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Artist's rendition of a brown dwarf
The motion of the stars and galaxies are influenced by material which
has not yet been detected.
Much of this invisible dark matter, which astronomers call "missing mass",
could be made up of brown dwarfs
- objects whose mass is between twice that of Jupiter and the lower mass
limit for nuclear reactions (0.08 times the mass of our sun).
Brown dwarfs are basically failed stars which did not have enough density
at their cores to start nuclear fusion. The conversion of hydrogen into
helium in a star's core by nuclear fusion is what fuels a star. This
fusion process requires an extremely high density at the star's core to
compress the hydrogen atoms together and produce helium.
Another component of the missing mass may be the burned-out cores of dead
stars. When most stars run out of fuel and their fusion reactions stop,
they eventually cool off to the point where they no longer radiate enough
visible light to be detected by optical telescopes.
Brown dwarfs are very dim and cool compared with stars.
The best hope for finding brown dwarfs is in using infrared telescopes, which
can detect the heat from these objects even though they are too cool to radiate
visible light.
Many brown dwarfs have also been discovered embedded in large clouds of gas and
dust. Since infrared radiation can penetrate through the dusty regions of space,
brown dwarfs can be discovered by infrared telescopes, even deep within thick
clouds.
Recently, 2MASS
(Two Micron All Sky Survey) data revealed the
coolest known brown dwarf.
To the right is an infrared image of the Trapezium star cluster in the Orion
Nebula. This image was part of a survey done at the United Kingdom Infrared
Telescope
(UKIRT)
in which over 100 brown dwarf
candidates were identified in the infrared.
Philip Lucas (Univ. Hertfordshire) and
Patrick Roche (Univ. Oxford), UKIRT
Artist's rendition (Robert Hurt, IPAC)
The discovery of the objects which make up the missing mass will
also give astronomers a better idea about the fate of
our universe. Our universe is currently expanding, due to the Big Bang.
If there is enough mass, it is thought that the expansion of the universe
will eventually slow down and then the universe will start collapsing.
This scenario could mean that the universe goes through an endless cycle
of expansions and contractions, with a new Big Bang occurring everytime the
universe
ends its collapse. If there is not enough mass for the universe to collapse,
then it will expand forever. We will only know the fate of the universe
when we can accurately estimate how much mass the universe has in it.
The detection of the missing mass will likely be a key to answering this
question.
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