Study Notes on Neutron Stars and Black Holes

Course Assignments and Upcoming Exam

Assignment due tonight.
Discussion Post #2 due next week.
Preclass assignment due next Wednesday, November 24.
Homework is the last assignment before the exam.
Exam 3 scheduled for the following Monday (24th of November).
Encouragement to start studying for Exam 3 by reviewing topics and equations relevant to the exam.

Open invitation for students to join office hours for questions.
Alternative communication via email for setting up an appointment if unable to attend office hours.
Emphasis on student success and encouragement for hard work leading up to Exam 3.

Overview of neutron stars.
Transition to discussion on black holes scheduled for Friday.
Following week’s topics include black holes and star clusters, galaxies, dark matter, and cosmology.

Previous discussions focused on white dwarfs.
Important to differentiate the eventual outcomes of high-mass stars (supernova type II leading to either neutron stars or black holes).

Neutron stars were discovered by graduate student Jocelyn Bell through radio observations.
Initial signals observed were periodic, leading to the term "pulsars."
Jocelyn Bell humorously referred to the signals as LGM - "Little Green Men."
Pulsars exhibit extreme periodicity, comparable to atomic clocks.

Neutron stars have a radius of approximately 10 kilometers, described as being slightly larger than Sac State.
They are remnants of supernova explosions and spin at rapid rates.
Rotation speed is explained through the conservation of angular momentum during core collapse.

The beam of light emitted by neutron stars is not aligned with the spin axis (lighthouse model analogy).
Visibility of pulsars depends on whether the beam aligns with Earth’s line of sight, similar to lighthouse beams.

Sparks interest with light emission and visual patterns that follow the pulsation rates (quick bursts).
The Crab Nebula's pulsar is cited as a notable example of a pulsating neutron star, rotating 30 times per second, illustrating conservation of angular momentum in action.
Comparison made with ice skaters speeding up when drawing limbs inward, a reflection of angular momentum principles at play during a star's collapse.

Neutron stars generate light due to strong magnetic fields rather than thermal emission.
Neutron stars lose rotational energy over time leading to phenomena classified as "spindown."
This gradual slowing down is measurable and is important for understanding the age and duration of neutron stars.

Neutron stars experience glitches that cause temporary increases in speed, attributed to brief contractions in the star’s interior, recalling conservation principles of rotation.

Neutron stars predominantly consist of neutrons within their cores, hypothesized composition remains partially unexplored (possibly an iron crust).

Neutron stars may exist in binary systems where they can accumulate mass or energy from a companion star.
Such interactions lead to phenomena like millisecond pulsars (fastest rotating due to accretion) or X-ray pulsars (due to intense magnetic fields and hotspots).

Discussion on binary neutron stars merging into kilonova explosions, believed to be a source of heavy elements like gold.
Explanation of how these events spread materials that eventually create elements found on planets and in the human body.

Brief transition into black holes, emphasizing common misconceptions about their behavior in space as cosmic vacuum cleaners.
Explanation on how black holes consume nearby matter yet do not inherently attract everything in their proximity, often simply sitting dormant with little surrounding material.
Introduction to the concept of gravitational attraction using Newton's law; black holes alter nothing regarding the gravitational influence as they relate to their mass.
Clarification of what black holes are, leading into a more detailed discussion planned for the next class meeting.