So, I've been listening to course lectures on the modern state of astronomy and cosmology. I can keep with most if it (helps that it's intro level), but there are some things the professor skims over that I wish would be more fully fleshed out.
As I understand it, scientists have concluded that dark matter must exist since the observed rotational velocities don't match the estimated mass of a given galaxy. This seems to have been concluded prior to the observation (and measurement) of supermassive black holes, but I might have some of the dates wrong. From what I understand, the mass of supermassive black holes is estimated in part by these same observed rotational velocities. However, as best I can tell the mass of these supermassive black holes are rough estimates, in some cases with a margin of error of +/- 15 billion solar masses. That seems like a pretty huge range.
What I don't understand, then, is why the presence of these supermassive black holes and their estimated mass doesn't account for the supposed discrepancies that gave rise to the suggestion of dark matter. Things like gravitational lensing and faster-than-expected rotational velocities would, to me, indicate that perhaps our estimate of supermassive black hole masses are instead quite low. I'm going to provide as a bit of vindication this particular article:
So...what am I missing? Is the actual mass of these supermassive black holes not enough to account for the missing matter? Are existing methods for measuring these masses accurate enough to suggest there is still missing matter to be found? As far as I can tell, we've spent 40+ years looking for dark matter without much success, and I'm definitely not sure I understand why we're still convinced it's a real thing. FWIW, I don't actually mind if it's a thing or not. I'm just trying to understand why we think it is, especially in the face of 'new' discoveries and information about things like supermassive black holes.
As I understand it, scientists have concluded that dark matter must exist since the observed rotational velocities don't match the estimated mass of a given galaxy. This seems to have been concluded prior to the observation (and measurement) of supermassive black holes, but I might have some of the dates wrong. From what I understand, the mass of supermassive black holes is estimated in part by these same observed rotational velocities. However, as best I can tell the mass of these supermassive black holes are rough estimates, in some cases with a margin of error of +/- 15 billion solar masses. That seems like a pretty huge range.
What I don't understand, then, is why the presence of these supermassive black holes and their estimated mass doesn't account for the supposed discrepancies that gave rise to the suggestion of dark matter. Things like gravitational lensing and faster-than-expected rotational velocities would, to me, indicate that perhaps our estimate of supermassive black hole masses are instead quite low. I'm going to provide as a bit of vindication this particular article:
"The calculations of the mass (weight) of the supermassive black holes at the heart of galaxies depends on two main factors: the rotational speed of the stars in the galaxy and how far it is from the black hole to the stars," he said. "The rotational speed can be observed, and the distance from the black hole out to the rotating disc of stars can now be calculated precisely using the new method."
Initial indications suggest that supermassive black hole masses have been underestimated by perhaps 40 percent. Researchers hope to extend their measurements to other active galaxies; the technique could eventually help astronomers better understand the rate at which the universe is expanding, study team members said.
Initial indications suggest that supermassive black hole masses have been underestimated by perhaps 40 percent. Researchers hope to extend their measurements to other active galaxies; the technique could eventually help astronomers better understand the rate at which the universe is expanding, study team members said.
So...what am I missing? Is the actual mass of these supermassive black holes not enough to account for the missing matter? Are existing methods for measuring these masses accurate enough to suggest there is still missing matter to be found? As far as I can tell, we've spent 40+ years looking for dark matter without much success, and I'm definitely not sure I understand why we're still convinced it's a real thing. FWIW, I don't actually mind if it's a thing or not. I'm just trying to understand why we think it is, especially in the face of 'new' discoveries and information about things like supermassive black holes.
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