Spectacular Stellar Deaths

Stars of the Sun's size lack the mass to create temperatures that will allow oxygen to be fused into heavier elements like carbon, silicon and sulfur. But stars the size of Betelgeuse can continue the process and as they die, they will fuse residual hydrogen, helium, beryllium, carbon, oxygen, silicon and sulfur in a series of shells and finally in the deep core, silicon and sulfur are fused into iron. Iron cannot be fused into anything else in an energy-creating reaction so after a time, a sufficient mass of iron is produced that any ongoing fusion cannot create enough outward-pushing energy to counter the power of gravity trying to collapse the star. So gravity finally wins out in the end, as it always does. When this happens, the iron atoms are compressed with such force that they are broken down into their sub-atomic particles (electrons, protons, neutrons). The entire core collapses or implodes to a volume only a few kilometers across. This collapse creates a shock wave (equal and opposite reaction) that rips through the surrounding fusion layers and completely destroys the star in an awesome explosion called a supernova. The star will increase in brightness by many thousands of times and the heat of the blast is so incredibly hot that the fusion layers of the star in their death throes will create all the elements of the periodic table up to uranium, scattering it throughout the universe. From such a spectacular death though can also come new life. If the shockwave from the supernova blast encounters an interstellar cloud of hydrogen and dust, it can cause that cloud to begin to contract and begin a new cycle of stellar birth. Such an explosion many billions of years ago started such a cloud contracting and created the Sun.

As the gases of the explosion are driven off into space they leave two markers behind. First is an ever-expanding cloud of gas illuminated by radiation created within the cloud by high temperatures and a strong magnetic field. This nebula is the grave of the deceased star marking where the titanic explosion took place. In the year 1054, skywatchers noted a brilliant new star in Taurus. The star grew so bright that it was visible for months in broad daylight before fading away to never be viewed again. At least that is, not until the telescope was invented. Astronomers searching that area found the remnant of the supernova and named the cloud the Crab Nebula for its crustacean-like appearance. The second marker is the core remnant itself. The core is called a neutron star because all that is left at the core is neutrons. The collapse of the core causes the protons, electrons and neutrons in each atom to become fused together into one enormous neutron. Because the center of the supernova explosion is not at the exact center of that core, the force of the blast imparts enormous rotational energy to the core and it begins to spin very rapidly. Each time it does so a blast of radio energy sweeps across our field of view and radio telescopes on Earth are able to detect it. This type of spinning neutron star is called a pulsar. The rotation rates of pulsars are extremely precise and if they are single pulsars (a pulsar that formed in a multiple star system) they will gradually slow down over time.

If the star is of sufficient mass, the combination of mass and high density produces a gravitational field so powerful that nothing, not even light can escape it. The stellar remnant then simply disappears. Material drawn into the star can be viewed spiraling down into the star and disappearing when the gravity becomes so strong that light can no longer escape. The star is now referred to with the descriptive name black hole. The point where light can no longer escape the black hole is called the event horizon.

This is the fate that awaits massive stars like Rigel and Betelgeuse. When they inevitably blow, they will do so in spectacular fashion. At 430 light-years distance, Betelgeuse will supernova with light equivalent to a bright crescent moon. It will cast shadows on Earth's surface and will be easily visible in the daytime. It will not likely happen for tens of millions of years. But it could happen tomorrow too.

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