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121-493: Wolf–Lundmark–Melotte is a rotating disk that is seen edge-on. It is relatively isolated from the rest of the Local Group, and does not seem to show much evidence of interaction. However, the rotation curve of Wolf–Lundmark–Melotte is asymmetrical, in that the receding side and approaching side of the galaxy are rotating in different ways. Although isolated, Wolf–Lundmark–Melotte shows evidence of ram pressure stripping. It

242-470: A "pristine" stellar population and state that make it particularly useful for comparative studies. WLM is currently forming stars, as evidenced by clumps of newly formed stars visible in ultraviolet light. These clumps are about 20 to 100 light-years (7 to 30 parsecs) in size. The youngest clumps are found in the southern half of the galaxy, which has more star formation. The James Webb Space Telescope (JWST) has provided an unprecedentedly detailed view of

363-558: A 1975 meeting of the American Astronomical Society the discovery that most stars in spiral galaxies orbit at roughly the same speed, and that this implied that galaxy masses grow approximately linearly with radius well beyond the location of most of the stars (the galactic bulge ). Rubin presented her results in an influential paper in 1980. These results suggested either that Newtonian gravity does not apply universally or that, conservatively, upwards of 50% of

484-402: A Jupiter-like giant. In 1944, German chemist and physicist Arnold Eucken considered the thermodynamics of Earth condensing and raining-out within a giant protoplanet at pressures of 100–1000 atm. In the 1950s and early 1960s, discussion of planetary formation at such pressures took place, but Cameron's 1963 low-pressure (c. 4–10 atm.) model largely supplanted the idea. Jeans, in 1931, divided

605-538: A Lambda-CDM framework that include baryonic feedback effects reproduce the same relation, without the need to invoke new dynamics (such as MOND). Thus, a contribution due to dark matter itself can be fully predictable from that of the baryons, once the feedback effects due to the dissipative collapse of baryons are taken into account. MOND is not a relativistic theory, although relativistic theories which reduce to MOND have been proposed, such as tensor–vector–scalar gravity (TeVeS), scalar–tensor–vector gravity (STVG), and

726-544: A binary plus the Sun, in which the binary merged and later split because of rotational instability and escaped from the system, leaving a filament that formed between them to be captured by the Sun. Objections of Lyman Spitzer apply to this model also. In 1954, 1975, and 1978, Swedish astrophysicist Hannes Alfvén included electromagnetic effects in equations of particle motions, and angular momentum distribution and compositional differences were explained. In 1954, he first proposed

847-418: A dark matter halo surrounding the galaxy. Though dark matter is by far the most accepted explanation of the rotation problem, other proposals have been offered with varying degrees of success. Of the possible alternatives , one of the most notable is modified Newtonian dynamics (MOND), which involves modifying the laws of gravity. In 1932, Jan Hendrik Oort became the first to report that measurements of

968-406: A flat disc, which then formed planets. However plausible it may appear at first sight, the nebular hypothesis still faces the obstacle of angular momentum ; if the Sun had indeed formed from the collapse of such a cloud, the planets should be rotating far more slowly. The Sun, though it contains almost 99.9 percent of the system's mass, contains just 1 percent of its angular momentum, meaning that

1089-646: A flat rotation curve, a density profile for a galaxy and its environs must be different than one that is centrally concentrated. Newton's version of Kepler's Third Law implies that the spherically symmetric, radial density profile ρ ( r ) is: ρ ( r ) = v ( r ) 2 4 π G r 2 ( 1 + 2   d log ⁡ v ( r ) d log ⁡ r ) {\displaystyle \rho (r)={\frac {v(r)^{2}}{4\pi Gr^{2}}}\left(1+2~{\frac {d\log v(r)}{d\log r}}\right)} where v ( r )

1210-404: A flattened mass distribution more extensive than the light. In 1959, Louise Volders used the same telescope to demonstrate that the spiral galaxy M33 also does not spin as expected according to Keplerian dynamics . Reporting on NGC 3115 , Jan Oort wrote that "the distribution of mass in the system appears to bear almost no relation to that of light... one finds the ratio of mass to light in

1331-420: A gravitational instability caused by primordial density fluctuations. Many cosmologists strive to understand the nature and the history of these ubiquitous dark haloes by investigating the properties of the galaxies they contain (i.e. their luminosities, kinematics, sizes, and morphologies). The measurement of the kinematics (their positions, velocities and accelerations) of the observable stars and gas has become

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1452-474: A high relative velocity in the inter-vortex boundaries and, in these regions, small roller-bearing eddies would coalesce to give annular condensations. This hypothesis was much criticized, as turbulence is a phenomenon associated with disorder and would not spontaneously produce the highly ordered structure required by the hypothesis. It also does not provide a solution to the angular momentum problem or explain lunar formation and other very basic characteristics of

1573-449: A later stage. Pressure fell as gas was lost and diamonds were converted to graphite, while the gas became illuminated by the Sun. Under these conditions, considerable ionization would be present, and the gas would be accelerated by magnetic fields, hence the angular momentum could be transferred from the Sun. Urey postulated that these lunar-size bodies were destroyed by collisions, with the gas dissipating, leaving behind solids collected at

1694-497: A magnetic torque occurred between the disk and the Sun, which came into effect immediately; otherwise, more and more matter would have been ejected, resulting in a massive planetary system exceeding the size of the existing one and comparable to the Sun. The torque caused a magnetic coupling and acted to transfer angular momentum from the Sun to the disk. The magnetic field strength would have to have been 1 gauss. The existence of torque depended on magnetic lines of force being frozen into

1815-519: A mass ratio of at least 8 to 1, and for inner planets, went into independent orbits, while for outer planets, one portion exited the Solar System. The inner protoplanets were Venus-Mercury and Earth-Mars. The moons of the greater planets were formed from "droplets" in the neck connecting the two portions of the dividing protoplanet. These droplets could account for some asteroids. Terrestrial planets would have no major moons, which does not account for

1936-416: A mass structure according to: v ( r ) = ( r d Φ d r ) 1 / 2 {\displaystyle v(r)=\left(r\,{\frac {d\Phi }{dr}}\right)^{1/2}} with Φ the galaxy gravitational potential . Since observations of galaxy rotation do not match the distribution expected from application of Kepler's laws, they do not match

2057-406: A normal star. Ter Haar and Cameron distinguished between those hypotheses that consider a closed system, which is a development of the Sun and possibly a solar envelope, that starts with a protosun rather than the Sun itself, and state that Belot calls these hypotheses monistic; and those that consider an open system, which is where there is an interaction between the Sun and some foreign body that

2178-489: A planetary system or a stellar companion. The two types of planets were assumed to have resulted from the Roche limit. No explanation was offered for the Sun's slow rotation, which Kuiper saw as a larger G-star problem. In Fred Whipple 's 1948 scenario, a smoke cloud about 60,000 AU in diameter and with 1 solar mass ( M ☉ ) contracted and produced the Sun. It had a negligible angular momentum, thus accounting for

2299-431: A process which could produce the massive amounts of energy required to power the Sun. In 1935, Eddington went further and suggested that other elements might also form within stars. Spectral evidence collected after 1945 showed that the distribution of the commonest chemical elements, such as carbon , hydrogen, oxygen , nitrogen , neon , and iron , was fairly uniform across the galaxy, suggesting that these elements had

2420-411: A relatively short period of about 1 million years, and the condensation into what Whipple calls cometismals took place. Aggregation of these cometismals produced giant planets, which in turn produced disks during their formation, which evolved into lunar systems. The formation of terrestrial planets, comets, and asteroids involved disintegration, heating, melting, and solidification. Cameron also formulated

2541-418: A rotation curve that rises from the center to the edge, and most low-surface-brightness galaxies (LSB galaxies) have the same anomalous rotation curve. The rotation curves might be explained by hypothesizing the existence of a substantial amount of matter permeating the galaxy outside of the central bulge that is not emitting light in the mass-to-light ratio of the central bulge. The material responsible for

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2662-399: A roughly 300  M E gas/ice shell that compressed the rocky kernel to about 66 percent of Earth's present diameter. T Tauri eruptions of the Sun stripped the gases away from the inner planets. Mercury was incompletely condensed, and a portion of its gases was stripped away and transported to the region between Mars and Jupiter, where it fused with in-falling oxidized condensate from

2783-635: A seminal 1996 paper. The authors then remarked that a "gently changing logarithmic slope" for a density profile function could also accommodate approximately flat rotation curves over large scales. They found the famous Navarro–Frenk–White profile , which is consistent both with N-body simulations and observations given by ρ ( r ) = ρ 0 r R s ( 1 + r R s ) 2 {\displaystyle \rho (r)={\frac {\rho _{0}}{{\frac {r}{R_{s}}}\left(1+{\frac {r}{R_{s}}}\right)^{2}}}} where

2904-488: A star had passed close to the Sun early in its life, causing tidal bulges, and that this, along with the internal process that leads to solar prominences, resulted in the ejection of filaments of matter from both stars. While most of the material would have fallen back, part of it would remain in orbit. The filaments cooled into numerous, tiny, solid planetesimals and a few larger protoplanets . This model received favorable support for about 3 decades, but passed out of favor by

3025-455: A tool to investigate the nature of dark matter, as to its content and distribution relative to that of the various baryonic components of those galaxies. The rotational dynamics of galaxies are well characterized by their position on the Tully–Fisher relation , which shows that for spiral galaxies the rotational velocity is uniquely related to their total luminosity. A consistent way to predict

3146-457: Is modified Newtonian dynamics (MOND), originally proposed by Mordehai Milgrom in 1983, which modifies the Newtonian force law at low accelerations to enhance the effective gravitational attraction. MOND has had a considerable amount of success in predicting the rotation curves of low-surface-brightness galaxies, matching the baryonic Tully–Fisher relation , and the velocity dispersions of

3267-441: Is a rather complicated process, it is straightforward to model the observables of rotating galaxies through this relationship. So, while state-of-the-art cosmological and galaxy formation simulations of dark matter with normal baryonic matter included can be matched to galaxy observations, there is not yet any straightforward explanation as to why the observed scaling relationship exists. Additionally, detailed investigations of

3388-544: Is far outside of the virial radius of the Milky Way, so it is possible that Wolf–Lundmark–Melotte is currently passing through some relatively dense medium. In 1994, A. E. Dolphin used the Hubble Space Telescope to create a color–magnitude diagram for WLM. It showed that around half of all the star formation in this galaxy occurred during a starburst that started ~13 Gyr ago. During the starburst,

3509-426: Is no consensus on how to explain these so-called hot Jupiters , but one leading idea is that of planetary migration , similar to the process which is thought to have moved Uranus and Neptune to their current, distant orbit. Possible processes that cause the migration include orbital friction while the protoplanetary disk is still full of hydrogen and helium gas and exchange of angular momentum between giant planets and

3630-446: Is supposed to have been the first step in the developments leading to the planetary system, and state that Belot calls these hypotheses dualistic. Hervé Reeves' classification also categorized them as co-genetic with the Sun or not, but also considered their formation from altered or unaltered stellar and interstellar material. He also recognized four groups: models based on the solar nebula, originated by Swedenborg, Kant, and Laplace in

3751-417: Is the radial orbital velocity profile and G is the gravitational constant . This profile closely matches the expectations of a singular isothermal sphere profile where if v ( r ) is approximately constant then the density ρ ∝ r to some inner "core radius" where the density is then assumed constant. Observations do not comport with such a simple profile, as reported by Navarro, Frenk, and White in

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3872-430: Is typically rendered graphically as a plot , and the data observed from each side of a spiral galaxy are generally asymmetric, so that data from each side are averaged to create the curve. A significant discrepancy exists between the experimental curves observed, and a curve derived by applying gravity theory to the matter observed in a galaxy. Theories involving dark matter are the main postulated solutions to account for

3993-486: The Moon . The hypothesis also predicts certain observations, such as the similar angular velocity of Mars and Earth with similar rotation periods and axial tilts. In this scheme, there are six principal planets: two terrestrial, Venus and Earth; two major, Jupiter and Saturn; and two outer, Uranus and Neptune, along with three lesser planets: Mercury, Mars, and Pluto. This hypothesis has some problems, such as failing to explain

4114-488: The Sun , were formed within this collapsing cloud. The gas that formed the Solar System was slightly more massive than the Sun itself. Most of the mass concentrated in the center, forming the Sun, and the rest of the mass flattened into a protoplanetary disk , out of which all of the current planets , moons , asteroids , and other celestial bodies in the Solar System formed. French philosopher and mathematician René Descartes

4235-417: The distribution of stars in spirals and mass-to-light ratios in the stellar disks, they do not match with the masses derived from the observed rotation curves and the law of gravity . A solution to this conundrum is to hypothesize the existence of dark matter and to assume its distribution from the galaxy's center out to its halo . Thus the discrepancy between the two curves can be accounted for by adding

4356-456: The f(R) theory of Capozziello and De Laurentis. A model of galaxy rotation based on a general relativity metric was also proposed, showing that the rotation curves for the Milky Way , NGC 3031 , NGC 3198 and NGC 7331 are consistent with the mass density distributions of the visible matter, avoiding the need for a massive halo of exotic dark matter. According to recent analysis of

4477-474: The formation and evolution of the Solar System began with the Copernican Revolution . The first recorded use of the term " Solar System " dates from 1704. Since the seventeenth century, philosophers and scientists have been forming hypotheses concerning the origins of the Solar System and the Moon and attempting to predict how the Solar System would change in the future. René Descartes was

4598-525: The giant-impact hypothesis for the origin of the Moon. The capture hypothesis, proposed by Michael Mark Woolfson in 1964, posits that the Solar System formed from tidal interactions between the Sun and a low-density protostar . The Sun's gravity would have drawn material from the diffuse atmosphere of the protostar, which would then have collapsed to form the planets. As captured planets would have initially eccentric orbits, Dormand and Woolfson proposed

4719-421: The mass distributions within those systems. The mass estimations for galaxies based on the light they emit are far too low to explain the velocity observations. The galaxy rotation problem is the discrepancy between observed galaxy rotation curves and the theoretical prediction, assuming a centrally dominated mass associated with the observed luminous material. When mass profiles of galaxies are calculated from

4840-473: The metallicity of WLM rose from [Fe/H] ~ −2.2 to [Fe/H] −1.3. There being no horizontal-branch population, Dolphin concludes that no more than ~20  M ☉ per Myr of star formation occurred in the period from 12 to 15 Gyr ago. From 2.5 to 9 Gyr ago, the mean rate of star formation was 100 to 200  M ☉ per Myr. Being at the edge of the Local Group has also protected WLM from interactions and mergers with other galaxies, giving it

4961-420: The "First Galaxy" (the Milky Way ) collided and passed through each other "edge-on" during the "planet-forming era"—implying that the "Lundmark's Nebula" of the series must necessarily be obscured from view by the Milky Way; however, according to others, it could have passed through at an angle and thus be identified with the galaxy described in this article; some have stated that this is the galaxy that E.E. Smith

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5082-475: The 1700s; hypotheses proposing a cloud captured from interstellar space, major proponents being Alfvén and Gustaf Arrhenius in 1978; the binary hypotheses which propose that a sister star somehow disintegrated and a portion of its dissipating material was captured by the Sun, with the principal hypothesizer being Lyttleton in the 1940s; and the close-approach filament ideas of Jeans, Jeffreys, and Woolfson and Dormand. Iwan P. Williams and Alan William Cremin split

5203-662: The German physicist and philosopher Carl Friedrich von Weizsäcker , hearkens back to the Cartesian model by involving a pattern of turbulence-induced eddies in a Laplacian nebular disc. In Weizsäcker's model, a combination of the clockwise rotation of each vortex and the anti-clockwise rotation of the whole system could lead to individual elements moving around the central mass in Keplerian orbits , reducing energy dissipation due to overall motion. However, material would be colliding at

5324-651: The Laplacian nebular model in his Modern Laplacian Theory by suggesting that the angular momentum problem could be resolved by drag created by dust grains in the original disc, which slowed down rotation in the centre. Prentice also suggested that the young Sun transferred some angular momentum to the protoplanetary disc and planetesimals through supersonic ejections understood to occur in T Tauri stars. However, his contention that such formation would occur in toruses or rings has been questioned, as any such rings would disperse before collapsing into planets. The birth of

5445-551: The New Earth Republic of the 101st Century and beyond, which spearheads a programme of colonisation, sending sleeper ships to the Wolf-Lundmark-Melotte galaxy and Andromeda. Rotation curve The rotation curve of a disc galaxy (also called a velocity curve ) is a plot of the orbital speeds of visible stars or gas in that galaxy versus their radial distance from that galaxy's centre. It

5566-414: The Solar System. This model was modified in 1948 by Dutch theoretical physicist Dirk Ter Haar , who hypothesized that regular eddies were discarded and replaced by random turbulence, which would lead to a very thick nebula where gravitational instability would not occur. He concluded the planets must have formed by accretion, and explained the compositional difference between the planets as resulting from

5687-419: The Sun and the other star by their mutual tidal forces , which could have then condensed into planets. In 1929, astronomer Harold Jeffreys countered that such a near-collision was massively unlikely. American astronomer Henry Norris Russell also objected to the hypothesis by showing that it ran into problems with angular momentum for the outer planets, with the planets struggling to avoid being reabsorbed by

5808-479: The Sun should be spinning much more rapidly. Attempts to resolve the angular momentum problem led to the temporary abandonment of the nebular hypothesis in favor of a return to "two-body" hypotheses. For several decades, many astronomers preferred the tidal or near-collision hypothesis put forward by James Jeans in 1917, in which the approach of some other star to the Sun ultimately formed the solar system. This near-miss would have drawn large amounts of matter out of

5929-410: The Sun was born in an open cluster , where stellar collisions are common. Lyttleton showed that terrestrial planets were too small to condense on their own and suggested that one very large proto-planet broke in two because of rotational instability, forming Jupiter and Saturn, with a connecting filament from which the other planets formed. A later model, from 1940 and 1941, involved a triple star system,

6050-404: The Sun's larger gravity. It includes fission in a protoplanetary nebula and excludes a solar nebula. Agglomerations of floccules, which are presumed to compose the supersonic turbulence assumed to occur in the interstellar material from which stars are born, formed the Sun and protoplanets, the latter splitting to form planets. The two portions could not remain gravitationally bound to each other at

6171-412: The Sun's similar property. This smoke cloud captured a smaller one with a large angular momentum. The collapse time for the large smoke and gas nebula is about 100 million years, and the rate was slow at first, increasing in later stages. The planets condensed from small clouds developed in or captured by the second cloud. The orbits would be nearly circular because accretion would reduce eccentricity due to

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6292-541: The Sun. In 1900, Forest Moulton showed that the nebular hypothesis was inconsistent with observations because of the angular momentum. Moulton and Chamberlin in 1904 originated the planetesimal hypothesis . Along with many astronomers of the time, they came to believe the pictures of "spiral nebulas" from the Lick Observatory were direct evidence of the formation of planetary systems , which later turned out to be galaxies. Moulton and Chamberlin suggested that

6413-576: The Whole-Earth Decompression Dynamics (WEDD) model, which includes natural nuclear-fission reactors in planetary cores; Herndon expounds upon it in eleven articles in Current Science from 2005 to 2013 and five books published from 2008 to 2012. He refers to his model as "indivisible" – meaning that the fundamental aspects of Earth are connected logically and causally and can be deduced from its early formation as

6534-537: The absorption of light within the galaxy or to modified dynamics in the outer portions of the spiral and not to any form of missing matter. Babcock's measurements turned out to disagree substantially with those found later, and the first measurement of an extended rotation curve in good agreement with modern data was published in 1957 by Henk van de Hulst and collaborators, who studied M31 with the newly commissioned Dwingeloo 25 meter telescope. A companion paper by Maarten Schmidt showed that this rotation curve could be fit by

6655-562: The age of the Earth. (This collapse time is known as the Kelvin–Helmholtz timescale .) Albert Einstein 's development of the theory of relativity in 1905 led to the understanding that nuclear reactions could create new elements from smaller precursors with the loss of energy. In his treatise Stars and Atoms , Arthur Eddington suggested that pressures and temperatures within stars were great enough for hydrogen nuclei to fuse into helium,

6776-462: The already-disproven binary accretion model as the most common explanation for the formation of the Moon. The most widely accepted model of planetary formation is known as the nebular hypothesis . This model posits that, 4.6   billion years ago, the Solar System was formed by the gravitational collapse of a giant molecular cloud spanning several light-years . Many stars , including

6897-456: The angular momentum problem by assuming that the Sun's slow rotation was peculiar to it and that the planets did not form at the same time as the Sun. Extensions of the model, together forming the Russian school, include Gurevich and Lebedinsky in 1950, Safronov in 1967 and 1969, Ruskol in 1981 Safronov and Vityazeff in 1985, and Safronov and Ruskol in 1994, among others However, this hypothesis

7018-593: The asteroid belt, moons of Jupiter, and Saturn's rings, while Pluto, Triton, the outer satellites of Saturn, the moons of Uranus, the Kuiper Belt, and the Oort cloud formed from the D-cloud. In 1943, Soviet astronomer Otto Schmidt proposed that the Sun, in its present form, passed through a dense interstellar cloud and emerged enveloped in a cloud of dust and gas, from which the planets eventually formed. This solved

7139-602: The band structure, in which he distinguished an A-cloud, containing mostly helium with some solid-particle impurities ("meteor rain"), a B-cloud with mostly carbon, a C-cloud having mainly hydrogen, and a D-cloud made mainly of silicon and iron. Impurities in the A-cloud formed Mars and the Moon (later captured by Earth), impurities in the B-cloud collapsed to form the outer planets, the C-cloud condensed into Mercury, Venus, Earth,

7260-458: The central density, ρ 0 , and the scale radius, R s , are parameters that vary from halo to halo. Because the slope of the density profile diverges at the center, other alternative profiles have been proposed, for example the Einasto profile , which has exhibited better agreement with certain dark matter halo simulations. Observations of orbit velocities in spiral galaxies suggest

7381-399: The core, with the resulting smaller fragments pushed far out into space and the larger fragments staying behind and accreting into planets. He suggested the Moon was such a surviving core. In 1960, 1963, and 1978, W. H. McCrea proposed the protoplanet hypothesis, in which the Sun and planets individually coalesced from matter within the same cloud, with the smaller planets later captured by

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7502-591: The data produced by the Gaia spacecraft , it would seem possible to explain at least the Milky Way 's rotation curve without requiring any dark matter if instead of a Newtonian approximation the entire set of equations of general relativity is adopted. In March 2021, Gerson Otto Ludwig published a model based on general relativity that explains galaxy rotation curves with gravitoelectromagnetism . History of Solar System formation and evolution hypotheses#Tidal theory The history of scientific thought about

7623-419: The disk only if their diameter at the Earth's orbit was less than 1 meter, so as the disk moved outward, a subsidiary disk consisting of only refractories remained behind, where the terrestrial planets would form. The model agrees with the mass and composition of the planets and angular momentum distribution provided the magnetic coupling. However, it does not explain twinning, the low mass of Mars and Mercury, and

7744-420: The disk, a consequence of a well-known magnetohydrodynamic (MHD) theorem on frozen-in lines of force. As the solar condensation temperature when the disk was ejected could not be much more than 1,000 K (730 °C; 1,340 °F), numerous refractories must have been solid, probably as fine smoke particles, which would have grown with condensation and accretion. These particles would have been swept out with

7865-410: The distribution of luminous matter. This implies that spiral galaxies contain large amounts of dark matter or, alternatively, the existence of exotic physics in action on galactic scales. The additional invisible component becomes progressively more conspicuous in each galaxy at outer radii and among galaxies in the less luminous ones. A popular interpretation of these observations is that about 26% of

7986-829: The dwarf galaxy Wolf–Lundmark–Melotte (WLM), demonstrating its capability to resolve individual stars within the galaxy. This high-resolution imagery, part of the Webb Early Release Science (ERS) program 1334 led by Kristen McQuinn of Rutgers University, reveals the structure and composition of WLM with remarkable clarity compared to previous observations by the Spitzer Space Telescope. WLM is a relatively isolated dwarf galaxy located about 3 million light-years from Earth, notable for its chemically unenriched gas similar to that of early universe galaxies. This makes it an excellent subject for studying star formation and evolution in environments that resemble

8107-482: The dynamics of galaxies. The same relation provided a good fit for 2693 samples in 153 rotating galaxies, with diverse shapes, masses, sizes, and gas fractions. Brightness in the near infrared, where the more stable light from red giants dominates, was used to estimate the density contribution due to stars more consistently. The results are consistent with MOND, and place limits on alternative explanations involving dark matter alone. However, cosmological simulations within

8228-447: The early stages of galactic development. WLM has one known globular cluster ( WLM-1 ) at 00 01 29.5 −15° 27′ 51″ that Hodge et al. (1999) determined as having an absolute magnitude of −8.8 and a metallicity of –1.5, with an age of ~15 billion years. This cluster has a luminosity that is slightly over the average for all globulars. The seeming lack of faint low-mass globular clusters cannot be explained by

8349-432: The ecliptic plane. However, most gas giants have substantial axial tilts with respect to the ecliptic, with Uranus having a 98° tilt. The Moon being relatively large with respect to the Earth and other moons in irregular orbits with respect to their planet is yet another issue. It is now believed these observations are explained by events that happened after the initial formation of the Solar System. Attempts to isolate

8470-419: The expansion of galaxies in that stars move away from the hub and moons move away from their planets. He also maintained that planets were expelled, one at a time, from the Sun, specifically from an equatorial bulge caused by rotation, and that one hypothetical planet shattered in this expulsion, leaving the asteroid belt. The Kuiper Belt was unknown at the time, but presumably it, too, would have resulted from

8591-510: The extra mass was dubbed dark matter , the existence of which was first posited in the 1930s by Jan Oort in his measurements of the Oort constants and Fritz Zwicky in his studies of the masses of galaxy clusters . The existence of non-baryonic cold dark matter (CDM) is today a major feature of the Lambda-CDM model that describes the cosmology of the universe . In order to accommodate

8712-434: The fact that the planets all orbit the Sun in the same direction with relatively low eccentricity, which would appear highly unlikely if they were each individually captured. In American astronomer Alastair G. W. Cameron 's hypothesis from 1962 and 1963, the protosun, with a mass of about 1–2 Suns and a diameter of around 100,000 AU, was gravitationally unstable, collapsed, and broke into smaller subunits. The magnetic field

8833-417: The first to hypothesize on the beginning of the Solar System; however, more scientists joined the discussion in the eighteenth century, forming the groundwork for later hypotheses on the topic. Later, particularly in the twentieth century, a variety of hypotheses began to build up, including the now–commonly accepted nebular hypothesis . Meanwhile, hypotheses explaining the evolution of the Sun originated in

8954-456: The galactic center (the dashed line in Fig. 1). Observations of the rotation curve of spirals, however, do not bear this out. Rather, the curves do not decrease in the expected inverse square root relationship but are "flat", i.e. outside of the central bulge the speed is nearly a constant (the solid line in Fig. 1). It is also observed that galaxies with a uniform distribution of luminous matter have

9075-414: The gas and dust disk surrounding the primitive Sun. To explain that volatile elements like mercury could be retained by the terrestrial planets, he postulated a moderately thick gas and dust halo shielding the planets from the Sun. To form diamonds, pure carbon crystals, moon-sized objects, and gas spheres that became gravitationally unstable would have to form in the disk, with the gas and dust dissipating at

9196-587: The impact of meteors on the Sun's surface. Theories at the time suggested that stars evolved moving down the main sequence of the Hertzsprung-Russell diagram , starting as diffuse red supergiants before contracting and heating to become blue main-sequence stars , then even further down to red dwarfs before finally ending up as cool, dense black dwarfs . However, the Sun only has enough gravitational potential energy to power its luminosity by this mechanism for about 30 million years—far less than

9317-420: The influence of the resisting medium, and orbital orientations would be similar because of the size of the small cloud and the common direction of the motions. The protoplanets might have heated up to such high degrees that the more volatile compounds would have been lost, and the orbital velocity decreased with increasing distance so that the terrestrial planets would have been more affected. However, this scenario

9438-663: The inner and smaller partner in each pair was subjected to enormous tidal stresses, causing it to blow up. The explosions took place before they were able to fission off moons. As the six were fluid, they left no trace. Solid planets fissioned off only one moon, and Mercury was a moon of Venus but drifted away as a result of the Sun's gravitational influence. Mars was a moon of Maldek. In J. Marvin Herndon 's model, inner, large-core planets formed by condensation and raining-out from within giant gaseous protoplanets at high pressures and high temperatures. Earth's complete condensation included

9559-457: The inward gravitational force, at different times, giving them different temperatures, sizes, and compositions, and having condensed thereafter with the nebular disk dissipating after some 100 million years, with six planets exploding. Four of these were helium-dominated, fluid, and unstable. These were V (Maldek, V standing for the fifth planet, the first four including Mercury and Mars), K (Krypton), T (transneptunian), and Planet X. In these cases,

9680-453: The key to solving the dwarf galaxy problem of structure formation . Very importantly, the analysis of the inner parts of low and high surface brightness galaxies showed that the shape of the rotation curves in the centre of dark-matter dominated systems indicates a profile different from the NFW spatial mass distribution profile. This so-called cuspy halo problem is a persistent problem for

9801-431: The late '30s and was discarded in the '40s due to the realization it was incompatible with the angular momentum of Jupiter. A part of the hypothesis, planetesimal accretion, was retained. In 1937 and 1940, Raymond Lyttleton postulated that a companion star to the Sun collided with a passing star. Such a scenario had already been suggested and rejected by Henry Russell in 1935, though it may have been more likely assuming

9922-480: The mass of Uranus, shattered to form Earth, Venus, possibly Mercury, the asteroid belt, and Oort Cloud. In 1951, 1962, and 1981, Swiss astronomer Louis Jacot, like Weizsäcker and Ter Haar, continued the Cartesian idea of vortices but proposed a hierarchy of vortices, or vortices within vortices, i.e. a lunar system vortex, a Solar System vortex, and a galactic vortex. He put forward the notion that planetary orbits are spirals, not circles or ellipses. Jacot also proposed

10043-453: The mass of galaxies was contained in the relatively dark galactic halo. Although initially met with skepticism, Rubin's results have been confirmed over the subsequent decades. If Newtonian mechanics is assumed to be correct, it would follow that most of the mass of the galaxy had to be in the galactic bulge near the center and that the stars and gas in the disk portion should orbit the center at decreasing velocities with radial distance from

10164-483: The mass of the Universe is composed of dark matter, a hypothetical type of matter which does not emit or interact with electromagnetic radiation . Dark matter is believed to dominate the gravitational potential of galaxies and clusters of galaxies. Under this theory, galaxies are baryonic condensations of stars and gas (namely hydrogen and helium) that lie at the centers of much larger haloes of dark matter, affected by

10285-477: The massive numbers of planets necessary to evolve into galactic civilizations in both the Milky Way and Lundmark's Nebula, as portrayed in the Lensman series, E.E. Smith thought it would have been necessary for another galaxy to have passed through the Milky Way to produce the large number of close encounters necessary to form so many planets. The Doctor Who novel Synthespians™ by Craig Hinton refers to

10406-507: The material for the formation of the planets is extracted either from the Sun or another star, and models where the material is acquired from interstellar space. They conclude that the best models are Hoyle's magnetic coupling and McCrea's floccules. Woolfson recognized monistic models, which included Laplace, Descartes, Kant, and Weizsäcker, and dualistic models, which included Buffon, Chamberlin-Moulton, Jeans, Jeffreys, and Schmidt-Lyttleton. In 1978, astronomer Andrew J. R. Prentice revived

10527-430: The models between two categories: those that regard the origin and formation of the planets as being essentially related to the Sun, with the two formation processes taking place concurrently or consecutively, and those that regard the formation of the planets as being independent of the formation process of the Sun, the planets forming after the Sun becomes a normal star. The latter category has 2 subcategories: models where

10648-511: The modern, widely accepted hypothesis of planetary formation, the Solar Nebular Disk Model (SNDM), can be traced to the works of Soviet astronomer Victor Safronov . His book Evolution of the protoplanetary cloud and formation of the Earth and the planets , which was translated to English in 1972, had a long-lasting effect on how scientists thought about the formation of the planets. In this book, almost all major problems of

10769-435: The near-circular orbits of the planets were a necessary consequence of their formation. Today, comets are known to be far too small to have created the Solar System in this way. In 1755, Immanuel Kant speculated that observed nebulae could be regions of star and planet formation. In 1796, Laplace elaborated by arguing that the nebula collapsed into a star, and, as it did so, the remaining material gradually spun outward into

10890-425: The nebular model must be revised to account for these discovered planetary systems, or new models considered. Among the extrasolar planets discovered to date are planets the size of Jupiter or larger, but that possess very short orbital periods of only a few hours. Such planets would have to orbit very closely to their stars, so closely that their atmospheres would be gradually stripped away by solar radiation. There

11011-462: The nineteenth century, especially as scientists began to understand how stars in general functioned. In contrast, hypotheses attempting to explain the origin of the Moon have been circulating for centuries, although all of the widely accepted hypotheses were proven false by the Apollo missions in the mid-twentieth century. Following Apollo, in 1984, the giant impact hypothesis was composed, replacing

11132-462: The outer parts of NGC 3115 to be about 250". On page 302–303 of his journal article, he wrote that "The strongly condensed luminous system appears imbedded in a large and more or less homogeneous mass of great density" and although he went on to speculate that this mass may be either extremely faint dwarf stars or interstellar gas and dust, he had clearly detected the dark matter halo of this galaxy. The Carnegie telescope (Carnegie Double Astrograph)

11253-642: The outer reaches of the Solar System and formed the parent material for ordinary chondrite meteorites, the Main-Belt asteroids, and veneer for the inner planets, especially Mars. The differences between the inner planets are primarily the consequence of different degrees of protoplanetary compression. There are two types of responses to decompression-driven planetary volume increases: cracks, which were formed to increase surface area, and folding, which created mountain ranges to accommodate changes in curvature. This planetary formation hypothesis represents an extension of

11374-433: The particles in the protoplanetary disc. One other problem is the detailed features of the planets. The solar nebula hypothesis predicts that all planets will form exactly in the ecliptic plane. Instead, the orbits of the classical planets have various small inclinations with respect to the ecliptic. Furthermore, for the gas giants, it is predicted that their rotations and moon systems will not be inclined with respect to

11495-558: The physical source of the Sun's energy, and thus determine when and how it might ultimately run out, began in the 19th century. In the 19th century, the prevailing scientific view on the source of the Sun's heat was that it was generated by gravitational contraction . In the 1840s, astronomers J. R. Mayer and J. J. Waterson first proposed that the Sun's massive weight would cause it to collapse in on itself, generating heat. Both Hermann von Helmholtz and Lord Kelvin expounded upon this idea in 1854, suggesting that heat may also be produced by

11616-433: The planetary formation process were formulated, and some of them were solved. Safronov's ideas were further developed in the works of George Wetherill , who discovered runaway accretion. By the early 1980s, the nebular hypothesis in the form of SNDM had come back into favor, led by two major discoveries in astronomy. First, several young stars, such as Beta Pictoris , were found to be surrounded by discs of cool dust, much as

11737-424: The planetoid belts. Alfvén formulated the concept of frozen-in magnetic field lines. Gerard Kuiper in 1944 argued, like Ter Haar, that regular eddies would be impossible and postulated that large gravitational instabilities might occur in the solar nebula, forming condensations. In this, the solar nebula could be either co-genetic with the Sun or captured by it. Density distribution would determine what could form,

11858-430: The possibility of a collision. They hypothesized that a filament was thrown out by a passing protostar and was captured by the Sun, resulting in the formation of planets. In this idea, there were 6 original planets, corresponding to 6 point-masses in the filament, with planets A and B , the two innermost, colliding. A , at twice the mass of Neptune, was ejected out of the Solar System, while B , estimated to be one-third

11979-457: The rotation curves of low-surface-brightness galaxies (LSB galaxies) in the 1990s and of their position on the Tully–Fisher relation showed that LSB galaxies had to have dark matter haloes that are more extended and less dense than those of galaxies with high surface brightness, and thus surface brightness is related to the halo properties. Such dark-matter-dominated dwarf galaxies may hold

12100-402: The rotational velocity of a spiral galaxy is to measure its bolometric luminosity and then read its rotation rate from its location on the Tully–Fisher diagram. Conversely, knowing the rotational velocity of a spiral galaxy gives its luminosity. Thus the magnitude of the galaxy rotation is related to the galaxy's visible mass. While precise fitting of the bulge, disk, and halo density profiles

12221-512: The same kind of shattering. The moons, like the planets, originated as equatorial expulsions from their parent planets, with some shattering, leaving the rings, and the Earth was supposed to eventually expel another moon. In this model, there were 4 phases to the planets: no rotation and keeping the same side to the Sun, very slow, accelerated, and daily rotation. Jacot explained the differences between inner and outer planets and inner and outer moons through vortex behavior. Mercury's eccentric orbit

12342-607: The small satellite galaxies of the Local Group . Using data from the Spitzer Photometry and Accurate Rotation Curves (SPARC) database, a group has found that the radial acceleration traced by rotation curves (an effect given the name "radial acceleration relation") could be predicted just from the observed baryon distribution (that is, including stars and gas but not dark matter). This so-called radial acceleration relation (RAR) might be fundamental for understanding

12463-488: The smaller moons exploded because of tidal stresses, leaving the four component belts of the two major planetoid zones. Planet LHB-A, the explosion for which is postulated to have caused the Late Heavy Bombardment (LHB) about 4 eons ago, was twinned with Jupiter, and LHB-B, the explosion for which is postulated to have caused another LHB, was twinned with Saturn. In planets LHB-A, Jupiter, LHB-B, and Saturn,

12584-411: The standard cold dark matter theory. Simulations involving the feedback of stellar energy into the interstellar medium in order to alter the predicted dark matter distribution in the innermost regions of galaxies are frequently invoked in this context. There have been a number of attempts to solve the problem of galaxy rotation by modifying gravity without invoking dark matter. One of the most discussed

12705-401: The star (Williams and Cremin, 1968, loc. cit.). In Hoyle's 1944 model, the Sun's companion star went nova with ejected material captured by the Sun and planets forming from this material. In a version a year later, it was a supernova. In 1955, he proposed a similar system to Laplace, and again proposed the idea with more mathematical detail in 1960. Hoyle's model differs from Laplace's in that

12826-425: The stars in the solar neighborhood indicated that they moved faster than expected when a mass distribution based upon visible matter was assumed, but these measurements were later determined to be essentially erroneous. In 1939, Horace Babcock reported in his PhD thesis measurements of the rotation curve for Andromeda which suggested that the mass-to-luminosity ratio increases radially. He attributed that to either

12947-548: The temperature difference between the inner and outer regions, the former being hotter and the latter being cooler, so only refractories (non-volatiles) condensed in the inner region. A major difficulty was that, in this supposition, turbulent dissipation took place over the course of a single millennium, which did not give enough time for planets to form. The nebular hypothesis was first proposed in 1734 by Swedish scientist Emanuel Swedenborg and later expanded upon by Prussian philosopher Immanuel Kant in 1755. A similar hypothesis

13068-463: The time of writing of these books, the name of Lundmark was associated with such classifications and Smith may have elected to use this as a "believable" name for an entirely fictional galaxy. At the time the Lensman series was written, most astronomers favored the tidal theory of Solar System formation, which required that planets be formed by the close approach of another star. In order to produce

13189-476: The variance. The rotational/orbital speeds of galaxies/stars do not follow the rules found in other orbital systems such as stars/planets and planets/moons that have most of their mass at the centre. Stars revolve around their galaxy's centre at equal or increasing speed over a large range of distances. In contrast, the orbital velocities of planets in planetary systems and moons orbiting planets decline with distance according to Kepler’s third law . This reflects

13310-413: The various models into two groups: those where the material for planet formation came from the Sun, and those where it did not and may be concurrent or consecutive. In 1963, William McCrea divided them into another two groups: those that relate the formation of the planets to the formation of the Sun and those where it is independent of the formation of the Sun, where the planets form after the Sun becomes

13431-534: The weak tidal forces of the WLM system. In E. E. Smith 's Lensman novels, the "Second Galaxy" is identified as "Lundmark's Nebula". However, some believe the "Second Galaxy" may not be the Wolf–Lundmark–Melotte galaxy, since the first chapter of the first novel in the series ( Triplanetary ) and the series-establishing material appearing at the beginning of subsequent novels states that the "Second Galaxy" and

13552-402: Was around 1/100,000 gauss. During the collapse, the magnetic lines of force were twisted. The collapse was fast and occurred due to the dissociation of hydrogen molecules, followed by the ionization of hydrogen and the double ionization of helium. Angular momentum led to rotational instability, which produced a Laplacean disk. At this stage, radiation removed excess energy, the disk would cool over

13673-426: Was developed entirely on observations of the Solar System because it was the only one known until the mid-1990s. It was not confidently assumed to be widely applicable to other planetary systems , although scientists were anxious to test the nebular model by finding protoplanetary discs or even planets around other stars. As of August 30, 2013, the discovery of 941 extrasolar planets has turned up many surprises, and

13794-468: Was explained by its recent expulsion from the Sun and Venus' slow rotation as its being in the "slow rotation phase", having been expelled second to last. The Tom Van Flandern model was first proposed in 1993 in the first edition of his book. In the revised version from 1999 and later, the original Solar System had six pairs of twin planets, and each fissioned off from the equatorial bulges of an overspinning Sun, where outward centrifugal forces exceeded

13915-497: Was independently formulated by the Frenchman Pierre-Simon Laplace in 1796. In 1749, Georges-Louis Leclerc, Comte de Buffon conceived the idea that the planets were formed when a comet collided with the Sun, sending matter out to form the planets. However, Pierre-Simon Laplace refuted this idea in 1796, stating that any planets formed in such a way would eventually crash into the Sun. Laplace felt that

14036-585: Was intended to study this problem of Galactic rotation. In the late 1960s and early 1970s, Vera Rubin , an astronomer at the Department of Terrestrial Magnetism at the Carnegie Institution of Washington , worked with a new sensitive spectrograph that could measure the velocity curve of edge-on spiral galaxies to a greater degree of accuracy than had ever before been achieved. Together with fellow staff-member Kent Ford , Rubin announced at

14157-501: Was predicted by the nebular hypothesis. Second, the Infrared Astronomical Satellite , launched in 1983, observed that many stars had an excess of infrared radiation that could be explained if they were orbited by discs of cooler material. While the broad picture of the nebular hypothesis is widely accepted, many of the details are not well understood and continue to be refined. The refined nebular model

14278-408: Was severely dented by Victor Safronov , who showed that the amount of time required to form the planets from such a diffuse envelope would far exceed the Solar System's determined age. Ray Lyttleton modified the hypothesis by showing that a third body was not necessary and proposing that a mechanism of line accretion, as described by Bondi and Hoyle in 1944, enabled cloud material to be captured by

14399-522: Was the first to propose a model for the origin of the Solar System in his book The World , written from 1629 to 1633. In his view, the universe was filled with vortices of swirling particles, and both the Sun and planets had condensed from a large vortex that had contracted, which he thought could explain the circular motion of the planets. However, this was before the knowledge of Newton's theory of gravity , which explains that matter does not behave in this way. The vortex model of 1944, formulated by

14520-555: Was thinking of when he wrote the series. However, the distance to Lundmark's nebula is defined quite precisely in Gray Lensman as approximately 24 million parsecs, much larger than the distance to Wolf–Lundmark–Melotte (approximately 930,000 parsecs). Additionally, in Second Stage Lensmen multiple references are made to the spiral arms of Lundmark's Nebula. Wolf–Lundmark–Melotte does not possess such structures. At

14641-459: Was weak in that practically all the final regularities are introduced as a prior assumption, and quantitative calculations did not support most of the hypothesizing. For these reasons, it did not gain wide acceptance. American chemist Harold Urey , who founded cosmochemistry , put forward a scenario in 1951, 1952, 1956, and 1966 based largely on meteorites. His model also used Chandrasekhar's stability equations and obtained density distribution in

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