{"id":53415,"date":"2024-01-11T09:35:46","date_gmt":"2024-01-11T09:35:46","guid":{"rendered":"http:\/\/f0a796fc-5e40-41b6-8175-cf0aaf4911b9"},"modified":"2024-01-11T10:33:42","modified_gmt":"2024-01-11T10:33:42","slug":"how-accretion-disks-form-around-stars","status":"publish","type":"rss_feed","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/rss_feed\/how-accretion-disks-form-around-stars\/","title":{"rendered":"How accretion disks form around stars"},"content":{"rendered":"

How does matter form an accretion disk around stars and black holes? <\/p>

By Paul Roche\n <\/p>

Published: Thursday, 11 January 2024 at 09:35 AM<\/p>

\n\n

An accretion disk is a flattened, circular or elliptical structure that is formed when material falls towards a strong gravitational force, such as a star<\/a> or a black hole<\/a>.<\/p>

Accretion disks are found surrounding a variety of celestial bodies, from relatively small regions of a few thousand kilometres around white dwarfs<\/a> and neutron stars<\/a>, to protoplanetary disks around very young stars.<\/p>

The biggest accretion disks, on the scale of the Solar System, are found surrounding the centres of active galaxies<\/a>.<\/p>

Radiation emanating from accretion disks is one way we can infer that a black hole exists. Credit: ESO\/L. Cal\u00e7ada<\/figcaption><\/figure>

The fact that accretion disks exist over a huge range of scales and in apparently very different types of systems suggests some common physics behind their formation.<\/p>

Because angular momentum is always conserved, small rotations in any in-falling material are amplified as it collapses inwards towards the star or black hole.<\/p>

This is something like the motion of spinning ice skaters, who speed up as they bring their arms inwards.<\/p>

\"An
An image of a protoplanetary or accretion disk around star HL Tauri. The dark rings could indicate newly-forming planets in orbit, pushing aside dust as they go. Credit: ALMA (ESO\/NAOJ\/NRAO)<\/figcaption><\/figure>

A \u2018centripetal force\u2019 \u2013 an inward-directed force on an orbiting body \u2013 then spreads the material out (sideways) to create the broad disk structure, while tidal forces pull it into an equatorial location.<\/p>

The combination of these two forces makes the shape of the disk wide, flat and thin.<\/p>

Within the accretion disk, colliding particles convert kinetic energy (the energy of motion) into heat and move inwards.<\/p>

\"A
A disk of infalling matter allowed astronomers to photograph the black hole at the centre of galaxy M87. Credit: EHT Collaboration<\/figcaption><\/figure>

As these particles move towards the central source, collisions occur more frequently due to the increased density of particles. As a result, they heat up and release X-rays.<\/p>

This radiation is an important tool for astronomers, as black holes can\u2019t be observed directly \u2013 not even light can escape the strength of their gravitiational pull.<\/p>

The X-rays released from accretion disks can be observed and used to locate black holes.<\/p> <\/body><\/html>\n

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