Author Question: An expanding shell of gas ejected from a medium-mass star during the latter stages of its evolution ... (Read 24 times)

BrownTown3 · **on:** Jul 27, 2018

An expanding shell of gas ejected from a medium-mass star during the latter stages of its evolution is known as a black hole.

Indicate whether the statement is true or false

Question 2

Explain the three kind of nebulae.

What will be an ideal response?

juliaf · **Reply #1 on:** Jul 27, 2018

Answer to Question 1

False

Answer to Question 2

The three kinds of nebulae are emission nebulae, reflection nebulae, and dark nebulae.Emission nebulae are produced when a hot star excites the gas near it to produce an emission spectrum. The star must be hotter than about B1 (25,000 K). Cooler stars do not emit enough ultraviolet radiation to ionize the gas. Emission nebulae have a distinctive pink color produced by the blending of the red, blue, and violet Balmer lines. Emission nebulae are also called H II regions, following the custom of naming gas with a roman numeral to show its state of ionization. H I is neutral hydrogen, and H II is ionized.A reflection nebula is produced when starlight scatters from a dusty nebula. Consequently, the spectrum of a reflection nebula is just the reflected absorption spectrum of starlight. Gas is surely present in a reflection nebula, but it is not excited to emit photons.Dark nebulae are dense clouds of gas and dust that obstruct the view of more distant stars. Some are generally round, but others are twisted and distorted, as shown at the left, suggesting that even when there are no nearby stars to ionize the gas or produce a reflection nebula, there are breezes and currents pushing through the interstellar medium.