Photo: ESO Online Digitized Sky Survey
HR 8210 or IK Pegasi is probably the most dangerous star in our stellar neighborhood. It is a narrow double made of a Delta Scuti star (A) and a very big white dwarf (B).Their separation from each other is too big for an interchange of matter. But this will change as soon as the A-star starts to expand to become a red giant. Then it will nearly reach the orbit of the white dwarf and this will suck off the hull of the red one. Thereby the white dwarf will soon exceed the Chandrasekhar limit of 1.44 solar masses.
It is quite certain that HR 8210 will explode as a type Ia supernova some time in the future. Maybe in 10 000 years, but more likely in several million years. Hopefully it won't be too soon and hopefully then the star will be much further away. Because an Ia supernova in a distance of 150 light-years could cause some serious problems for life on Earth.
Constellation: Pegasus
Distance: 150 light-years
Radial velocity: -11.4 km/sec
Space between HR 8210 A and B: 0.41 AU
Orbit period of HR 8210 A and B: 21.7 days
HR 8210 A
Spectral class: A8
Visual magnitude: 6.07
Mass: 1.7 * Sun
HR 8210 B
Mass: 1.15 * Sun
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