Do emission nebula glow because of ionised or excited electrons?

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  • Thread starter Nathi ORea
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Summary:
Do emission nebulae glow because of ionized electrons or excited ones?
I'm trying to figure out why emission nebulae glow.

I read various sites such as a NASA website explaining why they shine;

'The massive stars embedded within the nebula give off enormous amounts of ultraviolet radiation, ionizing the gas and causing it to shine.'

The Britanica article on emission nebula says;

'It was found that ultraviolet light from the star ionizes nearby hydrogen. The hydrogen atoms emit visible light after the electrons and nuclei recombine and the atoms drop to lower energy levels.'

My understanding is that we cannot see recombining ionised electrons in hydrogen, only those of the Balmer series which are only 'excited' electrons.

Wouldn't any electrons excited or ionized by UV simply reemmit emr in the ultraviolet again which we cant see?

Just fyi, I am just an astronomy enthusiast and real technical language and maths I probably wont get.

I'd appreciate any help
 

Answers and Replies

  • #2
Drakkith
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The electron often cascades downwards, transitioning from higher to lower energy levels like a ball bouncing down the stairs. From wiki's article on hydrogen alpha:

In the new atom, the electron may begin in any energy level, and subsequently cascades to the ground state (n = 1), emitting photons with each transition. Approximately half the time, this cascade will include the n = 3 to n = 2 transition and the atom will emit H-alpha light. Therefore, the H-alpha line occurs where hydrogen is being ionized.
 
  • #3
Greetings,
Summary:: Do emission nebulae glow because of ionized electrons or excited ones?

'It was found that ultraviolet light from the star ionizes nearby hydrogen. The hydrogen atoms emit visible light after the electrons and nuclei recombine and the atoms drop to lower energy levels.'
That is the correct physics. The gas is first ionized by the hot star. The resultant ion and a free electron recombine to form an atom in an excited electronic state. That excited state finally emits a photon as the excited atom decays to its ground state.

It appears that you are confused about a basic principle. The electrons do not emit light. The light is given off by an atom and the bound electron drops to a lower energy state.

This article from Scholarpedia may be of interest: Planetary nebulae

Best regards,
ES
 
  • #4
36
11
The electron often cascades downwards, transitioning from higher to lower energy levels like a ball bouncing down the stairs. From wiki's article on hydrogen alpha:

In the new atom, the electron may begin in any energy level, and subsequently cascades to the ground state (n = 1), emitting photons with each transition. Approximately half the time, this cascade will include the n = 3 to n = 2 transition and the atom will emit H-alpha light. Therefore, the H-alpha line occurs where hydrogen is being ionized.
Thanks so much. That makes sense!
I love the analogy of the ball bouncing down stairs!
thank you
 
  • #5
36
11
Greetings,

That is the correct physics. The gas is first ionized by the hot star. The resultant ion and a free electron recombine to form an atom in an excited electronic state. That excited state finally emits a photon as the excited atom decays to its ground state.

It appears that you are confused about a basic principle. The electrons do not emit light. The light is given off by an atom and the bound electron drops to a lower energy state.

This article from Scholarpedia may be of interest: Planetary nebulae

Best regards,
ES
Yes! Thank you!
I get it… the electron goes back to ground state (or I think n2 because of Balmer series) in stages.

Appreciate it
 

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