Travel atomic clock

The Large Millimeter Telescope in the Mexican state of Puebla

A few months ago I went to Cambridge, Mass. to check in with the Event Horizon Telescope crew and found Shep Doeleman, the project leader, fresh off the completion of a major purchase. He and his colleagues had just closed a deal on two hydrogen masers, among the most precise atomic clocks available. He displayed the weary pride of a guy who had just bought a new house. “We spent a half million dollars on clocks today, ” he said. “Ask me what time it is. I dare you.”

Einstein taught us that time is flexible. That doesn’t mean that time is no big deal. If you’re going to take a picture of a black hole, you must become obsessed with precision timekeeping. We’ve already covered the basic design of the Event Horizon Telescope: radio dishes around the world simultaneously observe a black hole, time-stamp the data they collect, and then astronomers later correlate all that data to mimic the performance of a single, planet-size dish. To match up the data from the various telescopes, you have to know to within a fraction of a microsecond when, exactly, specific photons struck specific telescopes. And so, to participate in Event Horizon Telescope observations, a telescope must have on site an atomic clock. Atomic clocks aren’t necessarily standard radio-telescope equipment, though. One of the big tasks now facing the astronomers of the Event Horizon Telescopes is getting suitable clocks to those telescopes that don’t have them.

One of the clocks Doeleman procured that day in Cambridge was bound for Mexico’s Large Millimeter Telescope, a 50-meter dish that should function as a useful stepping stone between the EHT’s North and South American observatories. In late April, Doeleman, Patrick Owings, a technician from the maser manufacturer Microsemi, and I met up with that clock. The three of us had flown separately into Mexico City the day before. Today, we and several others would haul this quarter-million-dollar instrument into the Pueblan hinterlands, drive it to the top of a 15, 000-foot extinct volcano, and install it in the LMT, the world’s largest millimeter-wave telescope.