The First Ever Image of a Black Hole

What does a black hole actually look like? What telescope can make such an observation? And what could possibly go wrong?

Sabrina Stierwalt, PhD
5-minute read
Episode #233

What telescope can observe a black hole?

So what telescope can even make this observation? Astronomers will require a telescope as large as the Earth, something they will achieve by observing simultaneously with multiple telescopes spanning the globe from the South Pole to Arizona and from Hawaii to Spain. This array of telescopes, which as of recently includes the Atacama Large Millimeter Array in the Chilean desert, is collectively known as the Event Horizon Telescope. All of these telescopes operate at 1.3 millimeters, or, in other words, will collect this data at radio wavelengths which are capable of penetrating the thick dust known to surround our central black hole.

Astronomers will require a telescope as large as the Earth.

Data collected at each telescope will be stored on hard drives which are then jetted to the Haystack Observatory near Boston. There the signals will then be combined via a supercomputer with the equivalent of ~800 CPUs. For more on how astronomers combine multiple smaller telescopes to act as one large telescope, check out my guest spot on the Titanium Physics podcast on interferometry.

The reason so many telescopes are required is because, given perfect observing conditions, the angular resolution achievable by a telescope is related to its size. The larger the telescope, or in this case, the larger the distance between individual telescopes in the telescope array, the finer detail that can be seen on the sky. The upcoming observation is expected to reach a resolution of <50 microarcseconds which is the equivalent of you being able to read the writing on a quarter sitting on a table in Los Angeles from an apartment in New York City. For comparison, that resolution is also about 2,000 times better than what the Hubble Space Telescope can see.

What could go wrong?

Although observations at radio wavelengths have the best chance of piercing through the dusty surroundings of the black hole, water vapour in the Earth’s atmosphere can still affect the clarity of the resulting images. The involvement of so many different telescopes thus requires that the weather be clear in every one of the locations.

Each data set is time stamped locally before being sent to the supercomputer where they will be processed together. Ultimately combining the information from the various telescopes requires extremely accurate atomic clocks, clocks that are custom built and rely on hydrogen masers. These clocks have to get the timing right down to a trillionth of a second per every second.

The amount of post-observing processing is so extensive that the final image is not expected until 2018. But it will have large implications for our understanding of something as fundamental as gravity.

Do event horizons actually exist? Are our theories on how light behaves in the presence of extreme gravity correct? How do black holes feed themselves through accretion? How are the large scale jets of collimated plasma that astronomers observe formed in the surroundings of the black hole?

If the experiment works works, the astronomers behind the Event Horizon Telescope project plan to move onto the supermassive black hole in the center of the giant elliptical galaxy M87. Although much farther away, this black hole is estimated to be 6 billion times the mass of our Sun, or 1,500 times the mass of Sag A*. So was Einstein right? Stay tuned …

Until next time, this is Sabrina Stierwalt with Ask Science’s Quick and Dirty Tips for helping you make sense of science. You can become a fan of Ask Science on Facebook or follow me on Twitter, where I’m @QDTeinstein. If you have a question that you’d like to see on a future episode, send me an email at everydayeinstein@quickanddirtytips.com.

Image courtesy of eventhorizontelescope.org


Please note that archive episodes of this podcast may include references to Ask Science. Rights of Albert Einstein are used with permission of The Hebrew University of Jerusalem. Represented exclusively by Greenlight.

About the Author

Sabrina Stierwalt, PhD

Dr Sabrina Stierwalt earned a Ph.D. in Astronomy & Astrophysics from Cornell University and is now a Professor of Physics at Occidental College.