Could we be making a mistake about the distribution for "dark matter" in galaxies?

[Unclear Engineer]

The descriptions I read about the distribution of "dark matter" in galaxies seems to show it as somewhat hollow, in a "halo" instead of a spherical blob with greatest density at the center.

I understand that this is inferred from the apparent lack of sufficient gravity from the detected luminous matter to explain the orbital velocities of stars around the galaxy center, as a function of their distance from the center. So, this distribution seems to be calculated on the basis of (enough matter) minus (visible matter).

And, that would make sense so long as the "dark" matter is normal matter that we just can't see in the dark.

However, once we postulate that "dark matter" is some other form of matter that does not interact with regular matter, except to be attracted to it (and itself) by gravity, this distribution does not seem to make sense any more.

For instance, why would the dark matter not be most dense where the regular matter is most dense? And why would dark matter not become dense blobs of its own accord, just like regular matter clumps to form stars, planets, etc.?

It is hard for me to come up with some sort of internal dark matter to dark matter interactions that would produce the "halo" result.

However, it does seem plausible that we could be calculating the combined gravitational effects of both regular and dark matter where we see luminous regular matter, and thus are over-estimating the actual mass of the regular matter. So, when we subtract that over-estimated mass of the regular matter to infer the remaining mass of the dark matter, we would be leaving a "halo" where we don't see so much luminous matter.

Thoughts?

 

[Catastrophe]

My understanding is that dark matter was introduced as a fudge factor. Originally known as "missing mass" I think it was upgraded to "dark matter" as this sounds less like a fudge.

A rose by any other name would small as sweet

In this case something sounds better if you give it a sweeter smelling name.

Originally known as the “missing mass,” dark matter's existence was first inferred by Swiss American astronomer Fritz Zwicky, who in 1933 discovered that the mass of all the stars in the Coma cluster of galaxies provided only about 1 percent of the mass needed to keep the galaxies from escaping the cluster's ...

dark matter | Definition, Discovery, Distribution, & Facts

Cat

 

[Helio]

The descriptions I read about the distribution of "dark matter" in galaxies seems to show it as somewhat hollow, in a "halo" instead of a spherical blob with greatest density at the center.

I understand that this is inferred from the apparent lack of sufficient gravity from the detected luminous matter to explain the orbital velocities of stars around the galaxy center, as a function of their distance from the center. So, this distribution seems to be calculated on the basis of (enough matter) minus (visible matter).

And, that would make sense so long as the "dark" matter is normal matter that we just can't see in the dark.

However, once we postulate that "dark matter" is some other form of matter that does not interact with regular matter, except to be attracted to it (and itself) by gravity, this distribution does not seem to make sense any more.

For instance, why would the dark matter not be most dense where the regular matter is most dense?

It’s my understanding that it does. The central area of a galaxy typically has a larger distribution of DM.

And why would dark matter not become dense blobs of its own accord, just like regular matter clumps to form stars, planets, etc.?

Indeed. There seems to be no evidence of any high density DM pockets, AFAIK.

 

[karlp295]

My understanding is that dark matter was introduced as a fudge factor. Originally known as "missing mass" I think it was upgraded to "dark matter" as this sounds less like a fudge.

I really enjoyed this comment and find it resonates with my thoughts exactly.
Science is always a best guess until it gets either rejected or accepted as truth. In any case, I don't think we have any real idea if it even exists let alone what exactly it might be.

 

[Helio]

Science is always a best guess until it gets either rejected or accepted as truth.

IMO, science is never about truth.

All theories are objective-based, meaning you better show testable evidence as the basis of the theory.

All theories make predictions, so there better be a way, even if in principle, for others to use instruments to test those predictions.

No theory is ever proven. Testable predictions means that all theories can potentially be falsified. If falsified, the theory can either be modified or, hopefully, replaced with a theory that does explain the phenomena.

In any case, I don't think we have any real idea if it even exists let alone what exactly it might be.

DM does exist in the same way black holes exist. It's impossible to observe a black hole, but they exist because of the vast amount of evidence for their existence. The extremely fast moving stars around the center of our galaxy, for instance, can only be explained by the presence of a supermassive black hole. [Interestingly, the first solution to Einstein's general relativity when he published his work was that of black holes, though no one thought they would exist.]

DM was first "seen" by Fritz Zwicky in the 1930's, IIRC. He said there was "missing mass", as Cat also stated -- I also enjoy all Cat's posts. But nothing more was found to support his claim. BTW, Zwicky was the one who coined the term "Dark matter".

When it was discovered that the Andromeda Galaxy did not exhibit Keplerian motion (Vera Rubin and Kent Ford; 1970) for the orbiting stars, then DM became far more interesting as an answer. The study of the Bullet Cluster, perhaps, is the most demonstrable evidence that DM exists. But is DM a particle or what? That is what science is attempting to discover.

DE (Dark Energy) only is a label to address the acceleration of space. It's a huge mystery, unlike DM.

 

[Unclear Engineer]

One of the ways that DM could not exist is that the motions of stars are more influenced by the General Relativity effect of "frame dragging" of space by the motion of masses than we have been able to calculate properly. I did see a paper that claimed to show that doing the frame dragging calculation properly for the spin of the central black hole plus the rotation of the orbiting stars could match the observed stellar motions without the addition of unseen "dark matter". But, I think others did not agree. The author's contention was that other calculations included simplifying assumptions to deal with the huge number of individual masses for the known stars in the galaxy, and those assumptions are the problem.

It has always been a question in my mind how we can estimate the masses of objects by observing their motions, and then turn around and claim that their motions do not match what we expect from their calculated masses. So, my thinking is at least open to the possibility that we are not perceiving some of these things correctly, especially when it comes to solving the General Relativity field equations for a black hole plus hundreds of billions of stars with a wide variety of masses, dust clouds, etc. and considering the strange effects of time dilation and frame dragging.

 

[Montezuma]

I really enjoyed this comment and find it resonates with my thoughts exactly.
Science is always a best guess until it gets either rejected or accepted as truth. In any case, I don't think we have any real idea if it even exists let alone what exactly it might be.

Hello! Dark Matter was invented to explain the observation that all the Milky Way stars travel at 220 km/sec, or 491,832 mph. But there is a logical alternative.
All matter did not form in a single Big Bang event. Instead, matter continuously forms on the outer edges of spiral galaxies, and matter gets continually recycled in the galactic centers. This is why all the Milky Way stars travel at the same speed, not because of Dark Matter.
The centers of galaxies feed on the inbound material, and eject elementary particles back into space; a perpetual cycle of creation and destruction. Since the centers eject matter, by definition they cannot be black holes.
Global Warming is a direct result of increasing proximity to the center of the Milky Way. Once the polar ice caps disappear, the oceans and air will quickly become inhospitable to all Life.

 

[Helio]

It has always been a question in my mind how we can estimate the masses of objects by observing their motions, and then turn around and claim that their motions do not match what we expect from their calculated masses.

The discovery of DM didn’t use mass this way. Zwicky used other methods to determine galactic mass, but discovered the galaxies of the cluster were moving much faster around each other than he could give account.

Vera Rubin never needed mass since she discovered the galaxy wasn’t exhibiting Keplerian motion for the visible disk. The stars all had about the same orbital velocity, contrary to the law.

So, my thinking is at least open to the possibility that we are not perceiving some of these things correctly, especially when it comes to solving the General Relativity field equations for a black hole plus hundreds of billions of stars with a wide variety of masses, dust clouds, etc. and considering the strange effects of time dilation and frame dragging.

We should be seeing a lot of lensing effects, etc., if this were the case.

 

[Montezuma]

The discovery of DM didn’t use mass this way. Zwicky used other methods to determine galactic mass, but discovered the galaxies of the cluster were moving much faster around each other than he could give account.

Vera Rubin never needed mass since she discovered the galaxy wasn’t exhibiting Keplerian motion for the visible disk. The stars all had about the same orbital velocity, contrary to the law.


We should be seeing a lot of lensing effects, etc., if this were the case.

The problem is that Modern Cosmology is making their observations fit their theory, instead of vice versa.
At 220 km/sec, or 491,832 mph, it takes all the Milky Way stars 1,364.27 years to travel one light year. Since Galileo discovered that the Earth is not the center of the Universe, all the Milky Way stars have traveled 30 percent of one light year.
There is no physical way that anyone can detect distant galaxies speeding up. It's speculation.

 

[Helio]

The problem is that Modern Cosmology is making their observations fit their theory, instead of vice versa.

Their theories are objective-based, meaning the evidence forms the theories. If altering the evidence occurs to fit a theory, then it is quickly condemned, thankfully.

At 220 km/sec, or 491,832 mph, it takes all the Milky Way stars 1,364.27 years to travel one light year.

That’s true for the Sun. Stars close to the center are as much as 8,000kps.

Since Galileo discovered that the Earth is not the center of the Universe, ...

Yes. He was the first to falsify the Ptolemy model that placed the Earth at the center.

There is no physical way that anyone can detect distant galaxies speeding up. It's speculation.

If cops can measure your car’s speed, how much better can astronomers measure redshifts?

 

[Montezuma]

Their theories are objective-based, meaning the evidence forms the theories. If altering the evidence occurs to fit a theory, then it is quickly condemned, thankfully.

That’s true for the Sun. Stars close to the center are as much as 8,000kps.

Yes. He was the first to falsify the Ptolemy model that placed the Earth at the center.

If cops can measure your car’s speed, how much better can astronomers measure redshifts?

Interesting beliefs, but incorrect.

There was no Big Bang, there is no Dark Matter, there are no black holes, and the Universe is not expanding. It is all misinformation to give logic to antiquated theories.
If you actually take the time to read about radar, instead of repeating what you have been told, you will discover that laser-based radar only functions at speeds much lower than the speed of light. It's not based on Doppler shift, it's based on calculation of change in distance over very short intervals.

 

[Maui]

The concept of dark matter was first proposed to account for observations that could not be adequately explained using the existing gravitational force laws and associated observational data. Even after decades of actively searching for it, no direct observations of dark matter have been made. None. This entire concept is analogous to the concept of the luminiferous aether that was proposed in the late 1800s to explain how light waves could propagate through the vacuum of free space. Every example of wave propagation up to that point required a medium in which the waves could move, and the idea that waves could propagate in a vacuum was apparently abhorrent to scientists of that era. So the concept of the aether was developed. But the aether had to possess some very unique and special properties. It could not directly interact with any physical objects, and it had to permeate all of free space, so it had to be everywhere (is this starting to sound familiar?). It had to possess some additional characteristics including the ability to induce drag on waves that passed through it, and this drag could vary depending upon the direction of propagation of the waves relative to the motion of the earth through the aether. Eventually the Michelson-Morely experiment proved that there was no aether, and that light waves could easily propagate through the vacuum of free space. There didn't have to be any medium to "wave" in when it came to light propagation after all. The concept of dark matter will probably fall by the wayside too one day. What the majority of scientists are unwilling to accept today is that the gravitational force laws aren't quite right, and they need to be corrected/adjusted. Once such a correction has been made properly, the need for the concept of dark matter will evaporate just like the luminiferous aether.

 

[Montezuma]

That comes as no surprise- nobody else does, either. People will believe in black holes and Dark Matter all day, but when offered a logical alternative, they are all a bunch of intellectual paramecium.
Unlike the Big Bang theory, my theory is supported by visual evidence. Every spiral galaxy clearly shows matter spiraling inward from the edge to the center. It explains why all the Milky Way stars travel at the same speed, as well as the abundance of heavy elements, galactic mergers, the even distribution of galaxies, why the furthest visible galaxies are fully developed, quasars, the Fermi Bubbles - and Global Warming.
The beauty of my theory is that we are traveling 11.8 million miles closer to the center each day, whether anyone believes me or not!
The polar ice caps are the hourglass for hospitable living conditions on Earth. Soon the oceans will become too warm to remain liquid. Mankind cannot stop a flood, or turn a hurricane; and we certainly cannot warm or cool the planet.

 

[Jzz]

I find the statement "distribution of dark matter" used by unclear engineer, confusing. When it is impossible to detect dark matter, how is it possible to talk about its distribution? To claim an uneven distribution of dark matter is an anomaly, it would mean that different parts of the Universe would have significantly different properties; which isn't the case. The Universe is homogenous, by all accounts. Further to talk about the amount of mass needed to keep galaxies together in such an offhand manner is misleading. It is my understanding that for galaxies to possess their present shape the matter to dark matter ratio is 10 : 90. That is to say, galaxies would have to contain 90 % more matter than can be detected to possess their present structure.

 

[Atlan0001]

Time?!

A traveler, whatever it might be, might speed up in space and time -- speeding forward in space and time -- and have dark matter (shadow matter?) begin to come to light for the traveler as a newer, or simply a different, universe in space and time, leaving an older, or again simply different, universe behind in both space and time. A Mulitverse-Universe existing.

 

[Catastrophe]

I find the statement "distribution of dark matter" used by unclear engineer, confusing. When it is impossible to detect dark matter, how is it possible to talk about its distribution? To claim an uneven distribution of dark matter is an anomaly, it would mean that different parts of the Universe would have significantly different properties; which isn't the case. The Universe is homogenous, by all accounts. Further to talk about the amount of mass needed to keep galaxies together in such an offhand manner is misleading. It is my understanding that for galaxies to possess their present shape the matter to dark matter ratio is 10 : 90. That is to say, galaxies would have to contain 90 % more matter than can be detected to possess their present structure.

It is not impossible to detect dark matter. That is the answer.

Dark matter is assumed from its gravitational effects. It cannot be "seen" (detected) via electromagnetic radiation (including light), so was called "dark".

Hope this helps.

Cat

Searching for the invisible | British Science Festival

We are delighted to announce that Dr XinRan Liu who’s based at the University of Edinburgh is the British Science Festival 2021 Award Lecture winner for Physical Sciences and Mathematics.

britishsciencefestival.org

 

[Unclear Engineer]

Jzz, you seem to have misunderstood my question.

The "distribution of dark matter," in and around galaxies, is inferred by astronomers on the basis of analyzing how much matter is needed inside the orbits of visible stars for those stars to be bound to the galaxy by gravity. The "dark matter" is what is hypothesized to be there after subtracting the mass of the visible matter. So, an implied distribution for the dark matter in galaxies is produced by working outwards from the center, looking at the velocities of stars at different distances from the center.

There is also an estimate of the total dark matter in and around the outside of galaxies based on how light from more distant galaxies gets bent around them on the way to Earth, where we see the lensing effect.

So, that is the basis for astronomers to define distributions of "dark matter" around galaxies.

My question is why does it have that distribution? It seems to be significantly different from the distribution of visible matter. Since it interacts with visible matter by gravity, why doesn't it have a similar distribution to the matter that we can see? The visible matter that we can see and call galaxies has theoretically coalesced from a uniform distribution of gas, and presumably dark matter, that was formed after the Big Bang cooled enough. And it is theorized to stil be pretty uniform when the cosmic microwave background radiation was released over 13 billion years ago. So, why did the dark matter and the visible matter end up with different distributions in and around galaxies?

Note that if both forms of matter had exactly the same distribution, everywhere, then our observations would just assign more mass to the visible matter, because we would have no way to realize that there were two parts to the masses we measure.

 

[Catastrophe]

and from NASA:

Dark Matter & Dark Energy - NASA Science

Overview Everything scientists can observe in the universe, from people to planets, is made of matter. Matter is defined as any substance that has mass and occupies space. But there’s more to the universe than the matter we can see. Dark matter and dark energy are mysterious substances that...

science.nasa.gov

Cat

 

[Jzz]

It is true that clocks on earth slow down the faster they go and speed up according to their height above the surface of the earth
BUT isn't that more due to the presence of gravity than an effect of general relativity? How does acceleration work in the absence of gravity? Are the facts known with any surety? Astronauts in the space station live in a constantly accelerating environment but seem to be oblivious of the fact. Even though this is due to the fact that they are in free fall and temporarily free of the influence of gravity. In deep space far from the effects of gravity, where everything is truly weightless, again due to an absence of gravity, would acceleration manifest differently?

 

[Helio]

Astronauts in the space station live in a constantly accelerating environment but seem to be oblivious of the fact. Even though this is due to the fact that they are in free fall and temporarily free of the influence of gravity.

But they are falling because of the influence of gravity, derived from the mass of the Earth. Their orbital velocity is what allows them to never hit the ground, or hardly lose their distance above the surface.

In deep space far from the effects of gravity, where everything is truly weightless, again due to an absence of gravity, would acceleration manifest differently?

Apparently not. Newton's laws work fine for calculating the acceleration in deep space if the force is known. F = ma.

But the curious question is the cause of inertia. Mach claimed that the mass of the universe is the cause, and this seems to be the general view, I think. There's an old debate about what happens if you swing a bucket of liquid round and round if you're in deep space.

 

[Jzz]

But they are falling because of the influence of gravity, derived from the mass of the Earth. Their orbital velocity is what allows them to never hit the ground, or hardly lose their distance above the surface.

Nevertheless in free fall, they are away from the effects of gravity and are wieghtless. Ofcourse, in all other respects, the effects of gravity are very much present in the space station. However, as you state, the question of inertial mass is still very much in the air. Consider a 100 ton metric mass in deep space, the calculations show that accelerating it is hardly going to make a difference to anything travelling inside it. If that is Newtons equations are used. Edit

'A rocket launches when the force of thrust pushing it upwards is greater than the weight force due to gravity downwards. ' In the absence of gravity what would be the effect of the force? suppose a spaceship with a mass of 100 metric tons is accelerated to 3g, with no gravity acting on the space ship to pull it back, surely weightlessness would still prevail inside the space ship although its speed would increase according to the acceleration applied to it. This is where the question of inertial mass comes in. Since the 100 kg mass would acquire the same velocity as the space ship, in the absence of external gravity, wouldn't that 100 kg mass just float around in the space ship? How is the 100 kg mass differentiated from the mass of the space ship?

But the curious question is the cause of inertia. Mach claimed that the mass of the universe is the cause, and this seems to be the general view, I think. There's an old debate about what happens if you swing a bucket of liquid round and round if you're in deep space.

If I remember correctly Mach's bucket had to be the size of our Galaxy! In any event when Einstein approached him in order to use his theory Mach peremptorily dismissed any idea of a collaboration!

 

[Helio]

Nevertheless in free fall, they are away from the effects of gravity and are wieghtless.

I'm unclear what you mean since even the Moon is under the influence of Earth's gravitational field, as we are with the Sun, as it is with the galaxy. The Newtonian view is that the orbiting spacecrafts are falling but going just fast enough to reach the next point that is the same height above the surface as the prior point.

'A rocket launches when the force of thrust pushing it upwards is greater than the weight force due to gravity downwards. ' In the absence of gravity what would be the effect of the force?

But they are really saying it moves upwards when the net force (Fengines - Fgravity > 0). The weaker the Fgravity is, the less Fengines you need. So small engines are fine for, say, the Moon.

Since the 100 kg mass would acquire the same velocity as the space ship, in the absence of external gravity, wouldn't that 100 kg mass just float around in the space ship? How is the 100 kg mass differentiated from the mass of the space ship?

So it's still F=ma. But since there is no Fgravity to oppose it, then less force is needed.

I erroneously place a 3 or 4 second-time delay Estes rocket engine in the lower stage of a 2 stage rocket that included a movie camera in it. I reversed it with the zero-second delay that I put in the top stage. I had to do this in the dark because of the film in the camera. When it launched, we kept waiting for the 2nd stage to ignite, but when it did, the rocket was pointed towards us! It was the fastest object I ever saw in my life, partly because of the fear it was coming our way.

Objects will accelerate much faster, of course, when the force of gravity can be added to the propelling force.

If I remember correctly Mach's bucket had to be the size of our Galaxy! In any event when Einstein approached him in order to use his theory Mach peremptorily dismissed any idea of a collaboration!

That's interesting. If you find something I can read on that, I would be interested. Einstein, being Jewish, had to leave his country. There was a public denouncement of Einstein's relativity authored by 100 prominent Germans, including one or two scientists. When Einstein was told of this he simply asked something like, "Why 100 when only 1 is needed?". Brilliant, but that's how science works; not by consensus.