BROWN DWARFSBROWN 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.

Stars like red dwarfs are massive enough to support thermonuclear reactions, so they emit light.

Brown Dwarfs generate a small

amount of energy from

fusion, but their supply is used

up quickly, leaving them

dark.

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

Orion Nebula's Trapezium cluster Visible light

In 2000, Hubble took images of a star cluster in In 2000, Hubble took images of a star cluster in visible and infrared wavelengths looking for visible and infrared wavelengths looking for brown dwarfs.brown dwarfs.

Orion Nebula's Trapezium cluster Infrared

In the infrared image the stars and brown dwarfs In the infrared image the stars and brown dwarfs in this young cluster can be seen easily.in this young cluster can be seen easily.

By measuring the By measuring the temperatures of the temperatures of the stars Hubble saw, stars Hubble saw, scientists discovered scientists discovered nearly 50 brown dwarfs.nearly 50 brown dwarfs.

From this data, researchers now From this data, researchers now believe brown dwarfs are nearly believe brown dwarfs are nearly as abundant as stars, and that as abundant as stars, and that there are more low mass brown there are more low mass brown dwarfs than high mass ones.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