X-rays are far more energetic than most other forms of radiation, so they can cause cancer and other health problems. Fortunately for life on Earth, our atmosphere blocks X-rays from space. Un-fortunately for astronomers, though, that makes it tough to study those X-rays, which come from some of the most extreme objects in the universe.

Still, there are ways to see the X-ray sky — by lofting X-ray telescopes on balloons and rockets. And 50 years ago tomorrow, astronomers used a rocket-borne instrument to discover an exotic source of X-rays in the constellation Vela.

Scientists launched an X-ray detector from a small island southwest of Hawaii. Its rocket pushed it above most of Earth’s atmosphere, where it detected a source of X-rays now known as Vela X-1.

Today, astronomers know that the system is about 6500 light-years away. It consists of two very different stars that are in a tight orbit.

One star is a supergiant — it’s much bigger, brighter, and hotter than the Sun. Its mate is a neutron star. It’s a mere dozen miles across, but it weighs more than the Sun. As a result, its gravity is immense. If you dropped a pebble from a height of a few feet, it would smash into the surface at millions of miles per hour, releasing an enormous amount of X-rays.

And material is falling onto the neutron star: gas from the companion. As the gas plunges in, it gets so hot that it produces X-rays — which astronomers first detected 50 years ago.

Script by Ken Croswell, Copyright 2016