scholarly journals Existence of Chandrasekhar’s limit in generalized uncertainty white dwarfs

2021 ◽  
Vol 8 (6) ◽  
pp. 210301
Author(s):  
Arun Mathew ◽  
Malay K. Nandy
Keyword(s):  
General Relativity ◽  
Stability Analysis ◽  
Gravitational Collapse ◽  
White Dwarfs ◽  
Generalized Uncertainty Principle ◽  
Compact Objects ◽  
Dynamical Instability ◽  
Astronomical Observations ◽  
Theoretical Investigations ◽  
Chandrasekhar Limit

The existence of Chandrasekhar’s limit has played various decisive roles in astronomical observations for many decades. However, various recent theoretical investigations suggest that gravitational collapse of white dwarfs is withheld for arbitrarily high masses beyond Chandrasekhar’s limit if the equation of state incorporates the effect of quantum gravity via the generalized uncertainty principle. There have been a few attempts to restore the Chandrasekhar limit but they are found to be inadequate. In this paper, we rigorously resolve this problem by analysing the dynamical instability in general relativity. We confirm the existence of Chandrasekhar’s limit as well as stable mass–radius curves that behave consistently with astronomical observations. Moreover, this stability analysis suggests gravitational collapse beyond the Chandrasekhar limit signifying the possibility of compact objects denser than white dwarfs.

The stellar graveyard

2019 ◽  
pp. 177-206
Author(s):  
Nils Andersson
Keyword(s):  
Black Holes ◽  
General Relativity ◽  
Neutron Stars ◽  
Gravitational Wave ◽  
Stellar Evolution ◽  
White Dwarfs ◽  
Supermassive Black Holes ◽  
Compact Objects ◽  
Fermi Gases ◽  
The 1950S

This chapter introduces the different classes of compact objects—white dwarfs, neutron stars, and black holes—that are relevant for gravitational-wave astronomy. The ideas are placed in the context of developing an understanding of the likely endpoint(s) of stellar evolution. Key ideas like Fermi gases and the Chandrasekhar mass are discussed, as is the emergence of general relativity as a cornerstone of astrophysics in the 1950s. Issues associated with different formation channels for, in particular, black holes are considered. The chapter ends with a discussion of the supermassive black holes that are found at the centre of galaxies.

Accretion-Induced Collapse of Old White Dwarfs

1987 ◽  
Vol 93 ◽  
pp. 665-669
Author(s):  
J. Isern ◽  
R. Canal ◽  
M. Hernanz ◽  
J. Labay
Keyword(s):  
Neutron Stars ◽  
Gravitational Collapse ◽  
White Dwarfs ◽  
Binary Systems ◽  
Observational Evidence ◽  
Dynamical Instability ◽  
Thermonuclear Explosion

AbstractThere is observational evidence of the presence of young neutron stars in old binary systems. A likely explanation is that those neutron stars were produced in the collapse of old CO white dwarfs. We show how mass accretion on initially solid white dwarfs can leave central solid cores when dynamical instability sets in and we study the different effects of the existence of such cores on the outcome of the competition between thermonuclear explosion and gravitational collapse.

Introduction

2018 ◽  
Author(s):  
Flavio Mercati
Keyword(s):  
Field Theory ◽  
General Relativity ◽  
Gravitational Collapse ◽  
Present State ◽  
Strong Gravity ◽  
Shape Dynamics

Shape Dynamics (SD) is a field theory that describes gravity in a different way than General Relativity (GR): it assumes a preferred notion of simultaneity, and the dynamical content of the theory consists of conformal 3- geometries. SD coincides with (GR) in most situations, in particular in the experimentally well-tested regimes, but it departs from it in some strong-gravity situations, for example at cosmological singularities or upon gravitational collapse. This chapter provides a quick introduction to the theory and a brief description of its present state.

THE GRAVITATIONAL ORIGIN OF THE DISTINCTION BETWEEN SPACE AND TIME

2009 ◽  
Vol 18 (14) ◽  
pp. 2155-2158 ◽  
Author(s):  
ASHER YAHALOM
Keyword(s):  
General Relativity ◽  
Stability Analysis ◽  
Linear Stability ◽  
Linear Stability Analysis ◽  
Flat Space ◽  
Gravitational Theory ◽  
Clear Distinction ◽  
Temporal Dimension ◽  
Spatial Dimensions ◽  
Standard Presentation

To the ordinary human it is obvious that there is a clear distinction between the spatial dimensions, in which one can go either way, and the temporal dimension, in which one seems only to move forward. But the uniqueness of time is also rooted in the standard presentation of general relativity, in which the metric of space–time is locally Lorentzian, i.e. ημν = diag (1, -1, -1, -1). This is presented as an independent axiom of the theory, which cannot be deduced. In this essay I will claim otherwise. I will show that the existence of time should not be enforced on the gravitational theory of general relativity but rather should be deduced from it. The method of choice is linear stability analysis of flat space–times.

scholarly journals The most massive white dwarfs in the solar neighbourhood

2021 ◽  
Vol 503 (4) ◽  
pp. 5397-5408
Author(s):  
Mukremin Kilic ◽  
P Bergeron ◽  
Simon Blouin ◽  
A Bédard
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Transverse Velocity ◽  
Maximum Mass ◽  
Model Calculations ◽  
Rapid Rotation ◽  
Rotation Rates ◽  
Binary Mergers ◽  
Chandrasekhar Limit

ABSTRACT We present an analysis of the most massive white dwarf candidates in the Montreal White Dwarf Database 100 pc sample. We identify 25 objects that would be more massive than $1.3\, {\rm M}_{\odot }$ if they had pure H atmospheres and CO cores, including two outliers with unusually high photometric mass estimates near the Chandrasekhar limit. We provide follow-up spectroscopy of these two white dwarfs and show that they are indeed significantly below this limit. We expand our model calculations for CO core white dwarfs up to M = 1.334 M⊙, which corresponds to the high-density limit of our equation-of-state tables, ρ = 109 g cm−3. We find many objects close to this maximum mass of our CO core models. A significant fraction of ultramassive white dwarfs are predicted to form through binary mergers. Merger populations can reveal themselves through their kinematics, magnetism, or rapid rotation rates. We identify four outliers in transverse velocity, four likely magnetic white dwarfs (one of which is also an outlier in transverse velocity), and one with rapid rotation, indicating that at least 8 of the 25 ultramassive white dwarfs in our sample are likely merger products.

ON THE POSSIBILITY OF FORMING ACCRETION INDUCED COLLAPSE IN MASSIVE CATACLYSMIC VARIABLES

2013 ◽  
Vol 23 ◽  
pp. 284-288
Author(s):  
ALI TAANI ◽  
MASHHOOR AL-WARDAT ◽  
YONGHENG ZHAO
Keyword(s):  
Cataclysmic Variables ◽  
Compact Objects ◽  
Significant Fraction ◽  
Formation And Evolution ◽  
Orbital Periods ◽  
Chandrasekhar Limit

We investigate the process of Accretion Induced Collapse (AIC) during the evolution of massive Cataclysmic Variables (CVs) type binaries, which possibly to occur in our galaxy. The relation between spin periods and orbital periods in different nature of compact objects in binaries, is investigated. We study also the implication and application of the AIC process of the MSPs population. We conclude that a significant fraction of MSPs may originate from AIC (4 - 40%). Hence, massive CVs are of key importance for the formation and evolution of binary MSPs, once they reach the Chandrasekhar limit then collapse to becomes an NS, or blow as apart in a supernova, consequently impart significant kick to the companion and creating long orbital periods. In some cases, this process disrupts the system and creates a single MSP.

scholarly journals Hot DQ white dwarfs: a pulsational test of the mixing scenario for their formation

2009 ◽  
Vol 5 (H15) ◽  
pp. 370-370
Author(s):  
A. Romero ◽  
A. H. Córsico ◽  
L. G. Althaus ◽  
E. García-Berro
Keyword(s):  
Stability Analysis ◽  
White Dwarf ◽  
White Dwarfs ◽  
Evolutionary Models ◽  
Instability Strip ◽  
Dwarf Stars ◽  
Photometric Variability ◽  
New Class ◽  
White Dwarf Stars ◽  
Born Again

Hot DQ white dwarfs constitute a new class of white dwarf stars, uncovered recently within the framework of SDSS project. There exist nine of them, out of a total of several thousands white dwarfs spectroscopically identified. Recently, three hot DQ white dwarfs have been reported to exhibit photometric variability with periods compatible with pulsation g-modes. In this contribution, we presented the results of a non-adiabatic pulsation analysis of the recently discovered carbon-rich hot DQ white dwarf stars. Our study relies on the full evolutionary models of hot DQ white dwarfs recently developed by Althaus et al. (2009), that consistently cover the whole evolution from the born-again stage to the white dwarf cooling track. Specifically, we performed a stability analysis on white dwarf models from stages before the blue edge of the DBV instability strip (Teff ≈ 30000 K) until the domain of the hot DQ white dwarfs (18000-24000 K), including the transition DB→hot DQ white dwarf. We explore evolutionary models with M*= 0.585M⊙ and M* = 0.87M⊙, and two values of thickness of the He-rich envelope (MHe = 2 × 10−7M* and MHe = 10−8M*).

Compact Objects in General Relativity and Beyond

2021 ◽  
pp. 329-355
Author(s):  
Jose Luis Blázquez-Salcedo ◽  
Burkhard Kleihaus ◽  
Jutta Kunz
Keyword(s):  
General Relativity ◽  
Compact Objects

scholarly journals Asymptotically flat vacuum solution in modified theory of Einstein’s gravity

2019 ◽  
Vol 79 (10) ◽  
Author(s):  
Surajit Kalita ◽  
Banibrata Mukhopadhyay
Keyword(s):  
General Relativity ◽  
Vacuum Solution ◽  
Compact Objects ◽  
Schwarzschild Solution ◽  
Asymptotically Flat ◽  
Symmetric Vacuum ◽  
Theory Of Gravity ◽  
Bound Orbits ◽  
Vacuum Spacetime ◽  
The Universe

Abstract A number of recent observations have suggested that the Einstein’s theory of general relativity may not be the ultimate theory of gravity. The f(R) gravity model with R being the scalar curvature turns out to be one of the best bet to surpass the general relativity which explains a number of phenomena where Einstein’s theory of gravity fails. In the f(R) gravity, behaviour of the spacetime is modified as compared to that of given by the Einstein’s theory of general relativity. This theory has already been explored for understanding various compact objects such as neutron stars, white dwarfs etc. and also describing evolution of the universe. Although researchers have already found the vacuum spacetime solutions for the f(R) gravity, yet there is a caveat that the metric does have some diverging terms and hence these solutions are not asymptotically flat. We show that it is possible to have asymptotically flat spherically symmetric vacuum solution for the f(R) gravity, which is different from the Schwarzschild solution. We use this solution for explaining various bound orbits around the black hole and eventually, as an immediate application, in the spherical accretion flow around it.

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