Gravity, Black Holes and Stars

[tapkaJohnD]

The nearest black hole to us is Sagittarius A*, the supermassive BH at the centre of the Milky Way, 27,000 light years away. At this moment, or rather at this moment 27,000 years ago, SgA* swallowed an enormous gas cloud. This is the first time we have been able to observe such events, and could turn SgA* from an unusually quiet object into something like the ravening monsters that live at the centre of many other galaxies.

Being so close to this event will undoubtedly give us more information about what happens at and near the event horizon of a BH. It will be observed by a whole pack of probes and telescopes, from Chandra, XMM, EVLA, INTEGRAL, Swift, and Fermi to the Keck and the Very Large Telescopes.

John

[im]

I think of it like this:

The natural state of the Universe is flat with no matter. Once you introduce matter you introduce 'warping' around that object and into that flat universe and things fall into that warping and towards the object responsible for it. The 'warping' is what we call Gravity.

Remove all matter from the Universe and you'd have no Gravity.

[Mojocvh]

Eric Mc said:

Why does electricity produce magnetism?

I think you may find that it's the other way round...

[Eric Mc]

Of course - it works both ways.

[Kenzle]

Eric Mc said:

...

Gravity is purely a property of mass - not a property of the material of which makes up the mass or the behaviour of that material. Whether it is spinning, hot or cold is of minor relevance to gravity. It is the mass that matters.

...

Strictly speaking it is energy that gravitates, not mass.

A pair of photons passing by each other will interact gravitationally.

[Eric Mc]

You can make a simple explanation more complicated if you want to.

Sometimes simple is best - at first. Once the OP understands the basic principles, then it is possible to start explaining the more esoteric aspects of what matter actually is.

[Kenzle]

Eric Mc said:

You can make a simple explanation more complicated if you want to.

Sometimes simple is best - at first. Once the OP understands the basic principles, then it is possible to start explaining the more esoteric aspects of what matter actually is.

I quite agree, simple is best - but all the responses seem to be referring to rubber sheets / warping of space-time etc which is a wholly Einsteinian (general relativity) way of looking at things rather than the Newtonian version of gravity. And one of the key things about GR is that because space itself is curved, everything, including light, is affected by the curvature of space, not just mass.

Anyway, just saying.