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Scientists know that there must be more mass than what is visible in galaxies as they manage to hold themselves together despite not being enough ordinary matter, so they call it dark matter as it doesn't emit anything but is observable through its gravity. Then if this dark matter can generate gravity similar to ordinary matter then can it not interact with itself and make dark matter clumps that are gravitationally detectable. Like a dark matter planet? If this was true i imagine a dark matter planet would be detectable as it would skew the orbits of ordinary matter planets?

Answer
Hello,

The conception of dark matter planets or solar systems for that matter is dependent on how well we can distinguish exotic forms from ordinary forms. In the latter case one might reference Fritz Zwicky's measurements of galaxy clusters which  highlighted a ‘missing mass’. He found that the mass needed to bind a cluster of galaxies together gravitationally was at least ten times the apparent mass visible.  Around the same time there were observations of stellar motions in the galactic plane by Dutch astronomer Jan Oort. He found there had to be at least three times the mass visibly presenting in order for stars not to escape the galaxy and fly off into space.


What exactly constituted this 'missing mass'.? The short answer is we don't know but there a number of candidates. By the late 1970s (with Cygnus X-1), astronomers realized there were other forms of dark matter. Among the most discussed candidates were black holes, marking the end stage of evolution for very massive stars. In the black hole, the gravity is so strong that no light escapes and the mass typically is much greater than that of the Sun.

Currently, we are aware of a super black hole at the center of our galaxy with 9.7 billion times the mass of the Sun.  Can such an entity form planets? Hardly! It would more likely 'devour' them.


Dark matter generally occurs in either baryonic or non-baryonic forms, depending on whether the matter reacts with radiation or not. If it doesn’t, it’s non-baryonic. Baryons include protons and neutrons, while non-baryons include electrons and neutrinos.

Non-baryonic dark matter further breaks down into cold dark matter and hot dark matter. The terms hot and cold are not so much indicative of current temperatures, as the phase of the early universe at which the particular dark matter ‘decoupled’ from the hot radiation background. An early decoupling implies a higher ambient background radiation temperature of the primeval cosmos. A later decoupling correlates to a cooler temperature. Perhaps the most widely studied candidate of hot dark matter is the neutrino.

By contrast, cold dark matter candidates tend to have larger mass and amongst the most likely suspects are: gravitinos, magnetic monopoles, and primordial black holes. However, there are a couple of exceptions to this, which include: WIMPs and Axions.

How any of these entities could leave specific gravity signatures that distinguish any one from their dark counterparts is a matter of continued inquiry.  Until such signatures are identified and clarified there is little chance of even remotely speculating on the existence of  "dark matter planets".

Leave out the nature of a dark matter planet, it is certainly plausible that a dark matter object (like a small black hole) could "skew the orbit" of an ordinary matter planet - or star.  

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Philip A. Stahl

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I specialize in stellar and solar astrophysics. Can answer questions pertaining to these areas, including: stellar structure and evolution, HR diagrams, binary systems, collapsars (black holes, neutron stars) stellar atmospheres and the spectroscopic analysis of stars – as well as the magnetohydrodynamics of sunspots and solar flares. Sorry – No homework problems done or research projects! I will provide hints on solutions. No nonsense questions accepted, i.e. pertaining to astrology, or 'UFOs' or overly speculative questions: 'traveling through or near black holes, worm holes, time travel etc. Absolutely NO questions based on the twaddle at this Canadian site: http://members.shaw.ca/warmbeach/FAQ.htm purporting to show a "new physics". Do not waste my time or yours by wasting bandwidith with reference to such bunkum.

Experience

Have constructed computerized stellar models; MHD research. Gave workshops in astrophysics (stellar spectroscopy, analysis) at Harry Bayley Observatory, Barbados. More than twenty years spent in solar physics research, including discovery of SID flares. Developed first ever consistent magnetic arcade model for solar flares incorporating energy dissipation and accumulation. Developed first ever loop-based solar flare model using double layers and incorporating cavity resonators. (Paper presented at Joint AGU/AAS Meeting in Baltimore, MD, May 1994)

Organizations
American Astronomical Society (Solar physics and Dynamical astronomy divisions), American Geophysical Union, American Mathematical Society, Intertel.

Publications
Papers appearing in Solar Physics, Journal of the Royal Astronomical Society of Canada, Journal of the Barbados Astronomical Society, Meudon Solar Flare Proceedings (Meudon, France). Books: 'Fundamentals of Solar Physics', 'Selected Analyses in Solar Flare Plasma Dynamics', 'Physics Notes for Advanced Level', 'Astronomy & Astrophysics: Notes, Problems and Solutions', 'Modern Physics: Notes, Problems and Solutions'

Education/Credentials
B.A. degree in Astronomy; M.Phil. degree in Physics - specializing in solar physics.

Awards and Honors
Postgraduate research award- Barbados government; Studentship Award in Solar Physics - American Astronomical Society. Barbados Astronomical Society award for service (1977-91) as Journal editor.

Past/Present Clients
Caribbean Examinations Council (as advisor, examiner), Barbados Astronomical Society (as Journal Editor 1977-91), Trinidad & Tobago Astronomical Society (as consultant on courses, methods of instruction, and guest speaker).

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