Density of Black Holes: Unveiling the Universe's Secrets

In summary, the paper discusses the effect of modified theories of gravity on the expected signal of an unresolved background of gravitational waves produced by coalescing binary black holes. The authors use simulations to analyze the detectability of this background by ground-based interferometers and find that Advanced LIGO could potentially set constraints on these modified theories. This work has implications for improving current bounds obtained from astrophysical observations of binary pulsars.
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wolram

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It seems by this paper that there are more black holes than expected, so what is the expected density of black holes in the nearby universe?

arXiv:1606.04996 (cross-list from gr-qc) [pdf, other]
Constraining modified theories of gravity with gravitational wave stochastic background
Andrea Maselli, Stefania Marassi, Valeria Ferrari, Kostas Kokkotas, Raffaella Schneider
Comments: 5 pages, 4 figures
Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Astrophysical Phenomena (astro-ph.HE)

The direct discovery of gravitational waves has finally opened a new observational window on our Universe, suggesting that the population of coalescing binary black holes is larger than previously expected. These sources produce an unresolved background of gravitational waves, potentially observables by ground-based interferometers. In this paper we investigate how modified theories of gravity, modeled using the ppE formalism, affect the expected signal, and analyze the detectability of the resulting stochastic background by current and future ground-based interferometers. We find the constraints that AdLIGO would be able to set on modified theories, showing that they may significantly improve the current bounds obtained from astrophysical observations of binary pulsars.
 
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  • #2
wolram said:
It seems by this paper that there are more black holes than expected, so what is the expected density of black holes in the nearby universe?

arXiv:1606.04996 (cross-list from gr-qc) [pdf, other]
Constraining modified theories of gravity with gravitational wave stochastic background
Andrea Maselli, Stefania Marassi, Valeria Ferrari, Kostas Kokkotas, Raffaella Schneider
Comments: 5 pages, 4 figures
Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Astrophysical Phenomena (astro-ph.HE)

The direct discovery of gravitational waves has finally opened a new observational window on our Universe, suggesting that the population of coalescing binary black holes is larger than previously expected. These sources produce an unresolved background of gravitational waves, potentially observables by ground-based interferometers. In this paper we investigate how modified theories of gravity, modeled using the ppE formalism, affect the expected signal, and analyze the detectability of the resulting stochastic background by current and future ground-based interferometers. We find the constraints that AdLIGO would be able to set on modified theories, showing that they may significantly improve the current bounds obtained from astrophysical observations of binary pulsars.
This isn't an experimental paper. They're running simulations on what Advanced LIGO might be able to detect in the future.

The statement in the first sentence is just the statement that because we have detected the merger of some intermediate-mass black holes (which were theorized but not known to exist until now), there may be quite a few black holes out there. The difficulty is that it's not really possible to say how many such black holes there are with a sample size of two. Give it a few years.
 

1. What is the density of a black hole?

The density of a black hole is extremely high, as it is a region of space where the gravitational pull is so strong that even light cannot escape. The density is typically measured in terms of solar masses per cubic kilometer, and can range from millions to billions of solar masses per cubic kilometer.

2. How is the density of a black hole calculated?

The density of a black hole is calculated using the mass and volume of the black hole. The mass can be determined by observing the orbital motion of objects around the black hole, while the volume can be estimated based on the size of the event horizon. Using these values, the density can be calculated using the formula D = M/V, where D is density, M is mass, and V is volume.

3. What is the relationship between the density of a black hole and its size?

The density of a black hole is inversely proportional to its size. This means that as the size of a black hole increases, its density decreases. This may seem counterintuitive, but it is due to the fact that the volume of a black hole increases much faster than its mass, leading to a lower overall density.

4. Can the density of a black hole change over time?

Yes, the density of a black hole can change over time if it is actively accreting matter. As matter falls into the black hole, it increases the mass and therefore decreases the density. However, this change in density is minimal and does not affect the overall properties of the black hole significantly.

5. Why is it important to study the density of black holes?

The density of black holes is important because it provides valuable information about the mass and size of these mysterious objects. By studying the density, scientists can better understand how black holes form and evolve, as well as their role in shaping the structure and evolution of galaxies. Additionally, the density of black holes can help us understand the fundamental laws of physics in extreme conditions, such as those found within the event horizon of a black hole.

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