Modelling reality

How thinking theoretically revealed the hidden secrets of Messier 87’s black hole

3 May 2019
What you’ll discover in this blog post:
  • How it feels to take an image of a black hole
  • How 60,000 simulated images uncovered the properties of the black hole
  • Why theorists are so important in major scientific discoveries
The recent release of the first “image” of a black hole can’t have escaped your notice. But how can we use this image to find out about the physical characteristics of the black hole? ...to unearth more details about these mysterious objects? The secret is in the simulations that theoretical physicists have spent years working on. Two theoreticians involved in the Event Horizon Telescope (EHT) tell us more.

Luciano Rezzolla is a theoretician in the Event Horizon Telescope collaboration. He uses sophisticated numerical simulations to deduce the characteristics of the black hole.
Credit: ESO

Name: Luciano Rezzolla
Job: Professor of relativistic astrophysics and numerical relativity at Goethe University, Germany
Roles in the EHT project: Theoretician

What were the biggest challenges you faced whilst getting to this result?

Early on, it was already very clear that our task as theorists in the EHT collaboration was to provide a physical explanation for what would be observed using the telescopes, and to use sophisticated numerical simulations to deduce the properties of the black hole. We were always aware that this would be a huge challenge. So following this strategy, we performed the most extensive numerical exploration of the dynamics of the plasma surrounding the black hole, to figure out how it swirls around and shines when it actually falls onto the black hole.

Once we established what physical properties were needed to create a “best-match simulated image”, we could guess the real physical properties of the black hole.

We considered hundreds of different physical and astrophysical scenarios by studying different properties (masses and spins) of the black hole, but also different thermodynamic properties of the orbiting plasma. For each scenario we constructed thousands of synthetic images that could theoretically be the result of the complex bending and lensing of the light near the black hole. At the end of this effort we had built a library of more than 60,000 synthetic images!

We had thought that based on this huge image library, we would easily be able to decide which scenario was the correct one. But what we instead realised is that many combinations of physical parameters can lead to simulated images that, once blurred with the telescope resolution, would match the actual observed image very well.

This was a relief because it meant that whatever our conclusions on the properties of the observed image, these would be very robust. But although we were very confident that this was a black hole, we weren’t sure what its characteristics would be. This meant that we had to go back to the blackboard and sharpen the techniques we were using to compare the theory with the observations. In practice this has meant a lot of sleepless nights especially for Dr. Fromm, a member of our team in Frankfurt, who eventually managed to single out the simulated images that best matched the observations after exploiting a sophisticated genetic algorithm.

Once we established what physical properties were needed to create a “best-match simulated image”, we could guess the real physical properties of the black hole. Therefore we managed to explain the physical origin of the emission ring surrounding the black hole — a very rewarding and reassuring feeling!

Monika Mościbrodzka is co-coordinator of a research group that looks at the polarisation of the light from the ring surrounding the black hole. She also contributes significantly to theoretical modelling and interpretation of EHT data.
Credit: ESO

Name: Monika Mościbrodzka
Job: Assistant professor, Radboud University, the Netherlands
Roles in the EHT project: Co-coordinator of a research group that looks at polarisation of the light from the ring surrounding the black hole. Leader of theoretical research, major contributor to theoretical modelling and interpretation of EHT data.

What emotions have you been through whilst getting to this result?

My work as a theoretical astrophysicist in the EHT project focuses on modelling the appearance of black holes depending on what is around them. Over many years of my academic research prior to making the EHT observations I sort of got used to seeing simulated pictures of black holes.

After months of secret-keeping, we could finally speak openly about our black hole, this extraordinary wonder of nature, with the rest of the world.

Then when the EHT data was calibrated and ready for imaging, I joined one of the imaging teams out of curiosity. I sensed that this would be a perfect opportunity for a theorist to get in touch with reality. This experience turned out to be very rewarding. It is hard to find words that describe the emotions that I felt when I first saw the initial images of M87 last summer. These images were MIND BLOWING.

But as a theorist I felt an additional thrill when looking at the image. The black hole appeared almost exactly how I imagined it to be, just exactly how I had predicted it would look in my models of its host galaxy, Messier 87. So in some sense this experiment did not reveal something completely unexpected.

During the press conference in Brussels, I was honestly moved. After months of secret-keeping, we could finally speak openly about our black hole, this extraordinary wonder of nature, with the rest of the world. I feel extremely privileged to be a part of the EHT team that made such a big impact on science. It’s truly a life-changing experience.

The next step for EHT scientists is to analyse the polarisation of light from the ring that surrounds the black hole. This will give us critical information about the magnetic fields at the black hole's event horizon, helping us to understand the exact nature of the light that is visible in the image that we see. We could start to discover, for example, how exactly this light is produced.

Send us your comments!
Subscribe to receive news from ESO in your language
Accelerated by CDN77
Terms & Conditions
Cookie Settings and Policy

Our use of Cookies

We use cookies that are essential for accessing our websites and using our services. We also use cookies to analyse, measure and improve our websites’ performance, to enable content sharing via social media and to display media content hosted on third-party platforms.

You can manage your cookie preferences and find out more by visiting 'Cookie Settings and Policy'.

ESO Cookies Policy


The European Organisation for Astronomical Research in the Southern Hemisphere (ESO) is the pre-eminent intergovernmental science and technology organisation in astronomy. It carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities for astronomy.

This Cookies Policy is intended to provide clarity by outlining the cookies used on the ESO public websites, their functions, the options you have for controlling them, and the ways you can contact us for additional details.

What are cookies?

Cookies are small pieces of data stored on your device by websites you visit. They serve various purposes, such as remembering login credentials and preferences and enhance your browsing experience.

Categories of cookies we use

Essential cookies (always active): These cookies are strictly necessary for the proper functioning of our website. Without these cookies, the website cannot operate correctly, and certain services, such as logging in or accessing secure areas, may not be available; because they are essential for the website’s operation, they cannot be disabled.

Cookie ID/Name
Description/Purpose
Provider (1st party or 3rd party)
Browser session cookie or Stored cookie?
Duration
csrftoken
XSRF protection token. We use this cookie to protect against cross-site request forgery attacks.
1st party
Stored
1 year
user_privacy
Your privacy choices. We use this cookie to save your privacy preferences.
1st party
Stored
6 months
_grecaptcha
We use reCAPTCHA to protect our forms against spam and abuse. reCAPTCHA sets a necessary cookie when executed for the purpose of providing its risk analysis. We use www.recaptcha.net instead of www.google.com in order to avoid unnecessary cookies from Google.
3rd party
Stored
6 months

Functional Cookies: These cookies enhance your browsing experience by enabling additional features and personalization, such as remembering your preferences and settings. While not strictly necessary for the website to function, they improve usability and convenience; these cookies are only placed if you provide your consent.

Cookie ID/Name
Description/Purpose
Provider (1st party or 3rd party)
Browser session cookie or Stored cookie?
Duration
Settings
preferred_language
Language settings. We use this cookie to remember your preferred language settings.
1st party
Stored
1 year
ON | OFF
sessionid
ESO Shop. We use this cookie to store your session information on the ESO Shop. This is just an identifier which is used on the server in order to allow you to purchase items in our shop.
1st party
Stored
2 weeks
ON | OFF

Analytics cookies: These cookies collect information about how visitors interact with our website, such as which pages are visited most often and how users navigate the site. This data helps us improve website performance, optimize content, and enhance the user experience; these cookies are only placed if you provide your consent. We use the following analytics cookies.

Matomo Cookies:

This website uses Matomo (formerly Piwik), an open source software which enables the statistical analysis of website visits. Matomo uses cookies (text files) which are saved on your computer and which allow us to analyze how you use our website. The website user information generated by the cookies will only be saved on the servers of our IT Department. We use this information to analyze www.eso.org visits and to prepare reports on website activities. These data will not be disclosed to third parties.

On behalf of ESO, Matomo will use this information for the purpose of evaluating your use of the website, compiling reports on website activity and providing other services relating to website activity and internet usage.

ON | OFF

Matomo cookies settings:

Cookie ID/Name
Description/Purpose
Provider (1st party or 3rd party)
Browser session cookie or Stored cookie?
Duration
Settings
_pk_id
Stores a unique visitor ID.
1st party
Stored
13 months
_pk_ses
Session cookie temporarily stores data for the visit.
1st party
Stored
30 minutes
_pk_ref
Stores attribution information (the referrer that brought the visitor to the website).
1st party
Stored
6 months
_pk_testcookie
Temporary cookie to check if a visitor’s browser supports cookies (set in Internet Explorer only).
1st party
Stored
Temporary cookie that expires almost immediately after being set.

Additional Third-party cookies on ESO websites: some of our pages display content from external providers, e.g. YouTube.

Such third-party services are outside of ESO control and may, at any time, change their terms of service, use of cookies, etc.

YouTube: Some videos on the ESO website are embedded from ESO’s official YouTube channel. We have enabled YouTube’s privacy-enhanced mode, meaning that no cookies are set unless the user actively clicks on the video to play it. Additionally, in this mode, YouTube does not store any personally identifiable cookie data for embedded video playbacks. For more details, please refer to YouTube’s embedding videos information page.

Cookies can also be classified based on the following elements.

Regarding the domain, there are:

As for their duration, cookies can be:

How to manage cookies

Cookie settings: You can modify your cookie choices for the ESO webpages at any time by clicking on the link Cookie settings at the bottom of any page.

In your browser: If you wish to delete cookies or instruct your browser to delete or block cookies by default, please visit the help pages of your browser:

Please be aware that if you delete or decline cookies, certain functionalities of our website may be not be available and your browsing experience may be affected.

You can set most browsers to prevent any cookies being placed on your device, but you may then have to manually adjust some preferences every time you visit a site/page. And some services and functionalities may not work properly at all (e.g. profile logging-in, shop check out).

Updates to the ESO Cookies Policy

The ESO Cookies Policy may be subject to future updates, which will be made available on this page.

Additional information

For any queries related to cookies, please contact: pdprATesoDOTorg.

As ESO public webpages are managed by our Department of Communication, your questions will be dealt with the support of the said Department.