Centaurus A is one of the brightest galaxies in the night sky. It’s especially bright at radio wavelengths. A supermassive black hole in its heart shoots out long “jets” of charged particles. They produce radio waves. And the first person to identify Centaurus A as a radio galaxy was born 100 years ago today.
John Bolton was born in Sheffield, England. He studied math and physics, then enlisted in the Royal Navy during World War II. He did research and development work on radar, then served on a ship in the Pacific. The ship was in Australia when the war ended, so Bolton decided to stay.
Radio astronomy barely existed then. But war-surplus radar equipment — and scientists who knew how to use it — boosted the field. Bolton built a telescope that used the ocean to reflect radio waves into his detectors. With it, he discovered many new radio sources.
To understand those sources, though, astronomers needed to link them to photographs. So Bolton and his team narrowed the field of view, allowing them to pinpoint the location of radio objects. That led to the discovery that some of the objects were galaxies — like Centaurus A.
Bolton later built and directed a much bigger radio telescope. It contributed to the discovery of quasars and many other intriguing objects — through radio.
From the southern half of the U.S., Centaurus A is due south at nightfall, barely above the horizon — a noisy galaxy powered by a black hole.