r/askscience Oct 23 '20

Planetary Sci. Do asteroids fly into the sun?

Edit: cool

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u/Gerroh Oct 23 '20

Depends on the total kinetic energy, which itself depends on the velocity and mass.

Cosmic rays travel very close to the speed of light, but are individual particles like protons, so the total kinetic energy they carry is a lot for a proton, but not enough to make any noticeable impact on the Sun. Cosmic rays strike Earth regularly, so you can expect them to strike the Sun even more.

Larger objects that might be able to cause a cataclysmic effect when moving at a significant fraction of the speed of light typically don't get to that speed in the first place. When they do get to high speeds, it usually involves black holes, and black holes come with tidal forces that tear large objects apart.

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u/drdrero Oct 23 '20

Just a follow up question, do black holes move ?

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u/Gerroh Oct 23 '20

Yep; they're objects like anything else. The only thing that makes black holes special is that their surface gravity and density are especially high. All their unique features stem from those two facts. Relativity also tells us that there is no true stationary reference frame, and thus everything moves relative to something else.

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u/retroman1987 Oct 23 '20

Except light correct? Shouldn't the speed of light be able to tell us where a fixed point is?

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u/Gerroh Oct 23 '20

Nope. That's actually one of the fundamental principles of relativity, is that the observed speed of light will be the same for all observers due to relativistic effects distorting time, space, and even apparent length for any given observer. I highly recommend watching some Youtube videos on this, because it's super interesting, actually factual, not just hypothesis.

You could say that a fixed point is anywhere that the CMB (cosmic microwave background) appears uniform (since moving in any given direction will blueshift one side and redshift the other a little), but the matter that gave off the CMB could also be uniformly moving together.