What is White dwarf: Definition and 62 Discussions

A white dwarf, also called a degenerate dwarf, is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: Its mass is comparable to that of the Sun, while its volume is comparable to that of Earth. A white dwarf's faint luminosity comes from the emission of stored thermal energy; no fusion takes place in a white dwarf. The nearest known white dwarf is Sirius B, at 8.6 light years, the smaller component of the Sirius binary star. There are currently thought to be eight white dwarfs among the hundred star systems nearest the Sun. The unusual faintness of white dwarfs was first recognized in 1910. The name white dwarf was coined by Willem Luyten in 1922.
White dwarfs are thought to be the final evolutionary state of stars whose mass is not high enough to become a neutron star or black hole. This includes over 97% of the other stars in the Milky Way. After the hydrogen-fusing period of a main-sequence star of low or medium mass ends, such a star will expand to a red giant during which it fuses helium to carbon and oxygen in its core by the triple-alpha process. If a red giant has insufficient mass to generate the core temperatures required to fuse carbon (around 1 billion K), an inert mass of carbon and oxygen will build up at its center. After such a star sheds its outer layers and forms a planetary nebula, it will leave behind a core, which is the remnant white dwarf. Usually, white dwarfs are composed of carbon and oxygen (CO white dwarf). If the mass of the progenitor is between 8 and 10.5 solar masses (M☉), the core temperature will be sufficient to fuse carbon but not neon, in which case an oxygen–neon–magnesium (ONeMg or ONe) white dwarf may form. Stars of very low mass will not be able to fuse helium, hence, a helium white dwarf may form by mass loss in binary systems.
The material in a white dwarf no longer undergoes fusion reactions, so the star has no source of energy. As a result, it cannot support itself by the heat generated by fusion against gravitational collapse, but is supported only by electron degeneracy pressure, causing it to be extremely dense. The physics of degeneracy yields a maximum mass for a non-rotating white dwarf, the Chandrasekhar limit—approximately 1.44 times M☉—beyond which it cannot be supported by electron degeneracy pressure. A carbon–oxygen white dwarf that approaches this mass limit, typically by mass transfer from a companion star, may explode as a type Ia supernova via a process known as carbon detonation; SN 1006 is thought to be a famous example.
A white dwarf is very hot when it forms, but because it has no source of energy, it will gradually cool as it radiates its energy. This means that its radiation, which initially has a high color temperature, will lessen and redden with time. Over a very long time, a white dwarf will cool and its material will begin to crystallize, starting with the core. The star's low temperature means it will no longer emit significant heat or light, and it will become a cold black dwarf. Because the length of time it takes for a white dwarf to reach this state is calculated to be longer than the current age of the known universe (approximately 13.8 billion years), it is thought that no black dwarfs yet exist. The oldest white dwarfs still radiate at temperatures of a few thousand kelvins.

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  1. Brzohn

    A Why do novas shine?

    It’s my understanding that a nova happens when you have a close binary star, and one component is a white dwarf. The white dwarf sucks hydrogen from its companion, the hydrogen piles up on the surface of the dwarf until it’s hot and dense enough to undergo nuclear fusion. Ka-boom. Right? Why is...
  2. S

    I What is theorized to be the coldest white dwarf in the Universe?

    Yes, I understand that once white dwarfs get cold enough, they aren't luminous enough to get observed, so my question could be interpreted as "when did the earliest white dwarf evolve, and how cold is it now"? This is the article that motivated this question...
  3. Astronuc

    B Evolution of planetary system around a white dwarf

    An article came up on Phys.org about a white dwarf drawing in material from the planetary system surrounding it. Is this the ultimate fate of our solar system? https://phys.org/news/2022-06-dead-star-cannibalism-planetary-far-reaching.html...
  4. GhostLoveScore

    I Exploring White Dwarf Composition: The Mystery of Electron Degeneracy Pressure"

    As this page says: "A burnt-out star is basically a gas of electrons and ions. " In white dwarf, further collapse of the star is stopped by electron degeneracy pressure. But, if the star material is just a soup of ions and almost free electrons, why don't the electrons and ions separate into...
  5. S

    B Process of a sun changing into a white dwarf

    This is part of the text from the link: I want to ask several things: 1. From the second paragraph: "As soon as the sun begins to burn more hydrogen, it would be considered a “red giant”. " But from first paragraph: "But when the star has nothing left in the core to burn, gravitational...
  6. D

    I Orbital distance increase during the white dwarf phase of the Sun

    Some estimates through calculating the sun mass loss and increase in mass loss say that the white dwarf phase of the Sun will have roughly about 50% the current mass of the Sun (not sure about it). Whatever the actual mass loss is going to be, assuming that the 50% mass loss is true, where would...
  7. P

    B Interested in Black Holes, Neutron Stars, and White Dwarf Stars

    How did you find PF?: duckduckGo search. My math is very weak and I don't like explanations done using math. I read books with very little math. I try to use reason based on what I've read. My understanding is time slows down in gravity and it will actually stop at the event horizon (see...
  8. lomidrevo

    B Planetary debris found in white dwarf atmospheres

    I read this interesting article today, the original paper here. Abstract:
  9. G

    I White dwarf Ultra-relativistic electrons

    Hi! I have read a calculation about a white dwarf star assuming the electrons are both ultra-relativistic and degenerate. My questions is - how come the ultra-relativistic assumption doesn't contradict the "degeneracy" assumption. Degenerate means the electrons are filling out all the lowest...
  10. tanaygupta2000

    Degeneracy pressure of a White Dwarf Star

    So far, I am provided with all the required values for calculation, except N. If N = total number of electrons in star, then using N = mass of star/ mass of an electron should be no problem. Am I right?
  11. P

    I Neutron vs electron degeneracy pressure

    How is neutron degeneracy pressure able to support a much higher density object such as a neutron star where electron degeneracy pressure only supports a comparatively less dense object such as a white dwarf. Conceptually I would think electron degeneracy pressure to be stronger due to the...
  12. P

    I Can a White Dwarf Collapse into a Neutron Star Without a Supernova?

    Is it possible for white dwarf star in binary system where it is feeding off its partner star to collapse directly into a neutron star? Or is something inherent in the formation of neutron stars where they must be formed from supernova?
  13. F

    I Computing a value of radius for a typical white dwarf

    I try to get a correct result for the radius of a standard white dwark (roughly 10000 km). I just want the order of magnitude , i.e with the common values of a solar mass into Earth radius sphere. From http://www.astro.umontreal.ca/~bergeron/CoolingModels/Synthetic_Calibration.pdf page 1223...
  14. YoungPhysicist

    B White dwarf quantum tunnelling

    I just finished watching the video "The Last Light Before Eternal Darkness – White Dwarfs & Black Dwarfs" At 5:17 he mentioned quantum tunneling will take up a timespan so long that calling it forever is ok. But nothing takes forever,so,how long will it actually take? ps:I later realized...
  15. donielix

    I White dwarf collapses into a neutron star and Energy is released

    Hello everyone. I am trying to solve a problem whose statement reads as follows: Neutron stars have radii of ##\sim 10## km. If we assume that before the collapse the nucleus of the white dwarf precursor has a mass equal to that of Chandrasekhar, estimate the energy generated in the collapse...
  16. A

    Magnetic flux in a white dwarf

    Homework Statement The sun has a rotational period of 25 days. Finding the rotational period if it can shrink to form a white dwarf (##R_{WD}=10^3Km##). Knowing that the density of magnetic flux of the Sun on the surface is ##1 Gauss##, finding the magnetic flux of the white dwarf. Homework...
  17. |Glitch|

    I What is the New White Dwarf Mass Limit?

    For the last 88 years we have used Subrahmanyan Chandrasekhar's calculations to determine the maximum mass of a white dwarf. As a result of that calculated mass limit, a peak brightness was derived and the Standard Candle was born. However, those calculations were made based upon certain...
  18. MathematicalPhysicist

    Stability of a White Dwarf Against Gravitational Collapse

    Homework Statement I have a problem with question (b), in what follows there's a quote of the problem and its solution. (again from Bergersen's and Plischke's textbook). Homework EquationsThe Attempt at a Solution [/B] My problem is with the last expression in (d) I get 54 instead of 36. To...
  19. Ryaners

    Mass-radius relation of a white dwarf - calculating radius

    Homework Statement Calculate the radius of a 1.3 Msun white dwarf using the mass-radius relation for white dwarfs. Give the answer in solar radius. Homework Equations Mass-radius relation: $$R \propto M^{-\frac{1}{3}}$$ The Attempt at a Solution So I've tried the following: $$R_{D} \propto...
  20. J

    B Surface Temperatures - White Dwarf vs Neutron Star

    Hi, My textbook has a multiple choice question about which stellar object has the highest surface temperature and the answer was a white dwarf. However, one of the options was a neutron star. Neutron stars are much denser and have been crushed by gravity even more plus they are rotating at...
  21. Leonardo Machado

    A Chandrasekhar Mass - White Dwarf

    Hello guys. I'm working to compute de max. mass for a white dwarf through solving the hidrostatic equilibrium equations. ( The classical ones, not TOV), and using an EoS made by my own, that considers the Fermi Pressure and stuff. When i use the EoS for a carbon white dwarf ( i do get the...
  22. M

    I What is the similarity between the spectra of white dwarfs and the sun?

    Hello, I read at a couple of places about white dwarfs having a spectrum similar to that of the sun. What does that mean or associate to? Thanks in advance.
  23. A

    What's the most massive white dwarf in the MW?

    I'm curious. I want to model it to understand stellar evolution better. Does anyone know what the most massive single white dwarf is?
  24. A

    Neutron Stars from White Dwarf Mergers: Under 1.4 SM?

    I think this could be a good chance that we see how neutron stars form from White Dwarf mergers. The combined mass of the two are less that than required for a type Ia Supernovae. Won't they merge and collapse into a neutron star? What does everyone else think might happen. I want to be sure if...
  25. Zeedr

    Is this idea remotely possible in the distant future?

    Hello, I was just brainstorming for futuristic inventions with context for a sci-fi, high fidelity game (because I'm too cool to revise for exams) - and I thought of one, but my physics and engineering knowledge is at best sketchy when it comes to gravity and nuclear fusion combinations, I was...
  26. B

    What is the semantic error in my code

    Note that the code I am using is Python. Currently, I am attempting to numerically solve the equations of state that give rise to the Chandrasekar limit for a white dwarf star. My code works for a simple harmonic oscillator given the correct equations of motion, but does not compute the correct...
  27. virgil1612

    Evolution toward a white dwarf

    Hello, I will need to talk to students about the evolution of a solar-like star. We will look at a diagram like the following: It will be a descriptive presentation, no mathematics. I know pretty well what happens until the formation of the carbon core. The linear upper line happens because...
  28. M

    White dwarf mass-radius relationship

    The mass-radius relationship for a white dwarf star is defined by : R= (9pi)^0.66 /8 * h^2/m1 * 1/(Gm2^1.66*M^.333), where m1= electron mass, m2=proton mass, G=grav. constant, h=planck's constant I want to take a proportion with the solar mass and solar radius, which would involve a division...
  29. avito009

    Why is stellar ash found in the core of a White Dwarf so dense?

    A normal star's core consists of Hydrogen but a white dwarf is itself the core and it consists of stellar ash. So the degeneracy pressure is exerted when this stellar ash becomes very dense (In other words when the white dwarf becomes very dense). Am I right? The density of a white dwarf is so...
  30. C

    What are some recommended books on white dwarf stars?

    Hi fellas, I have taken white dwarf stars as my undergrad thesis choice, so I need some suggestion on good books on dwarf. please suggest me books for both reading and for some mathematical derivations regarding the white dwarf
  31. C

    The application of of Fermi Dirac statistics in the white dwarf

    hi guys, I wonder if I have fully understood the Fermi Dirac statistics properly, but I have a question on it regarding its application in the white dwarf research. I read the Fermi energy is applicable for T=0, now if the core of a white dwarf is too hot then how can we apply the Fermi Dirac...
  32. C

    Chandrashekhar paper on white dwarf

    dear friends, can I get a link to the original paper by Chandrashekhar where he derived the limit for white dwarf? also you can suggest me other good papers deriving the limit. regards
  33. K

    The energy released for white dwarf collapsing into neutron star

    The question is attached. I'm not sure how to approach to part (b). The energy released could be in 3 forms, the rest mass energy for those matter ejected during supernova explosion, the binding energy released as the atomic structure changed, the ejected matter carries off some kinetic...
  34. Astronuc

    PSR J0348+0432, Pulsar with white dwarf companion

    Apparently this binary system is providing yet further confirmation of GR. It is only the second NS with a precisely determined mass ~ 2 solar masses. Pulsar-White Dwarf Pair Proves Einstein’s Theory of Relativity http://www.sci-news.com/astronomy/article01046.html...
  35. H

    Astrophysics- White dwarf collapse

    Homework Statement Calculate the kinetic energy generated when a white dwarf in a binary system accretes enough material to increase its mass beyond the Chandrasekhar limit (1.4 solar masses) and collapse to the radius of a neutron star. radius of white dwarf- 5520 km radius of neutron...
  36. C

    Schools White Dwarf Research in North America: Schools, Professors, Programs

    My advanced statistical mechanics professor claimed that there were very few doctorate-granting schools in North America doing research in white dwarves. While that professor might have some fame as far as white dwarf research is concerned (along with Winget, that professor is one of the biggest...
  37. P

    White dwarf mass-radius relationship

    instead of typing it out, here is the problem I know what to do, my math just isn't good enough to combine the equations properly. Been at it a few hours, brain hurts, please help!
  38. K

    Energy from White Dwarf Thermonuclear Runaway

    Hello! Homework Statement The question is "Calculate the energy released if a 1 solar mass white dwarf undergoes a thermonuclear runaway and converts 0.5 solar mass of carbon (A=12) to iron (A=56)." I've only ever done nuclear equations with hydrogen fusion, with four hydrogens to one...
  39. C

    White dwarf mass-radius relation

    Homework Statement Compute the numerical constant C for an electron gas (take Z = 6 and A = 12) and determine the radius of a white dwarf whose mass is 0.6 solar masses. h\ =\ 6.62606876(52)\ \times\ 10^{-34}\ Jh\ =\ 6.62606876(52)\ \times\ 10^{-34}\ J\ s\ s m_{e}\ =\ 9.10938188(72)\...
  40. Dotini

    White Dwarf, 12 Billion Years Old, Found Only 100LY Away

    What a wonderful coincidence to find such an old star so close by! http://phys.org/news/2012-04-astronomers-billion-year-old-white-dwarf-stars.html Respectfully submitted, Steve
  41. S

    Velocity of an apple before strikes the surface of a white dwarf.

    Homework Statement An apple is dropped from a height of 12.8*10^6 m above the surface of the white dwarf. With what speed does the apple strike the surface of the white dwarf? M of white dwarf= 1.99*10^30 gravity of white dwarf= 3.29*10^6 Homework Equations Vf^2=Vi^2+2a(deltaX)...
  42. M

    Neutron star and white dwarf material

    Neutron stars are held together by extremely strong gravitational force. What would happen to a chunk of the star if it had been removed and left to stand alone? Same question for a chunk of a white dwarf?
  43. B

    Can we explore white dwarfs with robotic missions?

    Hi all, If we develop the right kind of space ships, would it be possible to do non-human robotic missions to a white dwarf? What would it be like?
  44. H

    How Bright Would a White Dwarf Appear if It Replaced the Sun?

    Homework Statement This is a past exam question that I am trying to get my head around but keep getting stuck Show that if a white dwarf were at the centre of the solar system instead of the sun, it would have an apparent visual brightness of -18.6mag. Assume that the white dwarf has surface...
  45. Q

    Can Pure Helium White Dwarfs Support a Habitable Zone for Billions of Years?

    Just pondering Eric Agol's recent paper on White Dwarf habitable zones and the pace of cooling of white dwarfs (WDs.) He uses models of Carbon core WDs with helium atmospheres, but I am wondering if pure helium WDs would last three times longer. Opacity from the atmosphere slows down heat loss...
  46. S

    Source of energy for white dwarf and neutron star

    I know that nuclear fusion is the source of energy for our sun and most of the other stars. Neutron stars and white dwarfs have very high surface temperatures. What is the source of their energy?
  47. S

    White Dwarf Star Coupled Runge-Kutta

    Homework Statement Use a coupled fourth order Runge-Kutta, to find the structure of white dwarf stars. I think I am applying the Runge-kutta method wrong? Variables defined in C code notes Homework Equations Equations in c code. and in attached images. The Attempt at a Solution This is...
  48. V

    The Complex Relationship Between Mass & Volume in a White Dwarf

    We have the rate of change of number of electrons with energy directly proportional to the volume in an 3-D potential well. For a white dwarf, the mass is inversely proportional to its volume. If we consider the electrons in a white dwarf to be in such a potential well, dN/dE becomes...
  49. H

    Question about black holes and white dwarf

    hi i want to ask aquestion what is the biggest qatar: black hole or white dwarf or nutron star or the sun please i want to know the biggest one and then and then and the smallest one thaaaank you very much
  50. P

    Understanding White Dwarf Temperature

    So after a long time I finally figured out how the white Dwarf classification system works. Basically its first the letter D Followed by a temperature Correct me if I am wrong but, DO, DB, DC, DZ white dwarfs are associated with a specific effective temperature of the star. However...