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Astronomers have made the first unambiguous detection of an elusive type of object known as a brown dwarf. The evidence consists of observations from inch and inch telescopes on Mount Palomar, and a confirmatory image from the Hubble telescope.
The brown dwarf, called Gliese B GLB , is a small companion to the cool, red star Gliese , located 19 light-years from Earth in the constellation Lepus. Estimated to be 20 to 50 times the mass of Jupiter, GLB is too massive and hot to be classified as a planet, but too small and cool to shine like a star. At least , times dimmer than Earth's Sun, the brown dwarf is the faintest object ever seen orbiting another star.
Astronomers have made the first unambiguous detection and image of an elusive type of object known as a brown dwarf. The evidence consists of an image from the inch observatory on Mt.
Palomar, a spectrum from the inch Hale telescope on Mt. The brown dwarf, called Gliese B GLB , is a small companion to the cool red star Gliese , located 19 light-years from Earth in the constellation Lepus.
Estimated to be 20 to 50 times the mass of Jupiter, GLB is too massive and hot to be classified as a planet as we know it, but too small and cool to shine like a star. Kulkarni added, however, that "it looks like Jupiter, but that's what you'd expect for a brown dwarf. Methane is not seen in ordinary stars, but it is present in Jupiter and other giant gaseous planets in our solar system.
The Hubble data obtained and analyzed so far already show the object is far dimmer, cooler no more than 1, degrees Fahrenheit and less massive than previously reported brown dwarf candidates, which are all near the theoretical limit eight percent the mass of our Sun where a star has enough mass to sustain nuclear fusion.
Brown dwarfs are a mysterious class of long-sought object that forms the same way stars do, that is, by condensing out of a cloud of hydrogen gas. However, they do not accumulate enough mass to generate the high temperatures needed to sustain nuclear fusion at their core, which is the mechanism that makes stars shine.
Instead brown dwarfs shine the same way that gas giant planets like Jupiter radiate energy, that is, through gravitational contraction. In fact, the chemical composition of GLB's atmosphere looks remarkably like that of Jupiter. The discovery is an important first step in the search for planetary systems beyond the Solar System because it will help astronomers distinguish between massive Jupiter-like planets and brown dwarfs orbiting other stars.
Advances in ground- and space-based astronomy are allowing astronomers to further probe the "twilight zone" between larger planets and small stars as they search for substellar objects, and eventually, planetary systems. Follow-up observations a year later were needed to confirm it is actually a companion to Gliese The discovery was made with a inch reflecting telescope at Palomar Observatory in southern California, using an image-sharpening device called the Adaptive Optics Coronagraph, designed and built at the Johns Hopkins University.
Another Hubble observation six months from now will yield an exact distance to GLB. The astronomers suspect that the brown dwarf developed during the normal star-formation process as one of two members of a binary system. However, the astronomers say they cannot yet fully rule out the possibility that the object formed out of dust and gas in a circumstellar disk as a "super-planet.
Astronomers say the difference between planets and brown dwarfs is based on how they formed. Planets in the Solar System are believed to have formed out of a primeval disk of dust around the newborn Sun because all the planets' orbits are nearly circular and lie almost in the same plane. Brown dwarfs, like full-fledged stars, would have fragmented and gravitationally collapsed out of a large cloud of hydrogen but were not massive enough to sustain fusion reactions at their cores.
The orbit of GLB could eventually provide clues to its origin. If the orbit is nearly circular then it may have formed out of a dust disk, where viscous forces in the dense disk would keep objects at about the same distance from their parent star. If the dwarf formed as a binary companion, its orbit probably would be far more elliptical, as seen on most binary stars. The initial Hubble observations will begin providing valuable data for eventually calculating the brown dwarf's orbit.
However, the orbital motion is so slow, it will take many decades of telescopic observations before a true orbit can be calculated.
GLB is at least four billion miles from its companion star, which is roughly the separation between the planet Pluto and our Sun. Astronomers have been trying to detect brown dwarfs for three decades. Their lack of success is partly due to the fact that as brown dwarfs age they become cooler, fainter, and more difficult to see. An important strategy used by the researchers to search for brown dwarfs was to view stars no older than a billion years. Caltech's Nakajima reasoned that, although brown dwarfs of that age would be much fainter than any known star, they would still be bright enough to be spotted.
With the advent of sophisticated light sensors and adaptive optics, astronomers now have the powerful tools they need to resolve smaller and dimmer objects near stars. Hubble was used to look for the presence of other companion objects as bright as the brown dwarf which might be as close to the star as one billion miles. No additional objects were found, though it doesn't rule out the possibility of Jupiter-sized or smaller planets around the star, said the researchers.
The Palomar results will also appear in the November 30 issue of the journal Nature and the December 1 issue of the journal Science.
Today, you might just as easily find astronomers humming this nursery rhyme as well as children. Rapid advances in telescope technology — adaptive optics, space observatories, interferometry, image processing techniques — are allowing astronomers to see ever fainter and smaller companions to normal stars. As telescopic capabilities sharpen, conventional definitions for planets and stars may seem to be getting blurry.
In the search for other planetary systems, astronomers are turning up objects that straddle the dim twilight zone between planets and stars, and others that seem to contradict conventional wisdom, such as a planetary system accompanying a burned-out compacted star called a neutron star. Stars are large gaseous bodies that generate energy through nuclear fusion processes at their cores —where temperatures and pressures are high enough for hydrogen nuclei to collide and fuse into helium nuclei, converting matter to energy in the process.
Stars are born out of clouds of hydrogen, that collapse under gravity to form dense knots of gas. This collapse continues until enough pressure builds up to heat the gas and trigger nuclear fusion. The energy released by this "fusion-engine" halts the collapse, and the star is in equilibrium. A star's brightness, temperature, color and lifetime are all determined by its initial mass.
Our Sun is a typical middle-aged star halfway through its ten billion-year life. Following a fiery birth, stars lead tranquil lives as inhabitants of the galaxy. Late in a star's life, fireworks can begin anew as changes in the core heat the stars further, eject its outer layers, and cause it to pulsate. All stars eventually burn out.
Most collapse to white dwarf stars — dim planet-sized objects that are extraordinarily dense because they retain most of their initial mass.
Extremely massive stars undergo catastrophic core collapse and explode as supernovae — the most energetic events in the universe. Black holes and neutron stars — ultra dense stellar remnants with intense gravitational fields — can be created in supernova blasts. At least half of the stars in the galaxy have companion stars. These binary star systems can undergo complicated evolutionary changes as one star ages more rapidly than the companion and dies out.
If the two stars are close enough together, gas will flow between them and this can trigger nova outbursts. Supernovae and novae are key forces in a grand cycle of stellar rebirth and renewal. Heavier elements cooked up in the fusion furnaces of stars are ejected back into space, serving as raw material for building new generations of stars and planets.
Though the universe contains billions upon billions of stars, until recently only nine planets were known — those of our solar system. The Solar System provides a fundamental model for what we might expect to find around other stars, but it's difficult to form generalities from just one example. It may turn out that nature is more varied and imaginative when it comes to building and distributing planets throughout the Galaxy. In it simplest definition, a planet is a nonluminous body that orbits a star, and is typically a small fraction of the parent star's mass.
Planets form out of a disk of dust and gas that encircles a newborn star. These embryonic disks have been observed around young stars, both in infrared and visible light. The planets' orbits in our solar system trace out the skeleton of just such a disk that encircled the newborn Sun. Planets agglomerate from the collision of dust particles in the disk, and then snowball in size to solid bodies that continue gobbling up debris like cosmic Pac-Men.
In the case of our solar system this led to eight major bodies, thousands to tens of thousands of miles across. The ninth planet, Pluto, is probably a survivor of an early subclass of solar system inhabitants called icy dwarfs. A planet's mass and composition are determined by where it formed in the disk. In the case of our solar system the more massive planets are found far from the Sun, though not too far where material didn't have time to agglomerate because orbital periods were so slow that chances for collisions were minimal.
Unlike asteroids which are cold chunks of solar system debris, a planet must be massive enough to have at least once had a molten core that differentiated the planet's interior. This is a process where heavier elements sank to the center and lighter elements float to the surface. Depending how far they formed from their parent star, they may retain a dense mantle of primordial hydrogen and helium. In the case of our solar system this establishes two families of planets: Massive planet like Jupiter are still gravitationally contracting and shine in infrared light.
Ironically, the first bonafide planetary system ever detected beyond our Sun exists around a neutron star - a collapsed stellar core left over from the star's self-detonation as a supernova. Resembling our inner solar system in terms of size and distribution, these three planets orbiting the crushed star probably formed after the star exploded. Apparently a disk must have formed after the stellar death, from which the planets agglomerated.
Other suspected extrasolar planets also seem to defy conventional wisdom. An object orbiting the star 51 Pegasus may have the mass of Jupiter, but is 20 times closer to the star than Earth is from the Sun. Brown dwarfs are the galaxy's underachievers.
They never quite made it as stars. Like stars, brown dwarfs collapse out of a cloud of hydrogen. Like a planet they are too small to shine by nuclear fusion, and radiate energy only through gravitational contraction. More massive brown dwarfs might have initiated fusion, but could not sustain it. Their predicted masses range from several times the mass of Jupiter to a few percent the mass of our Sun. Spectroscopically, the cool dwarfs may resemble gas giant planets in terms of chemical composition.
The different type of so-called "dwarfs" in the Galaxy would even befuddle the storybook character, Snow White:. Ironically, their surface temperature rises as they collapse and so the star is white-hot.
The cooler a star the redder it is, just as a dying ember fades from yellow-orange to cherry-red. The universe isn't old enough yet for black dwarfs to exist. Nov 29, 3: Kulkarni Caltech , D.