Sagittarius a observational data
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Event Horizon Telescope Observations of Sagittarius A*: Imaging and Structure
Recent observations of Sagittarius A* (Sgr A*), the supermassive black hole at the center of the Milky Way, have been revolutionized by the Event Horizon Telescope (EHT). In 2017, the EHT used a global array of eight telescopes to observe Sgr A* at a wavelength of 1.3 mm, achieving unprecedented resolution. These observations revealed a bright, thick ring with a diameter of about 51.8 microarcseconds, consistent with the expected shadow of a black hole with a mass of approximately 4 million solar masses. The ring shows modest brightness asymmetry and a dim interior, matching predictions for a Kerr black hole and providing direct evidence for the black hole at the Galactic center . The EHT also produced the first resolved linear and circular polarization images of Sgr A*, showing a highly polarized emission ring with a spiral pattern, which gives new insights into the magnetic field structure near the event horizon .
Variability and Multi-Wavelength Monitoring of Sgr A*
Sgr A* is known for its variability across multiple wavelengths. During the 2017 EHT campaign, simultaneous observations with the Atacama Large Millimeter/submillimeter Array (ALMA) and the Submillimeter Array provided high-cadence millimeter light curves. These data showed that Sgr A* typically exhibits low variability, but following an X-ray flare, the variability increased significantly. The power spectral density of the light curves suggests a red-noise process, with a steepening at shorter timescales, and no significant time lag between closely spaced frequency bands, indicating low optical depth at event horizon scales 24.
Simultaneous X-ray and infrared (IR) observations have shown that every distinct X-ray flare is accompanied by a rise in IR flux, though not all IR peaks coincide with X-ray flares. Analysis of over 100 hours of coordinated Spitzer and Chandra data suggests that X-ray flares may lead IR flares by about 10–20 minutes, but the timing is also consistent with simultaneity, highlighting the need for further long-duration, multi-wavelength campaigns to better understand the emission mechanisms 34.
Intrinsic Size and Structure at Multiple Wavelengths
Very long baseline interferometry (VLBI) observations at 1.3 cm and 7 mm have been used to study the intrinsic structure of Sgr A*. After correcting for interstellar scattering, the emission is well described by a symmetric Gaussian model at both wavelengths. The intrinsic size of Sgr A* decreases with shorter observing wavelengths, following a power-law relationship. These results support models where the radio emission originates from a radiatively inefficient accretion flow, requiring a nonthermal electron population to match the observed sizes .
Sagittarius Stream and Dwarf Galaxy: Broader Context
While Sgr A* is the central black hole, the broader Sagittarius region includes the Sagittarius stream and the Sagittarius dwarf spheroidal galaxy (dSph). Observational data from Gaia and other surveys have mapped the 3D structure and kinematics of the Sagittarius dSph, revealing it as a prolate structure in the process of tidal disruption by the Milky Way. The remnant is expected to be fully disrupted within the next billion years . Studies of the Sagittarius stream using various stellar tracers have provided accurate distances and velocities, helping to refine models of the Milky Way’s dark matter halo and the dynamics of tidal debris .
Conclusion
Observational data from the EHT and multi-wavelength campaigns have provided a detailed view of Sgr A*, confirming its status as a supermassive black hole and revealing its dynamic variability and polarized emission structure. These findings, combined with broader studies of the Sagittarius region, continue to deepen our understanding of the Galactic center and its complex environment 2345+3 MORE.
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Simultaneous X-Ray and Infrared Observations of Sagittarius A*'s Variability
Simultaneous X-ray and infrared observations of Sagittarius A* reveal that flaring in the X-ray may lead the IR by 10-20 minutes, but the flaring remains statistically consistent with simultaneity.
First Sagittarius A* Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole in the Center of the Milky Way
The first Event Horizon Telescope observations confirm the presence of a supermassive black hole at the center of the Milky Way galaxy, supporting the theory of general relativity.
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