All of us have a certain amount of rubber necker inside us. We all turn to see the wrecked car, and as kids we paused to watch the fights in the school yard. As an adult, I have to admit to taking a secret (well, maybe not so secret anymore) thrill in watching the occasional academic smack down. While flipping through arXiv earlier this evening my abstract flipping slowed to a stand still as I caught sight of an intellectual head-on collision. “In this short essay (no flimsier than the original preprint where these extravagant claims appeared)”, writes K. Petrovay in a paper titled “BlackStarâ€šÃ„Ã¹ or Astrophysical Black Hole?”, “I demonstrate that these ill-considered claims are clearly wrong.” The paper he referred to was by T. Vachaspati and it claimed Black Holes do not exist.
Fighters, take your corners. At the bell, publishing round one will end.
In a paper submitted to the astronomy pre-print server on June 8, 2007 Tanmay Vachaspati of Case Western Reserve University argues that black holes don’t exist. This statement is based on the relativistic statement that time for objects (particles count) trying to form a black hole slows to the point that the objects appear to hover seemingly forever just outside the forming black hole’s event horizon. Thus, argues Vachapati, the black hole never actually forms.
Here is what happens: You have a giant star, on order of 10 solar masses in size or larger, and it stops generating light for some reason. When light stops pushing the outer layers of the star apart, the star begins to collapse. Initially, inter-particle forces try and prevent things from crushing to closely together, but they lose, and gravity crushes the atoms together causing explosive nuclear reactions. These nuclear reactions fire the outer layers of the star out as a supernova, but the inner regions just continue to crunch together, and the protons and electrons and neutrons are all crushed together until the lose their individual identities. Somewhere inside this infalling mess is a point at which the pull of the mass inside that radius is so strong that not even light is going fast enough to get escape (on Earth anything going faster than 11.2 km/s can escape. The speed of light is 300,000 km/s). As the infalling material accelerates toward this point of no return it goes faster and faster. As it goes faster, its time goes slower compared to clocks on a not infalling Earth (this oddly means the object actually appears slow down). Eventually, when an observer feels like they are going their fastest – a hairsbreadth slower than the speed of light perhaps – they appear, to us, to stop. Thus, a black hole, never quite finishes collapsing down to that mythical singularity as viewed by an external observer.
BUT… we see black holes doing things like merging, and eating things, and acting like fully formed black holes.
In the greatest stretch of semantics I have seen since I last graded exams, Vachaspati uses this failure of black holes to finish forming in the reference frame of the observer to argue that the objects merging aren’t black holes, but something he names black stars. He then talks about how when these non-black hole objects collide the particles can explosively collide and give off *observable* gamma ray bursts.
BUT… (in steps Petrovay), the same factors that cause the black holes to not finish forming in our reference frame also prevent two merging objects from physically touching in our reference frame. This in turn prevents them from giving off gamma ray bursts, as Vachaspati argues above. And even if they could physically collide, and they did emit gamma rays, that light would be gravitationally redshifted – the gravity of the system would pull on the light and suck energy out of it causing it to appear redder and redder. Petrovay actually says “it would be gravitationally redshifted+dilated into oblivion.”
In effect, from the perspective of the objects forming black holes, the suckers fully form, fully collide, and much violence occurs. From our perspective, they never actually finish forming. They act like fully formed objects, because time systematically slows for everything getting too close, making that stuff disappear as though it had fallen into a fully formed, mushed to a singularity, black hole. If it acts like a black hole (by not releasing light), smells like a black hole (by not releasing smells), and in every way is as sweet as a black hole (in a 1990’s ‘Swe-eet, dude’ kind of way), it is a black hole. You can call it a black star, but please don’t try and change its physics. You will just be wrong.
The judges’ scores for round one are in, and this round goes to relativity and its Hungarian physics fighter, K. Petrovay.
One interested note about these papers. At the end of Vachaspati’s “black hole’s are black stars” paper, he thanks several people for their input, including Martin Rees (and I’m assuming he means Sir Martin Rees, the Nobel Laureate). He also says that his work was supported by the US Department of Energy and NASA. On first reading, it could be assumed that Sir Rees gave positive feedback on this work and that funding was granted specifically to explore the possibility that Black Holes don’t exist. Now, that could be true. However, what he wrote could just as honestly be written if he had grants to pay for other research and this is a footnote to that other research program (sorta like if you get money to study Saturn’s rings and a really cool star does something really neat while it is in the same field of view as Saturn’s rings – you are purposely studying the rings, but something totally unrelated results was also produced). What he wrote could also honestly be written if Rees pointed out some problems and he added in a sentence to address each of these problems without getting Rees to give a second round of commentary to tell him if the problems were actually addressed. It is just impossible to know. I don’t think attempts were made to mislead, I just have trouble believing that Rees would have approved of this paper for publication (and in fact this isn’t a published peer reviewed paper – it is just a paper put into to public record).
Okay, rubber necking time is over. Move along. Good new science is waiting to be discovered.