Consumption of a galaxy by its central black hole

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Discussion Overview

The discussion revolves around the behavior of supermassive black holes (SMBHs) at the centers of galaxies, particularly regarding their consumption of surrounding matter, the implications for galaxy structure, and the nature of black holes in relation to dark matter and dark energy. Participants explore theoretical aspects, potential limits on black hole growth, and the dynamics of matter in galactic systems.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant questions whether a black hole can consume an entire galaxy over time and asks about the existence of size limits for black holes and their interaction with dark matter and dark energy.
  • Another participant suggests that while mass in a galaxy may eventually fall into the black hole, this process occurs over an incredibly long timescale, and black holes may eventually evaporate due to Hawking radiation.
  • A different participant clarifies that supermassive black holes do not continuously consume material and that their presence does not destabilize the orbits of surrounding stars and planets. They emphasize that black holes are not like vacuum cleaners and that the orbits of celestial bodies would remain unchanged if a star were replaced by a black hole of equal mass.
  • This participant also states that there is no size limit for black holes, noting that they can grow indefinitely and can consume dark matter, but not dark energy, which does not contribute to mass or gravity.
  • A later reply expresses gratitude for the clarification regarding the stability of systems with black holes, indicating a better understanding of the topic.

Areas of Agreement / Disagreement

Participants express differing views on the consumption of galaxies by black holes, the nature of black hole growth, and the effects of black holes on their surrounding systems. There is no consensus on the implications of these factors, and the discussion remains unresolved.

Contextual Notes

Participants acknowledge the complexity of black hole interactions with various forms of matter and energy, highlighting uncertainties regarding the long-term dynamics of galaxies and the role of dark energy.

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I was thinking about the supermassive black hole that is theorized to be at the center of our galaxy, and indeed, at the center of most galaxies. If that black hole is continuously consuming the stars, planets and gas around it, given enough time, will it not consume the entire galaxy that orbits it? Or is there a size limit for black holes? Do they just keep adding mass as long as there is matter and energy to consume? Does this include dark matter and dark energy? Are they affected by black holes like ordinary matter?

I have more, but the next questions depend on the answers to these. Thanks for any help.
 
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It was my own very limited understanding that the mass in a galaxy will eventually fall into the black hole in the centre. Just over an incredibly large timescale. THen these black hole will eventually evaporate due to Hawking radiation, leaving a universe full of leptons.
 
Supermassive black holes do not continuously suck up material. For example, the SMBH in the center of our galaxy currently has nothing to suck up. Orbital interactions between the nearby stars may swing one near enough to be torn apart, but this doesn't happen that often. (Depending on what time scale you're talking about)

Put simply, black holes, of any type, are not like vacuum cleaners. If the Sun were suddenly replaced by an equal mass black hole, nothing would happen to the Earth or any of the other planets. (Other than suddenly losing all of our light, obviously) Our orbits would remain exactly the same.

Or is there a size limit for black holes? Do they just keep adding mass as long as there is matter and energy to consume? Does this include dark matter and dark energy? Are they affected by black holes like ordinary matter?

There is no size limit. They grow to any size. It would include dark matter, but not dark energy. Dark energy is not "energy" in the usual sense, and does not add to mass or gravity.
 
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Ah...well, that answers that. I think the piece I was missing is that the presence of a black hole in any system doesn't necessarily destabilize that system. Thank you all for helping me understand this better. I think I get it now.
 

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