Disqus - Friends of laurele

Re: Trying out Disqus for Comments

DrFlimmer — Wed, 11 May 2011 14:16:51 -0000

Just tryin' it out myself....

P.S.: Is there a possibility to sort the comments with "oldest first" as the standard choice? I don't want to do it manually all the time....

Re: Energizing the Filaments of NGC 1275

DrFlimmer — Wed, 11 May 2011 14:37:43 -0000

A magnetic field may be produced by some current, but after that it can live on its own! And, as a matter of fact, Maxwell's equations say nothing about "where something came from". All they say is: Magnetic fields and electric fields obey these laws. Nothing more and nothing less.
What does it mean?
Well: Assume a constant magnetic field (B=const.). This, in fact, obeys

curl B = 0 ; div B = 0

So, everything is fine. A constant magnetic field obeys Maxwell's laws and needs NOTHING to exist. Not a displacement current, not moving particles, nothing.
So, please: That we observe magnetic fields does not necessarily imply that there is always an underlying current somewhere. This might have been true for the "first magnetic field there is", but as soon as it was there, no more currents are needed, necessarily. The magnetic fields could act on their own, and they still obey Maxwell's laws.

Re: Energizing the Filaments of NGC 1275

DrFlimmer — Wed, 11 May 2011 14:41:24 -0000

Not to complain too much, just as a small side note:
Since matter in space is typically fairly thin, it takes quite a while for atoms to recombine. The plasma will therefore have a lot of time before it really ceases to exist. Next point is, the thin matter distribution also implies that you do not need many photons to get some reionisation.
But you are right, of course, you always need an energy source, even if it's a weak one.

Re: Energizing the Filaments of NGC 1275

DrFlimmer — Wed, 11 May 2011 16:13:05 -0000

I totally agree with you!

Re: Energizing the Filaments of NGC 1275

DrFlimmer — Wed, 11 May 2011 16:26:32 -0000

No.
However, I also have no knowledge of any paper discussing this particular problem. This does not mean that they aren't there, I just don't know them.
On the other hand, a German astrophysicist (who also made a TV show to popularize difficult physical topics -- and he did very well!), Harald Lesch (professor at the LMU Munich) described it somehow like: differential rotation in a plasma (which is like a current in this case) caused the first magnetic field in the cosmos.
All that was needed were these seed fields. After that the magnetic fields could reestablish themselves, so to speak.

But that was not the point, I intended to make above. The major point is: The magnetic field does not care where electric currents are, once it is there. That's why we can have "magnetic clouds" leaving the sun and crashing into earth's atmosphere. That also means, although you observe a magnetic field, you cannot make any statements about an underlying current: where it is, how strong it is, and if it is there at all!

Screaming out loud: "Magnetic field, therefore current!" is not necessarily correct. That was and is my point.

Maybe I find the time, to make a calculation: Is there a solution to the equation div B = curl B, apart from the trivial one B = const.?

Re: Energizing the Filaments of NGC 1275

DrFlimmer — Thu, 12 May 2011 17:56:48 -0000

You may want to read my response to IanTresman a bit further down.

In short: a magnetic field does not imply a current. This is just not true. And even if it were, even the best measurements of the structure of the magnetic field would make it really hard to get any information of the current.

Btw: The approximation of ideal MHD is extremely valid in most astrophysical cases. Some special (and mostly violent) cases need more details and, especially, resistivity (magnetic reconnection). But they tend to be on very small scales compared to the rest.

And one clarification: An electric current is the RELATIVE movement of opposite electric charges. A proton and an electron with the same velocity is not a current.

Re: Energizing the Filaments of NGC 1275

DrFlimmer — Fri, 13 May 2011 05:17:09 -0000

No. They just show that you can have fairly strong magnetic fields without a current.
That this is not directly relevant to plasmas is something else. It just aims to show "Magnetic field = Electric current" is not necessarily correct.

Re: GALEX Confirms Nature of Dark Energy

DrFlimmer — Fri, 20 May 2011 07:50:26 -0000

This was discovered back in around 1998 by Hubble was it not?

:D You mixed up two things here (at least in my interpretation, as I realise, now). Edwin Hubble found in 1928 (+/- a few years) that galaxies were mostly receding from us, that is to say that the universe expands. In 1998 two different groups found simultaneously that the universe's expansion accelerates. (This might have involved the Hubble Space Telescope, which would make your statement correct, again. ;) )

Re: Best-Ever Radio Image of Black Hole Jets

DrFlimmer — Fri, 20 May 2011 17:40:28 -0000

I was about to give a thought on that anyway, since the article makes the usual "error" again of calling it a "paradox" (which it isn't), but I can also answer your question directly:

1) Whatever crosses the event horizon of a black hole can never come back out. It's ultimately doomed.
2) However, material that has not yet crossed that horizon (sometimes referred to as the surface of the black hole, although this is a bit misleading -- there is no membrane or something, it's just some point in space(time) where the escape velocity exceeds the speed of light) can escape again, and so can magnetic fields.

And here comes the story:
Material cannot fall as easy into a black hole as one might think. It accumulates in a flat disc around the black hole called the accretion disk. Due to friction this disk gets very hot (it shines brightly in X-rays!) and the material becomes a plasma which makes it interact with magnetic fields. Due to the rotation of the disk (which is also the reason why the material does not fall so easy into the black hole in the first place) the magnetic fields also need to rotate with the disk and become wound up around the poles of the black holes, forming two narrow channels.
And this is the important clue: The channels are formed (from the) outside of the black hole. Matter in them comes mostly directly out of the accretion disk. Nothing comes out of the black hole! It's all matter from close by.
As a matter of fact: I've just drawn the basic picture. The details are highly complicated and not yet fully understood. It's a very active field of research!

I hope this helped a bit....

Re: Best-Ever Radio Image of Black Hole Jets

DrFlimmer — Sat, 21 May 2011 18:49:41 -0000

So a galaxy is a black hole's accretion disc?

No. The accretion disk of a SMBH at the center of a galaxy is probably a few light-hours in diameter. A galaxy is typically a few tens of thousands of light-years wide.

I think a distinction is needed between a galaxy level SMBH and ye old regular stellar black holes and stars with jets; like Herbig-Haro objects.[...] however they are very different environments.

They are not very different. There is a central object, an accretion disk and a jet. It doesn't really matter what the central object is since the jet is mostly anchored in the disk and not the central object (maybe there is some entanglement with the magnetic field of the star, but it should be of lesser importance).
Indeed, details are not clear, but the overall picture makes a lot of sense, already.

What we do observe is that jets happen in pulses in both systems, [...] Alternatively this variability is a fluctuation of the dynamo itself.

The variability of the jet can come from both causes. Intense variability comes most likely from the disk itself. When a large clump of matter is accreted at one moment, there must also be an equal great loss of angular momentum, which is transferred into the jet. On the other hand, jet material can also interact with material passing too close to (or even right through) the jet. Both phenomena are plausible and surely happening, are not strange at all.

What is missing in our observational arsenal is a means of seeing gravity and magnetism without the aid of a medium that follows magnetic field lines.

In a classical "pre-Einsteinian" way to look at it, both gravity and magnetic fields are just forces, which are invisible and are only observable through there action on material. There is no other way to measure them as by their action on things.#

I can only imagine the structures that might occupy the blank spots in the image of HH-30.

This is completely unrelated, btw. The "blank spots" are the outer edges of the accretion disk (edge-on), or material that is left over at the outskirts of the gas cloud from which the star formed. This material is cool and therefore dark in optical wavelength. It also contains dust which is a very good absorber for optical light. I'm quite sure that this feature is much brighter in (far) infrared. The blueish hour-glass shaped object is also part of this gas and dust that is left over from the formation. However, this reflects the star's light. That's also why it appears blue (at least it does for me), since blue light is scattered more easily than redder wavelength (the reason for the blue sky on earth...).

Not to complain, but your last (longer) paragraph sounds a lot like some EU stuff (correct me, if I'm wrong!!). The first magnetic fields were most likely created during the epoch of reionisation. Once these "seed fields" were available, they were indeed reprocessed and also amplified by stellar dynamos (that's also how a dynamo on a bike works). However, stars are not powered by them. There is not enough power and energy in them to do such a thing. Also, jets do not transport "highly charged clouds". They transport charged particles (yes), but the clouds contain equal amounts of charges and are overall neutral.

Re: Best-Ever Radio Image of Black Hole Jets

DrFlimmer — Sun, 22 May 2011 05:43:15 -0000

Just to Correct, No Electric Universes Affiliations whatsoever.

My apologies! It's just that we are kind of biased here and probably tend to see it even if it's not meant to be.

Concerning the magnetic fields, I'm not quite sure what you mean with "magnetic variability in the universe". We know of interstellar and even intergalactic magnetic fields but both are extremely weak. They are not capable of doing a lot apart from deflecting electrons from the cosmic radiation (that's why mostly protons and alpha particles arrive here (apart from very few heavier nuclei), they are too heavy for the magnetic field to be deflected or "captured").
So, for a magnetic field in the universe to become turbulent or amplified you need a power source somewhere (not a source of magnetic fields (there are none) but a source for the amplification). Stars or accretion disk (or the earth's fluid-like core) are sources for such amplifications. There you can have pretty strong magnetic fields on the order of even a few Gauss. A neutron star is able to produce magnetic fields with a strength of 10^10 Tesla, but this is not the norm ;) .
Jets are created by due to the rotation of the accretion disk. They "swirl" the magnetic fields creating these very narrow funnels along the pole axis (in both directions). So, the cause is some violence in the plasma and not due to the magnetic field itself.

Re: Testing the Spiral Density Wave Theory

DrFlimmer — Mon, 30 May 2011 08:16:08 -0000

Hm. One thing I wonder about:

If the spiral patterns are short-lived, shouldn't we see a somehow equal mix of flat galaxies that are either in "spiral"-mode or in "no-spiral"-mode?
But, AFAIK, we see mostly spirals (and ellipticals) and only a minor fraction are irregulars. However, if I'm wrong about this than this could hint towards "short-life" spiral structures.

Re: Dead Galaxy? Don’t Think So.

DrFlimmer — Tue, 31 May 2011 05:11:21 -0000

Minor correction: Ellipticals do not evolve into spirals. That's what Hubble thought, and why he arranged his "tuning fork" the way he did.
AFAIK, it's the general agreement these days that it's the other way around: flat spirals evolve (e.g. by mergers) into fat ellipticals (the whole universe is just too human... or is it the other way around? ;)).

Re: Voyager 1 Measures Magnetic Mayhem

DrFlimmer — Wed, 01 Jun 2011 15:55:22 -0000

At least one probe has flown around the solar poles: the European probe Ulysses which was launched on a space shuttle. This poor thing is already frozen to death, but it send quite unique data.

Re: Supernova Discovered in M51 The Whirlpool Galaxy

DrFlimmer — Sun, 05 Jun 2011 06:27:03 -0000

How did I miss this type of comment of yours :D

Re: Astronomy Without A Telescope – Enough With The Dark Already

DrFlimmer — Sun, 05 Jun 2011 17:31:21 -0000

Sure. Any sources?
And why do we place space-probes around Saturn? Why does your GPS work? Because General Relativity is right, and ether is wrong.

Re: Nearby Galaxy Has Two Monster Black Holes

DrFlimmer — Sat, 11 Jun 2011 17:52:41 -0000

What you see does not come OUT of the black hole (that is to say from below its event horizon), but from the very close vicinity around the black hole -- but, and this is important, from OUTSIDE the black hole.

Re: Carbon Monoxide Reveals Distant Milky Way Arm

DrFlimmer — Mon, 13 Jun 2011 17:23:51 -0000

Well, well. Normally such news occur around the AAS meetings, don't they? ;)

Every now and then the Milky Way changes its appearance (neither literally nor physically, of course); I wonder, if we ever get a clear picture. It's just so hard to deduce a form while being imprisoned on the inside....

Re: Coming Up… June 15th Total Lunar Eclipse LIVE

DrFlimmer — Mon, 13 Jun 2011 17:26:13 -0000

It will be 2213 in Germany. It will be still bright outside, but this should be visible.... as long as the weather cooperates!

Re: Coming Up… June 15th Total Lunar Eclipse LIVE

DrFlimmer — Tue, 14 Jun 2011 13:47:21 -0000

I second that!

Re: Regular Solar Cycle Could Be Going on Hiatus

DrFlimmer — Wed, 15 Jun 2011 04:15:22 -0000

All right. But just assume for a moment that it may be due to the increased number of CO2 molecules in the atmosphere....

Is it really worth the risk? Do we really need to depend on oil (which will sooner or later run out anyway?) Why not change the economy and the infrastructure now, before oil runs out? What's wrong with less CO2 and other poisonous gases?

And why do you need to disagree with 99% of experts? Do you always need a conspiracy?

Re: Regular Solar Cycle Could Be Going on Hiatus

DrFlimmer — Wed, 15 Jun 2011 04:19:23 -0000

A new ice age will bring as much suffering to the developing world as the upcoming heat waves. And why only the developing world? What about the "developed" world that still can't refuse to abuse the planet as if we had another one?

And where did you get your information from? Are you an expert in the field on which one could rely? Have you studied all the available information to come to such conclusions?

Do you really think 99% of all experts around the globe are just working for an agenda? Do you always need such conspiracies?

Re: Regular Solar Cycle Could Be Going on Hiatus

DrFlimmer — Wed, 15 Jun 2011 04:20:53 -0000

From my point of view, a Maunder minimum could give us some more time to prevent the worst things to happen. But for that we need to act NOW....

Re: Regular Solar Cycle Could Be Going on Hiatus

DrFlimmer — Wed, 15 Jun 2011 08:55:00 -0000

[...] and they're already failing to occur [...]

Ah, yes. Because the effects are even worse.

An expert, for me, is someone who has studied that field, who works in that field for some time and has knowledge about the specific issues of that field. I, for one, am an astrophysicist at the beginning of my second year of PhD. I will never claim to be an expert in a field related to global warming. That is why I trust those who work in that field. Because they know what the heck they talk about. What about your credentials? Have you done more active research than reading internet pages to come to the conclusion that all is wrong? Have you studied all the available evidence? I didn't, and so I rely on those who did, and they say it's happening.

If people like you manage to force very expensive changes onto the public and end up being wrong

1) Changes are not always bad. We will face changes in our economy, either due to global warming or because we run out of fossil fuels. That is unavoidable. This also means, the future will look different than the present. And those who begin to make the future today will have a head-start over those who still want to preserve "good ol' economy". I am also convinced that the declining availability of (e.g.) oil will cause more wars. Changing now means that such things could also be avoided. And btw: Burning fossil fuel is not just bad for the climate. It's bad for ourselves, since the resulting gases are highly toxic.

2) I would be glad, if I were wrong, and global warming would not happen. But I am very much afraid that I am at least not wrong....

(the historic track record of scientist is not very good)

What the hell does that mean? GPS works because of a very good prediction of scientists. We do not have fusion by now, because the severe problems were not obvious 50 years ago. And if we will ever be able to have it is also not guaranteed. The climate involves many different topics and a lot of statistics. That there is also potential for error is not that surprising. Still, the models get better and better, and the predictions turned out to less severe than the actual result.

Concerning "Climategate" and other stuff:
Bad Astronomy
See especially the "related posts" at the end of the text.
Phil Plait may not be an expert on global warming, but he is a scientist and knows the methods "those" were using, and therefore also trusts them -- just as I do.

Re: Where In The Universe Challenge #149

DrFlimmer — Wed, 15 Jun 2011 13:48:06 -0000

It almost seems like water between the "dunes". I throw in that this could be a picture of the tideland while the moon has its grasps on the seas.