What would happen if Earth fell into a black hole?

Re: AC's don't surf! Naturally, we would no notice

"I don't think the AC or those who up voted him thought this through"

Same AC here - just to note that all I was commenting on was the (unfortunately) now widespread misconception that gravity was mediated by gravity waves.

The instantaneous appearance of a black hole next to earth is such a bizarre event that I'm struggling to see the source of the gravitation waves BTW

Re: AC's don't surf! Naturally, we would no notice

So yes, the waves would rip us apart long before what remains is sucked in to the event horizon.

The figures given for the recently-detected black hole merger can give some context. If the merger happened 1.3Gly away and the signal only created a disturbance a thousandth of the width of a proton, then it would only disturb something one lightyear away from it by about a millimetre. Knock that down to 1AU and the disturbance would be on the order of 300,000km. Having, say, an 8 solar mass black hole suddenly appear in our solar system would be a lot, lot less violent an intrusion into spacetime. Earth might not be ripped apart, although I wouldn't want to be living on a fault line or on a coast at the time.

Re: AC's don't surf! Naturally, we would no notice

"Hint. Find a pond / pool and toss a massive rock in to it. It goes splash now doesn't it?"

I'm not sure the analogy fits. A simple black hole doesn't emit sig. gw (AFAIK) except when another very large mass is in mutual close orbit. The two black holes that merged 'last week' emitted the largest amplitude waves at the point of merger but before the resultant object became symmetrical.

Are you suggesting that the hypothetical 'appearance' of a black hole next to Earht would generate large amplitude gw just by 'appearing' ?

(An interesting snippet is that the gw emitted by the Sun/Earth system are of the order of ~200W) BTW

Re: AC's don't surf! Naturally, we would no notice

"Hint. Find a pond / pool and toss a massive rock in to it. It goes splash now doesn't it?"

Not really, gravity waves that would be that disruptive would have to originate from two black holes or a black hole and a neutron star, Sol couldn't produce such gravity waves when interacting with a black hole.

Indeed, it's likely that the entire solar system could enter a galactic core sized black hole intact-ish.

"we might better first discuss the black hole's motivation in doing so."

Don't panic, it is clearly just to make way for a hyperspace bypass. I'm sure they will send us notice before doing so.

Well you've got this headline, or his scary views to choose from. Although this one really takes the biscuit.

I did quite enjoy some of his articles here, although I didn't always agree with them. I have said that before. But he's still a certifiable, misanthropic loon.

@Grikath -- Re: Worse than being sucked into a black hole is colliding with the sun in the process

Not to mention that the atmosphere and basically anything not bolted down would have been sucked away first.

Re: Spaghettification - not always

Here are some numbers using the mass of Earth (M) as a guideline...

c= 299792458 m/s

G= 6.6740831e-11

M= 5.97237e+24 kg

Key: Schwarzschild Radius = rs, Escape velocity at rs = evrs, Escape velocity at rs + 2m = evrs+2m

I give the evrs+2m i.e. two metres out from rs to give an idea of the relative escape velocity, and thus the gravitational gradient that a tall person would experience.

Mass= 5.97e+024 kg, rs= 0.0088700671 m, evrs= 299792458 m/s, evrs+2m= 19920866.79 m/s.

So the Schwarzchild radius for an Earth sized mass is a smidge under 9 mm and the difference in escape velocity 2m from its event horizon is about 279871591 m/s - that's a pretty steep and unhealthy gradient.

At ten times the Earth's mass...

Mass= 5.97e+25 kg, rs= 0.088700671 m, evrs= 299792458 m/s, evrs+2m= 61779736.59 m/s

The Schwarzchild radius is now a little under 90 mm and the +2m escape velocity difference is now about 238012721 m/s - still far too steep.

At one hundred times the Earth's mass...

Mass= 5.97e+26 kg, rs= 0.88700671 m, evrs= 299792458 m/s, evrs+2m= 166172922.8 m/s

...the ev difference has come down to 133619535.2 m/s - still too steep... In fact, it's not until we get to around a mass of 5.97e+35 that the ev difference is less than 1 m/s...

Mass= 5.97e+35 kg, rs= 887006709 m, evrs= 299792458 m/s, evrs+2m= 299792457.6 m/s

...the Schwarzchild radius is now 887,006.09 km and whilst you might survive the difference in ev it would still be uncomfortable. To get to less than 1 mm/s difference in escape velocity we need to increase the mass by another factor of 1000, to 5.97e+38 kg, at which point the Schwarzchild radius becomes 887006709435 m, or 887,006,709.4 km - that's pretty big. In fact, that radius is about 44 times greater than the current distance of Voyager 1 from Sol.

However, the estimated mass of our galaxy is between 1.15e+42 kg and 1.69e+42 kg, so it would seem that a sufficiently large BH would be between about 1/1930th and 1/2829th of our galaxy.

Proviso: I think I've got the numbers right but wouldn't mind someone checking them.

As DNA said "Space is big. Really big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space..."