Stars and Planets » Brown Dwarfs

Somewhere between a True Star ( a low mass red dwarf star) and a Gas Giant Planet are the Brown Dwarfs. Although they may not be much larger than Jupiter in size they are far larger in mass. The upper mass for a brown dwarf is that which is just insufficient for normal hydrogen fusion to be triggered in the core. Based on theoretical considerations, this is believed to be between 0.075 and 0.080 solar mass, or 75 to 80 times the mass of Jupiter. The lower mass limit is somewhat arbitrary as there is no obvious point of transition between a high-mass planet and a low-mass brown dwarf, but it is generally taken to be about 0.013 solar masses or about 13 times the mass of Jupiter.
Brown dwarfs are too cool to give off much visible light but they do emit substantial amounts of radiation in the infrared as a result of slow gravitational contraction and the fusion of deuterium and possibly lithium. They are thus amenable to detection by ground-based and spaceborne infrared telescopes. As in the case of extrasolar planets, brown dwarfs can also be found if they happen to be orbiting a star. 'Small' brown dwarfs burn deuterium (Deuterium + Proton gives helium 3) at around ½ million degrees Celsius. Higher mass brown dwarfs burn deuterium at ½ million and lithium at around 3 million degrees Celsius.

Ray Goodwin

Somewhere there are mountains
Glistening in the snow
Somewhere there are mountains
That we shall never know

Somewhere there are rivers
Flowing fast and free
Somewhere there are rivers
That we can never see

Somewhere there are oceans
And sun drenched island sands
Forests full of creatures
In vastly distant lands

Somewhere there’s a planet
Beneath an alien star
The people watch our tiny sun
And wonder where we are

One day perhaps we’ll find them
Across the void of space
Perhaps through ways as yet unknown
We’ll meet them face to face

The author of this web site Ray Goodwin holds B.Sc. Degrees from London University in Chemistry, Geology and Physiology and an M.Sc. in Biochemistry. He has spent most of his professional life teaching in Colleges of Technology. On his retirement he has entered the fields of astronomy, astrochemistry, astrobiology and space sciences. He has spent a great deal of his retirement in visiting amateur astronomy societies and in attending European Space Agency Symposia in ESTEC in the Netherlands and other scientific conferences in England and Sweden. He regularly attends the yearly European Astrofest in South Kensington London and other meetings in the UK. He has written scientific articles and given a number of lectures on diverse scientific subjects.

Readers of this web site are invited to e-mail the author ( and discuss their opinions of the topics dealt with and suggest any changes which they think may be helpful.

Life in the Cosmos Website
Version 01.00 - April 20, 2015.