https://www.nasa.gov/mission_pages/chandra/multimedia/black-hole-SagittariusA.html Please Register or Log in to view the hidden image! The center of the Milky Way galaxy, with the supermassive black hole Sagittarius A* (Sgr A*), located in the middle, is revealed in these images. As described in our press release, astronomers have used NASA’s Chandra X-ray Observatory to take a major step in understanding why material around Sgr A* is extraordinarily faint in X-rays. The large image contains X-rays from Chandra in blue and infrared emission from the Hubble Space Telescope in red and yellow. The inset shows a close-up view of Sgr A* in X-rays only, covering a region half a light year wide. The diffuse X-ray emission is from hot gas captured by the black hole and being pulled inwards. This hot gas originates from winds produced by a disk-shaped distribution of young massive stars observed in infrared observations. These new findings are the result of one of the biggest observing campaigns ever performed by Chandra. During 2012, Chandra collected about five weeks worth of observations to capture unprecedented X-ray images and energy signatures of multi-million degree gas swirling around Sgr A*, a black hole with about 4 million times the mass of the Sun. At just 26,000 light years from Earth, Sgr A* is one of very few black holes in the universe where we can actually witness the flow of matter nearby. The authors infer that less than 1% of the material initially within the black hole’s gravitational influence reaches the event horizon, or point of no return, because much of it is ejected. Consequently, the X-ray emission from material near Sgr A* is remarkably faint, like that of most of the giant black holes in galaxies in the nearby Universe. The captured material needs to lose heat and angular momentum before being able to plunge into the black hole. The ejection of matter allows this loss to occur. This work should impact efforts using radio telescopes to observe and understand the “shadow” cast by the event horizon of Sgr A* against the background of surrounding, glowing matter. It will also be useful for understanding the impact that orbiting stars and gas clouds might make with the matter flowing towards and away from the black hole. The paper is available online and is published in the journal Science. The first author is Q.Daniel Wang from University of Massachusetts at Amherst, MA; and the co-authors are Michael Nowak from Massachusetts Institute of Technology (MIT) in Cambridge, MA; Sera Markoff from University of Amsterdam in The Netherlands, Fred Baganoff from MIT; Sergei Nayakshin from University of Leicester in the UK; Feng Yuan from Shanghai Astronomical Observatory in China; Jorge Cuadra from Pontificia Universidad de Catolica de Chile in Chile; John Davis from MIT; Jason Dexter from University of California, Berkeley, CA; Andrew Fabian from University of Cambridge in the UK; Nicolas Grosso from Universite de Strasbourg in France; Daryl Haggard from Northwestern University in Evanston, IL; John Houck from MIT; Li Ji from Purple Mountain Observatory in Nanjing, China; Zhiyuan Li from Nanjing University in China; Joseph Neilsen from Boston University in Boston, MA; Delphine Porquet from Universite de Strasbourg in France; Frank Ripple from University of Massachusetts at Amherst, MA and Roman Shcherbakov from University of Maryland, in College Park, MD. Image credit: X-ray: NASA/UMass/D.Wang et al., IR: NASA/STScI <<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>> https://science.nasa.gov/astrophysics/focus-areas/black-holes extracts: Although the basic formation process is understood, one perennial mystery in the science of black holes is that they appear to exist on two radically different size scales. On the one end, there are the countless black holes that are the remnants of massive stars. Peppered throughout the Universe, these "stellar mass" black holes are generally 10 to 24 times as massive as the Sun. Astronomers spot them when another star draws near enough for some of the matter surrounding it to be snared by the black hole's gravity, churning out x-rays in the process. Most stellar black holes, however, lead isolated lives and are impossible to detect. Judging from the number of stars large enough to produce such black holes, however, scientists estimate that there are as many as ten million to a billion such black holes in the Milky Way alone. On the other end of the size spectrum are the giants known as "supermassive" black holes, which are millions, if not billions, of times as massive as the Sun. Astronomers believe that supermassive black holes lie at the center of virtually all large galaxies, even our own Milky Way. Astronomers can detect them by watching for their effects on nearby stars and gas. Please Register or Log in to view the hidden image! This chart shows the relative masses of super-dense cosmic objects. Read the full article Historically, astronomers have long believed that no mid-sized black holes exist. However, recent evidence from Chandra, XMM-Newton and Hubble strengthens the case that mid-size black holes do exist. One possible mechanism for the formation of supermassive black holes involves a chain reaction of collisions of stars in compact star clusters that results in the buildup of extremely massive stars, which then collapse to form intermediate-mass black holes. The star clusters then sink to the center of the galaxy, where the intermediate-mass black holes merge to form a supermassive black hole. <<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>
recent discoveries: 2020: https://chandra.harvard.edu/photo/2020/m87/ Chandra data show that the black hole in the galaxy M87 is propelling particles away from it faster than 99% the speed of light. These remarkable speeds were detected in changes in the X-ray emission between 2012 and 2017 in regions along a jet generated by the black hole. M87 became famous in April 2019 when the Event Horizon Telescope released the first-ever direct image of its black hole. The jet seen with Chandra is 500,000 times larger and shows much older activity from the black hole than the ring imaged by the EHT. These images show evidence from NASA's Chandra X-ray Observatory that the black hole in the galaxy Messier 87 (M87) is blasting particles out at over 99% the speed of light, as described in our latest press release. While astronomers have observed features in the M87 jet blasting away from its black hole this quickly at radio and optical wavelengths for many years, this provides the strongest evidence yet that actual particles are travelling this fast. Astronomers required the sharp X-ray vision from Chandra in order to make these precise measurements. more........ <<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>> http://www.esa.int/Science_Exploration/Space_Science/XMM-Newton_maps_black_hole_surroundings Material falling into a black hole casts X-rays out into space – and now, for the first time, ESA’s XMM-Newton X-ray observatory has used the reverberating echoes of this radiation to map the dynamic behaviour and surroundings of a black hole itself. Most black holes are too small on the sky for us to resolve their immediate environment, but we can still explore these mysterious objects by watching how matter behaves as it nears, and falls into, them. As material spirals towards a black hole, it is heated up and emits X-rays that, in turn, echo and reverberate as they interact with nearby gas. These regions of space are highly distorted and warped due to the extreme nature and crushingly strong gravity of the black hole. For the first time, researchers have used XMM-Newton to track these light echoes and map the surroundings of the black hole at the core of an active galaxy. Named IRAS 13224–3809, the black hole’s host galaxy is one of the most variable X-ray sources in the sky, undergoing very large and rapid fluctuations in brightness of a factor of 50 in mere hours. “Everyone is familiar with how the echo of their voice sounds different when speaking in a classroom compared to a cathedral – this is simply due to the geometry and materials of the rooms, which causes sound to behave and bounce around differently,” explains William Alston of the University of Cambridge, UK, lead author of the new study. “In a similar manner, we can watch how echoes of X-ray radiation propagate in the vicinity of a black hole in order to map out the geometry of a region and the state of a clump of matter before it disappears into the singularity. It’s a bit like cosmic echo-location.” more.................. <<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>> https://chandra.harvard.edu/photo/2020/ophiuchus/ Astronomers have discovered the biggest explosion seen in the Universe in the Ophiuchus galaxy cluster. A giant black hole in the central galaxy of the cluster caused the explosion, blasting out jets that carved a cavity in the surrounding hot gas. Astronomers obtained this result using data from NASA's Chandra X-ray Observatory, XMM-Newton, and two radio telescopes in Australia and India. The explosion released a factor of five more energy than the previous record holder and hundreds of thousands of times more than typical clusters. Evidence for the biggest explosion seen in the Universe is contained in these composite images. This discovery, covered in our latest press release, combines data from NASA's Chandra X-ray Observatory, ESA's XMM-Newton, the Murchison Widefield Array, and the Giant Metrewave Telescope. This extremely powerful eruption occurred in the Ophiuchus galaxy cluster, which is located about 390 million light years from Earth. Galaxy clusters are the largest structures in the Universe held together by gravity, containing thousands of individual galaxies, dark matter, and hot gas. The hot gas that pervades clusters like Ophiuchus gives off much of its light as X-rays. The main panel contains X-rays from XMM-Newton (pink) along with radio data from GMRT (blue), and infrared data from 2MASS (white). In the inset, Chandra's X-ray data are pink. In the center of the Ophiuchus cluster is a large galaxy containing a supermassive black hole. Researchers have traced the source of this gigantic eruption to jets that blasted away from the black hole and carved out a large cavity in the hot gas. (A labeled version includes a dashed line showing the edge of the cavity in the hot gas seen in X-rays from both Chandra and XMM-Newton.) Radio emission from electrons accelerated to almost the speed of light fills this cavity, providing evidence that an eruption of unprecedented size took place.
Paper with regards to Sag-A variable anomaly...... https://arxiv.org/pdf/1908.01777.pdf Unprecedented Near-Infrared Brightness and Variability of Sgr A* ABSTRACT: The electromagnetic counterpart to the Galactic center supermassive black hole, Sgr A*, has been observed in the near-infrared for over 20 years and is known to be highly variable. We report new Keck Telescope observations showing that Sgr A* reached much brighter flux levels in 2019 than ever measured at near-infrared wavelengths. In the K0 band, Sgr A* reached flux levels of ∼ 6 mJy, twice the level of the previously observed peak flux from > 13, 000 measurements over 130 nights with the VLT and Keck Telescopes. We also observe a factor of 75 change in flux over a 2-hour time span with no obvious color changes between 1.6 µm and 2.1 µm. The distribution of flux variations observed this year is also significantly different than the historical distribution. Using the most comprehensive statistical model published, the probability of a single night exhibiting peak flux levels observed this year, given historical Keck observations, is less than 0.3%. The probability to observe the flux levels similar to all 4 nights of data in 2019 is less than 0.05%. This increase in brightness and variability may indicate a period of heightened activity from Sgr A* or a change in its accretion state. It may also indicate that the current model is not sufficient to model Sgr A* at high flux levels and should be updated. Potential physical origins of Sgr A*’s unprecedented brightness may be from changes in the accretion-flow as a result of the star S0-2’s closest passage to the black hole in 2018 or from a delayed reaction to the approach of the dusty object G2 in 2014. Additional multi-wavelength observations will be necessary to both monitor Sgr A* for potential state changes and to constrain the physical processes responsible for its current variability. 5. CONCLUSIONS: Our recent observations of the Galactic center have captured Sgr A* in an unprecedented bright state in the near-infrared. Even more so, three of the four nights show Sgr A* in a clearly elevated state. The brightest flux levels observed in 2019 are over twice the peak flux value ever observed in the near-infrared from Keck and VLT. The distributions of flux variations from the four nights are also very unusual compared to the historical data, showing significant deviations from the model which was previously able to describe all historical Keck, VLT, & Spitzer measurements (Witzel et al. 2018; Chen et al. submitted). The 2019 measurements push the limits of the current statistical models. These models may need to be revised to gain a better understanding of the probability of observing very high flux levels. In addition, the statistical models for Sgr A* variability should be expanded to provide more robust tests for changes to the Sgr A* accretion properties over time. The major question is whether Sgr A* is showing increased levels of activity, and if so, how long it will last. Additional data, preferably multi-wavelength observations, throughout 2019 and beyond will be necessary to study the nature of its current variability.
