Brown dwarves are sub-stellar objects. Unlike most stars, their mass is below the necessary level required to maintain hydrogen-burning nuclear fusion reactions in their cores. Furthermore, they have fully convective surfaces and interiors, with no chemical differentiation by depth. These fascinating attributes make them the focus point of many astronomical researches; currently, the common debate is: do they form like planets or like stars?
According to the paper, brown dwarves do not get hot enough to trigger the nuclear fusion that burns hydrogen, because they have relatively little mass. Without enough matter, the gas at their core – which is the main component of these molecular clouds – cannot convert into helium. Due to their inability to ignite as stars, brown dwarfs end up as cooler, less luminous objects – making them barely visible for astronomers. This is the main reason for their mysterious nature, challenging observers from earth.
The birth of brown dwarfs is made out of the same dense, dusty clouds that spawn stars and planets. However, this is the last shared trait between these stellar elements; often, brown dwarfs are called “failed” stars, since they lack the mass of the hotter, brighter stars. Now, thanks to Spitzer’s long-wavelength infrared camera, astronomers have penetrated the dusty natal cloud containing two baby brown dwarves named SSTB213 J041757. Using collaborative data from Calar Alto Observatory in Spain, they revealed that these two – located in the dark cloud Barnard 213, a region of the Taurus-Auriga complex – might prove to be the faintest and coolest brown dwarfs ever observed.
“We decided to go several steps back in the process when (brown dwarfs) are really hidden,” said David Barrado of the Centro de Astrobiología in Madrid, Spain, lead author of the paper on the discovery in the Astronomy & Astrophysics journal. “During this step they would have an (opaque) envelope, a cocoon, and they would be easier to identify due to their strong infrared excesses. We have used this property to identify them. This is where Spitzer plays an important role because Spitzer can have a look inside these clouds. Without it this wouldn’t have been possible.”
This latest study had several difficulties, since young brown dwarfs evolve rapidly – making it difficult to catch them when they are first born. Although the first brown dwarf was discovered 1995, and hundreds have been found since, none were found in their earliest stages of formation. Moreover, the team has barely found these two brown dwarves. “We were able to estimate that these two objects are the faintest and coolest discovered so far,” Barrado said.
The so-called ‘twins’ had their properties measured and analyzed using a host of powerful astronomical tools. In order to capture the presence of the envelope around the young objects, the team used data from the Caltech Submillimeter Observatory in Hawaii. That information, coupled with what they had from Spitzer, enabled the astronomers to draw a diagram that shows the amount of energy emitted by the objects in each wavelength.
The study claims to bring a final solution to the mystery about whether brown dwarfs form more like stars or planets. The answer suggested is that they form like low-mass stars. The theory is bolstered by the change in brightness of the objects at various wavelengths, matching that of other very young, low-mass stars. While only further study will confirm whether these two celestial objects are in fact brown dwarfs, they are the best candidates so far, says Barrado. Furthermore, he says he enjoyed greatly the journey to their discovery, since “it is a story that has been unfolding piece by piece.” Pausing for a moment, he’s being poetic, and adds: “Sometimes nature takes its time to give up its secrets.”
TFOT has also covered a pair of newly discovered brown dwarves, which are gravitationally linked together, and the Formation of Planets, researched by the Multi-Object Apache Point Observatory Radial Velocity Exoplanet Large-Area Survey. Other TFOT related stories include the detection of Water Spirals around a Newborn Star, made by NASA’s Spitzer Space Telescope, and the images of Stars’ Birth at Orion, captured by NASA’s Spitzer and Hubble Space Telescopes.
For more information about the discovery of baby brown dwarves, see NASA’s press release.