You fell into a trap here "Already" would suggest that it happened, but that's the point, in our reference frame it didn't happen and never will. From our perspective, we have a collapsing star, which will never collapse completely. But, on the other hand, if you went there and flew into this star, you would fall into a completely formed black hole, because your frame of reference would be then very different from ours.Urwumpe said:No, there are things that are as close to a black hole as possible from our point of view. So close, that we can tell that, beyond the veil of relativity, there has to be a real black hole already.
I'd say it's a simplification. It's easier to talk about a black hole, than about an almost-black-hole-that-will-never-form-completely-from-our-point-of-view-but-you-would-still-be-able-to-fall-into-it.Jarvitä said:But how does that fit into the current trend of describing everything from our point of view, eg the "50 year old black hole" that's millions of light years away?
If you had a jar of air and a jar of nothing (vacuum), and you threw both in a pool, would they both float or would the vacuum jar sink?
Any object.if you have a hypothetical universe that is completely empty (like in a computer simulation) and you put an object in it ... say a sphere of solid iron 5 meters in diameter, what kinds of objects could orbit it?
Suppose you had a solid iron ball 1 centimeter in diameter and you wanted to put it in orbit around a much more massive solid sphere of iron ... what would the mass of the larger iron sphere have to be?
[ame="http://en.wikipedia.org/wiki/Schwarzschild_radius"]9mm[/ame]i thought of a question during physics today:
how small yould you have to compress the earth, to turn it into a black hole with a significant event horizon. IE the point where after you compressed it, it would further compress itself due to its own gravitational pul accross itself
Not really. Once stars go Nova and explode at the end of their lives, they spray out a lot of unfused hydrogen (and helium and other stuff) into the local area. As the universe expands, not all of this hydrogen can globulate (good word) under gravity to begin fusion again so you get a lot of hydrogen spread over the universe in an unfusing smear.and: if [stars] start use hydrogen as their fuel (followed by "short" bursts of using helium as fuel, then C + O and so on), doesnt that mean that eventually, all hydrogen and helium in the universe will eventually be depleted, and no stars will be able to form? or at least until a sufficient body of other materials forms to make a short-lived star fuelled by other means (probably carbon/oxygen IMHO)
Yes, but the outer layers can still have a large proportion of unfused hydrogen as it's just the hydrogen in the core that fuses. The lighter hydrogen atoms not in the core will 'float' to the surface of the star and be kept from fusing. I'm having trouble finding the proportion of hydrogen left in a main sequence star a the end of its life though.but surely, since huge amounts of hydrogen were fused, all the way up to the heaviest of metals, it should be depleted, yes, some unfused hydrogen/helium is ejected along with the stars outer layers (anything but the core), but alot of it is used to keep the star going for a few billion years
http://adsabs.harvard.edu/full/1973ApJ...185..937HA typical star burns about 12 percent of its hydrogen fuel while on the main sequence
No.yes, but the hydrogen that IS fused never returns to its original state in any significant process, so EVENTUALLY all the hydrogen in the universe wil be fused into heavier atoms
If you spread the hydrogen out thin enough across the universe (which is what will happen with the expanding universe) then this remaining hydrogen cannot coalesce into stars and fuse into helium or heavier elements.
I suppose yes, we're picking up mass from the solar wind. It's really negligible, though. The grand majority of ejected/radiated mass is flung off into empty space, and the very very little that actually encounters our magnetic field is mostly in the van Allen belts. For what actually makes it to the surface, it's really just a particle here and there.If sun is burning fuel and loosing mass is there a possibility that planet orbits are becoming larger for small amount?