One with a long fuse, fortunately. And one which may not go off in a way that will harm us. Maybe. We think. Probably not..... But call it just possibly the Biggest, Baddest shaped-charge IED the Universe can provide, and aimed approximately in our direction.
From The Gamma Ray Burster Threat:
The side of Earth facing the concentrated beam of an incoming gamma burst from a nearby source would suffer atmospheric shock waves which ignited everything in the air and on the surface of the planet. The immense heating of the atmosphere would begin causing catastrophic weather changes worldwide within only minutes. Everything which could burn would do so. However, taking refuge in sturdy shelters would offer some momentary protection. Following this brief (under one second) blast of gamma rays would be days of cosmic rays raining down upon Earth, and passing with killing energies through everything as deep as half a kilometer. It's unlikely even humanity's elite in the best and deepest underground shelters available could survive. Life in the depths of the oceans will be killed. Everything on the surface will be dead.
Fortunately these death rays consist of beams likely only one degree wide, and so will usually miss a particular world like Earth. Unfortunately, the stats still put us at risk about once every hundred million years.
The binary system known as WR 104, which consists of a Wolf-Rayet star and an OB companion, is well known for its spectacular dusty “pinwheel” nebula, which was revealed in spectacular detail by a team of astronomers lead by Peter Tuthill (now at Sydney University) in 1999. The nebula is formed by material contained within a wind that is driven away from the binary stars. As the material moves away from the stars, it curves as it rotates around the system.So the star may only Supernova. It may not result in a Gamma Ray Burst. Even if it does, the Jet of Megadeath is so narrow that it may miss. And even if not, we should be able to make shelters, not just for humanity (or the variant of the human species we've evolved into by then), but the complete biosphere. A kilometre of rock will make an adequate shield. And settlements on the opposite side of the moon to the Deathstar will ride out both the initial second or two of the gamma ray burst, and the days of the cosmic ray storm that follow.
That same team, expanded to include others from Australia and the United States, has now compiled observations (taken with the 10 metre Keck Telescope in Hawaii) of WR 104 spanning six years (their study is to be published in the Astrophysical Journal). Wolf-Rayet stars are candidates for turning into supernovae, and so their mass-loss history is of considerable interest.
Recent studies of supernovae have explored whether there is a link between these exploding stars and gamma-ray bursts (the most energetic events known in the Universe). In the case of WR 104, it is possible that when the Wolf-Rayet star explodes, much of the energy and matter will be ejected at the polar ends – and Earth is virtually pole-on to the system.
Our understanding of the connection between supernovae and gamma-ray bursts is still in its infancy, but Tuthill and his colleagues suggest that there is a possibility that WR 104 might produce a gamma-ray burst – one that would be only 7,000 light-years from us (as good as on our doorstep).
The good news is that we probably have several hundred thousand years before the Wolf-Rayet star in question does explode.
Of course the Earth would be a "fixer upper" as would any other planet in the solar system we'd terraformed.
We have a lot of time - but maybe we should start thinking about solutions, some of which could take many millennia to implement. Some people are.