The Dangers of Supernovas Video

Edward Sion, astronomer and astrophysicist at Villanova University, talks about a nearby star system going supernova in 10 million years, far sooner than scientists once predicted. The resulting explosion would outshine the galaxy.
Read the full transcript »

The Dangers of Supernovas Question: What is a Type 1A supernova? A Type 1A Supernova is thought to be a white dwarf that undergoes total thermonuclear detonation. It explodes and completely obliterates itself leaving no remnant. For example, we have yet to detect a neutron star or a black hole remnant of a Type 1A supernova explosion. It appears that the stellar explosion complete destroys the star. This explosion is extremely energetic. The amount of energy release is approximately 10 to the 51 – 10 to the 52 ergs of energy. In other words, a type 1A supernova can outshine the galaxy it’s in the entire galaxy for a short time. And so, they are extremely energetic. Question: What properties of the T Pyxidis binary system make it a likely candidate for going supernova? Yes. T Pyxidis is a recurrent nova, not a supernova, but a classical nova, but it recurs. Most classical novae we see only once. T Pyxidis has a classical nova explosion every roughly 20 years. And this continued from the early 1890s until 1967. So, there were five nova explosions interspersed every roughly 20 years up until the 1967 explosion. Since 1967, this 20 year cycle has disappeared. Nothing has happened yet. In other words, it’s 44 years overdue for the next thermonuclear explosion. What happens in a recurrent nova, and the reason I distinguish it from the supernova is the recurrent nova is a white dwarf. This is a star about the size of Earth, but it has an extremely high density. The density is a hundred million grams in a cubic centimeter. Except for a massive white dwarf, a hundred million grams in a cubic centimeter, which means a thimbleful of this material, would be hundreds of tons if we weighed it here on earth. What happens is, the white dwarf is so dense that the electrons surrounding the nuclei have all been stripped away from the nuclei and the electrons are actually forced to forma separate gas. We call it a generate electron gas. What happens is, when you squeeze matter tighter and tighter, there’s a principle in physics called the Pauli Exclusion Principle that states that no more than two electrons with opposite spins can occupy the same energy state. So, what happens is, when you squeeze matter tighter and tighter to higher density, there are fewer and fewer energy states available for the electrons to occupy because all the lowest lying energy states are filled first. So the electron is forced to move very, very fast and it can’t slow down. It can’t de-excite because the Pauli Principle prevents it. And so what happens is, the electrons move extremely fast and as the density goes up, they move faster and faster and that exerts pressure. Well, it’s the pressure of these degeneral electrons, the degeneral electron gas, that prevents gravity from pulling this stuff in. But what happens is that as the white dwarf mass increases, there’s an ultimate mass limit called the Chandrasekhar Limit beyond which a white dwarf cannot exist. Because at the Chandrasekhar Limit the degenerate electron gas pressure can no longer withstand the pull of gravity. It can no longer balance gravity and prevent the collapse of the white dwarf. Type 1A supernovae occur very close to the Chandrasekhar Limit. When the white dwarf mass is very close to the Chandrasekhar Limit, T Pyxidis has a white dwarf which is very close to the Chandrasekhar Limit. Its presently determined mass, fairly reliably well-determined, is 1.37 solar masses. The Chandrasekhar Limit for carbon oxygen white dwarf is 1.44 solar masses. So, it doesn’t have much more material to accumulate until it reaches the Chandrasekhar Limit in which case you would have instantaneous collapse. But just before that happens, as the white dwarf grows in mass, the compressional heating, the weight of the material from the neighboring star from its companion presses down and raises the temperature high enough to detonate carbon. That is to cause the carbon nuclei inside the white dwarf to fuse together, releas

Advertisement
Advertisement
Advertisement