Starship Asterisk*

Chris Peterson wrote:Saying light is affected by gravity is really the wrong way of expressing things, since it leads to confusion. Under GR, it would be better to say that mass affects the curvature of space, producing the effect we call gravity. It is the curvature of space that affects the path of a photon, and that does not require that the photon have mass.

Strictly speaking, you can say that a photon in motion behaves as if it has a finite mass. That allows for a classical approximation of the behavior of light in a gravitational field. The rest mass of a photon is zero (even though a photon is never actually at rest); any particle with a rest mass of zero falls outside the definition of "matter".

Light sails depend on radiation pressure, which exists because photons have momentum. Conservation of momentum requires a transfer of momentum when light is absorbed or reflected. Massless particles do have momentum.

Isn't momentum defined to be the product of mass and velocity?

bystander wrote:Isn't momentum defined to be the product of mass and velocity?

Only in classical mechanics, which fails at the scale of single particles. Under QM, the momentum of a photon is defined as h/lambda, that is, Planck's constant divided by the wavelength. For any massless particle, this is the same as E/c, the energy carried by the particle divided by c. Massless particles, including photons, do have momentum.

G'day from the land of ozzzz

Galactic Black Hole Fires a Jet at a Nearby Neighbour
http://www.universetoday.com/2007/12/17 ... neighbour/


Using the logic of the BBT. Not that I agree with it.
Did the Black Holes form at the start 13.7 Gyrs.


These links are interesting reading.
Ultra High Energy Cosmic Rays from decays of Holeums in Galactic Halos
http://arxiv.org/abs/0806.0454

Holeum,enigmas of cosmology and gravitational waves
http://arxiv.org/abs/gr-qc/0309044

harry wrote:Galactic Black Hole Fires a Jet at a Nearby Neighbour
http://www.universetoday.com/2007/12/17 ... neighbour/

Using the logic of the BBT. Not that I agree with it.

It's a fascinating observation. But it has nothing at all to do with Big Bang cosmology. The same thing would be observed in a Steady State Universe, or any other cosmology that allows black holes to exist.

Did the Black Holes form at the start 13.7 Gyrs.

The black hole that is producing this jet almost certainly did not form at the beginning of the Universe, because the galaxy containing it did not.

Chris Peterson wrote:

bystander wrote:

Chris Peterson wrote:Light sails depend on radiation pressure, which exists because photons have momentum.
Conservation of momentum requires a transfer of momentum when light is absorbed or reflected.
Massless particles do have momentum.

Isn't momentum defined to be the product of mass and velocity?

Only in classical mechanics, which fails at the scale of single particles. Under QM, the momentum of a photon is defined as h/lambda, that is, Planck's constant divided by the wavelength. For any massless particle, this is the same as E/c, the energy carried by the particle divided by c. Massless particles, including photons, do have momentum.

Unfortunately for Light sails, the large E/c denominator means that
photons have a MINIMAL amount of momentumfor their energy .

Which is why it is generally preferable to just capture the photon ENERGY
with solar panels and use that ENERGY to drive a ion thruster:
....................................................
<<Dawn's ion thruster is powered by large solar panels.
The power ionizes the fuel (Xenon) and then accelerates it with an electric field between two grids.
Electrons are injected into the beam after acceleration to maintain a neutral plasma.>>
----------------------------------------------------------
If one is trying to push an asteroid,
the solar power energy can be even more effectively utilized by using
electromagnetic mass ejectors on heavy asteroid boulders of mass M
where the momentum impulse = sqrt(2ME)
http://www.androidworld.com/prod15.htm
--------------------------------------------------
Likewise: The Crookes radiometer uses photon ENERGY to drive air convection and
generate a low pressure on the cool white side of the paddle due to the Bernoulli principle
to drive the radiometer in reverse from photon momentum radiation pressure:
http://www.youtube.com/watch?v=cey-JBeHrww
....................................................


<<The Crookes radiometer, also known as the light mill, consists of an airtight glass bulb, containing a partial vacuum. Inside are a set of vanes which are mounted on a spindle. The vanes rotate when exposed to light, with faster rotation for more intense light, providing a quantitative measurement of electromagnetic radiation intensity.

It was invented in 1873 by the chemist Sir William Crookes as the by-product of some chemical research. In the course of very accurate quantitative chemical work, he was weighing samples in a partially evacuated chamber to reduce the effect of air currents, and noticed the weighings were disturbed when sunlight shone on the balance. Investigating this effect, he created the device named after him. It is still manufactured and sold as a novelty item.Crookes incorrectly suggested that the force was due to the pressure of light. This theory was originally supported by James Clerk Maxwell who had predicted this force. This explanation is still often seen in leaflets packaged with the device. The first experiment to disprove this theory was done by Arthur Schuster in 1876, who observed that there was a force on the glass bulb of the Crookes radiometer that was in the opposite direction to the rotation of the vanes. This showed that the force turning the vanes was generated inside the radiometer. If light pressure was the cause of the rotation, then the better the vacuum in the bulb, the less air resistance to movement, and the faster the vanes should spin. In 1901, with a better vacuum pump, Pyotr Lebedev showed that in fact, the radiometer only works when there is low pressure gas in the bulb, and the vanes stay motionless in a hard vacuum. Finally, if light pressure were the motive force, the radiometer would spin in the opposite direction as the photons on the shiny side being reflected would deposit more momentum than on the black side where the photons are absorbed. The actual pressure exerted by light is far too small to move these vanes but can be measured with devices such as the Nichols radiometer.>>
--------------------------------------------------

The advantage to solar sails is that they have no need to carry reaction fuel. That, and their relative simplicity.

G'day from the land of ozzzzz

Chris you have read my post again out of context. Do you really understand the workings of the parts of the universe?

Galactic Black Hole Fires a Jet at a Nearby Neighbour
http://www.universetoday.com/2007/12/17 ... neighbour/
Mate these galaxies are older than 13.7 Gyrs

Jets are the means and process by which matter escapes ultra compact bodies such as the so called black holes.
If the BBT is correct than this will be the means of BB Nucleosynthesis.
============================================================================
The following are related to the BBT


Using the logic of the BBT. Not that I agree with it.
Did the Black Holes form at the start 13.7 Gyrs.


These links are interesting reading.
Ultra High Energy Cosmic Rays from decays of Holeums in Galactic Halos
http://arxiv.org/abs/0806.0454

Holeum,enigmas of cosmology and gravitational waves
http://arxiv.org/abs/gr-qc/0309044

harry wrote:Jets are the means and process by which matter escapes ultra compact bodies such as the so called black holes.

Jets are the result of material being pulled out of a black hole's accretion disk and accelerated to relativistic velocities, probably by interaction with the black hole's spinning magnetic field. I wouldn't use the word "escape" because it suggests the jets are composed of material from inside the black hole's event horizon, which is impossible. Not all black holes produce jets.

If the BBT is correct than this will be the means of BB Nucleosynthesis.

I don't understand this assertion. In fact, I don't understand exactly what you're trying to say at all. What will be the means of nucleosynthesis? Something to do with black holes? That makes no sense.

Qev wrote:The advantage to solar sails is that they have no need to carry reaction fuel. That, and their relative simplicity.

Right..but one pays for that with a lack of both thrust
and control (with no "keel" one can't "tack into the wind")

The Dawn spacecraft thrust = 90milliNewtons

2 x Solar constant/c = 2 x 1366 W/m²/c = 9.2 microNewtons/m²

A reflective solar sail of ~10,000 square meters is need
for a 90milliNewton thrust (mostly away from the sun)
------------------------------------------
http://dawn.jpl.nasa.gov/mission/ion_prop.asp

<<The Dawn spacecraft uses ion propulsion to get the additional velocity needed to reach Vesta once it leaves the Delta rocket. It also uses ion propulsion to spiral to lower altitudes on Vesta, to leave Vesta and cruise to Ceres and to spiral to a low altitude orbit at Ceres.

Dawn's ion thruster is powered by large solar panels.
The power ionizes the fuel (Xenon) and then accelerates it with an electric field between two grids. Electrons are injected into the beam after acceleration to maintain a neutral plasma.

Ion propulsion makes efficient use of the onboard fuel by accelerating it to a velocity ten times that of chemical rockets. This efficiency is measured in terms of the specific impulse of the fuel (Isp).
Dawn's engines have a specific impulse of 3100 s and a thrust of 90mN.>>
------------------------------------------
http://en.wikipedia.org/wiki/Specific_impulse

<<Essentially, the higher the specific impulse, the less propellant is needed to gain a given amount of momentum. In this regard a propulsion method is more propellant-efficient if the specific impulse is higher. This should not be confused with energy-efficiency, which can even decrease as specific impulse increases, since many propulsion systems that give high specific impulse require high energy to do so (discussed later).

In addition it is important that thrust and specific impulse not be confused with one another. The specific impulse is a measure of the impulse per unit of propellant that is expended, while thrust is a measure of the momentary or peak force supplied by a particular engine. In many cases, propulsion systems with very high specific impulses (some ion thrusters reach 10,000 seconds) produce low thrusts.>>
------------------------------------------

G'day Chris

You said not all black holes produce jets.

Mate how do you know?

Most are so far away and covered by clouds that you could never see the mini jets. The only jets that you do see are those that leave their mark.

What type of Black holes? Stellar medium, huge, monster BHs

You said

Jets are the result of material being pulled out of a black hole's accretion disk and accelerated to relativistic velocities, probably by interaction with the black hole's spinning magnetic field. I wouldn't use the word "escape" because it suggests the jets are composed of material from inside the black hole's event horizon, which is impossible. Not all black holes produce jets

Who said its impossible?
Steven Hawkins would disagree with you although he explains only a part of radiation evaporation.

As to the formation of jets and the mechansim, you may need to research Plasma properties for the answer. A prime example is the formation of jets on the surface of the Sun. You can actually see the plasma magnetic fields connecting and forming jets and ejecting matter out.

There are various jets sizes and they are related to the location and compaction of matter.

harry wrote:You said not all black holes produce jets.

Mate how do you know?

Most are so far away and covered by clouds that you could never see the mini jets.

Mini jets? Covered by clouds? Sorry, I prefer to stick to what theory describes and observation demonstrates. We do see black holes with accretion disks and no jets. We have probably also observed stellar mass black holes with no accretion disks at all, and obviously, therefore, no jets.

Jets are the result of material being pulled out of a black hole's accretion disk and accelerated to relativistic velocities, probably by interaction with the black hole's spinning magnetic field. I wouldn't use the word "escape" because it suggests the jets are composed of material from inside the black hole's event horizon, which is impossible. Not all black holes produce jets

Who said its impossible?
Steven Hawkins would disagree with you although he explains only a part of radiation evaporation.

Hawking would certainly agree that jet formation has nothing to do with Hawking radiation. In any case, Hawking radiation does not necessarily mean anything is escaping from inside a black hole. That isn't the only mechanism by which a black hole could lose mass and eventually evaporate.

There are various jets sizes and they are related to the location and compaction of matter.

Jets have absolutely nothing to do with "compaction of matter". They are a simple consequence of material falling into a deep gravity well, in the presence of a rotating magnetic field.

G'day Chris

Mate, I'm not trying to be smart, but! your understanding of jet formation needs updating.

What is the mecahnism that produces the jet?

What are the results to the matter?

If you wish to think the way you do than thats fine. Is it more important for you to feel that you are right or to have a better understanding of whats out there.

The following link is but a drop in the ocean on jet formation.

http://adsabs.harvard.edu/abs/2008APS..APR8HE019S
Formation of Magnetically Driven Radiatively Cooled Plasma Jets in the Laboratory
Apr-08

Abstract:
Previous experiments have successfully showed the formation of magnetically driven radiatively cooled plasma jets which are relevant to the launching of astrophysical jets. The jets in these experiments are driven by the pressure of the toroidal magnetic field produced by the MAGPIE generator which leads to the formation of a ``magnetic tower'' structure. This scenario is characterized by the formation of a magnetic ``bubble'' surrounding a collimated plasma jet on axis. A modification of this experimental configuration, in which radial wire array is replaced by radial metallic foil, results in the formation of episodic magnetic tower outflows which emerge periodically on timescales of ˜30ns. The subsequent magnetic bubbles propagate with velocities reaching ˜300km/s and interacting with previous eruptions leading to the formation of shocks. This research was supported by the European Community's Marie Curie JETSET network (contract MRTN-CT-2004 005592) and the SSAA program of the NNSA (DOE Cooperative Agreement DE-FC03-02NA00057).

harry wrote:What is the mecahnism that produces the jet?

Well, that would be what I suggested earlier, which is also what your linked abstract suggests: matter from an accretion disk falls inward and is captured by a rotating magnetic field, which ejects it at high velocity.

Theory, observation, and experiment are all in close agreement. You can't do better than that.

G'day Chris

Knowing what happens is different than knowing how it does it.

While we speak, its funny that I'm reading

The SAO/NASA Astrophysics Data System
http://www.adsabs.harvard.edu/
Search for
Plasma Jets Astrophyiscal 2005 to 2008

and

arXiv
http://arxiv.org/find/all/1/OR+au:Herbi ... /0/all/0/1
Herbig-Haro jets

The more I read the more I find how little we know.

harry wrote:Knowing what happens is different than knowing how it does it.

Yes, those are different things. However, in the case of jets, we do have a good working idea of how things work. That's because there is solid theory (theory is always about the "how") which is supported by observational data, both in the lab and in space. BTW, in the case of the jets seen around H-H objects, you still have material from an accretion disk being focused by magnetic fields, but the energy source is an ordinary, low density, stellar mass body that hasn't reached hydrostatic equilibrium. Nothing exotic at all.

The more I read the more I find how little we know.

We know an awful lot, especially in terms of the broad picture. A review of the literature suggests how many details remain to be filled in. There isn't much, however, to suggest that some radical new mechanism for jet formation is going to displace the general concepts that have already been developed.

G'day Chris

I agree, But! for one thing.


What is the mechanism?
How do magnetic fields focus and create jets that are able to approach the speed of light?

G'day from the land of ozzzzzz

This interesting reading, I hope this is not a repeat.

http://arxiv.org/abs/0809.5171
Evidence for powerful AGN winds at high redshift: Dynamics of galactic outflows in radio galaxies during the "Quasar Era"

Authors: N.P.H. Nesvadba, M.D. Lehnert, C. De Breuck, A.M.Gilbert, W. van Breugel
(Submitted on 30 Sep 2008 (v1), last revised 13 Oct 2008 (this version, v2))

Abstract: AGN feedback now appears as an attractive mechanism to resolve some of the outstanding problems with the "standard" cosmological models, in particular those related to massive galaxies. To directly constrain how this may influence the formation of massive galaxies near the peak in the redshift distribution of powerful quasars, z~2, we present an analysis of the emission-line kinematics of 3 powerful radio galaxies at z~2-3 (HzRGs) based on rest-frame optical integral-field spectroscopy obtained with SINFONI on the VLT. HzRGs are among the most massive galaxies, so AGN feedback may have a particularly clear signature. We find evidence for bipolar outflows in all HzRGs, with kinetic energies that are equivalent to 0.2% of the rest-mass of the supermassive black hole. Velocity offsets in the outflows are ~800-1000 km s^-1 between the blueshifted and redshifted line emission, FWHMs ~1000 km s^-1 suggest strong turbulence. Ionized gas masses estimated from the Ha luminosity are of order 10^10 M_s, similar to the molecular gas content of HzRGs, underlining that these outflows may indicate a significant phase in the evolution of the host galaxy. The total energy release of ~10^60 erg during a dynamical time of ~10^7 yrs corresponds to about the binding energy of a massive galaxy. Geometry, timescales and energy injection rates of order 10% of the kinetic energy flux of the jet suggest that the outflows are most likely driven by the radio source. The global energy density release of ~10^57 erg s^-1 Mpc^-3 may also influence the subsequent evolution of the HzRG by enhancing the entropy and pressure in the surrounding halo and facilitating ram-pressure stripping of gas in satellite galaxies that may contribute to the subsequent mass assembly of the HzRG through low-dissipation "dry" mergers.

'Dark Matter' is theorized to be micro black holes with no event horizon. Did you know event horizons can evaporate? They can, according to some theorists. Did you know black holes themselves can evaporate? They can according to some theorists. Did you know the universe could have begun by a quantum fluctuation in nothing. Yes. We know nothing yet as to what we could know or should know if new ideas weren't generally totally rejected by the consensus. I have not been wasting my time .. I have been READING the latest stuff!

mopedtothemoon wrote:I have not been wasting my time .. I have been READING the latest stuff!

You sound suspiciously similar to a former member of this forum who spent a little too much time with indiscriminate reading and not enough time thinking about what he read.

mopedtothemoon wrote:I have not been wasting my time .. I have been READING the latest stuff!

Chris Peterson wrote:You sound suspiciously similar to a former member of this forum who spent a little too much time with indiscriminate reading and not enough time thinking about what he read.

Good observation, Chris. It is as you thought.

bystander wrote:

mopedtothemoon wrote:I have not been wasting my time .. I have been READING the latest stuff!

Chris Peterson wrote:You sound suspiciously similar to a former member of this forum who spent a little too much time with indiscriminate reading and not enough time thinking about what he read.

Good observation, Chris. It is as you thought.

"Off with his head! Off with his head! He's a lunatic! He has all the wrong ideas! He isn't in the consensus! He doesn't bow down and worship what we think we know! And he can read books! Oh my God .. he can READ BOOKS! He's just too dangerous to have around! Off with his head! Off with his head! Accuse him of attacking people on the forum. We don't need evidence because WE HAVE THE POWER BUTTON!!!! PUSH THAT POWER BUTTON! OFF WITH HIS HEAD!!! Indiscriminate reading indeed. Recognized PHDs .. many of them .. every time a new idea comes along it's OFF WITH HIS HEAD. Let's have some evidence of my attacking anyone on the forum, Nereid. It's show and tell time. Hypocriscy or truth.
Science of lies.

G'day from the land of ozzzzz

To understand so called black holes one needs to understand phase transitions.

I was going to pick one or two links.

Here is the general link on papers for 2008

http://arxiv.org/find/all/1/all:+AND+20 ... /0/all/0/1

harry wrote:Hello All

It was said that nothing can escape a black hole.

and yet we have this:
New Energy Source "Wrings" Power from Black Hole Spin
http://www.gsfc.nasa.gov/topstory/20011 ... khole.html

"Never before have we seen energy extracted from a black hole," said co-author Christopher Reynolds of the University of Maryland, College Park. "We always see energy going in, not out."

"The gravity in this region appears to be so intense that the very fabric of space twists around the black hole, dragging magnetic field lines along with it," said Wilms. "The magnetic fields tighten about the black hole, slowing its spin. This 'friction' heats the region to even higher temperatures."

That is one opinion, the other is the jet is created by the plasma properties within the so called black hole, creating a z-pinch, that creates and drives the jet,ejecting matter away from the compacted core.

I was sent by a friend a url from which I got this .. "One of the characteristics of a black hole is that there is an event horizon beyond which we can obtain no information - scales smaller than that are hidden from the outside world. For a given enclosed mass, this limit is on the order of...."

However, we can get information as to what Black Holes contain and what is happening in them from observing the jets which come from black holes .. and I do believe this is what is happening in the example, the outward spiraling jet bringing to my mind the other 'spirals' found often in the universe .. for instance .. the stretched spiral of the earth's orbit around the sun as the sun travels through space .. the spiral (or corkscrew) of light in circularly polarized light. Cruious, artistic stuff.

aristarchusinexile wrote:I was sent by a friend a url from which I got this .. "One of the characteristics of a black hole is that there is an event horizon beyond which we can obtain no information - scales smaller than that are hidden from the outside world. For a given enclosed mass, this limit is on the order of...."

However, we can get information as to what Black Holes contain and what is happening in them from observing the jets which come from black holes .. and I do believe this is what is happening in the example, the outward spiraling jet bringing to my mind the other 'spirals' found often in the universe .. for instance .. the stretched spiral of the earth's orbit around the sun as the sun travels through space .. the spiral (or corkscrew) of light in circularly polarized light. Cruious, artistic stuff.

The jets seen coming from some black holes probably aren't useful for telling us what is happening inside a black hole, or for elucidating any possible internal structure. That's because they don't appear to be dependent on anything more than a combination of spin, magnetic field, and gravity field. Those are all external properties of a black hole.

Jets are useful, however, because the provide insight into basic physics in extreme conditions- relativistic environments where spacetime is highly curved or distorted.

Orca wrote:Good find, Harry. As I read the article, I thought to myself, "...I thought the energetic EM radiation was created by the friction of gas particles by the gravity well of the black hole." But then:

The total energy output, or luminosity indicated by the spectrum, however, was too bright to be powered by gravity and the free fall of matter alone. Some additional power source must exist to boost the luminosity to the observed intensity.

Innnnteresting...

'Time' in some way, I suspect, is the power source. Perhaps the spirals seen commonly in our universe, the spirals in the jet, the long spiral of the earth around the path of the sun .. perhaps time spirals and can become, in a black hole, a compressed spring, like the main spring in a mechanical timepiece, but much tighter of course.