XT805: What's inside Real Black Holes
"XT805: What's inside Real Black Holes" is an extract from an article about how the components of the Universe are recycled. Individual galaxies, stars, and planets each go through their individual cycles of birth, development, and death. The result is that the Greater Universe, infinite in time and space, keeps the same very-large-scale structure even as its components are recycled.
An important feature of this recycling is the action of Black Holes, including those at the centres of galaxies (AGNs). These are responsible for the greater part of energy/mass transformation, as well as some mass/energy conversion. For more background and explanation, refer to the full article, UG101: Recycling the Universe -- Neutron Stars, Black Holes, and the Science of Stuff.
Black Holes
If the theory behind neutron stars and pulsars is still far from settled, current understanding of Black Holes is just in its infancy. To try and make some sense of the confusion, we need to distinguish between Concept Black Holes (CBHs) and Real Black Holes (RBHs).
Concept Black Holes are the result of formulating assumptions and hypotheses, and applying mathematical tools to the mix. There is nothing wrong with this, it's a standard scientific approach. Its dangers lie in accepting the mathematical models or outcomes from the analyses as entities in their own right, and losing sight of the underlying assumptions.
We'll later look at an instance of this weakness, where a basic element in the CBH structure will be shown to have no relevance to RBHs, the real black holes existing in the Universe. Let's first look at what CBHs represent -- what is widely disseminated about black holes.
What is a Black Hole?
Asking this question of Google throws up a dictionary definition. "Noun (astronomy): a region of space having a gravitational field so intense that no matter or radiation can escape". Wikipedia [47] says more or less the same thing, and gives a lot more detail.
"A black hole is a region of spacetime exhibiting such strong gravitational effects that nothing -- not even particles and electromagnetic radiation such as light -- can escape from inside it. The theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole.
The boundary of the region from which no escape is possible is called the event horizon. Although the event horizon has an enormous effect on the fate and circumstances of an object crossing it, no locally detectable features appear to be observed. In many ways a black hole acts like an ideal black body, as it reflects no light.
Objects whose gravitational fields are too strong for light to escape were first considered in the 18th century by John Michell and Pierre-Simon Laplace. The first modern solution of general relativity that would characterize a black hole was found by Karl Schwarzschild in 1916.
Black holes of stellar mass are expected to form when very massive stars collapse at the end of their life cycle. After a black hole has formed, it can continue to grow by absorbing mass from its surroundings. By absorbing other stars and merging with other black holes, supermassive black holes of millions of solar masses may form. There is general consensus that supermassive black holes exist in the centers of most galaxies.
Despite its invisible interior, the presence of a black hole can be inferred through its interaction with other matter and with electromagnetic radiation such as visible light.
If there are other stars orbiting a black hole, their orbits can be used to determine the black hole's mass and location. In this way, astronomers have established that the radio source known as Sagittarius A*, at the core of our own Milky Way galaxy, contains a supermassive black hole of about 4.3 million solar masses."
So there we have it. Nothing can escape from a CBH, and general relativity proves it. Moreover, John Michell suggested it back in the 1700s. Michell, a don at Cambridge and born in Isaac Newton's last years, described as "a little short man, of black complexion, and fat", deserves much wider recognition. Here is a bit about him, from Wikipedia [48].
"John Michell (1724-1793) was an English clergyman and natural philosopher who provided pioneering insights in a wide range of scientific fields, including astronomy, geology, optics, and gravitation. Considered "one of the greatest unsung scientists of all time", he was the first person known to propose the existence of black holes in publication, the first to suggest that earthquakes travel in waves, the first to explain how to manufacture artificial magnets, and the first to apply statistics to the study of the cosmos, recognizing that double stars were a product of mutual gravitation.
He also invented an apparatus to measure the mass of the Earth. He has been called both the father of seismology and the father of magnetometry. According to one source, "a few specifics of Michell's work really do sound like they are ripped from the pages of a twentieth century astronomy textbook."
Figure UG101-F19. John Michell. From [49].
The American Physical Society has described Michell as being "so far ahead of his scientific contemporaries that his ideas languished in obscurity, until they were re-invented more than a century later." The APS states that while "he was one of the most brilliant and original scientists of his time, Michell remains virtually unknown today, in part because he did little to develop and promote his own path-breaking ideas."
Maybe he would have fared better if he'd had the Internet available!
The Schwartzschild Radius
At the heart of the CBH story is the mathematical formula for the "event horizon", the outer surface bounding a black hole. The calculation asserts that, if all the mass of an object is within a certain radius of its centre, the object is a black hole, and matter within it would have to move at greater than light speed to escape.
Here is a formal definition from [50]. The Schwarzschild radius is the radius of the event horizon surrounding a non-rotating black hole. Any object with a physical radius smaller than its Schwarzschild radius will be a black hole. This quantity was first derived by Karl Schwarzschild in 1916.
The inference from this, as nothing can exceed the speed of light, is that no radiation or matter can escape from a Black Hole. But wait. This relates to a CBH, a Concept Black Hole. When we pass on to a RBH, a Real Black Hole such as commonly exists in the real Universe, the position is quite different.
Galaxies spewing out matter and radiation
In the real Universe, black holes are quite commonly seen to be spewing out huge quantities of matter and radiation, pushing them out long distances into space. These emissions are known as astrophysical jets.
Figure UG101-F20. Inner Structure of an Active Galaxy. From [51].
Figure F20 is a diagram of the jets issuing from the supermassive black hole at the centre of a galaxy (also called an AGN, Active Galactic Nucleus). It is taken from Wikipedia [51], as are the following extracts.
"An astrophysical jet (hereafter 'jet') is a phenomenon often seen in astronomy, where streams of matter are emitted along the axis of rotation of a compact object. While it is still the subject of ongoing research to understand how jets are formed and powered, the two most often proposed origins are dynamic interactions within the accretion disk, or a process associated with the compact central object (such as a black hole or neutron star).
When matter is emitted at speeds approaching the speed of light, these jets are called relativistic jets, because the effects of special relativity become important. The largest jets are those from black holes in active galaxies such as quasars and radio galaxies.
Relativistic jets. The environment around the AGN where the relativistic plasma is collimated into jets which escape along the pole of the supermassive black hole.
Relativistic jets are very powerful jets of plasma with speeds close to the speed of light that are emitted by the central black holes of some active galaxies (notably radio galaxies and quasars), stellar black holes, and neutron stars.
Their lengths can reach several thousand or even hundreds of thousands of light years. If the jet speed is close to the speed of light, the effects of the Special Theory of Relativity are significant. The mechanics behind both the creation of the jets and the composition of the jets are still a matter of much debate in the scientific community".
So, as long as you are talking about RBHs rather than CBHs, it is routine that these will have matter and energy escaping from them. How is this fact reconciled with the CBH assertion that nothing can escape from a black hole?
The thing is this. Look again at the Schwartzchild calculation. The mathematics involved may be fine, but what about the underlying factors?
What Schwarzschild actually tries to define is the radius of the event horizon surrounding a non-rotating black hole. Note the factor "non-rotating". All RBHs actually rotate, extremely rapidly. Schwarzchild has no relevance to Real Black Holes.
Jets from Neutron Stars
As we have seen, black holes may result from the Explosion events of massive stars, a few multiples of the mass of the Sun. There will be large numbers of these within a galaxy, such as our Milky Way.
There are also supermassive black holes at the centres of galaxies. Most accounts will cautiously say that "it is accepted that most galaxies will have a supermassive black hole at their centre". We will see later that all galaxies must have such a supermassive black hole, as it is the black hole which controls the formation of the galaxy, rather than it being a chance component.
There will therefore only be one supermassive black hole or AGN in each galaxy. In our Milky Way galaxy, the AGN has 4.6 million times the mass of our Sun. In 2012, an AGN in a small galaxy about 250 million light-years from Earth, with 17 billion times the mass of the Sun, was announced as the largest found to date [52].
Jets may also be observed from neutron stars, an example being the pulsar IGR J11014-6103, which produces the largest jet observed in the Milky Way Galaxy. This jet is observed in x-rays and has no detected radio signature.
Figure UG101-F21. The pulsar IGR J11014-6103 with supernova remnant origin, nebula and jet. From [51].
IGR J11014-6103 has an estimated jet velocity of 0.8c (80% of the speed of light). This star was presumed to be rapidly spinning but later measurements indicate the spin rate is only 15.9 Hz. In the image the jet, aligned with the pulsar rotation axis, is perpendicular to the pulsar's trajectory and extends out over 37 light years (about 10 times the distance from our sun to the nearest visible star).
It should be remembered that photographs of jets like this only show the secondary effects of the jets striking material they encounter in space. The full force of a jet is only encountered on Earth when we happen to be directly on the axis of the black hole or neutron star. Our own galaxy is undoubtedly emitting jets along its axis, but we can only see its secondary effects as the jets are at right angles to the galactic disc.
Figure UG101-F22. Galaxies viewed at different angles. From [53].
In earlier days, when astronomers were investigating and classifying galaxies, various types were assigned names such as Radio Galaxies, Seyfert Galaxies, Quasars, and Blazars. Later it was realised that all these types were the same, just viewed from different angles. Only the Blazars were being viewed "head-on", directly along the axis of the galaxy.
It should be pointed out that the jets from these objects contain both Stuff1 (radiation) and Stuff2 (matter) components. The radiation (light) from distant objects, including galaxies, is very little affected by gravity and comes through to us in close to its original form, although red-shifted. This is even after travelling for as much as 13 billion years.
On the other hand, the matter in jets (mostly protons and electrons) is all charged particles. These are affected by the various magnetic fields they pass through, altering their trajectories. They will therefore lose most of the sharp collimation of the radiation component -- unlike light, the direction from which they are detected cannot be traced back to their source.
The post-explosion behaviour of stars
Looking back again to Figure F15, this showed various outcomes of the evolution of stars. Lighter stars ended up as White Dwarfs. Medium-size stars resulted in Neutron Stars. And the massive stars finished up as Black Holes.
From what we've seen above, it is apparent that these ostensibly different end results are really just the same, just different points along a common range. After explosion, all stars end up as rapidly spinning objects, emitting radiation and/or matter along their axes.
Black Holes and Stuff4
Here we refer to the substance within Black Holes (RBHs, mind) as Stuff4. Its nature has till now hardly been speculated upon. Stuff3 has been identified as Compacted Neutrons, as found in neutron stars.
Stuff4 is of a different order of density from Stuff3. A feel for the picture can be gained by considering how big the Earth would be, if made from the different stuffs.
The diameter of our Earth, mostly Stuff2, ordinary matter, is about 12,700 kilometres. If the Earth was made entirely from Stuff3, compressed neutrons, its diameter would be about 330 metres. And if it was made of Stuff4, black-hole substance, its diameter would be about 3 centimetres.
Assuming that Stuff3 is close to the maximum degree that matter can be compressed, what can Stuff4 be made of? So far, no-one seems to have been willing to answer this, so I'll put forward a tentative suggestion for discussion.
One of the essential points about Stuff3 and Stuff4 is that it is rotating, extremely rapidly. The energy in this rotation is extremely high. Just as mass has its energy equivalent, as in the Einstein equation E=mc2, so energy has a mass equivalent, using the same relationship. The suggestion is, that in Stuff4 most of its density is a reflection of its rotational energy content.
Summing Up
This article gives a very different picture of the Universe compared to the norm. Instead of a Universe born maybe 13.7 billion years ago, and on its slow way towards death, we have an ever-changing Universe in which matter and energy are continually recycled.
Like the chicken and the egg, the new picture has no beginning point. But individual galaxies do have individual histories. In general terms, stars and their solar systems are assembled from interstellar matter, mostly hydrogen gas, and become sucked up into new galaxies.
These galaxies, each with an accreting black hole at its centre, gather up stars at their outer rim. This rim is continually growing outwards as more stars are captured, in a vortex effect. The same effect gradually moves stars in towards the galaxy's centre.
During the course of this journey, most conventional stars will lose a big proportion of their mass in a giant explosion, which leaves behind white dwarfs, neutron stars, and black holes. These relict structures will continue to move towards their galactic centre, until they are swallowed by the supermassive black hole lying there.
Meanwhile, this AGN will be repatriating much of its material back to the Universe at large, through giant galactic jets proceeding out from its spin axis. And so, this material kicks on and may go to form new stars.
* * * * * * * * * * * * * * * * * * * * * * * *
Extract from UG101: Recycling the Universe -- Neutron Stars, Black Holes, and the Science of Stuff.
References and Links
[47] Black hole. https://en.wikipedia.org/wiki/Black_hole .
[48] John Michell. https://en.wikipedia.org/wiki/John_Michell .
[49] John Michell. http://pics-about-space.com/john-michell-black-hole?p=3#img11494485399856746759 .
[50] Schwarzschild Radius. astronomy.swin.edu.au/cosmos/S/Schwarzschild+Radius .
[51] Astrophysical jet. https://en.wikipedia.org/wiki/Astrophysical_jet .
[52] Monster Black Hole Is Biggest Ever Found. http://www.space.com/18668-biggest-black-hole-discovery.html .
[53] Slide 43 -- The Eye of the Beholder. http://slideplayer.com/slide/1416294/ .
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