A brown dwarf is a celestial body that has never quite become a star. A typical brown dwarf has a mass that is 8 percent or less than that of the Sun. The mass of a brown dwarf is too small to generate the internal temperatures capable of igniting the nuclear burning of hydrogen to release energy and light.
A brown dwarf contracts at a steady rate, and after it has contracted as much as possible, a process that takes about 1 million years, it begins to cool off. Its emission of light diminishes with the decrease in its internal temperature, and after a period of 2 to 3 billion years, its emission of light is so weak that it can be difficult to observe from Earth.
Because of these characteristics of a brown dwarf, it can be easily distinguished from stars in different stages of formation. A brown dwarf is quite distinctive because its surface temperature is relatively cool and because its internal composition-approximately 75 percent hydrogen- has remained essentially the same as it was when first formed. A white dwarf, in contrast, has gone though a long period when it burns hydrogen, followed by another long period in which it burns the helium created by the burning of hydrogen and ends up with a core that consists mostly of oxygen and carbon with a thin layer of hydrogen surrounding the core.
It is not always as easy, however, to distinguish brown dwarfs from large planets. Though planets are not formed in the same way as brown dwarfs, they may in their current have some of the same characteristics as a brown dwarf. The planet Jupiter, for example, is the largest planet in our solar system with a mass 317 times that of our planet and resembles a brown in that it radiates energy based on its internal energy. It is the mechanism by which they were formed that distinguishes a high-mass planet such as Jupiter from a low-mass brown dwarf. 2. Pulsars
There is still much for astronomers to learn about pulsars. Based on what is known, that term pulsar is used to describe the phenomenon of short, precisely timed radio bursts that are emitted from somewhere in space. Though all is not known about pulsars, they are now believed in reality to emanate from spinning neutron stars, highly reduced cores of collapsed attars that are theorized to exist.
Pulsars were discovered in 1967, when Jocelyn Bell, a graduate student at Cambridge University, noticed an unusual pattern on a chart from a radio telescope. What made this pattern unusual was that, unlike other radio signals from celestial objects, this series of pulses had a highly regular period of 1.33730119 seconds. Because day after day the pulses came from the same place among the stars, Cambridge researchers came to the conclusion that they could not have come from a local source such as an Earth satellite.
As more and more were found, astronomers engaged in debates over their nature. It was determined that a pulsar could not be a star in as much as a normal star is too big to pulse so fast. The question was also raised as to whether a pulsar might be a white dwarf star, a dying star that has collapsed to approximately the size of the Earth and is slowly cooling off. However, this idea was so rejected because the fastest pulsar known at the time pulsed around thirty times per second and a white dwarf, which is the smallest known type of star, would not hold together if it were to spin that fast.
The final conclusion among astronomers was that only a neutron star, which is theorized to be the remaining core of a collapsed star that has been reduced to a highly dense radius of only around 10 kilometers, was small enough to be a pulsar. Further evidence of the link between pulsars and neutron stars was found in 1968, when a pulsar was found in the middle of the Crab Nebula. The Crab Nebula is what remains of the supernova of the year 1054, and in as much as it has been theorized that neutron stars sometimes remain following supernova explosions, it is...