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Cake day: July 4th, 2023

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  • Great question!

    No, the Sun’s diameter will expand greatly but it’s mass will remain mostly the same, if anything it’ll be ejecting significant amounts of stellar matter when it turns into a red giant and will be losing mass.

    Mass is what dictates the gravity of a given object. If you replaced the sun with a black hole of the exact same mass, everything in the solar system would retain its exact same orbit outside of those few unfortunate objects that were very close to the sun (much closer than Mercury) when it got swapped out for a black hole of the same mass.

    So even though the Sun will eventually swell up into a red giant and eat most, if not all of the inner planets, it’s gravity will remain the same despite its massively increased diameter, and its gravity will get weaker as the red giant ejects stellar matter over its relatively quick life. Eventually it’ll eject its outer layers, creating a new nebula thanks to the star ejecting all of its outer layers and leaving behind the dead core of a star called a white dwarf. These dead stars are often similar in size to the Earth but typically have a mass close to that of our sun.


  • To add to this, the sun will expand into a red giant in approximately 5 billion years, which is likely to consume both Earth and the Moon. This will happen before the Moon is able to leave Earth’s orbit, so it’ll shrink in the sky but odds are it won’t leave the Earth’s orbit before both are destroyed by the expanding sun in the future.

    On top of that, the sun is slowly getting hotter as it gets older, so in approximately 1 billion years, the sun will have gotten hot enough to render most, if not all of the Earth uninhabitable for life as we know it.

    Space is fascinating.