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The life cycle of a neutron star - David Lunney


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About once every century, a massive star somewhere in our galaxy runs out of fuel. No longer able to produce sufficient energy to maintain its structure, it collapses under its own gravitational pressure and explodes in a supernova. The death of that star is the birth of a neutron star: one of the densest known objects in the universe. David Lunney explores what, exactly, a neutron star is.

Additional Resources for you to Explore

An explanation of how fusion forms heavy elements in stars can be found in this TED-Ed video and its Dig Deeper section.

Supernova only happen for heavy stars, about ten times the mass of the Sun. Heavier stars, like bonfires, burn more quickly. In lighter, more typical stars (like our Sun, which is called a main-sequence star) fusion of the light element takes billions of years but there is not enough material to synthesize elements beyond carbon and oxygen. Such stars end their lives as white dwarfs. A classic text book describing nucleosynthesis and stellar evolution is “Cauldrons in the Cosmos,” by C.E. Rolfs and W.S. Rodney (University of Chicago Press). The landmark paper describing the various processes of stellar nucleosynthesis is referred to as B2FH (after the authors): E. M. Burbidge; G. R. Burbidge; W. A. Fowler & F. Hoyle (1957), "Synthesis of the Elements in Stars" Reviews of Modern Physics 29 (4): 547.

A nice book describing neutron stars, gravity waves, and associated phenomenon is “New Eyes on the Universe: 12 cosmic mysteries and tools we need to solve them,” by Stephen Webb (Springer/Praxis Publishing, Chichester, 2012). A layman’s explanation is given by National Geographic.

An authoritative work on the physics of neutron stars is by Lattimer and Prakash, published in the magazine Science:(a pre-publication version is available from the arXiv).

The site of the r (for rapid neutron capture) process is one of the "top eleven questions of physics" (see question 3). Long associated with supernovae but never observed, the site of the r process was revealed by the dramatic detection of the neutron-star merger described in this animation, which produced a kilonova. The glow of a kilonova (not introduced during the animation) is caused by the decay of radioactive nuclides produced during the r process. A kilonova is about one thousand times brighter than a nova (which occurs when a compact white dwarf star accretes matter from a binary companion) but about one thousand times fainter than a typical supernova.

Wikipedia has good entries for neutron stars and for the pulsars that revealed their existence. Jocelyn Bell is famous for not having shared the Nobel Prize for the discovery of pulsars (won by Anthony Hewish and Martin Ryle, however she did win the (more lucrative) Breakthrough prize in 2018.

Binary pulsar: The so-called Taylor-Hulse pulsar is a binary system of two neutron stars but only one of which is detected as a pulsar. The contraction of the pulsar’s orbit over time is perfectly explained by the emission of gravity waves from the system, indirectly confirming their existence. Taylor and Hulse received the 1993 Nobel Prize for their discovery.

Gravitational waves are the oscillations of space-time itself and fundamentally different from electromagnetic waves, which propagate through space-time with oscillating charge. Since gravity is so much weaker than electric charge, their waves are much harder to detect. The first-ever gravity-wave detections were made by the instruments LIGO (Laser Interferometer Gravitational wave Observatory) and Virgo (named for the star cluster). These collaborations have excellent press and media kits available from their websites. You can also watch the press conference held to announce the neutron-star merger detection and subsequent observations. It is quite long (over 3 hours!) but there are numerous scientists discussing the different aspects of this landmark event and they could hardly contain their excitement!

The 2017 Nobel Prize was awarded for the detection of gravity waves.

A landmark paper was published in The Astrophysical Journal Letters summarizing all of the observations made of the very first neutron-star merger. This paper heralds the dawn of multi-messenger astronomy and is exceptional for the vast number of authors.

Here’s another TED-Ed lesson that is very helpful for learning about gravity waves (including the “Dig Deeper” section).

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Meet The Creators

  • Educator David Lunney
  • Director Jody Ghani Nordby
  • Narrator Addison Anderson
  • Art Director Jody Ghani Nordby
  • Designer Jody Ghani Nordby
  • Illustrator Jody Ghani Nordby
  • Storyboard Artist Jody Ghani Nordby
  • Character Designer Jody Ghani Nordby
  • Animator Jody Ghani Nordby
  • Compositor Jody Ghani Nordby
  • Editor Jody Ghani Nordby
  • Composer Jody Ghani Nordby
  • Producer The Animation Workshop
  • Content Producer Gerta Xhelo
  • Editorial Producer Alex Rosenthal
  • Associate Producer Bethany Cutmore-Scott
  • Script Editor Eleanor Nelsen
  • Fact-Checker Brian Gutierrez

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