Chapter 13

A galaxy is A) a larger collection of stars B) a region of gas C) an exploding star D) a planet-sized object

A) a larger collection of stars Galaxies contain billions of stars.

To make a black hole, we need A) high mass in a small radius B) high mass in a large radius C) low mass in a small radius

A) high mass in a small radius

What was made in the first 4 minutes after the Big Band (all that apply) A) hydrogen B) helium C) carbon D) iron

A) hydrogen B) helium Only hydrogen and helium were made in the first 4 minutes after the Big Bang. The universe cooled quickly and became too low in density to forge heavier elements except for a little bit of lithium. Heavier element synthesis would have to wait until the first generation of stars formed much later.

Doppler shift for galaxies A) is usually toward red B) is usually towards blue C) is blue and red about equally D) has not yet been observed

A) is usually toward red Most galaxies are moving away, hence their light is red shifted.

When you look at a galaxy 5 billion light years away, you A) see this galaxy as it was 5 billion years ago B) see this galaxy as it was about a million years ago C) see the galaxy the way it is now D) you can never see a galaxy 5 billion light-years away

A) see this galaxy as it was 5 billion years ago The distance in "light years" is equal to the "look back time" in years. Telescopes are time machines, literally

A light year is A) dilated time B) a distance C) longer than a year D) the same as an ordinary year

B) a distance A light year is the distance light travels in one year, d = ct ≈ (3x108m/s)(3 x 107s) = 9 x 1015 m = 9 x 1012 km.

Oxygen and nitrogen were created A) in the first few million years of the earth's existence B) within a star C) in the big bang D) in a supernova explosion

B) within a star "I stepped out of a supernova, and so did you!" It took stars to make everything except all the hydrogen and most of the helium present in the Universe today (massive stars have added a small amount of helium to the mix).

The Age of the Universe is closest to A) 100 million years B) 1 billion years C) 10 billion years D) 1 trillion years

C) 10 billion years The age of the Universe is about 13.8 billion years old, and the Earth is about 4.6 billion years old, so the Earth has only been around for about 1/3 the age of the Universe

If we turn the Sun into a black hole, then the force on the Earth will A) increase by a factor less than a million B) increase by a factor much greater than a million C) be unchanged

C) be unchanged We did this when talking about gravity earlier in the semester. Black holes don't exhibit strong gravity until you are very close to them. At normal distances, Newton is correct, i.e. the force only depends on the center-to-center distance between the two masses.

The expansion of the Universe is accelerating. Physicists attribute this to A) the hubble expansion B) dark matter C) dark energy D) antimatter

C) dark energy

most of the mass in the universe is made of A) planets B) stars C) dark matter D) comets

C) dark matter

Dark energy makes the Universe A) slow down B) speed up C) expand D) maintain constant size

C) expand see 3.

To become a black hole, an object must A) have a mass much greater than that of the earth B) have a size much smaller than that of the earth C) have enough mass that the escape velocity exceeds c D) have been formed in a supernova explosion

C) have enough mass that the escape velocity exceeds c An object with sufficient mass and small size obtains an enormous critical density where the escape velocity becomes equal to or greater than the speed of light, hence no light can escape the object, and it truly appears black.

Choose all of the following that are NOT part of our solar system A) jupiter B) asteroids C) the andromeda galaxy D) halley's comet

C) the andromeda galaxy Galaxies are not solar system objects.

In the Big Bang theory A) the earth is at the center of the universe B) the earth is near the center of the universe C) the center of the universe is not known D)there is no center to the universe

C) the center of the universe is not known The center of the Universe is everywhere and nowhere. Every observer would think he was at the center of the expansion.

The discovery of dark energy means that A) the universe is heading toward a "big Crunch" B) most stars have burned out C) the expansion of the universe is accelerating D) the expansion of the universe is slowing down

C) the expansion of the universe is accelerating Dark energy is the current explanation for an expanding universe whose expansion rate is accelerating.

Most of the mass of the Universe is (be careful) A) hydrogen B) helium C) starlight D) dark matter

D) dark matter 1. Dark matter makes up the majority of mass in the universe, around 27%, with normal matter (protons, neutrons, electrons, neutrinos, etc.) constituting around 5%; dark matter is about 6 times more abundant. "Dark energy" constitutes the remaining 68% of the total mass and energy of the Universe.

Dark matter is made of A) ordinary stars B) MACHOs C) WIMPs D)we dont know

D)we dont know We are currently working to detect dark matter particles in the lab and in space. Some early results were recently reported, but this does not confirm the existence of dark matter. The hunt for dark matter could be as elusive as that for the Higgs boson which was finally observed after more than 35 years of searching.