Starship Asterisk*

mark swain wrote:I Awoke this morning with Dark Matter On Mind. With I hope a very interesting thought...

The hypothesis of an 'invisible' axion was made by Misha Shifman and others, approximately thirty years ago. It has turned out to be an unusually fruitful idea, crossing boundaries between particle physics, astrophysics and cosmology. An axion with mass of order 10-5 eV (with large uncertainties) is one of the leading candidates for the dark matter of the universe. It was found recently that dark matter axions thermalize and form a Bose-Einstein condensate (BEC). Because they form a BEC, axions differ from ordinary cold dark matter (CDM) in the non-linear regime of structure formation and upon entering the horizon. Axion BEC provides a mechanism for the production of net overall rotation in dark matter halos, and for the alignment of cosmic microwave anisotropy multipoles. Because there is evidence for these phenomena, unexplained with ordinary CDM, an argument can be made that the dark matter is axions.

harry wrote:Dark/Enery matter is nuclear matter in various phase forms and this could be from extreme light to ultra dense matter found in the centres of stars and galaxies. The nuclear matter can have a neutral charge, positive or negative charge or spins.

Composition
Unsolved problems in physics What is dark matter? How is it generated? Is it related to supersymmetry?

Although dark matter was inferred by gravitational lensing in August 2006,[27] many aspects of dark matter remain speculative. The DAMA/NaI experiment and its successor DAMA/LIBRA have claimed to directly detect dark matter passing through the Earth, though most scientists remain skeptical since negative results of other experiments are (almost) incompatible with the DAMA results if dark matter consists of neutralinos.


Estimated distribution of dark matter and dark energy in the universeThe dark matter component would have much more mass than the "visible" component of the universe.[40] Only about 4.6% of the mass of Universe is ordinary matter. About 23% is thought to be composed of dark matter. The remaining 72% is thought to consist of dark energy, an even stranger component, distributed diffusely in space.[41]

Some hard-to-detect baryonic matter is believed to make a contribution to dark matter but would constitute only a small portion.[42][43]

Determining the nature of this missing mass is one of the most important problems in modern cosmology and particle physics. It has been noted that the names "dark matter" and "dark energy" serve mainly as expressions of human ignorance, much like the marking of early maps with "terra incognita."[41]

At present, the most common view is that dark matter is primarily non-baryonic, made of one or more elementary particles other than the usual electrons, protons, neutrons, and known neutrinos. The most commonly proposed particles are axions, sterile neutrinos, and WIMPs (Weakly Interacting Massive Particles, including neutralinos).

None of these are part of the standard model of particle physics, but they can arise in extensions to the standard model. Many supersymmetric models naturally give rise to stable dark matter candidates in the form of the Lightest Supersymmetric Particle (LSP). Heavy, sterile neutrinos exist in extensions to the standard model that explain the small neutrino mass through the seesaw mechanism.

Data from a number of lines of evidence, including galaxy rotation curves, gravitational lensing, structure formation, and the fraction of baryons in clusters and the cluster abundance combined with independent evidence for the baryon density, indicate that 85-90% of the mass in the universe does not interact with the electromagnetic force. This "nonbaryonic dark matter" is evident through its gravitational effect.

Historically, three categories of nonbaryonic dark matter have been postulated[44]:

Hot dark matter – nonbaryonic particles that move ultrarelativistically[45]
Warm dark matter – nonbaryonic particles that move relativistically
Cold dark matter – nonbaryonic particles that move non-relativistically[46]
Davis et al. wrote in 1985:

Candidate particles can be grouped into three categories on the basis of their effect on the fluctuation spectrum (Bond et al. 1983). If the dark matter is composed of abundant light particles which remain relativistic until shortly before recombination, then it may be termed "hot". The best candidate for hot dark matter is a neutrino ... A second possibility is for the dark matter particles to interact more weakly than neutrinos, to be less abundant, and to have a mass of order 1eV. Such particles are termed "warm dark matter", because they have lower thermal velocities than massive neutrinos ... there are at present few candidate particles which fit this description. Gravitinos and photinos have been suggested (Pagels and Primack 1982; Bond, Szalay and Turner 1982) ... Any particles which became nonrelativistic very early, and so were able to diffuse a negligible distance, are termed "cold" dark matter (CDM). There are many candidates for CDM including supersymmetric particles.[47]

Hot dark matter consists of particles that travel with relativistic velocities. One kind of hot dark matter is known, the neutrino. Neutrinos have a very small mass, do not interact via either the electromagnetic or the strong nuclear force and are therefore very difficult to detect. This is what makes them appealing as dark matter. However, bounds on neutrinos indicate that ordinary neutrinos make only a small contribution to the density of dark matter.

Hot dark matter cannot explain how individual galaxies formed from the Big Bang. The microwave background radiation as measured by the COBE and WMAP spacecraft, while incredibly smooth, indicates that matter has clumped on very small scales. Fast moving particles, however, cannot clump together on such small scales and, in fact, suppress the clumping of other matter. Hot dark matter, while it certainly exists in our universe in the form of neutrinos, is therefore only part of the story.

The Concordance Model requires that, to explain structure in the universe, it is necessary to invoke cold (non-relativistic) dark matter. Large masses, like galaxy-sized black holes can be ruled out on the basis of gravitational lensing data. However, tiny black holes are a possibility.[48] Other possibilities involving normal baryonic matter include brown dwarfs or perhaps small, dense chunks of heavy elements; such objects are known as massive compact halo objects, or "MACHOs". However, studies of big bang nucleosynthesis have convinced most scientists that baryonic matter such as MACHOs cannot be more than a small fraction of the total dark matter.

harry wrote:What makes up nuclear matter is one of the LHC experiments.

Maybe science really is back in vogue. Or maybe "dark matter" is a case of remarkably successful scientific branding—who wouldn't be drawn in by a name like that? Then again, maybe people just want to know what the heck makes up the vast majority of the universe, a question to which science has provided only sketchy answers.

Whatever the reason, a dark matter lecture by physicist Peter Fisher at the American Museum of Natural History in New York City drew a sellout crowd April 12 in a theater that seats more than 400, with museum staff turning away disappointed comers and at least one gentleman trying to talk his way in as if he were working to get past the velvet rope at a nightclub.

Spinning stars

"Since we know a lot about the background sources of positrons and electrons, we know what fraction we would expect to see at this particular energy level," explained Nigel Smith, who carries out research into dark matter at the UK's Rutherford Appleton Laboratory but was not involved in this research.

THE PAMELA MISSION

Pamela stands for: Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics
The satellite carries instruments to identify particles and anti-particles
It is expected to orbit the Earth for a minimum of three years
"It's like light; when you see different colours, you're looking at photons - light particles - with different energies."

However, there could be another explanation for the positrons. They may come from pulsars - rapidly rotating, super-dense, dead stars that release lots of energy into the cosmos.

Nasa's Fermi Gamma-ray Space Telescope, which was launched in June 2008, is already taking measurements from pulsars and should produce data that could clarify the mysterious signal.

Professor Smith thinks pulsars provide the most likely explanation.

"It's the simplest solution," he said. "I think everyone will be waiting for the Fermi data to come in."

Professor Picozza agrees that pulsars offer a plausible, if less exciting, origin.

"Many leading theoreticians think this signal must come from dark matter," he continued.

"But I don't think this data alone is enough to claim that discovery. What we have found is another primary source of positrons."

He believes that the particles thought to constitute dark matter could be reproduced in the Large Hadron Collider (LHC) in Switzerland.

harry wrote:Signals could be from dark matter
http://news.bbc.co.uk/2/hi/science/nature/7977102.stm

Chris Peterson wrote:

harry wrote:What makes up nuclear matter is one of the LHC experiments.

Your point? There's is nothing in the discussion of dark matter about "nuclear matter". You are using a term that has no single definition, and which you haven't defined for us. What is "nuclear matter"? The term is usually used to describe a phase state, and one that is likely to have no physical meaning at all, or to describe matter only in extreme environments, like the core of neutron stars. Again, nothing to do with dark matter, which most likely is made of of non-baryonic particles.

alter-ego wrote: First of all, everything has a wavelength whose value depends on energy. Quantum Mechanics dictates that only at Absolute Zero Temperature (a state of zero energy) does a particle NOT oscillate.

1. Does gravity have mass? Of course I don't know for sure. Mass and gravity go hand in hand, but ultimately, General Relativity defines gravity as curvature of space.

2. Neutrinos supposedly are very light particles that travel near the speed of light. The fact they oscillate is not the reason they travel fast. They travel fast because they are byproducts of high energy reactions, and the conservation of energy requires they travel VERY fast. You're right, if particles have non-zero (but real) mass, the most accurate theory to date (GR) says they must travel < c.

3. DM randomly distributed (ultra)relativistic particles or not? Of the little I've read, the thoughts appear to support slow-moving particles to help explain the observed clumpiness. If that's the claim, I have questions myself. For a region in space, where for a snapshot in time it takes hundreds of million of years for light to traverse, and more than enough time for life-cycles of high-energy cosmoslogical events to occur, I can see relativistic particles producing clumpiness. This concept only works for transient, non-steady state phenomena occurring over vast regions of space. This is all speculation on my part. If there are random high-energy phenomena that generate random high-energy byproducts in random locations and directions in space (galaxy collisions, star formation and death, black-hole creation, etc) at random times, then I would expect to not only see inhomogeneity in the distribution of the byproduct energy distributions, but also a changing distribution of this energy distribution over a long enough observation time. To me this is thought provoking. Maybe DM is NOT slow-moving particles (relative to human time scale). I've not seriously considered any consistency to existing theories for this "hot" high velocity particle discussion. Very likely the whole thing falls apart and only "static" heavy particles work for DM. I'm just thinking out loud here. If neutrinos are the DM particles (I believe current theory predicts there is not enough neutrinos to account for all DM believed to exist), then my thoughts are they don't have to coagulate or clump, exept due to self-gravity from the self-induced space curvature. There are other reasons why DM may appear to clump.

Take my last item with a grain of salt. As I said earlier, I'm looking forward to what the next breakthroughs are, not what I believe today. For today, having enough self-confidence to share possibly outlandish ideas in a public forum is my personal breakthrough.

alter-ego wrote:In defense of harry, I have a comment ... at generic level of discussion, I think I might know what harry's point is.

this is the level to which harry's comments apply to main-stream thinking.

• Pay no attention to that man behind the curtain.

hstarbuck wrote:I was actually not asking if gravity had mass, but if all gravity was tied to mass. According to Newton's law or Einstein's theory (I am told) the quick answer is yes. Can we actually prove that all gravity is tied to matter? or at least matter from this visible universe? By observing gravitational effects we infer dark matter/mass but there could be a totally different connection. Kind of funny to think that black holes are like familiar objects (from the outside) compared to dark matter at the present.

alter-ego wrote:I'm waiting for a new player: Dark Black Holes.

hstarbuck wrote:All matter has mass>>all mass has gravity>>Does all gravity have mass?

astrolabe wrote:So, if we don't honestly KNOW what Gravity is we are left with an observation of an effect seemingly caused by a force(?) that needed a name. Isaac called the force(?) Gravity but he, like us don't know what it is. It's no wonder we struggle with DM. We know it's nature and that's all- just like Gravity.