What's at the center
The fuel runs out. As long as reactions continue, pressure from within supports the star. Once they stop, there's nothing left to hold it up.
The core collapses inward. The collapse takes fractions of a second. Matter is compressed to a density unimaginable under ordinary conditions.
The outer layers blast outward. A reflected shock wave and a stream of particles eject the outer layers at thousands of kilometers per second.
The core remains. With less mass, it's a ball of neutrons the size of a city. With more, it's an object that not even light can escape.
The fourth step gives you the hardest number to imagine. Neutron-star matter is so dense that a thimbleful of it would weigh about as much as a mountain.
These remnants often spin rapidly and send out a tightly focused beam. From Earth, it appears as pulses with an incredibly precise period - so precise that the first detected signal was jokingly labeled a possible message.
What's outside
The first tile describes a rare case of an astronomical event appearing both in the sky and in written records. Observers described a new bright star, visible even during the day, and today an expanding cloud can be seen in that spot.
The third tile explains why this concerns everyone. Heavy elements in Earth's crust and in the human body formed in stars and spread through the galaxy in explosions like these - there is no other way to deliver them.
The expanding cloud does not simply disappear. It collides with interstellar gas, compresses it, and triggers the formation of new stars - one star's end becomes the beginning of others.
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Sources
- When a massive star exhausts its nuclear fuel, its core collapses, forming a neutron star or black hole and ejecting the outer layers
- heavy elements spread into interstellar space and become part of later generations of stars and planets