Event Horizon Telescope – How They Capture The First Image Of The Black Hole

(Last Updated On: August 19, 2019)

Finally – We Capture It !

The world was quite under the delusion of not having visualized, an absolute visualization of a black hole while the scientists at Harvard University, University of  Arizona and other eminent scientists came together to bring to us the first ever image of black hole, thereby putting the delusion to rest. The algorithm was put forward by Katie Bouman, CalTech also the woman responsible for imaging the black hole.

The black hole seems to be at the center of the Galaxy M87. The super massive giant is seen like a black depression surrounded by luminous intensity of light radiating with radiation concentration more at the bottom of the circumference.

First image of the black hole
First image of the black hole

The above image is the first ever shadow of the black hole produced  on 10th April at 13:00 GST. The shift or variation of intensity in light is due to the fact that the super massive giant is rotating clockwise and thus bending light at the event horizon which under the centrifugal force is deflected towards one of the end while the image was captured. After the view of this black hole the Scientist concluded that they are capable of powering Active Galactic Nuclei’s (AGN’s) which can outshine the stellar population of the host galaxy.


Fundamental concept involves that the photon capture radius of the black hole is greater than the Schwarzschild radius which marks the event horizon of the non rotating black hole (although the scientists claim the black hole to be rotating clockwise) when viewed from infinity. Thus Schwarzschild radius R nearly equal to 2r where r=(GM) /(c^2). Now the impact factor plays a vital role at this point.

If the impact factor k<R’ where R’=(27^0.5)r then the photons will be plunged into the black hole where as if the the vice versa happens that is k> R’ photons will escape to infinity. Now considering the boundary value issue k=R’ then  the photons get captured in an unstable orbit which can be particularly referred to as “photon ring” or “photon ellipse”.

EHT – Event Horizon Telescope

Coming to the EHT,, the Event Horizon Telescope is a VLBI measurement system that focuses in measuring the Fourier components of the radio distribution in the sky. VLBI stands for Very Large Baseline Interferometry that works generally on the mm or cm range but with the technological advancements they made it possible to work at a range below 1.3 mm. VLBI involves the receiving radio signal of an astronomical source into several receiving end radio telescopes.

In this process they used at least 7 telescopes all over the earth surface to gather different signals from different portions of the black hole (rather the shadow). The distance can be calculated between two receiving end telescopes by the time difference according to the atomic clock like hydrogen maser. The resolution of the technique is proportionate with the frequency used.

Here is the list of 8 observatories / telescopes that make possible the first image of the black hole ? – 


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The data are correlated along the other data received from the other telescopes and they are put together using super computing to produce the image with higher resolution. The algorithm proposed by Katie Bouman helped in speeding up the process although the resolution was quite acceptable.

Overall the produced image does have strong resemblance with the Kerr black hole as predicted by general relativity. The central mass was calculated using a complex mechanism known as ray traced  general relativistic magneto hydrodynamics which gave the result to be (6.5+-0.7)x (10^9) M.


While gathering and calibration of the images the two major issues faced were the lack or limitation of spatial frequencies which led to the lag of baselines and as well as the”measured visibilities” lack phase calibration along with large displacement uncertainties.

However even after these difficulties the scientists brought to us the image of a black hole which provided a doorway to explore gravity to a new extreme limit and on a mass scale which was so far not accessible.

Wondering about this image that what secrets it will unveil ? Then check out our another article on that – Click Here

Let me know in comments what do you think about that article!

2 thoughts on “Event Horizon Telescope – How They Capture The First Image Of The Black Hole

  • April 15, 2019 at 11:00 am

    Please do breifly explain me the relevance of Schwarzschild radius…. Thanks for this article… well written and explained.

    • April 16, 2019 at 9:27 am

      Schawrzschild radius is defined as the boundary of a black hole of Schwarzchild type where the curvature of
      space time becomes infinite and no object crossing that radius can ever escape from the gravitational pull of the black hole. Generally a Schwarzchild type black hole is non rotating and electrically neutral.


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