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TOPIC: Our black hole
Blobrana


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Milky Way black hole
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Hubble Dates Black Hole's Last Big Meal

About 6 million years ago, when our very remote ancestors began to evolve away from chimpanzees, our Milky Way galaxy's hefty black hole was enjoying a sumptuous feast. It gulped down a huge clump of interstellar hydrogen.
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Blobrana


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Our Galaxy's Black Hole is Spewing Out Planet-size "Spitballs"

Every few thousand years, an unlucky star wanders too close to the black hole at the center of the Milky Way. The black hole's powerful gravity rips the star apart, sending a long streamer of gas whipping outward. That would seem to be the end of the story, but it's not. New research shows that not only can the gas gather itself into planet-size objects, but those objects then are flung throughout the galaxy in a game of cosmic "spitball."
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Blobrana


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Sgr A*
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Sagittarius A*: NASA X-ray Telescopes Find Black Hole May Be a Neutrino Factory

While the Sun produces neutrinos that constantly bombard the Earth, there are also other neutrinos with much higher energies that are only rarely detected. Scientists have proposed that these higher-energy neutrinos are created in the most powerful events in the Universe like galaxy mergers, material falling onto supermassive black holes, and the winds around dense rotating stars called pulsars.
Using three NASA X-ray telescopes, Chandra, Swift, and NuSTAR, scientists have found evidence for one such cosmic source for high-energy neutrinos: the 4-million-solar-mass black hole at the center of our Galaxy called Sagittarius A* (Sgr A*, for short). After comparing the arrival of high-energy neutrinos at the underground facility in Antarctica, called IceCube, with outbursts from Sgr A*, a team of researchers found a correlation. In particular, a high-energy neutrino was detected by IceCube less than three hours after astronomers witnessed the largest flare ever from Sgr A* using Chandra. Several flares from neutrino detections at IceCube also appeared within a few days of flares from the supermassive black hole that were observed with Swift and NuSTAR.
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Blobrana


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Title: A star disrupted by a stellar black hole as the origin of the cloud falling towards the Galactic center
Authors: Jordi Miralda-Escude

We propose that the cloud of gas moving on a highly eccentric orbit around the central black hole in our Galaxy, reported by Gillessen et al., is produced by a wind from photoevaporating debris orbiting around a star with a small circumstellar disk. The disk is tidally truncated to less than 1 AU at the peribothron passage, and a cloud like the observed one is recreated by the wind at every orbit. The star-disk system, which may have been producing the cloud for hundreds of orbits in the past, is proposed to have formed when the star flew by a stellar black hole and was tidally disrupted and deflected to its present orbit. Encounters of low-mass stars with stellar black holes are likely to occur at the location of this cloud, because of the high density of stellar black holes expected to have migrated to the Galactic center by mass segregation. The rate of these encounters at a small enough impact parameter to disrupt the star may reasonably be ~ 10^{-6} per year. The flyby should have spun up the star and pulled out a substantial fraction of its mass as tidal debris, part of which fell back onto the star and created a small disk. Since then, the disk may have expanded by absorbing angular momentum from the star up to the tidal truncation radius. Thereafter, the strong tidal perturbation of the outer disk edge at every peribothron may create gas streams moving out to larger radius that can photoevaporate and generate the wind that produces the cloud at every orbit. The model predicts that when the cloud is disrupted at the next peribothron passage in 2013, a smaller unresolved cloud will follow the star on the same orbit that will gradually grow. An increased infrared luminosity from the disk may also become detectable during the peribothron passage.

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Blobrana


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Has our black hole been blowing bubbles?

Our galaxy is a relatively quiet neighbourhood with the supermassive black hole at its heart gently dozing: or is it?
The recent discovery of huge gamma-ray emitting 'bubbles' around the Milky Way is challenging this assumption and posing a new puzzle: just where do these bubbles come from?
Philipp Mertsch and Subir Sarkar of Oxford University's Department of Physics recently reported in Physical Review Letters a model that could explain the origins of these strange phenomena.
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Blobrana


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The Black Hole at the Center of Our Galaxy



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Blobrana


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Star tracked as it orbits the Milky Way's black hole


Over a period of 16 years, astronomers tracked stars as they orbited the Milky Way's central region, which is thought to harbour a colossal black hole. One star, called S2, was observed over its complete 15.8-year-long orbit. The star approached the black hole to within one light day, which is only about five times the distance between Neptune and the Sun. (Courtesy of ESO)

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Astronomers believe they have come up with concrete proof for the existence of black holes.
Ever since Albert Einstein came up with his general theory of relativity, black holes has been central to our knowledge of the Universe.
Now experts say they have shown that the theoretical phenomenon, whose gravitational pull is thought to hold galaxies together, exist "beyond any reasonable doubt".
The team of scientists spent 16 years studying the existence of a super massive black hole thought to be at the centre of our galaxy, the Milky Way.
While the black hole itself is invisible to the eye, the team proved its existence by tracking the motions of 28 stars circling around it.
Just as swirling leaves caught in a gust of wind can provide clues about air currents, so the stars' movements reveal information about forces at work at the galactic centre.

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There is a giant black hole at the centre of our galaxy, a study has confirmed.
German astronomers tracked the movement of 28 stars circling the centre of the Milky Way, using the European Southern Observatory in Chile.
The black hole is four million times heavier than our Sun, according to the paper in The Astrophysical Journal.

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Blobrana


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Sagittarius A*
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Two separate telescopes in Chile picked up the same black hole flare recently, allowing them to see for the first time what it looks like when superheated gas orbits the black hole's event horizon as it is being devoured. The black hole in question is the Milky Way's own supermassive Sagittarius A*, with a mass of about four million times that of the Sun.

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Title: Measuring Distance and Properties of the Milky Way's Central Supermassive Black Hole with Stellar Orbits
Authors: A. M. Ghez, S. Salim, N. N. Weinberg, J. R. Lu, T. Do, J. K. Dunn, K. Matthews, M. Morris, S. Yelda, E. E. Becklin, T. Kremenek, M. Milosavljevic, J. Naiman

We report new precision measurements of the properties of our Galaxy's supermassive black hole. Based on astrometric (1995-2007) and radial velocity (2000-2007) measurements from the W. M. Keck 10-meter telescopes, a fully unconstrained Keplerian orbit for the short period star S0-2 provides values for Ro of 8.0+-0.6 kpc, M_bh of 4.1+-0.6x10^6 Mo, and the black hole's radial velocity, which is consistent with zero with 30 km/s uncertainty. If the black hole is assumed to be at rest with respect to the Galaxy, we can further constrain the fit and obtain Ro = 8.4+-0.4 kpc and M_bh = 4.5+-0.4x10^6 Mo. More complex models constrain the extended dark mass distribution to be less than 3-4x10^5 Mo within 0.01 pc, ~100x higher than predictions from stellar and stellar remnant models. For all models, we identify transient astrometric shifts from source confusion and the assumptions regarding the black hole's radial motion as previously unrecognised limitations on orbital accuracy and the usefulness of fainter stars. Future astrometric and RV observations will remedy these effects. Our estimates of Ro and the Galaxy's local rotation speed, which it is derived from combining Ro with the apparent proper motion of Sgr A*, (theta0 = 229+-18 km/s), are compatible with measurements made using other methods. The increased black hole mass found in this study, compared to that determined using projected mass estimators, implies a longer period for the innermost stable orbit, longer resonant relaxation timescales for stars in the vicinity of the black hole and a better agreement with the M_bh-sigma relation.

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