While astronomers and science fiction fans often wish otherwise, there are times when the vastness of space works to our advantage, simply because it keeps us out of harm's way. For example: supernova explosions are some of the most violent events in the cosmos, sometimes outshining their entire host galaxy. The supernova appearing in the sky on July 4, 1054 was brighter than Venus; its remnant, the Crab Nebula, is still an intense X-ray source. However, the star that went kaboom was about 6,500 light-years away from Earth, meaning our planet wasn't in any danger.
No star that will go supernova in the foreseeable future is close enough to the Solar System to pose a risk to us. But what stars might be close enough to provide us with a lovely show—and a great example for study? Here are just a few, all within the Milky Way, with at least a slim chance of going boom before humans go extinct from other causes.
-
Currently the closest supernova candidate, IK Pegasi is a mere 150 light-years away from the Solar System. It's actually a binary system, consisting of a normal star about 1.7 times the mass of the Sun locked in mutual orbit with a white dwarf. While a low-mass star like that isn't big enough to explode on its own (the minimum supernova mass is 8 times the Sun's), its companion changes the situation. White dwarfs are the remains of Sun-like stars, but they have a maximum mass—the Chandrasekhar limit—beyond which they explode. When the primary star in IK Pegasi runs out of nuclear fuel in a few million years' time, it will expand enough that it transfers gas to its companion. Eventually, enough gas will transfer to the white dwarf and the whole system will explode as a type Ia supernova. A similar binary system, Sirius, is even closer at 8.6 light-years' distance. However, it's much farther from death, and may not even die as a type Ia supernova. This is an artist's impression with the Sun at right for comparison. The inset is an actual image of the primary star (the white dwarf is too small to see).
-
The brightest star in the constellation Virgo is Spica (pronounced "SPIKE-a" or "SPEE-ca," if you want to be pedantic), which lies about 260 light-years away. While it also resides in a binary system, the primary star is about 11 times the Sun's mass. That high mass means it burns through its nuclear fuel rapidly, and its spectrum indicates that it has entered the end stages of its life. When all usable fuel is gone, the core will collapse into a neutron star and the outer layers will be blown off as a core-collapse supernova. Exactly how many years it has left is a matter of conjecture, but it's probably pretty far (meaning: millions of years) from its end. Interestingly, by the time it goes supernova, it will likely have moved closer to Earth than IK Pegasi.
-
One of the brightest stars in the night sky, Betelgeuse is also familiar, thanks to its location in the constellation Orion. (Well, and a movie with Michael Keeton, though the pronunciation is different.) Betelgeuse is about 643 light-years away, but it's much closer to its end than the previous two candidates. In fact, despite being farther away than Spica, the star has grown so much in its twilight years that it's one of the few on this list that we can image directly. The outer layers are as wide as Jupiter's orbit, and material shed by the star covers a region 250 times greater than the star. While most astronomers don't think Betelgeuse will go supernova anytime in the immediate future, the uncertainties are great enough that it could be the most likely close candidate of this list. To put it another way, Betelgeuse may already be gone, though we might not know it for 640 years.
-
The Gamma Velorum system is a messy one, consisting of at least six stars. One of these is of a type known as a Wolf-Rayet star. This object has shed a lot of its mass in preparation for exploding as a special class of core-collapse supernova: a type Ic. The system's distance of 1,100 light-years makes it possibly the closest realistic possibility for this type of supernova. The star also bears the name Regor, or "Roger" spelled backward, after astronaut Roger Chaffee.
-
Type Ia supernovas can result from the merger and violent explosion of two white dwarfs. The closest known binary system consisting of two white dwarfs (known as a double degenerate binary) is V396 Hya, a scant 200 light-years away. However, the stars in that system are getting further apart instead of heading for collision, so no supernova for us. A far better candidate is the binary white dwarf known as J0806 or HM Cancri. The distance to that system isn't known precisely, though it's certainly more than 1,600 light-years away. These white dwarfs are so close together that they complete one mutual orbit in about 5 minutes—and they're getting closer every day as gravitational radiation carries away energy. They're still many thousands of years away from making a type Ia supernova, though.
-
For a brief time in 1843, Eta Carinae was the second-brightest star in the night sky, despite being about 8,000 light-years away, almost 1,000 times farther than the brightest star, Sirius. While its light faded over time, modern observations have revealed the star is huge: more than 100 times the mass of the Sun. The brightening was due to shedding mass, but what's left is still unstable and could explode in a hypernova—an excessively energetic supernova. Of all the candidates on this list, Eta Carinae seems the most likely to blow at any time. For that reason, astronomers have been monitoring it carefully. The nebula surrounding it contains at least one more star, though, which could complicate the dynamics of its explosion.
-
The Pistol Star, named for the Pistol Nebula in which it resides, is one of the most massive stars known: possibly as much as 150 times the mass of the Sun. Even though it's 25,000 light-years away, it would be visible to the unaided eye, if it weren't swathed in gas. As with Eta Carinae, its fate could be a hypernova. These explosions are highly directional, beaming much of their energy along powerful jets. When Earth is aligned with a jet, we observe the supernova as a gamma ray burst. Thankfully, the Pistol Star is unlikely to be aligned directly at us.
-
The Sun is by far the closest star to Earth, but it's also one we can definitively say will not go supernova—it's not massive enough. While it will leave a white dwarf behind on its death in 5 billion years, it won't be close to the Chandrasekhar limit. Even if it was near that critical mass, there's no nearby star to feed it enough matter to push it over the edge to make a type Ia supernova. No supernova Sun for us, no black hole Sun for Soundgarden.
If you want a list of all stars within 1,000 light-years that could potentially go supernova, check out Phil Plait's book, Death from the Skies. He doesn't list prognoses for the time death or include type Ia candidates, but the book has a lot more info if you want to have some fun.
Listing image by Earthsky
reader comments
53