Brown dwarfs are substellar objects, often dismissively referred to as “failed stars”, that never managed to acquire sufficient mass to sustain hydrogen fusion–so necessary for the attainment of true stardom. Clearly, the runts of the stellar litter, brown dwarfs occupy the mass range between the heaviest of gas-giant planets and the very lightest of true stars, with an upper limit of approximately 75 to 80 Jupiter-masses. In July 2015, astronomers using the Karl G. Jansky Very Large Array (VLA) announced that they have detected tattle-tale jets of material being hurled out into space by still-forming baby brown dwarfs. This discovery is important because it provides the first direct evidence that these “failed stars” are born as a result of a scaled-down version of the same process that gives birth to true baby stars. Brown dwarfs are born to be stars but, tragically, never grow big enough for nuclear fusion to light their stellar fires!
The Karl G. Jansky VLA is a radio astronomy observatory located on the Plains of San Agustin, between the towns of Magdalena and Datil, about 50 miles west of Socorro, New Mexico. A component of the National Radio Astronomy Observatory (NRAO), the VLA has enabled astronomers to make extremely valuable observations of black holes and protoplanetary disks circling youthful stars, discover magnetic filaments, and trace complex gas motions at our Milky Way Galaxy’s center. The VLA has also investigated cosmological parameters and provided insight into the physical mechanisms that produce radio emissions.
Brown dwarfs are genuine “oddballs”, weird and bewitching objects whose existence challenges the neat distinction between true stars and giant planets. It has long been thought by many astronomers that these relatively tiny, cool denizens of the Cosmos, form the same way as true stars. Stars form within extremely dense blobs that are embedded within the billowing, churning folds of one of the numerous dark and very cold molecular clouds that haunt the space between stars like gigantic ghosts. When this especially dense blob collapses under the pull of its own gravity, it starts to churn out a sparkling host of fiery, newborn stars–brilliant, dazzling protostars. 바카라사이트
As the baby star emerges within the contracting cloud of gas, the temperature at the center of the blob soars to the point that hydrogen atoms start to fuse together to form helium atoms. Hydrogen is the lightest and most abundant atomic element in the Cosmos, and helium is the second-lightest. All stars are primarily composed of hydrogen, and both hydrogen and helium came into being in the searing-hot fireball of the Big Bang that heralded our Universe’s mysterious birth about 13.8 billion years ago (Big Bang nucleosynthesis). All of the atomic elements that are heavier than helium formed in the intensely hot hearts of our Universe’s billions upon billions of stellar sparklers–or, alternatively, in the supernovae blasts that marked their deaths. The cores of all the stars in the Cosmos progressively fused increasingly heavier and heavier atomic elements from lighter ones (stellar nucleosynthesis). The process of nuclear fusion produces an enormous amount of energy, which is the reason why stars shine so brilliantly.
Planets do not form the same way as stars. Forming within a ring of sticky, tiny dust motes and gas that surrounds a young star–termed the protoplanetary accretion disk–planets never manage to put on enough weight to heat up sufficiently to cause their constituent particles to fuse and emit dazzling, blazing energy. Planets do not become massive and hot enough to shine with their own fierce and ferocious light.
Puny brown dwarfs are unfortunate failures. They are too small to attain true stardom like their more massive, roiling, and searing-hot stellar kin. These relatively tiny “failed stars” have sizes somewhere between those of a gas-giant planet–like Jupiter in our own Solar System–and small red dwarf stars. Red dwarfs are the smallest true stars inhabiting our Cosmos, and they live for a very long time, and are quite cool by star-standards. Nonetheless, red dwarfs are sufficiently massive for their nuclear-fusing furnaces to catch fire, and they only experience a leisurely cool burn. The smaller the star, the longer it “lives”. Massive, large stars lead fast stellar “lives”, and die young. This is because massive stars burn their supply of hydrogen fuel very rapidly, and blast themselves to pieces in supernovae explosions when the radiation pressure that they have derived from burning their necessary supply of hydrogen fuel is depleted, and they can no longer hold their own against the horrific crush of their own gravity. Smaller, less massive stars–like red dwarfs–very lazily burn their hydrogen fuel, and “live” to be very, very old. In fact, red dwarfs–the most numerous stars in the Cosmos–can theoretically “live” for trillions of years.
Because brown dwarfs possess merely the small quantity of heat that they were born with, they never light up the Universe like true, successful stars. Most astronomers classify an object that is between 15 and 75 times the mass of Jupiter as a brown dwarf. This specific range of masses does not allow the object to fuse hydrogen into helium in the same dazzling manner as larger red dwarfs, and other much more massive true stars.