24 Jan 2023 15:38:PM
Astronomers have discovered and directly imaged a brown dwarf in orbit around HIP 21152, a young yellow dwarf star in the Hyades star cluster. The Hyades star cluster is the closest open cluster to the Sun, at a distance of about 153 lightyears, and as such, is a well-studied star cluster. The newly found brown dwarf, designated as HIP 21152 B is the first confirmed substellar companion of a main sequence star in the Hyades star cluster. It has a mass equivalent to between 22 and 36 times that of Jupiter. HIP 21152 B is the lightest known brown dwarf that has an accurate estimate of its mass. Considering its proximity, HIP 21152 B is expected to be a benchmark object for studying the evolution of brown dwarfs and giant planets.
Brown dwarfs are celestial objects that are intermediate in mass between stars and planets. They are not massive enough to sustain nuclear fusion in their cores, the process that makes stars shine, but they are more massive than the largest gas giant planets. As a result, brown dwarfs are sometimes referred to as ‘failed stars.’ There are no brown dwarfs within our own Solar System. Brown dwarfs are typically between 13 and 80 times the mass of Jupiter. They can have surface temperatures ranging from a few hundred degrees to around 1725°C. They emit primarily infrared radiation and are much dimmer than stars. Because of this, they are difficult to detect, with the first one only being discovered in 1995.
Brown dwarfs are thought to form in the same way as stars, through the collapse of a dense cloud of gas and dust. However, due to their lower mass, they are unable to sustain nuclear fusion and instead slowly cool and fade over time. Thousands of brown dwarfs have been discovered so far, with a few having planets in orbit around them. Very few brown dwarfs are known to be companions of other stars, with a frequency of only a few per 100 stars. Brown dwarfs are important objects to study because they can help us to understand the boundary between stars and planets, and provide insights into the processes of star and planet formation. With the development of new observing technologies, scientists are able to study these objects in greater detail and learn more about their properties and behavior.
The astronomers have developed a new method for discovering companion brown dwarfs and giant planets. The motion of the stars, with their own unique velocity, is known as the proper motion. The astronomers looked for acceleration to the host star provided by an orbiting companion, using the Subaru Telescope and ESA’s astrometry satellite, Gaia, which tracks the proper motions of one billion objects. The survey was used to identify stars with potential substellar companions, with the direct imaging by the Subaru telescopes on one of the targets leading to the discovery of HIP 21152 B. This is expected to be the first of many new substellar companions that can be discovered using the new method.
Lead author of the study, Masayuki Kuzuhara says, “This result can provide an important clue to understand the atmospheres of giant planets and brown dwarfs based on how and when they show atmospheric characteristics similar to those seen in the planets of the HR 8799 system and HIP 21152 B. It is expected that HIP 21152 B will play an important role as a benchmark for future progress in astronomy and planetary science.” A paper describing the findings has been published in The Astrophysical Journal Letters.
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