Untitled Quiz

The star nearest to Earth is

• Sirius

• the Sun

• 3C 273

• Proxima Centauri

• Supernova 1987A

   The carbon, nitrogen, oxygen, and heavier elements in our bodies

•     existed from the moment the Universe was born.

• were made in giant clouds of interstellar gas undergoing nuclear fusion.

• were made on planets from chemical reactions among lighter elements.

• were made in stars and supernovae billions of years ago.

• were created only about 6000 years ago, along with the rest of Earth.

Pulsars are rapidly rotating neutron stars that have two oppositely directed beams of particles and radiation moving along their magnetic axis.

• True

• False

If an emission line in the spectrum of an active galaxy is measured to be at a wavelength of 750 nm, and in a laboratory setting (at rest) it is measured to be at a wavelength of 150 nm, what is the galaxy's redshift, z?

• 5

• 4

• 1/4

• 1/5

• 4/5

Which one of the following is an assumption that is made when estimating the age of a cluster of stars?

• Stars in a cluster differ significantly in age from one another.

• All of the stars in a cluster are on the main sequence.

• All stars in the cluster with the same surface temperature have the same mass.

• Stars having a wide variety of masses were formed in the cluster.

• Stars move "up" along the main sequence before moving off it.

The rotation curve of the Milky Way Galaxy tells us that mass, M, enclosed within a circle of radius R increases exponentially with increasing R.

• True

• False

Which one of the following statements about black holes is TRUE?

•     The surface of the singularity of a black hole is known as the event horizon.

• (a)      Being more massive, a supermassive black hole has a greater gravitational pull than a stellar-mass black hole, so if you approach the event horizon of a supermassive black hole, you will be torn apart more easily than if you approach the event horizon of a stellar-mass black hole.

• (a)      If the Sun were to become a black hole of the same mass, Earth would spiral into the black hole and be eaten.

• (a)      The "photon sphere" is a region inside a black hole where photons orbit the center, so they cannot escape.

• I­n principle, energy can be extracted from a region outside a rotati­ng black hole.

(4)     A main-sequence star with mass of 20 solar masses produces energy primarily from

• fusion of hydrogen into helium.

• fusion of helium into carbon and oxygen.

• (b)      fusion of silicon into iron.

• (b)      gravitational contraction.

• (b)      chemical reactions that cause the gases to burn.

In class, we learned that the simple relation between redshift and an object's recession velocity is just an approximation that is valid for v < 0.2c. If we are studying a spectral feature that has a rest-frame wavelength of 650 nm, then this approximation will not be very accurate if we measure the wavelength of the spectral feature to be greater than about

• 78 nm

• 130 nm

• 780 nm

• 3250 nm

• 7800 nm

If the Schwartzchild radius of a 10 solar mass nonrotating black hole is 30 km, the event horizon of a 100 solar mass nonrotating black hole would have a radius of 3000 km.

• True

• False