N6946-BH1

A red supergiant that brightened briefly, then went out and never came back -- the best-known candidate for a star that collapsed with no explosion at all.

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What it is

Failed supernova: A heavy star that collapses to a black hole and simply goes out, with no explosion at all. Every kind of thing there is →

Can you see it?

No. No telescope on Earth will show you this one; it is here to be understood, not seen. It is here because it is worth knowing about — and because leaving it out would make the sky look emptier than it is.

Worth knowing about N6946-BH1

Well outside our galaxy. On the 100-meter-track scale model of the Milky Way, this would be 22 kilometres away. Light takes 22.0 million years to get here from N6946-BH1, so what you are looking at is N6946-BH1 as it was 22.0 million years ago.

What it is made of: A red supergiant, around 25 times the Sun's mass -- exactly the sort of star that is supposed to end in a supernova.
What makes it worth knowing: If it is what it looks like, this is the only star anyone has watched vanish.
What happened: Astronomers had been photographing this galaxy for years, watching a list of big stars to catch one exploding. In 2009 this star glowed a little brighter for a few months. Then it faded, and by 2015 it was simply gone from the pictures. There was never an explosion.; How we know: Repeated imaging of the same galaxy over more than a decade: the star is in the early pictures and absent from the later ones.
One explanation: The star may have collapsed straight into a black hole and taken its own light with it -- a failed supernova. If that is right, some heavy stars end without a bang, which would help explain why we find fewer supernovae than the number of heavy stars suggests we should.
Why it is still an argument: Something faint still glows there in infrared, which is heat, not starlight. That could be gas falling into a new black hole -- or it could be dust hiding a star that is still alive. Later observations raised the possibility that two stars merged here and wrapped themselves in dust. Nobody has settled it. This is a candidate, not a confirmed case.