The idea of an object so massive that light cannot escape from it actually goes back to the 18th century. It wasn’t until early in the 20th century that the modern concept of a black hole was put into a theoretical framework by Einstein, Schwarzschild, and Chandrasekhar (among others). (5) This has been built upon since by many notable physicists including Penrose and Hawking. A black hole has only three measurable properties, mass, electrical charge, and angular momentum or spin. (7) Black holes also have a non-zero temperature due to Hawking radiation. When an object falls into a black hole all information about these three properties becomes part of the event horizon. All other information such as size, shape, or the properties of the particles that it was composed of is supposedly lost.
At the center of a black hole is a region of space called a gravitational singularity. This is a point in space where the curvature of spacetime becomes infinite and it has zero volume. To date physicists have been unable to devise a framework that avoids this singularity despite much work in the field of quantum gravity theory. It is in this singularity where all of our theories of modern physics break down.
For a long time black holes were thought to be a theoretical construct and it wasn’t until the 1970’s that observations showed that they actually exist. Stellar mass black holes are created in core collapse supernovas when the original star has a mass of over about 20 solar masses. There are super massive black holes at the center of all galaxies ranging in size from millions to billions of stellar masses. These could be remnants from the big bang or they could be the result of the merger of smaller objects. It is theoretically possible to create micro black holes in high energy collisions of particles.
Massive stars live fast and die young. The more mass that a star has the faster it fuses the original hydrogen into progressively heavier elements. Let’s follow the life of a 50 stellar mass star on its way to becoming a black hole.
Stars like our sun are main sequence objects. They generate their heat and light by fusing hydrogen into helium. At the core of our sun the temperature and pressure are so great that the nuclei of two hydrogen atoms (protons) can be squeezed together along with a pair of neutrons to form an atom of helium. In the process energy is released. This mechanism is the underlying process in a hydrogen bomb. As this happens the core of the sun becomes progressively enriched in helium and this layer of hydrogen fusion migrates out. In stars that are more massive than our sun the helium can be fused into progressively heavier elements and there will be successive layers where helium is fusing into carbon, carbon into neon, neon into oxygen, oxygen into silicon, and silicon into nickel which decays into iron. These processes produce less energy at each stage and happen over smaller time frames. The progression from silicon to iron may be as short as a few days. The fusion of iron atoms into heavier elements uses energy rather than creating it and when the iron-nickel core exceeds about 1.4 stellar masses it collapses because the gravitational pressure exceeds the strength of the forces that hold atomic nuclei apart.
When this happens the core of the star implodes at a very high velocity, freefalling in on itself. Temperatures rise rapidly and a flood of high energy photons tear iron nuclei apart absorbing energy. Protons and electrons crush together into neutrons releasing a burst of neutrinos. Even at these incredible densities matter is transparent to these neutrinos and they exit the core carrying a significant amount of energy with them. The first indication of the supernova 1987a in the Large Magellanic Cloud was a burst of neutrinos that was detected in three separate observatories (a total of 25 neutrinos were counted) several hours before it was visible by any other means. (9)
If the progenitor star was less massive the collapse would stop at the stage where there is a solid core of neutrons. The outer shell of the star would hit this solid sphere of neutrons and rebound, tearing what remained of the star apart. What would remain is what we call a neutron star, an incredibly dense object just a few kilometers in diameter and having several solar masses. When born these objects spin at an incredible rate and have a temperature of billions of degrees. There has been some recent work that indicates that matter in these objects can form a superconducting super-fluid similar to the state that liquid helium is in at just a fraction above absolute zero.
In our massive star the in falling matter continues to pile up on the neutron core until the strong force between the individual quarks that the neutrons are composed of gives away. Now the collapse cannot be stopped and the core freefalls towards the center, possibly as a disk of super-fluid. The magnetic fields that originally were part of the star and the angular momentum are carried in with this collapsing matter and become incredibly compressed. These fields funnel matter and energy (there isn’t much difference between the two at this stage) out in narrow jets along the rotational axis. These jets, traveling at very near the speed of light, produce a flash of gamma rays that for a moment outshine the rest of the universe. We observe these gamma ray bursts on a daily basis from stars that died billions of years ago.
At the center of this object the density and temperature has reached the stage where our laws of physics break down. When the density reaches the point where there is a region of space where light cannot escape because the escape velocity of the gravitational field becomes equal to the speed of light, something incredible happens. Space curls in on itself, time stops, an event horizon forms, and a black hole is born.
At this stage our nascent black hole is not in its final form. But let’s pause here and take a look at what just happened. This point in space where our black hole just formed was in a very special state. Let’s consider the size. It had to start in a volume that is very small. If it is a point then it is dimensionless from our four dimensional perspective. One of our dimensions is time, and from our perspective that stopped at the newly formed event horizon. If the volume of this object is zero and it has any mass at all then its density is infinite. This is what we call a singularity. At its instant of creation it also formed an event horizon, this membrane in space that holds all of its remaining physical attributes as seen from the perspective of our universe, so it is not what physicists call a naked singularity. It also sheds other properties other than the basic spin, electrical charge, and the mass of the original contribution of matter as weighed in our universe. The intense magnetic field is shed, possibly contributing to the gamma ray burst. Our universe is protected from anything that happens within the singularity by the event horizon.
Now let’s look at the view from inside the event horizon. The density and temperature are infinite. Density is the product of mass and volume (or space) so both of those are infinite as well. Space is still curled up tightly on itself. This newly created mass (or energy, they’re equivalent) cannot have any effect on our universe on the other side of the event horizon. We have the beginning of a new universe. Let’s step over to the other side of the event horizon into our supernova.
The event horizon of our newly formed black hole doesn’t remain at a pinpoint. It has just formed in the center of an incredibly dense soup of photons and energetic particles. It expands outward from the initial poit sweeping up a volume of space in our universe and adding to the measurable property of mass. What remains of the star is either blasted away by the powerful jets or forms an accretion disk that spirals into the event horizon.
This brief period of expansion inflates the singularity at a speed that could compare to the inflationary phase that was supposed to have happened just after the big bang. There are so many similarities between these two events that I propose that they are one and the same.
If it is true that our universe is simply the inside of a black hole in some parent universe then can properties of that black hole be measured from the inside? Hawking radiation will eventually cause an isolated black hole to evaporate. Would that mean the end of the universe inside of it? Would the inhabitants of that universe see some sort of effect, perhaps a mysterious speeding up of the expansion rate as implied by dark energy? Much of what surrounds us in our universe is unexplained. We know that dark matter and dark energy exist but we don’t know what it is. Is it a projection of the surrounding event horizon or the space outside of it on our local view?