仙女座星系Andromeda Galaxy

【翻译自wiki,不要和仙女座搞混啦】

The Andromeda Galaxy (IPA: /ænˈdrɒmɪdə/), also known as Messier 31M31, or NGC 224 and originally the Andromeda Nebula (see below), is a spiral galaxy approximately 780 kiloparsecs (2.5 million light-years) from Earth, and the nearest major galaxy to the Milky Way.[4] The galaxy’s name stems from the area of the Earth’s sky in which it appears, the constellation of Andromeda.

仙女座星系(IPA:/ ænˈdrɒmɪdə /),也称为Messier 31,M31或NGC 224,最初被认为只是仙女座星云(见下文),是距地球约780千帕秒(250万光年)的螺旋星系,并且是最接近银河系的主要星系。[4] 这个星系的名字起源于它出现的地球天空区域,即仙女座(星座)。

The virial mass of the Andromeda Galaxy is of the same order of magnitude as that of the Milky Way, at a trillion solar masses (1012M). The mass of either galaxy is difficult to estimate with any accuracy, but it was long thought that the Andromeda Galaxy is more massive than the Milky Way by a margin of some 25% to 50%. This has been called into question by a 2018 study which cited a lower estimate on the mass of the Andromeda Galaxy,[12] combined with preliminary reports on a 2019 study estimating a higher mass of the Milky Way.[13][14] The Andromeda Galaxy has a diameter of about 220,000 light-years, making it the largest member of the Local Group at least in terms of extension, if not mass.

仙女座星系的  virial mass  与银河系的  virial mass  数量级相同,万亿太阳质量(1012M☉)。 很难准确估计出两个星系的质量,但长期以来人们一直认为仙女座星系比银河系质量大25%到50%。 2018年的一项研究对此提出了质疑,该研究引用了仙女座星系质量的较低估计值,[12]以及2019年研究中估计银河系质量较高的初步报告。[13] [14] 仙女座星系的直径约为220,000光年,至少在延伸方面(如果不是质量的话)使其成为Local Group的最大成员。

The number of stars contained in the Andromeda Galaxy is estimated at one trillion (1×1012), or roughly twice the number estimated for the Milky Way.[15]

仙女座星系中包含的恒星数估计为1万亿(1×1012),大约是银河系估计数的两倍。[15]

The Milky Way and Andromeda galaxies are expected to collide in around 4.5 billion years, merging to form a giant elliptical galaxy[16] or a large lenticular galaxy.[17] With an apparent magnitude of 3.4, the Andromeda Galaxy is among the brightest of the Messier objects[18] making it visible to the naked eye from Earth on moonless nights,[19] even when viewed from areas with moderate light pollution.

银河系和仙女星系预计将在大约45亿年内发生碰撞,合并成一个巨大的椭圆形星系[16]或一个大型双凸透镜星系。[17] 仙女星系的视星等为3.4,是Messier 天体中最明亮的天体之一[18],即使在月光较暗的夜晚,即使从中度光污染的地区观看,它也可以从地球肉眼看到[19]。

观察历史Observation history

Great Andromeda Nebula by Isaac Roberts, 1899.

Around the year 964, the Persian astronomer Abd al-Rahman al-Sufi was the first to describe the Andromeda Galaxy. He referred to it in his Book of Fixed Stars as a “nebulous smear”.[20]

大约在964年,波斯天文学家Abd al-Rahman al-Sufi率先描述了仙女星系。 他在《固定星刊》中将其称为“模糊星云”。[20]

Star charts of that period labeled it as the Little Cloud.[21] In 1612, the German astronomer Simon Marius gave an early description of the Andromeda Galaxy based on telescopic observations.[22] Pierre Louis Maupertuis conjectured in 1745 that the blurry spot was an island universe.[23] In 1764, Charles Messier cataloged Andromeda as object M31 and incorrectly credited Marius as the discoverer despite it being visible to the naked eye. In 1785, the astronomer William Herschel noted a faint reddish hue in the core region of Andromeda. He believed Andromeda to be the nearest of all the “great nebulae“, and based on the color and magnitude of the nebula, he incorrectly guessed that it was no more than 2,000 times the distance of Sirius, or roughly 18,000 light years.[24] In 1850, William Parsons, 3rd Earl of Rosse made the first drawing of Andromeda’s spiral structure.

那个时期的星图将其标记为小云。[21] 1612年,德国天文学家西蒙·马吕斯(Simon Marius)根据望远镜的观测结果,对仙女座星系进行了早期描述。[22] 皮埃尔·路易斯·莫佩图伊斯(Pierre Louis Maupertuis)在1745年推测,这个模糊的地方是一个岛屿宇宙。[23] 1764年,查尔斯·梅西耶(Charles Messier)将仙女星系(Andromeda)列为对象M31,并把马吕斯(Marius)误认为发现者,尽管肉眼看不到它。 1785年,天文学家威廉·赫歇尔(William Herschel)在仙女星系(Andromeda)的核心区域发现了淡淡的淡红色调。 他认为仙女星系是所有“大星云”中最接近银河系的星系,并且根据星云的颜色和大小,他错误地猜想它不超过天狼星距离的2,000倍,即大约18,000光年。[24] ] 1850年,罗瑟三世伯爵威廉·帕森斯(William Parsons)绘制了仙女座螺旋结构的第一张图纸。

In 1864, William Huggins noted that the spectrum of Andromeda differed from that of a gaseous nebula.[25] The spectra of Andromeda displays a continuum of frequencies, superimposed with dark absorption lines that help identify the chemical composition of an object. Andromeda’s spectrum is very similar to the spectra of individual stars, and from this, it was deduced that Andromeda has a stellar nature. In 1885, a supernova (known as S Andromedae) was seen in Andromeda, the first and so far only one observed in that galaxy. At the time Andromeda was considered to be a nearby object, so the cause was thought to be a much less luminous and unrelated event called a nova, and was named accordingly; “Nova 1885”.[26]

1864年,威廉·哈金斯(William Huggins)注意到仙女座星系的光谱不同于气态星云的光谱。[25] 仙女座星系的光谱显示出连续的频率,并与暗吸收线重叠,以帮助识别物体的化学成分。 仙女座星系的光谱与单个恒星的光谱非常相似,由此可以推断出仙女座星系具有恒星性质。 1885年,在仙女座星系中发现了超新星(称为S Andromedae),这是该星系中第一个,迄今为止也是唯一的一个被观察到的超新星。 在当时仙女座被认为只是附近的天体,因此起因被认为是发光程度较低且无关的事件,称为新星,并据此命名,“新星1885”。[26]

In 1887, Isaac Roberts took the first photographs of Andromeda, which was still commonly thought to be a nebula within our galaxy. Roberts mistook Andromeda and similar spiral nebulae as solar systems being formed.[citation needed] In 1912, Vesto Slipher used spectroscopy to measure the radial velocity of Andromeda with respect to our Solar System—the largest velocity yet measured, at 300 kilometres per second (190 miles per second).[27]

1887年,艾萨克·罗伯茨(Isaac Roberts)拍摄了仙女座星系的第一张照片,仙女座星系仍被认为是我们银河系中的星云。 Roberts误认为仙女座星系和类似的螺旋状星云正在形成太阳系。[需要引证] 1912年,Vesto Slipher使用光谱法测量了仙女座星系相对于我们太阳系的径向速度,这是迄今为止测得的最大速度,为每秒300公里( 每秒190英里)。[27]

基本信息General


The estimated distance of the Andromeda Galaxy from our own was doubled in 1953 when it was discovered that there is another, dimmer type of Cepheid. In the 1990s, measurements of both standard red giants as well as red clump stars from the Hipparcos satellite measurements were used to calibrate the Cepheid distances.[38][39]

1953年,当发现还有另一种较暗的造父变星时,仙女座星系与我们自己之间的估计距离增加了一倍。 在1990年代,使用Hipparcos卫星测量值对标准的红色巨星和红色团块星的测量值来校准造父变星距离。[38] [39]

形成与历史Formation and history

The Andromeda Galaxy as seen by NASA’s Wide-field Infrared Survey Explorer.
The Andromeda Galaxy was formed roughly 10 billion years ago from the collision and subsequent merger of smaller protogalaxies.[40]

NASA的广域红外勘测浏览器所见的仙女座星系。
仙女座星系大约在100亿年前形成,这是由较小的原星系的碰撞和随后的合并所致。[40]

This violent collision formed most of the galaxy’s (metal-rich) galactic halo and extended disk. During this epoch, its rate of star formation would have been very high, to the point of becoming a luminous infrared galaxy for roughly 100 million years. Andromeda and the Triangulum Galaxy had a very close passage 2–4 billion years ago. This event produced high rates of star formation across the Andromeda Galaxy’s disk—even some globular clusters—and disturbed M33’s outer disk.

这种剧烈的碰撞形成了此星系(富含金属的)大多数的银河晕和扩展盘。 在这个时期,它的恒星形成率将非常高,以至于只大约一亿年就成为发光的红外星系。 仙女座星系和三角星系在2-4亿年前非常接近。 该事件在仙女座星系的星盘(甚至一些球状星团)上产生了很高的恒星形成率,并扰乱了M33的外盘。

Over the past 2 billion years, star formation throughout Andromeda’s disk is thought to have decreased to the point of near-inactivity. There have been interactions with satellite galaxies like M32, M110, or others that have already been absorbed by Andromeda Galaxy. These interactions have formed structures like Andromeda’s Giant Stellar Stream. A galactic merger roughly 100 million years ago is believed to be responsible for a counter-rotating disk of gas found in the center of Andromeda as well as the presence there of a relatively young (100 million years old) stellar population.[40]

在过去的20亿年中,整个仙女座星系盘被认为已经几乎不再形成行星。并且与诸如M32,M110或其他已被仙女座星系吸收的卫星星系发生了相互作用。 这些相互作用形成了像仙女座的巨星流这样的结构。 大约一亿年前的一次星系合并,被认为是仙女座中心发现的反向旋转气体盘以及那里有相对年轻(一亿年前)恒星群的原因。[40]

距离推测Distance estimate

At least four distinct techniques have been used to estimate distances from Earth to the Andromeda Galaxy. In 2003, using the infrared surface brightness fluctuations (I-SBF) and adjusting for the new period-luminosity value and a metallicity correction of −0.2 mag dex−1 in (O/H), an estimate of 2.57 ± 0.06 million light-years (1.625×1011 ± 3.8×109 astronomical units) was derived. A 2004 Cepheid variable method estimated the distance to be 2.51 ± 0.13 million light-years (770 ± 40 kpc).[2][3]

至少使用了四种不同的技术来估计地球到仙女座星系的距离。 2003年,使用红外表面亮度波动(I-SBF)并针对新的周期发光度值进行了调整,并以(O / H)进行了-0.2 mag dex-1的金属度校正,估计为2.57±0.06百万光-年(1.625×1011±3.8×109天文单位)。 2004年的造父变星方法估计距离为2.51±13万光年(770±40 kpc)。

In 2005, an eclipsing binary star was discovered in the Andromeda Galaxy. The binary is two hot blue stars of types O and B. By studying the eclipses of the stars, astronomers were able to measure their sizes. Knowing the sizes and temperatures of the stars, they were able to measure their absolute magnitude. When the visual and absolute magnitudes are known, the distance to the star can be calculated. The stars lie at a distance of 2.52×106 ± 0.14×106 ly (1.594×1011 ± 8.9×109 AU) and the whole Andromeda Galaxy at about 2.5×106 ly (1.6×1011 AU).[4] This new value is in excellent agreement with the previous, independent Cepheid-based distance value. The TRGB method was also used in 2005 giving a distance of 2.56×106 ± 0.08×106 ly (1.619×1011 ± 5.1×109 AU).[5] Averaged together, these distance estimates give a value of 2.54×106 ± 0.11×106 ly (1.606×1011 ± 7.0×109 AU).[a] And, from this, the diameter of Andromeda at the widest point is estimated to be 220 ± 3 kly (67,450 ± 920 pc).[original research?] Applying trigonometry (angular diameter), this is equivalent to an apparent 4.96° angle in the sky.

2005年,在仙女座星系中发现了一颗黯淡的双星。双星是两颗O型和B型炽热蓝星。通过研究类似日食的现象,天文学家能够测量其大小。知道了恒星的大小和温度,他们就能够测量其绝对大小。当已知视大小和绝对大小时,可以计算到恒星的距离。恒星的距离为2.52×106±0.14×106 ly(1.594×1011±8.9×109 AU),整个仙女座星系的距离约为2.5×106 ly(1.6×1011 AU)。[4]这个新值与以前基于造父变星的独立距离值非常一致。 2005年还使用了TRGB方法,距离为2.56×106±0.08×106 ly(1.619×1011±5.1×109 AU)。[5]将这些距离估算值平均在一起得出的值为2.54×106±0.11×106 ly(1.606×1011±7.0×109 AU)。[a]并且,据此,最宽处的仙女座直径估计为220。 ±3 kly(67,450±920 pc)。[原始研究?]应用三角学(角直径),相当于天空中明显的4.96°角。

质量推测Mass estimates

The Andromeda Galaxy pictured in ultraviolet light by GALEX (2003).

Illustration showing both the size of each galaxy and the distance between the two galaxies, to scale.

该图显示了每个星系的大小以及两个星系之间的距离(按比例)。

Giant halo around Andromeda Galaxy.[41]
Until 2018, mass estimates for the Andromeda Galaxy’s halo (including dark matter) gave a value of approximately 1.5×1012 M☉[15] (or 1.5 trillion solar masses) compared to 8×1011 M☉ for the Milky Way. This contradicted earlier measurements, that seemed to indicate that Andromeda Galaxy and the Milky Way are almost equal in mass. In 2018, the equality of mass was re-established by radio results as approximately 8×1011 M☉[42] [43] [44] [45] In 2006, Andromeda Galaxy’s spheroid was determined to have a higher stellar density than that of the Milky Way[46] and its galactic stellar disk was estimated at about twice the diameter of that of the Milky Way.[10] The total stellar mass of Andromeda Galaxy is estimated to be between 8×1011 M☉[42] and 1.1×1012 M☉.,[47][48] (i.e., around twice as massive as that of the Milky Way) and 1.5×1012 M☉, with around 30% of that mass in the central bulge, 56% in the disk, and the remaining 14% in the halo.[49] The radio results (similar mass to Milky Way galaxy) should be taken as likeliest as of 2018, although clearly this matter is still under active investigation by a number of research groups worldwide.

直到2018年,仙女座星系晕圈(包括暗物质)的质量估计值约为1.5×1012M☉[15](或1.5万亿太阳质量),而银河系为8×1011M☉。这与先前的测量相矛盾,这似乎表明仙女座星系和银河系的质量几乎相等。在2018年,通过无线电结果重建了质量相等,约为8×1011M☉[42] [43] [44] [45]在2006年,仙女座星系的球体被确定为具有比银河系更高的恒星密度,[46]其银河系恒星盘的直径大约是银河系直径的两倍。[10]仙女座星系的总恒星质量估计在8×1011M☉[42]和1.1×1012M☉。,[47] [48]之间(即约为银河的两倍)至1.5 ×1012M☉,其中约30%位于中央凸起,其56%位于圆盘中,其余14%位于光晕中。[49]尽管显然这一问题仍在全世界许多研究小组的积极调查中,但直到2018年,其射电结果(与银河系类似的质量)才应被认为是最可能的。

As of 2019 current calculations based on escape velocity and dynamical mass measurements puts the Andromeda Galaxy at 0.8×1012 M☉ [50], which is only half of the Milky Way’s new mass calculations done in 2019, at 1.5×1012 M☉ [51].

截至2019年,基于逃逸速度和动态质量测量的当前计算得出仙女座星系的质量为0.8×1012M☉[50],这只是银河系2019年新质量计算的1.5×1012M☉的一半[51] ]。

In addition to stars, Andromeda Galaxy’s interstellar medium contains at least around 7.2×109 M☉[52] in the form of neutral hydrogen, at least 3.4×108 M☉ as molecular hydrogen (within its innermost 10 kiloparsecs), and 5.4×107 M☉ of dust.[53]

除恒星外,仙女座星系的星际介质还包含至少约7.2×109M☉[52]的中性氢,至少3.4×108M☉的分子氢(在其最里面的10千帕秒内)和5.4×107 M☉的灰尘。[53]

Andromeda Galaxy is surrounded by a massive halo of hot gas that is estimated to contain half the mass of the stars in the galaxy. The nearly invisible halo stretches about a million light-years from its host galaxy, halfway to our Milky Way galaxy. Simulations of galaxies indicate the halo formed at the same time as the Andromeda Galaxy. The halo is enriched in elements heavier than hydrogen and helium, formed from supernovae and its properties are those expected for a galaxy that lies in the “green valley” of the Galaxy color–magnitude diagram (see below). Supernovae erupt in Andromeda Galaxy’s star-filled disk and eject these heavier elements into space. Over Andromeda Galaxy’s lifetime, nearly half of the heavy elements made by its stars have been ejected far beyond the galaxy’s 200,000-light-year-diameter stellar disk.[54][55][56][57]

仙女座星系被巨大的热气环包围,据估计,它们占星系中恒星质量的一半。 从它的宿主星系到我们的银河系的中途,几乎看不见的光晕延伸了约一百万光年。 星系模拟表明与仙女座星系同时形成的光晕。 晕圈富含由超新星形成的比氢和氦重的元素,其性质是色度图“绿色山谷”中的仙女座系预期的性质(请参见下文)。 超新星在仙女座星系的恒星盘中爆发,并将这些较重的元素喷射到太空中。 在仙女座星系的一生中,由其恒星产生的重元素中几乎有一半被抛射到了仙女座星系直径为20万光年的恒星盘之外。[54] [55] [56] [57]

Luminosity estimates

Compared to the Milky Way, the Andromeda Galaxy appears to have predominantly older stars with ages >7×109 years.[49][clarification needed] The estimated luminosity of Andromeda Galaxy, ~2.6×1010 L☉, is about 25% higher than that of our own galaxy.[58] However, the galaxy has a high inclination as seen from Earth and its interstellar dust absorbs an unknown amount of light, so it is difficult to estimate its actual brightness and other authors have given other values for the luminosity of the Andromeda Galaxy (some authors even propose it is the second-brightest galaxy within a radius of 10 mega-parsecs of the Milky Way, after the Sombrero Galaxy,[59] with an absolute magnitude of around -22.21[d] or close[60]).

与银河系相比,仙女座星系似乎主要是年龄大于7×10^9年的较旧恒星。[49] [需要澄清]仙女座星系的估计光度约为2.6×10^10L☉,比我们的银河系高约25%。 。[58] 但是,从地球上看,该星系具有很高的倾角,并且星际尘埃吸收的光量未知,因此很难估算其实际亮度,其他作者也对仙女座星系的光度给出了其他值(有些作者甚至 提出,它是银河系中10兆秒差距内第二明亮的星系,仅次于草帽星系[59],绝对星等约为-22.21 [d]或接近[60]。

An estimation done with the help of Spitzer Space Telescope published in 2010 suggests an absolute magnitude (in the blue) of −20.89 (that with a color index of +0.63 translates to an absolute visual magnitude of −21.52,[b] compared to −20.9 for the Milky Way), and a total luminosity in that wavelength of 3.64×1010 L☉.[61]

The rate of star formation in the Milky Way is much higher, with Andromeda Galaxy producing only about one solar mass per year compared to 3–5 solar masses for the Milky Way. The rate of novae in the Milky Way is also double that of Andromeda Galaxy.[62] This suggests that the latter once experienced a great star formation phase, but is now in a relative state of quiescence, whereas the Milky Way is experiencing more active star formation.[58] Should this continue, the luminosity of the Milky Way may eventually overtake that of Andromeda Galaxy.

银河系中恒星形成的速率要高得多,仙女座星系每年仅产生约1个太阳质量,而银河系则为3-5个太阳质量。 银河系中的新星比率也是仙女座星系的两倍。[62] 这表明后者曾经经历了巨大的恒星形成阶段,但现在处于相对静止状态,而银河正在经历更活跃的恒星形成。[58] 如果这种情况继续下去,银河系的光度最终可能会超过仙女座星系。

According to recent studies, the Andromeda Galaxy lies in what in the galaxy color–magnitude diagram is known as the “green valley”, a region populated by galaxies like the Milky Way in transition from the “blue cloud” (galaxies actively forming new stars) to the “red sequence” (galaxies that lack star formation). Star formation activity in green valley galaxies is slowing as they run out of star-forming gas in the interstellar medium. In simulated galaxies with similar properties to Andromeda Galaxy, star formation is expected to extinguish within about five billion years from the now, even accounting for the expected, short-term increase in the rate of star formation due to the collision between Andromeda Galaxy and the Milky Way.[63]

根据最近的研究,仙女座星系位于星系颜色-幅值图中被称为“绿色山谷”的区域,该区域由银河系(如银河系)从“蓝云”过渡而成(银河系积极形成新的恒星) )到“红色序列”(缺少恒星形成的星系)。 绿谷星系中的恒星形成活动正在放缓,因为它们耗尽了星际介质中的恒星形成气体。 在性质类似于仙女座星系的模拟星系中,恒星形成有望从现在起约50亿年内消失,甚至可以解释由于仙女座星系与恒星系之间碰撞而造成的恒星形成速率的短期预期增长。 银河系。[63]

结构Structure

The Andromeda Galaxy seen in infrared by the Spitzer Space Telescope, one of NASA’s four Great Space Observatories.

斯皮策太空望远镜是美国宇航局的四个大空间天文台之一,在红外线下看到了仙女座星系。

Image of the Andromeda Galaxy taken by Spitzer in infrared, 24 micrometres (Credit:NASA/JPL–Caltech/Karl D. Gordon, University of Arizona).
File:A Swift Tour of M31.ogv
A Swift Tour of Andromeda Galaxy.

A Galaxy Evolution Explorer image of the Andromeda Galaxy. The bands of blue-white making up the galaxy’s striking rings are neighborhoods that harbor hot, young, massive stars. Dark blue-grey lanes of cooler dust show up starkly against these bright rings, tracing the regions where star formation is currently taking place in dense cloudy cocoons. When observed in visible light, Andromeda Galaxy’s rings look more like spiral arms.

仙女座星系的Galaxy Evolution Explorer图像。 组成星系引人注目的环的蓝白色带是一个聚集着炽热,年轻,巨大恒星的社区。 较冷的尘埃的深蓝灰色轨道与这些明亮的环形成鲜明对比,描绘出当前在稠密的多云茧中正在形成恒星的区域。 在可见光下观察时,仙女座星系的戒指看起来更像是螺旋臂。

The ultraviolet view shows that these arms more closely resemble the ring-like structure previously observed in infrared wavelengths with NASA’s Spitzer Space Telescope. Astronomers using the latter interpreted these rings as evidence that the galaxy was involved in a direct collision with its neighbor, M32, more than 200 million years ago.

紫外线视图显示,这些臂更类似于以前使用NASA的Spitzer太空望远镜在红外波长下观察到的环状结构。 使用后者的天文学家将这些环解释为证据,证明这与仙女座星系与两亿多年前的邻居M32直接碰撞有关。

Based on its appearance in visible light, the Andromeda Galaxy is classified as an SA(s)b galaxy in the de Vaucouleurs–Sandage extended classification system of spiral galaxies.[1] However, data from the 2MASS survey showed that Andromeda is actually a barred spiral galaxy, like the Milky Way, with Andromeda’s bar oriented along its long axis.[64]

根据其在可见光下的出现,仙女座星系在螺旋星系的de Vaucouleurs-Sandage扩展分类系统中被分类为SA(s)b星系。[1] 但是,来自2MASS调查的数据表明,仙女座实际上是一个禁止的旋涡星系,就像银河系一样,仙女座的星条沿其长轴定向。[64]

In 2005, astronomers used the Keck telescopes to show that the tenuous sprinkle of stars extending outward from the galaxy is actually part of the main disk itself.[10] This means that the spiral disk of stars in the Andromeda Galaxy is three times larger in diameter than previously estimated. This constitutes evidence that there is a vast, extended stellar disk that makes the galaxy more than 220,000 light-years (67,000 parsecs) in diameter. Previously, estimates of the Andromeda Galaxy’s size ranged from 70,000 to 120,000 light-years (21,000 to 37,000 pc) across.

2005年,天文学家使用凯克望远镜证明,从星系向外延伸的恒星散落实际上是主盘本身的一部分。[10] 这意味着仙女座星系中恒星的螺旋盘直径是先前估计的三倍。 这表明存在着巨大的,延伸的恒星盘,使星系的直径超过了220,000光年(67,000帕秒)。 以前,仙女座星系的大小估计范围为70,000至120,000光年(21,000至37,000 pc)。

The galaxy is inclined an estimated 77° relative to Earth (where an angle of 90° would be viewed directly from the side). Analysis of the cross-sectional shape of the galaxy appears to demonstrate a pronounced, S-shaped warp, rather than just a flat disk.[65] A possible cause of such a warp could be gravitational interaction with the satellite galaxies near the Andromeda Galaxy. The Galaxy M33 could be responsible for some warp in Andromeda’s arms, though more precise distances and radial velocities are required.

该星系相对于地球倾斜约77°(其中从侧面直接观察90°的角度)。 对银河系的横截面形状的分析似乎显示出明显的S形翘曲,而不仅仅是平坦的圆盘。[65] 这种扭曲的可能原因可能是与仙女座星系附近的卫星星系的引力相互作用。 尽管需要更精确的距离和径向速度,但Galaxy M33可能导致仙女座的手臂有些变形。

Spectroscopic studies have provided detailed measurements of the rotational velocity of the Andromeda Galaxy as a function of radial distance from the core. The rotational velocity has a maximum value of 225 kilometres per second (140 mi/s) at 1,300 light-years (82,000,000 astronomical units) from the core, and it has its minimum possibly as low as 50 kilometres per second (31 mi/s) at 7,000 light-years (440,000,000 AU) from the core.

光谱学研究提供了仙女座星系旋转速度作为距岩心径向距离的函数的详细测量结果。 距核心1,300光年(82,000,000天文单位)时,旋转速度的最大值为225公里/秒(140英里/秒),最小值可能低至每秒50公里(31英里/秒) )距离核心7,000光年(440,000,000 AU)。

Further out, rotational velocity rises out to a radius of 33,000 light-years (2.1×109 AU), where it reaches a peak of 250 kilometres per second (160 mi/s). The velocities slowly decline beyond that distance, dropping to around 200 kilometres per second (120 mi/s) at 80,000 light-years (5.1×109 AU). These velocity measurements imply a concentrated mass of about 6×109 M☉ in the nucleus. The total mass of the galaxy increases linearly out to 45,000 light-years (2.8×109 AU), then more slowly beyond that radius.[66]

再往外走,旋转速度上升到半径33,000光年(2.1×109 AU),达到每秒250公里(160 mi / s)的峰值。 速度缓慢下降到该距离之外,在80,000光年(5.1×109 AU)时降至每秒约200公里(120 mi / s)。 这些速度测量意味着在原子核中的集中质量约为6×109M☉。 银河系的总质量线性增加到45,000光年(2.8×109 AU),然后逐渐超出该半径。[66]

The spiral arms of the Andromeda Galaxy are outlined by a series of HII regions, first studied in great detail by Walter Baade and described by him as resembling “beads on a string”. His studies show two spiral arms that appear to be tightly wound, although they are more widely spaced than in our galaxy.[67] His descriptions of the spiral structure, as each arm crosses the major axis of the Andromeda Galaxy, are as follows[68]§pp1062[69]§pp92:

仙女座星系的螺旋臂由一系列HII区域勾勒出轮廓,首先由Walter Baade对其进行了详尽的研究,他将其描述为类似于“串珠”。 他的研究表明,尽管两个螺旋臂的间距比我们银河系中的要宽,但它们似乎缠绕得很紧。[67] 他对每条臂穿过仙女座星系主轴的螺旋结构的描述如下[68]§pp1062[69]§pp92:

【此处省略一张图表~】

Since the Andromeda Galaxy is seen close to edge-on, it is difficult to study its spiral structure. Rectified images of the galaxy seem to show a fairly normal spiral galaxy, exhibiting two continuous trailing arms that are separated from each other by a minimum of about 13,000 light-years (820,000,000 astronomical units) and that can be followed outward from a distance of roughly 1,600 light-years (100,000,000 AU) from the core. Alternative spiral structures have been proposed such as a single spiral arm[70] or a flocculent[71] pattern of long, filamentary, and thick spiral arms.[1][72]

由于只可以看到仙女座星系接近边缘,因此很难研究其螺旋结构。 校正后的星系图像似乎显示出一个相当正常的旋涡星系,显示出两个连续的拖曳臂,它们相互之间的间隔至少约13,000光年(8.2亿天文单位),并且可以从大约大约330毫米的距离向外追踪 距核心1,600光年(100,000,000 AU)。 已经提出了替代的螺旋结构,例如单个螺旋臂[70]或长,丝状和厚螺旋臂的絮状[71]模式。[1] [72]

The most likely cause of the distortions of the spiral pattern is thought to be interaction with galaxy satellites M32 and M110.[73] This can be seen by the displacement of the neutral hydrogen clouds from the stars.[74]

人们认为,最有可能造成螺旋形扭曲的原因是与银河卫星M32和M110的相互作用。[73] 这可以通过从恒星中移出的中性氢云来看出。[74]

In 1998, images from the European Space Agency‘s Infrared Space Observatory demonstrated that the overall form of the Andromeda Galaxy may be transitioning into a ring galaxy. The gas and dust within the galaxy is generally formed into several overlapping rings, with a particularly prominent ring formed at a radius of 32,000 light-years (2.0×109 AU) (10 kiloparsecs) from the core,[75] nicknamed by some astronomers the ring of fire.[76] This ring is hidden from visible light images of the galaxy because it is composed primarily of cold dust, and most of the star formation that is taking place in the Andromeda Galaxy is concentrated there.[77]

1998年,来自欧洲航天局红外太空天文台的图像表明,仙女座星系的整体形式可能正在转变为环形星系。 仙女座星系中的气体和尘埃通常形成几个重叠的环,其中一个特别突出的环形成在距核32,000光年(2.0×109 AU)(10千帕秒)的半径内,[75]由一些天文学家昵称。 火环。[76] 该环在银河系的可见光图像中是隐藏的,因为它主要由冷尘组成,仙女座星系中发生的大多数恒星形成都集中在此。[77]

Later studies with the help of the Spitzer Space Telescope showed how Andromeda Galaxy’s spiral structure in the infrared appears to be composed of two spiral arms that emerge from a central bar and continue beyond the large ring mentioned above. Those arms, however, are not continuous and have a segmented structure.[73]

后来在Spitzer太空望远镜的帮助下进行的研究表明,仙女座星系的红外螺旋结构似乎是由两个螺旋臂组成的,这些臂从中心杆上伸出并超过上述大环。 但是,这些臂不是连续的,而是分段的。[73]

Close examination of the inner region of the Andromeda Galaxy with the same telescope also showed a smaller dust ring that is believed to have been caused by the interaction with M32 more than 200  million years ago. Simulations show that the smaller galaxy passed through the disk of the Andromeda Galaxy along the latter’s polar axis. This collision stripped more than half the mass from the smaller M32 and created the ring structures in Andromeda.[78] It is the co-existence of the long-known large ring-like feature in the gas of Messier 31, together with this newly discovered inner ring-like structure, offset from the barycenter, that suggested a nearly head-on collision with the satellite M32, a milder version of the Cartwheel encounter.[79]

用相同的望远镜仔细观察仙女座星系的内部区域,还发现一个较小的尘埃环,据认为是由两亿多年前与M32的相互作用引起的。 模拟表明,较小的星系沿着仙女座星系的极轴穿过仙女座星系的圆盘。 这次碰撞使较小的M32失去了一半以上的重量,并在仙女座中形成了环形结构。[78] 正是 Messier 31 气体中众所周知的大型环形特征与这种新发现的,远离重心的内部环形结构并存,表明与卫星近乎正面碰撞 M32,  Cartwheel encounter 的温和版本。[79]

Studies of the extended halo of the Andromeda Galaxy show that it is roughly comparable to that of the Milky Way, with stars in the halo being generally “metal-poor“, and increasingly so with greater distance.[46] This evidence indicates that the two galaxies have followed similar evolutionary paths. They are likely to have accreted and assimilated about 100–200 low-mass galaxies during the past 12 billion years.[80] The stars in the extended halos of the Andromeda Galaxy and the Milky Way may extend nearly one third the distance separating the two galaxies.

对仙女座星系扩展光晕的研究表明,它与银河系的光晕大致相当,光晕中的恒星通常“贫金属”,并且距离越来越远。[46] 这一证据表明,两个星系都遵循相似的进化路径。 在过去的120亿年中,它们可能吸收并吸收了100-200个低质量星系。[80] 仙女座星系和银河系延伸光晕中的恒星可能会延伸将两个星系分开的距离近三分之一。

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