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Finding Exoplanets in Debris Disks

An artist’s impression of a star’s dusty debris disk, thought to be produced when asteroids or other planetesimals collide and fragment. Astronomers studying the debris disk around the star HD 206893 have imaged a wide gap in the disk extending from about 50 to 185 au from the star. After modeling the system, they conclude it contains a 1.4 Jupiter-mass planet orbiting about 79 au from the central star. Credit: NAOJ

Debris disks around main-sequence stars are tenuous belts of dust thought to be produced when asteroids or other planetesimals collide and fragment. They are common: more than about a quarter of all main-sequence stars have debris disks and, since these disks can be hard to detect, it is likely that the fraction is even higher. Current instruments are only able to detect debris disks in systems that are at least an order of magnitude more luminous than the disk generated by the solar system’s Kuiper Belt (the region extending from the orbit of NeptuneNeptune is the farthest planet from the sun. In our solar system, it is the fourth-largest planet by size, and third densest. It is named after the Roman god of the sea.”>Neptune at about thirty astronomical units out to about fifty au).

The dust in debris disks is worthy of study in its own right but also offers an opportunity to trace the properties of planetary systems. The largest dust grains (those as big as a millimeter), whose collective thermal emission is measured with telescopes like ALMAThe Atacama Large Millimeter/submillimeter Array (ALMA) is the largest ground-based facility for observations in the millimeter/submillimeter regime in the world. ALMA comprises of 66 high-precision dish antennas of measuring either 12 meters across or 7 meters across and is an international partnership between Europe, the United States, Japan and the Republic of Chile. “>ALMA (Atacama Large Millimeter/submillimeter Array), are relatively unaffected by stellar winds or radiation pressure. Rather, their distribution reveals the effects of gravity and collisions. The “chaotic zone” is the extended region around a planet within which dust has no stable gravitational orbits, resulting in a gap whose width depends among other things on the planet’s mass. A planet in a debris disk can create such a gap, and measurements of the gap’s dimensions can thus be used to deduce the mass of the planet – a key exoplanetAn exoplanet (or extrasolar planet) is a planet that is outside the Solar System, orbiting around a star other than the Sun. The first suspected scientific detection of an exoplanet occurred in 1988, with the first confirmation of detection coming in 1992.”>exoplanet parameter that is otherwise difficult to obtain.

CfAThe Harvard-Smithsonian Center for Astrophysics (CfA) is a joint venture between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. Founded in 1973, the Harvard-Smithsonian Center for Astrophysics is comprised of six research divisions: Atomic and Molecular Physics; Optical and Infrared Astronomy; High Energy Astrophysics; Radio and Geoastronomy; Stellar, Solar, and Planetary Sciences; and Theoretical Astrophysics.”>CfA astronomers Sean Andrews and David Wilner were members of a team that used ALMA to study the known debris disk around the star HD 206893 about 135 light-years away from us. The star also has a brown dwarf binary companion orbiting at about 10au and whose mass is about 15-30 JupiterJupiter is the largest planet in the solar system and the fifth planet from the sun. It is a gas giant with a mass greater then all of the other planets combined. Its name comes from the Roman god Jupiter.”>Jupiter-masses. The ALMA images spatially resolve the disk — it extends from about 50 -185 au — and the astronomers find evidence for a gap stretching from about 63 – 94 au. If the gap was carved by a single planet in a circular orbit, chaotic zone theory implies the planet should have a mass of about 1.4 Jupiter-masses and orbit at about 79 au. Future, higher resolution ALMA observations have the potential to help constrain the dynamical behavior of the brown dwarf as well as to improve the characterization of the inferred new planet.

Reference: “Resolving Structure in the Debris Disk around HD 206893 with ALMA” by Ava Nederlander, A. Meredith Hughes, Anna J. Fehr, Kevin M. Flaherty, Kate Y. L. Su, Attila Moór, Eugene Chiang, Sean M. Andrews, David J. Wilner and Sebastian Marino, 6 August 2021, The Astrophysical Journal.
DOI: 10.3847/1538-4357/abdd32

Source: SciTechDaily