The California Institute of Technology astronomers said they are calling the new objects L dwarfs and that the discovery will force revision of a century-old system of classifying stars based on their chemistry and temperature.
J. Davy Kirkpatrick told the American Astronomical Society that he and his colleagues discovered that some objects have a surface temperature three times lower than the sun, a mass about a third of the sun and a diameter about like Jupiter.
"They are radically different and require a new classification," said Kirkpatrick. He said they have distinctive temperature and chemistry.
"These look like stars," said I. Neill Reid, part of the Cal Tech team, "but they just haven't managed to get enough mass together to start nuclear fusion," the process that makes stars shine.
The objects are thought to have heated as they formed from the gravitational accumulation and compression of gas. But this heat is slowly fading, like dying embers. A star is created when the mass is great enough to compress the gas to a point that fusion fires are ignited in its core.
Kirkpatrick said the team discovered 20 of the objects in a survey of just 1 percent of the sky out to about 100 light-years from the sun.
A statistical projection of this number suggests that about half of every 2,000 stellar points of light in the Milky Way galaxy may, in fact, be these L dwarfs, he said. A light-year is the distance light travels in a year in a vacuum, about 5.8 trillion miles.
"L's are the most common type of objects," said Kirkpatrick. "There are just about as numerous as all of the other types combined."
By splitting the light into colors, or spectrum, astronomers can determine the distinctive chemistry of stellar objects. This allows them to calculate the temperature and mass of the objects.
Using this technique, astronomers since 1817 have divided stars into classes based on the spectral characteristics. At first, the star classes were designated alphabetically, A through M, but some were dropped due to duplication. And in 1901, a Harvard astronomer, Annie Jump Cannon, arranged the remaining classes by temperature, from hottest to coolest.
Cannon's work produced a sequence of classes identified, in order, as OBAFGKM. Astronomy students have been taught for decades to remember this sequence by using the mnemonic "Oh, be a fine girl (or guy), kiss me."
Kirkpatrick said that since the object his team has discovered is the coolest, it would follow the M class the spectral sequence of objects. He proposed that they carry the letter L, creating a new hottest-to-coolest sequence of OBAFGKML.
For the mnemonic, Kirkpatrick suggests "Oh, be a fine girl/guy, kiss my lips."/b>
Kirkpatrick said the spectra of six of the new objects show the presence of lithium. This reading disappears if objects are cooler than 4.5 million degrees Fahrenheit and too cold to ever achieve the nuclear fusion process of stars.
This means they are actually not stars, but "brown dwarfs," a type of failed star that is bigger than a planet, but smaller than a star such as the sun.
Over millions of years, the L objects will cool, like dying embers, and eventually become too cold to be detected from Earth, he said.
Written by Paul Recer
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