Chapter 12 the deaths of stars
Download
1 / 40

Chapter 12 The Deaths of Stars - PowerPoint PPT Presentation


  • 122 Views
  • Uploaded on

Chapter 12 The Deaths of Stars. What do you think?. Will the Sun explode? If so, what is the explosion called? Where did carbon, silicon, oxygen, iron, uranium, and other heavy elements on Earth come from? What is a pulsar? What is a nova?.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' Chapter 12 The Deaths of Stars' - bell-webb


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
Chapter 12 the deaths of stars

Chapter 12The Deaths of Stars


What do you think
What do you think?

  • Will the Sun explode? If so, what is the explosion called?

  • Where did carbon, silicon, oxygen, iron, uranium, and other heavy elements on Earth come from?

  • What is a pulsar?

  • What is a nova?



Stages in the evolution of low mass stars beyond the helium flash
Stages in the evolution of low-mass stars beyond the helium flash:

  • Movement to horizontal branch

  • Core helium fusion

  • Asymptotic GIANT branch (AGB)

  • Planetary nebula formation



white dwarf expanding into planetary nebulae

The burned-out core of a low-mass star becomes a white dwarf


white dwarf expanding into planetary nebulae

Sirius and its white dwarf companion


The burned out core of a low mass star becomes a white dwarf
The burned-out core of a low-mass star becomes a white dwarf expanding into planetary nebulae

  • Stable stars are supported by

    • gas pressure

    • radiation pressure

    • electron degeneracy pressure

  • Star loses hydrostatic equilibrium

  • Gravitational contraction of the core

  • Temporary, nuclear fusion-based stability

  • Surrounding planetary nebula disperses

  • Remaining core is WHITE DWARF


The starting MASS determines the exact pathway expanding into planetary nebulae

Mass-loss causes the end-state, a planetary nebula and a white dwarf, to have substantially less mass than the original red supergiant.


What s a nova
What’s a nova? expanding into planetary nebulae

  • A nova is a relatively gentle explosion of hydrogen gas on the surface of a white dwarf in a binary star system.

  • It occurs when the white dwarf steals mass from its companion and the external layers quickly ignite and shine brightly.

  • This process does not damage the white dwarf and it can repeat.


Yeah but what about the really big stars
Yeah, but what about the really expanding into planetary nebulaeBIG stars?



A series of different types of fusion reactions in high mass stars lead to luminous supergiants1
A series of different types of fusion reactions in high-mass stars lead to luminous supergiants

  • When helium fusion ceases in the core, gravitational compression increases the core’s temperature above 600 million K at which carbon can fuse into neon and magnesium.

  • When the core reaches 1.5 billion K, oxygen begins fusing into silicon, phosphorous, sulfur, and others

  • At 2.7 billion K, silicon begins fusing into iron

  • This process immediately stops with the creation of iron which can not fuse into larger elements and a catastrophic implosion of the entire star initiates.




The most famous “before and after” picture millennia afterwardSupernova 1987 A



Consider the change in brightness with time for some supernovae ….

There are at least two distinctly different types of brightness fall-off observed.


Accreting white dwarfs in close binary systems can also explode as supernovae

white dwarf supernovae ….

Accreting white dwarfs in close binary systems can also explode as supernovae


white dwarf supernovae ….

White dwarfs in close binary systems can rapidly gain mass from a companion and create powerful explosions


White dwarfs in close binary systems can create powerful explosions if it exceeds 1.4 solar masses (Chandrasekar limit)

after

before

Called a TYPE I supernova




The cores of may type ii supernovae become neutron stars
The cores of may Type II supernovae become neutron stars brightness

  • When stars between 4 and 9 times the mass of the Sun explode as supernovae, their remnant cores are highly compressed clumps of neutrons called neutron stars.

  • These tiny stars are much smaller than planet Earth -- in fact, are about the diameter of a large city.

  • Spinning neutron stars are called pulsars.


Neutron star
Neutron Star brightness


Pulsars
Pulsars brightness

  • first detected in 1967 by Cambridge University graduate student Jocelyn Bell

  • Radio source with an regular on-off-on cycle of exactly 1.3373011 seconds


Pulsars1
Pulsars brightness

  • first detected in 1967 by Cambridge University graduate student Jocelyn Bell

  • Radio source with an regular on-off-on cycle of exactly 1.3373011 seconds

  • Some scientists speculated that this was evidence of an alien civilization’s communication system and dubbed the source LGM

    Little Green Men

  • Today, we know pulsars are rapidly spinning neutron stars.


T he l ight h ouse m odel a rotating magnetic field explains the pulses from a neutron star
T brightnessHE LIGHT HOUSE MODELA rotating magnetic field explains the pulses from a neutron star




Neutron stars in binary systems can also emit powerful isolated bursts of x rays
Neutron stars in binary systems can also emit powerful isolated bursts of X-rays

X-ray bursters probably arise from mass transfer in binary star systems where one star is a neutron star rather than a white dwarf. A helium layer 1km thick would be enough to cause a flash across the surface that emits X-rays

Recently discovered gamma-ray bursters, which happen over fractions of seconds, might have a similar origin.


What did you think
What did you think? isolated bursts of X-rays

  • Will the Sun explode? If so, what is the explosion called?

    The Sun will explode as a planetary nebula in about five billion years.

  • Where did carbon, silicon, oxygen, iron, uranium, and other heavy elements on Earth come from?

    These elements are created by supernovae.

  • What is a pulsar?

    A pulsar is a rotating neutron star in which the magnetic field does not pass through the rotation axis.

  • What is a nova?

    A nova is a relatively gentle explosion of hydrogen gas on the surface of a white dwarf in a binary star system.


Self check
Self-Check isolated bursts of X-rays

1: List the stages in the evolution of low-mass stars beyond the helium flash.

2: List the stages in the evolution of high-mass stars beyond the initial red giant or supergiant stage.

3: Name the objects that represent the end phases of evolution for main-sequence stars and indicate the mass range for each.

4: Compare and contrast the physical and observable properties of Type I and Type II supernovae.

5: Describe the properties of gas clouds that are produced by late stages of stellar evolution and indicate from which type of stars they are formed.

6: Review the observational evidence that links pulsars with neutron stars.

7: Compare and contrast pulsars with X-ray sources that pulsate.

8: Compare and contrast the physical processes that occur in supernovae with those in novae and bursters.


ad