Astronomy: White Dwarfs, Neutron Stars, Black Holes

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Questions and Answers

What phenomenon occurs as an object approaches a black hole?

  • Time appears to run more slowly for the object. (correct)
  • The object's mass decreases significantly.
  • The object emits bright visible light instead of redshifted light.
  • The object appears to move faster than light.

What is a likely cause of gamma-ray bursts?

  • Unusually powerful supernova explosions. (correct)
  • Internal reactions in neutron stars.
  • Collisions between planets.
  • The explosion of weak stars.

What process occurs when two neutron stars in a binary system merge?

  • They split into smaller neutron stars.
  • They form a black hole with no gravitational waves emitted.
  • They produce a supernova explosion that destroys both stars.
  • They emit gravitational waves as their orbital distance decreases. (correct)

How do black holes provide evidence of their existence?

<p>By the detection of gravitational waves from merging black holes. (C)</p> Signup and view all the answers

What element is primarily produced from mergers of neutron stars?

<p>Gold, platinum, and uranium. (A)</p> Signup and view all the answers

What provides support against the gravitational collapse of a white dwarf?

<p>Electron degeneracy pressure (C)</p> Signup and view all the answers

What phenomenon may occur when a white dwarf in a close binary system undergoes nuclear fusion?

<p>A nova explosion (A)</p> Signup and view all the answers

What is a defining characteristic of neutron stars?

<p>They have a radius of about 10 kilometers (D)</p> Signup and view all the answers

How were neutron stars first detected?

<p>As pulsars emitting beams of radiation (D)</p> Signup and view all the answers

What happens when a neutron star in a close binary system accretes hydrogen?

<p>It can produce x-ray bursts (C)</p> Signup and view all the answers

What defines a black hole's size?

<p>Schwarzschild radius (A)</p> Signup and view all the answers

What phenomenon can occur if you approach a black hole?

<p>You would experience time dilation (A)</p> Signup and view all the answers

What emerges from the collapse of the iron core of a massive star?

<p>A neutron star (B)</p> Signup and view all the answers

Flashcards

White Dwarf

The core left over from a low-mass star, supported by electron degeneracy pressure.

White Dwarf Nova

A sudden brightening of a white dwarf system due to hydrogen fusion on the surface.

Neutron Star

A dense ball of neutrons, formed by the collapse of a massive star's core in a supernova.

Pulsar

A rapidly rotating neutron star that emits beams of radiation.

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Neutron Star X-ray Binary

A binary system where a neutron star accretes matter from a companion, producing strong X-ray emissions.

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Black Hole

An object with such strong gravity that nothing, not even light, can escape.

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Event Horizon

The boundary around a black hole beyond which nothing can escape.

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Schwarzschild Radius

The size of a black hole, determined by its mass.

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What causes gamma-ray bursts?

Gamma-ray bursts are incredibly powerful explosions, often associated with powerful supernova explosions creating black holes, or the merging of neutron stars.

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What happens when neutron stars merge?

Neutron stars in close binary systems emit gravitational waves, causing them to spiral closer and eventually merge. This event releases tremendous energy and may be the primary source of elements like gold, platinum, and uranium.

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What happens when black holes merge?

Binary systems of black holes also emit gravitational waves, leading to mergers. These mergers emit even stronger waves that we can detect, providing direct evidence for black holes.

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Black Hole Evidence

The existence of black holes is supported by observations of x-ray binaries containing objects too massive to be neutron stars. Additionally, the detection of gravitational waves from merging black holes provides direct proof.

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Redshifting near Black Holes

As an object falls towards a black hole, its light becomes increasingly redshifted. The object appears to slow down and eventually disappears from view as its light becomes undetectable.

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Study Notes

White Dwarfs

  • White dwarfs are the remnants of low-mass stars.
  • They are supported by electron degeneracy pressure.
  • They have the Sun's mass compressed into the size of Earth.
  • In close binary systems, white dwarfs can accrete hydrogen from a companion.
  • Accretion can trigger novae, shining intensely for weeks.
  • Extreme accretion or mergers can lead to white dwarf supernova explosions.

Neutron Stars

  • Neutron stars are created from the collapse of iron cores in massive star supernovae.
  • They are extremely dense with a radius of about 10 kilometers.
  • They have a mass greater than the Sun.
  • Neutron stars' rapid spin and strong magnetic fields produce pulsars.
  • Pulsars are the first direct evidence of neutron stars.
  • In close binary systems, neutron stars accrete hydrogen from their companions.
  • This accretion creates hot accretion disks, detectable as x-ray binaries.
  • Helium fusion on the neutron star's surface can cause X-ray bursts.

Black Holes

  • Black holes are regions of spacetime with gravity so strong that nothing can escape, not even light.
  • The boundary is the event horizon.
  • The size is described by the Schwarzschild radius.
  • Orbiting a black hole would be similar to any other massive object.
  • Observing objects falling into black holes reveals time dilation and redshift.
  • Objects disappear from view as light becomes too redshifted to detect.
  • Black holes are predicted by theory and observed via X-ray binaries.
  • No force can stop the collapse of stellar corpses with masses exceeding neutron star limits (2-3 solar masses).

Extreme Events

  • Gamma-ray bursts are powerful explosions in distant galaxies.
  • They are likely due to very powerful supernovae, creating black holes.
  • Short gamma-ray bursts may result from neutron star mergers.
  • Neutron star mergers produce gravitational waves and potentially heavy elements (gold, platinum, uranium).
  • Black hole mergers also produce gravitational waves (detected).

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