Sorry, see above. It was below when I started typing my response. :-) On 25 September 2014 14:18, LizR <[email protected]> wrote:
> 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.
