Andromeda Galaxy looks like a spindle shaped elliptical light spot in the northeast sky, which is one of the most distant objects visible to the naked eye.It is generally believed thatAndromeda galaxyyesLocal galaxy groupThe largest galaxy in the Milky Way, similar in appearance to the Milky Way.The members of the local galaxy group include the Andromeda galaxy, the Milky WayTriangle galaxyAnd about 50 small galaxies.According to the improved measurement technology and recent research data, scientists believe that there is a lot of dark matter in the Milky Way, and the proportion of dark matter mass is the largest in this galaxy group.
The Andromeda Galaxy and the Milky Way are located togetherLocal galaxy group, at least 1.6 times the diameter of the Milky Way.Andromeda Galaxy is the largest galaxy in the local galaxy group, moving towards the Milky Way at a speed of 300 kilometers per second, and may collide with the Milky Way in 3-4 billion years, and finally mergeElliptical galaxy。Spitzer Space Telescope The Andromeda Galaxy has nearly one trillion stars, far more than the Milky Way.In 2006, the mass of the Milky Way was re estimated to be about 50% of that of the Andromeda galaxy[1]。
In February 2024, Chinese astronomerThe mass of Andromeda Galaxy is about 1.14 trillion times the mass of the sun.[34]
The earliest observation record of Andromeda galaxy may come from the Persian astronomer Abdul Rahman Sufi（Alsuf），[3]He described it as a "small cloud", and the marks on the star map were also "small clouds" at that time.The first telescope to observe and record isSimon Marius In 1612.
1764messier He was cataloged as M31, and believed that Simon Marius was the discoverer, not aware of the earlier work of Arsufei.
In 1785, astronomerWilliam Herschel He noticed that the core region of the galaxy had reddish mottling, which made him believe that it was the closest "big nebula" among all nebulae, and estimated (incorrect) the distance according to the color and brightness of the nebula should beSiriusWithin 2000 times of[4]。
In 1786,F·W·herschel The first is to list it as a nebula that can be decomposed into stars.
In 1885, aSupernovaAndromeda galaxy (isAndromeda S）[6]This is the first time to see stars in such a distant galaxy.At that time, his brightness was underestimated and was only considered as a new star, so he was called1885 Nova。
In 1917,Heber CurtisA new star in M31 was observed, and 11 new stars were found in the record of search photography.Curtis noticed that the average luminosity of these new stars is about 10 degrees, which is far lower than the magnitude of stars occurring in the Milky Way.This result increases the estimated distance to 500000Light yearHe became“Island universe”Proponents of hypotheses.This hypothesis believes thatSpiral nebulaIs also an independent galaxy[7]。
In 1920, it happenedHarlow Shapley andHeber CurtisBetweenGrand DebateDebate on the scale of the Milky Way, spiral nebula, and the universe.In order to support his claim that M31 is an external galaxy, Curtis proposed that our own Milky Way also has dust clouds that create similar black trails, and there are obviousDoppler shift。
From 1924 to 1925, Hubble identified theCepheid variable, and according toPeripheral light relationCalculate the distance and confirm that it is a star system outside the Milky Way, and then the debate will subside.Use 2.5 meters (100 inches)Reflecting telescopePhotos taken,The distance of M31 is confirmed.Hubble's measurements have confirmed conclusively that these stars and gases are not in our Milky Way, but are all galaxies with a great distance from our Milky Way[8]。
1939BabcockAnd others, measuring the rotation from the center to the edgeSpeed curveFrom which we can know the mass of the galaxy.It is estimated that,The mass of M31 is not less than 3.1tenThe mass of the sun, which is more than twice that of the Milky Way, isLocal galaxy groupThe one with the largest mass in the.M31 has a quasar core at its center, with a diameter of only 25 light-years and a mass equivalent to 10Solar mass, i.e. oneCubic second gapIt gathers 1500 stars.Quasar coreinfrared radiationVery strong, about equal to the radiation of the entire core of the Milky Way.But the radio there is only 1/20 of that of the silver core radio.Radio observations indicate that neutral hydrogen is mostly concentrated in a wide ring with a radius of 10 kiloseconds.The content of hydrogen is 1% of the total mass, which is smaller than that of the Milky Way (1.4-7%).It can be concluded that,Most of M31's gas has formed stars.
Andromeda galaxy
1943-1944,Walter Baade DistinguishAndromeda galaxyThe core part of the celestial body, identify theclusterAnd stars.Based on his observations of the galaxy, he distinguished two stars of different star families. He called the young, fast-moving stars in the galaxy diskFirst Star FamilyIn the old and red nuclear sphereSecond Star FamilyThis naming principle was later quoted in ourGalaxyAnd other occasions.(The phenomenon that stars are divided into two star families was noticed by Ott before that.) He also pointed out that the spatial distribution of star families is similar to that of the Milky Way.Dr. Budd also found thatCepheid variableThere are two different types, which doubled the distance estimation of M31 and also affected the rest of the universe.M31 swivel arm is extremeStar Family I, includingO-B star、Bright supergiant、OB Satellite Association、Ionized hydrogenZone.stayGalactic diskObserved onClassical Cepheid Variable, Nova, Red GiantPlanetary nebulaIsodisk family objects.The central area hasStar Family IICepheid variable stars.Halo familyMember'sGlobular clusterThe distance from the main plane of the galaxy can be more than 30 thousand seconds.It was also found that,The content of heavy elements in M31 members gradually increases from the periphery to the center.This phenomenon shows that the process of star ejected matter causing the increase of heavy elements in interstellar matter is much more frequent in the central region of the galaxy than in the peripheral region[9]。
Andromeda galaxy
In the 1850s,Andromeda galaxyFirst ofRadio electrogramIs created byJohn Baldwin andCambridge Radio Astronomy GroupIt was jointly completed through cooperation.stay2C catalogIn the radio astronomy catalogue, the core of Andromeda galaxy is listed as 2C 56.
In 2006, nine galaxies were found extending along the plane across the core of Andromeda galaxy, rather than randomly scattering around.This may explain thisSatellite galaxyThey have a common origin.
M31It has an important position in the history of astronomy and plays an important role in the study of galaxies, because although it is not the nearest galaxy, it is the nearest giantspiral galaxy。
In February 2023, an international research team led by scientists from Harvard University in the United States, with the help of the Dark Energy Spectrometer (DESI), found a surprising new evidence that a large-scale "galaxy migration" event had occurred in the Andromeda galaxy.This is the first time that scientists have found "galaxy migration" in other galaxies outside the Milky Way, and the related results will be published in the Astrophysical Journal;The researchers explained that this new observation of Andromeda galaxy revealed a "galaxy migration" event in great detail.Although the night sky seems unchanged, the universe is a vibrant place, and galaxies like M31 and the Milky Way contain many components.The research team pointed out that the latest research not only revealed the history of the Andromeda galaxy, but also indirectly revealed the history of the Milky Way.[32]
On September 17, 2023, the Mozi Sky Survey Telescope, which has the strongest optical time domain sky survey capability in the Northern Hemisphere, will be officially put into operation at the Qinghai Lenghu Astronomical Observation Base, which will enable China's time domain astronomical research capability to reach the international advanced level.A photo of the Andromeda galaxy taken by this telescope during its trial observation was released on the same day, which is also the largest high-resolution image of the Andromeda galaxy in the world.[33]
research findings
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Andromeda Galaxy Structure
As early as the 18th century, Emmanuel·Kant Immanuel Kant believed that such nebulae might be huge beyond the Milky WayStellar systemThis insight was not confirmed even at the beginning of the 20th century.Another marketable view is that nebulae are regions of the Milky Way where gas and dust clouds form stars.In the 1920s,Edwin Hubble useMount Wilson ObservatoryThe newly built 100 inch (2.54 meter) telescopeAndromeda NebulaThe outside area card offixed starTo be resolved.
Some of these stars are Cepheid variables.Because of the changes of Cepheid variables and theirAbsolute magnitudeSo Hubble can calculateAndromeda galaxyThis proves that it is indeed another independent galaxy.
Hubble's estimated distance, later mainly through Walter·BudWalter Baade's research has increased after several amendments.Hubble's work confirmed that the Milky Way is just one of many star systems, and the universe extends far beyond the boundaries of the Milky Way.At a distance of 700 kiloseconds, the Andromeda Galaxy will have a diameter of 50 kiloseconds, roughly twice the size of our Milky Way, and contain about 400 billion stars.
It is generally believed that the appearance of the Milky WayAndromeda Galaxy Very similar, both dominateLocal galaxy group。The diffuse light of Andromeda Galaxy is contributed by hundreds of billions of star members.Several bright stars around the image of Andromeda Galaxy are actually stars in our Milky Way Galaxy, which are much closer than the background objects.Andromeda galaxy is also called M31 because it is the 31st diffuse object in the famous Messier Cluster nebula.Stars in the nebula can be divided into about 20 communities, which means they may come fromAndromeda galaxyFor the smaller galaxy "devoured", the diameter of Andromeda galaxy is at least 50 thousand seconds (160000 light years), 1.5 times the diameter of the Milky Way (the diameter of the Milky Way is 100000 light years), and it is the largest galaxy in the local galaxy group.Andromeda galaxy and the Milky Way have many similarities. A comparative study of the two can provide important clues for understanding the movement, structure and evolution of the Milky Way.
Andromeda Galaxy It is the most beautiful celestial body in the autumn sky, and also the first one proved to beExtragalactic galaxyIt is also the farthest celestial body visible to the naked eye.dark substance, probably the highest quality in the group.Spitzer Space Telescope Observation displayAndromeda galaxyThere are nearly one trillion stars, far more than our Milky Way.In 2006, the mass of the Milky Way was re estimated to be about 50% of that of the Andromeda galaxy, about
Solar mass (symbol: M ⊙).
Andromeda galaxy is easy to see with the naked eye in moderately dark sky environment, but such sky only exists in small towns, isolated areas, and places far away from populated areas, and is only slightly light polluted.The Andromeda galaxy visible to the naked eye is very small, because it only has a small area in the center with enough brightness, but this galaxy is completeAngular diameterSeven times the size of the full moon.
In August 2022, the joint research team of Shanghai Astronomical Observatory of the Chinese Academy of Sciences and Shanghai Jiaotong University made important progress in the structure research of Andromeda Galaxy (M31)Exhibition.[31]
In February 2024, Chinese astronomerThe mass of Andromeda Galaxy is about 1.14 trillion times the mass of the sun.Relevant research results were published online in the Monthly Journal of the Royal Astronomical Society.[34]
Satellite galaxy
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Similar to the Milky Way, the Andromeda Galaxy also hasSatellite galaxyThere are 14 dwarf galaxies known, and the most famous and easily observed satellite galaxies areElliptical galaxyM32 and M110.
According to the existing evidence, M32 and M31 seem to have met in the recent past[10]。M32 might have been a large galaxy, but its core was removed from the disk by M31, and experienced a burst of star formation in the core region.
M110 seems to have interacted with M31, and astronomers found thatSatellite galaxyA stripped stream of metal rich stars.[11]M110 contains some dusty paths, suggesting that stars have been continuously forming recently.This isDwarf elliptical galaxyElliptical galaxies are usually devoid of dust and gas.
In 2006, nine galaxies were found crossingAndromeda galaxyThe plane of the core extends rather than scattering around randomly.This may indicate that these satellite galaxies have a common origin[12]。
The satellite galaxy of Andromeda galaxy discovered 1900 years ago
Andromeda galaxy approaches the sun at a speed of about 300 kilometers (180 miles/second) per second, so it is one of the fewblue shiftOne of the galaxies in the Milky Way.Taking into account the speed of the solar system in the Milky Way, the Andromeda Galaxy will approach the Milky Way at a speed of 100-140 km/s (62-87 miles/s).Even so, this does not mean that there will be a collision with the Milky Way in the future, but according to the latest observation data in 2015, the Milky Way may be approaching M31 at a speed of 200 kilometers per second.Even if collision happens, it will be 3 billion (± 10) years later.In this case, the two galaxies will merge into a larger galaxy.stayGalaxy clusterThis kind of event happens frequently.
In 1953, it was found thatCepheid variable, makeAndromeda Galaxy The distance has doubled.In the 1990sIbaku satelliteUsing the distance measured by standard red giant stars and red clusters, calibrate the distance measured by Cepheid variables.
Estimating distance
At least three methods are used to measure the distance of M31.In 2004, usingCepheid variableThe estimated distance is 251 ± 130000 light years (770 ± 40 thousand seconds)[1]。
In 2005, including Ignasi Ribas (Spanish Research Council,CSIC、Institute of Space Studies in Catalonia) and his colleagues, announced the discovery of the Andromeda galaxyEclipsing binary。This pairKonductraThe name (number) of is M31VJ00443799+4129236. The two stars are bright and hot respectivelyO starandB-type star。The study found that the eclipse period is 3.54969 days, which allows astronomers to measure their size.Knowing the size and temperature of the star, we can measureAbsolute magnitude。And I knowApparent magnitudeAnd the absolute magnitude, the distance can be measured.The distance between the two stars was measured as 2.52 million ± 140000 light years, andAndromeda galaxyThe overall distance is 2.5 million light years[13]。This new value is considered to be used alone earlierCepheid variableThe measured distance is more accurate.
Andromeda galaxyIs close enough to take advantage of the Red Giant Branch,TRGB).In 2005, the distance measured by this method was 256 ± 80000 light years (785 ± 25 thousand second difference).
Average the above values, and the distance given by these measurements is estimated to be 253 ± 70000 light years (775 ± 22 thousand seconds difference).
Based on the above distance,The widest diameter of M31 is estimated to be 220000 ± 4000 light years.
quality
Estimating the mass of the Andromeda galaxy (includingdark substance）About 1.23 × 10M⊙ (or 1.23 trillionSolar mass）, equivalent to the mass of the Galaxy (5.8 × 10M⊙).Although the range of error is still too large to be fully confirmed, such results will have confirmed that M31 has a larger mass than the Milky Way, and that M31 is larger and contains more stars than the Milky Way.
M31 seems to have more ordinary stars than the Milky Way, and its estimated brightness is twice that of the Milky Way.But in terms of star formation rate, the Milky Way is much higher,M31 can only produce one solar mass star every year, while the Milky Way is 3-5 solar masses.NovaThe Milky Way is twice as high as M31[14]。This shows that M31 has gone through the stage of star formation, and the Milky Way isStar formationIn the stage of.This means that in the future, the number of stars in the Milky Way will be comparable to that observed in M31.
luminosity
Compared with the Milky Way,Andromeda galaxySeems to be older than
Years old star.[15]The estimated luminosity of Andromeda galaxy is about
L ⊙, 25% higher than our Milky Way.However, when observing the Milky Way from the Earth, it has a high tilt angle, and its interstellar dust absorbs an unknown amount of light, so it is difficult to estimate its actual brightness. Some scientists have given different values of the brightness of the Andromeda Galaxy (some scientists even proposed that it is the second bright galaxy within the 10 trillion second gap of the Milky Way, behind the Sombrero Galaxy[16], the absolute magnitude is about -22.21[17]。
According to recent research,Andromeda galaxyIt is located in the place called "Green Valley" in the color magnitude map of galaxies. This area is composed of galaxies such as the Milky Way. It transits from "blue cloud" (galaxies actively forming new stars) to "red sequence" (galaxies lacking star formation).Star forming activity in Green Valley galaxies is slowing down because they are running out of star forming gas in the interstellar medium.In the simulation galaxy with similar characteristics to Andromeda galaxy, star formation is expected to disappear within about 5 billion years, which can explain the expected short-term growth of star formation rate due to the collision between Andromeda galaxy and galaxies[19]。
Galactic structure
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According to the shape seen in visible light, Andromeda galaxy is classified as SA (s) b under the extension and expansion classification system of de Vaucouleurs Sandagespiral galaxy。However, in the data of 2MASS sky survey,The nuclear sphere of M31 is box shaped, which means that M31 is actuallyBarred spiral galaxy, and we are looking at this galaxy almost in the direction of the long axis.[20]Andromeda galaxy is also a LINRER galaxy (low free nuclear radiation region), which is very common in classificationActive galactic nucleus。
In 2005, astronomers usedKeck telescopeIt is observed that the tiny stars that are sprayed outward are actually part of the main disk body.This meansAndromeda galaxyThe spiral disk surface of is three times larger than that estimated earlier.This evidence shows that the Andromeda Galaxy Disk, with a diameter of more than 220000 light-years, is a huge and extended disk.Earlier estimates of diameter ranged from 70000 to 120000 light years.
The tilt of the galaxy relative to the Earth is estimated to be 77 ° (90 ° is viewed directly from the side). The shape of the cross section of the analyzed galaxy is like the letter S, rather than a flat plane.One of the reasons for this shape warping may be due to the gravity of the satellite galaxy adjacent to M31Interaction。Spectroscopic observations provide detailed measurements of the rotational velocity of galaxies at different radii from the core.In the area near the core, the rotation speed reached a peak of 225 km/s (140 miles/s);It began to decline at a radius of 1300 light years and reached a minimum of 50 km/s (31 miles/s) at 7000 light years.Then, the speed rises steadily, reaching a peak value of 250 km/s (155 miles/s) over a distance of 33000 light years.Beyond this distance, the speed slowly decreased to 200 km/s (124 miles/s) at 80000 light years.These velocity measurements suggest that the mass of the core is about 6 × 10M ⊙, the total mass linearly increases to the radius of 45000 light years, and then gradually slows down with the increase of the radius[21]。
AndromedaSpiral armA series ofIonized hydrogen regionBud described it as "a string of pearls".They seem to be tightly intertwined, but they are far apart in our Milky Way Galaxy.The corrected galaxy map clearly shows that the spiral arm rotates clockwise around thespiral galaxyInside.Two continuous spiral arms are dragging outward from the core about 1600 light years away, and the nearest distance between them is about 13000 light years.The spiral pattern is probably caused byM32Interaction of.These substitutions can be derived from theNeutral hydrogen cloudObserved.
In 1998, fromEuropean Space AgencyOfinfrared space observatory 's image showsAndromeda galaxyThe overall image of the galaxy may be transformed into a ring galaxy.The gas and dust in the Andromeda Galaxy form several overlapping rings, and the most prominent ring is 32000 light-years away from the core.The ring is composed of cold dust, so it is invisible in the visible light image.
More detailed observation shows that there are smaller dust rings inside, which is believed to be caused by the interaction with M32 2 2 million years ago.The simulation shows that the smaller galaxyPolar axisThe direction crossesAndromeda galaxyDisk surface of.The collision stripped more than half of the mass from the smaller M32 and created the ring structure in the Andromeda galaxy[22]。
The research on M31 extended halo shows that it can be compared with the Milky Way in general. The stars in the halo are also metal poor, and become more and more poor with the increase of distance.These evidences show that the two galaxies are following a similar evolutionary path. In the past 12 billion years, they may have swallowed 1-2 hundred low-quality galaxies each.Stars in M31's expanding halo and stars in the Milky Way may be as close as one-third of the distance between the two galaxies.
Galactic core
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M31 has long been known to have a dense and compact star cluster at its core.Under the large telescope, there are many fuzzy stars around the core.The brightness of the core also far exceeds that of the brightestGlobular cluster。
In 1991,Tod R. LauerHubble Space TelescopeWFPC onAndromeda galaxyThe image of the kernel.There are two cores with a gap of 1.5 seconds. The brighter core is marked as P1, which looks like a giantGlobular cluster, the position deviates from the center of the galaxy;The darker one is marked P2, located in the real galaxydynamicsThe center is more like an expansion disk superimposed under a compact ultraviolet radiation star cluster, which is considered to be a relatively massive and ancient core.The motion of the two nuclei suggests that both of them are interacting with a more massive object at the core, which is supposed to be a black hole with a mass of 33 million solar masses, which can explain the observed motion very well.[23]
Subsequently, ground-based observations also confirmed the existence of the two cores, and speculated that the two cores were moving relatively, one of which was a small galaxy swallowed by M31 and undergoing tidal disintegration.The core of many galaxies, including M31, is full of very wild and violently fluctuating regions, and often hasSupermassive black holeIt exists to explain.
Scott Tremaine proposed the following explanation to explain the dual core: P1 is the projection of a star orbiting the central black hole in an abnormal orbit on the disk.This abnormal eccentricity makes the star stay in orbit for a long timeApocentric pointAnd caused the concentration of stars.P2 also contains the high thermal, spectralA-type star。Under the red filter,Type A stars are not obvious, but under blue and ultraviolet light, they are brighter than the main core, causing P2 to appear more prominent than P1[24]。
useEuropean Space AgencyXMM Newton orbital observatory found that M31 has several X-ray sources.Dr. Robin Barnard and others assume that these areblack holeorneutron starThe candidate who heats the incoming gas to tens of millions of KX-ray。Neutron stars and hypothetical black holes have the same spectrum, but can be distinguished from the difference in mass[25]。
Andromeda galaxyAbout 460Globular cluster, the most massive of these clusters, named Mayar II, nicknamed G1 (Gloup one), isLocal galaxy groupOne of the brightest globular clusters in the.It has millions of stars, and its brightness is aboutCentaur omega- Twice as many bright globular clusters as are known in the Milky Way.G1 has several different star families, and its structure is too large in terms of general globular clusters.Therefore, some people believe that G1 was swallowed by M31 beforeDwarf galaxyDebris.
Another large and obvious globular cluster is located in the southwestSwivel armG76 on the east half position.
There are about 200Star AssociationCompared with the galaxy association, the two contain bright blue stars of the same kind, but the former can be up to 10 times larger than the latter.The star association in M31 spans about 1500 light-years, while the Orion and Sirius associations in the Milky Way span 150 light-years.[23]
In 2005, astronomers found a new type of star cluster in M31.The newly discovered star cluster has thousands of stars, which is similar toGlobular clusterbe similar.The difference is that the volume is very large, the diameter reaches hundreds of light years, and the density is hundreds of times lower;The distance between stars is also far[26]。
Collision with the Milky Way
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Andromeda galaxyIs approaching the Milky Way at 110 kilometers per second.[27]When the sun moves around the center of the Milky Way galaxy at a speed of about 225km/s, its speed relative to the sun has been measured to be close to 300km/s[2]。This makes Andromeda galaxy one of about 100 observable blue shifting galaxies.[28]The tangential or lateral velocity of Andromeda galaxy relative to the Milky Way is relatively smaller than the tangential approaching velocity, so it is expected that it will directly collide with the Milky Way in about 4 billion years.One possible result of the collision is that galaxies will merge to form a hugeElliptical galaxy[29], and may even form a largeDisk galaxy。Such events are common in galaxies in galaxy clusters.The fate of the Earth and the solar system at the time of the collision is unknown.Before galaxy merging, it was very unlikely that the solar system would pop out of the Milky Way or join the Andromeda galaxy[30]。
