Contrabang #4 Black Dark Matter

This Is How To Bring Dark Skies Back In An Increasingly Developed World (link)

An overview on the growing problem of light pollution, which affects nearly everyone in the developed world. 

Scientists Didn’t Really Find The First Molecule In The Universe (link)

There was a buzz last week because scientists found the spectrographic signature of helium hydride, theorized to have been the first molecule formed in the universe. However, the helium hydride they found was not primordial, but generated in some nebular region. Ethan took the opportunity to explain the Big Big Theory to his supposedly astronomy-savvy audience, which he likes to do. The whole thing is a non-event.

Ask Ethan: How Can A Black Hole’s Singularity Spin? (link)

How [is] angular momentum conserved when stars collapse to black holes? What [does] it means for a black hole to spin? What is actually spinning? How can a singularity spin? Is there a “speed limit” to this spin rate and how does the spin affect the size of the event horizon and the area immediately around it?

As usual, Ethan doesn't shy away from the difficult questions. Now, if only he'd ever deliver a reasonable answer! Let's see how this one goes...

While the laws of physics break down at this point — some physicists cheekily refer to singularities as places where “God divided by zero” — no one doubts that all the matter and radiation that passes inside the event horizon heads towards this point-like region of space.

No one doubts accretion disk theories? He must have forgotten about me! Not only are singularities places where God divides by zero, but they are places where he counts to infinity, which is what the angular momentum question is going after.

Just as a spinning figure skater speeds up when they bring their arms and legs in, astrophysical masses rotate more quickly if you decrease their radius.

Exactly. If the figure skater could decrease her radius to zero, her angular velocity would become infinite, which isn't possible. Yet, that is what must happen when a spinning star is reduced to a point mass.

If [the sun] became a neutron star — with the same mass but a radius of 20 km — it would rotate once every 2.4 milliseconds: consistent with what we observe for the fastest pulsars. 

Neutron stars are complete rubbish. If he'll believe that, he'll believe anything. Those who make analogies to neutron stars to build their case are only making a mockery of their own arguments.

This is okay! Einstein put forth his theory of General Relativity in 1915, and it was only a few months later that Karl Schwarzschild found the first exact solution: for a point mass, the same as a spherical black hole. The next step in modeling this problem in a more realistic fashion — to consider what if the black hole also has angular momentum, instead of mass alone — wasn’t solved until Roy Kerr found the exact solution in 1963.

It's okay guys, there's a mathematical solution! **pushes up glasses**

The exact solution for a black hole with both mass and angular momentum was found by Roy Kerr in 1963. It revealed, instead of a single event horizon with a point-like singularity, an inner and outer event horizon, as well as an inner and outer ergosphere, plus a ring-like singularity of substantial radius.

Just add a ring-like singularity, and now you have angular momentum accounted for. Hypothetical mass at far distance to account for unexpected angular momentum...where have we heard this line before? It is the dark matter of black holes! Perhaps we should call it...black dark matter.

There is a maximum ratio of angular momentum to mass that is allowed; if there is too much angular momentum, the black hole will radiate that energy away (via gravitational radiation) until it’s below that limit.

What do you do if your system has unaccounted-for energy? You just assume that it is radiated away by black holes - which are called dark because they fundamentally don't radiate anything. So easy.

All of this is true for a rotating black hole from the instant you create the event horizon for the first time.

So for all black holes, since all the systems are assumed to be rotating. There really is no such thing as singularities, but singularity rings. Then why do we keep talking about singularities?

There’s also an important distinction between a mathematical solution and a physical solution...…you should not physically trust in the inner horizon or the inner ergosurface. Although they are certainly there as mathematical solutions of the exact vacuum Einstein equations, there are good physics reasons to suspect that the region at and inside the inner horizon, which can be shown to be a Cauchy horizon, is grossly unstable — even classically — and unlikely to form in any real astrophysical collapse.

It's okay, there's a mathematical solution - which you should not physically trust. That's actually the answer!

Perhaps the most profound takeaway from all of this, though, is that in a rotating spacetime, space itself can indeed move without any sort of speed limit at all. It’s only the motion of matter and energy through space that’s limited by the speed of light; space itself has no such speed limit. In the case of a rotating black hole, there is a region of space beyond the event horizon where space is dragged around the black hole at a speed faster than the speed of light, and this is just fine. Matter still cannot move through that space at speeds exceeding the ultimate cosmic speed limit, and all of this is consistent with both relativity and what we observe.

Not content that spacetime must be expanding as necessary to accommodate for redshift theory, we must now believe that spacetime rotates as necessary to allow for black holes. It's the trick of last resort for the modern astrophysicist. If you can't add in enough dark matter, dark energy, or ring-like singularity to make the math work, you can always just let spacetime do whatever is needed, since it is free to violate any laws of mathematics or the fundamental constants of their own theories. Very profound indeed!

Hyabusa2 Followup

In Japanese Asteroid Bomb, we covered a mission to find water in a near-Earth asteroid. In the three weeks that have passed since then, the vessel has moved back within view of the impact site, and reported that the crater is twice as large as anticipated. In hindsight, we should have expected that, because they always seem to be surprised at the magnitude of space collisions. They were surprised at the magnitude of the explosion caused on a comet by the Deep Impact probe a decade ago, as well as the dramatic demise of comet Shoemaker-Levy 9 into Jupiter a couple decades ago.

Regarding the asteroid impact, we stated,

The question isn't whether they will find the water they are looking for, but how they will respond when they don't. We'll likely hear excuses like the crater wasn't deep enough, drying by radiation was stronger than expected, etc.

The first excuse has been removed. There won't be any credible claims that the crater impact was insufficient. It will be interesting to hear their reports when the probe returns to Earth next year.