Citizen scientists have helped astronomers discover two of the most extreme brown dwarfs found yet. Brown dwarfs, in general, are considered almost like a missing link between stars and giant planets. These newly discovered ones are quintessentially so: they have the lowest masses and temperatures for their type.
As reported in The Astrophysical Journal, the two objects don’t match up exactly with previously established classes of brown dwarfs. Researchers have classified them as “the first extreme T-type subdwarfs”. They appear to have only a small concentration of heavy elements, their temperatures are at most 1,130 °C (2,060 °F), and they have a mass about 75 times that of Jupiter. This means they don't have enough mass to power themselves as stars do, making them the most planet-like brown dwarfs discovered.
The most massive exoplanet known, HR 2562 b, is estimated to be between 15 and 45 times the mass of Jupiter, very close to the mass of these brown dwarfs. The distinction between the two classes is often blurred but these two objects provide some new insights. A typical brown dwarf has about 30 times more iron and other metals as these two objects. These T-type subdwarfs have just 3 percent of the iron concentration than the Sun has, and this metal content might be key to the separation of exoplanets and brown dwarfs.
“A central question in the study of brown dwarfs and exoplanets is how much does planet formation depend on the presence of metals like iron and other elements formed by multiple earlier generations of stars. The fact that these brown dwarfs seem to have formed with such low metal abundances suggests that maybe we should be searching harder for ancient, metal-poor exoplanets, or exoplanets orbiting ancient metal-poor stars,” co-author Marc Kuchner, an astrophysicist at NASA's Goddard Space Flight Center, said in a statement.
Kuchner is the principal investigator of Backyard Worlds: Planet 9 the citizen science project that discovered these two brown dwarfs. The project’s goal is to find evidence of the hypothetical Planet 9 that may or may not exist many times further away from the Sun. Given it is so far away, it would be very difficult to discover it using the light it reflects from the Sun, but it should be detectable in infrared.
Backyard Worlds: Planet 9 used infrared data to spot moving objects in the sky. No evidence of Planet 9 has yet been uncovered but over 150,000 citizen scientists participating in the project have helped to discover 1,600 brown dwarfs, the oldest and coldest white dwarf, and many other astronomical objects.
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