Theory Sgr A* or the Milky Way Galaxy Center

Sagittarius A* (pronounced 'Sagittarius A-star') is a tilted ring of gas and dust orbiting the Milky Way's black hole. The magnetic field there is strong enough to constrain the turbulent motions of gas and may, or not, direct that into the black hole. Using the infrared or X-ray light astronomers are now able to peer our Galaxy's core where a massive galactic black hole, the size of the orbit of Mercury and 4 million times the mass of our Sun, is lurking, nearly four million times more massive than our Sun. As some stars are orbiting at a distance from the black hole, the whole region is surely the most intricated and populated in the Milky Way Galaxy. In that space of some light-years, hundreds of thousands of stars or even millions are crammed into a gas and dust cloud. By comparison, in that same volume in our environment, only one star, the Sun, is found. Dozens of massive stellar giants with fierce winds blowing off their surfaces are found in the region covering a few light years surrounding Sgr A*. Such winds provide a buffet of material for the supermassive black hole to potentially feed upon. Clumps of gas are swirling around at about 30 percent of the speed of light on a circular orbit just outside Sagittarius A* event horizon, close to the point of no return. Magnetic interactions in the very hot gas orbiting very close to Sagittarius A* also exist. Astronomers until now have not been able to image our Milky Way Galaxy supermassive black hole, or 'Sagittarius A*.' They have observed however how stars are orbiting swiftly around that place, with such speeds like about 3,000 miles per second (5,000 km per second) in a 16-year orbit as the black hole should have the size of the orbit of Mercury and a mass 4 million times the mass of the Sun. A recent international project, the 'Event Horizon Telescope' as it will federate several instruments into a single giant interferometer should eventually be sharp enough to distinguish Sagittarius A*. The search for Sagittarius A*, or 'Sgr A*' for short, also has implications in terms of relation between Einstein's Relativity and quantum mechanics, as both theories are required to describe black holes, generally. The black hole of our own Milky Way Galaxy is a mild-mannered one, which only produces some flares of X-rays when he gobbles some celestial object passed too close. The evidence for a black hole at our Milky Way center came from the studies by the mid-1990's or how stars were orbiting in a dense cluster near the suspected location of the black hole. The radius and period of each orbit gave the central object's mass, and the distance of closest approach would put an upper limit on its size. Even young stars are orbiting close to the black hole as no good explanation exists for that nor why stars, generally, are there. A spinning dead star, or pulsar, is near the giant black hole as a population of other miscellaneous types of dead stars might also be found there and generating a emission of X-rays. Or the diffuse emission could also be cosmic rays originating from the supermassive black hole. Astronomers also found that a hot, red unknown object of three times the mass of Earth -it could be a cloud of gas or a star moving inside such a cloud- is heading straight towards the Galactic Centre, with a closest by fall 2013 or later. That could hint to that a series of gas clouds are orbiting our galactic black hole, likely the remaining of a star gobbled up by it. A intermediate-mass black hole with 32,000 times the mass of our Sun might be wandering near the center of the Milky Way Galaxy, at 20 light-years from it

The 300 light-year wide area surrounding Sgr A* at the center of the Milky Way Galaxy seen like a composite image in the near-infrared, infrared and X-rays (right) and in the infrared (left). picture courtesy site 'Amateur Astronomy'

The supermassive black hole region first, a powerful source of radiation is a bright spiral embedded within a circum-nuclear dusty inner-tube-shaped torus. The Galaxy central black hole endures short-duration bursts, strongly influenced by the interaction of the black hole with the enhanced gas density present within a ring-like central molecular zone. A inner 200-parsec region is characterized by large amounts of warm molecular gas, a high cosmic-ray ionization rate, unusual gas chemistry, enhanced synchrotron emission, and a multitude of radio-emitting magnetized filaments. A bipolar bubble structure, with dimensions 140×430 parsecs, extending above and below the Galactic plane and apparently associated with the Galactic Centre exist in the area and likely created by a energetic event in the Galactic center, and a age a few million years. All black holes are characterized by an accretion disk, surrounding them, which is where the infalling matter is orbiting before being definitively swallowed. Usually, a supermassive black hole is surrounded by an accretion disk, which itself is surrounded by a dark doughnut-like dusty structure called a dust torus. The supermassive black hole of the Milky Way Galaxy is feeding from about 0.1 percent only of the material brought there by the stellar winds of the neighbouring stars. Those winds might well be contained by a conduction process by which collisions between particles close to the hot, inner region -or 'event horizon'- of the black hole transfer energy by conduction to particles lying in a cooler, outer region, which host stars serving like a fuel for the black hole. A haze also is found around the center of the Galaxy as featuring cold gas and electrons accelerated through magnetic fields. Our supermassive black hole further is sided by two lobes of hot gas extending for a dozen light years either side, likely evidence of powerful eruptions of the black hole which occurred several times over the last ten thousand years. Mysterious X-ray filaments around the black hole might be huge magnetic structures interacting with streams of energetic electrons produced by rapidly spinning neutron stars close to Sgr A* and known like pulsar wind nebulas. The last episode of activity of our supermassive black hole occurred about 300 years ago, with a giant star exploding nearby and sweeping gas into the black hole, leading to a temporary feeding frenzy that awoke the black hole from its slumber. The black hole of the Milky Way Galaxy otherwise is a relatively calm one. That renewed activity is still affecting the region even though it ended about one hundred years ago. Astronomers suspect that it might awaken in a undetermined future and unleash, after a flurry of star formation about it, two polar jets. A jet of high-energy particles is also currenty blasting out of the Milky Way’s supermassive black hole with a shock front resulting from the hit of the jet into gas several light-years away. A weaker outflow, which might be like a sheath or cocoon surrounding the jet with an opening angle of around 25 degrees, also exists. 25 Wolf-Rayet stars orbit within about 1.5 light years from Sgr A* as they continuously eject stellar winds taking away some of their external layers. These winds collide with each other, and produce shock waves, similar to sonic booms, which permeate the area and heat the gas to millions of degree and then some of this material spirals towards Sgr A*. Tidal forces stretch the clumps as they get closer to the galactic black hole. The Sgr A* area may lie in a calm state or a more violent when the black hole is expelling material, thereby clearing away some of the gas produced by the Wolf-Rayet winds and turning off the accretion of clumped material. Such outburst episodes have X-rays in the shape of a disk extending about 0.6 light years from Sgr A*

->The Case of The G2 Object
A increased rate of X-ray flares exists from the usually quiet Sagittarius A* which is due to limited monitoring, or triggered by the recent close passage of a mysterious, dusty object. Sgr A* has been producing one bright X-ray flare about every ten days as that recent activity by mid-2015 had a ten-fold increase in the rate of bright flares at about one every day. This increase happened soon after the close approach to Sgr A* by a mysterious object called G2. Originally, astronomers thought G2 was an extended cloud of gas and dust. However, after passing close to Sgr A* in late 2013, its appearance did not change much, apart from being slightly stretched by the gravity of the black hole. This led to new theories that G2 was not simply a gas cloud, but instead a star swathed in an extended dusty cocoon. There isn’t universal agreement on what G2 is. Such a increase in activity, generally, is common among other galactic black holes. The increased X-ray activity could be due not to G2 but to a change in the strength of winds from nearby massive stars that are feeding material to the black hole instead, for example. The G objects generally -- as more are now known -- show the characteristics of gas and dust clouds but display the dynamical properties of stellar-mass objects

->. check a detailed view of both the images above, The 300 light-year wide area surrounding Sgr A* at the center of the Milky Way Galaxy seen like a composite image by NASA's Hubble and Spitzer Space Telescopes and the Chandra X-ray Observatory (left) and a combined view of the Hubble Space Telescope's Near Infrared Camera and Multi-Object Spectrometer (NICMOS) with color imagery from a previous Spitzer Space Telescope survey done with its Infrared Astronomy Camera (IRAC) (right). Both views are at scale. The pictures measure 300 x 115 light-years. The lower left region shows pillars of gas sculpted by winds from hot massive stars in the Quintuplet cluster. At the center of the image, ionized gas surrounding the supermassive black hole at the center of the Galaxy where it is confined, as magnetic structures at upper left, large arcs of ionized gas resolving into arrays of organized linear filaments are perhaps indicating locally strong magnetic fields. The Central cluster, the Arches cluster, and the Quintuplet cluster are easily seen as tight concentrations of bright, massive stars in the picture below. picture courtesy site 'Amateur Astronomy'

The position and mass of the supermassive black hole lurking at the center of our Milky Way Galaxy, have been known since 2002 through accurate measurements of the motions of stars orbiting around. The whole region surrounding Sgr A* in a diameter of 300 light-years is featuring vibrant regions of star birth, young hot stars, or old cool stars along with seething remnants of stellar death called black holes. Spanning 190 light-years a set of long, thin strands of ionized gas called filaments that emit radio waves, exist near Sgr A*. A ring about 10 light-years in diameter plays a key role in feeding matter closer to our Galaxy central black hole and how matter in that ring is replenishing is still badly known. Thousands of stellar-mass black holes are found within three light years of Sgr A* -- knowing that number will help in better predicting how many gravitational wave events may be associated with them in that area. Such a activity occurs in the crowded, hostile environment of the galaxy's core, with complex structures in the hot ionized gas swirling around the central 300 light-years, or locally strong magnetic fields playing a critical role. Permeating the region is a diffuse blue haze of X-ray light from gas that has been heated to millions of degrees by outflows from the supermassive black hole as well as by winds from massive stars and by stellar explosions. Infrared light reveals more than a hundred thousand stars along with glowing dust clouds that create complex structures including compact globules, long filaments, and finger-like "pillars of creation," where newborn stars are just beginning to break out of their dark, dusty cocoons. Massive stars also exist in the central, 300 light-years-wide region of our Galaxy, as they are mostly condensed into three clusters, the Central, Arches and Quintuplet clusters as some also formed in isolation or found themselves isolated when their cluster where disrupted by strong gravitational tidal forces. Massive stars however are not confined to one of the three known clusters of massive stars. The distributed stars may have formed in isolation, or they may have originated in clusters that have been disrupted by strong gravitational tidal forces. The winds and radiation from these stars form complex structures and in some cases, they may be triggering new generations of stars. Using the Stratospheric Observatory for Infrared Astronomy (SOFIA), astronomers captured our Milky Way Galaxy's circumnuclear ring (CNR), a ring of gas and dust seven light-years in diameter surrounding Galaxy's supermassive black hole, and of neighboring Quintuplet cluster (QC), a cluster of extremely luminous young stars embedded in dust cocoons. Galactic center generally hosts several exceptionally large star clusters containing some of the most luminous young stars in the Galaxy, due to that a large activity occurred in the Milky Way's center within the past 4 million to 6 million years which resulted in several bursts of star formation. Of them, for example, the Central Cluster and the Quintuplet Cluster. The molecular gas in the innermost central region of the Galaxy gets very hot as at least some of it is around 1,832° F (1000° C), much hotter than typical interstellar clouds, which are usually only a few tens of degrees above 0° K as it also holds a great variety of simple molecules including carbon monoxide, water vapour and hydrogen cyanide. While some of the heating is due to a fierce ultraviolet radiation pouring from a cluster of massive stars that lies very close to the Galactic Centre, and emission from strong shocks in the highly-magnetised gas might also be a significant contributor. Such shocks can be generated in collisions between gas clouds, or in material flowing at high speed from stars and protostars, for example. Observations are also consistent with streamers of hot gas speeding towards Sgr A*. Two lobes of hot gas are extending above and below our Milky Way's central black hole as they might be caused either directly by the black hole, which swallows part of the material that flows onto it but spews out most of it, or by the cumulative effect of the numerous stellar winds and supernova explosions that occur in such a dense environment. A large, elliptical structure existing in the vicinity is a super-bubble of hot gas, likely puffed up by the remnants of several supernovas at its centre. Another huge pocket of hot gas, or the 'Arc Bubble,' also exists. Warm plasma in the area could be the effect of outflows generated by star formation throughout the entire central zone of our Galaxy, or of the turbulent past of the now not-so-active supermassive black hole, a legacy of its ancient activity

A view (left) of the Milky Way galaxy’s nucleus showing the Circumnuclear Ring (CNR) of gas and dust clouds around the Milky Way Galaxy's supermassive black hole. The bright feature is believed to be material falling from the ring toward the black hole that is located where arms of the feature intersect. And a view (right) of a region including the Quintuple Cluster (QC), a group of young stars near the right margin of the frame, located about 35 parsecs (100 light years) from the Milky Way Galaxy’s nucleus. picture site 'Amateur Astronomy' based upon pictures NASA/SOFIA/FORCAST team/Lau et al. (left) and NASA/SOFIA/Hankins et al. (right)

->More About How the Center of Our Galaxy is Populated
The massive stars are not confined to one of the three known clusters of massive stars in the galactic Center, known as the Central cluster, the Arches cluster, and the Quintuplet cluster. The distributed massive stars are well present in the field as they may have formed in isolation, or they may have originated in clusters that have been disrupted by strong gravitational tidal forces. The winds and radiation from these stars form complex structures and in some cases they may be triggering new generations of stars. Large arcs of ionized gas resolved into arrays of organized linear filaments indicate also a critical role of the influence of locally strong magnetic fields. At the center, ionized gas surrounding the supermassive black hole at the center of our Galaxy is confined to a bright spiral embedded within a circum-nuclear dusty inner-tube-shaped torus

A twisted ring of dense gas exists at the center of our Milky Way galaxy, or the inner ring composed of a dense tube of cold gas mixed with dust where new stars are forming. It stretches across more than 600 light-years has it features a infinity symbol, or sideways 8, as seen in the infrared. It's a continuous strip of dense and cold clumps of material and it harbours a number of star-forming regions and young stars as it is part of the Central Molecular Zone, a region permeated with molecular clouds with two lobes pointing to the side. The inner ring is also slightly offset from 'Sagittarius A*,' the center of our Milky Way Galaxy. Precisely the ring lies at the center of our Milky Way's bar as the bar itself is actually inside an even larger ring. Such features, generally, are also seen at other galaxies. How bars and rings form in spiral galaxies are not well understood as computer simulations demonstrate how gravitational interactions -between two different galaxies included- can produce the structures. Not including dark matter, the Milky Way Galaxy weighs about 150 to 300 billion times the weight of the Sun as about 65 billion solar masses were missing from the observations. A massive, super-hot bubble of gas expanding from the neighborhood of Sagittarius A* might account for. 6 million years ago as the Milky Way's supermassive black hole was absorbing much of its environment, that created a bubble of relatively empty space but it also also pumped out a low-density gas into that space, composed of much oxygen and probably also hydrogen and other elements. That bubble of gas is expanding at a rate of about a million miles an hour as it will reach Earth in a few million years. The bubble however is much less dense than the normal interstellar medium and will be thinner still then

The center of the Milky Way may observed naked-eye or with a instrument as it lies in the constellation Sagittarius, the Archer