Starship Asterisk*

by **apodman** » Fri Feb 15, 2008 11:55 pm

Okay, the Forum ain't sophisticated with text line wrap. So help it out by putting spaces between your words or by not using words or multiple run-together web addresses that are dozens or hundreds of characters long. Somebody has booby-trapped this entire thread by using long character strings, and instead of scrolling left and right and left and right to read every super-wide line I'll just find another thread to read.

by **starnut** » Fri Feb 15, 2008 2:24 am

triastro wrote:OK, fair enough, they only mention 'likely', but I'm getting weary of this 'instant' science where pictures are said to depict things that are only conjecture or at best unproven theory such as dark matter.

I'll retreat to the background on this. No further replies are necessary.

Don't retreat. Stay engaged and learn. While the existence of dark matter may be unproven, it is the best fit the astronomers can come up with to explain the behavior of the galaxies they observed and measured. If you can come up with a better explanation, with supporting evidences based on direct observations, data and calculations, please do let us know. In other words, do your homework first. Just remember that the astronomers have access to very expensive instruments, including gigabucks worth of space telescopes that you and I can never hope to have. If we poor under-privileged amateurs can't come up with alternative explanations, then we should accept what the professionals say, with of course a little bit of skepticism.

by **triastro** » Thu Feb 14, 2008 4:14 pm

OK, fair enough, they only mention 'likely', but I'm getting weary of this 'instant' science where pictures are said to depict things that are only conjecture or at best unproven theory such as dark matter.

I'll retreat to the background on this. No further replies are necessary.

by **jd-f** » Thu Feb 14, 2008 2:08 am

If you click on the link "dark matter" there's an explanation of this question. Also note that it says "likely" not "certainly"!

It's a fantastic picture - love those background galaxies!

by **triastro** » Wed Feb 13, 2008 9:57 pm

The caption for today's image of Elliptical Galaxy NGC 1132 raises a question. The caption states that the
X-ray image traces the location of the dark matter. How is this
done/known? Up to now, my understanding of dark matter is it is
theoretical and the only way that astronomers deduce it's presence is
through gravitational lensing. Now you are saying dark matter can be
seen directly in X-rays? What are the physics of this process?

If in fact, X-rays do not detect dark matter directly, I think you
should print a retraction or correction. We already have way too much
misinformation and speculation on the nature of dark matter.

Thanks for the response.

by **neufer** » Wed Feb 13, 2008 7:43 pm

Qev wrote:http://en.wikipedia.org/wiki/Intracluster_medium

And what about the Cooling Flow Problem?

<<As the ICM in the core of many galaxy clusters is dense, it emits a lot of X-ray radiation (the emission is proportional to the density-squared). In the absence of heating, the ICM should be cooling. As it cools, hotter gas will flow in to replace it. This is known as a cooling flow. The cooling flow problem is the lack of evidence of cooling of the ICM.>>

by **Qev** » Wed Feb 13, 2008 7:02 pm

http://en.wikipedia.org/wiki/Intracluster_medium

by **henk21cm** » Wed Feb 13, 2008 5:22 pm

Art,

Aren't you yourself arguing against black hole "dust panning" interstellar space due to a general lack of cool gas.

Thats right, i never forget that my concepts can be wrong, so approach it from the opposite direction: "suppose its true, then X and Y must be valid, but since we see the opposite of X and Y happen, the assumption is not true" (reductio ad absurbum type of proof)

An old galaxy should have lots of old stars in their last stages expanding into red giants whose shells can be sucked into neighboring neutron stars or black holes.

Yes, that is a valid argument. The argument leads to the result that X-ray emission and elliptical galaxies should be abundant. I did not know that. Google reports over 100k hits for "elliptical galaxies" and "X ray". I read only some (articles); they support your argument.

Thanks for clarifying this puzzle.

by **neufer** » Wed Feb 13, 2008 3:59 pm

henk21cm wrote:What puzzles me, why an old elliptical system is emitting so much X-ray radiation. In an elliptical system there is hardly any cold gas left for new stars to be formed (http://heritage.stsci.edu/2008/07/caption.html)
If there isn't much cold gas, then where does all the hot gas come from?

X-rays are associated with rather violent phenomena in the universe: accretion disks around pulsars, small parasitic stars which suck matter from larger stars, black holes "dust panning" interstellar space. Generally spoken, these kind of processes, in which cool gas spirals inbound towards a havy object. Due to concentration of flow, the gas is heated up to temperatures which allow for X-ray emission. Such processes usually do not last for long times (compared to the lifetime of a star).

The X-rays seem to come from the outer regions of the galaxy, where the concentration of gas is likely to be less than in the inner regions of the galaxy. Is the galaxy still dust panning?

Aren't you yourself arguing against black hole "dust panning" interstellar space due to a general lack of cool gas.

Why not the alternative you suggest: accretion disks around pulsars (or black holes) which suck matter from larger stars?

An old galaxy should have lots of old stars in their last stages expanding into red giants whose shells can be sucked into neighboring neutron stars or black holes.

by **orin stepanek** » Wed Feb 13, 2008 2:54 pm

Indigo_Sunrise wrote:Thank you, orin, for the tutorial on link-inserting! As you can tell, I had just copied/pasted the address from the webpage!

And as for looking at it under magnification, I only looked at the hi-res image by clicking on the image itself, but it's definitely worth further investigation - so I guess that means I'm off to follow more links!

The nice thing is that if you make a mistake; you can click the edit button and correct them. I try to preview and proof read before submitting; but once in a while, one still slips past me.

Orin

by **Indigo_Sunrise** » Wed Feb 13, 2008 2:38 pm

Thank you, orin, for the tutorial on link-inserting! As you can tell, I had just copied/pasted the address from the webpage!

And as for looking at it under magnification, I only looked at the hi-res image by clicking on the image itself, but it's definitely worth further investigation - so I guess that means I'm off to follow more links!

by **henk21cm** » Wed Feb 13, 2008 1:53 pm

What puzzles me, why an old elliptical system is emitting so much X-ray radiation. In an elliptical system there is hardly any cold gas left for new stars to be formed (http://heritage.stsci.edu/2008/07/caption.html)
/heritage.stsci.edu/2008/07/caption.html�http://heritage.stsci.edu/2008/07/capti ... ion.htmlIf there isn't much cold gas, then where does all the hot gas come from?

X-rays are associated with rather violent phenomena in the universe: accretion disks around pulsars, small parasitic stars which suck matter from larger stars, black holes "dust panning" interstellar space. Generally spoken, these kind of processes, in which cool gas spirals inbound towards a havy object. Due to concentration of flow, the gas is heated up to temperatures which allow for X-ray emission. Such processes usually do not last for long times (compared to the lifetime of a star).

The X-rays seem to come from the outer regions of the galaxy, where the concentration of gas is likely to be less than in the inner regions of the galaxy. Is the galaxy still dustpanning? If the system is the result of a merger between two or more galaxies in a (local) cluster, such a merger is not instantaneous. If several galaxies merge, they will not merge each of them at the same moment. The shape of the remaining galaxy is irregular, like in http://antwrp.gsfc.nasa.gov/apod/ap061105.html. After enough time the resulting system takes a more common shape. The fact that the system is regularly shaped, is an indication to me that the merger took place at least 100 million years ago. That is quite a long time for an X-ray afterglow.

Apart from the puzzling X-rays, the technique as in overlaying different parts of the EM spectrum and subsequent visualisation in pseudo colors, is amazing, not in the least for reasons of graceful pictures.

by **orin stepanek** » Wed Feb 13, 2008 1:50 pm

Indigo_Sunrise wrote:http://antwrp.gsfc.nasa.gov/apod/astropix.html

Now, reading the description, I am wondering what the "fascinating background galax[y]" is at about the nine o'clock position, on the far left....? What a beautiful galaxy! *Of course, the entire image is gorgeous, but that galaxy really leaps out at me!
Anyway, another great image - keep up the great work, PTB!

[P.S. I'm not too good with inserting links, so I hope that I did it right. Apologies in advance if not.]

If you go to the APOD archive and Click on Feb 13' you can cut the http and you will have the right link.
http://apod.nasa.gov/apod/ap080213.html
Good luck!

It is indeed a beautiful picture. All of the stars in this galaxy are difficult to make out. almost like grains of sand. The galaxy you mention looks like it has vast star forming regions. Have you looked at it under magnification?

Orin

by **Indigo_Sunrise** » Wed Feb 13, 2008 11:54 am

http://antwrp.gsfc.nasa.gov/apod/astropix.html

Now, reading the description, I am wondering what the "fascinating background galax[y]" is at about the nine o'clock position, on the far left....? What a beautiful galaxy! *Of course, the entire image is gorgeous, but that galaxy really leaps out at me!
Anyway, another great image - keep up the great work, PTB!

[P.S. I'm not too good with inserting links, so I hope that I did it right. Apologies in advance if not.]

Starship Asterisk*

Elliptical Galaxy NGC 1132 - caption? (13 Feb 2008)

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Elliptical Galaxy NGC 1132 Caption Question

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Why so much X-ray activity?

Re: Elliptical Galaxy NGC 1132

Elliptical Galaxy NGC 1132 - caption? (13 Feb 2008)