Blackhole at the center of each galaxy, think again

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Discussion Overview

The discussion revolves around the existence of massive black holes at the centers of galaxies, particularly focusing on observational evidence and theoretical implications. Participants explore the dynamics of stars near the galactic center, the visibility of these stars, and the challenges in observing black holes in various galaxies.

Discussion Character

  • Debate/contested
  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants argue that if a massive black hole exists at the center of a galaxy, stars should orbit it at high speeds, allowing for observable revolutions in a short time frame.
  • Others note that while stars do move rapidly near the Milky Way's center, the presence of gas and dust makes it difficult to observe similar phenomena in other galaxies.
  • It is suggested that black holes are relatively small, making the likelihood of them eclipsing neighboring stars very low.
  • Some participants propose that while black holes may not hide stars, gravitational lensing could make their effects observable.
  • There is mention of existing evidence for black holes in some galaxies, though the specifics of this evidence are not detailed in the discussion.
  • Participants express frustration over perceived attitudes in responses, indicating a meta-discussion about communication styles within the thread.
  • Some argue that while we cannot see the core of our galaxy due to dust, advancements in infrared technology are beginning to allow observations of the galactic center.
  • Concerns are raised about the feasibility of observing individual stars in the cores of distant galaxies due to the required technology and resolution.

Areas of Agreement / Disagreement

Participants generally disagree on the implications and evidence surrounding black holes at galaxy centers. While some assert that evidence exists for their presence, others challenge the conditions under which such evidence can be observed, leading to an unresolved discussion.

Contextual Notes

Limitations include the dependence on observational technology, the obscuring effects of dust, and the unresolved nature of the evidence for black holes in various galaxies.

  • #31
Chandra Observations

I'm surprised these haven't been mentioned in this context:

http://http://www.sciencedaily.com/print.php?url=/releases/2005/01/050111090506.htm

I think stuff is awesome because it demonstrates well both the curvature of space and the illusion of dimension from outside the core. That is, while we might measure the diameter in light years from our perspective using angular measurement the actual dimensions from the perspective within the core may very well be much larger.

Clearly our understanding of "Black Holes" is still in its infancy.
 
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  • #32
The evidence indicating SMBH reside in the cores of most, if not all reasonably sized galaxies, is not derived from observations of individual stars. That is well beyond our technology. It is hard enough to resolve individual stars in the core of our own galaxy. Some armchair material to consider:

http://webdisk.berkeley.edu/~kshapiro/cosmo_project.htmlhttp://webdisk.berkeley.edu/~kshapiro/cosmo_project.html
 
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  • #34
SpaceTiger said:
This is an observational upper limit, meaning the black hole must be smaller than that (we can't actually see it). In actuality, it's probably more like 25 light-seconds wide.
The 20 light minutes probably refers to the diameter of an accretion disc around the BH.

Garth
 
  • #35
Garth said:
The 20 light minutes probably refers to the diameter of an accretion disc around the BH.

No, we have not imaged an accretion disk around the black hole in our galaxy. They simply give numbers like this to support the idea that the object is a black hole. They can't acutally observe the event horizon itself, so they don't say that it's light-seconds across. They look at the motions of objects around it and use those place to dynamical limits on the extent of the object.
 

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