A binary star system about 30 million light-years away is an impostor. When astronomers first saw it, they thought it was a supernova — the titanic explosion of a massive star. They even called it one: Supernova 2000ch. But the system is still there.

The system is in the spiral galaxy NGC 3432, in a clump of young, bright, heavy stars.

By the end of last year, 2000ch had produced 23 outbursts. They’ve been about six and a half months apart. Based on that interval, the way the system brightens and fades, and other details, astronomers have developed a model of what’s going on.

The system’s main star is dozens of times the mass of the Sun, and a million times brighter. It’s also unstable — it puffs in and out.

A smaller companion star follows a lopsided orbit. During its close approaches, it stirs up the brighter star, triggering an outburst. And if the main star is in its “puffier” phase, then the outburst is especially bright.

The system may be building up to a much bigger outburst in the fairly near future. And after that, the massive star could explode as a supernova — no longer an “impostor,” but the real thing.

NGC 3432 is in Leo Minor, the little lion. It’s too faint to see without a telescope. But it’s high above the Moon as darkness falls tonight. The bright star Regulus — the heart of the big lion — is to the left of the Moon. More about that meeting tomorrow.

Script by Damond Benningfield