The planet AB Aurigae b formed in a way that is difficult to describe in theory.
REPUBLIKA.CO.ID, JAKARTA — The discovery of a gas giant exoplanet that is still in the process of forming could change the understanding of planet formation. The protoplanet was named AB Aurigae b.
This protoplanet appears to have formed at a great distance from its star, AB Aurigae and assembled in a rather unusual way.
Evidence suggests the planet formed through the top-down gravitational collapse of a gas cloud, rather than a model bottom-up the more commonly accepted one, in which planets formed from the gradual accumulation of dust and rock. This supports the idea that there were multiple pathways for formation, indicating the rich and amazing diversity of planetary systems in the Milky Way.
AB Aurigae has been studied intensively in recent years. AB Aurigae is a very young star, still forming itself, no more than five million years old (the Sun is 4.6 billion years old).
The star is still surrounded by a thick, turbulent disk of gas and dust. When a protostar grows, it is this gas and dust that feeds that growth. Because the star is relatively close-only 508 light-years away, it is an excellent laboratory for studying the formation of planetary systems.
What’s left of that disk will go on to form the other elements that make up the planetary system, and smaller objects such as asteroids, dwarf planets, comets, and other rocks.
Planetary formation theory
According to our current understanding of planet formation, these smaller objects could begin to form planets in the so-called core accretion model. In this model, pieces of rock in the disk of dust and gas protoplanet stick together, first through electrostatic forces, then through gravity, forming bigger and bigger bodies, building a planet from the ground up. The resulting exoplanet has a solid core, which is relatively cold and dim.
Another model for planet formation is known as the disk instability model. For a planet to form in this way, the cooling protoplanetary disk caused gravitational instability and ruptured.
Part of the disk then gravitationally collapses directly into a gas giant. In this model, exoplanets do not have solid cores, and are formed hotter and brighter.
What happens in the disk AB Aurigae, a protostar with a mass about 2.4 times the mass of the Sun, is difficult to decipher. First, astronomers thought they saw an exoplanet forming at a distance similar to Neptune. This interpretation was later questioned by other astronomers, who said that the object could be a second star.
In a new study led by astrophysicist Thayne Currie of the National Astronomical Ibservatory of Japan’s Subaru Telescope, a team of scientists used Subaru and the Hubble Space Telescope to make more detailed observations of the star.
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