what's really going to blow your mind is

while you probably assumed or knew spinning black holes move space around them

spinning black holes also move TIME around them

* https://www.science.org/doi/10.1126/sciadv.ady9068

so in theory a spinning black hole that's been around for billions of years has a time drag around it in a path that is billions of years old

(no we can't navigate it because yes that would be time travel to the past and violates causality)

black holes are just so weird with every new detail even more weird

oddly more interesting to me to try to grasp neutron stars (densest objects before black holes and are still visible, our entire solar system in a neutron star would be only 10km 6.2miles across)

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My_Name 7 hours ago | parent | next [-]

Another thing that may blow the minds of some is that M87* is less dense than air at 0.44kg/m³ so if you could bring it to sea level (in a large enough theoretical test area) it would float like a helium balloon (sea level air is 1.2kg/m³).

Of course if you did do that, the air itself would collapse into a black hole larger than M87*...

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srean 8 hours ago | parent | prev | next [-]

Consider the magnetar.

https://en.wikipedia.org/wiki/Magnetar

"A magnetar's 10^10 tesla field, by contrast, has an energy density of 4.0×1025 J/m3, with an E/c2 mass density more than 10,000 times that of lead."

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1970-01-01 7 hours ago | parent [-]

Yes, magnetars are considerably more rare than black holes and considerably more interesting to study in terms of raw horsepower. Imagine a type-2 civilization using them as engines or launchers for spacecraft to zip around the galaxy.

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ck2 7 hours ago | parent [-]

the radiation from a magnetar exceeds any other star, overcoming that would seem implausible

still trying to wrap my mind around kilonovas (colliding neutron stars)

ie. they can pop out earth-sized chunks of gold, in theory, and since they aren't black holes that would be VISIBLE, albeit also "in theory" lol

* https://www.nasa.gov/image-article/unfolding-story-of-kilono...

maybe Roman can spot one someday, that would be something

	▲	pfdietz 3 hours ago \| parent [-]
		> they can pop out earth-sized chunks of gold The can produce Earth masses of gold, but of course not in the form of "chunks". The gold starts as atoms in a highly ionized gas and only much later cools enough to form solids (dust).

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mdavidn 6 hours ago | parent | prev | next [-]

It blows my mind that, in the frame of an outside observer, time appears to stop at the event horizon. An observer falling through the horizon (who survived the radiation and tidal forces) would not perceive this.

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aeve890 an hour ago | parent | prev | next [-]

>what's really going to blow your mind is while you probably assumed or knew spinning black holes move space around them spinning black holes also move TIME around them

Well, isn't called space-time for nothing. You can't have one without the other. Like in electromagnetism. I thought it was kinda obvious since Einstein and Minkowsky.

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SoftTalker 5 hours ago | parent | prev [-]

> densest objects before black holes

Not quite, I think a (theoretical) quark star would be higher density?