Danielle Smith-Llera - First Look at a Black Hole: How a Photograph Solved a Space Mystery

The EHT may not look like a camera, but to take a black hole photograph it must do everything a regular camera does. Photographers working with dim visible light must keep the cameras shutter open longer to collect enough light bouncing off their subjects. Radio astronomers must observe dim targets for a long time too. Since , or distance between telescopes, would need to be larger than Earth.

A clean, high-quality lens gives a camera its viewing power. The polished surface inside a parabolic dish gives a radio telescope its viewing power. Even tiny bumps or scratches on the polished metal tiles inside a parabolic dish can disrupt radio waves. They must bounce off these mirrors toward a central antenna. The radio waves are converted into electricity and travel through cables to the control room. There, the electricity is recorded in sequences of numbers as digital information.

Like cameras, radio telescopes must aim at their subjects. The equipment that moves a radio telescope is complex and expensive. But without it, the polished dish cannot bounce radio waves at the antennas with accuracy. Machines swivel and tilt the dish to adjust its position. Computer-controlled machines also adjust the angle of each mirrored tile inside the dish.

The 28 radio telescopes of the Very Large Array in New Mexico help scientists study faraway astronomical objects, including black holes.

A black hole is so far away that the data gathered from the array of telescopes. The EHTs 79 dishes at eight locations spread across three continents was the worlds largest VLBI experiment.

This is a NASA artists rendering of star debris gathered into an accretion disk around a black hole.

But so much can go wrong with VLBI. Clouds in Arizona could creep near Mount Grahams Doelemans team could not afford to be too picky about conditions. Scheduling time on all eight observatories required negotiation and patience. Other astronomers used these sophisticated tools also. And weather conditions were clear at the observatories in Chiles Atacama Desert, Californias Inyo Mountains, Spains Sierra Nevada mountains, and on Hawaiis Mauna Kea.

I think we should call it a go, Doeleman announced to the room. On a laptop, he typed a message into a private online chat used by the teams at the eight EHT observatories: GO for VLBI. This is NOT a drill.

Doeleman asked a teammate for a dramatic countdown. Five. Four. Three. Two. One. All right, things should be recording,interferometry works correctly, the telescopes move in sync on preprogrammed tracks, following identical targets. The EHT design turned Earth into a giant disco ball scattered with mirrors. As Earth turned, each of the arrays mirrored dishes would collect light to combine into a photograph.

The telescope at the South Pole was one of many dishes around the world that kept watch on the black holes Shep Doeleman hoped to finally photograph.

The EHT arrays spun into position one after the other. First, Spains dish rolled into position to fix on a distant target. As Earth rotated, its instruments captured many angles of each target and recorded the information. After a few hours, the next telescopes rolled into position to begin observing the same target: Mexicos dish and, in Chile, another dish, along with a giant array of 66 dishes. Next, a dish in Arizona and an array of 23 dishes in California slid into position. Hours later, another telescope with an array of eight dishes in Hawaii took over the observation work. All the while, yet another dish at the South Polethough it had technical problems that first observation day kept steady watch on the distant target.

For more than a week, each day at EHT headquarters in Cambridge began with nervous phone calls to EHT locations around the world. The team analyzed weather data and checked whether the telescopes were ready for another day of observation. Turning on the EHT if the weather or telescope technology was not cooperating was a waste of time and money.