"the Milky Way contained only the mass observed in stars, gas, and other baryonic (ordinary) matter, the rotation speed would decrease with distance from the center. However, the observed curve is relatively flat, indicating that there is additional mass that cannot be detected directly with electromagnetic radiation. This inconsistency is attributed to dark matter. The rotation curve of the Milky Way agrees with the universal rotation curve of spiral galaxies, the best evidence for the existence of dark matter in galaxies. Alternatively, a minority of astronomers propose that a modification of the law of gravity may explain the observed rotation"
"Milky Way The Milky Way is the galaxy that contains our Solar System. The name describes the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. The term ""Milky Way"" is a translation of the Latin ', from the Greek (', ""milky circle""). From Earth, the Milky Way appears as a band because its disk-shaped structure is viewed from within. Galileo Galilei first resolved the band of light into individual stars with his telescope in 1610. Until the early 1920s, most astronomers thought"
"of the Milky Way. The ESA spacecraft ""Gaia"" provides distance estimates by determining the parallax of a billion stars and is mapping the Milky Way with four planned releases of maps in 2022. Milky Way The Milky Way is the galaxy that contains our Solar System. The name describes the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. The term ""Milky Way"" is a translation of the Latin ', from the Greek (', ""milky circle""). From Earth, the Milky Way appears as"
"quarter (), the Milky Way would be approximately the size of the contiguous United States. There is a ring-like filament of stars rippling above and below the relatively flat galactic plane, wrapping around the Milky Way at a diameter of , which may be part of the Milky Way itself. Estimates of the mass of the Milky Way vary, depending upon the method and data used. The low end of the estimate range is 5.8 solar masses (), somewhat less than that of the Andromeda Galaxy. Measurements using the Very Long Baseline Array in 2009 found velocities as large as"
"Like many other galaxies of similar type, the Milky Way consists of a large mass of stars shaped into the form of a relatively flat disc by gravity. The disc is rotating, with the dense central body of stars moving at greater speeds than those toward the rim of the disc. As a result, the pattern of stars within the Galaxy as viewed from directly above or below the disc has formed into a spiral. Because of localised gravitational variations, the spiral pattern has itself formed several distinct 'spiral arms', where particularly large numbers of stars can be found. Norma"
"Milky Way and the position of the Sun was undertaken by William Herschel in 1785 by counting the number of stars in different regions of the sky. He produced a diagram of the shape of the galaxy with the Solar System close to the center. Using a refined approach, Kapteyn in 1920 arrived at the picture of a small (diameter about 15 kiloparsecs) ellipsoid galaxy with the Sun close to the center. A different method by Harlow Shapley based on the cataloguing of globular clusters led to a radically different picture: a flat disk with diameter approximately 70 kiloparsecs and"
"confirmed, this finding would represent the first such substantiation. The Milky Way, and probably most other galaxies too, are surrounded by a halo of dark matter. The shape of the Milky Way has been determined. The research is the first time scientists have measured the three-dimensional shape of a dark matter halo . This section will be expanded. If a massive white dwarf star explodes millions of years from now it could threaten the earth. The Hubble Space Telescope has taken the deepest look into the universe yet, revealing some of the most distant, earliest galaxies to form after the"
"of the mass of the Milky Way appears to be dark matter, an unknown and invisible form of matter that interacts gravitationally with ordinary matter. A dark matter halo is conjectured to spread out relatively uniformly to a distance beyond one hundred kiloparsecs (kpc) from the Galactic Center. Mathematical models of the Milky Way suggest that the mass of dark matter is 1–1.5 . Recent studies indicate a range in mass, as large as 4.5 and as small as 8 . The total mass of all the stars in the Milky Way is estimated to be between 4.6 and 6.43"
"This conjectural mass has been termed ""dark matter"". The rotational period is about 240 million years at the radius of the Sun. The Milky Way as a whole is moving at a velocity of approximately 600 km per second with respect to extragalactic frames of reference. The oldest stars in the Milky Way are nearly as old as the Universe itself and thus probably formed shortly after the Dark Ages of the Big Bang. The Milky Way has several satellite galaxies and is part of the Local Group of galaxies, which form part of the Virgo Supercluster, which is itself"
"of the Milky Way is estimated to have been formed 8.8 ± 1.7 billion years ago. It may have collided with a smaller satellite galaxy, causing the stars in the thin disk to be shaken up and creating the thick disk, while the gas would have settled into the galactic plane and reformed the thin disk. Thin disk The thin disk is a structural component of spiral and S0-type galaxies, composed of stars, gas and dust. The Milky Way's thin disk is thought to have a scale height of around in the vertical axis perpendicular to the disk, and a"
"a component of the Laniakea Supercluster. The Milky Way is visible from Earth as a hazy band of white light, some 30° wide, arching across the night sky. In night sky observing, although all the individual naked-eye stars in the entire sky are part of the Milky Way, the term “Milky Way” is limited to this band of light. The light originates from the accumulation of unresolved stars and other material located in the direction of the galactic plane. Dark regions within the band, such as the Great Rift and the Coalsack, are areas where interstellar dust blocks light from"
"galactic pole is near α Sculptoris. Because of this high inclination, depending on the time of night and year, the arch of the Milky Way may appear relatively low or relatively high in the sky. For observers from latitudes approximately 65° north to 65° south, the Milky Way passes directly overhead twice a day. The Milky Way is the second-largest galaxy in the Local Group, with its stellar disk approximately in diameter and, on average, approximately thick. To compare the relative physical scale of the Milky Way, if the Solar System out to Neptune were the size of a US"
"unknown component termed dark matter. The Milky Way Galaxy is only one of billions of galaxies in the known universe. Galaxies are classified into spirals, ellipticals, irregular, and peculiar. Sizes can range from only a few thousand stars (dwarf irregulars) to 10 stars in giant ellipticals. Elliptical galaxies are spherical or elliptical in appearance. Spiral galaxies range from S0, the lenticular galaxies, to Sb, which have a bar across the nucleus, to Sc galaxies which have strong spiral arms. In total count, ellipticals amount to 13%, S0 to 22%, Sa, b, c galaxies to 61%, irregulars to 3.5% and peculiars"
"of mass is best explained as a supermassive black hole (SMBH) with an estimated mass of 4.1–4.5 million times the mass of the Sun. The rate of accretion of the SMBH is consistent with an inactive galactic nucleus, being estimated at around y. Observations indicate that there are SMBH located near the center of most normal galaxies. The nature of the Milky Way's bar is actively debated, with estimates for its half-length and orientation spanning from and 10–50 degrees relative to the line of sight from Earth to the Galactic Center. Certain authors advocate that the Milky Way features two"
"allows for very precise measurements: Using this information the shape of the Milky Way has been determined to be a spiral galaxy, though the exact number and position of the spiral arms is the subject of ongoing research. Dust and molecules in the interstellar medium not only obscures photometry, but also causes absorption lines in spectroscopy. Their spectral features are generated by transitions of component electrons between different energy levels, or by rotational or vibrational spectra. Detection usually occurs in radio, microwave, or infrared portions of the spectrum. The chemical reactions that form these molecules can happen in cold, diffuse"
"by mutual gravitational attraction. As the Earth is located within the dusty outer arms, there are large portions of the Milky Way that are obscured from view. In the center of the Milky Way is the core, a bar-shaped bulge with what is believed to be a supermassive black hole at its center. This is surrounded by four primary arms that spiral from the core. This is a region of active star formation that contains many younger, population I stars. The disk is surrounded by a spheroid halo of older, population II stars, as well as relatively dense concentrations of"
"Milky Way (Antarctica) The Milky Way is a col situated between the southernmost extremity of the LeMay Range and the Planet Heights mountain range, in the eastern part of Alexander Island, Antarctica. It is the highest point on a possible sledging route between Jupiter Glacier and Uranus Glacier. The col was first mapped from air photos taken by the Ronne Antarctic Research Expedition in 1947–48, by D. Searle of the Falkland Islands Dependencies Survey in 1960. It was named after the Milky Way by the UK Antarctic Place-Names Committee from association with the nearby Planet Heights and the glaciers which"
"curve. The Milky Way began as one or several small overdensities in the mass distribution in the Universe shortly after the Big Bang. Some of these overdensities were the seeds of globular clusters in which the oldest remaining stars in what is now the Milky Way formed. Nearly half the matter in the Milky Way may have come from other distant galaxies. Nonetheless, these stars and clusters now comprise the stellar halo of the Milky Way. Within a few billion years of the birth of the first stars, the mass of the Milky Way was large enough so that it"
"his view, the Milky Way is celestial. According to Mohani Mohamed, the Arabian astronomer Alhazen (965–1037) made the first attempt at observing and measuring the Milky Way's parallax, and he thus ""determined that because the Milky Way had no parallax, it must be remote from the Earth, not belonging to the atmosphere."" The Persian astronomer al-Bīrūnī (973–1048) proposed the Milky Way galaxy to be ""a collection of countless fragments of the nature of nebulous stars."" The Andalusian astronomer Ibn Bâjjah (""Avempace"", 1138) proposed that the Milky Way is made up of many stars that almost touch one another and appear"
"the Milky Way are Canis Major Dwarf (the closest), Sagittarius Dwarf Elliptical Galaxy, Ursa Minor Dwarf, Sculptor Dwarf, Sextans Dwarf, Fornax Dwarf, and Leo I Dwarf. The smallest dwarf galaxies of the Milky Way are only 500 light-years in diameter. These include Carina Dwarf, Draco Dwarf, and Leo II Dwarf. There may still be undetected dwarf galaxies that are dynamically bound to the Milky Way, which is supported by the detection of nine new satellites of the Milky Way in a relatively small patch of the night sky in 2015. There are also some dwarf galaxies that have already been"
"Milky Way is moving at with respect to the photons of the CMB, toward 10.5 right ascension, −24° declination (J2000 epoch, near the center of Hydra). This motion is observed by satellites such as the Cosmic Background Explorer (COBE) and the Wilkinson Microwave Anisotropy Probe (WMAP) as a dipole contribution to the CMB, as photons in equilibrium in the CMB frame get blue-shifted in the direction of the motion and red-shifted in the opposite direction. In the Babylonian epic poem ""Enûma Eliš"", the Milky Way is created from the severed tail of the primeval salt water dragoness Tiamat, set in"
"are named for the planets of the Solar System. Milky Way (Antarctica) The Milky Way is a col situated between the southernmost extremity of the LeMay Range and the Planet Heights mountain range, in the eastern part of Alexander Island, Antarctica. It is the highest point on a possible sledging route between Jupiter Glacier and Uranus Glacier. The col was first mapped from air photos taken by the Ronne Antarctic Research Expedition in 1947–48, by D. Searle of the Falkland Islands Dependencies Survey in 1960. It was named after the Milky Way by the UK Antarctic Place-Names Committee from association"
"galaxy appears to be slightly off-center, with one side of the disk appearing to extend further away from the core than the opposite side. The galaxy is similar in size and structure to the Milky Way, and is often referred to as ""the Milky Way's twin"". However, discoveries in the 2000s regarding the structure of the Milky Way may call this similarity into doubt, particularly because the latter is now believed to be a barred spiral, compared to the unbarred status of NGC 7331. In spiral galaxies the central bulge typically co-rotates with the disk but the bulge in the"
"on account of their concentration and smallness, seem to be cloudy patches. Because of this, it was likened to milk in color."" Actual proof of the Milky Way consisting of many stars came in 1610 when Galileo Galilei used a telescope to study the Milky Way and discovered that it is composed of a huge number of faint stars. In a treatise in 1755, Immanuel Kant, drawing on earlier work by Thomas Wright, speculated (correctly) that the Milky Way might be a rotating body of a huge number of stars, held together by gravitational forces akin to the Solar System"
"Clouds may be moving too fast to be orbiting the Milky Way. Of the galaxies confirmed to be in orbit, the largest is the Sagittarius Dwarf Elliptical Galaxy, which has a diameter of or roughly a fifth that of the Milky Way. Satellite galaxies that orbit from of the edge of the disc of the Milky Way Galaxy to the edge of the dark matter halo of the Milky Way at from the center of the galaxy, are generally depleted in hydrogen gas compared to those that orbit more distantly. This is because of their interactions with the dense hot"
"gas halo of the Milky Way that strip cold gas from the satellites. Satellites beyond that region still retain copious quantities of gas. The Milky Way's satellite galaxies include the following: The Sagittarius Dwarf Spheroidal Galaxy is currently in the process of being consumed by the Milky Way and is expected to pass through it within the next 100 million years. The Sagittarius Stream is a stream of stars in polar orbit around the Milky Way leeched from the Sagittarius Dwarf. The Virgo Stellar Stream is a stream of stars that is believed to have once been an orbiting dwarf"
"absorbed by the Milky Way, such as the progenitor of Omega Centauri. In 2014 researchers reported that most satellite galaxies of the Milky Way actually lie in a very large disk and orbit in the same direction. This came as a surprise: according to standard cosmology, the satellite galaxies should form in dark matter halos, and they should be widely distributed and moving in random directions. This discrepancy is still not fully explained. In January 2006, researchers reported that the heretofore unexplained warp in the disk of the Milky Way has now been mapped and found to be a ripple"
"the center of West. A study was done with the measured parallaxes and motions of 10 massive regions in the Sagittarius spiral arm of the Milky Way where stars are formed. Data was gathered using the BeSSeL Survey with the VLBA, and the results were synthesized to discover the physical properties of these sections (called the Galactocentric azimuth, around −2 and 65 degrees). The results were that the spiral pitch angle of the arms is 7.3 ± 1.5 degrees, and the half-width of the arms of the Milky Way were found to be .2 kpc. The nearest arm from the"
"remote from the earth and did not belong to the atmosphere."" The Persian astronomer Abū Rayhān al-Bīrūnī (973–1048) proposed the Milky Way galaxy to be ""a collection of countless fragments of the nature of nebulous stars."" The Andalusian astronomer Ibn Bajjah (""Avempace"", d. 1138) proposed that the Milky Way was made up of many stars which almost touched one another and appeared to be a continuous image due to the effect of refraction from sublunary material, citing his observation of the conjunction of Jupiter and Mars on 500 AH (1106/1107 AD) as evidence. Ibn Qayyim Al-Jawziyya (1292–1350) proposed the Milky"
"Mpc (33 million–490 million ly) in diameter. The Milky Way is in the Local Group of galaxies, which in turn is in the Laniakea Supercluster. This supercluster spans over 500 million light years, while the Local Group spans over 10 million light years. The Universe also has vast regions of relative emptiness; the largest known void measures 1.8 billion ly (550 Mpc) across. The observable Universe is isotropic on scales significantly larger than superclusters, meaning that the statistical properties of the Universe are the same in all directions as observed from Earth. The Universe is bathed in highly isotropic microwave"
"with the Milky Way during galaxy formation. A search for a stellar stream from the Sagittarius Dwarf Elliptical Galaxy - which is currently merging with the Milky Way - in the vicinity of the sun yielded a null result, which helps constrain the shape of the Milky Way's dark halo. Another study of the highest velocity stars was used to constrain the local Galactic escape velocity and so the mass of the dark halo. RAVE is a precursor to ESA's Gaia mission and studies with RAVE show the science potential of this upcoming survey of stars in the Milky Way."
"disturbance in the spiral arms. Sagittarius Stream In astronomy, the Sagittarius Stream is a long, complex, structure made of stars that wrap around the Milky Way galaxy in an almost polar orbit. It consists of tidally stripped stars from the Sagittarius Dwarf Elliptical Galaxy resulting from the process of merging with the Milky Way over a period of billions of years. This stellar stream was originally proposed in 1995 by Donald Lynden-Bell after analyzing the distribution of globular clusters in the Milky Way. The actual structure was identified by Newberg et al. (2002) and Majewski et al. (2003) using data"
"of faint stars. In 1750 the English astronomer Thomas Wright, in his ""An original theory or new hypothesis of the Universe"", speculated (correctly) that the galaxy might be a rotating body of a huge number of stars held together by gravitational forces, akin to the Solar System but on a much larger scale. The resulting disk of stars can be seen as a band on the sky from our perspective inside the disk. In a treatise in 1755, Immanuel Kant elaborated on Wright's idea about the structure of the Milky Way. The first project to describe the shape of the"