On this day in 2004, an explosion from SGR 1806-20 reached the earth. It is thought to be the largest explosion to be observed on the earth since a supernova was observed in 1604. SGR 1806-20 is neutron star with a particularly strong magnetic field. I have a certain fondness for neutron stars because the first paper I published involved a mathematical model of a neutron star. They are bizarre objects.
After a supernova, the star can experience a gravitational collapse — becoming small and unimaginably dense. For example, SGR 1806-20 is less than 20 km in diameter with a mass of over 12 times that of the Sun. Because all this mass is so compact, in order for angular momentum to be conserved, neutron stars spin very fast. In the case of SGR 1806-20, it rotates on its axis every 7.5 seconds.
The magnetic fields on neutron stars are enormous, but SGR 1806-20 is in a special category with even larger fields, magnetar. During the event that caused the 27 December 2004 observation, SGR 1806-20 released more energy in 0.1 seconds than the Sun does in 100,000 years. If SGR 1806-20 had been one of our closest neighboring stars, that one event would have killed all higher life forms on Earth. SGR 1806-20 is 50,000 light-years away. The closest magnetar to us is 9,000 light-years away. But that’s an evolutionary thing. If the Earth were close to such an object, advanced life would never have developed here.
Other people torture themselves thinking about terrorism. But I find this kind of stuff far more edifying. The universe is horrible. We really do exist on a particle of dust floating through space. We survive because of dumb luck. But at least it is cool. For example, if you took the entire human population and put them on the surface of a neutron star, they would be squeezed to the size of an aspirin. Where else but science do you learn things like that?