How an Astrophysicist Saw the First Image of a Black Hole

The Event Horizon Telescope collaboration imaged this picture of the black hole in the center of the M87 galaxy, which is about 55 million light-years from Earth. Credit: Event Horizon Telescope Collaboration
Friday, April 19, 2019 


On April 10, 2019, I tuned into the National Science Foundation press conference from the Event Horizon Telescope (EHT) collaboration and saw, along with the rest of the world, the first-ever image of a black hole. I have to admit that in the week leading up to the press conference, I was a bit skeptical of the hype.  Science Twitter was full of warnings about how this would likely be a pixelated image, and how not to be disappointed with what would still be an important result.  But, wow did the EHT team deliver!

On the morning of the announcement, a beautiful ring-like image appeared on the screen to much applause from the audience.  Overnight, astronomy became the focus of the world’s attention as the image spread like wildfire, appearing on the cover of most major publications.  It is impossible not to get caught up in the excitement. How lucky am I to get to think about astronomy every day, not just when it makes national and international news?

A man in the streets of Rome reads the Italian newspaper Il Messaggero, which dedicated a substantial part of its April 11 front page to the black hole image. Photo: Roberto Molar Candanosa, Carnegie DTM. 

Besides the general excitement over imaging the first black hole, this result stuck with me for two reasons.  First, I completed my PhD at the Center for Astrophysics | Harvard & Smithsonian and personally know many of the scientists involved with the discovery.  They were my colleagues and friends for many years and still are today.  I had heard about the progress of the EHT as the project developed and observations were taken.  It was fun to share in their joy and accomplishment from afar when they announced the discovery.

Second, this discovery was enabled by millimeter interferometry, a technique that I use in my own research studying circumstellar disks and planetary systems.  Imaging a black hole in another galaxy or a nearby planetary system requires very high resolution.  It’s impossible to build a single telescope large enough to accomplish this.  Instead, we build many single telescopes, spread them out over large distances, and correlate their signals as they observe the same object.  That’s interferometry!  For my work, I often use the Atacama Large Millimeter/submillimeter Array (ALMA) in the Atacama Desert in Chile, which has telescopes spread over about 10 miles.  To take an image of a black hole, the EHT team needed telescopes that spanned the entire Earth.  They did use the ALMA antennas, too, but it was only one piece of the full array of telescopes involved.

Map of the EHT array showing stations active in 2017 and 2018 shown in yellow connected with lines. Green stations indicate comissioned sites, and red stations indicate legacy sites. Credit: EHT Collaboration.

People are often confused by interferometry.  These arrays detect millimeter and radio emission—wavelengths of light that we can’t see with our own eyes.  The technique is not as intuitive as simply pointing an optical telescope at the sky and looking through an eyepiece or taking a picture with a CCD camera.  Even professional astronomers are often scared away by working with ‘visibilities’—the technical term for the raw data obtained from a telescope like ALMA.  I’ve always been drawn to the challenge of interferometry, and to the technological and computing power that is required in order to make it work.  So, it was especially fun to see my favorite astronomical technique getting the spotlight for once.  Perhaps some young students are now convinced that they want to become radio astronomers!

As the hype starts to fade a little bit and the next big news story steals the headlines, I’m left to stare in awe at this beautiful image—if you look closely, it looks an awful lot like a protoplanetary disk, doesn’t it?  Maybe the universe is trying to send us a subliminal message to get a donut with our coffee today.

 

 

Meredith MacGregor
NSF Astronomy and Astrophysics Postdoctoral Fellow



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