Milky Way Galaxy









The Milky Way is the galaxy that contains the 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 Milky Way is a barred spiral galaxy with a visible diameter between 150,000 and 200,000 light-years. It is estimated to contain 100400 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. The stars in the innermost 10,000 light-years form a bulge and one or more bars that radiate from the bulge. Read more


Galactic Center


The Galactic Center is the rotational center of the Milky Way galaxy; it is a supermassive black hole of 4.100 0.034 million solar masses which powers the compact radio source Sagittarius A*. It is far from Earth in the direction of the constellations Sagittarius, Ophiuchus, and Scorpius where the Milky Way appears brightest. Read more




Discovery

As Aristotle (384-322 BC) informs us in Meteorologica (DK 59 A80), the Greek philosophers Anaxagoras (ca. 500-428 BC) and Democritus (450-370 BC) proposed that the Milky Way might consist of distant stars. However, Aristotle himself believed the Milky Way to be caused by "the ignition of the fiery exhalation of some stars which were large, numerous and close together" and that the "ignition takes place in the upper part of the atmosphere, in the region of the world which is continuous with the heavenly motions."

The Arabian astronomer, Alhazen (965-1037 AD), refuted this by making 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 was very remote from the earth and did not belong to the atmosphere."

The Persian astronomer, Abu Rayhan al-Biruni (973-1048), proposed the Milky Way galaxy to be a collection of countless nebulous stars.

Avempace (d. 1138) proposed the Milky Way to be made up of many stars but appears to be a continuous image due to the effect of refraction in the Earth's atmosphere.

Ibn Qayyim Al-Jawziyya (1292-1350) proposed the Milky Way galaxy to be "a myriad of tiny stars packed together in the sphere of the fixed stars" and that that these stars are larger than planets.

Actual proof of the Milky Way consisting of many stars came in 1610 when Galileo Galilei used a telescope to study the Milky Way and discovered that it was composed of a huge number of faint stars.

In a treatise in 1755, Immanuel Kant, drawing on earlier work by Thomas Wright, speculated (correctly) that the Milky Way might be a rotating body of a huge number of stars, held together by gravitational forces akin to the Solar System but on much larger scales. The resulting disk of stars would be seen as a band on the sky from our perspective inside the disk. Kant also conjectured that some of the nebulae visible in the night sky might be separate "galaxies" themselves, similar to our own.

The first attempt to describe the shape of the Milky Way and the position of the Sun within it was carried out by William Herschel in 1785 by carefully counting the number of stars in different regions of the visible sky. He produced a diagram of the shape of the Galaxy with the Solar System close to the center.

In 1845, Lord Rosse constructed a new telescope and was able to distinguish between elliptical and spiral-shaped nebulae. He also managed to make out individual point sources in some of these nebulae, lending credence to Kant's earlier conjecture.

In 1917, Heber Curtis had observed the nova S Andromedae within the "Great Andromeda Nebula" (Messier object M31). Searching the photographic record, he found 11 more novae. Curtis noticed that these novae were, on average, 10 magnitudes fainter than those that occurred within our galaxy. As a result he was able to come up with a distance estimate of 150,000 parsecs. He became a proponent of the "island universes" hypothesis, which held that the spiral nebulae were actually independent galaxies.

In 1920 the Great Debate took place between Harlow Shapley and Heber Curtis, concerning the nature of the Milky Way, spiral nebulae, and the dimensions of the universe. To support his claim that the Great Andromeda Nebula was an external galaxy, Curtis noted the appearance of dark lanes resembling the dust clouds in the Milky Way, as well as the significant Doppler shift.

The matter was conclusively settled by Edwin Hubble in the early 1920s using a new telescope. He was able to resolve the outer parts of some spiral nebulae as collections of individual stars and identified some Cepheid variables, thus allowing him to estimate the distance to the nebulae: they were far too distant to be part of the Milky Way. In 1936, Hubble produced a classification system for galaxies that is used to this day, the Hubble sequence.




Mythology

The name is from the Greek root galaxy, meaning "milky," a reference to the Milky Way Galaxy.

There are numerous legends in many traditions around the world regarding the creation of the Milky Way. In particular there are two similar ancient Greek stories that explain the etymology of the name 'Galaxias' and its association with milk.

One legend describes the Milky Way as a smear of milk created when the baby Herakles suckled from the Goddess Hera. When Hera realized that the suckling infant was not her own but the illegitimate son of Zeus and another woman, she pushed it away and the spurting milk became the Milky Way Galaxy.

Another story tells that the milk came from the goddess Rhea, the wife of Cronus, and the suckling infant was Zeus himself. Cronus swallowed his children to ensure his position as head of the Pantheon and sky god, and so Rhea conceived a plan to save her newborn son Zeus: She wrapped a stone in infant's clothes and gave it to Cronus to swallow. Cronus asked her to nurse the child once more before he swallowed it, and the milk that spurted when she pressed her nipple against the rock eventually became the Milky Way.

Older mythology associates the constellation with a herd of dairy cows/cattle, whose milk gives the blue glow, and where each cow is a star. As such, it is intimately associated with legends concerning the constellation of Gemini, which it is in contact with. Firstly, with Gemini, it may form the origin of the myth of Castor and Polydeuces, concerning cattle raiding. Secondly, again with Gemini, but also with other features of the Zodiac sign of Gemini (i.e. Canis Major, Orion, Auriga, and the deserted area now regarded as Camelopardalis), it may form the origin of the myth of the Cattle of Geryon, one of The Twelve Labours of Herakles.

Civilizations in Eastern Asia believed that the hazy band of stars were "Silvery River" of the Heaven. Also, Altair and Vega were thought to be lovers, who were bound not to meet each other but on the seventh day of the seventh month, Qi Xi (Tanabata in Japan and Chilseok in Korea), when the magpies form the bridge over the galactic river.




Suntelia Aion

The Milky Way Galaxy is the inspiration for the symbol of the Ouroboros. In mythology the Milky Way Galaxy keeps a 'great time cycle' that ends in catastrophic change. This refers to a serpent of light (Milky Way) residing in the heavens, who, when viewed at the galactic central point near Sagittarius, eats its own tail. Suntelia Aion refers to the sun (light) rising out of the mouth of the ouroboros (aion) on the winter solstice December 21, 2012. Ancient historians, and especially Plato, referred to a cycle of catastrophe at the End of that Age.




Milky Way Galaxy in the News ....





Mysterious 'Fermi Bubbles' may be the result of black hole indigestion 6 million years ago   Live Science - May 28, 2020
In November 2010, it was announced that two gamma-ray and X-ray emitting bubbles were detected around Earth's galaxy, the Milky Way. The bubbles, named Fermi Bubbles, extend about 25 thousand light-years distant above and below the galactic center.




ALMA spots twinkling heart of Milky Way   PhysOrg - May 22, 2020

Astronomers presume that a supermassive black hole with a mass of 4 million suns is located at the center of Sgr A*. Flares of Sgr A* have been observed not only in millimeter wavelength, but also in infrared light and X-ray. However, the variations detected with ALMA are much smaller than the ones previously detected, and it is possible that these levels of small variations always occur in Sgr A*. The black hole itself does not produce any kind of emission. The source of the emission is the scorching gaseous disk around the black hole. The gas around the black hole does not go straight to the gravitational well, but it rotates around the black hole to form an accretion disk.




Milky Way Galaxy is warped and twisted, not flat   BBC - August 2, 2019

Analysis of the brightest stars in the galaxy shows that they do not lie on a flat plane as shown in academic texts and popular science books. Astronomers speculate that it might have been bent out of shape by past interactions with nearby galaxies. The popular picture of the Milky Way as a flat disc is based on the observation of 2.5 million stars out of a possible 2.5 billion. The artists' impressions are therefore rough approximations of the truer shape of our galaxy.




Gaia detects a shake in the Milky Way   PhysOrg - September 20, 2018

A team led by researchers has found, through the analysis of Gaia data, substructures in the Milky Way that were previously unknown. The findings, which appeared when combining positions and speed of 6 million stars from the galactic disk.




Idaho spot that is the one of the best places in the world to see the Milky Way named America's first 'International Dark Sky Reserve'   Daily Mail - December 20, 2017
A giant chunk of central Idaho with a dazzling night sky has become the nation's first International Dark Sky Reserve. The International Dark-Sky Association late Monday designated the 1,400-square-mile Central Idaho Dark Sky Reserve. The sparsely populated area's night skies are so pristine that interstellar dust clouds are visible in the Milky Way.




Extremely massive exoplanet discovered in the Milky Way's bulge   PhysOrg - November 6, 2017
As a result of NASA's Spitzer Space Telescope observations of a microlensing event, astronomers have found an extremely massive alien world circling a star located in the Milky Way's bulge. The newly discovered planet, designated OGLE-2016-BLG-1190Lb, is the first Spitzer microlensing exoworld residing in the galactic bulge.




Complex gas motion in the center of the Milky Way   PhysOrg - July 14, 2017
How does the gas in the centre of the Milky Way behave? Researchers from Heidelberg University, in collaboration with colleagues from the University of Oxford, recently investigated the motion of gas clouds in a comprehensive computer simulation. The new model finally makes it possible to conclusively explain this complex gas motion.




Origin of Milky Way's hypothetical dark matter signal may not be so dark   PhysOrg - May 2, 2017
A mysterious gamma-ray glow at the center of the Milky Way is most likely caused by pulsars - the incredibly dense, rapidly spinning cores of collapsed ancient stars that were up to 30 times more massive than the sun. That's the conclusion of a new analysis by an international team of astrophysicists, including researchers from the Department of Energy's SLAC National Accelerator Laboratory. The findings cast doubt on previous interpretations of the signal as a potential sign of dark matter - a form of matter that accounts for 85 percent of all matter in the universe but that so far has evaded detection.




X marks the spot at the center of the Milky Way galaxy   Science Daily - July 19, 2016
Two astronomers -- with the help of Twitter -- have uncovered the strongest evidence yet that an enormous X-shaped structure made of stars lies within the central bulge of the Milky Way Galaxy. Previous computer models, observations of other galaxies, and observations of our own galaxy have suggested that the X-shaped structure existed. But no one had observed it directly; and some astronomers argued that previous research that pointed indirectly to the existence of the X could be explained in other ways.




A source accelerating Galactic cosmic rays to unprecedented energy discovered at the center of the Milky Way   Science Daily - March 18, 2016
For more than ten years the H.E.S.S. observatory in Namibia, run by an international collaboration of 42 institutions in 12 countries, has been mapping the center of our galaxy in very-high-energy gamma rays. These gamma rays are produced by cosmic rays from the innermost region of the Galaxy. A detailed analysis of the latest H.E.S.S. data reveals for the first time a source of this cosmic radiation at energies never observed before in the Milky Way: the supermassive black hole at the center of the Galaxy, likely to accelerate cosmic rays to energies 100 times larger than those achieved at the largest terrestrial particle accelerator.




Event Horizon Telescope reveals magnetic fields at Milky Way's central black hole   PhysOrg - December 3, 2015
Most people think of black holes as giant vacuum cleaners sucking in everything that gets too close. But the supermassive black holes at the centers of galaxies are more like cosmic engines, converting energy from infalling matter into intense radiation that can outshine the combined light from all surrounding stars. If the black hole is spinning, it can generate strong jets that blast across thousands of light-years and shape entire galaxies. These black hole engines are thought to be powered by magnetic fields. For the first time, astronomers have detected magnetic fields just outside the event horizon of the black hole at the center of our Milky Way galaxy.




Bubbles from the Galactic Center: A key to understanding dark matter and our galaxy's past   PhysOrg - January 27, 2015
Compared to other galaxies, the Milky Way is a peaceful place. But it hasn't always been so sleepy. In 2010, a team of scientists working at the Harvard-Smithsonian Center for Astrophysics discovered a pair of "Fermi bubbles" extending tens of thousands of light-years above and below the Milky Way's disk. These structures are enormous balloons of radiation emanating from the center of our galaxy. They hint at a powerful event that took place millions of years ago, likely when the black hole at the center of our galaxy feasted on an enormous amount of gas and dust - perhaps several hundreds or even thousands of times the mass of the sun.




Hidden galactic nuclei   PhysOrg - August 10, 2012
At the core of most galaxies including our own Milky Way is a massive black hole. Material falling into the environment of the black hole heats up, and can radiate dramatically, sometimes also powering the ejection of bipolar jets of rapidly moving charged particles. These so-called active galactic nuclei (AGN) are observed to have roughly two types of characteristics: bright, rapidly moving hot gas with dust emission features, or dust absorption with modest (or no) fast gas




Milky Way may have formed 'inside-out': Gaia provides new insight into Galactic evolution   PhysOrg - January 20, 2014

A breakthrough using data from the Gaia-ESO project has provided evidence backing up theoretically predicted divisions in the chemical composition of the stars that make up the Milky Way's disc the vast collection of giant gas clouds and billions of stars that give our Galaxy its 'flying saucer' shape.




Milky Way shaken... and stirred   PhysOrg - January 20, 2014
team of scientists headed by Ivan Minchev from the Leibniz Institute for Astrophysics Potsdam (AIP), has found a way to reconstruct the evolutionary history of our galaxy, the Milky Way, to a new level of detail. The investigation of a data set of stars near the Sun was decisive for the now published results. The astronomers studied how the vertical motions of stars - in the direction perpendicular to the galactic disc - depend on their ages. Because a direct determination of the age of stars is difficult, the astronomers instead analyzed the chemical composition of stars: an increase in the ratio of magnesium to iron ([Mg/Fe]) points to a greater age.




The peanut at the heart of our galaxy   PhysOrg - September 12, 2013
This artist's impression shows how the Milky Way galaxy would look seen from almost edge on and from a very different perspective than we get from the Earth. The central bulge shows up as a peanut shaped glowing ball of stars and the spiral arms and their associated dust clouds form a narrow band. Two groups of astronomers have used data from ESO telescopes to make the best three-dimensional map yet of the central parts of the Milky Way. They have found that the inner regions take on a peanut-like, or X-shaped, appearance from some angles. This odd shape was mapped by using public data from ESO's VISTA survey telescope along with measurements of the motions of hundreds of very faint stars in the central bulge.




Astronomers discover star racing around black hole at Milky Way center   PhysOrg - October 4, 2012
UCLA astronomers report the discovery of a remarkable star that orbits the enormous black hole at the center of our Milky Way galaxy in a blistering 11-and-a-half years - the shortest known orbit of any star near this black hole.




Astronomers weigh in on Milky Way's true colors   BBC - January 12, 2012
Astronomers have determined exactly what color our home galaxy the Milky Way is - and find it is aptly named. They wanted to find out how our galaxy looked from the outside - a difficult task given the Earth is inside it. A comparison of star types in other galaxies gives perhaps an unsurprising result: white. But not just any white: specifically, like spring snow at an hour after sunrise or before sunset.




Astronomers determine color of the Milky Way Galaxy   PhysOrg - January 11, 2012
A team of astronomers in Pitt's Kenneth P. Dietrich School of Arts and Sciences announced today the most accurate determination yet of the color of the (aptly named) Milky Way Galaxy: "a very pure white, almost mirroring a fresh spring snowfall."




"Diamond" Planet Found; May Be Stripped Star   Live Science - August 25, 2011
The newfound planet orbits the pulsar so closely the entire system would fit inside the sun. An exotic planet as dense as diamond has been found in the Milky Way, and astronomers think the world is a former star that got transformed by its orbital partner. The odd planet was discovered orbiting what's known as a millisecond pulsar - a tiny, fast-spinning corpse of a massive star that died in a supernova. Astronomers estimate that the newfound planet is 34,175 miles (55,000 kilometers) across, or about five times Earth's diameter.




Space telescopes reveal previously unknown brilliant X-ray explosion in our Milky Way galaxy   PhysOrg - October 22, 2010
Astronomers in Japan, using an X-ray detector on the International Space Station, and at Penn State University, using NASA's Swift space observatory, are announcing the discovery of an object newly emitting X-rays, which previously had been hidden inside our Milky Way galaxy in the constellation Centaurus.




Scientists get a look at the birth of the Milky Way   PhysOrg - June 22, 2010
For the first time, a team of astronomers has succeeded in investigating the earliest phases of the evolutionary history of our home Galaxy, the Milky Way. The scientists, from the Argelander Institute for Astronomy at Bonn University and the Max-Planck Institute for Radioastronomy in Bonn, deduce that the early Galaxy went from smooth to clumpy in just a few hundred million years.




There is a giant black hole at the center of our galaxy, a study has confirmed.    BBC - December 10, 2008
There is a giant black hole at the centre of our galaxy, a 16-year study by German astronomers has confirmed. They tracked the movement of 28 stars circling the centre of the Milky Way, using two telescopes in Chile. The black hole, said to be 27,000 light years from Earth, is four million times bigger than the Sun, according to the paper in The Astrophysical Journal. Black holes are objects whose gravity is so great that nothing - including light - can escape them. According to Dr Robert Massey, of the Royal Astronomical Society (RAS), the results suggest that galaxies form around giant black holes in the way that a pearl forms around grit.




Milky Way's Giant Black Hole 'Awoke From Slumber' 300 Years Ago Science Daily - April 17, 2008
Using NASA, Japanese, and European X-ray satellites, a team of Japanese astronomers has discovered that our galaxy's central black hole let loose a powerful flare three centuries ago. The finding helps resolve a long-standing mystery: why is the Milky Ways black hole so quiescent? The black hole, known as Sagittarius A* (pronounced "A-star"), is a certified monster, containing about 4 million times the mass of our Sun. Yet the energy radiated from its surroundings is billions of times weaker than the radiation emitted from central black holes in other galaxies.




Radio Waves Detected Coming From Center of Galaxy   National Geographic - March 2, 2005
Astronomers have detected an unusual, powerful burst of intermittent radio waves emanating from the direction of the center of our galaxy. Now the search is on to trace the source of the mystery radio bursts, or at least find more like it. Was it a dying star "burping" its last radio emissions? Or is there something out there completely new to science? Astronomical radio sources are objects in outer space that emit strong radio waves. Radio emission comes from a wide variety of sources. Such objects represent some of the most extreme and energetic physical processes in the universe.





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