What's Next for the Event Horizon Telescope?

An international array of radio telescopes, like the ones in this photo, comprise the Event Horizon Telescope. (Photo: sdecore/Shutterstock)

After two years of crunching the data, creating new algorithms to piece it all together, and double-checking results, the team behind the ambitious Event Horizon Telescope (EHT) project finally unveiled the fruits of their labors: humanity's first-ever direct image of a black hole.

"This is a huge day in astrophysics," National Science Foundation Director France Córdova said in a statement. "We're seeing the unseeable. Black holes have sparked imaginations for decades. They have exotic properties and are mysterious to us. Yet with more observations like this one they are yielding their secrets."

The now-famous black hole, nicknamed M87*, is located some 55 million light-years away at the center of Messier 87, a massive galaxy in the nearby Virgo galaxy cluster. Classified as a supermassive black hole, M87* has the mass of roughly 6.5 billion suns and an estimated diameter of more than 24 billion miles.

For comparison, our entire solar system could easily fit within the gaping maw of this cosmic nightmare.

"We have seen the gates of hell at the end of space and time," astrophysicist Heino Falcke of Radboud University in Nijmegen said about the below photo at a press conference in Brussels.

The first-ever image of the event horizon surrounding a distant black hole. (Photo: National Science Foundation)

With its first big milestone now firmly etched in the history of human exploration, what's next for the Event Horizon Telescope? As you might expect, the success of leveraging an array of telescopes to create one massive virtual "planet-sized" telescope has the team of more than 200 researchers excited to both refine and expand its capabilities.

In 2017, during five days of observations of M87*, the EHT used an array of eight radio telescopes located in regions ranging from the South Pole to South America. A dish from Greenland joined the fold in 2018, and another, located atop a peak in southern Arizona, will soon increase the total to 10.

"These will all increase the imaging fidelity," EHT director Shepard Doeleman said during a press conference yesterday. "They'll fill out that virtual mirror that we're trying to build."

There's also the matter of Sagittarius A* (Sgr A*), another supermassive black hole located at the heart of our own Milky Way galaxy.

Detection of an unusually bright X-ray flare from Sgr A*. (Photo: NASA)

When researchers first announced their work to capture the first image of a black hole, their focus was on making Sgr A* –– located "only" 26,000 light-years from Earth –– the star attraction. As it turns out, imaging a supermassive black hole in our own backyard isn't as easy as one tens of millions of light-years away.

"M87 is indeed much further away than Sgr A*, but also about 1500 times more massive," team member Freek Roelofs shared in a Reddit AMA. "The apparent size of the event horizon is therefore about the same. Because M87 is so heavy, the timescale for the gas to move around the black hole is much longer than for Sgr A*. For Sgr A*, the gas flow is variable on a timescale of minutes, which makes it more difficult to get an image."

The other issue plaguing a clear view of Sgr A*, according to Roelofs, is the vast amount of gas and dust in our galaxy that combines to blur the image. Nonetheless, the team is determined to add an image of Sgr A* to our new black hole photo album.

"When we saw the quality of the M87 data and obtained the first image reconstructions, we decided to fully focus on this black hole first," said Roelofs. "Now that these results are out, we will work on the Sgr A* data as well."

The Atacama Pathfinder Experiment (APEX) is a radio telescope located 5,100 meters above sea level in northern Chile. It is part of the original eight of the Event Horizon Telescope array. (Photo: ESO/B. Tafreshi/TWAN/Wikimedia Commons)

Utilizing the new additions to the EHT will allow the team to sample black holes like M87* and Sgr A* in new frequencies. Instead 1mm wavelengths, as was done with the image of M87*, the researchers plan to collect data in the 0.87mm frequency.

"It sounds like a small jump, but it increases your angular resolution — the resolving power — by over 30%," Space.com quoted Doeleman as saying. "So, you wind up sharpening your image just by observing at higher frequencies."

As well as targeting other sources throughout the universe, the team also wants to perform variability studies to see how black holes like the fast-spinning Sgr A* change over time.

"Imagine if we can make a movie of a black hole instead of a still image,” Doeleman said in an EHT talk last month at the South by Southwest (SXSW) festival in Austin, Texas. "We want to make a movie in real time of things orbiting around the black hole. That's what we want to do over the next decade."

Spectacular jets powered by the gravitational energy of a super massive black hole in the core of the elliptical galaxy Hercules A. (Photo: NASA/Hubble Space Telescope)

Further into the future, the EHT team is exploring adding several space-based telescopes to their global network. This orbiting array would have the distinct advantage of avoiding interference from Earth's atmosphere.

"One [idea] is to launch just two or three satellites into circular orbits around the Earth, and have them observe each black hole for about a month or more to produce images that have about a factor 5 higher resolution than what is achievable from Earth," writes Roelofs. "A big advantage of having a fully space-based array is that we could observe at high radio frequencies that are blocked by water vapor in the Earth's atmosphere."

A radio telescope under the Milky Way. (Photo: zhengzaishuru/Shutterstock)

While the opportunities to further unravel the mysteries of one of the universe's most enigmatic forces stretch limitless before them, the team in the wake of yesterday's unveiling is taking a well-earned moment in time to celebrate their historic achievement.

"It's truly a global effort, both in terms of the array of telescopes we have equipped and used and in sheer collaborative work of people from different backgrounds, career stages, expertise, to make all this come together," team member Sara Issaoun wrote on Reddit. "We are all extremely proud to be part of it, but more than that we are all extremely thrilled to finally be sharing our results, excitement, and love of astronomy and black holes with the rest of the world."