Question

All of this is nice, but stars don't do much as they exist on the Main Sequence except stay extremely stable and fuse hydrogen into helium in the core. But for a high-mass star like Betelgeuse what will we expect to happen when hydrogen runs out in the core? Helium will start fusing in the core, a shell of hydrogen will start fusing around the core, and the rest of the star will expand causing the radius to increase, the luminosity to increase, and the surface temperature to decrease Helium will start fusing in the core and all of the remaining hydrogen throughout the rest of the star will start fusing causing the radius to increase, the luminosity to increase, and the surface temperature to increase The core will instantly collapse into a neutron star or black hole, depending on the mass of the star. The rest of the star will explode as a supernova, creating all of the elements heavier than helium The star as a whole will contract (shrink) as there is no longer a source of pressure to stabilize the star and it will form a black hole

Answer 1

The correct option is A.

Explanation :

Fate has something very different, and very dramatic, in store for stars which are some 5 or more times as massive as our Sun. After the outer layers of the star have swollen into a red supergiant (i.e., a very big red giant), the core begins to yield to gravity and starts to shrink. As it shrinks, it grows hotter and denser, and a new series of nuclear reactions begin to occur, temporarily halting the collapse of the core. However, when the core becomes essentially just iron, it has nothing left to fuse (because of iron's nuclear structure, it does not permit its atoms to fuse into heavier elements) and fusion ceases. In less than a second, the star begins the final phase of its gravitational collapse. The core temperature rises to over 100 billion degrees as the iron atoms are crushed together. The repulsive force between the nuclei overcomes the force of gravity, and the core recoils out from the heart of the star in an explosive shock wave. As the shock encounters material in the star's outer layers, the material is heated, fusing to form new elements and radioactive isotopes. In one of the most spectacular events in the Universe, the shock propels the material away from the star in a tremendous explosion called a supernova. The material spews off into interstellar space -- perhaps to collide with other cosmic debris and form new stars, perhaps to form planets and moons, perhaps to act as the seeds for an infinite variety of living things.

So what, if anything, remains of the core of the original star? Unlike in smaller stars, where the core becomes essentially all carbon and stable, the intense pressure inside the supergiant causes the electrons to be forced inside of (or combined with) the protons, forming neutrons. In fact, the whole core of the star becomes nothing but a dense ball of neutrons. It is possible that this core will remain intact after the supernova, and be called a neutron star. However, if the original star was very massive (say 15 or more times the mass of our Sun), even the neutrons will not be able to survive the core collapse and a black hole will form!