First Image of Blackhole ⚫

Introduction :-

» First ever image of Blackhole was captured by Event horizon telescope

» It was present in galactic center of galaxy named as M-87

» Mass = (6.5 ± 0.7) × 10^9 M

» Brightness of ring was not same

» Emission ring was of same size

Instruments use to capture Blackhole

Event horizon Telescope

In order to capture shadow of blackhole at center of M-87, we need baseline of Earth diameter scale and wavelength of 1.3mm. So EHT was used. The EHT (Event Horizon Telescope) is a telescope that uses very long baseline interferometry (VLBI) to directly measure the "visibilities" of radio sources. The telescope has a network of many small telescopes around the world that work together to create a virtual telescope.

More about Telescope

All of these telescopes are synchronized by GPS. Each telescope has a thing called a hydrogen maser frequency standard. This allows them to keep track of the recordings from each telescope and compare them to one another.

Observations, Correlation, and Calibration

A series of observations were scheduled where M87 would be looked at for 3-7 minutes (on April 5,6,10 and 11 2017) and then 3C 279 (A Quasar) would be looked at for the same amount of time.

This project used a very sensitive telescope to study very faint astronomical signals. The telescope was set up at two different locations, and each location recorded data from two frequency bands

The data from each location was then combined to create a more complete picture of the astronomical signals

Next step

The second step in the process was to look for patterns in the signal power that indicated a detection. This was done by calibrating the data for things like residual delays and atmospheric effects. Because ALMA is a very sensitive reference station, it was able to be used to make corrections for ionospheric and tropospheric distortions at the other sites.

Fringe fitting is a process of matching up detected patterns, and it was done using three different automated pipelines. Each one was designed to work with the specific characteristics of the EHT observations, like the wide bandwidth or the array heterogeneity. The accuracies of the derived station sensitivities were estimated to be 5%–10% in amplitude, although certain uncharacterized losses (e.g., from poor pointing or focus) can exceed the error budget

Challenges

There are two major challenges in taking these pictures. The first challenge is that the machine can only see a limited range of spatial frequencies. The second challenge is that the machine can only see things that are really bright

GRMHD Model and EHT observation

Imaging algorithms are used to create images from data. These images are designed to be physically plausible (e.g., positive and compact) or conservative (e.g., smooth).

General-relativistic magnetohydrodynamics (GRMHD) models were looking same as EHT simulation

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