📝 Original Info
- Title: Astrophysical Black Holes in the Physical Universe
- ArXiv ID: 1003.0291
- Date: 2011-09-19
- Authors: Researchers from original ArXiv paper
📝 Abstract
In this chapter I focus on asking and answering the following questions: (1) What is a black hole? Answer: There are three types of black holes, namely mathematical black holes, physical black holes and astrophysical black holes. An astrophysical black hole, with mass distributed within its event horizon but not concentrated at the singularity point, is not a mathematical black hole. (2) Can astrophysical black holes be formed in the physical universe? Answer: Yes, at least this can be done with gravitational collapse. (3) How can we prove that what we call astrophysical black holes are really black holes? Answer: Finding direct evidence of event horizon is not the way to go. Instead I propose five criteria which meet the highest standard for recognizing new discoveries in experimental physics and observational astronomy. (4) Do we have sufficient evidence to claim the existence of astrophysical black holes in the physical universe? Answer: Yes, astrophysical black holes have been found at least in some galactic binary systems, at the center of almost every galaxy, and as the central engines of at least some long gamma-ray bursts. (5) Will all matter in the universe eventually fall into black holes? Answer: Probably "no", because "naked" compact objects, if they do exist with radii smaller than the radii of event horizons for their masses but are not enclosed by event horizons, can rescue the universe from an eternal death by re-cycling out the matter previously accreted into astrophysical black holes. Finally I also discuss briefly if we need a quantum theory of gravity in order to further understand astrophysical black holes, and what further astronomical observations and telescopes are needed to make further progress on our understanding of astrophysical black holes.
💡 Deep Analysis
Deep Dive into Astrophysical Black Holes in the Physical Universe.
In this chapter I focus on asking and answering the following questions: (1) What is a black hole? Answer: There are three types of black holes, namely mathematical black holes, physical black holes and astrophysical black holes. An astrophysical black hole, with mass distributed within its event horizon but not concentrated at the singularity point, is not a mathematical black hole. (2) Can astrophysical black holes be formed in the physical universe? Answer: Yes, at least this can be done with gravitational collapse. (3) How can we prove that what we call astrophysical black holes are really black holes? Answer: Finding direct evidence of event horizon is not the way to go. Instead I propose five criteria which meet the highest standard for recognizing new discoveries in experimental physics and observational astronomy. (4) Do we have sufficient evidence to claim the existence of astrophysical black holes in the physical universe? Answer: Yes, astrophysical black holes have been foun
📄 Full Content
163
10 Astrophysical Black Holes
in the Physical Universe
Shuang-Nan Zhang
IntroductIon
In modern astronomy, the mystery of black holes (BHs) attracts extraordinary interest for both
researchers and the general public. Through the 1930s, the applications of general relativity and
quantum mechanics to the studies of the late evolution of stars predicted that stars with different
initial masses, after exhausting their thermal nuclear energy sources, may eventually collapse to
become exotic compact objects, such as white dwarfs, neutron stars, and BHs. A low-mass star,
such as our Sun, will end up as a white dwarf, in which the degeneracy pressure of the electron
gas balances the gravity of the object. For a more massive star, the formed compact object can be
more massive than around 1.4 solar masses (M⊙), the so-called Chandrasekhar limit, in which the
degeneracy pressure of the electron gas cannot resist the gravity, as pointed out by Chandrasekhar.
In this case, the compact object has to further contract to become a neutron star, in which most of
the free electrons are pushed into protons to form neutrons and the degeneracy pressure of neutrons
balances the gravity of the object, as suggested by Zwicky and Landau. Then as Oppenheimer and
others noted, if the neutron star is too massive, for example, more than around 3 M⊙, the internal
pressure in the object also cannot resist the gravity and the object must undergo catastrophic col-
lapse and form a BH.
contents
Introduction .................................................................................................................................... 163
What Is a Black Hole? ...................................................................................................................164
Can Astrophysical Black Holes Be Formed in the Physical Universe? .........................................164
How Can We Prove That What We Call Astrophysical Black Holes Are Really Black Holes? .... 169
Do We Have Sufficient Evidence to Claim the Existence of Astrophysical Black Holes in the
Physical Universe? ......................................................................................................................... 169
Luminous Accreting Black Holes ............................................................................................. 170
Faint Accreting Black Holes ..................................................................................................... 172
The Supermassive Black Hole at the Center of the Milky Way ................................................ 172
Comparison with Accreting Neutron Stars ............................................................................... 175
Isolated Black Holes ................................................................................................................. 175
Luminous “Naked” Compact Objects? ..................................................................................... 176
Relativistic Jets .......................................................................................................................... 177
Gamma-Ray Bursts ................................................................................................................... 177
Putting It All Together: Astrophysical Black Holes Have been Detected ................................. 178
Will All Matter in the Universe Eventually Fall into Black Holes? ............................................... 180
Summary, Concluding Remarks, and Future Outlooks ................................................................. 181
Acknowledgments .......................................................................................................................... 183
References ...................................................................................................................................... 183
164
The Astronomy Revolution: 400 Years of Exploring the Cosmos
Up to now, about 20 BHs with masses around 10 M⊙, called stellar-mass BHs, have been identi-
fied observationally. On the other hand, the concept of a BH has been extended to galactic scales.
Since the discovery of quasars in the 1960s, these BHs with masses between 105 and 1010 M⊙,
which are called supermassive BHs, are believed to be located in the centers of almost all galaxies.
Therefore, tremendous observational evidence supporting the existence of BHs in the Universe is
gradually permitting the uncovering of the mysteries of BHs. BH astrophysics has become a fruitful,
active, and also challenging frontier research field in modern astrophysics.
Despite tremendous progress in BH research, many fundamental characteristics of astrophysical
BHs in the physical Universe remain not fully understood or clarified. In this chapter, I will try to
address the following questions: (1) What is a BH? (2) Can astrophysical BHs be formed in the physi-
cal Universe? (3) How can we prove that what we call astrop
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Reference
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