In April, scientists announced the first images of the black hole at the center of galaxy M87. The galaxy is over 52 million light years away from Earth, so it appears to cover only a tiny portion of the night sky. Using a network of radio telescopes spread across the globe, astronomers were finally able to image the black hole at the center of M87.
The image of the black hole at the center of M87. Image from the Event Horizon Telescope team
To learn more about how electrical engineers contributed to this historic milestone, AAC’s Mark Hughes and Kate Smith interviewed Jason SooHoo and John Barrett, engineers who work at MIT’s Haystack Observatory on the Event Horizon project.
Shown above are MIT Haystack team-members John Barrett and Jason SooHoo.
AAC: What brought you both to MIT Haystack?
Jason SooHoo (JS): I came in as an IT associate providing basic technical support. But there was a need for some development of part of the digital back-end hardware. Since I had a computer-science degree, I was able to help develop that sort of stuff. Then I started learning how the software was used and became an operator—I would travel to the various locations to help support the observations. I traveled to Goddard, Mexico, Owens Valley, and the South Pole. My job description quickly turned from IT work to project development and support.
An idyllic view of MIT's Haystack Observatory. Image from MIT
John Barrett (JB): I found out by word-of-mouth. One of my friends let me know they were looking for someone with a background in software development. I spent a great deal of time doing high-performance computing in grad-school, so this was right down my alley.
AAC: What was your background that brought you to this project?
JS: I came from a software background but then got turned towards the electrical engineering field. I got a bachelor's degree in computer science but was immediately turned on to circuits and electrical design work with a software focus. A lot of the work that I do now is actually developing software for the electrical circuits I love.
JB: I majored in physics in undergrad and I did a PhD at MIT studying neutrino physics. I've since changed fields and now I'm doing radio astronomy.
AAC: Ok, let's start there. Can you please briefly explain what radio astronomy is?
JB: Radio astronomy is the study of astronomical objects using radio waves. Optical astronomy is concerned with the intensities [brightness] of objects, whereas radio astronomy is also concerned with the phase of incoming signals. Without phase, we wouldn’t be able to perform interferometry.
AAC: And what got you interested in radio astronomy, John?
JB: I think it was mostly the opportunity to get to do some really cool computing. I was a little bit data-starved during grad school so when I came up here and saw they had racks and racks of data modules and their own personal supercomputer, that got me pretty excited.
"I was a little bit data-starved during grad school, so when I came up here and saw they had racks and racks of data modules and their own personal supercomputer, that got me pretty excited."
AAC: Can you tell us, briefly, what the Event Horizon Telescope is?
JB: The Event Horizon Telescope is a network of telescopes running VLBI with the goal of imaging a black hole.
AAC: Aren't there only two black holes that we are even capable of seeing?
JB: With the current technology and the current constraint of having telescopes on the Earth's surface, you are limited in what frequencies you can actually look at because of all the dust and gas in between. You are also limited by the size of the black hole, itself. So it's really serendipitous that you can do this imaging from the Earth's surface at these wavelengths and still actually be able to observe these couple or a handful of black holes.
The Event Horizon Telescope is observing in 230 GHz and the plan is to go shorter wavelengths, say 345 GHz [0.8 mm] in the future.
AAC: There's been a huge global response to that the first image of the M87 black hole. Can you explain why it is so important that we've been able to image a black hole?
JB: It is the first evidence of the existence of an event horizon. Before that, we had very good reason to believe that black holes really are black, [but no evidence].
A lot of Einstein's predictions have been confirmed: Gravitational waves were confirmed by LIGO, and we have a history of general relativity tests going back to 1919, I think. But none of these have actually been able to say anything about the fact that light is trapped by a black hole, and there isn't some exotic place of super-dense matter instead. This is really the first confirmation of [an event horizon].
"[This image] is the first evidence of the existence of an event horizon."
AAC: How faint are the signals that you are detecting?
JB: The signals are on the order of femtowatts, maybe less. The noise power is much greater—perhaps by a factor of a million or more. The power of interferometry is that when you correlate them, and you integrate over long enough [time] all of the noise goes away and the only thing you’re left with is the signal. This technique requires that you are synchronized very precisely. A typical integration period is on the order of a second.
AAC: What experiments can you do with interferometry?
JS: In addition to Event Horizon Telescope (EHT), we are also involved with the Space Geodesy Project from NASA. The geodesy project is the reverse of the EHT. The EHT is trying to image objects in the sky, while the geodesy project uses objects in the sky to infer information about the Earth’s shape and motion.
When observing a celestial object, there ends up being a delay between the two stations. You can turn that into a distance projection along the baseline. That data, taken over a long period of time, can be used to determine motion between the two stations at either end of the baseline. That data, taken for stations all over Earth, allows us to build a picture of how the Earth itself is moving, whether it is: orientation in space over time; length of the day; continental drift; or other motions such as glacial rebound.
Interferometer baselines are established between stations of all distances. By tracking how the separation changes over time, astronomers can infer changes in the Earth. Image by Mark Hughes.
AAC: How much data are you dealing with in this project?
JS: Each station records many terabytes of data for an observation. The data is stored on large hard-drives and then shipped back to MIT’s Haystack Observatory where we have the correlator.
The correlator is a large computer server—it has over 1,200 cores that are tied together through a network backplane to make one massive computer. The detection software that John works on computes all of the data that is loaded into it.
Block diagram of the MIT Haystack Observatory's correlator PCB. Image from MIT
AAC: There are only a few places on the planet that might be able to duplicate your work. How do you know that you collected your data correctly and that there is something to process?
JS: The nice thing about VLBI is that it doesn’t lie. If you do anything wrong in the process along the way, you get nothing. There is no result in the signal and the noise integrates to zero. If you have a signal along a baseline that is thousands of kilometers in separation then you’re almost guaranteed to have been observing what you thought you were observing.
"The nice thing about VLBI is that it doesn’t lie. If you do anything wrong in the process along the way, you get nothing."
AAC: How do you align the time-coded data from multiple antennas?
JB: The antennas are all synchronized with the GPS network.
JS: The data is time-tagged with very precise masers—so we know where we are to the order of picoseconds. So we use the data with some possible offsets.
AAC: Are there any projects—other than this one—that you are particularly proud of?
JS: One project that we’re working on right now is developing a GPS system to monitor the total electron content in the Alaska-Canada Border. That’s actually what our student intern is working on right now. She’s developing a solution that we will deploy all over the Alaska-Canadian border to monitor the ionosphere for electrical storms and disturbances.
JB: One undergrad research opportunity was at [National Astronomy and Ionosphere Center Aricebo Observatory]—it was a software project that performed image analysis of satellite data to study the plasmapause of the earth.
AAC: What advice do you have for students that might want to follow your career paths?
JB: Most of the computer science knowledge that I have comes not from taking classes, but from working on external projects. I would encourage someone looking to get into the field to find as many research opportunities as they can, especially opportunities that involve computing. You learn a lot more when you are forced to do it yourself in a new and unsupported way. You need to work on things that do not have textbook answers and find the answers for yourself.
"Most of the knowledge that I have comes not from taking classes, but from working on external projects. Work on things that do not have textbook answers and find the answers for yourself."
JS: I totally agree with that. We actually have an electrical engineering student right now—she’s a senior from Merrimack College. She is working on new circuit board development, completely outside of what her school is giving her opportunities for. Being able to find research opportunities as a student is a great way to gain hands-on experience.
Huge thanks to Jason and John for their time. Please check out MIT Haystack Observatory for more radio astronomy!