Debris disks may not sound familiar to many, but they are common in the universe. They can be found around a quarter of all main-sequence stars or perhaps more since current instruments used in finding them can only detect debris disks in planetary systems that are at least more luminous than the disk in Kuiper's Belt.
Some examples of debris disks are the asteroid belt between Mars and Jupiter, and the region called Oort cloud or Kuiper belt in the Solar System that extends from the orbit of Neptune about 30 astronomical units (au) to 50 au.
K-type main-sequence star (triple system) 25 ly away in the constellation Piscis Austrinus - Surrounded by several debris disks and possibly by planets - The second brightest star from the Solar System known to have a planetary system, after Pollux -
How are Debris Disks Formed?
Debris disks are tenuous belts of dusts formed when asteroids or other planetesimals collide and fragmented. Most of the main-sequence stars have debris disks, but they are hard to detect because current instruments only noticed them when its order of magnitude is more luminous than the disk generated by the solar system's Kuiper Belt.
The National Radio Astronomy Observatory (NRAO) explains that to answer the question of how debris disks form also means finding some answers that could help us understand the planets, exoplanets and the universe. In addition, it would also lead to answering how the universe evolved up until a planetary system has formed.
But since that is too many questions, scientists usually assume that the universe has formed and evolved in a way that led to the formation of planetary systems rich in heavy elements, molecules, gas, and dust.
That means clouds of gas and dust that span 10s of light-years are scattered through the galaxies and other galaxies that soon clumped and collapsed on themselves due to turbulence or self-gravity within the gas and dust particles. Then, these clumps form a protostar at the center after thousands of years.
The protostar is so hot that it also heats the material surrounding it. During its early stages of formation, lots of dust and gas are pulled towards the protostar. Scientists predict that the conservation of angular momentum has led to the material flattening and becoming disks, also known as protoplanetary disks.
Through lots of mechanisms over the next millions of years, larger clumps form inside the disk and their gravity allows them to pull more material from the disk. Scientists believe that they eventually can carve out gaps in the disk or become planets. The gap's dimension is significant in tracing the mass of the planet, which is a key exoplanet parameter that is otherwise difficult to determine. But since not all material is consumed, some clumps of materials that are big enough to be planets remain and become comets or asteroids, depending on the temperature where they were formed.
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Why Study Debris Disks?
According to Phys.org, debris disks are worthy of studying because it offers an opportunity to trace the formation of planetary systems. Telescopes, such as the Atacama Large Millimeter/submillimeter Array (ALMA), measure the largest dust grains as big as a millimeter and are relatively unaffected by stellar winds or radiation pressure.
Furthermore, scientists said that the distribution of dust grains reveals the effects of gravity and collisions within the disk's "chaotic zone" where planets or exoplanets form.
For instance, astronomers Sean Andrews and David Wilner, who used ALMA, found that the debris disk around the brown dwarf star HD 206893 has a gap stretching about 63-94 au. Chaotic zone theory implies that a planet should have a mass that is 1.4 times the mass of Jupiter and orbits at about 79 au to cause this kind of gap if a single planet indeed created it.
The team noted that higher resolution ALMA observations are needed to potentially constrain the dynamic behavior of the brown dwarf star to properly characterize the new planet.
They described in full the findings of their study, titled "Resolving Structure in the Debris Disk around HD 206893 with ALMA," in The Astrophysical Journal.
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