Soft x ray source, find radius, suggest object

In summary, A soft x ray source with an observed luminosity of 10^30W and peak emission at 4KeV has a radius estimated to be 550 metres or 13.5 km, depending on the method used. The second method is considered more accurate and suggests that the source could be a neutron star. The first method is usually used for order of magnitude calculations and may have been hinted at in the lecture notes.
  • #1
ghosts_cloak
16
0
Hi guys!
Question:
A soft x ray source has an observed luminosity of 10^30W. The spectral shape indicates black body radiation with a peak in the emmision at 4KeV. Estimate the radius of the object. Suggest what source this might be.

So, using L=sigma*A*T^4 and the peak energy is approx kT and taking surface area to be 4*Pi*r^2 I get a radius of 550 metres, hmm low!

I then tried using Weins law and get a radius of 13.5 Km, which would be reasonable for a neutron star?

Any suggestions for the 550m radius, and which method is correct?

Thanks,

~Gaz
 
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  • #2
ghosts_cloak said:
Any suggestions for the 550m radius, and which method is correct?

The second method will be more accurate and yes, 13.5 km is a reasonable size for a neutron star. For comparison, a solar mass black hole has a Schwarzschild radius of ~3 km.
 
  • #3
Hi :-)
Thanks for the reply. Yup, I thought the second method gave a better result!
I wouldn't normally have bothered about posting it on here but the lecture notes kind of hint towards the first method, and we haven't covered Weins law in this course (although we have in previous courses).
Cheers,
~Gaz
 
  • #4
ghosts_cloak said:
I wouldn't normally have bothered about posting it on here but the lecture notes kind of hint towards the first method, and we haven't covered Weins law in this course (although we have in previous courses).

If it's a perfect blackbody, the peak is given exactly by Wein's Law. The other method is usually just for order of magnitude calculations (that is, to get an equivalent temperature from an energy, just divide by Boltzmann's constant).
 

1. What is a soft x-ray source?

A soft x-ray source is a device or object that emits electromagnetic radiation in the soft x-ray region of the electromagnetic spectrum, typically with wavelengths between 0.1 and 10 nanometers. Soft x-rays are often used in medical imaging and scientific research.

2. How can I find the radius of a soft x-ray source?

The radius of a soft x-ray source can be determined by measuring the distance from the source to the point where the x-rays start to diverge. This can be done using techniques such as X-ray radiography or X-ray diffraction.

3. Can you suggest an object that can act as a soft x-ray source?

One possible object that can act as a soft x-ray source is a cathode ray tube (CRT) which is commonly used in older television sets. Other possible sources include synchrotron radiation facilities and certain types of lasers.

4. What factors can affect the radius of a soft x-ray source?

The radius of a soft x-ray source can be affected by various factors such as the energy and intensity of the x-rays, the material and size of the object emitting the x-rays, and the distance between the source and the point of measurement.

5. What are some potential uses for soft x-ray sources?

Soft x-ray sources have a wide range of potential uses, including medical imaging, material analysis, and surface modification. They are also commonly used in astronomy to study objects in the universe that emit soft x-rays, such as black holes and supernovae.

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