Milky Way GalaxyBarred spiral galaxy（spiral galaxy The Milky Way has four clear and symmetrical spiral arms, which are 4500 light-years apart.The number of stars in the Milky Way is between 100 billion and 400 billion[1]。
Galaxy as a wholePoor autorotation。The rotation speed at the sun is about 220 km/s. The sun revolves around the silver center for about 250 million years.Visual inspection of the Milky WayAbsolute magnitude- 20.5, the total mass of the Milky Way is aboutSolar mass1.5 trillion times.The Milky Way is about 10 billion years old[2]The scientific community believes that the Big Bang occurred about 13.8 billion years ago.[3]The Milky Way has twoCompanion galaxy：Large Magellanic GalaxyandMagellanic galaxy。[4]They are all members of the local galaxy group, and areVirgo Supercluster Part of;And it is composed ofRanyakia superclusterPart of.[5]
The Milky Way Galaxy is divided fromSilver core、Silver nucleus、Silver plate、Silver haloandSilver crownform.The central region of the Milky Way is mostly composed of old stars (White dwarfMainly)[6]Most of the outer regions are newborn and young stars.A dozen satellite galaxies are distributed in the area of hundreds of thousands of light years around, and the Milky Way keeps growing by slowly devouring the surrounding dwarf galaxies.[7]
On May 14, the National Astronomical Observatory of the Chinese Academy of Sciences released a news to the media that Dr. Xu Jun and researcher Han Jinlin of the observatory, by analyzing the distribution data of the pulsar in the Milky Way and the Faraday rotation effect of radio sources outside the Milky Way, found that there is a huge magnetic ring structure in the halo (silver halo) of the Milky Way, and its magnetic ring is from the center (silver center) of the Milky Way6000 light years extends to 50000 light years.... Details
Content from
Chinese name
Galaxy
Foreign name
Milky Way Galaxy、Galactic System、galaxy、Milky Way system
The Milky Way in the sky varies in brightness and width.The narrowest is only 4 °~5 °, and the widest is about 30 °.However, the individual stars seen by the naked eye everywhere in the sky are all part of the Milky Way.The light from this band arc is the accumulated light from stars and other celestial bodies on the plane of the Milky Way that cannot be resolved by the naked eye.For the Northern Hemisphere, the Milky WayStarry sky in summerAnd three bright stars on both sides of the Milky WayVega、Niulang StarAnd galacticTianjin IVConstituted“Summer Triangle”。In summer, the Milky Way stretches northward from the east side of Scorpio, traversing the sky, magnificent and magnificent.But only in the field without light interference (the limiting visible star magnitude is above 5.1)[14]To appreciate it.The Milky Way is very dim in winter (OrionAndCanis Major）, but the bright Orion can be seen in the sky, andSirius、Betelgeuse、Nanhe IIIConsisting of bright“Winter Triangle”。(Note: This section is from the northern hemisphere)
The Milky Way's fisheye photography works, it looks like an arch bridge across the night sky.
Viewed from the earth, the center of the Milky Way is the brightest region of the Milky Way, and its direction is in Sagittarius.From Sagittarius, the hazy white light belt seems to pass to Auriga on the back.The light belt then continues the rest of the way back to nearby Sagittarius, dividing the celestial sphere into two roughly equal hemispheres.The north pole of the Milky Way is located at 12 right ascensionhforty-ninem, declination+27.4 °, close toZhou Dingyi(Rear engine seatβ）；The Milky Way South Pole is in the constellation YufuαNearby.Due to this high inclination, the Milky Way's arc can appear at a very high or very low position in the sky at different times of the year.Between 65 degrees north latitude and 65 degrees south latitude on Earth, the Milky Way passes through the observer's zenith twice a day.
Main structure
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Silver core
The first picture of a black hole taken by humans is located at the center of M87 galaxy.[15]
The geometric center of the Milky Way isAutorotation shaftAndGalactic surfaceThe intersection of.It is a bright spherical bulge in the center of the galaxy, with a diameter of about 20000 light-years and a thickness of 10000 light-years.This region is composed of high-density stars, mainly red stars aged over 10 billion years.The evidence shows that there is a huge black hole in the central region.Astronomers observed that there were as many as 42 million stars distributed in the space of one second difference (3.26 light years) between the length, width and height of the center of the Milky Way, or the density of stars there was as high as 289000 stars per cubic light year, 72 million times higher than the density of stars near the solar system.[16]
In addition to being a geometric point, the galactic center also refers to the central region of the Milky Way Galaxy.Silver heart inSagittariusDirection, 1950 epoch coordinates: right ascension 17 ° 42 ′ 29 ″, right latitude - 28 ° 59 ′ 18 ″.The sun is about 25000~28000 ly (7.7~8.6 kpc) away from the silver center.This value is a geometry based method, which is measured byStandard candleCelestial objects, we use different methods to obtain these approximate but different values.[17-19]Inside the thousands of seconds gap (about 10000 light years radius) is a dense area of old stars, roughly spherical, called the nuclear sphere.
There are a lot of interstellar dust between the silver core and the solar system, which is used in the Northern HemisphereOptical telescopeIt is difficult to see the silver core in the visible light band.After the rise of radio astronomy and infrared observation technology, people canInterstellar dustThe information of the silver core is detected in the wave band from 2 μ m to 73 cm.Neutral hydrogen 21 cm spectral lineThe observation of“3000 second gap arm”(The distance was initially mistakenly defined as the 3000 second gap, but it was later revised to the 4000 second gap, but the old name was still used).There are about 10 million solar mass neutral hydrogen flowing into the solar system at the speed of 53km/s.On the other side of the silver core, there is a neutral hydrogen expansion arm with roughly the same mass, leaving the silver core at a speed of 135km/s.At a distance of 300 seconds from the silver coreTianquInside, there is a hydrogen disk rotating rapidly around the silver core, which expands outward at the speed of 70-140 km/s.There are hydrogen molecular clouds with an average diameter of 30 seconds in the disk.
These two giant bubbles are caused by gamma rays from the center of the Milky Way.
In December 2010, American astronomer Professor Doug Finkbeiner and others found two giant "Fermi bubbles" in the Milky Way.These two "bubbles" extend from the center of the Milky Way to the north and south respectively, from Virgo to Crane. They may be millions of years old, and each is 25000 light years wide.[20]But according to astrophysical theory, these gamma ray bubbles should not exist, and scientists have been very puzzled about this so far.One view is that the supermassive black hole in the center of the Milky Way Galaxy forms a giant jet, and the black hole may form a mass jet near its poles that is close to the speed of light;In other words, they may be formed by giant stars, which are formed by a large amount of gas around the black hole, and they have supernova explosions at about the same time;Another view is that the "Fermi bubble" is the result of the collision of dark matter particles.[21]
Several star orbits around Sagittarius A.This implies the enormous mass of Sagittarius A *.
The center of the Milky Way is marked asSagittarius A*A strong source of radio waves.The motion law of the stars moving around Sagittarius A * shows that there is a massive compact object there。The infrared observation data of 12.8 μ m indicates that the silver core with a diameter of 1 second has a mass equivalent to several millionSolar massAbout one million solar masses are in the form of stars.The best explanation for this mass concentration is the existence of SMBH (supermass black hole),[22]Its mass is estimated to be between 4.1 and 4.5 million solar masses.[23]The accretion rate of the supermassive black hole is consistent with the inactive galactic nucleus with an estimated value of about 1 × 10 − 5 M ⊙ y − 1.Very long baseline interferometerThe detection shows that the central area of the silver core radio source is very small, even less than tenAstronomical unitThat is, it is not larger than the orbit of Jupiter around the sun.Flow into dense coreAccretion diskRelativistic electrons in strongmagnetic fieldThe synchrotron acceleration radiation is generated.[15][24]
Radio images near Sagittarius A *.
On November 11, 2012, an international astronomical team, using NASA's Chandra X-ray Space Telescope, detected a bright X-ray flare from Sagittarius A * in the center of the Milky Way Galaxy. The brightness of the flare was 150 times the normal brightness of the black hole, and the flare burst time exceeded 1 hour, then gradually darkened.[25]On August 9, 2019, within two hours, the brightness of Sagittarius A * increased 75 times.Astronomers believe it was even brighter before this observation began.[26]One explanation for these changes in brightness is that it is devouring certain substances around it.When these substances fall into the black hole, they generate heat by friction, which is converted into energy and released, thus causing the brightness change of Sagittarius A *.
In the photographic works of the Milky Way, what crosses the sky is part of the silver plate.
The silver disk is a major part of the Milky WayA flat disk of stars, dust, and gas。Of the detectable substances in the Milky Way, nine are within the range of the silver plate.The shape of the silver disk is like a thin lens, which is distributed around the silver center in an axisymmetric form. Its central thickness is about 10000 light-years, but it is slightly convexNucleosphereThe thickness of the silver plate itself is only 2000 light-years, and the diameter is nearly 200000 light-years[27]On the whole, the silver plate is very thin.[28]
Section of the spatial structure of the silver disk. The red and white areas are silver disks, and the blue areas are silver halos.
At the end of 2017, researcher Liu Chao from the National Astronomical Observatory and others took the lead in usingLAMOSTThe data successfully mapped the spatial structure profile around the silver disk.The researchers analyzed that although the number of stars in the silver disk is decreasing with the radius of the silver disk, it does not stop at 50000 light years, but extends to 62000 light years away from the center.[29]Previous studies believed that the radius of the silver disk was only about 14-15 thousand seconds apart, and then there would be an obvious truncation. Many theoretical studies deduced the history of the formation and evolution of the Milky Way.Although some studies have found a small number of young stars 20 thousand seconds away from the center of the Milky Way, it was not until this work that people really saw the true nature of the outer disk of the Milky Way.[30]
Except the silver core within the range of 1000 secondsFixed axis rotation of rigid bodyIn addition, other parts of the silver plate are made around the silver corePoor autorotation, that is, the farther away from the silver core, the slower it turns.The matter in the silver disk mainly exists in the form of stars. The interstellar matter accounting for less than 10% of the total mass of the Milky Way Galaxy is also scattered in the silver disk.In interstellar matter, except ionized hydrogenMolecular hydrogenAnd variousInterstellar moleculeIn addition, there are 10%Interstellar dustThese solid particles with a diameter of about 1 μ m are caused byInterstellar extinctionThe main reason is that they are mostly concentrated near the galactic plane.
The rendering of the structure of the Milky Way.The spherical structure around the silver disk is called silver halo.
The disk of the Milky Way is surrounded by a spherical silver halo with a diameter of 250000~400000 light-years.Because the gas and dust on the disk will absorb part of the wavelengthelectromagnetic waveTherefore, the composition and structure of the silver halo are not clear.The disk (especially the spiral arm) is the active region for star birth, but there is no such activity in the silver halo,Open clusterIt also mainly appears on the disk.The silver halo is scattered in a spherical area around the silver disk. The diameter of the silver halo is about 100000 light-years. The density of stars here is very low. There are some spherical star clusters composed of old stars. Outside the silver halo, there is a huge spherical radio radiation area calledSilver crownThe silver crown extends at least 320000 light years away from the silver core.[24]The disk of the Milky Way is surrounded by a spherical silver halo with an estimated diameter of 250000 to 400000 light-years.Since the gas and dust on the disk can absorb electromagnetic waves of some wavelengths, the composition and structure of the silver halo is not clear.The disk (especially the spiral arm) is the active region for star birth, but there is no such activity in the silver halo. Open star clusters are mainly distributed on the disk.
Most of the mass in the Milky Way is dark matter, and the dark matter halo formed is estimated to be 5.8 × 1011M⊙, which is gathered around the Milky Way.[32]
Simple horizontal structure map of the Milky Way.
On January 9, 2006, Mario Juric and some people from Princeton University announced that Sloan Digital Sky Survey found a huge cloud structure in the northern hemisphere sky (spanning an area about 5000 full moons in size) within the Milky Way, but it seems to be incompatible with all current galactic models.He gathered some stars on a vertical line perpendicular to the disk where the spiral arm is located, which may be explained by the merger of small dwarf galaxies and the Milky Way.This structure is located in the direction of Virgo, about 30000 light-years away, and is temporarily called the Virgo Starstream.
In 2017, researchers at the National Astronomical Observatory usedLAMOSTThe observed halo family red giant stars directly drew a three-dimensional profile within the 40 thousand second gap (1 second gap is about 3.26 light-years) of the Milky Way, thus revealing the complex composition of the halo, which is flat spherical inside and gradually spherical outside.The number density of stars decreases from inside to outside according to a single power law[33]。
Three-dimensional position and velocity distribution of halo stars
In August 2019, the National Astronomical Observatory of the Chinese Academy of Sciences found more than 40 sets of sub structures in the galactic halo, including nearly 2000 stars, using the three-dimensional position and three-dimensional velocity of the K giant star in LAMOST DR5.This includes a large number ofSagittarius stream The six dimensional parameter information of the large sample substructure in the galactic halo is given for the first time.This information more accurately shows the current structure of the Milky Way Galaxy and its past accretion history.Usually, when galaxies are accreting and merging, they will leave remnants of protogalaxies in the space (halo) around them, such as substructures such as stream, density, shell, etc.
In order to find these sub structures, the researchers used the spatial position and visual velocity of K giant star in LAMOST DR5, combined with the tangential velocity information matched from Gaia DR2, to obtain more than 13000 halo stars with complete six dimensional phase space information, which is also the largest halo star list of the Milky Way with complete six dimensional information available at present (2020).
Spatial distribution of halo neutron structure (X-Z plane), different colors and shapes represent different
After classifying and grouping the stars with similar velocities and positions in the samples, researchers found more than 40 groups in 13000 halo star samples, and nearly 2000 halo stars belong to sub structures. These stars have clustering characteristics (position and velocity space) that are obviously different from local halo stars.[34]
Schematic diagram of giant magnetic ring structure in the halo of the Milky Way
May 2024, National Astronomical ObservatoryXu JunDoctor andHan JinlinThrough analysis and research, researchers revealed that there is a huge magnetic ring structure in the halo of the Milky Way Galaxy.This provides important observation results for the propagation of cosmic ray particles, the dynamics of galactic gas and the evolution of cosmic magnetic field.[83]
Swivel arm
The Milky Way has four main spiral arms, which arePerseus armHunter arm, bottom of the boat - man and horse armNomaArm And shield-Centaurus arm [11][35]。
The radius of the Perseid Arm is about 10700 seconds, which is located between the swan arm and the centaur arm. It is called the Perseid Arm because it is in the Perseid constellation when viewed from the earth.The shield centaur arm, also known as the shield south cross arm, is a long string of star streams that spiral outward from the center of the Milky Way Galaxy and close to the end of the bar, composed of diffuse gas and dust.The region where it connects with the bar of the Milky Way is rich in star forming regions.In addition, the Milky Way has other spiral arms.The spiral structure of the Milky Way is still uncertain, and there is no consensus on the nature of the Milky Way Arm.Because the spiral arms of the Milky Way often have branches, mergers, unexpected twists, and varying degrees of irregularity, the perfect log spiral model can only roughly describe the characteristics near the sun.
The solar systemHunter armOn.This arm is located between the Perseid arm and the Sagittarius bottom arm, with a length of about 20000 light years.Its shape and rich massive star forming regions can be compared with the other four spiral arms.The local arm may not be isolated, but it is most likely a part of the arm adjacent to the Perseid arm and the centaur bottom arm.[36]The distance from the sun to the center of the Milky Way is 26000 light years, the speed of rotation around the center of the Milky Way is 236 km/s, and it takes about 212 million years to make a circle.The sun is almost on the central plane of the silver disk, and the vertical distance from the central plane is about 20 light-years, which is smaller than the previous estimate of 82 light-years.
solar system
The sun is in the Orion spiral arm of the Milky Way.
The solar system is located near the inner edge of the Orion spiral arm, about 26400 light-years away from the center of the Milky Way Galaxy. It rotates counterclockwise, and it takes about 220 million years to rotate around the center of the Milky Way.[37]The direction of the sun's movement is basically towardVega, nearHerculesAbout 86 degrees away from the center of the Milky Way.The sun's orbit around the Milky Way is roughly elliptical, but it will be disturbed by the uneven distribution of spiral arms and mass.
The solar system orbits once every 225 million to 250 million years, which can be calledGalactic Year。Therefore, based on the sun's age, the sun has circled the Milky Way 20-25 times.The orbital speed of the sun is 217km/s. In other words, it can move one astronomical unit every eight days, and it can travel a distance of one light year in 1400 years.
The sun is in the Milky Way
Distance from the sun to the silver center
About 28000 light years[38]
Northern silver pole
α=12h51m，δ=+27 ° 07 '(rear engine seat)
Silver core direction
α=17h45m，δ=-28 ° 56 ′ (Sagittarius)
Rotation speed of the Milky Way galaxy at the sun
About 250 km/s
Rotation period of the Milky Way at the sun
About 220 million years
Motion speed relative to 3K background
About 600 km/s (towardsα=10h，δ=-20 ° direction)
reference material:[2]
Warped structure
In 2019, Chen Xiaodian, Deng Licai and Wang Shu of Peking University from the National Astronomical Observatory of the Chinese Academy of Sciences constructed a robust model of the galactic disk based on the classical Cepheid variable stars, and provided an intuitive three-dimensional map of the warping structure of the Milky Way.Cepheid variable stars are a kind of young pulsating variable stars with medium mass, which are 3 to 20 times heavier than the sun and tens of thousands of times brighter.Because their pulsation period is strictly related to the luminosity, the distance can be measured accurately with an accuracy of 3% to 5%.
Three dimensional map of the warped structure of the galactic silver disk.
Scientists found that the farther away from the center of the Milky Way Galaxy, the more Cepheid variable deviates from the silver disk, showing an "S" shape as a whole;At the same time, the warping outward from the silver core presents a complex precession phenomenon.This work shows that the origin of the warpage of the outer disk of the Milky Way Galaxy is related to the torque exerted by the huge inner disk, and the structure of the stellar disk traced by Cepheid variable is very consistent with that of the gas disk, which extends outward at least to about 65000 light-years.Although warping often occurs in extragalactic galaxies, theorists have different opinions on how it was formed.One possible explanation is that the outer disk is formed by some torque.[39-42]
On December 19, 2013, the Gaia Space Telescope was successfully launched in French Guiana and flew to the point L2 of Earth Sun Lagrange, which is 1.5 million kilometers away from the Earth. This is one of the balance points of the sun and the earth's gravity.
Through the Gaia Space Telescope, it was further confirmed that the galactic galactic galactic galactic plane, previously considered to be horizontal, is actually a warped structure with one end high and one end low.The thickness of the silver disk at the location of the solar system is about 500 light-years. The degree of warping outside the solar location is about 4500 light-years away from the galactic plane, and the thickness of the silver disk at the corresponding other end is about 3000 light-years.It was previously suggested that dark matter, magnetic field, etc. or the cause of this warping structure, but it was later found that dark matter and other factors could not explain the movement speed of this structure in the next 600 to 700 million years, and it seems that this speed is still changing with time
Gaia telescope
Therefore, scientists put forward a conjecture: the warping structure may originate from the collision between the Milky Way and other galaxies:A satellite galaxy of the Milky Way——Centaurus dwarf galaxyThe most suspect.Previous studies have shown that it did penetrate the galactic disk several times, and may be being absorbed by the galaxy.This collision has a great impact on the objects in both galaxies.Because the probability of frontal collision of celestial bodies is very small, this kind of influence mainly focuses on the change of motion orbit and the disturbance of local material density.The Gaea Space Telescope observation data shows that about 6.2 billion to 4.2 billion years ago, the Sagittarius dwarf galaxy collided with the Milky Way for the first time, resulting in the disturbance of the gas matter in the Milky Way.[34]
The data collected by Gaia Space Telescope not only revealed the influence of Sagittarius dwarf galaxy on the Milky Way, but also the ripples generated by collision seemed to trigger major star forming events.A new study reveals the past of the Milky Way 5.7 billion years ago - the Milky Way or the Centaurus dwarf galaxy had three collisions, and the first collision produced the sun, because the age of the sun is consistent with the age of the stars formed by the collision effect of the Centaurus dwarf galaxy.[43]
One of the companion galaxies: the Large Magellanic Galaxy.
The Milky Way is surrounded by some dwarf galaxies in the local galaxy group. The largest is the Large Magellanic Galaxy with a diameter of 21000 light-years, and the smallest isCarina dwarf galaxy。Other galaxies surrounding the Milky Way are the Small Magellanic Galaxy, the nearest one is the Canis Major dwarf galaxy, then the Sagittarius dwarf galaxy, the Little Bear dwarf galaxy, the Yufu dwarf galaxy, the sextant dwarf galaxy, the Scorpius dwarf galaxy, and the Lion I dwarf galaxy.
The estimated mass of the Milky Way Galaxy varies, depending on the methods and information used.[45]The lowest estimated value range, the mass of the Milky Way is 5.8 × 10elevenSolar mass（M☉）, slightly less than the mass of the Andromeda galaxy.In 2009, using the ultra long baseline array, it was found that the star speed at the outer edge of the Milky Way Galaxy reached 254 km/s (570000 mph).Because the orbital speed depends on the total mass within the orbital radius, it is speculated that the Milky Way has a larger mass, which is about the same as the Andromeda galaxy. Within the distance of 160000 ly (49 kpc) from the center, the mass is 7 × 10elevenM☉。In 2010, the radial velocity of halo stars was measured, and it was found that the mass within 8000 seconds was 7 × 10elevenM☉。According to a study published in 2014, the total mass of the Milky Way is estimated to be 8.5 × 10elevenM☉This is about half the mass of the Andromeda galaxy.
In 2020, international research teams will useNASAHubble Space TelescopeandEuropean Space AgencyThe Gaia probe has carried out the most accurate "weighing" of the Milky Way to date, and believes that the mass of the Milky Way is about 1.5 trillion solar masses.Of the total mass of the galaxy,About 200 billion stars and a super large black hole in the center of the Milky Way only account for a small proportion, most of the mass comes fromdark substance。This invisible mysterious matter, like the "scaffolding" of the universe, fixes the stars in a certain position in the galaxy.[46]Dark matter halos are relatively evenly distributed to a distance of 100000 seconds from the center of the Milky Way.The mathematical model of the Milky Way Galaxy shows that the mass of dark matter is 1 – 1.5 × 10twelveM☉。Recent research shows that the mass range can be as large as 4.5 × 10twelveM☉, as small as 8 × 10elevenM☉。
The total value of all stars in the Milky Way is estimated at 4.6 × 10tenM☉To 6.43 × 10tenM☉between.In addition to stars, there are interstellar gases composed of 90% hydrogen and 10% helium. Two thirds of hydrogen is atomic, and the rest is molecular hydrogen.The mass of these gases is equivalent to 10% to 15% of the total mass of galaxy stars.Additional interstellar dust accounts for 1% of the total gas mass.
On April 20, 2023, according to the National Astronomical Observatory of the Chinese Academy of Sciences, the "weight" of the Milky Way Galaxy is about 805 billion solar masses。[82]
Research chronology
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Early exploration
In 1584, Italian Bruno clearly put forward that the universe is infinite, stars are distant suns, and the sun is just an ordinary member of countless stars[47]。
On August 25, 1609, Italian scientist Galileo Galilei made the first astronomical observation with a telescope[48]Then, T. Wright, I. Kant, JH. Lambert and others believe that the Milky Way and all the stars may converge into a hugeStellar system。
In 1612, German astronomer Marius first discovered the Andromeda Nebula with a telescope[47]。
Astronomer William Herschel.
In 1718, British astronomer Harry pointed out for the first time that the concept of star immobility was wrong through observation and analysis.Later, Herschel correctly realized that the motion of stars is the result of the combination of the motion of stars themselves and the motion of the sun in space.[47]
In 1750, the British astronomer Wright published the book New Theory of the Universe.According to the condition of the Milky Way, the Milky Way is flat[49]As the sun and the earth are located in the interior of this system, we can see the Milky Way and scattered stars from different directions[47]。Wright conjectured that some of these nebulae might be giant star systems similar to the Milky Way[47]。
In 1755, Kant, a German, made it clear for the first time that there are countless similar celestial systems in the outer space of the Milky Way, called extragalactic galaxies, or simply galaxies[47]。
In 1783, Herschel found that the sun was moving in the direction of Vega at a speed of about 20 kilometers per second through the statistical analysis of a large number of observed star movements. The discovery of solar space movement completely shook the concept of the sun's immobility in Copernicus' heliocentric system[47]。
Herschel's hand-painted structure of the Milky Way.
In 1785, British astronomerFrederick William Herschel Use“Star counting”He drew a map of the Milky Way. He used the method to draw a conclusion that the stars in the Milky Way are distributed in a flat disk, surrounded by stars, with a length of 7000 light-years and a width of 1400 light-years. The sun is at the center of the Milky Way.This is the first model of the Milky Way built by human beings. Although it is not perfect, it has expanded human vision from the solar system to the vast star world of the Milky Way.
In the late 18th century, the British astronomer William Herschel made a systematic star counting observation with his self-made reflection telescope. He counted 117600 stars, and thus came to the conclusion that a star system was in the shape of a flat disk[50]。
nineteenth century
In the 19th century, John Herschel extended the work of star counting to the southern sky[50]。
In 1845,RossLord discovers the first spiral galaxyM51。
In 1852, American astronomer Stephen Alexander claimed that the Milky Way was a spiral galaxy, but he could not prove it.
Modern observation
An early picture of the structure of the Milky Way.
At the beginning of the 20th century, the Mount Wilson Observatory of the United States built the 2.5 meter astronomical telescope with the largest aperture in the world at that time[47]。Astronomers call the stellar system whose appearance is the Milky Way the Milky Way.J. C. Captan application statisticsparallaxBy measuring the average distance of stars and combining with star counting, aGalaxy model。In this model, the sun is in the middle, and the Milky Way Galaxy is a disk with a diameter of 8000Second gap, with a thickness of 2000 seconds.H. Sapril applicationCepheid variableOfPeripheral light relation, measure the distance of globular clusters, and study the structure and size of the Milky Way from the distribution of globular clusters.His model is that the Milky Way is aLenticularThe sun is not at its center.Shapley calculated that the distance between the diameter of the Milky Way Galaxy and the distance between the sun and the silver center is 80 thousand seconds. These values are too large becauseSaprilNot included in the calculation of distanceInterstellar extinction。
Dutch astronomy writer, 1900Cornelis·EastonThe vortex structure map of the Milky Way was published, but the spiral arms and the silver center were drawn incorrectly.
In 1904, the discovery of ionized calcium spectral lines in the stellar spectrum revealed the existence of interstellar matter.Subsequent spectroscopic and polarization studies identified the gas and dust components in the nebula.
In 1906, in order to re-examine the structure of the stellar world, Captan put forward the plan of "selecting star regions", which later became known as“Kaptan constituency”。In 1922, he concluded thatW. Herschel's similar model is also a flat system, with the sun in the center, the stars in the center are dense, and the edges are sparse.On the premise that there is no obvious interstellar extinction, a lens model of the Milky Way was established in 1918, with the sun out of center.By the 1920s, the Shapley model had been recognized by the astronomical community.Shapley overestimated the size of the Milky Way galaxy because he did not include the interstellar extinction effect.By 1930,TrumplerThis deviation can be corrected only after the existence of interstellar matter is confirmed.
In 1917, American astronomer Shapley confirmed that the sun is not located at the center of the Milky Way, but relatively close to the edge of the Milky Way, through the analysis of the distribution of stars in the Milky Way, thus correcting the error of the Herschel model of the Milky Way[47]。
In 1918, Mount Wilson Observatory built a 2.54m aperture reflecting telescope - Hooke Telescope[50]。American astronomer HSapril(Harlow Shapley) After four years of observation, he proposed that the solar system should be located at the edge of the Milky Way.To study the spatial distribution of globular clusters, a lens model of the Milky Way is established, with the sun out of the center.It's on the edge of the Milky Way.The center of the galaxy should be in the direction of Sagittarius[49]。Shapley proposed the observation and analysis results that the sun is not at the center of the Milky Way.After the observation of the rotation of the Milky Way, Shapley's model of the Milky Way was recognized by astronomers[50]。
In the 1920s,Galaxy rotationAfter being found,SaprilOur model of the Milky Way is generally accepted.But because it is not includedInterstellar extinctionThe numerical value of Shapley model is not accurate.The study of the structure of the Milky Way Galaxy has traditionally used optical methods, but there are some limitations.Developed in recent decadesradioMethods and infrared technology have become powerful tools for studying the structure of the Milky Way Galaxy.
In 1922, Duncan of Mount Wilson Observatory found some variable stars in galaxy M31[50]。
In 1923, Hubble used the Hooke Telescope of Mount Wilson Observatory to take photos and observe, and decomposed the outer part of M31 into a single star, and recognized one of them as a Cepheid variable, and then found several Cepheid variables in M31.In addition, some such variable stars have also been found in M33 and NGC6822[50]。On October 6, the American astronomer Hubble used this telescope to take a picture of the Andromeda Nebula, in which the outer edge of the nebula has been broken down into stars.Hubble found several such variable stars.Using these Cepheid variables, Hubble calculated that the distance of the Andromeda Nebula is 2.25 million light years, far beyond the scope of the Milky Way.The existence of extragalactic galaxies was finally confirmed[47]。
In 1926,SwedenastronomerLindbradIt is analyzed that the Milky Way is also rotating.Has greatly advanced our understanding of the Milky Way[49]。
In 1927, Holt, a Dutch astronomer, proved that the Milky Way is indeed rotating around the center, and that the whole Milky Way is not a solid.Therefore, the closer to the center, the faster the rotation is, and the edge of the Milky Way rotates slowly[49]。
In 1929, Dutch astronomer Bart Bock planned to use the star counting method to detect the structure of the Milky Way Galaxy, which failed more than a decade later.
In 1942, Swedish astronomer Lindblad put forward the concept of "density wave". Later, American scientists put forward a systematic density wave theory, which initially explained the stability of the spiral arm[51]。
In 1943, William Morgan and spectroscopist Philip Keenan jointly published a complete set of spectral atlases to describe the spectral characteristics of stars with different spectral types and luminosity levels, called MK (Morgan Keenan) classification system.
In 1944, Bud determined that stars can be divided intoStar Family IAnd family II.Star family I is a young and metal rich celestial body, distributed on the spiral arm, and associated with interstellar matter.Star Family II is old andLean metalThere is no tendency to concentrate towards the galactic plane.
In 1951, Morgan proposed that the Milky Way is spiral.According to Morgan, the Milky Way has three spiral arms composed of hot constellations, namely Perseus, Orion and Sagittarius.Benjamin said that in recent years, people generally insist that there are four main spiral arms in the Milky Way, namely, the stereotypical spiral arm, the centaur spiral arm, the centaur spiral arm and the Perseus spiral arm.The sun is located near the Orion spiral arm, a small spiral arm between Sagittarius and Perseus[51]。
In 1964, Chinese American scientistLin JiaqiaoAndXu YaoshengThe theory of maintaining density waves in spiral arms of spiral galaxies is proposed, which preliminarily explains the stability of spiral arms. They suggest that spiral arms are only the display of spiral density waves[52]。
During the 1970s, people accidentally discovered the fourth spiral arm of the Milky Way by detecting the distribution of carbon monoxide molecules in the Milky Way, which spans Foxy and Cygnus[51]。
In 1971, British astronomers Linden Bell and Martin Ness analyzed the infrared observation and other properties of the central region of the Milky Way, and pointed out that the energy source of the central region of the Milky Way should be a black hole[53]。
In 1976, two French astronomers also mapped out the positions of the above four arms in the Milky Way, which is the best image of the vortex structure of the Milky Way so far[51]。
The Hubble Space Telescope.
In 1982, American astronomers Janus and Adler published a shocking new statement -- they found that the Milky Way has no vortex structure, but only small pieces of scattered spiral arms, and the vortex is only a phantom, because stars produced everywhere in the Milky Way always form a "string of beads" along the direction of rotation of the Milky Way,And the constantly generated new stars continuously show the illusion of vortex[51]。
Infrared Scanning Panorama of the Galaxy Plotted by Spitzer Space Telescope
In 2003Spitzer Space Telescope More than 10 years of research has been carried out from asteroids in the solar system to distant galaxies at the edge of the observable universe.This is the first time that all the pictures of stars are spliced and reproduced in a huge panorama.The Milky Way is a flat spiral disk, and the solar system is located on one of the spiral arms.Due to the large amount of dust and gas blocking the visible light, it is impossible to directly observe the region near the center of the Milky Way Galaxy with optical telescopes on Earth.Since the wavelength of infrared light is longer than that of visible light, the Spitzer Space Telescope can penetrate dense dust and observe the central region of the Milky Way galaxy farther away.On March 21, 2003, astronomers drew a more accurate map of the central belt of the Milky Way based on the data obtained, and pointed out that the Milky Way was larger than previously thought.These data enable scientists to build a more comprehensive and three-dimensional model of galaxies[54]。
In 2004, astronomers used the Ultraviolet Vision Matrix Spectrometer (UVVIS) of the Very Large Telescope (VLT) to conduct research, and found for the first time in two stars of the globular cluster NGC 6397berylliumElement.This discovery pushed forward the time of alternation between the first generation stars and the second generation stars by 200 to 300 million years, so it is estimated that the age of the globular cluster is 13.4 ± 800 million years old, so the age of the Milky Way Galaxy will not be less than 13.6 ± 800 million years old[55]。
BothSingle star。Most of the matter in the Milky Way isdark substanceThe dark silver halo formed has a solar mass of 0.6 trillion to 3 trillion, and is centered on the silver core.It is generally believed that most stars in the Milky Way areKonductraorGather stars.The researchers' report points out that the disk of the Milky Way has been found to tilt for unknown reasons in the past, but now it has been found to be the size of the Milky WayMagellanic Clouds The ripple caused by the disturbance of.It is caused by vibrations of certain frequencies when they cross the edge of the Milky Way Galaxy.Scientists announced that they had confirmed that the Milky Way galaxy had undergone bending deformation, and the force that caused its deformation came from the dark matter surging around its periphery.Scientists explained that although dark matter is invisible, its mass may be 20 times that of the visible matter in the Milky Way, so its impact on the stars in the Milky Way cannot be underestimated[56]。On May 9, 2006, astronomers discovered two new dwarf galaxies in the Milky Way.These two dwarf galaxies are ellipsoidal dwarf galaxies, respectively located in the direction of the constellation Hound and Hercules in the sky, and both are about 640000 light-years away from the sun.According to experts, a galaxy whose brightness is less than 10% of the Milky Way is considered as a dwarf galaxy, and the brightness of a galaxy is mainly related to the number of stars in the galaxy.The newly discovered dwarf galaxy in the direction of Hercules is the darkest dwarf galaxy known so far, but its brightness is equivalent to 100000 suns[57]。
2008，Scientists announced that they confirmed the existence of silver coreblack hole。Scientists spent 16 years tracking 28 stars around the silver center at the European Southern Observatory in Chile, thus confirming the existence of black holes, because black holes affect the operation of these stars.The detection shows that this giant black hole, called Sagittarius A *, has a mass 4 million times that of the sun and is about 27000 light years away from the Earth[58]。
Kepler Space Telescope.
On March 6, 2009, Delta was used in the United StatesΙΙKepler, the world's first space telescope specially used to find Earth like planets, was launched by the X - type rocket.Its mission is to find planets similar to the earth and solve the historical problem of "whether the earth is lonely".If many Earth like planets are found, it means that life may be widespread in the Milky Way.Experts predict that Kepler can find more than 50 Earth like planets.On May 14, the European Space Agency's "Herschel" and "Planck" space telescopes were launched by the Ariane 5-ECA rocket. Their observation results will overturn human understanding of the universe[48]。From May 14 to 18, the astronauts of the space shuttle Atlantis successfully completed the fifth maintenance and upgrade of the Hubble Space Telescope through a space walk. Hubble's detection capability will be enhanced by 70 times and its service life will be extended to 2014[48]。On December 4, the United States released the latest infrared mappingPanorama of the Galaxy, this image is composed of 800000 piecesSpitzer Space Telescope The total length is 37 meters.The resolution is 100 times higher than the clearest picture of the Milky Way before.With the help of this picture, scientists carried outfixed starAfter counting, they thought that the Milky Way had only two main spiral arms.On the map of the Milky Way drawn based on this study, people can see two main spiral arms originating from the nuclear sphere. The sun is still located near the edge of the Milky Way Galaxy. Its specific location is the inside of the Orion spiral arm, which is a small spiral arm, between the Sagittarius arm and the Perseus arm.Most of the arms of the horse and the square are gas, with only a few stars dotted in them[59]。
A panoramic view of the Milky Way taken by the Spitzer Space Telescope.
In 2014, the latest observational data released by scientists showed that the mass of the Milky Way is onlyandromedaHalf of.This research result comes from an international research group, includingCarnegie Mellon UniversityOfCosmologistMatthew Walker, their research paper was published inRoyal Astronomical SocietyIn our monthly magazine.The paper points out that the research team has used a new method to measure the mass of galaxies, which is more accurate than previous measurement methods[60]。NASA(NASA) released a digital version of the 360 degree panorama of the Milky Way, which was created by“Spitzer”Two million photos taken by the space telescope in the past 10 years were spliced together, including more than half of the stars in the Milky Way, with 20 billion pixels. If printed, it would need a place as large as a stadium to display. Therefore, NASA decided to release its digital version for easy query by astronomical fans.In fact,This picture shows only about 3% of the earth's skyBut contains more than half of the stars in the Milky Way[61]。
In March 2015, scientists usedSloan Digital Sky SurveyThe survey data analyzed the brightness and distance of stars on the edge of the Milky Way, and found that the edge image of the Milky WayCorrugated cardboardSame, existingFrillStructure, there are stars in the grooves.Actually, thesefixed starThe region is also part of the Milky Way, and the real Milky Way is 50% larger than previously thought[62]。On November 7, the latest observation of the galactic center showed that the core of the Milky Way is basically composed of white dwarfs, with a number of at least 100000.The core of the core is composed of about 70 large white dwarfs.As for how to observe more content, scientists said that it needs to rely on the next generation of observation equipment, such as the James Webb astronomical telescope under construction by NASA[6]。
On April 10, 2018, NASA reported that astronomers used the Hubble Space Telescope to accurately measure the distance between the Earth and one of the oldest celestial systems in the universe, the globular cluster NGC 6397, for the first time[63]。
In March 2019, scientists estimated the mass of the Milky Way Galaxy using the observational data of the Hubble Space Telescope and Gaia, and the result is about 1.5 trillion solar mass[64]。On October 6, research teams from Australia and the United States recently found that the supermassive black hole at the center of the Milky Way Galaxy ejected huge energy beams 3.5 million years ago, spreading along the poles like beacon beams to form two conical eruption clouds.Research shows that the explosion intensity of this scale can only come from the nuclear activity related to the Sagittarius A black hole, which has a mass about 4.2 million times that of the sun[65]。
Look up at the Milky Way.
On March 25, 2020, British scientist Alice Dyson, an astrophysicist at Durham University, and her colleagues found the boundary of the Milky Way by using the nearby galaxies.Their latest research shows that the precise diameter of the Milky Way Galaxy is 1.9 million light years, with an error of no more than 400000 light years (one light year is equal to 9460 billion kilometers)[66]。On May 9, the National Astronomical Observatory reported that the scientific research team found a new moving star cluster near the Orion Nebula in the Milky Way, which contains 206 member stars, 74 of which are pre main sequence stars, that is, protostars whose central hydrogen has not been ignited, using the observation data of Guo Shoujing Telescope and ESA Gaia Space Telescope.Astronomers said that the discovery of the moving star cluster has provided observational evidence for studying the possibility that the spiral arm density wave of the Milky Way drives stars to gather, thus triggering the collapse of the nebula, and is of great significance for understanding the formation, structure and evolution of the Milky Way[67]。
On March 24, 2022, researchers from the Max Planck Institute of Astronomy, GermanyXiang MaoshengDoctor andHans WaltrixProfessor, published a major achievement in the form of a cover article on the international scientific journal Nature. The study believes that the Milky Way Galaxy may have gone through different stages of evolution, starting from the formation of disc family stars about 13 billion years ago.[79]
In August 2022, researchers from the National Astronomical Observatory of the Chinese Academy of Sciences released the first batch of wide field X-ray images and energy spectra of celestial bodies observed by EP-WXT pathfinders.With this instrument, scientists first observed the central sky region of the Milky Way Galaxy,We also observed the nearby galaxy of the Milky Way, the Large Magellanic Cloud。The results show that the instrument can detect X-ray sources in multiple directions at the same time in one observation.These include stellar mass black holes and neutron stars.[80]
In December 2022, the research team of Han Jinlin, a researcher at the National Astronomical Observatory, used the Chinese Celestial Eye FAST to detect the gas medium in the Milky Way Galaxy and obtain high-definition images.While conducting point by point surveys and searching for pulsars in the Milky Way, we simultaneously recorded the spectral line data of interstellar gas, and recently completed the observation of a part of the Milky Way, processed about 44000 radio spectral line data, and obtained the distribution structure of hydrogen atom gas and the diffuse characteristics of ionized gas in the Milky Way with the highest sensitivity and clarity in the world.[81]
Interstellar hydrogen atom gas distribution map of the Milky Way revealed by FAST (cumulative velocity range - 150 km/s to+150 km/s)
Interstellar Ionized Gas Distribution Map of the Galaxy Revealed by FAST (cumulative velocity range - 40 km/s to+120 km/s)
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Dwarf galaxy
On February 6, 2019, the Hubble Space Telescope found a previously unknown dwarf galaxy in the "backyard" of the Milky Way. The newly discovered star system is weak in brightness, with a diameter of about 3000 light-years, which is only equivalent to a piece of "debris" of the Milky Way.The researchers named it "Bedin 1".With a history of 13 billion years, it is astronomically equivalent to the "living fossil" of the early universe and can help reveal the mystery of the early evolution of the universe[68]。
Observation companion
Scientists use NASA's far ultraviolet spectrometer to explore the satellite and detect the ship base for the first timeη(Eta Carinae).Ship baseηIt is the heaviest and strangest star in the Milky Way, located at the base of the ship 7500 light years away from the Earth, and can be clearly seen with the naked eye in the southern hemisphere.Scientists believe that Itar Carinae is an unstable star that is rapidly declining[69]。
Cosmic expansion
Astronomers of Sloan Digital Sky Observation Program determined that,Dark energyIs driving the expansion of the universe[70]。About 23% of the cosmic matter is dark matter. Nobody knows what they are because they cannot be detected, but their mass is much more thanVisible universeThe sum of.Nearly 73% of the universe is newly discoveredDark energy。This strange force seems to be accelerating the expansion of the universe.Martin Rees, a British astronomer, called this discovery "the most important discovery".This discovery is orbitingWilkinson Microwave Anisotropy Detector(WMAP) and Sloan Digitalobservatory（SDSS) Results.It has solved a series of long-term disputes about the age of the universe, the rate of expansion, the composition of the universe and other issues.Astronomers now believe that the age of the universe is 13.8 billion years[71]。
NASA released pictures of the Large Magellanic Cloud in 2013.
NASAThe latest pictures of the Large Magellanic Cloud and the Small Magellanic Cloud taken by Swift were released in June 2013.These images are from the ultraviolet optical telescope carried by Swift detector.
The original image of the Large Magellanic Cloud has a pixel count of 160 million and is composed of 2200 local photos, which took 5.4 days to take.The original image of the Little Magellan Nebula has 57 million pixels, which is composed of 656 local photos. It took 1.8 days to capture[72]。
According to NASA official data, both the Large Magellanic Cloud and the Small Magellanic Cloud are companion galaxies of the Milky Way.Among them, the Large Magellanic Cloud is about 163000 light-years away from the Milky Way, its size is about 20% of the Milky Way, and its mass is only 2% of the Milky Way, while the Small Magellanic Cloud is about 200000 light-years away from the Milky Way, and its mass isLarge Magellanic Cloud50% of.[72]
Galactic waves
A hypothetical picture of the wave structure of the Milky Way.
In August 2019, the three-dimensional map of the Milky Way, drawn by an international scientific research team, showed that the shape of the Milky Way is a wavy disk.In the study, Mrutz and colleagues from Ohio State University in the United States and Warwick University in the United Kingdom used Cepheid variables as a reference.These stars will pulsate in a very regular period, and their temperature and diameter will change accordingly.The direct correlation between the luminosity and the pulsation period of Cepheid variable can be used as an important distance indicator inside and outside the galaxy.The article explains that the luminosity of the classical Cepheid is 100 to 10000 times that of the sun.It is bright enough to be detected outside the Milky Way.The periodicity of Cepheid pulsations helps to infer their absolute magnitude.If the phenomenon of interstellar extinction has been understood, the distance can be determined by comparing absolute magnitude and apparent magnitude.After determining the three-dimensional coordinates of each Cepheid variable relative to the sun, researchers built a large-scale three-dimensional model of the Milky Way.This model more appropriately presents the shape of the Milky Way like a wavy disk.[73]
Precision quality
Scientists from Columbia University calculated the mass of the Milky Way accurately. The latest results believe that the mass of the Milky Way is about 210 billion times that of the sun, including the star cluster with thousands of stars on the edge of the Milky Way.
The research team led by Andreas Kupper, a doctor from Columbia University, believes that they can use the supercomputer of Columbia University to simulate how much mass can induce fluctuations of this scale through the fluctuations in the Milky Way observed by Sloan Digital Sky Survey.In this way, combined with the Milky Way's diameter of about 120000 light years, scientists calculated that the Milky Way's mass is 210 billion times the mass of the sun.
Although this figure is relatively accurate as of 2015, there is still uncertainty, and the deviation may reach about 20%, which is much smaller than the deviation of the previous estimate of the quality of the Milky Way Galaxy.Earlier data suggested that the mass of the Milky Way is 750 billion times that of the sun, even 1 trillion times, with an error rate of 100%. It is almost impossible to determine the specific mass of the Milky Way.However, there is still a large amount of dark matter in the Milky Way that cannot be observed. Most stars gather within the radius of 40000 light years, and the outside is almost completely dominated by dark matter.[74]
Number of Earth like Planets
On June 18, 2020, Canadian scientists wrote an article in the latest issue of Astronomy Journal, pointing out that their calculations show that there are about 6 billion Earth like planets in the Milky Way.Researcher Michele Guoben of the University of British Columbia explained that if a planet is to be regarded as a planet similar to the Earth, it must be a rocky planet, about the same size as the Earth, surrounding a star similar to the sun（G star）Rotate.Moreover, this planet must be located in the habitable area of the star. In this area, the surface of the rocky planet can contain liquid water, so it has the potential to be suitable for life reproduction.
Guoben believes that the maximum number of Earth like planets per G-type star is 0.18.Previously, scientists estimated that the number of potentially habitable planets in each sun like star varied from 0.02 to more than 1.Another researcher, UBC astronomer Jamie Mathew, pointed out: "The Milky Way has at most 400 billion stars, of which 7% are G-type stars, which means that there may be less than 6 billion Earth like planets in the Milky Way."[75]
Galaxy age
2004, based onEuropean Southern Observatory(ESO) reported that the Milky Way is about 13.6 billion years old, almost as old as the universe.A team of many astronomers used it in 2004Very large telescope(VLT)ultraviolet raysVisual matrixa spectrometerFor the first time in globular clustersNGC 6397Beryllium has been found in two stars of.This discovery led them toFirst generation starsAndSecond generation starsThe time of alternation is advanced by 200 million to 300 million years, so it is estimated thatGlobular clusterIs about 12.9 ± 0.5 billion years old, so the age of the Milky Way Galaxy will not be less than 12.2 ± 0.8 billion years old[76]。
The Future of the Galaxy
Andromeda Galaxy, one of the few blue shifting galaxies, is approaching the Milky Way.
Current observations suggest thatAndromeda galaxy（M31）It is moving towards the Milky Way at a speed of 300 kilometers per second, and may hit the Milky Way in 3 billion to 4 billion years.But even if there is a collision, the sun and other stars will not collide with each other, but the two galaxies may take billions of years to merge intoElliptical galaxy。[77-78]
Astronomers useHawaii、CaribbeanRegional and northeastern United StatesAstronomical telescopeThe observation concluded that the volume of the Milky Way Galaxy was about 50% larger than previously estimated[62]。Scientists pointed out that the larger the size, the greater the possibility of catastrophic collision with neighboring galaxies.However, even if it happens, it will be 2 billion to 3 billion years later.
