Starship Asterisk*

http://www.universetoday.com/86490/astronomy-without-a-telescope-oh-my-god-particles/#more-86490 wrote: Astronomy Without A Telescope – Oh-My-God Particles
by Steve Nerlich on June 12, 2011

Left image: The energy spectrum of cosmic rays approaching Earth. Cosmic rays with low energies come in large numbers from solar flares (yellow range). Less common, but higher energy cosmic rays originating from elsewhere in the galaxy are in the blue range. The least common but most energetic extragalactic cosmic rays are in the purple range. Right image: The output of the active galactic nucleus of Centaurus A dominates the sky in radio light - this is its apparent size relative to the full Moon.[b][color=#FF00FF] It is likely that nearly all extragalactic cosmic rays that reach Earth originate from Centaurus A.[/color][/b]

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<<Cosmic rays are really sub-atomic particles, being mainly protons (hydrogen nuclei) and occasionally helium or heavier atomic nuclei and very occasionally electrons. Cosmic ray particles are very energetic as a result of them having a substantial velocity and hence a substantial momentum.

The Oh-My-God particle detected over Utah in 1991 was probably a proton traveling at 0.999 (and add another 20 x 9s after that) of the speed of light and it allegedly carried the same kinetic energy as a baseball traveling at 90 kilometers an hour.

Its kinetic energy was estimated at 3 x 10²⁰ electron volts (eV) and it would have had the collision energy of 7.5 x 10¹⁴ eV when it hit an atmospheric particle – since it can’t give up all its kinetic energy in the collision. Fast moving debris carries some of it away and there’s some heat loss too. In any case, this is still about 50 times the collision energy we expect the Large Hadron Collider (LHC) will be able to generate at full power. So, this gives you a sound basis to scoff at doomsayers who are still convinced that the LHC will destroy the Earth.

Now, most cosmic ray particles are low energy, up to 1010 eV – and arise locally from solar flares. Another more energetic class, up to 1015 eV, are thought originate from elsewhere in the galaxy. It’s difficult to determine their exact source as the magnetic fields of the galaxy and the solar system alter their trajectories so that they end up having a uniform distribution in the sky – as though they come from everywhere.

But in reality, these galactic cosmic rays probably come from supernovae – quite possibly in a delayed release process as particles bounce back and forth in the persisting magnetic field of a supernova remnant, before being catapulted out into the wider galaxy.

And then there are extragalactic cosmic rays, which are of the Oh-My-God variety, with energy levels exceeding 10¹⁵ eV, even rarely exceeding 10²⁰ eV – which are more formally titled ultra-high-energy cosmic rays. These particles travel very close to the speed of light and must have had a heck of kick to attain such speeds.

However, a perhaps over-exaggerated aura of mystery has traditionally surrounded the origin of extragalactic cosmic rays – as exemplified in the Oh-My-God title.

In reality, there are limits to just how far away an ultra-high-energy particle can originate from – since, if they don’t collide with anything else, they will eventually come up against the Greisen–Zatsepin–Kuzmin (GZK) limit. This represents the likelihood of a fast moving particle eventually colliding with a cosmic microwave background photon, losing momentum energy and velocity in the process. It works out that extragalactic cosmic rays retaining energies of over 10¹⁹ eV cannot have originated from a source further than 163 million light years from Earth – a distance known as the GZK horizon.

Recent observations by the Pierre Auger Observatory have found a strong correlation between extragalactic cosmic rays patterns and the distribution of nearby galaxies with active galactic nuclei. Biermann and Souza have now come up with an evidence-based model for the origin of galactic and extragalactic cosmic rays – which has a number of testable predictions.

They propose that extragalactic cosmic rays are spun up in supermassive black hole accretion disks, which are the basis of active galactic nuclei. Furthermore, they estimate that nearly all extragalactic cosmic rays that reach Earth come from Centaurus A. So, no huge mystery – indeed a rich area for further research. Particles from an active supermassive black hole accretion disk in another galaxy are being delivered to our doorstep.

• arXiv.org > astro-ph > arXiv:1106.0625 > 03 Jun 2011

rfvyhnal@cox.net wrote:
How is it determined that the jets from this galaxy are emanating from the black hole, as opposed to being pulled into the black hole?

http://en.wikipedia.org/wiki/Penrose_process wrote:

[b][i][color=#0000FF]A rotating black hole can produce large amounts of energy at the expense of its rotational energy through the Penrose process in the black hole's ergosphere, an area just outside its event horizon.[/color][/i][/b]

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<<The Penrose process (also called Penrose mechanism) is a process theorised by Roger Penrose wherein energy can be extracted from a rotating black hole. That extraction is made possible because the rotational energy of the black hole is located, not inside the event horizon of the black hole, but on the outside of it in a region of the Kerr spacetime called the ergosphere, a region in which a particle is necessarily propelled in locomotive concurrence with the rotating spacetime. All objects in the ergosphere become dragged by a rotating spacetime. In the process, a lump of matter enters into the ergosphere of the black hole, and once it enters the ergosphere, it is split into two. The momentum of the two pieces of matter can be arranged so that one piece escapes to infinity, whilst the other falls past the outer event horizon into the hole. The escaping piece of matter can possibly have greater mass-energy than the original infalling piece of matter, whereas the infalling piece has negative mass-energy. In summary, the process results in a decrease in the angular momentum of the black hole, and that reduction corresponds to a transference of energy whereby the momentum lost is converted to energy extracted.

The process obeys the laws of black hole mechanics. A consequence of these laws is that if the process is performed repeatedly, the black hole can eventually lose all of its angular momentum, becoming non-rotating, i.e. a Schwarzschild black hole.

The outer surface of the ergosphere is described as the ergosurface and it is the surface at which light-rays that are counter-rotating (with respect to the black hole rotation) remain at a fixed angular coordinate, according to an external observer. Since massive particles necessarily travel slower than the speed of light, massive particles must rotate with respect to a stationary observer "at infinity". A way to picture this is by turning a fork on a flat linen sheet; as the fork rotates, the linen becomes twirled with it, i.e. the innermost rotation propagates outwards resulting in the distortion of a wider area. The inner boundary of the ergosphere is the event horizon, that event horizon being the spatial perimeter beyond which light cannot escape.

Inside this ergosphere, the time and one of the angular coordinates swap meaning (time becomes angle and angle becomes time) because timelike coordinates have only a single direction (and remember the particle is necessarily rotating with the black hole in a single direction only). Because of this weird and unusual coordinate swap, the energy of the particle can assume both positive and negative values as measured by an observer at infinity.

If particle A enters the ergosphere of a Kerr black hole, then splits into particles B and C, then the consequence (given the assumptions that conservation of energy still holds and one of the particles is allowed to have negative energy) will be that particle B can exit the ergosphere with more energy than particle A while particle C goes into the black hole, i.e. E(A)=E(B)+E(C) and say E(C)<0, then E(B)>E(A). In this way, rotational energy is extracted from the black hole, resulting in the black hole being spun down to a lower rotational speed. The maximum amount of energy is extracted if the split occurs just outside the event horizon and if particle C is counter-rotating to the greatest extent possible. In the opposite process, a black hole can be spun up (its rotational speed increased) by sending in particles that do not split up, but instead give their entire angular momentum to the black hole.>>

RADDAD wrote:I found the term "light" quite off-putting since nothing in the image was visible light. Electromagnetic radiation I believe is the best term. It is not the light spectrum, but the electromagnetic spectrum. If you were writing this for fourth graders "light" would be fine. I have never heard "light" being anything but a subset of the electromagnetic spectrum.

It may not be "technically wrong" but I think this is one time when you could say "Oops, we dumbed it down too much." Call it what it is commonly referred to in most scientific circles - electromagnetic radiation. After all, this is Astronomy POD, not Astrology Pics.

rfvyhnal@cox.net wrote:How is it determined that the jets from this galaxy are emanating from the black hole, as opposed to being pulled into the black hole?

rfvyhnal@cox.net wrote:How is it determined that the jets from this galaxy are emanating from the black hole, as opposed to being pulled into the black hole?

Ann wrote:Bob Berman was making the point that when astronomers say that they aren't sure, they mean that they haven't a clue. (That's what he meant when he said we should grab a dictionary.) So it seems to me that Bob Berman is saying that astronomers don't have a clue as to why the jet of M87 behaves the way it does. Do you agree with him, Chris?

Chris Peterson wrote:

biddie67 wrote:It doesn't seem unreasonable that black holes could have several different behavior characteristics and, depending upon sizes, strength or what else, could have critical internal pressure points where they have to start ejecting energies of different kinds.

Actually, within the context of modern physics, that is unreasonable. In fact, black holes are amongst the best understood, simplest of objects- similar in many respects to a fundamental particle.

The behavior of Cen A seems to be at some very extreme limit. Could a black hole implode or explode?

No- there is nothing to suggest that is possible. In a very general sense, jets like this are understood as an interaction between a black hole and surrounding media. While there are lots of missing details, I don't think you'll find many physicists who doubt that this is fundamentally what is going on. No new black hole physics is required.

A couple hundred light-years from its origin at the center of M87, the jet has a brilliant swirling knot named HST-1.Its brightness changes unpredictably. But why? And what exactly causes those jets? A leading astronomer said, "We're not yet sure." Grab the dictionary.

drollere wrote:minor but important point of language: "light" is radiation that can stimulate the human eye to produce a visual sensation. there is no such thing as "xray light" or "microwave light", because these are invisible -- unless one wants to admit "heat light" and "radio light" into the popular science lexicon of photon avatars ... and then we're forced to use the redundant "light light" or "visible light" for the original concept.

it's great that APOD wants to keep science lite, but there's nothing arcane or unintelligible about "xray radiation" or "microwave energy".

biddie67 wrote:It doesn't seem unreasonable that black holes could have several different behavior characteristics and, depending upon sizes, strength or what else, could have critical internal pressure points where they have to start ejecting energies of different kinds.

The behavior of Cen A seems to be at some very extreme limit. Could a black hole implode or explode?