Calculation Of A Big Boom

Credit: NASA/CXC/JPL

Infrared image of Tycho's Nova which is the remnant of Type Ia supernova.

Because of the work of our guest last Wednesday, Dr. Ryan Foley, and some events earlier this year, I feel that it is time to study something about the supernova.

When a high-mass star reaches the end point of its life, it explodes into a big ball of flame called supernova.  Astronomers have calculated that around 3 massive stars will go through a special Type Ia supernova every thousand year in our Milky Way galaxy. In other words, within distance of several thousand light year from Earth, a fair amount (20+) of stars is about to give a big boom. The picture above shows a nice picture of the remnant of supernova. It is beautiful to observe from some distance but we don't want to get too close to the explosion. That is why we are trying to determine when a star will blow up.

Even though astronomers know that there are plenty of massive stars in the outer space, they are having a hard time figure out which star is near its supernova time. However, the recent study might give a hope in finding those "time bombs" by using some details that were looked over before.

A theory behind the Type Ia supernova is that when a super dense star, called white dwarf, gradually steals mass from its neighbor star until its mass reaches the Chandrasekhar mass, it is too massive to fright with its own gravity and starts to shrink. The Chandrasekhar mass is approximately 1.4 times of Solar mass.

If the theory were true, scientists should found the neighbor star left over after the blast of supernova has faded away. They also predict that there should be some left over hydrogen and helium which come from gas of the neighbor star. However, we never have found any of these before.

Thus, the theory gets some modification. When a white dwarf reaches its Chandrasekhar mass, it avoids exploding by spinning faster. When a star "eats" more mass, its angular momentum increases too. That is, spinning faster should adjust the equilibrium and make a white dwarf go pass the Chandrasekhar mass limit without exploding.

Nevertheless, when the white dwarf finishes "eating" its neighbor, it spins slower and slower until the gravity acts and starts the supernova. The spinning technique should delay explosion time by around 1 thousand million years.

From the new model, astronomers are looking for a white dwarf that reaches the Chandrasekhar mass and has decelerating spinning. Those stars would be good candidates for "proto-supernova" stars.