Recently, researchers released the second direct image of a black hole’s accretion disk, involving Sagittarius A* at the center of our galaxy, after the first one was released in April 2019 for the black hole at the center of M87. What does it take for astronomers to take images of unprecedentedly small points in the sky? Let’s find out.
The Event Horizon Telescope
To estimate just how small the black hole’s view is from Earth, it is akin to taking an image of a “donut on the Moon” (Event Horizon Telescope, 2022). The object is so small that scientists needed to develop a creative way to create a telescope that would be as large as the size of our planet if it was in one piece. Therefore, the Event Horizon Telescope, the telescope that takes the images of black holes, is actually a network of telescopes around the globe. This essentially makes it a virtual telescope. But how can setting up individual telescopes achieve the same sensitivity as a very large telescope? Let’s find out in the next section of this article.
Analyzing the Data
The Event Horizon Telescope relies on a technology known as Very Long Baseline Interferometer, also known as VLBI. This works by pointing multiple telescopes to the same target. The sources of light are supposed to be focused on a single point, but they’re not. Now this is the interesting part, which is analyzing the data from the telescopes.
Firstly, the astronomers need to determine what set of light rays will get reflected to the hypothetical center of the telescopes based on the images. Note that they are not limited to just a few points, and that’s why telescopes are round. Secondly, the computer simulates the reflection of light waves to the imager, and obtains the image based on that. While these steps seem simple enough to understand, they require some excellent knowledge of the math behind the system, which determines the distribution of telescopes around their needs, and, ultimately, the custom program used to generate the photo.
Furthermore, according to many news reports, it takes an enormous amount of data to generate one such tiny image. The data collected probably needs to be full images that the telescope captures, which contains many details and takes up lots of disk space even with lossy compression, let alone lossless compression. Moreover, the photo collected after the analysis of the data is tremendous as well, and the famous images of black holes we see today are only a microscopic part of it.
The Anatomy of the Image of the Black Hole
Even if the imagers are advertised as actual images of black holes, there’s nothing to see inside the black hole. Remember that it is a region with a strong gravitational pull that absorbs all light that arrives at its event horizon. Therefore, the bright part of the picture around the hollow part is actually the accretion disk, which contains material orbiting the black hole so quickly that they generate blackbody radiation due to the heat they receive from friction with other particles.
In this short article, we introduced you to a piece of technology that enables us to create resolution from low-resolution images. We also mentioned the structure of the pictures of the black hole. Remember that the bright part of it is not the event horizon, it’s the accretion disk around it. If you find any significant mistakes in this article, express your opinions at the comments below to improve this essay. Also, if you want more information on this, please visit the webpages in the references below.
References and Credits
- Carlisie, C. M. (2019, April 15). How Does the Event Horizon Telescope Work? Retrieved May 22, 2022, from https://skyandtelescope.org/astronomy-blogs/black-hole-files/how-does-very-long-baseline-interferometry-work/
- (n.d.). Event Horizon Telescope (EHT). Retrieved May 22, 2022, from https://pweb.cfa.harvard.edu/facilities-technology/telescopes-instruments/event-horizon-telescope-eht
- (2022, May 12). Astronomers Reveal First Image of the Black Hole at the Heart of Our Galaxy. Retrieved May 22, 2022, from https://eventhorizontelescope.org/blog/astronomers-reveal-first-image-black-hole-heart-our-galaxy