Brown Dwarfs

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Transcript Brown Dwarfs

BROWN DWARFS
Failed Stars of the Universe
Stars come in many shapes and sizes,
but they all have one thing in
common-they are massive enough to
ignite the process of nuclear fusion
that makes them shine.
However, untold numbers of
stellar-like objects are not born
massive enough to light up,
making them too faint to be
studied through optical
telescopes.
Brown Dwarfs
generate a small
amount of
energy from
fusion, but their
supply is used
up quickly,
leaving them
dark.
Stars like red
dwarfs are
massive enough
to support
thermonuclear
reactions, so
they emit light.
Planets such as
Jupiter are
similar in size to
brown dwarfs,
but they form
differently and
can not burn
hydrogen.
The mass of a brown
dwarf is no more than
eight percent of the
Sun’s mass, and many
are not much bigger
than Jupiter.
If Brown Dwarfs do not shine and are
almost as small as Jupiter. . .
How do we find them?
Brown Dwarfs, although relatively cool
compared to stars, glow because of the
heat generated by the release of
gravitational energy as they slowly
contract.
Using infrared telescopes,
this heat can be seen
against the even colder
background of deep space.
Visible
In 2000, Hubble took images of a star cluster
in visible and infrared wavelengths looking for
brown dwarfs.
Orion Nebula's Trapezium cluster
Visible light
In the infrared image the stars and brown dwarfs
in this young cluster can be seen easily.
Orion Nebula's Trapezium cluster
Infrared
By measuring the
temperatures of the
stars Hubble saw,
scientists discovered
nearly 50 brown dwarfs.
From this data, researchers now
believe brown dwarfs are nearly
as abundant as stars, and that
there are more low mass brown
dwarfs than high mass ones.
Another method used to search for Brown Dwarfs is
based on the effects of gravitational microlensing.
When a massive object, such as a brown dwarf, gets
between a distant star and an observer, the gravity
of the interfering object bends the distant star's light
similar to a lens, magnifying the star's light.
Recently, a group led by UCLA astronomy
professor Ian S. McLean has made the
most systematic and comprehensive
analysis of more than 50 brown dwarfs by
obtaining their infrared spectra.
The infrared spectra of a brown dwarf
reveals its physical and chemical properties.
Infrared Spectra of a Red Dwarf and a Brown Dwarf
The major difference
in the two is the high
level of methane
found only in brown
dwarfs.
This research has helped to:
• Show Brown dwarfs are the missing
link between gas giant planets like
Jupiter and small stars like red dwarfs
• Allow future astronomers to obtain the
infrared spectrum of a newly
discovered brown dwarf and compare
the spectrum with those already
published so they can identify what
kind of brown dwarf they have found