More Cassiopeia A

In the late 17th century as seen from Earth, a star in the constellation Cassiopeia blasted itself to bits as a supernova. Today, we see the star’s remains as Cassiopeia A — an expanding cloud of gas and dust around the star’s dead core.

Cas A should have blazed as brightly as billions of normal stars. So even though it’s 11,000 light-years away, it should have been one of the brightest objects in the night sky. Yet there are no confirmed reports that anyone on Earth actually saw it.

That could mean that no one recorded the appearance of the new star, or that the records have all vanished. More likely, though, is that the light from the explosion was blocked by something between Earth and Cas A.

One possibility is that the star had staged an earlier outburst — a blast known as a supernova impostor. Such an eruption isn’t powerful enough to rip a star apart, but it expels a lot of material into space. The material could stick together to form grains of dust. This material would form a cloud around the star, absorbing its light — including most of the light from the supernova.

Researchers say there’s evidence of an impostor in records from 1592 and ’93. Korean astronomers recorded a “guest” star at about the same spot in the sky where Cas A is found today. The researchers suggest that the guest star could have been an impostor outburst from Cas A. So far, though, there’s no confirmation that a little blast blocked the big blast from view.

Script by Damond Benningfield

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