Tag Archives: black hole

First image of a Black hole (and Abstract & Conclusion of scientific paper, published by American Astronomical Society 10th April 2019)

Today the Scientific community and indeed the whole world (especially that of social media) is bubbling up with excitement of the release of photos – first images of a black hole.   I’ve tracked the various links to the original scientific letter published at IOPScience site. Without breaching their brilliant presentation (the Physicist in me struggles to decipher it all), here are some key sections..  like the actual images, Abstract and Conclusion.

-Mani Navasothy

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The following Images, Abstract & Conclusion are taken from the article titled:

First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole .

(Published 2019 April 10 • © 2019. The American Astronomical Society- link at the bottom of the blog.

Eight stations of the EHT 2017 campaign over six geographic locations as viewed from the equatorial plane. Solid baselines represent mutual visibility on M87* (+12° declination).
Fig 1: Eight stations of the EHT 2017 campaign over six geographic locations as viewed from the equatorial plane. Solid baselines represent mutual visibility on M87* (+12° declination).
apjlab0ec7f3_lr
EHT image of M87* from observations on 2017 April 11 as a representative example of the images collected in the 2017 campaign. The image is the average of three different imaging methods after convolving each with a circular Gaussian kernel to give matched resolutions. The largest of the three kernels (20 μas FWHM) is shown in the lower right. The image is shown in units of brightness temperature, ${T}_{{\rm{b}}}=S{\lambda }^{2}/2{k}_{{\rm{B}}}{\rm{\Omega }}$, where S is the flux density, λ is the observing wavelength, kB is the Boltzmann constant, and Ω is the solid angle of the resolution element. Bottom: similar images taken over different days showing the stability of the basic image structure and the equivalence among different days. North is up and east is to the left.
apjlab0ec7f4_lr
three example models of some of the best-fitting snapshots from the image library of GRMHD simulations for April 11 corresponding to different spin parameters and accretion flows. Bottom: the same theoretical models, processed through a VLBI simulation pipeline with the same schedule, telescope characteristics, and weather parameters as in the April 11 run and imaged in the same way as Figure 3. Note that although the fit to the observations is equally good in the three cases, they refer to radically different physical scenarios; this highlights that a single good fit does not imply that a model is preferred over others

 

Abstract:

When surrounded by a transparent emission region, black holes are expected to reveal a dark shadow caused by gravitational light bending and photon capture at the event horizon. To image and study this phenomenon, we have assembled the Event Horizon Telescope, a global very long baseline interferometry array observing at a wavelength of 1.3 mm. This allows us to reconstruct event-horizon-scale images of the supermassive black hole candidate in the center of the giant elliptical galaxy M87. We have resolved the central compact radio source as an asymmetric bright emission ring with a diameter of 42 ± 3 μas, which is circular and encompasses a central depression in brightness with a flux ratio gsim10:1. The emission ring is recovered using different calibration and imaging schemes, with its diameter and width remaining stable over four different observations carried out in different days. Overall, the observed image is consistent with expectations for the shadow of a Kerr black hole as predicted by general relativity. The asymmetry in brightness in the ring can be explained in terms of relativistic beaming of the emission from a plasma rotating close to the speed of light around a black hole. We compare our images to an extensive library of ray-traced general-relativistic magnetohydrodynamic simulations of black holes and derive a central mass of M = (6.5 ± 0.7) × 109 M⊙. Our radio-wave observations thus provide powerful evidence for the presence of supermassive black holes in centers of galaxies and as the central engines of active galactic nuclei. They also present a new tool to explore gravity in its most extreme limit and on a mass scale that was so far not accessible.

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Conclusion and Outlook (first 2 paragraphs).

We have assembled the EHT, a global VLBI array operating at a wavelength of 1.3 mm and imaged horizon-scale structures around the supermassive black hole candidate in M87. Using multiple independent calibration, imaging, and analysis methods, we find the image to be dominated by a ring structure of 42 ± 3 μas diameter that is brighter in the south. This structure has a central brightness depression with a contrast of >10:1, which we identify with the black hole shadow. Comparing the data with an extensive library of synthetic images obtained from GRMHD simulations covering different physical scenarios and plasma conditions reveals that the basic features of our image are relatively independent of the detailed astrophysical model. This allows us to derive an estimate for the black hole mass of M = (6.5 ± 0.7) × 109 M. Based on our modeling and information on the inclination angle, we derive the sense of rotation of the black hole to be in the clockwise direction, i.e., the spin of the black hole points away from us. The brightness excess in the south part of the emission ring is explained as relativistic beaming of material rotating in the clockwise direction as seen by the observer, i.e., the bottom part of the emission region is moving toward the observer.

Future observations and further analysis will test the stability, shape, and depth of the shadow more accurately. One of its key features is that it should remain largely constant with time as the mass of M87* is not expected to change measurably on human timescales. Polarimetric analysis of the images, which we will report in the future, will provide information on the accretion rate via Faraday rotation (Bower et al. 2003; Marrone et al. 2007; Kuo et al. 2014; Mościbrodzka et al. 2017) and on the magnetic flux. Higher-resolution images can be achieved by going to a shorter wavelength, i.e., 0.8 mm (345 GHz), by adding more telescopes and, in a more distant future, with space-based interferometry (Kardashev et al. 2014; Fish et al. 2019; Palumbo et al. 2019; F. Roelofs et al. 2019b, in preparation).

Essential links to full scientific Paper:

Focus on the First Event Horizon Telescope Results –   Shep Doeleman (EHT Director) on behalf of the EHT Collaboration.  April 2019.  

First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole .