ASTR 2 Final Exam Prep

Why don’t all supernova remnants contain pulsars?   a. All supernova remnants do contain pulsars.   b. Some supernova explosions form white dwarfs instead of the neutron stars necessary for pulsars.   c. Pulsars slow down and quit producing the pulses before the supernova remnant dissipates.   d. The pulsar may be tipped so that the beams do not sweep past Earth.   e. b and c

1

5

If a star is to eventually form a stellar black hole at any point in its life cycle what must happen? A. Gravity must be strong enough to compress all its material to be smaller than its schwartzchild radius B. it must pass by a supermassive black hole and tidal forces will do the rest C. Gravity must expand it so it can over power the nuclear forces that compress it and keep it from exploding by giving off all its heat D. A star will always have the same mass and radius and the only black holes that exist are ones that have existed shortly after the big bang

4. What is the upper limit of a brown dwarf’s size? a. no upper limit b. 0.50 solar masses c. 0.10 solar masses d. 0.08 solar masses e. less than 0.08 solar massesOn this one, I feel like E is the answer because the book mentions a red dwarf that is .08 solar masses in the section about brown dwarfs. I just want to be sure that D is not what they are looking for. (I've asked the professor, but I am not having any luck getting in touch with him.)

5

As a white dwarf cools, its radius will not change because   a. pressure resulting from nuclear reactions in a shell just below the surface keeps it from collapsing.   b. pressure does not depend on temperature for a white dwarf because the electrons are degenerate.   c. pressure does not depend on temperature because the white dwarf is too hot.   d. pressure does not depend on temperature because the star has exhausted all its nuclear fuels.   e. material accreting onto it from a companion maintains a constant radius.

Answer..

Plz answer all parts otherwise skip.

What kind of star is most likely to become a white-dwarf supernova? A. a star like our Sun B. a white dwarf star with a red giant binary companion C. a pulsar D. an O star   Is the answer B?  For D, as the surface temperature of a star would change over time so spectral type cannot tell us about the fate of the stars?

4

Astronomers us the P-Cygni line features in a spectrum of a supernova to... Select one alternative: ...measure the velocity of the supernova ejecta. ...to measure the rotation speed of the star that exploded. ...measure the composition of the supernova ejecta more accurately than with other lines. ...to measure the mass of the neutron star or black hole formed in the supernova.

The peculiar system SS 433   I. is emitting beams of energy and matter.   II. is producing a spectrum with both a redshift and a blueshift.   III. probably contains an accretion disk.   IV. is the result of a planetary nebula.   a. I   b. III   c. II & III   d. I, II, & III   e. I, II, III, & IV

4. Suppose we observe a binary star system in which one star is much more massive than the other and both are on the main sequence. We measure that the smaller star orbits the larger at a distance of 10¹3 m with a speed of 10 m/s. a. What is the mass of the larger star? b. Which star has a higher luminosity? c. Which has a larger radius? d. Which is hotter?

2GM What is the escape velocity (in km/s) from the surface of a 1.6 Mo neutron star? From a 3.0 M. neutron star? (Hint: Use the formula for escape velocity, V. ; make sure to express quantities in units of meters, kilograms, and seconds. Assume a neutron star has a radius of 11 km and assume the mass of the Sun is 1.99 x 1030 kg.) 1.6 Mo neutron star km/s 3.0 Me neutron star km/s

3.   Brown dwarfs are ____.  a.  stars with a very thick dust sphere around them, so they appear “brown”  b.  low mass M type stars with hundreds of planets   c.  an anomaly because they are extremely small but have relatively high temperature   d.  protostars that could not ignite the fusion of hydrogen at their core  e.  has a surface temperature of 2500 K by fusing hydrogen I asked this question onece already, but the answer I got said the answer was C because "AT 2700K THEY ARE HOT" or something to that effect. I tried to find a way to reply to that thread. My argument was that even if brown dwarfs were 2700k (and my book says that's closer to the temperature of red dwarfs and that brown dwarfs are usually around 1000K). Seeing that we are studying the life cycle and evolution of all stars, wouldn't either of those temperatures be on the relatively COOL side of all star temperatures? Wouldn't the most appropriate answer be D.?

B4