Are White Dwarfs Stars? Understanding the Classification and Characteristics

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Discussion Overview

The discussion revolves around the classification of white dwarfs as stars, exploring the criteria that define a star and the implications of such classifications. Participants engage with concepts related to stellar evolution, definitions of astronomical terms, and the subjective nature of categorization in astrophysics.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Exploratory

Main Points Raised

  • Some participants argue that white dwarfs should not be classified as stars since they do not undergo nuclear fusion, which is often seen as a defining characteristic of stars.
  • Others suggest that white dwarfs are remnants of former stars and thus can be considered stars in a broader sense, similar to how a deceased person is still recognized as having been a person.
  • There is a discussion about the ambiguity of the term "star," with some noting that definitions vary widely and often do not encompass all types of stars, such as red giants or white dwarfs.
  • A participant points out that definitions from sources like dictionaries or astronomical organizations may not align with practical usage in the field, indicating that the classification of stars is more about shared characteristics than strict definitions.
  • Some participants express that the classification of objects like white dwarfs is useful for understanding their properties and behaviors, despite the lack of a universally accepted definition.
  • There is a comparison made between white dwarfs and other exotic objects like neutron stars and black holes, with a viewpoint that a "star" implies an active core.
  • Participants also mention the Hertzsprung–Russell diagram and its limitations in representing all types of stars, particularly those without significant luminosity or temperature.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether white dwarfs should be classified as stars. Multiple competing views remain regarding the definitions and implications of such classifications.

Contextual Notes

Participants highlight the subjective nature of definitions in astrophysics and the potential disconnect between official definitions and practical usage among astronomers. The discussion reflects ongoing uncertainties and differing perspectives on classification criteria.

  • #31
Puzzling, isn't it? IAU stands for "international astronomical union", which translates literally to "group involving many countries that is concerned with the laws pertaining to stars." You'd think a group like that would have a clear definition of what a star is, wouldn't you? But this is the whole problem-- cut-and-dried definitions are not actually very conducive to research efforts. Instead, what is effective is having a somewhat flexible working meaning of these terms. That's what flies everywhere except in the tests they give in elementary school classes, so beware of "authoritative definitions."
 
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  • #32
Ken G said:
Puzzling, isn't it?
Yes, that is why I asked.
 
  • #33
http://iopscience.iop.org/article/10.1086/307414/pdf

"For objects this cool, the presence of lithium proves that they are substellar."

"Some of these dwarfs certainly are substellar but such a designation cannot be tied uniquely to any particular spectroscopic trait."

"Because some of these objects are substellar and thus not truly stars, the entire collection should be referred to as 'L dwarfs,' not 'L stars.'"

https://arxiv.org/pdf/astro-ph/0608359.pdf

"3. Definitions:
(1) A “primary” body is a star or substar formed by core accretion from an
interstellar cloud, not by secondary accretion from a disk.
(2). A “substar” is a body with less than 80 Jupiter masses, the lower limit for
stellar hydrogen fusion."
 
Last edited:
  • #34
Yes, so none of that tells you if a white dwarf is a star. But as said above, the answer to that is, no if you look in a dictionary or encyclopedia, yes if you go to an astronomy meeting.
 

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