Could brown dwarves account for Dark Matter?

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Helge Holler

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Could brown dwarves account for Dark Matter?
« on: 20/11/2011 13:01:02 »
Helge Holler  asked the Naked Scientists:

I recently read about how brown dwarves (smaller than stars, bigger than planets) were discovered and how astronomers suspect there might be a lot more than can be detected with current technology.

If that is so and there really are a lot more brown dwarves in the universe, could these explain the gravitational movements of galaxies? Could there be so many that they account for the mass that is currently attributed to dark matter? In other words: how many brown dwarves would be necessary to refute the theory of dark matter?

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Helge Holler

What do you think?
« Last Edit: 20/11/2011 13:01:02 by _system »


Offline yor_on

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Could brown dwarves account for Dark Matter?
« Reply #1 on: 20/11/2011 20:52:37 »
What is the Universe Made Of? answer what mainstream science define as 'normal mass.', that is atoms. And then you have it (the rest) split in 'dark matter', and 'dark energy'.

"Dark matter must exist to account for the gravity that holds galaxies together. If the only matter in the universe was matter we could directly detect, galaxies would not have had enough matter to have ever formed. The galaxies we observe today would fly apart because they wouldn't have enough matter to create a strong enough gravitational force to hold themselves together. Dark matter is also responsible for amplifying small fluctuations in the Cosmic Microwave Background back in the early universe to create the large scale structure we observe in the universe today.

Dark energy, which also goes by the names of the cosmological constant or quintessence, must exist due to the rate of expansion we observe for our universe. Not only is the universe expanding, but this expansion is also accelerating so the unknown 'anti-gravity' force at work is termed 'dark energy'.

Some researchers are searching for an explanation that encompasses both dark matter and dark energy. One example of such a theory uses a form of energy called a scalar field (it is a field because it has magnitude, energy and pressure, but it is scalar so it has no direction). Things would certainly be easier if we didn't need to have separate theories to explain dark matter and dark energy. However, other researchers look at dark matter and dark energy as two separate problems. For example, many string thoeries use supersymmetric particles to explain dark matter and make no connnection to dark energy at all." From What's the difference between dark matter and dark energy.

So depending on what your definitions are 'brown dwarfs' then need to answer to 23% of the mass of the universe, us/ordinary matter being approximately 4.6%, or they need to answer for ? make a guess :)
« Last Edit: 20/11/2011 20:57:11 by yor_on »
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Offline Soul Surfer

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Could brown dwarves account for Dark Matter?
« Reply #2 on: 20/11/2011 22:55:13 »
brown dwarves, planets, comets and gas definitely make up some of the matter that cannot be detected but they cannot make up the whole of the dark matter because there are other observation related to the modelling of the origins of the universe that indicate  that this matter cannot be normal baryons that is atoms or the particles that make up atoms or the intensity of interactions would be too high.  this matter can only interact via gravitational forces.
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Could brown dwarves account for Dark Matter?
« Reply #3 on: 22/11/2011 17:39:21 »
Though brown dwarf stars are cool, such a number as to account for DM would give us endless "hot spots" in our galaxy (around room temperature to hundreds of degrees centigrade) against a background temperature between stars of just a few degrees above absolute zero.

There is said to be about six times as much dark matter as light matter. In and/or around our galaxy. I have always found it strange that when you look at any spiral galaxy, it looks like it is made of light matter only.

Some say DM is in the halo of a galaxy but I think that if you have six times as much mass in the halo as in the galaxy itself, then that is where the 6/7's of the gravity is so that is where the LM would go, so we'd have ring donut shaped galaxies instead of spirals.

The only thing that we can say about DM is that it reacts gravitationally. Apart from that I don't think we know anything else about it.