X-rays from center of galaxy

1. Aug 2, 2004

turin

How can we see the x-ray emission from the center of our galaxy? I thought that the intersteller dust extinguished practically all of the visible light from that direction, which is why we can't "see" the bulge. How then, can even shorter wavelength photons manage to get through? I thought that the shorter wavelengths would be blocked to an even higher degree.

2. Aug 3, 2004

mathman

This just isn't so. To cite a simple example, you can't see inside your body with visible light, but you can with x-rays. Interstellar dust blocks visible light, but not x-rays.

3. Aug 3, 2004

Moose352

Mathman, can you please explain. I thought that molecules scatter smaller light waves better. Hence why visible light much more than radio waves. Is this incorrect?

4. Aug 3, 2004

turin

interesting point, mathman. I will have to chew on that for a while. Is the issue that the x-rays are able to pass straight through the atoms statistically unaffected (that is, not counting the "every-once-in-a-while" that an x-ray actually hits an atomic nucleas)? I suppose, then, that gamma rays have an even higher penetrability?

I just thought of another example:
Large radio dishes collect radio waves, however, they can be made of a mesh that allows visible light to pass through them like chicken wire.

Last edited: Aug 3, 2004
5. Aug 3, 2004

selfAdjoint

Staff Emeritus
Here's another one that puzzled me as a child (I had been told about the electromagnetic waves inluding radio and light).

I sit by the window. I can see out, so light passes through it. The sun shining through it warms me, so infra-red passes throught it. Obviously radio waves, a fraction of a mile long pass through it as if it weren't there.

But I can't get a tan through the window. So evidently ultra-violet radiation does not pass through glass. Yet UV is shorter waved than light, and X-ray is still shorter waved than UV, but X-rays pass through the window and through me too!

6. Aug 3, 2004

marcus

I wouldnt be surprised if "shorter wavelengths are scattered more" by molecules in the earth's atmosphere had to do with resonance peaks in the UV---and applied only to visible and near visible, at least not to Xray

so as long as the light is visible, then the bluer it gets the closer to the UV resonant peak it get

but above the UV, with Xrays, I would not suppose that it works like that
so that gas molecules and dust should not scatter so much.

I suppose the location of resonance peaks of atoms and molecules depends some on their ionization energies which are in the UV

all this is a long way of saying I tend to agree with mathman but am not quite sure about the reason. hope for better advice

7. Aug 3, 2004

sol2

How we are Looking At the Universe

I thought I would add this too

http://www-glast.sonoma.edu/index.html [Broken]

What also might be nice is to see the electromagnetic spectrum for consideration, so that we can see what self adjoint and Marcus are talking about in regards to the long and the short

http://imagine.gsfc.nasa.gov/Images/introduction/em_same.gif

and wonders of wonder, what else moves through anything and makes it go up and down, from side to side and we call them transverse waves?

Last edited by a moderator: May 1, 2017
8. Aug 3, 2004

Nereid

Staff Emeritus
Absorption and scattering are the two main processes for 'blocking' EM in the ISM (below the microwave region). The gas component of the ISM will absorb (and re-emit, not always at the same wavelength) discrete frequencies (atomic transitions, molecular bands) and continua (e.g. above the ionisation threshhold); the dust component will scatter - think blue sky/red sunset. The ISM is all but opaque to UV short of the Lyman limit, because everywhere you look you find H atoms; at IR and longer wavelengths, only dust really matters, and the grain sizes are small, so the ISM becomes more transparent ... until the far IR, when the thermal emission of the dust becomes a nuisance (this is the component that's the most difficult to remove from the microwave signals, to recover the CMBR).

What can scatter X-rays?

How can X-rays be absorbed? Photo-electric effect, which becomes weaker as the photon energy rises.

Result? The universe is pretty transparent to high energy X-rays and gammas ... until pair-production (and later inverse Compton). You can 'see' distant quasars 'near' SagA*

Last edited: Aug 3, 2004
9. Aug 3, 2004

sol2

http://hyperphysics.phy-astr.gsu.edu/hbase/imgmod/radm.gif

http://www.airynothing.com/high_energy_tutorial/detection/images/compton_scatter.gif [Broken]

At what energies can we see where this may have its limits 2 TEV?

For a more http://wc0.worldcrossing.com/WebX?14@76.M60jczxSsAc.4@.1ddf4a5f/71 [Broken]

Last edited by a moderator: May 1, 2017
10. Aug 4, 2004

Nereid

Staff Emeritus
I must be in the slow class today sol2, I don't get your point (other than to explain Compton scattering) - what does this have to do with x-rays from the centre of the Milky Way?

11. Aug 4, 2004

sol2

On the contrary.

Bubbles from Dirac sea and the encapsulation of M theory?

The early universe and how bubbles form, attach.

See what happens is a light switch tends to turn on.

Could have used neuron synapse ignition

If they are wanted to be looked at in the future, I will have them stored for reference in another "time". :rofl:

This returns the thread to the owner

Regards

Last edited: Aug 4, 2004
12. Aug 4, 2004

selfAdjoint

Staff Emeritus
Not a highjack, but the level of discussion is all over the scale map:
1. Bubbles in the Dirac sea: old way of describing quantum vacuum
2. encapsulation of M-theory. Something private of yours?
3. Time for a light switch to go on: basic circuit theory

Not only do I not see how any of these bear on the x-ray question, I don't see how they relate to each other. At least not in any directed derivation.

13. Aug 4, 2004

sol2

the temperature

INteraction of Radiation with Matter

What is the energy relationship between energy and early universe at planck scale?

Apologize for what it seems, "like hijacking thread" but far from the truth.

No further responses coming here.

Last edited: Aug 4, 2004
14. Aug 11, 2004

Chronos

Absorption and re-emission depends on composition of the intervening media. Some wavelengths are absorbed, others sail right through [like SelfAdjoints window puzzle]. The ones that get absorbed get re-emitted at different frequencies [an excitation state thing]. Red glass, for instance, absorbs the non-red portion of the spectrum. What happens to the other colors? They are re-emitted in the infrared frequency [and the glass get hot]. The earths atmosphere is transparent to ultraviolet radition, glass is not. Glass, on the other hand, is transparent to X-rays and gamma rays, but, the atmosphere is not. Fortunately, this arrangement works out in our favor. We observe the galactic core in the X-ray spectrum because not all of the intervening matter is opaque in this range.

15. Aug 11, 2004

Olias

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