Starship Asterisk*

G'day from the land of ozzz

Maybe reading about Jets and there formation may explain whats in black holes.

At the end of the day, nobody really knows because we have not seen a black hole or even an event horizon.
But the folowing links for those interested in reading up, is quite fascinating.


Relativistic poynting jets
http://arxiv.org/find/all/1/all:+AND.../0/1/0/all/0/1


Accretion flow transonic
http://arxiv.org/find/all/1/all:+AND.../0/1/0/all/0/1

Than again what do you think degenerate matter is?

http://arxiv.org/abs/0811.2034
Transonic properties of the accretion disk around compact objects

Authors: Banibrata Mukhopadhyay
(Submitted on 13 Nov 2008)

Abstract: An accretion flow is necessarily transonic around a black hole. However, around a neutron star it may or may not be transonic, depending on the inner disk boundary conditions influenced by the neutron star. I will discuss various transonic behavior of the disk fluid in general relativistic (or pseudo general relativistic) framework. I will address that there are four types of sonic/critical point possible to form in an accretion disk. It will be shown that how the fluid properties including location of sonic points vary with angular momentum of the compact object which controls the overall disk dynamics and outflows

.


and

http://arxiv.org/abs/0812.3401
The X-ray Jets of Active Galaxies

Authors: D.M. Worrall (University of Bristol)
(Submitted on 17 Dec 2008)

Abstract: Jet physics is again flourishing as a result of Chandra's ability to resolve high-energy emission from the radio-emitting structures of active galaxies and separate it from the X-ray-emitting thermal environments of the jets. These enhanced capabilities have coincided with an increasing interest in the link between the growth of super-massive black holes and galaxies, and an appreciation of the likely importance of jets in feedback processes. I review the progress that has been made using Chandra and XMM-Newton observations of jets and the medium in which they propagate, addressing several important questions, including: Are the radio structures in a state of minimum energy? Do powerful large-scale jets have fast spinal speeds? What keeps jets collimated? Where and how does particle acceleration occur? What is jet plasma made of? What does X-ray emission tell us about the dynamics and energetics of radio plasma/gas interactions? Is a jet's fate determined by the central engine?

and

http://arxiv.org/abs/0810.0923
Dynamics of black holes

Authors: Sean A. Hayward
(Submitted on 6 Oct 2008)

Abstract: This is a review of current theory of black-hole dynamics, concentrating on the framework in terms of trapping horizons. Summaries are given of the history, the classical theory of black holes, the defining ideas of dynamical black holes, the basic laws, conservation laws for energy and angular momentum, other physical quantities and the limit of local equilibrium. Some new material concerns how processes such as black-hole evaporation and coalescence might be described by a single trapping horizon which manifests temporally as separate horizons.

This process of forming jets will be the most important process to understand.

It will explain the phase changes in star formation and the various forms of galaxy evolution

harry wrote:G'day from the land of ozzz

Maybe reading about Jets and there formation may explain whats in black holes.

Wonderfully edifying to me, Harry, that we think alike about many things.

Do Naked Singularities Break the Rules of Physics?
Scientific American - January, 2009

• Conventional wisdom has it that a large star eventually collapses to a black hole, but some theoretical models suggest it might instead become a so-called naked singularity. Sorting out what happens is one of the most important unresolved problems in astrophysics.
  
  The discovery of naked singularities would transform the search for a unified theory of physics, not least by providing direct observational tests of such a theory.

bystander wrote:Do Naked Singularities Break the Rules of Physics?
Scientific American - January, 2009

• Conventional wisdom has it that a large star eventually collapses to a black hole, but some theoretical models suggest it might instead become a so-called naked singularity. Sorting out what happens is one of the most important unresolved problems in astrophysics.
  
  The discovery of naked singularities would transform the search for a unified theory of physics, not least by providing direct observational tests of such a theory.

One theory is that the event horizon evaporates, leaving the naked singularity. These have been proposed as being Dark Matter.

G'day from the land of ozzzz

Its great to talk about black holes and singulaities.

What does actually occur when you apply physics to quantum.?

Can quantume mechanics explain the extreme gravity and behavior of the so called black hole.

http://arxiv.org/abs/0810.0079
Return of the quantum cosmic censor

Authors: Shahar Hod
(Submitted on 1 Oct 2008)

Abstract: The influential theorems of Hawking and Penrose demonstrate that spacetime singularities are ubiquitous features of general relativity, Einstein's theory of gravity. The utility of classical general relativity in describing gravitational phenomena is maintained by the cosmic censorship principle. This conjecture, whose validity is still one of the most important open questions in general relativity, asserts that the undesirable spacetime singularities are always hidden inside of black holes. In this Letter we reanalyze extreme situations which have been considered as counterexamples to the cosmic censorship hypothesis. In particular, we consider the absorption of fermion particles by a spinning black hole. Ignoring quantum effects may lead one to conclude that an incident fermion wave may over spin the black hole, thereby exposing its inner singularity to distant observers. However, we show that when quantum effects are properly taken into account, the integrity of the black-hole event horizon is irrefutable. This observation suggests that the cosmic censorship principle is intrinsically a quantum phenomena.

A little off topic perhaps, but the 777 is here ..
Discuss Anything Astronomy Related
the Asterisk Café
Moderators: makc, Nereid, bystander
Subforums: Wide Angle Sky Monitoring, Former Night Sky Live forum posts 777 Topics 9403 Posts Last post by aristarchusinexile
on Thu Jan 29, 2009 5:25 pm

Hello bystander,

bystander wrote:Do Naked Singularities Break the Rules of Physics?
Scientific American - January, 2009

• Conventional wisdom has it that a large star eventually collapses to a black hole, but some theoretical models suggest it might instead become a so-called naked singularity. Sorting out what happens is one of the most important unresolved problems in astrophysics.
  
  The discovery of naked singularities would transform the search for a unified theory of physics, not least by providing direct observational tests of such a theory.

Where in the quoted text does the article actually answer it's own question?

astrolabe wrote:Where in the quoted text does the article actually answer it's own question?

I don't think it does. The way I read it is theoretically, naked singularities should exist, but no one has observed one. It is believed that GR breaks down at a singularity, but the event horizon of BHs masks this break down. If a singularity could be observed, it would provide a laboratory for quantum gravity and other esoteric quantum theories. I think the question they are really asking is if naked singularites can exist, then where are they?

Hello bystander,

A good honest post, thank you. I think sensationalistic titles on articles do serve to pique interest but are, as I have found on numerous occasions, sometimes wanting in accurate portrayal of their content. A bit of a let down in some instances when the expectation of new knowledge is not forthcoming.

G'day from the land of ozzzzz

This link maybe of interest

http://arxiv.org/abs/0806.0845
Black hole mimickers: regular versus singular behavior

Authors: José P. S. Lemos, Oleg B. Zaslavskii
(Submitted on 4 Jun 2008 (v1), last revised 14 Aug 2008 (this version, v2))

Abstract: Black hole mimickers are possible alternatives to black holes, they would look observationally almost like black holes but would have no horizon. The properties in the near-horizon region where gravity is strong can be quite different for both type of objects, but at infinity it could be difficult to discern black holes from their mimickers. To disentangle this possible confusion, we examine the near-horizon properties, and their connection with far away properties, of some candidates to black mimickers. We study spherically symmetric uncharged or charged but non-extremal objects, as well as spherically symmetric charged extremal objects. Within the uncharged or charged but non-extremal black hole mimickers, we study non-extremal $\epsilon$-wormholes on the threshold of the formation of an event horizon, of which a subclass are called black foils, and gravastars. Within the charged extremal black hole mimickers we study extremal $\epsilon$-wormholes on the threshold of the formation of an event horizon, quasi-black holes, and wormholes on the basis of quasi-black holes from Bonnor stars. We elucidate, whether or not the objects belonging to these two classes remain regular in the near-horizon limit. The requirement of full regularity, i.e., finite curvature and absence of naked behavior, up to an arbitrary neighborhood of the gravitational radius of the object enables one to rule out potential mimickers in most of the cases. A list ranking the best mimickers up to the worse is given. Since, in observational astrophysics it is difficult to find extremal configurations (the best mimickers in the ranking), whereas non-extremal configurations are really bad mimickers, the task of distinguishing black holes from their mimickers seems to be less difficult than one could think of.

No one has seen a naked singularity or a black hole or an event horizon. The question is. Do black holes exist and if they do what is their make up?

another interesting paper

http://arxiv.org/abs/0805.3926
Quantum singularities in the BTZ spacetime

Authors: João Paulo M. Pitelli, Patricio S. Letelier
(Submitted on 26 May 2008)

Abstract: The spinless Ba\~nados-Teiltelboim-Zanelli (BTZ) spacetime is considered in the quantum theory context. Specially, we study the case of negative mass parameter using quantum test particles obeying the Klein-Gordon and Dirac equations. We study if this classical singular spacetime, with a naked singularity at the origin, remains singular when tested with quantum particles. The need of additional information near the origin is confirmed for massive scalar particles and all the possible boundary conditions necessary to turn the spatial portion of the wave operator self-adjoint are found. When tested by massless scalar particles or fermions, the singularity is ``healed'' and no extra boundary condition are needed. Near infinity, no boundary conditions are necessary.

G'day from the land of ozzzzzz

This link is quite relevant to black holes( Stellar and main) and compact matter such as Neutron stars.

The question of dark matter and dark energy will always be an issue until they have evidence.

http://arxiv.org/abs/0804.1588
Dark Fluid: Towards a unification of empirical theories of galaxy rotation, Inflation and Dark Energy

Authors: HongSheng Zhao (SUPA, St Andrews) Baojiu Li (DAMTP, Cambridge)
(Submitted on 10 Apr 2008)

Abstract: Empirical theories of Dark Matter like MOND gravity and of Dark Energy like f(R) gravity were motivated by astronomical data. But could these theories be branches rooted from a more general hence natural framework? Here we propose the natural Lagrangian of such a framework based on simple dimensional analysis and co-variant symmetry requirements, and explore various outcomes in a top-down fashion. Our framework preserves the co-variant formulation of GR, but allows the expanding physical metric be bent by a single new species of Dark Fluid flowing in space-time. Its non-uniform stress tensor and current vector are simply functions of a vector field of variable norm, resembling the 4-vector electromagnetic potential description for the photon fluid, but is dark (e.g., by very early decoupling from the baryon-radiation fluid). The Dark Fluid framework naturally branches into a continuous spectrum of theories with Dark Energy and Dark Matter effects, including the $f(R)$ gravity, TeVeS-like theories, Einstein-Aether and $\nu\Lambda$ theories as limiting cases. When the vector field degenerates into a pure Higgs-like scalar field, we obtain the physics for inflaton and quintessence. In this broad setting we emphasize the non-constant dynamical field behind the cosmological constant effect, and highlight plausible corrections beyond the classical MOND predictions. Choices of parameters can be made to pass BBN, PPN, and causality constraints. The Dark Fluid is inspired to unify/simplify the astronomically successful ingredients of previous constructions: the desired effects of inflaton plus quintessence plus Cold DM particle fields or MOND-like scalar field(s) are shown largely achievable by one vector field only.

Binary Black Hole System Identified
Science Centric - 2009 March 4

• Astronomers from the National Optical Astronomy Observatory in Tucson have found what looks like two massive black holes orbiting each other in the centre of one galaxy.

G'day Bystander

You will also find a swan of large so called black holes in many galaxies including our own at the centre of the galaxy.

harry wrote:G'day Bystander

You will also find a swan of large so called black holes in many galaxies including our own at the centre of the galaxy.

Swans at the centre of our galaxy? Nice!

G'day from the land of ozzzzzz

oops Swarm not swan,,,,,,,,,,,,,,,

http://antwrp.gsfc.nasa.gov/apod/ap060729.html
The Swarm

What do you call a group of black holes ... a flock, a brace, a swarm? Monitoring a region around the center of our Galaxy, astronomers have indeed found evidence for a surprisingly large number of variable x-ray sources - likely black holes or neutron stars in binary star systems - swarming around the Milky Way's own central supermassive black hole. Chandra Observatory combined x-ray image data from their monitoring program is shown above, with four variable sources circled and labeled A-D. While four sources may not make a swarm, these all lie within only three light-years of the central supermassive black hole known as Sgr A* (the bright source just above C). Their detection implies that a much larger concentration of black hole systems is present. Repeated gravitational interactions with other stars are thought to cause the black hole systems to spiral inward toward the Galactic Center region.

harry wrote:G'day from the land of ozzzzzz

oops Swarm not swan,,,,,,,,,,,,,,,

'Swans' was nice, Harry. Maybe we can't see them because they're Black Swans?

G'day rom the land of ozzzzzzz

Aris the so called black holes in the true definition do not exist. The compact object that has extreme density greater than 10^18 Kg/m3 creates vector fields that prevents EMR from escaping, but it aslo creates jet streams that are able to eject matter at about 90 Deg to the vectore field. Main stream thinking states that this is not correct and that a black hole prevent nothing from escaping, but lately Steven Hawking has changed his thinking.

The objects are so small and too far away that it makes it quite difficult to see. So we treat it as a black box and whatch how the surrounding objects move and so on.

harry wrote:G'day rom the land of ozzzzzzz

Aris the so called black holes in the true definition do not exist. The compact object that has extreme density greater than 10^18 Kg/m3 creates vector fields that prevents EMR from escaping, but it aslo creates jet streams that are able to eject matter at about 90 Deg to the vectore field. Main stream thinking states that this is not correct and that a black hole prevent nothing from escaping, but lately Steven Hawking has changed his thinking.

The objects are so small and too far away that it makes it quite difficult to see. So we treat it as a black box and whatch how the surrounding objects move and so on.

Also according to MOG black holes do not exist. I find it easy to accept your explanation.

harry wrote:Main stream thinking states that this is not correct and that a black hole prevent nothing from escaping, but lately Steven Hawking has changed his thinking.

Hawking radiation has nothing to do with polar jets.

by harry:
"But it aslo creates jet streams that are able to eject matter at about 90 Deg to the vectore field.
Main stream thinking states that this is not correct and that a black hole prevent nothing from escaping, but lately Steven Hawking has changed his thinking."

Hawking radiation: http://en.wikipedia.org/wiki/Hawking_radiation

"As an example, a black hole of one solar mass has a temperature of only 60 nanokelvin; in fact, such a black hole would absorb far more cosmic microwave background radiation than it emits. A black hole of 4.5 × 1022 kg (about the mass of the Moon) would be in equilibrium at 2.7 kelvin, absorbing as much radiation as it emits. Yet smaller primordial black holes would emit more than they absorb, and thereby lose mass."

So a black hole having the mass of the moon wouls receive as much energy as it emits and that just from the cosmic microwave background radiation (If a sun is close by then that moon mass black hole will receive more energy then it give away). It show that black hole with the mass of the earth or bigger (Million sun mass to more...) do not create a jet streams that are able to eject matter at about 90 Deg to the vectore field. Just a sun mass black hole emit energy at 60 nanokelvin. Gee that's cold and weak.

G'day from the land of ozz

Doum your right, the release of any matter against the vector field would be close to Zero and so would indicate close to 2.7K to the observer.

The issue is this and has not been proven by any at the present moment.

The jets that are created by many objects from Stars to Neutron stars to exotic stars such as black holes have various types of jets some created on the surface, within the solar envelope and some main jets in conjunction with the core and the surrounding infalling matter. The magnetic fields thatare created Pinch and create these jets. The stability of the jet particularly the main jet in dependent on the inner core. Mega jets are shown to have a stability of several million light years. If the jets were created only by the disc of infalling matter than there would be minmimal stability. There is alot of unknown factors and for some to say left or right is expressing an opinion. So! I think its up in the air for now.

Papers on this work goes back to 90's.

http://adsabs.harvard.edu/abs/1998ApJ...500..591T
Dark Matter Concentration in the Galactic Center
(c) 1998: The American Astronomical Society


Abstract

It is shown that the matter concentration observed through stellar motion at the Galactic center is consistent with a supermassive object of 2.5 x 10^6 solar masses composed of self-gravitating, degenerate, heavy neutrinos. This result is opposed to the alternative black hole interpretation. According to the observational data, the lower bounds on possible neutrino masses are m nu >= 12.0 keV/c2 for g = 2 or m nu >= 14.3 keV/c2 for g = 1, where g is the spin degeneracy factor. The advantage of this scenario is that it could naturally explain the low X-ray and gamma-ray activity of Sgr A*, i.e., the so-called blackness problem of the Galactic center.

I will come back to this, just got a call to go and pickup the kids.

G'day from the land of ozzzzzz

Magnetic pinches experiments maybe the key to many issues in jet formation and supernova events.

Neutron generation from Z-pinches
May-07
http://adsabs.harvard.edu/abs/2007PlPhR..33..356V

Quote:
Recent advances in both experimental and theoretical studies on neutron generation in various Z-pinch facilities are reviewed. The main methods for enhancing neutron emission from the Z-pinch plasma are described, and the problems of igniting a thermonuclear burn wave in this plasma are discussed.

Neutron production and implosion characteristics of a deuterium gas-puff Z pinch
Feb-07
http://adsabs.harvard.edu/abs/2007PhPl...14b2706C


Quote:
Experiments on the Z accelerator with deuterium gas puff implosions have produced up to 3.9×1013 (+/-20%) neutrons at 2.34 MeV (+/-0.10 MeV). Experimentally, the mechanism for generating these neutrons has not been definitively identified through isotropy measurements, but activation diagnostics suggest multiple mechanisms may be responsible. One-, two-, and three-dimensional magnetohydrodynamic (MHD) calculations have indicated that thermonuclear outputs from Z could be expected to be in the (0.3-1.0)×1014 range. X-ray diagnostics of plasma conditions, fielded to look at dopant materials in the deuterium, have shown that the stagnated deuterium plasma achieved electron temperatures of 2.2 keV and ion densities of 2×1020 cm-3, in agreement with the MHD calculations.

and

Z-pinch plasma neutron sources
Feb-07
http://adsabs.harvard.edu/abs/2007PhPl...14b2701V


Quote:
A deuterium gas-puff load imploded by a multi-MA current driver from a large initial diameter could be a powerful source of fusion neutrons, a plasma neutron source (PNS). Unlike the beam-target neutrons produced in Z-pinch plasmas in the 1950s and deuterium-fiber experiments in the 1980s, the neutrons generated in deuterium gas-puffs with current levels achieved in recent experiments on the Z facility at Sandia National Laboratories could contain a substantial fraction of thermonuclear origin. For recent deuterium gas-puff shots on Z, our analytic estimates and one- and two-dimensional simulations predict thermal neutron yields ~3×1013, in fair agreement with the yields recently measured on Z [C. A. Coverdale et al., Phys. Plasmas (to be published)]. It is demonstrated that the hypothesis of a beam-target origin of the observed fusion neutrons implies a very high Z-pinch-driver-to-fast-ions energy transfer efficiency, 5 to 10%, which would make a multi-MA deuterium Z-pinch the most efficient light-ion accelerator. No matter what mechanism is eventually determined to be responsible for generating fusion neutrons in deuterium gas-puff shots on Z, the deuterium neutron yield is shown to scale as Yn~Im4, where Im is the peak current of the pinch. Theoretical estimates and numerical modeling of deuterium gas-puff implosions demonstrate that the yields of thermonuclear fusion neutrons that can be produced on ZR and the next-generation machines are sufficiently high to make PNS the most powerful, cost- and energy-efficient laboratory sources of 2.5-14 MeV fusion neutrons, just like plasma radiation sources are the most powerful sources of soft and keV x rays. In particular, the predicted deuterium-tritium thermal neutron-producing capability of PNS driven by the next-generation ZR and ZX accelerators is ~5×1016 and ~1018, respectively.


and this one

Structure of the dense cores and ablation plasmas in the initiation phase of tungsten wire-array Z pinches
Jan-07
http://adsabs.harvard.edu/abs/2007PhPl...14a2704D

Quote:
The early stages of tungsten (W) wire-array Z-pinch implosions have been studied using two-frame point projection x-ray backlighting on the 1 MA COBRA pulsed power generator [J. D. Douglass, J. B. Greenly, D. A. Hammer, and B. R. Kusse, in Proceedings of the 15th IEEE International Pulsed Power Conference, Monterey, 2005 (to be published)]. X-pinch backlighter images with subnanosecond time resolution and 4-10 μm spatial resolution have been obtained of individual W exploding wires in 8-wire arrays that show evolution of wire-core and coronal plasma structures. The timing of the X-pinch x-ray bursts relative to the Z-pinch initiation time was adjusted over a 50 ns time interval by varying the X-pinch mass per unit length. Wire-cores seen in two images separated in view by 120° show that the expansion is remarkably azimuthally symmetric. A strong correlation is observed between the structure on the dense exploding wire-cores and the structure of the >=1018/cm3 ablation plasma being drawn from radial prominences. Plasma ablation velocity was estimated to have a lower bound of 24 km/s. The wire-core expansion rate was found to be approximately constant with time over the interval 50-100 ns after the start of the current pulse. Finally, micron-scale axial gaps, seen as early as 70 ns into the current pulse and persisting from that time, were observed along the wire-core.

I will post the astrophysics related links later.

During a supernova there has to be some mechanism to change to create Neutron at such a fast rate to form a Neutron star in some cases or a compact composite star of some form.

The process once understood could explain the origin and evolution of many universe bodies.

HEAPOW: Onto and Out (2009 March 30)

Chandra: DG Tau: Energetic Jets from a Budding Solar System


X-ray: NASA/CXC/ETH Zuerich/M.Guedel et al.; Illustration: NASA/CXC/M.Weiss

G'day bystander

re link

http://heasarc.gsfc.nasa.gov/docs/objec ... andra.html

Onto and Out
Young stars sure do some strange things. The image above left is a Chandra X-ray image of the very young star DG Tau. DG Tau is a star with a mass of about half that of the Sun, and is only about 300,000 years old (only 0.006% the age of the Sun). By studying such young stars, astronomers begin to understand how stars and planets form. We know that stars are built by accreting material from the interstellar clouds in which they form. The accretion process is a precarious balancing act between gravitational and centrifugal forces; the result is the formation of an accretion disk near the equator of the star. This accretion process can be, and often is, accompanied by the ejection of material normal to the disk, in a high-powered jet. The Chandra image on the left shows X-ray emission from the double-sided jet from DG Tau. The jet in DG Tau extends to about 10 times the size of our solar system, and the Chandra data show that the bottom jet is probably pointing towards us, while the top jet is pointing away from us. X-rays from the young star itself can be seen between the two jets. The image on the right is an artist conception of the DG Tau system showing the accretion disk plus high-energy jets with a clarity of which scientists can only dream. What was our Sun doing at a similar age? And did such X-rays affect the formation of our planetary system?
Published: March 30, 2009

Lately I think I have become a critic.

I tend not to think of a star being so old or ageing it. But! date it in relation to the phase that its undergoing.
As to the formation of stars there are varies means and the slowest is probably via infalling matter over time. The quickest is probably the seeding via matter ejected by jets.
There are many other means and I remain open to those.

The size of the jets indicates a compact object much much heavier than our sun. So being younger than our sun is questionable.

harry wrote:G'day bystander

re link

http://heasarc.gsfc.nasa.gov/docs/objec ... andra.html

Onto and Out
Young stars sure do some strange things. The image above left is a Chandra X-ray image of the very young star DG Tau. DG Tau is a star with a mass of about half that of the Sun, and is only about 300,000 years old (only 0.006% the age of the Sun). By studying such young stars, astronomers begin to understand how stars and planets form. We know that stars are built by accreting material from the interstellar clouds in which they form. The accretion process is a precarious balancing act between gravitational and centrifugal forces; the result is the formation of an accretion disk near the equator of the star. This accretion process can be, and often is, accompanied by the ejection of material normal to the disk, in a high-powered jet. The Chandra image on the left shows X-ray emission from the double-sided jet from DG Tau. The jet in DG Tau extends to about 10 times the size of our solar system, and the Chandra data show that the bottom jet is probably pointing towards us, while the top jet is pointing away from us. X-rays from the young star itself can be seen between the two jets. The image on the right is an artist conception of the DG Tau system showing the accretion disk plus high-energy jets with a clarity of which scientists can only dream. What was our Sun doing at a similar age? And did such X-rays affect the formation of our planetary system?
Published: March 30, 2009

Lately I think I have become a critic.

I tend not to think of a star being so old or ageing it. But! date it in relation to the phase that its undergoing.
As to the formation of stars there are varies means and the slowest is probably via infalling matter over time. The quickest is probably the seeding via matter ejected by jets.
There are many other means and I remain open to those.

The size of the jets indicates a compact object much much heavier than our sun. So being younger than our sun is questionable.

Personally, I think guessing the age of stars will be about as difficult as proving Big Bang.