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Which of these describes a nebula?(1 point) Responses star close in size to the sun star close in size to the sun cloud of gravity and pressure cloud of gravity and pressure star much larger than the sun star much larger than the sun cloud of gas and dust

The answer is "cloud of gas and dust."

What do supernova remnant and planetary nebulae have in common? Select the three correct answers.(2 points) Responses They emit non-visible radiation. They emit non-visible radiation. They have planets circling them. They have planets circling them. They contribute matter to interstellar space. They contribute matter to interstellar space. They are composed only of hydrogen and helium. They are composed only of hydrogen and helium. They are composed of matter from dying stars. They are composed of matter from dying stars. They are diffuse.

The three correct answers are:

- They contribute matter to interstellar space.
- They are composed of matter from dying stars.
- They are diffuse.

The universe's galaxies have evolved since what point in time?(1 point) Responses approximately 50 million years ago, after initial clumps of material were formed approximately 50 million years ago, after initial clumps of material were formed 800 million years ago, when gas concentrations were optimal for galaxy formation 800 million years ago, when gas concentrations were optimal for galaxy formation 13.8 billion years ago, right after the universe first formed 13.8 billion years ago, right after the universe first formed 23.4 billion years ago, when the universe first formed

The correct answer is 13.8 billion years ago, right after the universe first formed.

Which event triggers the start of black hole formation?(1 point) Responses The gravitational forces acting on a massive star decline rapidly. The gravitational forces acting on a massive star decline rapidly. A massive star depletes its stores of hydrogen and helium. A massive star depletes its stores of hydrogen and helium. A supernova blows a massive star apart. A supernova blows a massive star apart. Radiation emitted by a massive star increases.

The correct answer is: A supernova blows a massive star apart.

Which proportion of the universe's galaxies can be seen from Earth?(1 point) Responses approximately 10 percent approximately 10 percent approximately 25 percent approximately 25 percent far less than 1 percent far less than 1 percent nearly half

The correct answer is: far less than 1 percent.

Why are most stars not destroyed in a galaxy collision?(1 point) Responses Galaxies are mostly empty space. Galaxies are mostly empty space. Galaxies don't have stars. Galaxies don't have stars. Galaxies move too slowly for that type of damage. Galaxies move too slowly for that type of damage. Gravity keeps them away from each other.