PHYS 1303, Chap. 21, Homework, Prof. Kaim, DMC

Place the evolutionary stages of low-mass stars in order from earliest to latest in the star's life: a) hydrogen-> helium burning in core b) red giant c) cooling white dwarf d) planetary nebula

Left a) hydrogen-> helium burning in core b) red giant d) planetary nebula c) cooling white dwarf Right (Fortunately, the Sun will not expand to be a red giant for about 5 billion more years.)

Roughly how often would we expect a supernova to occur in our own Galaxy?

No astronomer with modern equipment has ever observed a supernova in our galaxy, therefore the chance is very rare, only happening approximately every 100,000 years. The chances of us observing a galactic supernova are much greater, once every 100 years.

How are nuclei heavier than iron formed? A

Once a massive star has reached the iron fusion stage, it can no longer fuse into heavier elements. The creation of heavier elements occurs after the massive star has exploded into a Supernova and new nuclei with heavier masses form. A

How do supernovae help "recycle" galactic matter? A2

supernovae recycle galactic matter by fusing lots of atoms together (up to iron) but then when the core shrinks rapidly and the supernova occurs, the outer layers in all its particles are scattered far across the universe. A2

What makes an ordinary star a become a red giant?

When a star runs out of hydrogen in its core, the core collapses. As a result, the core's temperature increases and additional energy is radiated away. With a higher temperature, the fusion in the hydrogen shell around the core becomes more efficient. So the core puts out even more energy than it did as a main sequence star. The increased gas pressure pushes on the outer part of the star, expanding it into a red giant

Which of the following is not evidence for supernovae in our Galaxy? a) The rapid expansion and filamentary structure of the crab nebula. b) Historical records from China and Europe. c) The existence of binary stars in our Galaxy. d) The existence of iron on the Earth.

c) The existence of binary stars in our Galaxy.

The silver in our jewelry formed in a) the Sun; b) the core of a red-giant star; c) a supernova; d) a nearby galaxy.

c) a supernova;

An observable supernova should occur in our Galaxy about once every a) year. b) decade. c) century. d) millennium.

c) century.

An observable supernova should occur in our Galaxy about once every a) year; b) decade; c) century; d) millennium.

c) century;

Where was supernova 1987a located? a) in the Orion Nebula, M 42 b) in Sagittarius, near the Galactic nucleus c) in our companion galaxy, the Large Magellanic Cloud d) in M 13, one of the closest of the evolved globular clusters e) near the core of M 31, the Andromeda Galaxy

c) in our companion galaxy, the Large Magellanic Cloud

The silver atoms found in jewelry originated in a) nearby galaxy. b) the core of a red-giant star. c) supernova. d) the core of the Sun.

c) supernova.

Which of the following stars will become hot enough to form elements heavier than oxygen? Check all that apply. a) A star that is half the mass of the Sun. b) A star having the same mass as the Sun. c) A star that is twice as massive as the Sun. d) A star that is eight times more massive than the Sun

d) A star that is eight times more massive than the Sun

Which of the following stars will become hot enough to form elements heavier than oxygen? a) A star that is half the mass of the Sun. b) A star having the same mass of the Sun. c) A star that is twice as massive as the Sun. d) A star that is eight times more massive than the Sun.

d) A star that is eight times more massive than the Sun.

Which one of the following does not provide evidence that supernovae have occurred in our Galaxy? a) The existence of iron on Earth. b) Historical records from China and Europe. c) The rapid expansion and filamentary structure of the Crab nebula. d) The existence of binary stars in our Galaxy.

d) The existence of binary stars in our Galaxy.

A white dwarf can dramatically increase in brightness only if it: a) is descended from a very massive star. b) is spinning very rapidly. c) can avoid nuclear fusion in its core. d) has another star nearby.

d) has another star nearby. (binary companion)

A nova differs from a supernova in that the nova a) can only occur once; b) is much more luminous; c) involves only high-mass stars; d) is much less luminous.

d) is much less luminous.

A nova differs from a supernova in that the nova a) involves only high-mass stars. b) is much more luminous. c) can occur only once. d) is much less luminous.

d) is much less luminous.

How do the mechanisms responsible for Type I and Type II supernovae explain their observed differences?

- Type I supernova will exhibit no hydrogen lines on a light spectrum. This is because there is no hydrogen involved in this process, and very little hydrogen exists in these stars. This is because the star has already become a white dwarf, its elemental layers have already been depleted. This type dies due to a carbon-detonation which happens when an accreting white dwarf exceeds Chandrasekhar mass (1.4 solar masses). The electrons are no longer able to withstand the pull of gravity and the stars temp begins to rise, causing frequent carbon fusion. This fusion causes the star to collapse. - Type II supernova will show hydrogen lines, because hydrogen is still very present at the time of the collapse of this star. The disappearance of the electrons and escape of neutrinos make the core of a large star very unstable (equilibrium of gravity and pressure is now off, gravity is taking over). Neutrons in the core are now extremely dense, and neutrons offer resistance to further compression of the already shrinking core, slowing the gravitational collapse. But by the time the collapse is halted, the core has overshot its point of equilibrium and is extremely dense. The core then begins to re-expand, and like a fast-moving ball hitting a brick wall and bouncing back, the core becomes compressed, stops, then rebounds. An enormously large shock wave sweeps through the star at high speed, blasting all the overlying layers, including the heavy elements, into space.

What are the observational differences between Type I and Type II supernovae?

-Type I Supernova have a light curve similar to that of a nova. They are hydrogen poor. -Type II Supernova have a light curve with a plateau (hydrogen rich)

Match the words in the left-hand column to the appropriate blank in the sentences in the right-hand column. Use each word only once. white dwarf supernova massive star supernova white dwarf limit (1.4 solar masses) nova accretion disk electron degeneracy pressure 1. The radius of a white dwarf is determined by a balance between the inward force of gravity and the outward push of _____________. 2. A(n) ______________ occurs when hydrogen fusion ignites on the surface of a white dwarf in a binary system. 3. A(n) _____________ occurs when fusion creates iron in the core of a star. 4. A white dwarf in a close binary system will explode as a supernova if it gains enough mass to exceed the _______________. 5. A(n) ______________ consists of hot, swirling gas captured by a white dwarf (or neutron star or black hole) from a binary companion star. 6. A(n) _____________ can occur only in a binary system, and all such events are thought to have the same luminosity.

1. electron degeneracy pressure 2. nova 3. massive star supernova 4. white dwarf limit (1.4 solar masses) 5. accretion disk 6. white dwarf supernova

How can astronomers estimate the age of an isolated star?

Astronomers use spectroscopic analysis to measure the emission of electromagnetic radiation - with this information and an understanding of how elements fuse together to form new elements, they can determine where the stars are in the evolutionary process. Younger massive stars will have a larger amount of the heavier elements and younger Sun-like stars will have only two elements. By studying different stars, astronomers can use the culmination of information to prove stellar evolution.

Under what circumstances will a binary star produce a nova?

A binary star will produce a nova when it is in the white dwarf stage. The white dwarf will pull materials from its binary star and these materials will then create an accretion disk around it. The accretion disk will cause the dwarf to heat up, and eventually at about 10(7) K, hydrogen will begin fusing helium. This is when the nova is most luminous.

What is an accretion disk, and how does one form?

A binary star will produce a nova when it is in the white dwarf stage. The white dwarf will pull materials from its binary star and these materials will then create an accretion disk around it. The accretion disk will cause the dwarf to heat up, and eventually at about 10(7) K, hydrogen will begin fusing helium. This is when the nova is most luminous.

What is a light curve? How can it be used to identify a nova or supernova?

A light curve is the measure of Luminosity and Absolute Magnitude along a time continuum. It is used to identify a nova as there is shown to be a rapid rise and slow decline in luminosity as well as max brightness attained; a supernova type 1 resembles the nova line but the total release of energy (luminosity) is much larger; a supernova's type 2 curves have a characteristic plateau during the declining phase.

A nova produces a characteristic light curve, which provides astronomers with details about the nova event. Select the appropriate light curve that shows how a nova's brightness changes over time.

A light curve of a nova event shows a sudden increase in luminosity in a matter of days, followed by a gradual fade over several months, until the white dwarf's luminosity returns to normal.

As a star evolves, why do heavier elements tend to form by helium capture rather than by fusion of like nuclei?

Because helium capture is much more common than fusion. For fusion to happen, the stars temperature must be extremely high.

How and where are nuclei heavier than iron formed? B

By neutron capture, whereby heavier nuclei are formed by the absorption of neutrons. Deep in the interiors of highly evolved stars, conditions are ripe for neutrons to occur... adding neutrons doesn't change an element, however, a more massive isotope of the same element is produced. B

In a binary-star system that produces a nova, the white dwarf pulls matter from the companion star. The matter forms an accretion disk that orbits the white dwarf. Then a specific sequence of events must take place for a nova event to occur. Rank the steps leading up to the observed nova event in chronological order from first to last. a) Material accumulates onto the white dwarf's surface, increasing in temperature and density. b) Nuclear fusion reactions cause an enormous but temporary increase in luminosity. c) At a temperature of 10 million K, the accumulated surface hydrogen begins nuclear fusion. d) As nuclear fuel is burned up or blown into space, fusion ceases and the star dims.

First a) Material accumulates onto the white dwarf's surface, increasing in temperature and density. c) At a temperature of 10 million K, the accumulated surface hydrogen begins nuclear fusion. b) Nuclear fusion reactions cause an enormous but temporary increase in luminosity. d) As nuclear fuel is burned up or blown into space, fusion ceases and the star dims. Last (Once nuclear fusion starts for the material on the surface, it proceeds at a furious rate. The white dwarf flares up, then fades away as some of the nuclear fuel is exhausted. The rest of it is blown into space. Neither the companion nor the white dwarf is destroyed in the nova process, so once fusion ceases, they return to their original states and repeat the process. Astronomers have observed many such scenarios, called recurrent novae.)

No nuclear reactions occur in the interior of a white dwarf. Its brilliance comes from stored heat. Therefore, the fate of an isolated white dwarf is to slowly lose its stored energy and dim over a long period of time. However, if a white dwarf is a member of a binary-star system with specific properties, the white dwarf can become explosively active. Label the components of such a binary-star system capable of producing a nova event. mass-transfer stream accretion disk main-sequence or giant companion star white dwarf

For a white dwarf to become explosively active, the distance between the dwarf and the companion must be small enough that the white dwarf's gravitational field can pull matter away from the surface of the companion. Due to the rotation of the binary system, the matter flowing through the mass-transfer stream from the companion star forms a flattened disk, called an accretion disk, which orbits around the white dwarf.

Rank the following steps that lead to a Type II supernova event in order of when they occur from first to last. a) Fusion Ceases b) Neutron Core c) Core Rebound d) Photodisintegration of Core Atoms e) Neutronization Begins

Initial a) Fusion Ceases d) Photodisintegration of Core Atoms e) Neutronization Begins c) Core Rebound b) Neutron Core Last (A Type II supernova occurs when a high-mass star's core becomes dominated by iron, halting the nuclear fusion process. The star's core can no longer maintain equilibrium, and the core begins to contract. The gravitational compression generates heat, which initiates photo-disintegration. During photo-disintegration, high-energy photons split large atoms into smaller and smaller atoms until only protons, neutrons, and electrons are left. Protons and electrons combine to form neutrons and neutrinos. The neutrinos are able to escape the star, carrying off energy, causing further contraction of the core. When the core contracts to the point where neutrons come into contact with each other, the core rebounds, sending out an energetic shockwave. This shockwave blasts the outer layers of the star into space, leaving behind a neutron core.)

Some of the most energetic events in the universe occur when stars explode in an incredible release of energy known as a supernova. Although every supernova is characterized by a sudden, intense brightening, the differences in types of progenitor stars and the mechanisms of detonation produce two distinct supernova types: Type I and Type II. a) detonation b) white dwarf at Chandrasekhar limit c) accretion disk on growing white dwarf d) carbon fusion begins

Initial State c) accretion disk on growing white dwarf b) white dwarf at Chandrasekhar limit d) carbon fusion begins a) detonation Final State (A Type I supernova occurs in a binary system with a white dwarf and a companion star. The white dwarf gains mass by accreting matter from the companion, until enough mass accumulates and it cannot support its own weight. The white dwarf begins to collapse, causing carbon fusion to begin throughout the star, which leads to its detonation.)

Why do the cores of massive stars evolve into iron, not heavier elements?

Iron is said to have the greatest nuclear binding energy of any element, more energy per particle is required to break up an iron-56 nucleus than the nucleus of any other element. All other elements are too weak, unsupported, etc for them to last long, they will become supernova

Why was supernova 1987a so important? Why are neutrino detectors important to the study of supernovae?

Part 1: It was one of the most dramatic changes observed in the universe in nearly 400 years. It provided astronomers with a wealth of detailed information on supernovae, allowing them to make key comparisons between theoretical models and observational reality. (Its parent star had been studied before the explosion. Its distance was already known. It was observed early, as its light was still increasing. Its evolution was captured with detailed images from the Hubble Space Telescope.) Part 2: Protons and electrons combine to form neutrons and neutrinos. The neutrinos are able to escape the star, carrying off energy, causing further contraction of the core. When the core contracts to the point where neutrons come into contact with each other, the core rebounds, sending out an energetic shockwave. This shockwave blasts the outer layers of the star into space, leaving behind a neutron core.

How do supernovae help "recycle" galactic matter? A1

Small stars, like our Sun, can fuse hydrogen into helium and helium into oxygen. This is the final stage for smaller Sun-like stars. More massive stars (that are at least 8 times the mass of our Sun) are able to fuse together the elements until they reach the iron stage. At this point, iron is unable to fuse because of its density. This process causes the massive star to explode into a supernovae , thus releasing galactic matter back into the universe to be recycled into a new star-creating cycle. A1

What proof do astronomers have that heavy elements are formed in stars?

The are formed by stellar nucleosynthesis. Through spectroscopic studies, the abundance of heavy elements in the stars has been observed.

How can a light curve be used to identify a nova or supernova?

Time is plotted on the horizontal axis; brightness on the vertical axis. The light curves of novae and supernovae appear rather different. In particular, if the amount of brightening were observed, supernovae are known to brighten about one million times more than novae. How the light dims after the explosion is noticeably different for novae and supernovae.

Each supernova type is distinct in initial components, process, and observational properties. Sort the following characteristics as to whether they describe a Type I or Type II supernova. a) low-mass star b) high-mass star c) carbon-detonation supernova d) hydrogen-poor e) hydrogen-rich f) core-collapse supernova g) graph with green line (initial increase followed by steady decrease) h) graph with red line (higher initial luminosity but luminosity constant from 25 to 100 days before decrease)

Type I: a) low-mass star d) hydrogen-poor c) carbon-detonation supernova g) graph with green line (initial increase followed by steady decrease) Type II: b) high-mass star e) hydrogen-rich f) core-collapse supernova h) graph with red line (higher initial luminosity but luminosity constant from 25 to 100 days before decrease) (Although both Type I and Type II supernovae are similar in their impressive release of energy, the two events occur under vastly different circumstances and are produced by different mechanisms.)

What evidence is there that many supernovae have occurred in our Galaxy?

We have plenty of evidence. Occasionally, explosions are visible from earth. In other cases, we detect the glowing remains, or supernova remnants.

What is a light curve diagram?

a diagram that plots the changes in the brightness of an object such as a star, as a function of time.

A massive star will collapse when iron is produced in the core because a) Iron will not fuse, so the core doesn't produce energy to oppose the inward gravitational pull of the star. b) Iron is dense enough to exert a much greater gravitational pull on the outer layers of the star. c) When iron fuses it generates much more energy than the previous elements in the core. d) The iron circulates to the outer part of the star, and since iron is very dense, the star will collapse.

a) Iron will not fuse, so the core doesn't produce energy to oppose the inward gravitational pull of the star. (While such a star might live for a few million years, this last phase in its evolution lasts only hours.)

Figure 21.8 in the textbook ("Supernova Light Curves") indicates that a supernova whose luminosity declines steadily in time is most likely associated with a star that is a) comparable in mass to the Sun. b) without a binary companion. c) on the main sequence. d) more than eight times the mass of the Sun.

a) comparable in mass to the Sun.

A massive star becomes a supernova when it a) forms iron in its core. b) suddenly increases in mass. c) collides with a stellar companion. d) suddenly increases in surface temperature.

a) forms iron in its core.

A white dwarf can dramatically increase in brightness only if a) it has a binary companion; b) fusion restarts in its core; c) it spins very rapidly; d) it was the core of a very massive star.

a) it has a binary companion;

Elements like oxygen, magnesium, and silicon are produced by a) massive stars only. b) low-mass stars only. c) all stars.

a) massive stars only. (It is remarkable to think that the oxygen you inhale with each breath was once generated in the hearts of massive stars billions of years ago.)

Nuclear fusion in the Sun will a) never create elements heavier than helium. b) create elements up to and including oxygen. c) create all elements up to and including iron. d) create some elements heavier than iron.

b) create elements up to and including oxygen.

Nuclear fusion in the Sun will a) never create elements higher than helium; b) create elements up to and including oxygen; c) create all elements up to and including iron; d) create some elements heavier than iron.

b) create elements up to and including oxygen;

A massive star becomes a supernova when it a) collides with a stellar companion; b) forms iron in its core; c) suddenly increases in surface temperature; d) suddenly increases in mass.

b) forms iron in its core;

During a "helium flash," which occurs during the red giant phase of a low-mass star: a) the star becomes visibly brighter due to the emission of helium b) helium fuses into carbon in the star's core c) hydrogen fuses into helium in the star's core

b) helium fuses into carbon in the star's core (A helium flash is a very brief (on the order of minutes to hours) and violent event that releases an enormous amount of energy. This energy however is mainly absorbed by the star's outer layers and therefore not directly visible to us.)

Most of the carbon in our bodies originated in a) the Sun; b) the core of a red-giant star; c) a supernova; d) a nearby galaxy.

b) the core of a red-giant star

Most of the carbon in our bodies was formed in a) supernova. b) the core of a red-giant star. c) nearby galaxy. d) the core of the Sun.

b) the core of a red-giant star.

Most of the carbon in our bodies originated in a) the Sun; b) the core of a red-giant star; c) a supernova; d) a nearby Galaxy.

b) the core of a red-giant star;