On 25 September 2014 12:53, Russell Standish <[email protected]> wrote:
> On Thu, Sep 25, 2014 at 12:21:52PM +1200, LizR wrote: > > This appears to be saying that all the Hawking radiation that would be > > emitted by a BH over its lifetime actually comes out in one huge burst > > before the BH can finish collapsing. That would surely affect the > > characteristics of supernovae in which BHs are thought to form? ... The > > entire mass of the BH coming out as radiation??? > > > > Also, what's at the centre of our galaxy. and others? > > > > I haven't RTFA, but it could be that the claim is that singularities > don't exist. This is widely suspected in any case. Black holes are > defined as having an escape velocity greater than the speed of > light. A big enough concentration of mass should exhibit this. > My reading of it - and now, I think, Brent's too (see below) - is that the article is claiming that BHs fail to form, and that they in fact explode, releasing their mass as radiation, or at least a substantial amount of it. As it says... But now Mersini-Houghton describes an entirely new scenario. She and Hawking both agree that as a star collapses under its own gravity, it produces Hawking radiation. However, in her new work, Mersini-Houghton shows that by giving off this radiation, the star also sheds mass. So much so that as it shrinks it no longer has the density to become a black hole. This implies that the star sheds enough mass to be below the whatsit limit where it becomes a neutron star instead (1.4 solar masses iirc). Given that stars could start off with several solar masses, not all of which is lost as supernova debris, the implication is that maybe 1 solar mass becomes Hawking radiation. Converting that much mass into photons (or even neutrinos) is going to be a huge blast, to say the least. A back of the envelope calculation suggests ... A supernova radiates about the same energy the sun produces over its lifetime. The mass converted to energy when the Sun fuses hydrogen is around 1% I think so a supernova radiates about 0.01 solar masses as energy. If we add in say 1 extra solar mass turning to Hawking radiation that's therefore about 100 times more energy than a supernova is currently thought to emit. Where does it go to? Also as I and Brent said there's the mass at the galactic centre. That could be a collapsed object that isn't a singularity and / or doesn't have an event horizon, but it's got to be something. And since Mersini-Houghton only suggests STARS fail to form BHs, galactic sized ones may in any case form from a different mechanism, so if BHs are physically possible, they could well be them. -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
