what is in the center of the milky way galaxy
a supermassive black hole
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Galactic Center The Galactic Center, or Galactic Centre, is the rotational center of the Milky Way. It is away from Earth in the direction of the constellations Sagittarius, Ophiuchus, and Scorpius where the Milky Way appears brightest. It coincides with the compact radio source Sagittarius A*. There are around 10 million stars within one parsec of the Galactic Center, dominated by red giants. There is also a significant population of massive supergiants and Wolf-Rayet stars from a star formation event around one million years ago. There is a supermassive black hole of 4.100 ± 0.034 million solar masses at the
Galactic Center
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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. The complex astronomical radio source Sagittarius A appears to be located almost exactly at the Galactic Center (approx. 18 hrs, −29 deg), and contains an intense compact radio source, Sagittarius A*, which coincides with a supermassive black hole at the center of the Milky Way. Accretion of gas onto the black hole, probably involving a disk around it, would release energy to power the radio source, itself much larger than
Galactic Center
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Sagittarius, near its western boundary with Ophiuchus. Astronomers believe that one of its components, known as Sagittarius A*, is associated with a supermassive black hole at the center of the galaxy, with a mass of 2.6 million solar masses. The Sagittarius Dwarf Elliptical Galaxy is located just outside the Milky Way. Baade's Window is an area with very little obscuring dust that shows objects closer to the Milky Way's center that would normally be visible. NGC 6522, magnitude 8.6, and NGC 6528, magnitude 9.5, are both globular clusters visible through Baade's Window. 20,000 and 24,000 light-years from Earth, with Shapley
Sagittarius (constellation)
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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
Satellite galaxies of the Milky Way
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Galactocentrism In astronomy, Galactocentrism is the theory that the Milky Way Galaxy, home of Earths Solar System, is at or near the center of the Universe. Observations by William Herschel in 1785 suggested that the Milky Way was a disk-shaped galaxy with the sun in a central position. Although heliocentric, Herschel's observations were the first attempt at an observational cosmology. Herschel's heliocentric theory was overthrown by astronomer Harlow Shapley's work on globular clusters in 1918. Shapley's research marked the transition from heliocentrism to galactocentrism, placing the Galactic Center of the Milky Way Galaxy far away from the sun, towards Sagittarius.
Galactocentrism
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Local Group The Local Group is the galaxy group that includes the Milky Way. The Local Group comprises more than 54 galaxies, most of them dwarf galaxies. Its gravitational center is located somewhere between the Milky Way and the Andromeda Galaxy. The Local Group has a diameter of (about 10 meters) and has a binary (dumbbell) distribution. The group itself is a part of the larger Virgo Supercluster, which may be a part of the Laniakea Supercluster. The three largest members of the group (in descending order) are the Andromeda Galaxy, the Milky Way and the Triangulum Galaxy. The larger
Local Group
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this discussion regarding the new McKay-Carter Intergalactic Gate Bridge, General Hank Landry states that the distance between the Pegasus and Milky Way galaxies is "three million light-years," suggesting that the series takes place in the Pegasus Dwarf Irregular Galaxy. Also, in a few episodes the Pegasus galaxy has been seen from between the Milky Way and Pegasus, showing an irregular galaxy. Unlike what happened in the Milky Way, the human population of the Pegasus galaxy is a product of Ancient seeding. The Lanteans arrived in the Pegasus galaxy via the Ancient city ship of Atlantis. As there was seldom interbreeding
Mythology of Stargate
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is now in a relative state of quiescence, whereas the Milky Way is experiencing more active star formation. Should this continue, the luminosity of the Milky Way may eventually overtake that of Andromeda Galaxy. According to recent studies, the Andromeda Galaxy lies in what in the galaxy color–magnitude diagram is known as the "green valley", a region populated by galaxies like the Milky Way in transition from the "blue cloud" (galaxies actively forming new stars) to the "red sequence" (galaxies that lack star formation). Star formation activity in green valley galaxies is slowing as they run out of star-forming gas
Andromeda Galaxy
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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 . According to a study published in 2014, the mass of the entire Milky Way is estimated to be 8.5 , but this is actually only half the mass of the Andromeda Galaxy. Much
Milky Way
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that other galaxies apart from the Milky Way therefore existed. By 1925, Edwin Hubble had confirmed that many objects previously thought to be clouds of dust and gas and classified as "nebulae" were actually galaxies beyond the Milky Way. When astronomers realized that starlight can be absorbed by clouds of gas and dust, infrared radiation was used to penetrate the dust clouds. Estimates dating after 2000 locate our solar system within the range from the Galactic Center of the Milky Way galaxy. Galactocentrism In astronomy, Galactocentrism is the theory that the Milky Way Galaxy, home of Earths Solar System, is
Galactocentrism
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optical astronomical maps, Jansky concluded that the radiation was coming from the Milky Way Galaxy and was strongest in the direction of the center of the galaxy, in the constellation of Sagittarius. An amateur radio operator, Grote Reber, was one of the pioneers of what became known as radio astronomy. He built the first parabolic "dish" radio telescope, in diameter, in his back yard in Wheaton, Illinois in 1937. He repeated Jansky's pioneering work, identifying the Milky Way as the first off-world radio source, and he went on to conduct the first sky survey at very high radio frequencies, discovering
Radio telescope
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can pull material out of galaxies and create small satellite galaxies in either prograde or retrograde orbits around larger galaxies. A galaxy called Complex H, which was orbiting the Milky Way in a retrograde direction relative to the Milky Way's rotation, is colliding with the Milky Way. NGC 7331 is an example of a galaxy that has a bulge that is rotating in the opposite direction to the rest of the disk, probably as a result of infalling material. The center of a spiral galaxy contains at least one supermassive black hole. A retrograde black hole – one whose spin
Retrograde and prograde motion
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Center, both of which lack hard boundaries. NGC 5964 NGC 5964 is a barred spiral galaxy in the constellation Serpens Caput. NGC 5964 is also known by the names IC 4551 and PGC 55637. NGC 5964 has relatively unwound spiral arms; it lacks the clear defined spiral arms the Milky Way galaxy has. The central bar is very small, long and thin. NGC 5964 thus does not have a galactic habitable zone like 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
NGC 5964
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Galaxy 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*,
Galaxy
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was detected in the Andromeda Galaxy. The progenitor black hole is located near the galactic center and has about 10 formula_1. Discovered through a data collected by the European Space Agency's XMM-Newton probe, and subsequently observed by NASA's Swift Gamma-Ray Burst Mission and Chandra X-Ray Observatory, the Very Large Array, and the Very Long Baseline Array, the microquasar was the first observed within the Andromeda Galaxy and the first outside of the Milky Way Galaxy. Like the Milky Way, the Andromeda Galaxy has satellite galaxies, consisting of 14 known dwarf galaxies. The best known and most readily observed satellite galaxies
Andromeda Galaxy
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HI (atomic hydrogen) disk of the Milky Way Galaxy to the tidal effects of a perturbing galaxy. The unseen perturber's mass was calculated to be about 1% of that of the Milky Way, which would make it the third heaviest satellite of the Milky Way, after the Magellanic Clouds (Large Magellanic Cloud and Small Magellanic Cloud, each some 10x larger than Galaxy X). In this hypothetical model, the putative satellite galaxy would have interacted with the Milky Way some 600 million years ago, coming as close as , and would now be moving away from the Milky Way. The name
Galaxy X (galaxy)
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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
NGC 7331
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Carina–Sagittarius Arm The Carina–Sagittarius Arm (also known as Sagittarius Arm or Sagittarius–Carina Arm, labeled "-I") is generally thought to be a minor spiral arm of the Milky Way galaxy. Each spiral arm is a long, diffuse curving streamer of stars that radiates from the galactic center. These gigantic structures are often composed of billions of stars and thousands of gas clouds. The Carina–Sagittarius Arm is one of the most pronounced arms in our galaxy as a large number of HII regions, young stars and giant molecular clouds are concentrated in it. The Milky Way is a barred spiral galaxy, consisting
Carina–Sagittarius Arm
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Milky Way Galaxy (~0.8-1.5 solar masses vs the Milky Way's 8.5 solar masses), though a 2018 study found that the Andromeda Galaxy's mass is roughly the same as the Milky Way's. The Andromeda Galaxy, spanning approximately 220,000 light-years, is the largest galaxy in our Local Group, which is also home to the Triangulum Galaxy and other minor galaxies. The Milky Way and Andromeda galaxies are expected to collide in ~4.5 billion years, merging to form a giant elliptical galaxy or a large disc galaxy. With an apparent magnitude of 3.4, the Andromeda Galaxy is among the brightest of the Messier
Andromeda Galaxy
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being tidally disrupted by the Milky Way galaxy. Carina Dwarf Spheroidal Galaxy The Carina Dwarf Spheroidal Galaxy is a dwarf galaxy in the Carina constellation. It was discovered in 1977 with the UK Schmidt Telescope by Cannon et al. The Carina Dwarf Spheroidal galaxy is a satellite galaxy of the Milky Way and is receding from it at 230 km/s. The diameter of the galaxy is about 1600 light-years, which is 75 times smaller than the Milky Way. Most of the stars in the galaxy formed 7 billion years ago, although it also experienced bursts of star formation about 13
Carina Dwarf Spheroidal Galaxy
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it toward the center of our galaxy at about 67 km/sec (Li et al., 2016: 5, Table 1). While these observations solve the problem of radial velocity, the movement of Eridanus II towards the center of our galaxy, they cannot solve the problem of transverse velocity, motion at right angles to the line between Eridanus II and the Milky Way. That is, we cannot determine whether Eridanus II is orbiting the Milky Way, or simply moving in its direction from outside the system. Li et al. (2016: 7–8) report that Eridanus II does not exhibit a "tail" or gradient of
Eridanus II
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1.5 trillion solar masses) compared to for the Milky Way. This contradicts earlier measurements, that seem to indicate that Andromeda Galaxy and the Milky Way are almost equal in mass. Even so, Andromeda Galaxy's spheroid actually has a higher stellar density than that of the Milky Way and its galactic stellar disk is about twice the size of that of the Milky Way. The total stellar mass of Andromeda Galaxy is estimated to be between ., (i.e., around twice as massive as that of the Milky Way) and , with around 30% of that mass in the central bulge, 56%
Andromeda Galaxy
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Andromeda–Milky Way collision The Andromeda–Milky Way collision is a galactic collision predicted to occur in about 5 billion years between two galaxies in the Local Group—the Milky Way (which contains the Solar System and Earth) and the Andromeda Galaxy. The stars involved are sufficiently far apart that it is improbable that any of them will individually collide. Some stars will be ejected from the resulting galaxy, nicknamed "Milkomeda" or "Milkdromeda". The Andromeda Galaxy is approaching the Milky Way at about as indicated by blueshift. However, the lateral velocity is very difficult to measure with a precision to draw reasonable conclusions:
Andromeda–Milky Way collision
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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. A few galaxies outside the Milky Way are visible on a dark night to the unaided eye, including the Andromeda Galaxy, Large Magellanic Cloud and the Small Magellanic Cloud. In the 10th century, the Persian astronomer Al-Sufi made the earliest recorded identification of the Andromeda Galaxy, describing it as a
Galaxy
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Center. The Far 3 kpc Arm was discovered in 2008 by astronomer Tom Dame (Harvard-Smithsonian CfA). It is located in the first galactic quadrant at a distance of 3 kpc (about 10,000 ly) from the Galactic Center. A simulation published in 2011 suggested that the Milky Way may have obtained its spiral arm structure as a result of repeated collisions with the Sagittarius Dwarf Elliptical Galaxy. It has been suggested that the Milky Way contains two different spiral patterns: an inner one, formed by the Sagittarius arm, that rotates fast and an outer one, formed by the Carina and Perseus
Milky Way
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that the Milky Way contained all the stars in the Universe. 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 a diameter between 150,000 and 200,000 light-years (ly). It is estimated to contain 100–400 billion stars and more than 100 billion planets. The Solar System is located at a radius of 26,490 (± 100) light-years from the Galactic Center, on the inner edge of the Orion Arm, one of the spiral-shaped concentrations
Milky Way
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the Triangulum Galaxy—the third-largest and third-brightest galaxy of the Local Group—will participate in the collision event, too. Its most likely fate is to end up orbiting the merger remnant of the Milky Way and Andromeda galaxies and finally to merge with it in an even more distant future. However, a collision with the Milky Way, before it collides with the Andromeda Galaxy, or an ejection from the Local Group cannot be ruled out. While the Andromeda Galaxy contains about 1 trillion () stars and the Milky Way contains about 300 billion (3), the chance of even two stars colliding is
Andromeda–Milky Way collision
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result is the first measurement of the beryllium content of two stars in a Milky Way globular cluster. With this measurement, astronomers found that the first generation of stars in our galaxy must have formed soon after the end of the 200-million-year "Dark Age" following the Big Bang. Astronomers long suspected that a black hole exists at the center of the Milky Way, but their theory was unproven. Conclusive evidence was obtained after 16 years of monitoring the Galactic Center with ESO telescopes at the La Silla and Paranal observatories. Stars at the centre of the Milky Way are so
European Southern Observatory
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the Milky Way galaxy. Up until this time the structure and location of the galactic center was not known with certainty. Baade's Window is frequently used to study distant central bulge stars in visible and near-visible wavelengths of light. Important information on the internal geometry of the Milky Way is still being refined by measurements made through this "window". It is in the direction of the constellation of Sagittarius. The window is now known to be slightly "south" of the main central galaxy bulge. The window is irregular in outline and subtends about 1 degree of the sky. It is
Baade's Window
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Messier 79 Messier 79 (also known as M79 or NGC 1904) is a globular cluster in the constellation Lepus. It was discovered by Pierre Méchain in 1780 and is at a distance of about 42,000 light years away from Earth and 60,000 light years away from the Galactic Center. Like Messier 54 (the other extragalactic globular on Messier's list), it is thought that M79 is not native to the Milky Way galaxy at all, but instead to the putative Canis Major Dwarf Galaxy, which is currently experiencing a very close encounter with the Milky Way. This is, however, a contentious
Messier 79
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suggests an absolute magnitude (in the blue) of −20.89 (that with a color index of +0.63 translates to an absolute visual magnitude of −21.52, compared to −20.9 for the Milky Way), and a total luminosity in that wavelength of . The rate of star formation in the Milky Way is much higher, with Andromeda Galaxy producing only about one solar mass per year compared to 3–5 solar masses for the Milky Way. The rate of novae in the Milky Way is also double that of Andromeda Galaxy. This suggests that the latter once experienced a great star formation phase, but
Andromeda Galaxy
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of known Local Group members had increased from his initial 12 to 36. Local Group The Local Group is the galaxy group that includes the Milky Way. The Local Group comprises more than 54 galaxies, most of them dwarf galaxies. Its gravitational center is located somewhere between the Milky Way and the Andromeda Galaxy. The Local Group has a diameter of (about 10 meters) and has a binary (dumbbell) distribution. The group itself is a part of the larger Virgo Supercluster, which may be a part of the Laniakea Supercluster. The three largest members of the group (in descending order)
Local Group
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bar, the galaxy thus does not have a galactic habitable zone like 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. SN 2004dk was first reported by James Graham and Weidong Li on 1
NGC 6118
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Messier 82 Messier 82 (also known as NGC 3034, Cigar Galaxy or M82) is a starburst galaxy approximately 12 million light-years away in the constellation Ursa Major. A member of the M81 Group, it is about five times more luminous than the whole Milky Way and has a center one hundred times more luminous than our galaxy's center. The starburst activity is thought to have been triggered by interaction with neighboring galaxy M81. As the closest starburst galaxy to Earth, M82 is the prototypical example of this galaxy type. SN 2014J, a type Ia supernova, was discovered in the galaxy
Messier 82
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as Hubble's law, predicted by a universal expansion. The Milky Way Galaxy is moving through space and many astronomers believe the velocity of this motion to be approximately relative to the observed locations of other nearby galaxies. Another reference frame is provided by the Cosmic microwave background. This frame of reference indicates that the Milky Way is moving at around . 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
Motion (physics)
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Terzan 5 Terzan 5 is a heavily obscured globular cluster belonging to the bulge (the central star concentration) of the Milky Way galaxy. It was one of six globulars discovered by French astronomer Agop Terzan in 1968 and was initially labeled "Terzan 11". The cluster was cataloged by the Two-Micron Sky Survey as IRC–20385. It is situated in the Sagittarius constellation in the direction of the Milky Way's center. Terzan 5 probably follows an unknown complicated orbit around the center of the galaxy, but currently it is moving towards the Sun with a speed of around 90 km/s. The absolute
Terzan 5
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attraction. Interferometric measurements of stellar positions over the course of the mission would have permitted SIM to precisely measure the distances between stars throughout the Milky Way. This would have allowed astronomers to create a "roadmap" of the Galaxy, answering many questions about its shape and size. Currently, astronomers know little about the shape and size of our galaxy relative to what they know about other galaxies; it is difficult to observe the entire Milky Way from the inside. A good analogy is trying to observe a marching band as a member of the band. Observing other galaxies is much
Space Interferometry Mission
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as the Sloan Digital Sky Survey (SDSS) and the Dark Energy Survey (DES). In particular, the Milky Way is currently known to host 59 satellite galaxies (see satellite galaxies of the Milky Way), however two of these satellites known as the Large Magellanic Cloud and Small Magellanic Cloud have been observable in the Southern Hemisphere with the unaided eye since ancient times. Nevertheless, modern cosmological theories of galaxy formation and evolution predict a much larger number of satellite galaxies than what is observed (see missing satellites problem). However, more recent high resolution simulations have demonstrated that the current number of
Satellite galaxy
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from Earth. Like neighboring 47 Tucanae, NGC 362 is a Shapley class III cluster and among the brightest globular clusters in the sky. Unusually for a globular cluster, its orbit takes it very close to the center of the Milky Way—approximately 3,000 light-years. It was discovered in the 1820s by James Dunlop. Its stars become visible at 180x magnification through a telescope. Located at the southern end of Tucana, the Small Magellanic Cloud is a dwarf galaxy that is one of the nearest neighbors to the Milky Way galaxy at a distance of 210,000 light-years. Though it probably formed as
Tucana
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that of the Sun. HVSs with smaller masses are also expected and G/K-dwarf HVS candidates have been found. HVSs that have come into the Milky Way came from the dwarf galaxy Large Magellanic Cloud. When the dwarf galaxy made its closest approach to the center of the Milky Way, it underwent intense gravitational tugs. These tugs boosted the energy of some of its stars so much that they broke free of the dwarf galaxy entirely and were thrown into space, due to the slingshot-like effect of the boost. Some neutron stars are inferred to be traveling with similar speeds. This
Stellar kinematics
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galaxy that has been completely distended by the Milky Way's gravity. <BR> Satellite galaxies of the Milky Way The Milky Way has several smaller galaxies gravitationally bound to it, as part of the Milky Way subgroup, which is part of the local galaxy cluster, the Local Group. There are 59 small galaxies confirmed to be within of the Milky Way, but not all of them are necessarily in orbit, and some may themselves be in orbit of other satellite galaxies. The only ones visible to the naked eye are the Large and Small Magellanic Clouds, which have been observed since
Satellite galaxies of the Milky Way
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after the Andromeda Galaxy (M31), the Milky Way, and the Triangulum Galaxy (M33). The LMC is classified as a Magellanic spiral. It contains a stellar bar that is geometrically off-center, suggesting that it was a barred dwarf spiral galaxy before its spiral arms were disrupted, likely by tidal interactions from the Small Magellanic Cloud (SMC), and the Milky Way's gravity. With a declination of about -70°, the LMC is visible as a faint "cloud" only in the southern celestial hemisphere and from latitudes south of 20° N, straddling the border between the constellations of Dorado and Mensa, and appears longer
Large Magellanic Cloud
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of the galaxy were much greater than had been previously thought. His error was due to interstellar dust in the Milky Way, which absorbs and diminishes the amount of light from distant objects, such as globular clusters, that reaches the Earth, thus making them appear to be more distant than they are. Shapley's measurements also indicated that the Sun is relatively far from the center of the galaxy, also contrary to what had previously been inferred from the apparently nearly even distribution of ordinary stars. In reality, most ordinary stars lie within the galaxy's disk and those stars that lie
Globular cluster
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Barnard said: Great Rift (astronomy) In astronomy, the Great Rift (sometimes called the Dark Rift, or less commonly the Dark River), is an area of dark bands that appear to obscure the center of the Milky Way galaxy when seen from the earth. They are thought to be an aggregation of overlapping, non-luminous, molecular dust clouds that lie between the Solar System and the Sagittarius Arm of the galaxy. They form a dark lane through the starry path of the Milky Way which, seen from Earth, is a hazy band of white light, some 30° wide, arching across the night
Great Rift (astronomy)
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Great Rift (astronomy) In astronomy, the Great Rift (sometimes called the Dark Rift, or less commonly the Dark River), is an area of dark bands that appear to obscure the center of the Milky Way galaxy when seen from the earth. They are thought to be an aggregation of overlapping, non-luminous, molecular dust clouds that lie between the Solar System and the Sagittarius Arm of the galaxy. They form a dark lane through the starry path of the Milky Way which, seen from Earth, is a hazy band of white light, some 30° wide, arching across the night sky. These
Great Rift (astronomy)
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meaning the stars have a low abundance of elements other than hydrogen and helium—what astronomers term metallicity. As recently as 1995, it was considered the most metal-poor globular cluster in the Milky Way. The chemical abundances of the stars in NGC 5053 are more similar to those in the dwarf galaxy Sagittarius Dwarf Spheroidal Galaxy than to the Milky Way halo. Along with the kinematics of the globular cluster, this suggests that NGC 5053 may have been stripped from the dwarf galaxy. There are ten known RR Lyrae variable stars in this cluster with masses ranging from 68% to 78%
NGC 5053
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being independent galactic systems of gas and dust, rather than just nebulae in the Milky Way. With a diameter of about 60,000 light-years, the Triangulum galaxy is the third largest member of the Local Group of galaxies, roughly 40% the size of the Milky Way. It may be a gravitationally bound companion of the Andromeda Galaxy. (See below.) Triangulum may be home to 40 billion stars, compared to 400 billion for the Milky Way, and 1 trillion stars for Andromeda Galaxy. The disk of Triangulum has an estimated mass of solar masses, while the gas component is about solar masses.
Triangulum Galaxy
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DES makes it an ideal probe for finding more dwarf or ‘satellite’ galaxies around our Milky Way Galaxy. The number of dwarf galaxies gives important information about the evolution of galaxies and structure in the universe. Cosmological simulations have tended to predict many more dwarf galaxies around large galaxies than we see around our Milky Way Galaxy, leading to what is known as the missing satellite problem. Dwarf galaxies are also interesting in that they appear to be the most dark matter dominated objects in the universe, based on their mass to light ratio. This makes them interesting targets for
Dark Energy Survey
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than those nearer the center. The Galaxy does not therefore rotate as a uniform whole but exhibits what is known as 'differential rotation'." These early discoveries by Oort about the Milky Way overthrew the Kapteyn system, named after his mentor, which had envisioned a galaxy that was symmetrical around the Sun. As Oort later noted, "Kapteyn and his co-workers had not realized that the absorption in the galactic plane was as bad as it turned out to be." Until Oort began his work, he later recalled, "the Leiden Observatory had been concentrating entirely on positional astronomy, meridian circle work and
Jan Oort
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suspect that the Milky Way is a barred spiral galaxy, rather than an ordinary spiral galaxy, in the 1960s. Their suspicions were confirmed by the Spitzer Space Telescope observations in 2005 that showed the Milky Way's central bar to be larger than previously thought. A galactic quadrant, or quadrant of the Milky Way, refers to one of four circular sectors in the division of the Milky Way. In actual astronomical practice, the delineation of the galactic quadrants is based upon the galactic coordinate system, which places the Sun as the origin of the mapping system. Quadrants are described using ordinals—for
Milky Way
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Large Magellanic Cloud The Large Magellanic Cloud (LMC) is a satellite galaxy of the Milky Way. At a distance of about 50 kiloparsecs (≈163,000 light-years), the LMC is the second- or third-closest galaxy to the Milky Way, after the Sagittarius Dwarf Spheroidal (~16 kpc) and the possible dwarf irregular galaxy known as the Canis Major Overdensity. Based on readily visible stars and a mass of approximately 10 billion solar masses, the diameter of the LMC is about , making it roughly one one-hundredth as massive as the Milky Way. This makes the LMC the fourth-largest galaxy in the Local Group,
Large Magellanic Cloud
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circumvent the Ancients' rules that the Ori cannot directly use their powers to conquer the Milky Way galaxy. Adria is one step higher than the Doci, but equal in terms of her role in the Milky Way galaxy, which is to lead the armies of the Ori in the Milky Way galaxy, converting the galaxy to Origin in the process. Adria possesses several Prior-like superhuman abilities, and leads the armies of the Ori until her Ascension in the penultimate episode of "Stargate SG-1". From a creative standpoint, Adria's character was created to give Vala Mal Doran a story and personality
Ori (Stargate)
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such as toward the galactic plane or the galactic center). Because the Milky Way galaxy has a very flat structure, if gamma-ray bursts were to originate from within the Milky Way, they would not be distributed isotropically across the sky, but instead concentrated in the plane of the Milky Way. Although the luminosity of the bursts suggested that they had to be originating within the Milky Way, the distribution provided very strong evidence to the contrary. BATSE data also showed that GRBs fall into two distinct categories: short-duration, hard-spectrum bursts ("short bursts"), and long-duration, soft-spectrum bursts ("long bursts"). Short bursts
History of gamma-ray burst research
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were determined to be satellites of the Milky Way (Li et al. (2016: 8)). For reasons to be discussed in the concluding section, most researchers now believe that Eridanus II is an extremely long-period (i.e., several billion years per orbit) satellite of the Milky Way, probably beginning only its second approach to our galaxy. To put these numbers into their proper context, it may be worth reminding ourselves that the expansion of the universe is a significant factor on these distance scales. Eridanus II is moving toward the center of the Milky Way at 67 km/sec. However, applying the current
Eridanus II
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Sagittarius Dwarf Spheroidal Galaxy The Sagittarius Dwarf Spheroidal Galaxy (Sgr dSph), also known as the Sagittarius Dwarf Elliptical Galaxy (Sgr dE or Sag DEG), is an elliptical loop-shaped satellite galaxy of the Milky Way. It consists of four globular clusters, the main cluster having been discovered in 1994. Sgr dSph is roughly 10,000 light-years in diameter, and is currently about 70,000 light-years from Earth, travelling in a polar orbit (i.e. an orbit passing over the Milky Way’s galactic poles) at a distance of about 50,000 light-years from the core of the Milky Way (about 1/3 the distance of the Large
Sagittarius Dwarf Spheroidal Galaxy
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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
Galaxy
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encircles the Galactic disk. The Sloan Digital Sky Survey of the northern sky shows a huge and diffuse structure (spread out across an area around 5,000 times the size of a full moon) within the Milky Way that does not seem to fit within current models. The collection of stars rises close to perpendicular to the plane of the spiral arms of the Milky Way. The proposed likely interpretation is that a dwarf galaxy is merging with the Milky Way. This galaxy is tentatively named the Virgo Stellar Stream and is found in the direction of Virgo about away. In
Milky Way
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Laevens 1 Laevens 1 is a faint globular cluster in the constellation Crater that was discovered in 2014. It is also known as Crater, the Crater cluster and PSO J174.0675-10.8774. At a distance of it is the most distant Milky Way globular cluster yet known, located in the galactic halo surrounding the Milky way galaxy. With an age of only 7.5 Gyr, it is likely to have been incorporated into our galaxy long after the formation of the Milky Way, probably during an interaction with the Small Magellanic Cloud. Some analyses initially categorized it as a satellite galaxy, because of
Laevens 1
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merging into a single elliptical galaxy. In the Local Group, the Milky Way and the Andromeda Galaxy are gravitationally bound, and currently approaching each other at high speed. Simulations show that the Milky Way and Andromeda are on a collision course, and are expected to collide in less than five billion years. During this collision, it is expected that the Sun and the rest of the Solar System will be ejected from its current path around the Milky Way. The remnant could be a giant elliptical galaxy. One observation (see above) that must be explained by a successful theory of
Galaxy formation and evolution
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and from the Galactic Center. It has a roughly elliptical shape and is thought to contain as many stars as the Sagittarius Dwarf Elliptical Galaxy, the previous contender for closest galaxy to our location in the Milky Way. The existence of a strong elliptical-shaped stellar overdensity was reported in November 2003 by an international team of French, Italian, British and Australian astronomers, who claimed their study pointed to a newly discovered dwarf galaxy: the Canis Major Dwarf Galaxy. This structure is located closer to the Sun than the center of our galaxy, at approximately from the Sun. The team of
Canis Major Overdensity
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the Milky Way. This black hole is suspected to be Sgr A*, with a mass of 4.2 × , where is the solar mass. Proper motions of the galaxies in the Local Group are discussed in detail in Röser. In 2005, the first measurement was made of the proper motion of the Triangulum Galaxy M33, the third largest and only ordinary spiral galaxy in the Local Group, located 0.860 ± 0.028 Mpc beyond the Milky Way. The motion of the Andromeda Galaxy was measured in 2012, and an Andromeda–Milky Way collision is predicted in about 4 billion years. Proper motion
Proper motion
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Sky Survey. Both of these stars being cool red giants, they are extremely bright which is one of the key factors in their discovery. Their distance was estimated with a number of different techniques, which all pointed towards 900,000 light years away. ULAS J0015+01 is, at the current time, 900,000 light years away from the Milky Way galaxy. The Milky Way's disk is 180,000 light years in diameter, putting it far beyond the Milky Way stellar disk, or only 3 times closer than the Andromeda galaxy. In comparison, in distance to the Milky Way's satellite galaxy, the Large Magellanic Cloud,
ULAS J0015+01
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objects in our Galaxy - all of which are, in principle, observable quantities. However, there are a number of complications. The simple derivation above assumed that both the Sun and the object in question are traveling on circular orbits about the Galactic center. This is not true for the Sun (the Sun's velocity relative to the local standard of rest is approximately 13.4 km/s), and not necessarily true for other objects in the Milky Way either. The derivation also implicitly assumes that the gravitational potential of the Milky Way is axisymmetric and always directed towards the center. This ignores the
Oort constants
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NGC 45 NGC 45 is a low surface brightness spiral galaxy in the constellation of Cetus. It was discovered on 11 November 1835 by the English astronomer John Herschel. Unlike the Milky Way, NGC 45 has no clear defined spiral arms, and its center bar nucleus is also very small and distorted. NGC 45 thus does not have a galactic habitable zone. 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 45
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NGC 45 NGC 45 is a low surface brightness spiral galaxy in the constellation of Cetus. It was discovered on 11 November 1835 by the English astronomer John Herschel. Unlike the Milky Way, NGC 45 has no clear defined spiral arms, and its center bar nucleus is also very small and distorted. NGC 45 thus does not have a galactic habitable zone. 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 45
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and the opening sequence from Earth through the Solar System and its galaxy and beyond for the "Contact" film. At Sagan's request, Lomberg designed the original sailing ship logo for the Planetary Society in 1981. The Smithsonian Institution commissioned Lomberg in the early 1990s to paint ""A Portrait of the Milky Way"", a scientifically accurate artistic representation of the Milky Way galaxy as seen by a hypothetical observer from a vantage point 10 degrees above the galactic plane and 60,000 light years from the galactic center. The by painting, which was described in a peer reviewed academic paper in 1994
Jon Lomberg
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it much later. Two other possibilities are a collision with the Milky Way before the Andromeda Galaxy arrives or an ejection out of the Local Group. Triangulum Galaxy The Triangulum Galaxy is a spiral galaxy approximately 3 million light-years (ly) from Earth in the constellation Triangulum. It is catalogued as Messier 33 or NGC 598. The Triangulum Galaxy is the third-largest member of the Local Group of galaxies, behind the Milky Way and the Andromeda Galaxy. It is one of the most distant permanent objects that can be viewed with the naked eye. The galaxy is the smallest spiral galaxy
Triangulum Galaxy
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asleep so that the baby will drink her divine milk and will thus become immortal. Hera wakes up while breastfeeding and then realizes she is nursing an unknown baby: she pushes the baby away, some of her milk spills, and it produces the faint band of light known as the Milky Way. In the astronomical literature, the capitalized word "Galaxy" is often used to refer to our galaxy, the Milky Way, to distinguish it from the other galaxies in our universe. The English term "Milky Way" can be traced back to a story by Chaucer : Galaxies were initially discovered
Galaxy
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brought into the Milky Way triggered a fresh round of star formation and replenished the thin disk. The debris from the dwarf galaxy provides most of the metal-rich halo. Gaia Sausage The Gaia Sausage is the remains of a dwarf galaxy, the "Sausage Galaxy", that merged with the Milky Way about 8 - 11 billion years ago. At least eight globular clusters were added to the Milky Way along with 50 billion solar masses of stars, gas and dark matter. The "Gaia Sausage" is so-called because of the characteristic sausage shape of the population in velocity space, the appearance on
Gaia Sausage
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Carina Dwarf Spheroidal Galaxy The Carina Dwarf Spheroidal Galaxy is a dwarf galaxy in the Carina constellation. It was discovered in 1977 with the UK Schmidt Telescope by Cannon et al. The Carina Dwarf Spheroidal galaxy is a satellite galaxy of the Milky Way and is receding from it at 230 km/s. The diameter of the galaxy is about 1600 light-years, which is 75 times smaller than the Milky Way. Most of the stars in the galaxy formed 7 billion years ago, although it also experienced bursts of star formation about 13 and 3 billion years ago. It is also
Carina Dwarf Spheroidal Galaxy
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more massive (approx. 10 solar masses) than our Milky Way Galaxy, and the central black hole is nearly 1,000 times more massive (approx. 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 Hercules A is a bright astronomical radio source within the vicinity of the constellation Hercules corresponding to the galaxy 3C 348. During a survey of bright radio sources in the
Hercules A
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possibility of the disk of the Milky Way extending further 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. 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
Milky Way
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Sculptor Dwarf Galaxy The Sculptor Dwarf Galaxy (also known as Sculptor Dwarf Elliptical Galaxy or the Sculptor Dwarf Spheroidal Galaxy) is a dwarf spheroidal galaxy that is a satellite of the Milky Way. The galaxy lies within the constellation Sculptor. It was discovered in 1937 by American astronomer Harlow Shapley using the 24-inch Bruce refractor at Boyden Observatory. The galaxy is located about 290,000 light-years away from the Solar System. The Sculptor Dwarf contains only 4 percent of the carbon and other heavy elements in our own galaxy, the Milky Way, making it similar to primitive galaxies seen at the
Sculptor Dwarf Galaxy
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Small Magellanic Cloud The Small Magellanic Cloud (SMC), or "Nubecula Minor", is a dwarf galaxy near the Milky Way. Classified as a dwarf irregular galaxy, the SMC has a diameter of about 7,000 light-years, contains several hundred million stars, and has a total mass of approximately 7 billion solar masses. The SMC contains a central bar structure and is speculated to once be a barred spiral galaxy that was disrupted by the Milky Way to become somewhat irregular. At a distance of about 200,000 light-years, the SMC is among the nearest intergalactic neighbors of the Milky Way and is one
Small Magellanic Cloud
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present. Several Mormon authors have attempted to situate Kolob within modern astronomy. Skousen speculated that Kolob is a star at the Galactic Center, Sagittarius A*, of our own Galaxy. This view also had the support of several former general authorities of the LDS Church, including J. Reuben Clark and George Reynolds (with Janne M. Sjödahl). In the mid-19th century, early efforts to find a single "central sun" in the galaxy resulted in failure. Another Mormon author has hypothesized that Kolob exists outside the Milky Way Galaxy at a place called the "metagalactic center", and that this galaxy and other galaxies
Kolob
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of "Galaxy X" Galaxy X (galaxy) Galaxy X is a postulated dark satellite dwarf galaxy of the Milky Way Galaxy. If it exists, it would be composed mostly of dark matter and interstellar gas with few stars. Its proposed location is some from the Sun, behind the disk of the Milky Way, and some in extent. Galactic coordinates would be (l= -27.4°,b=-1.08°). Observational evidence for this galaxy was presented in 2015, based on the claimed discovery of four, Cepheid variable stars by Sukanya Chakrabarti (RIT) and collaborators. Search for the stars was motivated by an earlier study that linked a
Galaxy X (galaxy)
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Baby Boom Galaxy The Baby Boom Galaxy is a starburst galaxy located 12.2 billion light years away. Discovered by NASA's Spitzer Science Center at the California Institute of Technology, the galaxy is the record holder for the brightest starburst galaxy in the very distant universe, with brightness being a measure of its extreme star-formation rate. The Baby Boom Galaxy has been nicknamed "the extreme stellar machine" because it is seen producing stars at a rate of up to 4,000 per year (one star every 2.2 hours). The Milky Way galaxy in which Earth resides turns out an average of just
Baby Boom Galaxy
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brighter than the LMC appears to us. Large Magellanic Cloud The Large Magellanic Cloud (LMC) is a satellite galaxy of the Milky Way. At a distance of about 50 kiloparsecs (≈163,000 light-years), the LMC is the second- or third-closest galaxy to the Milky Way, after the Sagittarius Dwarf Spheroidal (~16 kpc) and the possible dwarf irregular galaxy known as the Canis Major Overdensity. Based on readily visible stars and a mass of approximately 10 billion solar masses, the diameter of the LMC is about , making it roughly one one-hundredth as massive as the Milky Way. This makes the LMC
Large Magellanic Cloud
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near the center of the Milky Way, which is also where most are thought to be produced. One of the fastest known stars in our Galaxy is the O-class sub-dwarf US 708, moving away from the Milky Way with a total velocity of around 1200 km/s. The existence of HVSs was first predicted by Jack G. Hills in 1988, and their existence confirmed by Warren Brown, Margaret Geller, Scott Kenyon, and Michael Kurtz in 2005. As of 2008, 10 unbound HVSs were known, one of which was believed to have originated from the Large Magellanic Cloud rather than the Milky
Stellar kinematics
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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
Milky Way
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dark matter bodies for each observable galaxy the size of our own Milky Way galaxy (Koposov et al. 2015; Bechtol et al., 2015). These should contain much less baryonic matter than a “normal” galaxy. Thus, we should observe many, very faint, satellite galaxies around the Milky Way. Until about 1990, however, only about 11 Milky Way satellites were known (Pawlowski et al., 2015; Bechtol et al., 2015). The difference between the number of satellites known and the number expected in ΛCDM is referred to as the "missing dwarf" or "substructure" problem. Simon & Geha (2007) also discuss various cosmological and
Eridanus II
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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.
RAVE (survey)
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all other universes – finally removed from the WSOGMM. Places in The Hitchhiker's Guide to the Galaxy This is a list of places featured in Douglas Adams's science fiction series "The Hitchhiker's Guide to the Galaxy". The series is set in a fictionalised version of the Milky Way galaxy and thus, while most locations are pure invention, many are based on "real world" settings such as Alpha Centauri, Barnard's Star and various versions of the Earth. "The Galaxy" is our home galaxy, the Milky Way, though it is referred to exclusively as "the Galaxy" in the series. Apart from a
Places in The Hitchhiker's Guide to the Galaxy
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Places in The Hitchhiker's Guide to the Galaxy This is a list of places featured in Douglas Adams's science fiction series "The Hitchhiker's Guide to the Galaxy". The series is set in a fictionalised version of the Milky Way galaxy and thus, while most locations are pure invention, many are based on "real world" settings such as Alpha Centauri, Barnard's Star and various versions of the Earth. "The Galaxy" is our home galaxy, the Milky Way, though it is referred to exclusively as "the Galaxy" in the series. Apart from a very brief moment during the first radio series, when
Places in The Hitchhiker's Guide to the Galaxy
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Galaxy X (galaxy) Galaxy X is a postulated dark satellite dwarf galaxy of the Milky Way Galaxy. If it exists, it would be composed mostly of dark matter and interstellar gas with few stars. Its proposed location is some from the Sun, behind the disk of the Milky Way, and some in extent. Galactic coordinates would be (l= -27.4°,b=-1.08°). Observational evidence for this galaxy was presented in 2015, based on the claimed discovery of four, Cepheid variable stars by Sukanya Chakrabarti (RIT) and collaborators. Search for the stars was motivated by an earlier study that linked a warp in the
Galaxy X (galaxy)
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(CO). Dame discovered the Far 3 kpc Arm of the Milky Way in 2008 and the Outer Sct-Cen Arm in 2011. Dame has authored or co-authored more than 100 research papers in astronomy. Tom Dame Thomas M. Dame is Director of the Radio Telescope Data Center at the Harvard-Smithsonian Center for Astrophysics, a Senior Radio Astronomer at the Smithsonian Astrophysical Observatory, and a Lecturer on Astronomy at Harvard University. He is best known for mapping the Milky Way galaxy in Carbon Monoxide and for the discovery of both the Far 3 kpc Arm and the Outer Scutum–Centaurus Arm of the
Tom Dame
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Tom Dame Thomas M. Dame is Director of the Radio Telescope Data Center at the Harvard-Smithsonian Center for Astrophysics, a Senior Radio Astronomer at the Smithsonian Astrophysical Observatory, and a Lecturer on Astronomy at Harvard University. He is best known for mapping the Milky Way galaxy in Carbon Monoxide and for the discovery of both the Far 3 kpc Arm and the Outer Scutum–Centaurus Arm of the Milky Way. Dame graduated from Boston University in 1976 with a BA in Astronomy and Physics. He earned his Master's degrees and Ph.D. from Columbia University. His dissertation, earned under Patrick Thaddeus in
Tom Dame
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been described by a member of the team that discovered it as "a rather pathetic galaxy" in comparison to the Milky Way. Many of the stars have been known for centuries and thought of as normal Milky Way stars, although they have a lower metallicity than normal Population I stars in the Milky Way. The stream lies within the Milky Way, approximately 10 kiloparsecs (30,000 light-years) from the Sun, and extending over a region of space at least 10 kpc across in three dimensions. It is close on the plane of the sky to the Sagittarius Dwarf Elliptical Galaxy, which
Virgo Stellar Stream
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believe the largest globular cluster in the Milky Way, Omega Centauri, is in fact the core of a dwarf galaxy with a black hole at its centre, which was at some time absorbed by the Milky Way. In astronomy, a blue compact dwarf galaxy (BCD galaxy) is a small galaxy which contains large clusters of young, hot, massive stars. These stars, the brightest of which are blue, cause the galaxy itself to appear blue in colour. Most BCD galaxies are also classified as dwarf irregular galaxies or as dwarf lenticular galaxies. Because they are composed of star clusters, BCD galaxies
Dwarf galaxy
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of our Solar System, our galaxy, or our Universe. Shapley participated in the "Great Debate" with Heber D. Curtis on the nature of nebulae and galaxies and the size of the Universe. The debate took place on April 26, 1920, in the hall of the United States National Academy of Sciences in Washington D.C. Shapley took the side that spiral nebulae (what are now called galaxies) are inside our Milky Way, while Curtis took the side that the spiral nebulae are 'island universes' far outside our own Milky Way and comparable in size and nature to our own Milky Way.
Harlow Shapley
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February 1800, and the planet Uranus in March 1781; he had made important improvements to the reflecting telescope by increasing the mirror diameter. Herschel then built a 20-ft reflecting telescope and invented the star count, working out that the Milky Way was a disc, which he called a "grindstone", and the Milky Way was a galaxy but that that was all the universe contained; he had noticed other nebulas but did not recognise what these were; only when the Hooker telescope was built sufficiently large-enough in California in 1924, did Edwin Hubble realise that these nebulas (Andromeda Galaxy) were other
South West England
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is contained in a ring between from the center of the Milky Way (the Sun is about 8.5 kiloparsecs from the center). Large scale CO maps of the galaxy show that the position of this gas correlates with the spiral arms of the galaxy. That molecular gas occurs predominantly in the spiral arms suggests that molecular clouds must form and dissociate on a timescale shorter than 10 million years—the time it takes for material to pass through the arm region. Vertically to the plane of the galaxy, the molecular gas inhabits the narrow midplane of the galactic disc with a
Molecular cloud
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Galactic astronomy Galactic astronomy is the study of the Milky Way galaxy and all its contents. This is in contrast to extragalactic astronomy, which is the study of everything outside our galaxy, including all other galaxies. Galactic astronomy should not be confused with galaxy formation and evolution, which is the general study of galaxies, their formation, structure, components, dynamics, interactions, and the range of forms they take. The Milky Way galaxy, where the Solar System belongs, is in many ways the best studied galaxy, although important parts of it are obscured from view in visible wavelengths by regions of cosmic
Galactic astronomy
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smaller galaxies such as the Milky Way. In the case of the Milky Way, its 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 (with both radii lacking hard boundaries). Galactic habitable-zone theory has been criticized due to an inability to quantify accurately the factors making a region of a galaxy favorable for the emergence of life. In addition, computer simulations suggest that stars may change their orbits around the galactic center significantly, therefore challenging at least part of the view that
Galactic habitable zone
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long, oval bulge and a mottled galactic disc. Although the bulge appears only slightly brighter than the rest of the galaxy, it is fairly extended compared to the disk. In 400 mm scopes and larger, a dark dust lane northwest of the nucleus is visible, and over a dozen faint stars can be seen superimposed on the bulge. The Sculptor Galaxy is located at the center of the Sculptor Group, one of the nearest groups of galaxies to the Milky Way. The Sculptor Galaxy (the brightest galaxy in the group and one of the intrinsically brightest galaxies in the vicinity
Sculptor Galaxy
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Milky Way and is obscured by galactic dust. The Circinus Galaxy is a Type II Seyfert galaxy and is one of the closest known active galaxies to the Milky Way, though it is probably slightly farther away than Centaurus A. Circinus Galaxy produced supernova SN 1996cr, which was identified over a decade after it exploded. This supernova event was first observed during 2001 as a bright, variable object in a Chandra X-ray Observatory image, but it was not confirmed as a supernova until years later. The Circinus Galaxy is one of twelve large galaxies in the "Council of Giants" surrounding
Circinus Galaxy
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in the interstellar medium. In simulated galaxies with similar properties to Andromeda Galaxy, star formation is expected to extinguish within about five billion years from the now, even accounting for the expected, short-term increase in the rate of star formation due to the collision between Andromeda Galaxy and the Milky Way. Based on its appearance in visible light, the Andromeda Galaxy is classified as an SA(s)b galaxy in the de Vaucouleurs–Sandage extended classification system of spiral galaxies. However, data from the 2MASS survey showed that Andromeda is actually a barred spiral galaxy, like the Milky Way, with Andromeda's bar oriented
Andromeda Galaxy
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fairly narrow range of distances from the Galactic Center. Lineweaver et al. calculate this zone to be a ring 7 to 9 kiloparsecs in radius, including no more than 10% of the stars in the Milky Way, about 20 to 40 billion stars. Gonzalez, et al. would halve these numbers; they estimate that at most 5% of stars in the Milky Way fall in the galactic habitable zone. Approximately 77% of observed galaxies are spiral, two-thirds of all spiral galaxies are barred, and more than half, like the Milky Way, exhibit multiple arms. According to Rare Earth, our own galaxy
Rare Earth hypothesis
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Galaxy lie in what in the galaxy color–magnitude diagram is known as the "green valley", a region populated by galaxies in transition from the "blue cloud" (galaxies actively forming new stars) to the "red sequence" (galaxies that lack star formation). Star-formation activity in green valley galaxies is slowing as they run out of star-forming gas in the interstellar medium. In simulated galaxies with similar properties, star formation will typically have been extinguished within about five billion years from now, even accounting for the expected, short-term increase in the rate of star formation due to the collision between both the Milky
Milky Way
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Fornax Dwarf The Fornax Dwarf Spheroidal is an elliptical dwarf galaxy in the constellation Fornax that was discovered in 1938 by Harlow Shapley. He discovered it while he was in South Africa on photographic plates taken by the 24 inch (61 cm) Bruce refractor at Boyden Observatory, shortly after he discovered the Sculptor Dwarf Galaxy. The galaxy is a satellite of the Milky Way and contains six globular clusters; the largest, NGC 1049, was discovered before the galaxy itself. The galaxy is also receding from the Milky Way at 53 km/s. It mostly contains population II stars. Using the Hubble
Fornax Dwarf
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due to the gravitational field of the Milky Way or other galaxy that they orbit. For example, the Sextans dwarf spheroidal galaxy has a velocity dispersion of 7.9±1.3 km/s, which is a velocity dispersion that could not be explained solely by its stellar mass according to the Virial Theorem. Similar to Sextans, previous studies of Hercules dwarf spheroidal galaxy reveal that its orbital path does not correspond to the mass contained in Hercules. Furthermore, there is evidence that the UMa2, a dwarf spheroidal galaxy in the Ursa Major constellation, experiences strong tidal disturbances from the Milky Way. Dwarf spheroidal galaxy
Dwarf spheroidal galaxy