Astronomy Chapter 23
Although centuries ago, astronomers thought that a nova was a new star, appearing for the first time in the heavens, today we know that it is:
a binary star system in which one star is a white dwarf and mass is being transferred to it
In a supernova like SN1987A, once the crisis of iron fusion has begun, roughly how long does it take the star's core to collapse?
a few tenths of a second
Which of the following statements about the life of a star with a mass like the Sun is correct?
as the star is dying, a considerable part of its mass will be lost into space
Which of the following is the largest (in diameter)?
red giant
Astronomers have concluded that pulsars are
rotating neutron stars
Which of the following statements about Supernova 1987A is TRUE?
- It was observed with instruments in space as well as on the ground - It was only visible from the Southern Hemisphere of the Earth - Neutrinos from the explosion were actually detected on Earth - Astronomers believe it was the explosion of a star that was originally a massive type O
Which of the following statements about the Crab Nebula is TRUE?
- the nebula still puts out more energy (at all wavelengths) than 100,000 Suns - we can detect. a pulsar inside the nebula using both radio waves and visible light - the neutron star inside shows clear evidence of slowing down just a little bit in its rotation - it is the remnant of a supernova explosion first seen on Earth in 1054 AD
Which of the following statements about a Type II Supernova is true?
A Type II supernova occurs at the end of the life of a star 10 times the mass of our Sun or more
The astrophysicist who first calculated the highest mass that a dying star can have and still be a white dwarf was
S. Chandrasekhar
Astronomers have discovered pulsars spinning 500 x per second or more. How do astronomers think pulsars got to be spinning so outrageously fast?
Such fast-spinning pulsars have companion stars near them, which dump material on the pulsar and that spins it faster and faster
A member of the college football team wants to weigh as much as possible. Assuming he could somehow survive on all of them, at the surface of which object would he weigh the most?
a neutron star
When the mass of a star's core is greater than 1.4 times the mass of the Sun, degenerate electrons can't keep it stable as a white dwarf. Instead it becomes:
a neutron star
Where does the energy come from that allows the Crab Nebula to keep shining almost 1000 years after the star exploded?
a neutron star is slowing down (losing rotation energy)
Elements heavier than iron can be created during
a supernova explosion
A charming friend of yours who has been reading a little bit about astronomy accompanies you to the campus observatory and asks to see the kind of star that our Sun will ultimately become, long, long after it has turned into a white dwarf. Why is the astronomer on duty going to have a bit of a problem satisfying her request?
after a white dwarf cools off it becomes too cold and dark to emit visible light
In the model that astronomers have developed for pulsars, why fo they suggest that there must be two beams of energy coming from the pulsar?
because neutron star beams come out of the north and south poles of a magnetic field
Because white dwarfs are small, as their name implies, they are hard to see. What is a way astronomers have to find white dwarfs that distinguishes them from main sequence stars?
because white dwarfs get really hot, we can search for their ultraviolet radiation
After the core of a massive star becomes a neutron star, the rest of the star's material
explodes outward as a supernova
Astronomers have noticed that the visible filaments in the Crab Nebula are moving toward us at great speed. How can they know about motions like this?
from the Doppler shift in the line radiation from the nebula
A star with a mass like the Sun which will soon die is observed to be surrounded by a large amount of dust and gas -- all material it has expelled in the late stages of its life. If astronomers want to observe the radiation from such a giant star surrounded by its own debris, which of the following bands of the spectrum would be the best to use to observe it?
infrared
Which of the following statements about the Crab Nebula is FALSE?
inside, there are a number of newly formed massive stars (O and B type stars)
The most stable (tightly bound) atomic nucleus in the universe is:
iron
Which of the following statements about Supernova 1987A is FALSE?
it exploded relatively close to us, in a spiral arm of the Milky Way Galaxy
In a collapsing star of high mass, when electrons and protons are squeezed together with enormous force, they turn into a neutron and a:
neutrino
Astronomers have long realized that supernovae -- when the explode -- give off an enormous amount of light, but observations of Supernova 1987A ( in the Large Magellanic Cloud) revealed that the supernova gives off even more energy in another form? That form is:
neutrinos
Which of the following is the smallest?
neutron star
Which of the following is NOT a result of supernova explosions?
neutron star is disrupted and tears apart into many pieces
What kind of telescope did Jocelyn Bell use to discover pulsars in 1968?
radio
A white dwarf, compared to a main sequence star with the same mass, would always be:
smaller in diameter
Astronomers observe a young cluster of stars, where stars with three times the mass of the Sun are still on the main sequence of the H-R diagram. Yet the cluster contains two white dwarfs, each with a mass less than 1.4 times the mass of the Sun. If we can show that the white dwarfs are definitely part of the cluster, how can their presence so soon in the life of the cluster be explained?
some stars can lose a lot of mass on their way to becoming white dwarfs; thus the white dwarfs could have started out as quite massive stars
Which of the following stages will the Sun definitely go through as it gets older?
source of a planetary nebula black dwarf red giant white dwarf
Astronomers believe that the many supernova explosions that happened in the Milky Way Galaxy could have played a role in the evolution of life over billions of years. How would they have influenced the development of life on Earth?
the cosmic rays produced by supernova explosions would have contributed to the rate of mutations over many generations
If observations of supernovae in other galaxies show that such an explosion happens in a Spiral galaxy like the Milky Way on average every 25 to 100 years, why have astronomers on Earth not seen a supernova explosion in our Galaxy since 1604?
the disk of our Galaxy contains a great deal of dust, which tends to block the light of supernova explosions from more distant parts of our Galaxy
Which of the following is a characteristic of degenerate matter in a white dwarf star?
the electrons get as close to each other as possible and resist further compression
How did Supernova 1987A demonstrate that new elements are made in supernova explosions?
the light output was kept at high levels by the energy released from radioactive elements that decay very quicky; these must have been made by the supernova
A neutron star is as dense as
the nucleus of an atom
Some of the energy produced in the event we call Supernova 1987A was used to blow the star apart. Out of the following places that the energy of this event could go, which absorbed by far the most energy?
the production of huge numbers of neutrinos
Which of the following is one reason we do not detect a pulsar in many remnants of supernova explosions?
the pulsar beam doesn't happen to point toward is in many cases
When a star undergoes a nova explosion, it may return to its "quiet state" and later become a nova again. What would allow a nova explosion to happen to a star more than once
the star that goes nova has a companion star near it, which dumps material onto the first star and continues to do so even after the first nova explosion
In a Type Ia supernova, the cause of the violent outburst is:
the transfer of so much mass from a companion star that a white dwarf goes "over the limit" and collapses, causing an enormous amount of sudden fusion
A type Ia supernova involves the transfer of mass from one star to a companion white dwarf? Yet, in some cases, astronomers cannot locate a star near where they see Type Ia explosions. How do they explain the absence of a companion star>
they suggest that some type Ia supernova are caused by the collision of two white dwarfs, both of which then explode
Your sweetheart gives you a piece of gold jewelry as a present to celebrate you passing your astronomy class. Where did the gold atoms in that gift originally come from (where were they most likely made)?
they were built up from smaller nuclei during a supernova explosion
When neutron stars were first predicted theoretically, no scientist expected to be able to detect one of them across interstellar distances. What enabled astronomers to find neutron stars in the late 1960's?
we found strongly magnetic neutron stars whose whirling beams of energy were detected as pulsars
When a single star with a mass equal to the Sun dies, it will become a
white dwarf
