Dark matter and its effect on the orbit of stars

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petercl14
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dark matter or black holes effect on star orbits
Hi all, As I understand it scientists have postulated that dark matter exists to explain the unexplained orbit of stars around the centre of our galaxy. The orbits not being as they should be by Newtonian or Einstein calculations. At the same time they postulate that there are perhaps 1000s of black holes in our milky way galaxy alone. Not just the massive black hole at the center of the milky way galaxy.

Have the scientists that believe in dark matter considered that the unexplained star orbits could in fact be due to the black holes? Have they found even one black hole other than the one at the center of the milky way galaxy? If they have then this would also confirm that there may in fact be 1000s of black holes as they also suggest. There would then be no need to bring in the idea of dark matter.
 
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Do you seriously think none of this has been thought of by the thousands of cosmologists who have thought about this stuff over many years?

Have you done any research on this or is this just some random idea you've come up with?
 
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Black holes have been considered, yes. You need more than thousands of them - you need more mass in them than there is in the visible stars, so at least in the billions of them per galaxy. And with that many floating around you ought to see gravitational lensing of stars as the black holes pass in front of them fairly frequently. And we never have. So we're fairly confident that whatever dark matter is, it's not black holes.

Yes, we're aware of objects that are probably stellar-mass black holes with accretion discs, along with super massive black holes (of which we are aware of more than one, by the way). The Cygnus X1 x-ray source is probably the most famous.
 
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No such thing as a stupid question. Just continue your quest for knowledge at your own pace @petercl14.

[Mentor Note: Post edited to remove mild insult.]
 
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IS80 said:
No such thing as a stupid question.
Yes there most certainly is.

"Will this be on the test?"
"I missed the last three weeks. Did we cover anything important?"
Need I go on?
 
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Back to the post at hand.

(1) The premise that scientists are a bunch of ignorant yahoos that need the OP to point the way is...um...not supported by the facts.
(2) Most, if not all, of the OPs questions can be answered by typing them into Google. Verbatim. Now, he may still have questions, but now we can discuss them better since he's put in some effort to educate himself.
(3) Stellar-mass black holes were once stars. The Dark Matter distribution is not the same as the stellar distribution. One would need to explain how they moved from here to there.
(4) Most former stars do not become black holes. If DM were black holes, the ordinary matter would be primarily in other stellar remnants: neutron stars and white dwarfs. That is not what we see.
 
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Vanadium 50 said:
(1) The premise that scientists are a bunch of ignorant yahoos that need the OP to point the way is...um...not supported by the facts.
(2) Most, if not all, of the OPs questions can be answered by typing them into Google. Verbatim. Now, he may still have questions, but now we can discuss them better since he's put in some effort to educate himself.
what he said (small).jpg
 
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Ibix said:
Black holes have been considered, yes. You need more than thousands of them - you need more mass in them than there is in the visible stars, so at least in the billions of them per galaxy. And with that many floating around you ought to see gravitational lensing of stars as the black holes pass in front of them fairly frequently. And we never have. So we're fairly confident that whatever dark matter is, it's not black holes.

Yes, we're aware of objects that are probably stellar-mass black holes with accretion discs, along with super massive black holes (of which we are aware of more than one, by the way). The Cygnus X1 x-ray source is probably the most famous.
Apparently the only effect dark matter has is it gravitational effect on real matter. It is suggested that it is like a web in intergalactic space. It is well established that large gravitational objects bend light such as the sun. It makes you wonder then how we can even see with clarity distant galaxies with this intergalactic dark matter in the way. You either couldn't see at all distant galaxies or there would just be a blur of light in the sky at night.
Scientists are now suggesting dark energy as well. When will it stop for things that can be easily explained be other means. This will be in another blog.
 
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petercl14 said:
This will be in another blog.
I certainly hope not.

We ignorant yahoos in the sciences have actually done the calculation of what is the impact of dark matter on gravitational lensing. And you know what? It matches what we see - not what you guess.
 
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petercl14 said:
It is well established that large gravitational objects bend light such as the sun.
As I said in the post you quoted, this is why we know dark matter isn't black holes.
 
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petercl14 said:
This will be in another blog.
Please don't
 
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petercl14 said:
Apparently the only effect dark matter has is it gravitational effect on real matter.
And radiation.
petercl14 said:
It makes you wonder then how we can even see with clarity distant galaxies with this intergalactic dark matter in the way. You either couldn't see at all distant galaxies or there would just be a blur of light in the sky at night.
It's not 'in the way'. That implies that it impedes the transmission of light through the universe, which it doesn't. It doesn't interact with light in any way except gravitationally, which merely alters the path of the light, not block it.
petercl14 said:
Scientists are now suggesting dark energy as well. When will it stop for things that can be easily explained be other means.
If by "now suggesting" you mean "have been suggesting for nearly 30 years", yes. And no, the issues in cosmology cannot be explained by another means. That's why dark energy and dark matter are still the prime suspects. If things could be better explained without using dark energy and dark matter then cosmologists would do so.

petercl14 said:
This will be in another blog.
No one cares.
 
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petercl14 said:
Have the scientists that believe in dark matter considered that the unexplained star orbits could in fact be due to the black holes?
Yes. But this possibility is heavily constrained, mostly to the point of being all but ruled out. See, e.g., this Wikipedia article and the sources cited therein.

The kind of black holes most often suggested for this possibility are called "primordial black holes" and if they are the source of dark matter phenomena, they'd have to have masses similar to asteroids. There are no processes that can make black holes of this size now, but there might have been in the very early universe, so this is why they are called "primordial black holes." There is no observational evidence which has supported the existence of even a single particular primordial black hole.

In the time period after the very early universe, it takes a neutron star with a mass not less than somewhere between 2.14 and 3 solar masses (the exact cutoff is a matter of ongoing research) to be massive enough to collapse into a black hole and there is no other known method of black hole formation.

Small black holes are believed to evaporate over time in a process called Hawking radiation (and the smaller they are, the faster they evaporate), so only those large enough to not evaporate completely over 13 billion years or so would remain. Black holes larger than asteroids can be detected through "micro-lensing" of light in their vicinity.

Black holes which are stellar black holes or larger are predicted to absorb more matter from their surroundings including light, dust, and cosmic background radiation, than they would emit in Hawking radiation, so they don't evaporate.
petercl14 said:
Have they found even one black hole other than the one at the center of the milky way galaxy?
Yes. They have found many (more than 40) "star sized" (a.k.a. stellar) black holes, and many intermediate sized black holes which are typically 10-200 time the mass of the Sun (which is much smaller than the black holes at the center of galaxies which are called "supermassive" black holes). Supermassive black holes are classically defined as black holes with a mass above 100,000 solar masses.

Intermediate sized black holes were only discovered definitively and in large numbers once gravitational wave detectors were invented and deployed. The first possible detection of one, in the year 2004, however, predated gravitational wave detection devices.
petercl14 said:
If they have then this would also confirm that there may in fact be 1000s of black holes as they also suggest. There would then be no need to bring in the idea of dark matter.
It would not. The number of stellar and intermediate sized black holes isn't large enough to explain the gravitational effects observed (there are too few of them by many orders of magnitude) and it is possible to rule out the possibility that we just aren't seeing enough black holes to cause the observed effects.

Mostly this ruling out is due to gravitational lensing, i.e. to the bending of light you would see if there was a black hole near the path of light that arrives on or near Earth. There isn't enough of that to involve enough black holes to account for dark matter.

There are also qualitative aspects of observed dark matter phenomena (like its tight alignment with ordinary mass distributions and wave-like apparent impact) which also disfavor black holes as a source of dark matter.
 
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Vanadium 50 said:
Yes there most certainly is.

"Will this be on the test?"
"I missed the last three weeks. Did we cover anything important?"
Need I go on?
I have never, even as a grade school student, understood asking "Will this be on the test?" Indeed, I've found the best of my teachers, instructors, and professors ALWAYS answered either 'yes' or 'take it and find out'. The only truly useless knowledge is the knowledge you don't have.
 

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