All Topics  
Accretion (astrophysics)

 

 
   Email Print
   Bookmark   Link
 

 

Accretion (astrophysics)
 
 
  Topics Accretion (astrophysics) Topic Home

In astrophysics
Astrophysics

Astrophysics is the branch of astronomy that deals with the physics of the universe, including the physical properties of astronomical objects such as galaxy, stars, planets, exoplanets, and the interstellar medium, as well as their interactions....
, the term accretion is used for at least two distinct processes.

The first and most common is the growth of a massive object by gravitationally attracting more matter, typically gas
Gas

In physics, a gas is a state of matter, consisting of a collection of particles without a definite shape or volume that are in more or less random motion....
eous matter in an accretion disc
Accretion disc

An accretion disc is a structure formed by diffuse material in orbital motion around a central body. The central body is typically a young star, a protostar, a white dwarf, a neutron star, or a black hole....
. Accretion discs are common around smaller stars or stellar remnants in a close binary
Binary star

A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star or secondary....
, or black hole
Black hole

In general relativity, a black hole is a region of space in which the gravitational field is so powerful that nothing, including electromagnetic radiation , can escape its pull after having fallen past its event horizon....
s in the centers of spiral galaxies
Galaxy

A galaxy is a massive, gravitation system that consists of stars and stellar remnants, an interstellar medium of gas and cosmic dust, and an important but poorly-understood component tentatively dubbed dark matter....
. Some dynamics in the disc are necessary to allow orbiting gas to lose angular momentum
Angular momentum

In physics, the angular momentum of a particle about an origin is a vector quantity related to rotation, equal to the mass of the particle multiplied by the cross product of the position vector of the particle with its velocity vector....
 and fall onto the central massive object.

The second process is somewhat analogous to the one in atmospheric science
Accretion (atmosphere)

In atmospheric science, accretion stands for growth of a precipitation particle by the collision of an ice crystal or snowflake with a supercooled liquid droplet that freezes upon impact....
.






Discussion
Ask a question about 'Accretion (astrophysics)'
Start a new discussion about 'Accretion (astrophysics)'
Answer questions from other users
Full Discussion Forum



Encyclopedia


In astrophysics
Astrophysics

Astrophysics is the branch of astronomy that deals with the physics of the universe, including the physical properties of astronomical objects such as galaxy, stars, planets, exoplanets, and the interstellar medium, as well as their interactions....
, the term accretion is used for at least two distinct processes.

The first and most common is the growth of a massive object by gravitationally attracting more matter, typically gas
Gas

In physics, a gas is a state of matter, consisting of a collection of particles without a definite shape or volume that are in more or less random motion....
eous matter in an accretion disc
Accretion disc

An accretion disc is a structure formed by diffuse material in orbital motion around a central body. The central body is typically a young star, a protostar, a white dwarf, a neutron star, or a black hole....
. Accretion discs are common around smaller stars or stellar remnants in a close binary
Binary star

A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star or secondary....
, or black hole
Black hole

In general relativity, a black hole is a region of space in which the gravitational field is so powerful that nothing, including electromagnetic radiation , can escape its pull after having fallen past its event horizon....
s in the centers of spiral galaxies
Galaxy

A galaxy is a massive, gravitation system that consists of stars and stellar remnants, an interstellar medium of gas and cosmic dust, and an important but poorly-understood component tentatively dubbed dark matter....
. Some dynamics in the disc are necessary to allow orbiting gas to lose angular momentum
Angular momentum

In physics, the angular momentum of a particle about an origin is a vector quantity related to rotation, equal to the mass of the particle multiplied by the cross product of the position vector of the particle with its velocity vector....
 and fall onto the central massive object.

The second process is somewhat analogous to the one in atmospheric science
Accretion (atmosphere)

In atmospheric science, accretion stands for growth of a precipitation particle by the collision of an ice crystal or snowflake with a supercooled liquid droplet that freezes upon impact....
. In the nebular theory, accretion refers to the collision and sticking of cooled microscopic dust and ice particles electrostatically, in protoplanetary discs and Gas giant
Gas giant

A gas giant is a large planet that is not primarily composed of Rock or other solid matter. There are four gas giants in our Solar System: Jupiter, Saturn, Uranus, and Neptune....
 protoplanet
Protoplanet

Protoplanets are moon-sized planets, or larger embryos within protoplanetary discs. They are believed to form out of kilometer-sized planetesimals that attract each other gravitationally and collide....
 systems, eventually leading to planetesimals which gravitationally accrete more small particles and other planetesimals.

Use of the term accretion disc for the protoplanetary disc thus leads to confusion over the planetary accretion process, although in many cases it may well be that both accretion processes are happening simultaneously (e.g. T Tauri
T Tauri star

T Tauri stars are a class of variable stars named after their prototype ? T Tauri. They are found near molecular clouds and identified by their optical variable star and strong chromosphere lines....
).

Example

The Jovian protoplanets probably have discs of their own, in close analogy to the solar system
Solar System

The Solar System consists of the Sun and those Astronomical object bound to it by gravity: the eight planets and five dwarf planets, their 173 known Natural satellite, and billions of Small Solar System body....
 as a whole. The Jovian protoplanet may be accreting gas from its surrounding disc in the first process, at the same time that dust and ice particles in the disc are accreting into moonlets and ring systems, in the second process.

See also

  • Accretion disc
    Accretion disc

    An accretion disc is a structure formed by diffuse material in orbital motion around a central body. The central body is typically a young star, a protostar, a white dwarf, a neutron star, or a black hole....