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A Short History of Black Holes on Radio Telescopes

So, you’ve probably heard by now that we have our first ever photographs of a black hole and its event horizon. But it’s not like black holes have just been theoretical entities this entire time, awaiting photography’s blessing to finally be anointed as real. We’ve been detecting black holes for a long time now using radio telescopes and infrared cameras. It may be outside the visible spectrum, but that doesn’t mean it ain’t real, son!

The story begins in the mid-1900s when astronomers expanded their horizons beyond the very narrow range of wavelengths to which our eyes are sensitive. Very strong sources of radio waves were discovered and, when accurate positions were determined, many were found to be centered on distant galaxies. Shortly thereafter, radio antennas were linked together to greatly improve angular resolution. These new “interferometers” revealed a totally unexpected picture of the radio emission from galaxies—the radio waves did not appear to come from the galaxy itself, but from two huge “lobes” symmetrically placed about the galaxy….

Ultimately this led to the technique of Very Long Baseline Interferometry (VLBI), in which radio signals from antennas across the Earth are combined to obtain the angular resolution of a telescope the size of our planet! Radio images made from VLBI observations soon revealed that the sources at the centers of radio galaxies are “microscopic” by galaxy standards, even smaller than the distance between the sun and our nearest star.

When astronomers calculated the energy needed to power radio lobes they were astounded. It required 10 million stars to be “vaporized,” totally converting their mass to energy using Einstein’s famous equation E = mc2! Nuclear reactions, which power stars, cannot even convert 1 percent of a star’s mass to energy. So trying to explain the energy in radio lobes with nuclear power would require more than 1 billion stars, and these stars would have to live within the “microscopic” volume indicated by the VLBI observations. Because of these findings, astronomers began considering alternative energy sources: supermassive black holes.

We’ve also been tracing the orbits of planets, stars, and other objects that do give off conventional light. All this tracks back to suggest the supermassive black holes that Laplace et al first theorized about hundreds of years ago.

So, we knew what we were looking for. That’s how we were able to find it. And boom! Now we’ve got its photograph too. No more hiding from us, you goddamn light-devouring singularities. We’ve got your number.