Ultra Massive Black Holes......

[polymath257]

No.  Sagittarius A* ‘s Star denoted the notation used to mark the object, not the nature of the object.    A black star’s star denotes the blackish object’s nature.  A black star is not a black hole into which things can fall but never come back out.   A black star has no event horizon.   Things falling onto a black star can in theory come back out.  But that happens rarely enough that our power of observation is not precise enough to see it. So we can’t tell the difference through observation yet.

The debate between black hole and black star is not what happens inside the event horizon.  It is about whether there in fact is a event horizon.

Meh. When quantum effects are brought into play, that definition of a black hole fails. It is quite possible that any object approximated by the 'black hole' concept from geeral relativity actually evaporates over time. In fact, that is considered quite likely.

At the very least, we have incredibly massive objects that we cannot otherwise see that agree with the theoretical predictions concerning black holes. We have gravitational waves that have the signature of merging black holes as predicted by GR. We have the accretion disks and other phenomena as predicted for black holes.

So, for at least a second order of approximation, we have black holes. The existence or non-existence of an event horizon that likely wouldn't have the properties predicted by GR because of quantum effects is rather trivial against what we already have.

So, it is quite reasonable to call the objects we have found 'black holes'. If, later, our theories or observations change a bit, we may have to change our designation.

[Anomalocaris]

Evaporation of blackhole through quantum effects is a different concept from black star. Black star hypothesizes that vacuum energy will stop any object from collapsing completely under its own gravity.

[polymath257]

Evaporation of blackhole through quantum effects is a different concept from black star.  Black star hypothesizes that vacuum energy will stop any object from collapsing completely under its own gravity.

OK, so as of this point, the difference between the two is theoretical rather than observational? And that we understand the theory of BH more than black stars, with the latter being speculative based on vacuum energy effects (which are, themselves, rather weakly limited by observation)?

Yes, that counts as an observation of a BH to me.

[Peebothuhlu]

At work.

*Raises hand*

Uhm..... about that 'Spin' thing?

[Anomalocaris]

Evaporation of blackhole through quantum effects is a different concept from black star.  Black star hypothesizes that vacuum energy will stop any object from collapsing completely under its own gravity.

OK, so as of this point, the difference between the two is theoretical rather than observational? And that we understand the theory of BH more than black stars, with the latter being speculative based on vacuum energy effects (which are, themselves, rather weakly limited by observation)?

Yes, that counts as an observation of a BH to me.

Yes, but the black star hypothesis also counts as a (still) plausible alternative explanation for observations, so it satisfy as a legitimate reason why actual black holes MIGHT not exist.

[BrianSoddingBoru4]

To be fair, one can be culturally Jewish and not be religious.

Boru

I was doing Brian a favor by introducing him to scientific skepticism about blackholes. It had absolutely nothing to do with religion. Brian simply can't discuss science without making it about religion. I don't consider myself to be a cultural Jew because cultural Jews are assholes. I'm a lapsed Jew.

I understand about Brian37, believe me.

What is it about cultural Jews that makes them 'assholes'?

Boru

[Yonadav]

I was doing Brian a favor by introducing him to scientific skepticism about blackholes. It had absolutely nothing to do with religion. Brian simply can't discuss science without making it about religion. I don't consider myself to be a cultural Jew because cultural Jews are assholes. I'm a lapsed Jew.

I understand about Brian37, believe me.

What is it about cultural Jews that makes them 'assholes'?

Boru

It's sort of hard to explain. Cultural Jews are self absorbed. They will tell you that they are Jewish at cocktail parties, and that's your cue to tell them how interesting you think that is and profess your admiration for the Jewish people. They are obsessed with the idea that being Jewish makes them different from other people, and say bizarre things about being Jewish in a non Jewish world-- even though they are about as different from non Jews as non practicing Catholics are from non practicing Presbyterians.  It is tedious.

[Anomalocaris]

At work.

*Raises hand*

Uhm..... about that 'Spin' thing?

Can you point to the original article?   There is no minimum spin for black holes. Black holes possesses whatever angular momentum was possessed by its progenitor object and by whatever is carried by everything falling into it.  Since angular mometum had a sign, it is possible for incoming angular momentum to cancel out existing angular momentum.  It in theory is possible for a black hole to have no spin whatsoever. There is a maximum spin when the black hole forms. Anymore and the angular momentum would prevent the progenitor object from collapsing into a blackhole.

[polymath257]

OK, so as of this point, the difference between the two is theoretical rather than observational? And that we understand the theory of BH more than black stars, with the latter being speculative based on vacuum energy effects (which are, themselves, rather weakly limited by observation)?

Yes, that counts as an observation of a BH to me.

Yes, but the black star hypothesis also counts as a (still) plausible alternative explanation for observations, so it satisfy as a legitimate reason why actual black holes MIGHT not exist.

OK, I took a closer look at the reasoning for 'black stars'. As far as I can see, the distinction between them and 'true' black holes is that they do not have singularities or event horizons. Instead, they are 'frozen' at what would be the event horizon boundary. This, by the way, is expected to happen in the formation of a black hole because of observer effects concerning time dilation near an event horizon.

Again, truthfully, the difference seems minimal. We expect BHs to form via collapse and thereby be subject to the observer effect. From the view of a distant observer, they will *look* like a black star. Since, from the view of a distant observer, there will *always* be matter outside of the event horizon and since the infall takes an infinite amount of time, there is no real difference between a BH and a black star. This is doubly true if the EH and singularity are 'smoothed over' due to quantum effects.

As far as I can see, this is a distinction without an observable difference, which means there is no difference at all.

[BrianSoddingBoru4]

I understand about Brian37, believe me.

What is it about cultural Jews that makes them 'assholes'?

Boru

It's sort of hard to explain. Cultural Jews are self absorbed. They will tell you that they are Jewish at cocktail parties, and that's your cue to tell them how interesting you think that is and profess your admiration for the Jewish people. They are obsessed with the idea that being Jewish makes them different from other people, and say bizarre things about being Jewish in a non Jewish world-- even though they are about as different from non Jews as non practicing Catholics are from non practicing Presbyterians.  It is tedious.

Pretty broad brush you're painting with.

Boru