The Milky Way is the second-largest galaxy in the Local Group (after the Andromeda Galaxy), with its stellar disk approximately in diameter and, on average, approximately thick. The Milky Way is approximately 890 billion times the mass of the Sun. To compare the relative physical scale of the Milky Way, if the Solar System out to Neptune were the size of a US 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.
Size and mass
Milky Way
Milky Way | Size and mass
Sorry. I cannot find the answer based on the context. It consists of a bar-shaped core region surrounded by a warped disk of gas, dust and stars. it consists of a bar-shaped core region surrounded by a warped disk of gas, dust and stars. The Milky Way consists of a bar-shaped core region surrounded by a warped disk of gas, dust and stars
where is the solar system located in our galaxy
user
The Solar System, is located in the Milky Way's galactic habitable zone.
assistant
what is the milky way?
user
It is the galaxy that contains our Solar System.
assistant
can you tell me the names of the stars that form a part of this galaxy?
user
The Milky Way may contain ten billion white dwarfs, a billion neutron stars, and a hundred million stellar black holes.
assistant
can this galaxy be seen from earth in the northern hemisphere?
user
The Milky Way is visible from Earth as a hazy band of white light, some 30° wide, arching across the night sky.  As viewed from Earth, the visible region of the Milky Way's galactic plane occupies an area of the sky that includes 30 constellations.
assistant
how would you describe its size?
user
The Milky Way is the second-largest galaxy in the Local Group with its stellar disk approximately in diameter and, on average, approximately thick. The Milky Way is approximately 890 billion times the mass of the Sun.
assistant
name the structural parts of this.
user
The Milky Way is the second-largest galaxy in the Local Group (after the Andromeda Galaxy), with its stellar disk approximately in diameter and, on average, approximately thick. The Milky Way is approximately 890 billion times the mass of the Sun. To compare the relative physical scale of the Milky Way, if the Solar System out to Neptune were the size of a US 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.
Milky Way | Size and mass
The Sun is from the Galactic Center. This value is estimated using geometric-based methods or by measuring selected astronomical objects that serve as standard candles, with different techniques yielding various values within this approximate range. In the inner few kpc (around 10,000 light-years radius) is a dense concentration of mostly old stars in a roughly spheroidal shape called the bulge. It has been proposed that the Milky Way lacks a bulge formed due to a collision and merger between previous galaxies, and that instead it only has a "pseudobulge" formed by its central bar. However, confusion in the literature between the (peanut shell)-shaped structure created by instabilities in the bar, versus a possible bulge with an expected half-light radius of 0.5 kpc, abounds.
Milky Way | Galactic Center
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 for stars at the outer edge of the Milky Way. Because the orbital velocity depends on the total mass inside the orbital radius, this suggests that the Milky Way is more massive, roughly equaling the mass of Andromeda Galaxy at 7 within of its center. In 2010, a measurement of the radial velocity of halo stars found that the mass enclosed within 80 kiloparsecs is 7 .
Milky Way | Size and mass
The Milky Way consists of a bar-shaped core region surrounded by a warped disk of gas, dust and stars. The mass distribution within the Milky Way closely resembles the type Sbc in the Hubble classification, which represents spiral galaxies with relatively loosely wound arms. Astronomers first began to conjecture that the Milky Way is a barred spiral galaxy, rather than an ordinary spiral galaxy, in the 1960s. These conjectures were confirmed by the Spitzer Space Telescope observations in 2005 that showed the Milky Way's central bar to be larger than previously thought.
Milky Way | Structure
According to a study published in 2014, the mass of the entire Milky Way is estimated to be 8.5 , but this is only half the mass of the Andromeda Galaxy. A recent mass estimate for the Milky Way is 1.29 . Much of the mass of the Milky Way seems 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 .
Milky Way | Size and mass
For comparison, the Milky Way has a diameter of at least 30,000 parsecs (100,000 ly) and is separated from the Andromeda Galaxy, its nearest large neighbor, by 780,000 parsecs (2.5 million ly.)
Galaxy | Introduction
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 the Sun far from the center. Both analyses failed to take into account the absorption of light by interstellar dust present in the galactic plane, but after Robert Julius Trumpler quantified this effect in 1930 by studying open clusters, the present picture of our host galaxy, the Milky Way, emerged.
Galaxy | Milky Way
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 . In addition to the stars, there is also interstellar gas, comprising 90% hydrogen and 10% helium by mass, with two thirds of the hydrogen found in the atomic form and the remaining one-third as molecular hydrogen. The mass of the Milky Way's interstellar gas is equal to between 10% and 15% of the total mass of its stars. Interstellar dust accounts for an additional 1% of the total mass of the gas.
Milky Way | Size and mass
The stars in the innermost 10,000 light-years form a bulge and one or more bars that radiate from the bulge. The galactic center is an intense radio source known as Sagittarius A*, a supermassive black hole of 4.100 (± 0.034) million solar masses. Stars and gases at a wide range of distances from the Galactic Center orbit at approximately 220 kilometers per second. The constant rotation speed contradicts the laws of Keplerian dynamics and suggests that much (about 90%) of the mass of the Milky Way is invisible to telescopes, neither emitting nor absorbing electromagnetic radiation. This conjectural mass has been termed "dark matter".
Milky Way | Introduction
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 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.
Galaxy | Milky Way
In March 2019, observations from Hubble and data from the European Space Agency's Gaia space observatory were combined to determine that the Milky Way Galaxy weighs approximately 1.5 trillion solar units and has a radius of 129,000 light years.
Hubble Space Telescope | Mass and size of Milky Way
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 Arm | Introduction
The Initial Mass Function of LH 95 does not seem to differ from that typical for the Milky Way.
LH 95 | Introduction
The Galactic Center is marked by an intense radio source named Sagittarius A* (pronounced Sagittarius A-star). The motion of material around the center indicates that Sagittarius A* harbors a massive, compact object. This concentration 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 per year. Observations indicate that there are SMBHs 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.
Milky Way | Galactic Center
Due to conservation of angular momentum, this led the gaseous interstellar medium to collapse from a roughly spheroidal shape to a disk. Therefore, later generations of stars formed in this spiral disk. Most younger stars, including the Sun, are observed to be in the disk. Since the first stars began to form, the Milky Way has grown through both galaxy mergers (particularly early in the Milky Way's growth) and accretion of gas directly from the Galactic halo. The Milky Way is currently accreting material from several small galaxies, including two of its largest satellite galaxies, the Large and Small Magellanic Clouds, through the Magellanic Stream.
Milky Way | Formation
Following the 1920 Great Debate between the astronomers Harlow Shapley and Heber Curtis, observations by Edwin Hubble showed that the Milky Way is just one of many galaxies. The Milky Way is a barred spiral galaxy with an estimated visible diameter between 170,000 and 200,000 light-years (ly). It is estimated to contain 100–400 billion stars and at least that number of planets. The dark matter halo around the Milky Way may span as much as 2 million light years. The Solar System is located at a radius of about 27,000 light-years from the Galactic Center, on the inner edge of the Orion Arm, one of the spiral-shaped concentrations of gas and dust.
Milky Way | Introduction
Many barred spiral galaxies are active, possibly as a result of gas being channeled into the core along the arms. Our own galaxy, the Milky Way, is a large disk-shaped barred-spiral galaxy about 30 kiloparsecs in diameter and a kiloparsec thick. It contains about two hundred billion (2×10) stars and has a total mass of about six hundred billion (6×10) times the mass of the Sun.
Galaxy | Barred spiral galaxy
4 billion solar masses) than the black hole at our Milky Way's center, one of the largest known. The physics that creates the jets is poorly understood, with a likely energy source being matter ejected perpendicular to the accretion disc of the central black hole.
Hercules A | Galaxy
Other astronomers such as Simon Marius, Giovanni Battista Riccioli, and Martinus Hortensius made similar measurements of stars, and Marius and Riccioli concluded the smaller sizes were not small enough to answer Tycho's argument.
Galileo Galilei | Milky Way and stars
Active star formation takes place in the disk (especially in the spiral arms, which represent areas of high density), but does not take place in the halo, as there is little cool gas to collapse into stars. Open clusters are also located primarily in the disk. Discoveries in the early 21st century have added dimension to the knowledge of the Milky Way's structure. With the discovery that the disk of the Andromeda Galaxy (M31) extends much farther than previously thought, the possibility of the disk of the Milky Way extending farther is apparent, and this is supported by evidence from the discovery of the Outer Arm extension of the Cygnus Arm and of a similar extension of the Scutum–Centaurus Arm.
Milky Way | Halo
The total mass of M87 may be 200 times that of the Milky Way.
Messier 87 | Properties
The Solar System orbits within the Milky Way, a barred spiral galaxy that is a prominent member of the Local Group of galaxies. It is a rotating mass of gas, dust, stars and other objects, held together 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.
Astronomy | Galactic astronomy
PKS1353-341 is estimated to have a total mass of 690 trillion solar masses, making it over 1000 times as massive as the Milky Way. Its central galaxy is an extremely bright quasar at a luminosity 46 billion times that of the Sun. This brightness is produced by a superheated disk of matter circling the supermassive black hole at the center of the central galaxy.
PKS1353-341 | Properties
The Milky Way contains between 100 and 400 billion stars and at least that many planets. An exact figure would depend on counting the number of very-low-mass stars, which are difficult to detect, especially at distances of more than from the Sun. As a comparison, the neighboring Andromeda Galaxy contains an estimated one trillion (10) stars. The Milky Way may contain ten billion white dwarfs, a billion neutron stars, and a hundred million stellar black holes. Filling the space between the stars is a disk of gas and dust called the interstellar medium. This disk has at least a comparable extent in radius to the stars, whereas the thickness of the gas layer ranges from hundreds of light-years for the colder gas to thousands of light-years for warmer gas.
Milky Way | Contents
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 was spinning relatively quickly.
Milky Way | Formation
Three stellar components with varying scale heights can be distinguished within the disc of the Milky Way (MW): the "young thin disc", the "old thin disc", and the "thick disc". The "young thin disc" is a region in which star formation is taking place and contains the MW's youngest stars and most of its gas and dust. The scale height of this component is roughly 100 pc. The "old thin disc" has a scale height of approximately 325 pc while the "thick disc" has a scale height of 1.5 kpc. Although stars move primarily within the disc, they exhibit a random enough motion in the direction perpendicular to the disc to result in various scale heights for the different disc components.
Galactic disc | Structure of the Milky Way Disc
The disk of stars in the Milky Way does not have a sharp edge beyond which there are no stars. Rather, the concentration of stars decreases with distance from the center of the Milky Way. For reasons that are not understood, beyond a radius of roughly 40,000 ly (13 kpc) from the center, the number of stars per cubic parsec drops much faster with radius. Surrounding the galactic disk is a spherical Galactic Halo of stars and globular clusters that extends farther outward, but is limited in size by the orbits of two Milky Way satellites, the Large and Small Magellanic Clouds, whose closest approach to the Galactic Center is about .
Milky Way | Contents
To determine the number of stars in the Milky Way, volumes in cubic kiloparsecs (kpc) are selected in various directions. All the stars in these volumes are counted and the total number of stars statistically determined. The number of globular clusters, dust clouds, and interstellar gas is determined in a similar fashion. To determine the number of galaxies in superclusters, volumes in cubic megaparsecs (Mpc) are selected. All the galaxies in these volumes are classified and tallied. The total number of galaxies can then be determined statistically. The huge Boötes void is measured in cubic megaparsecs. In physical cosmology, volumes of cubic gigaparsecs (Gpc) are selected to determine the distribution of matter in the visible universe and to determine the number of galaxies and quasars.
Parsec | Volume units
The Color-color diagram shows ~100 GPs (green crosses), 10,000 comparison galaxies (red points) and 9,500 comparison quasar (purple stars) at similar redshifts to the GPs. The black lines show how these figures are on the diagram. Comparing a GP to the Milky Way can be useful when trying to visualize these star-forming rates. An average GP has a mass of ~3,200 million (~3,200 million solar masses). The Milky Way (MW) is a spiral galaxy and has a mass of ~1,125,000, million (~1,125,000 million solar masses). So the MW has the mass of ~390 GPs.
Pea galaxy | Analysis of the Cardamone 2009 paper
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.
Milky Way | Environment
The Milky Way is the galaxy that contains our Solar System, with the name describing 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 that the Milky Way contained all the stars in the Universe.
Milky Way | Introduction
In 2015, building on the 2002 studies which revealed the Monoceros Ring, an international team of scientists sorting and sifting through galactic data from the Sloan Digital Sky Survey suggested that the Milky Way is actually 50 percent larger than previously thought. It turned out that the disk of the Milky Way is not just a disk of stars in a flat plane, but is instead corrugated. As it radiates outward from the Sun, there appear to be at least four ripples in the disk of the Milky Way. Scientists assume that this pattern is going to be found throughout the disk.
Monoceros Ring | Dispute
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 Galaxy, 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. Brighter regions around the band appear as soft visual patches known as star clouds. The most conspicuous of these is the Large Sagittarius Star Cloud, a portion of the central bulge of the galaxy.
Milky Way | Appearance
This has been called into question by a 2018 study that cited a lower estimate on the mass of the Andromeda Galaxy, combined with preliminary reports on a 2019 study estimating a higher mass of the Milky Way. The Andromeda Galaxy has a diameter of about , making it the largest member of the Local Group in terms of extension, if not mass. The number of stars contained in the Andromeda Galaxy is estimated at one trillion (), or roughly twice the number estimated for the Milky Way.
Andromeda Galaxy | Introduction
The Milky Way is the galaxy that contains our Solar System. Milky Way may also refer to:
Milky Way (disambiguation) | Introduction
As an elliptical galaxy, the galaxy is a spheroid rather than a flattened disc, accounting for the substantially larger mass of M87. Within a radius of , the mass is times the mass of the Sun, which is double the mass of the Milky Way galaxy. As with other galaxies, only a fraction of this mass is in the form of stars: M87 has an estimated mass to luminosity ratio of ; that is, only about one part in six of the galaxy's mass is in the form of stars that radiate energy. This ratio varies from 5 to 30, approximately in proportion to "r" in the region of from the core.
Messier 87 | Properties
The nature of the Milky Way's bar, which extends across the Galactic Center, is also actively debated, with estimates for its half-length and orientation spanning between 1–5 kpc (short or a long bar) and 10–50°. Certain authors advocate that the Milky Way features two distinct bars, one nestled within the other. The bar is delineated by red-clump stars (see also red giant); however, RR Lyrae variables do not trace a prominent Galactic bar. The bar may be surrounded by a ring called the "5-kpc ring" that contains a large fraction of the molecular hydrogen present in the Milky Way, and most of the Milky Way's star formation activity.
Galactic Center | Distance to the Galactic Center
A large enough volume means that the mean motion of galaxies within this volume is equal to the Hubble flow. Astronomers believe the Milky Way is moving at approximately with respect to this local co-moving frame of reference. The Milky Way is moving in the general direction of the Great Attractor and other galaxy clusters, including the Shapley supercluster, behind it. The Local Group (a cluster of gravitationally bound galaxies containing, among others, the Milky Way and the Andromeda Galaxy) is part of a supercluster called the Local Supercluster, centered near the Virgo Cluster: although they are moving away from each other at as part of the Hubble flow, this velocity is less than would be expected given the 16.8 million pc distance due to the gravitational attraction between the Local Group and the Virgo Cluster.
Milky Way | Velocity
The Milky Way and the Andromeda Galaxy are a binary system of giant spiral galaxies belonging to a group of 50 closely bound galaxies known as the Local Group, surrounded by a Local Void, itself being part of the Virgo Supercluster. Surrounding the Virgo Supercluster are a number of voids, devoid of many galaxies, the Microscopium Void to the "north", the Sculptor Void to the "left", the Bootes Void to the "right" and the Canes-Major Void to the South. These voids change shape over time, creating filamentous structures of galaxies. The Virgo Supercluster, for instance, is being drawn towards the Great Attractor, which in turn forms part of a greater structure, called Laniakea.
Milky Way | Environment
Each stream removed is characterized by six parameters: percent of stars in the stream; the angular position in the stripe; the three spatial components (two angles, plus the radial distance from Earth) defining the removed cylinder; and a measure of width. For each search, the server application keeps track of a population of individual stars, each of which is attached to a possible model of the Milky Way.
MilkyWay@home | Purpose and design
A galaxy is a gravitationally bound system of stars, stellar remnants, interstellar gas, dust, and dark matter. The word galaxy is derived from the Greek "" (), literally "milky", a reference to the Milky Way. Galaxies range in size from dwarfs with just a few hundred million () stars to giants with one hundred trillion () stars, each orbiting its galaxy's center of mass. Galaxies are categorized according to their visual morphology as elliptical, spiral, or irregular. Many galaxies are thought to have supermassive black holes at their centers. The Milky Way's central black hole, known as Sagittarius A*, has a mass four million times greater than the Sun.
Galaxy | Introduction
Outside the gravitational influence of the Galactic bar, the structure of the interstellar medium and stars in the disk of the Milky Way is organized into four spiral arms. Spiral arms typically contain a higher density of interstellar gas and dust than the Galactic average as well as a greater concentration of star formation, as traced by H II regions and molecular clouds. The Milky Way's spiral structure is uncertain, and there is currently no consensus on the nature of the Milky Way's spiral arms. Perfect logarithmic spiral patterns only crudely describe features near the Sun, because galaxies commonly have arms that branch, merge, twist unexpectedly, and feature a degree of irregularity.
Milky Way | Spiral arms
However, only about half of those baryons are accounted for in the modern Universe based on observations of nearby galaxies like the Milky Way. If the finding that the mass of the halo is comparable to the mass of the Milky Way is confirmed, it could be the identity of the missing baryons around the Milky Way.
Milky Way | Gaseous halo
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 0.2 kpc. The nearest arm from the Sun is around 1.4 ± 0.2 kpc away.
Sagittarius A | Sagittarius spiral arm
The luminosity and size of this galaxy is mid-way between the Large and Small Magellanic Clouds. De Vaucouleurs and associates classed it as type SAc, suggesting more loosely wound arms. It is inclined at an angle of 65° to the line of sight from the Earth. Although appearing as a disk, there is evidence for a non-axisymmetric form of gas distribution, with a suggestion of central bar plus large-scale spiral arms. The inner structure contains many dark lanes and stellar condensations in its disk. There are two strong H II regions, one to each side. The overall star formation rate is y.
NGC 2976 | Introduction
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 scale length of around in the horizontal axis, in the direction of the radius. For comparison, the Sun is out from the center. The thin disk contributes about 85% of the stars in the Galactic plane and 95% of the total disk stars. It can be set apart from the thick disk of a galaxy since the latter is composed of older population stars created at an earlier stage of the galaxy formation and thus has less heavy elements.
Thin disk | Introduction
Each of them is about 1.3 parsecs from the source star, making whole complex appear 2.6 parsecs long in the sky plane. The whole structure is projected at approximately 30° with respect to the sky plane; this makes its actual length around 3 parsecs. The combined luminosity of the source star and disk is about 24 . It is accreting mass at the rate of per year. Mass loss rate in the approaching jet has been determined to be about per year, which is approximately 7% of the total mass accreted in a year. Around 3.6% of total material in the jet is ionized and average jet density is roughly 1400 cm.
HH 46/47 | Properties
According to Jamil Ragep, the Persian astronomer Naṣīr al-Dīn al-Ṭūsī (1201–1274) in his "Tadhkira" writes: "The Milky Way, i.e. the Galaxy, is made up of a very large number of small, tightly clustered stars, which, on account of their concentration and smallness, seem to be cloudy patches. Because of this, it was likened to milk in color."
Milky Way | Astronomical history
If these arms contain an overdensity of stars compared to the average density of stars in the Galactic disk, it would be detectable by counting the stars near the tangent point. Two surveys of near-infrared light, which is sensitive primarily to red giants and not affected by dust extinction, detected the predicted overabundance in the Scutum–Centaurus arm but not in the Carina–Sagittarius arm: the Scutum–Centaurus Arm contains approximately 30% more red giants than would be expected in the absence of a spiral arm. This observation suggests that the Milky Way possesses only two major stellar arms: the Perseus arm and the Scutum–Centaurus arm.
Milky Way | Spiral arms
The Milky Way is rotating around its dense galactic center, thus the sun is moving in a circle within the galaxy's gravity. Away from the central bulge, or outer rim, the typical stellar velocity is between . All planets and their moons move with the sun. Thus, the solar system is moving.
Motion | Sun and solar system
This was explained by the interstellar dust scattered through the galaxy, resulting in the absorption (extinction) of light or interstellar extinction of light. Trumpler further studied and catalogued open clusters in order to determine the size of the Milky Way galaxy. At first he thought his analysis placed an upper limit on the Milky Way's diameter of about 10,000 parsecs with the Sun located somewhat near the center although he later revised this. While cataloguing open clusters, he also devised a system for their classification according to the number of stars observed within them, how concentrated these stars are in the center of the cluster and the range of their apparent brightness.
Robert Julius Trumpler | Career
M101 is a large galaxy, with a diameter of 170,000 light-years. By comparison, the Milky Way has a diameter of 100,000 light-years. It has around a trillion stars, twice the number in the Milky Way. It has a disk mass on the order of 100 billion solar masses, along with a small central bulge of about 3 billion solar masses. M101 has a high population of H II regions, many of which are very large and bright. H II regions usually accompany the enormous clouds of high density molecular hydrogen gas contracting under their own gravitational force where stars form.
Pinwheel Galaxy | Structure and composition
At this distance or beyond, the orbits of most halo objects would be disrupted by the Magellanic Clouds. Hence, such objects would probably be ejected from the vicinity of the Milky Way. The integrated absolute visual magnitude of the Milky Way is estimated to be around −20.9. Both gravitational microlensing and planetary transit observations indicate that there may be at least as many planets bound to stars as there are stars in the Milky Way, and microlensing measurements indicate that there are more rogue planets not bound to host stars than there are stars. The Milky Way contains at least one planet per star, resulting in 100–400 billion planets, according to a January 2013 study of the five-planet star system Kepler-32 with the Kepler space observatory.
Milky Way | Contents
Certain authors advocate that the Milky Way features two distinct bars, one nestled within the other. However, RR Lyrae variables do not trace a prominent Galactic bar. The bar may be surrounded by a ring called the "5-kpc ring" that contains a large fraction of the molecular hydrogen present in the Milky Way, as well as most of the Milky Way's star formation activity. Viewed from the Andromeda Galaxy, it would be the brightest feature of the Milky Way. X-ray emission from the core is aligned with the massive stars surrounding the central bar and the Galactic ridge. In 2010, two gigantic spherical bubbles of high energy emission were detected to the north and the south of the Milky Way core, using data from the Fermi Gamma-ray Space Telescope.
Milky Way | Galactic Center
The AGN is radio-quiet with no evidence for a relativistic jet. It is powered by one of the largest known supermassive black holes: 23 billion solar masses (based on the molecular disk velocities); or alternatively 10 billion solar masses (based on reverberation mapping). The black hole is surrounded by an accretion disk of material spiraling into it, a few parsecs in size. Further out is a dust torus, a doughnut shaped cloud of dust and gas with a radius of about 100 parsecs. Both the accretion disk and dust torus appear to be almost face-on to us. The radiation from the molecular gas is coming from a flattened disk at the center of the galaxy with a radius of 550 pc.
APM 08279+5255 | Galactic structure
Studies of the Milky Way galaxy have found that approximately 0.1-1% of its total stellar mass is contained within the stellar halo, and that it extends to over 100 kiloparsecs from the galactic centre.
Stellar halo | Milky Way
A study of 27 Milky Way neighbors found that in all dwarf galaxies, the central mass is approximately 10 million solar masses, regardless of whether the galaxy has thousands or millions of stars. This has led to the suggestion that galaxies are largely formed by dark matter, and that the minimum size may indicate a form of warm dark matter incapable of gravitational coalescence on a smaller scale.
Galaxy | Dwarfs
In the core region there is a central condensation with a 230 parsec diameter, which has two concentration peaks. This condensation is being fed by inflow from the spiral arms. The supermassive black hole at the core of this galaxy has 10 solar masses, or about 80 million times the mass of the Sun.
Messier 88 | Properties
This time estimate means that structure seen in BX442 developed roughly 3 billion years after the Big Bang, 10 kiloparsecs (30,000 ly) in diameter, and has a mass of .
BX442 | Introduction
The band then continues the rest of the way around the sky, back to Sagittarius, dividing the sky into two roughly equal hemispheres.
Milky Way | Appearance
This is what determines the size of the HCSS: its radius is roughly the radius of the orbit that has the same velocity around the SMBH as the kick velocity, or where is the mass of the SMBH and the gravitational constant. The size works out to be roughly one-half parsec (pc) (two light years) for a kick of 1000 km/s and a SMBH mass of 100 million solar masses. The largest HCSSs would have sizes of about 20 pc, roughly the same as a large globular cluster, and the smallest would be about a thousandth of a parsec across, smaller than any known star cluster.
Hypercompact stellar system | Properties
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.
Milky Way | Introduction
The Galactic disk is surrounded by a spheroidal halo of old stars and globular clusters, of which 90% lie within of the Galactic Center. However, a few globular clusters have been found farther, such as PAL 4 and AM1 at more than 200,000 light-years from the Galactic Center. About 40% of the Milky Way's clusters are on retrograde orbits, which means they move in the opposite direction from the Milky Way rotation. The globular clusters can follow rosette orbits about the Milky Way, in contrast to the elliptical orbit of a planet around a star. Although the disk contains dust that obscures the view in some wavelengths, the halo component does not.
Milky Way | Halo
3MM-1 has a mass of about 10 solar masses, and stars form in it at about 100 times the rate as in the Milky Way.
3MM-1 | Introduction
A supercluster is a large group of smaller galaxy clusters or galaxy groups; it is among the largest known structures of the universe. The Milky Way is part of the Local Group galaxy group (which contains more than 54 galaxies), which in turn is part of the Virgo Supercluster, which is part of the Laniakea Supercluster. The large size and low density of superclusters means that they, unlike clusters, expand with the Hubble expansion. The number of superclusters in the observable universe is estimated to be 10 million.
Supercluster | Introduction
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 galaxy NGC 7331 is rotating in the opposite direction to the rest of the disk. In both visible light and infrared photos of the NGC 7331, the core of the 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.
NGC 7331 | Introduction
Column 1: Name of the galaxy Column 2: Right ascension for epoch J2000 Column 3: Declination for epoch J2000 Column 4: Blue apparent magnitude of the galaxy Column 5: Galaxy type: E=Elliptical; S0=Lenticular; Sa, Sb, Sc, Sd=Spiral (degree of woundedness of spiral arms); SBa, SBb, SBc, SBd=Barred Spiral; SAB= Intermediate Spiral (between barred and unbarred); Sm, SBm, Irr=Irregular; (r),(rs)=Ring Structure Column 6: Angular diameter of the galaxy (arcminutes) Column 7: Diameter of the galaxy (thousands of light years) Column 8: Recessional velocity (km/s) of the galaxy relative to the cosmic microwave background
Eridanus Cluster | Table of galaxies
To inquire into the origin and fate of a galaxy's halo gas is to inquire into the evolution of said galaxy. HVCs and IVCs are significant features of a spiral galaxy's structure. These clouds are of primary importance when considering a galaxy's Star formation rate (SFR). The Milky Way has approximately 5 billion solar masses of star forming material within its disk and a SFR of 1–3 formula_1 yr. Models for galactic chemical evolution find that at least half of this amount must be continuously accreted, low-metallicity material to describe the current, observable structure. Without this accretion, the SFRs indicate that the current star formation material will only last for another few gigayears (Gyr) at most.
High-velocity cloud | Galactic evolution
NGC 891 looks as the Milky Way would look like when viewed edge-on (some astronomers have even noted how similar to NGC 891 our galaxy looks as seen from the Southern Hemisphere) and, in fact, both galaxies are considered very similar in terms of luminosity and size; studies of the dynamics of its molecular hydrogen have also proven the likely presence of a central bar. Despite this, recent high-resolution images of its dusty disk show unusual filamentary patterns. These patterns are extending into the halo of the galaxy, away from its galactic disk. Scientists presume that supernova explosions caused this interstellar dust to be thrown out of the galactic disk toward the halo.
NGC 891 | Properties
Globular clusters are among the oldest objects in the Milky Way, which thus set a lower limit on the age of the Milky Way. The ages of individual stars in the Milky Way can be estimated by measuring the abundance of long-lived radioactive elements such as thorium-232 and uranium-238, then comparing the results to estimates of their original abundance, a technique called nucleocosmochronology. These yield values of about for CS 31082-001 and for BD +17° 3248. Once a white dwarf is formed, it begins to undergo radiative cooling and the surface temperature steadily drops. By measuring the temperatures of the coolest of these white dwarfs and comparing them to their expected initial temperature, an age estimate can be made.
Milky Way | Age and cosmological history
The spiral structure extends outward from the ring. The ring structure of M95 has a mass of in molecular gas and a star formation rate of yr. The star formation is occurring in at least five regions with diameters between 100 and 150 pc that are composed of several star clusters ranging in size from 1.7 to 4.9 pc. These individual clusters contain of stars, and may be on the path to forming globular clusters.
Messier 95 | Introduction
In contrast, the Milky Way produces only the equivalent of one Sun per year, so these galaxies at the core of the cluster are producing stars at a rate three thousand times greater than the Milky Way on average. Other galaxy clusters at ten billion light years and closer have far less star formation, and this suggests that star formation slows down in large galaxies within clusters after the galaxies have already come together during the development of a galaxy cluster.
CL J1001+0220 | Introduction
This study suggests a high star forming rate of about 2500 "M yr " or a thousand times the star forming rate of the Milky Way. In the paper the name 9io9 is used instead of 9Spitch. The source reconstruction supports a compact core and an extended region, maybe indicative of a jet or lobe coming from an active galactic nucleus (AGN). The galaxy might be in the center of a large galaxy group or cluster and it will likely evolve into a massive elliptical galaxy. Observations with the Northern Extended Millimeter Array (NOEMA) and detailed reconstruction of the lensed galaxy suggests an approximately diameter rotating disk of gas.
9Spitch | Observations
Some estimates have about 85000 in the Milky Way.
RR Lyrae variable | Distribution
Stars with mass less than the Sun's mass, have very long lifetimes, long enough to be discovered. The distinctive chemical patterns of these low mass stars can be used to estimate the mass of the first generation stars. In the past thirty years astronomers have conducted large-scale investigations to find low-mass and metal-poor stars formed in the early Universe. The Sloan Digital Sky Survey (SDSS) and Sloan Extension for Galactic Understanding and Exploration (SEGUE) projects are the latest to obtain evidence for the age, chemical composition and distribution of stars in the Milky Way, and provided crucial clues to understand the structure, formation and evolution of the Milky Way Galaxy.
SDSS J001820.5−093939.2 | Background
ULAS J0015+01 has been thought to either be a remnant of the Milky Way's formation or a merge with a different galaxy. Analysis of the surrounding environment does not favor the presence of a star within such a place of low density important for star formation. Another explanation was that this star was part of a population of stars that was stripped from their parent galaxy by the Milky Way. If it were originally part of the Milky Way, it would have been ejected at a high velocity of around 600 km/s. Another hypothesis was it is part of an unknown galaxy with low surface brightness, but that seems unlikely.
ULAS J0015+01 | Formation
The Milky Way's satellite galaxies include the following:
Satellite galaxies of the Milky Way | List
The stars and gas in the Milky Way rotate about its center differentially, meaning that the rotation period varies with location. As is typical for spiral galaxies, the orbital speed of most stars in the Milky Way does not depend strongly on their distance from the center. Away from the central bulge or outer rim, the typical stellar orbital speed is between . Hence the orbital period of the typical star is directly proportional only to the length of the path traveled. This is unlike the situation within the Solar System, where two-body gravitational dynamics dominate, and different orbits have significantly different velocities associated with them.
Milky Way | Galactic rotation
Whirlpool Galaxy lies 23 million light-years from Earth and has an estimated diameter of 76,000 light-years. Overall the galaxy is about 43% the size of the Milky Way. Its mass is estimated to be 160 billion solar masses. or around 10.3% of the mass of Milky Way Galaxy. A black hole, once thought to be surrounded by a ring of dust, but now believed to be partially occluded by dust instead, exists at the heart of the spiral. A pair of ionization cones extend from the active galactic nucleus.
Whirlpool Galaxy | Properties
With the discovery of the Sagittarius Dwarf Elliptical Galaxy came the discovery of a ribbon of galactic debris as the polar orbit of the dwarf and its interaction with the Milky Way tears it apart. Similarly, with the discovery of the Canis Major Dwarf Galaxy, it was found that a ring of galactic debris from its interaction with the Milky Way encircles the Galactic disk.
Milky Way | Halo
A majority of spiral galaxies, including our own Milky Way galaxy, have a linear, bar-shaped band of stars that extends outward to either side of the core, then merges into the spiral arm structure. In the Hubble classification scheme, these are designated by an "SB", followed by a lower-case letter ("a", "b" or "c") which indicates the form of the spiral arms (in the same manner as the categorization of normal spiral galaxies). Bars are thought to be temporary structures that can occur as a result of a density wave radiating outward from the core, or else due to a tidal interaction with another galaxy.
Galaxy | Barred spiral galaxy
The rest of the arms contain excess gas but not excess old stars. In December 2013, astronomers found that the distribution of young stars and star-forming regions matches the four-arm spiral description of the Milky Way. Thus, the Milky Way appears to have two spiral arms as traced by old stars and four spiral arms as traced by gas and young stars. The explanation for this apparent discrepancy is unclear.
Milky Way | Spiral arms
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 absorbed by the Milky Way, such as the progenitor of Omega Centauri. In 2014 researchers reported that most satellite galaxies of the Milky Way lie in a very large disk and orbit in the same direction.
Milky Way | Environment
A mass deficit is the amount of mass (in stars) that has been removed from the center of a galaxy, presumably by the action of a binary supermassive black hole. The density of stars increases toward the center in most galaxies. In small galaxies, this increase continues into the very center. In large galaxies, there is usually a "core", a region near the center where the density is constant or slowly rising. The size of the core – the "core radius" – can be a few hundred parsecs in large elliptical galaxies. The greatest observed stellar cores reach 3.2 to 5.7 kiloparsecs in radius.
Mass deficit | Introduction
The line strengths yield abundances of different elemental isotopes, from which an estimate of the age of the star can be derived using nucleocosmochronology. Another star, HD 140283, is 14.5 ± 0.7 billion years old.
Milky Way | Age and cosmological history
The Sun orbits the center of the Milky Way, and it is presently moving in the direction of the constellation of Cygnus. A simple model of the motion of a star in the galaxy gives the galactic coordinates , , and as: where , , and are the respective velocities with respect to the local standard of rest, and are the Oort constants, formula_4 is the angular velocity of galactic rotation for the local standard of rest, formula_5 is the "epicyclic frequency", and ν is the vertical oscillation frequency. For the sun, the present values of , , and are estimated as formula_6 km/s, and estimates for the other constants are = 15.5 km/s/kpc, = −12.2 km/s/kpc, κ = 37 km/s/kpc, and ν=74 km/s/kpc.
Sun | Orbit in Milky Way
where formula_11 is the cumulative mass inside the shell at formula_7 and "G" is the gravitational constant. The cumulative mass increases with radius according to the "mass continuity equation:"
Stellar structure | Equations of stellar structure
Finally, the "cd" suffix represents a stage along the spiral sequence that describes the openness of the arms. A rating of "cd" indicates relatively loosely wound arms. This galaxy has an inclination of 54° to the line of sight from the Earth, allowing the structure to be examined without significant obstruction by gas and dust. The disk of the Triangulum galaxy appears warped out to a radius of about 8 kpc. There may be a halo surrounding the galaxy, but there is no bulge at the nucleus. This is an isolated galaxy and there are no indications of recent mergers or interactions with other galaxies, and it lacks the dwarf spheroidals or tidal tails associated with the Milky Way.
Triangulum Galaxy | Structure
To put this in perspective, the mass of all such books required to write out a googolplex would be vastly greater than the masses of the Milky Way and the Andromeda galaxies combined (by a factor of roughly 2.0 x 10), and greater than the mass of the observable universe by a factor of roughly 7 x 10.
Googolplex | Size
The Milky Way appears as a hazy band of faint stars. It is the disc of our own galaxy, viewed edge-on from within it. It appears as a 10°-wide band of diffuse light passing all the way around the sky. It crosses the ecliptic at a high angle. Its most prominent feature is a large dust cloud that forms a dark rift in its southern and western part. There is no almanac in the codices that refers specifically to the Milky Way but there are references to it in almanacs concerned with other phenomena.
Maya astronomy | The Milky Way
For the Milky Way, the galactic habitable zone is commonly believed to be an annulus with an outer radius of about 10 kiloparsecs and an inner radius close to the Galactic Center, both of which lack hard boundaries. NGC 6118 is difficult to see with a small telescope. Amateur astronomers have nicknamed it the "Blinking Galaxy", as it has a tendency to flick in and out of view with different eye positions.
NGC 6118 | Introduction
Timeline of galaxies, clusters of galaxies, and large-scale structure of the universe
Timeline of knowledge about galaxies, clusters of galaxies, and large-scale structure | Introduction
A galaxy is a large gravitational aggregation of stars, dust, gas, and an 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 to 0.9%.
Galactic orientation | Galaxies
The universe can be viewed as having a hierarchical structure. At the largest scales, the fundamental component of assembly is the galaxy. Galaxies are organized into groups and clusters, often within larger superclusters, that are strung along great filaments between nearly empty voids, forming a web that spans the observable universe. Galaxies have a variety of morphologies, with irregular, elliptical and disk-like shapes, depending on their formation and evolutionary histories, including interaction with other galaxies, which may lead to a merger. Disc galaxies encompass lenticular and spiral galaxies with features, such as spiral arms and a distinct halo. At the core, most galaxies have a supermassive black hole, which may result in an active galactic nucleus.
Astronomical object | Galaxy and larger
But it is small, appearing only 4' by 2'. The morphological classification of this galaxy is SAB(rs)bc, indicating a spiral galaxy with a weak central bar (SAB), an incomplete ring structure around the bar (rs), and moderately–wound arms (bc). The plane of the galactic disk is inclined by 64° to the line of sight from the Earth, with the major axis aligned along a position angle of 178°. Within the galaxy's core is an active galactic nucleus tentatively classified as a type I Seyfert. The central supermassive black hole has a relatively low mass, estimated as . The core is a source for X-ray emission that is seen to vary dramatically on time scales as low as hours.
NGC 7314 | Introduction
Its mass has been measured to be around 0.36 solar masses and its radius is about 36% solar radii. Its metallicity is likely slightly less than that of the Sun. Observations at infrared wavelengths rule out the presence of a circumstellar disk around it.
Gliese 251 | Introduction
Alternatively, a hierarchical galaxy formation model is hypothesized under which a portion, possibly large, of the Milky Way's globular clusters would have originated in the accretion of other dwarf spheroidals like Sag DEG. The best candidate for this idea is Palomar 12.
Terzan 7 | Hierarchical galaxy formation
While the inner section of the galaxy shows a symmetrical two-arm structure, it has a single outer spiral arm that wraps 180° around the nucleus, giving the galaxy an overall asymmetric, lopsided appearance. The outer spiral arm has a red component that indicates a significant age. However, the existence of this structure is difficult to explain. The galaxy shows indications of recent starburst activity that may have terminated around 15 million years ago. The active central nucleus shows weak LINER behavior, and it may be an intermediate form between a LINER and an H II region. The luminosity of the X-ray source at the nucleus is in the 0.3–7 keV band.
NGC 1637 | Introduction
Based upon the motion of stars in the nucleus, this object may have a mass of up to three million times the mass of the Sun.
NGC 3621 | Introduction
The diameter of each of the bubbles is about ; they stretch up to Grus and to Virgo on the night-sky of the southern hemisphere. Subsequently, observations with the Parkes Telescope at radio frequencies identified polarized emission that is associated with the Fermi bubbles. These observations are best interpreted as a magnetized outflow driven by star formation in the central of the Milky Way.
Milky Way | Galactic Center