoretical studies have proposed that the "wall" shaped structure around Betelgeuse is caused by the matter ejected from the star evolution stage, the analysis of new space telescope image data shows that it may be associated with the galactic magnetic field, but it is located at the edgeInterstellar gas cloudIt is also being illuminated by the light of the four stars of Betelgeuse.If the "wall" structure is a completely independent celestial body (matter), scientists believe that the outer arc shock wave of Betelgeuse will collide with the former within 5000 years[3]。
