GeeKay

Many thanks - I'll do just that.

Yes, I understand. I know this must be obvious to many, but it isn't to me. The 'sensation' of gravity that one feels would appear to be entirely due to its differential tidal pull. And since spheres offer the minimum surface area for mass (MigL's point about the variability between surface area and volume over size notwithstanding) this means that gravity, or 'curved space' must always have a tidal pull associated with it. This gives gravity its sense of 'direction' - at least in the universe we inhabit. Or am I off-target here? On a different point, I've had it pointed out to me that a 11 billion tonne MBH would exert a one third gravitational pull (G) at a distance of 15 metres. Now I don't have the maths, but given that a MBH with the mass of Phobos is around 10.8 trillion tonnes, I would imagine an observer would feel a heck of a lot more than 0.3 G at the same distance. Only a half-educated guess, mind.

With regards to high-gravity objects, such as neutron stars and black holes, I've been studying the excellent Xaonon Hawking Radiation Calculatior, which I found elsewere in this forum. I have just one question: what are 'surface tides'? I understand surface gravity and the tidal effects of gravity at varying distances from the star in question. But surface tides is something I just don't get.

I don't know if this is worth bringing to the party, but with regards to Hawking radiation and possible local gravitational effects concerning MBHs, this may be of interest: http://casa.colorado.edu/~ajsh/hawk.html

0.016 nanometres? That is a small radius, indeed! Yes, about the effects of Hawking radiation, this quantum effect I do understand. I just wonder at what level of mass is required for it to begin to have a drastic effect upon the MBH concerned. Also, I wonder if I had been somewhat vague in using the word 'micro' to describe what otherwise could be referred to as 'mini' or 'primeordial' black holes. But then, hey, what's in a name? Still, I mention this because, while accepting that such objects must be accounted truly minuscule in the grand scheme of things, nonetheless there would appear to be an appreciable difference - leastways in terms of observable effects - concerning MBHs ranging in mass between those of small mountains to seriously large asteriods. Another way of addressing the problem would be to put it like this: at what minimal mass would such a hyphothetical MBH need to be for it to exhibit the sort of effects I posited in my original post? In other words (once again dragging the observer into the experiment) at what distance could a person safely remain before feeling the gravitational effects from such an object? By the by, I have a fourteen-year old niece who is mad on astronomy and who likewise is also very keen to know the answer to this seemingly unfathomable question. Many thanks again. GeeKay

Hi I understand that micro-black holes probably don't exist in nature - at least it would appear to be the case, according to current received wisdom on the subject. Be that as it may, I would be interested to learn about the properties of such objects. As an example: if one posits a MBH with (say) the mass of Phobos (vital statistics: 22.2 Km diameter; mass: 1.08 x 10*16 Kg) how small would the event horizon be, for example? Also, in view of the gravitational tides, how near would a person be able to approach such a collapsed object without risk to life and limb? An inch? A metre? Half a furlong? I must admit that my maths isn't all that good at present - although I'm doing my level best to rectify this situation. Still, I would appreciate a largely non-mathematical, 'lay reader' style response, if at all possible. Many thanks for hearing me out. GeeKay

Hi This is a simple question but one which I personally can't find an answer to, despite exhaustive trawls through the internet. It is this: can gravity waves physically endanger organisms - in the same way, for instance, that an intense gravitational tidal field is said to 'spaghettify' all matter, including living matter? Could similarly powerful gravity waves have the same effect? Geekay