Cassiopeia A

The brightest object beyond our own solar system wheels high overhead on winter nights. It’s in Cassiopeia the queen, whose brightest stars form a big letter M. It’s high in the north at nightfall.

Cassiopeia A outshines all the stars that make up the M. Don’t bother looking for it, though — it’s invisible to the eye alone. But it’s a different story at radio wavelengths — Cas A outshines everything except the Sun and a few other objects in the solar system. Yet Cassiopeia A is 11,000 light-years away, which provides an idea of its power.

Cas A is the remnant of a star that exploded as a supernova. The blast took place more than 300 years ago as seen from Earth, although there are no confirmed cases of anyone actually seeing it — a veil of gas and dust might have blocked its light.

The massive star quickly consumed the nuclear fuel in its core. The core collapsed, forming an ultra-dense neutron star. The layers of gas around the core then were blasted into space. Today those layers form a glowing cloud that’s expanding at millions of miles per hour.

The neutron star at the center of the cloud produces a powerful magnetic field. Electrons move through that field at high speeds. As they do so, they produce radio waves — making Cassiopeia A the brightest source of radio waves beyond the solar system.

Before the supernova explosion that blasted it to bits, Cas A might have produced a smaller outburst; more about that tomorrow.

Script by Damond Benningfield