Re: Macho's/ Dark matter

Piet den Dulk wrote:
Dear Physicists, 

<http://en.wikipedia.org/wiki/MACHO>


A Macho is build with dark matter. Which kind of Macho's do exist?

The most popular candidates are brown dwarfs, black dwarfs, neutron stars and black holes, AFAIK


A Macho kind Brown dwarf consists of Helium and hydrogen. But why is it
called darkmatter as Helium and Hydrogen is just ordinary matter?


Dark Matter is not necessarily non-baryonic. It is well know that a lot of
"ordinary" matter is "dark".


A brown dwarf is a clumb of helium and hydrogen gas. So a brown dwarf is a
cloud of gas.

"clumb" and "cloud" are not the same. And I don't think it is really only gas througout. I would think that there is plasma somewhere in it, or that the pressure might be even so high that one gets liquids
or even solids.


Can we travel right across a brow dwarf theoretically? Because
it is a cloud so is not solid.


Can you travel right through the sun? You know, it is also only gas and
plasma.

Think about the pressure - and also the temperature.



And if so would we notice it? 

Yes, obviously!


Do we feel the gravity like on a planet. 

Yes!


And
if we travel more and more across the middle of  a brown dwarf, wouldn't we
be crushed by that gravity?

More to the point, by the pressure. The gravity does not *increase* when you go inwards, but actually decreases.


I've read that a brown dwarf is born from a cloud of hydrogen and Helium but
couldn't end up in a Star but it has enought gravity to hold together and
don't evaporate in space. But I don't understand why it is called dark
matter then.


Because it is not luminous???


A star exists of ordinary matter Helium and Hydrogen. Or could
stars be born from dark matter too?


Not from *non-baryonic* dark matter.



And are there elements of dark matter others then Helium and Hydrogen.

Black dwarfs usually contain a lot of heavier elements, and are considered to be part of *baryonic* dark matter, yes.


Bye,
Bjoern
.

Relevant Pages

  • Re: OT: Trivia about clouds
    ... others until you see "a cloud" you wish to convey, ... Mostly disagreed about stars. ... > Meet my heap of sand. ... Heaps of sand on a beach are pretty much meaningless. ...
    (talk.origins)
  • Seeing through the Dark: Mapping the interior of interstellar clouds in great detail (Forwarded)
    ... ESO Education and Public Relations Dept. ... in a molecular cloud with an amazing level of detail and to great depth. ... The vast expanses between stars are permeated with giant complexes of cold ... that are as reliable as the use of background stars while providing much ...
    (sci.astro)
  • Seeing through the Dark: Mapping the interior of interstellar clouds in great detail (Forwarded)
    ... Text with all links and the photos are available on the ESO Website at URL: ... a molecular cloud with an amazing level of detail and to great depth. ... The vast expanses between stars are permeated with giant complexes of cold ... that are as reliable as the use of background stars while providing much ...
    (sci.space.news)
  • Re: Dark matter hides, physicists seek (Forwarded)
    ... NV> invisible or dark mass in the outer parts of the galaxy " ... NV> What this quote implies that dark matter is the sole and only ... Correct, but if you look at the mass of the KBOs, it's tiny compared ... If it were stars, we'd ...
    (sci.astro)
  • Re: Dark matter hides, physicists seek (Forwarded)
    ... NV> What this quote implies that dark matter is the sole and only ... Correct, but if you look at the mass of the KBOs, it's tiny compared ... to, say, Jupiter, to say nothing of the Sun. ... If it were stars, we'd ...
    (sci.astro)