Some of the Interstellar Gas in Our Galaxy Has Been

Multiple Choice

Some of the interstellar gas in our Galaxy has been heated to millions of degrees, a temperature that surprised astronomers when it was first discovered. How do we now think that gas between stars gets that hot?

A) any gas close to a star will naturally get that hot
B) very powerful shock waves from exploding stars heat the gas they come into contact with
C) gas gets to be this hot when hydrogen atoms flip their spin and give off 21-cm radiation
D) such gas is heated by the radiation given off by complex molecules in clouds
E) astronomers have no idea how gas gets this hot; this is an unsolved mystery in astronomy