In a Q&A interview, author and science writer David Baron discusses the turn-of-the-century Mars craze, which he covers in his new book, "The Martians."
In 1964, astronomers discovered the first black hole. It's called Cygnus X-1 and the evidence for its existence was discovered by x-ray detectors on a sub-orbital sounding rocket. Cygnus X-1 is about 7,300 light-years away and has about 21 solar masses. Since then, astronomers have discovered increasingly more massive black holes, including supermassive black holes (SMBH) at the heart of large galaxies like ours.

