To the eye (through a telescope), much of the Orion Nebula looks like a glowing cloud of gas.
What type of spectrum would you expect to see from the glowing parts of the nebula? Explain
your answer in 1–2 sentences.
6. Black Hole
Black holes are objects whose gravity is so strong that not even an object moving at the speed
of light can escape from their surface. Hence, black holes do not themselves emit light. But it is
possible to detect radiation from material which is falling TOWARD a black hole. Calculations
suggest that as this matter falls in, it is compressed and heated (a thermal spectrum!) to
temperatures around 106 Kelvin (K).
(a) Calculate the wavelength of maximum intensity for this temperature.
(b) In what part of the electromagnetic spectrum does this wavelength lie.
(c) If you were near the black hole (yikes!), what would be the eﬀect of this radiation on you?
7. The Doppler Eﬀect
In hydrogen, the transition from level 2 to level 1 has a rest wavelength of 121.6 nm. Suppose
you see this line at a wavelength of 129.9 nm in Star A, at 121.9 nm in Star B, at 121.2 nm in
Star C, and at 120.5 nm in Star D. Which stars are coming toward us? Which stars are moving
away? Which star is moving fastest relative to us? Explain your answers without doing any
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