Skip to main content

What is an accretion disk?

Image
By
An accretion disk is an astronomical term that refers to the rapidly spiraling  matter that is in the process of falling into an astronomical object. In principle, any  star could have  an accretion disk, but in practice, accretion disks are often associated with highly collapsed stars such as black holes or  neutron stars. 


The matter that serves as the base of the accretion disk can be obtained when a star passes through a region where the  interstellar matter is thicker than normal. Normally, however, a star gets an accretion disk from a companion star.  When two stars  orbit each other, there is an invisible figure eight around the two stars, called the Roche lobes.  The Roche lobes represent all the points in space where the gravitational potential from each star is equal.  Therefore any matter on the Roche lobes could just as easily fall into either star. If one star in a binary system becomes larger than the Roche lobes, matter will fall from it onto the other star, forming an accretion disk.

The matter falling into a collapsing star hole tends to form a disk because a spherical  mass of gas that is spinning will tend to flatten out.  The faster it is spinning, the flatter it gets. So, if the falling material is orbiting the central mass, the spinning flattens the matter into an accretion disk. 

Black holes are objects that have  collapsed to the point that nothing, not even  light, can escape the incredible  force of their gravity. Because no light can escape, however, there is no way to directly observe it. However, if the  black hole has an accretion disk, we can observe  the black hole indirectly by observing the accretion disk, which will emit x rays.  Without accretion disks there would be little hope of astronomers ever observing black hole.

 Accretion disks can also occur with a  white dwarf in a binary system.  A white dwarf is a collapsed star that is the final stage in the evolution of stars similar to the  Sun. White dwarfs contain as much mass as the Sun, compressed to about the size of  Earth. Normally the nuclear reactions in a white dwarf have  run out of fuel, but the  hydrogen from the accretion disk falling onto a white dwarf fuels additional nuclear reactions.  White dwarfs have  some unusual properties that do not allow them to expand slowly to release the  heat pressure generated by these nuclear reactions.  This heat pressure therefore builds up until the surface of the whited dwarf explodes.  This type of explosion is called a  nova (not to be confused with a  supernova), and typically releases as much  energy in the form of protons in less than a year as the Sun does in 100,000 years.
Labels:

Comments

Post a Comment

Popular posts from this blog

How Energy conversion from coal is done?

By
Single generator sets of over 600 MW are now used in the UK, though there are many smaller generators in use. A 600 MW generator can supplythe average needs of over 1 million UK households. Three or four such generators are typically installed in a single large coal-fired station which isoften sited close to a coal mine, away from the city dwellers who consume the electricity. Such generators are usually driven by a compound arrangement of highpressure, intermediate-pressure and low-pressure turbines, increasing in size as the pressure decreases. Modern turbines rotate in a speed range from 1500 to 3500 r.p.m., usually 3000 r.p.m. for the UK’s 50 Hz system. For large coal-fired plant the steam pressure could be 25 megapascals (MPa) with steam temperatures of 500–600 °C to improve the thermodynamic efficiency. In nuclear reactors, which operate under less demanding conditions, the steam is superheated to about 5 MPa and 300 °C. Modern water tube boilers are complex and have ...
Post a Comment
Read more

How Bulletproof glass works?

By
Shattering the science behind what makes the breakable unbreakable Bullet-resistant glass works by absorbing a bullet’s kinetic (movement) energy and dissipating it across a larger area. Multiple layers of toughened glass are reinforced with alternated layers of polycarbonate – a tough but fl exible transparent plastic which retains the see-through properties of glass. As a bullet strikes the fi rst glass layer, the polycarbonate layer behind it forces the glass to shatter internally rather than outwards.  This process absorbs some of the bullet’s kinetic energy. The high velocity impact also fl attens the bullet’s head. Imagine trying to pierce through a sheet of cotton with the top end of a pencil. It would be very diffi cult compared to using the sharp pointed end. The same principle applies here. The fl at-headed bullet struggles to penetrate the layer of polycarbonate. As the bullet travels through each layer of glass and polycarbonate, the process is repeated until it no l...
Post a Comment
Read more

20 Interesting science fact (PART 2)

By
1/ Astronauts cannot belch - there is no gravity to separate liquid from gas in their stomachs. 2/ The air at the summit of Mount Everest, 29,029 feet is only a third as thick as the air at sea level. 3/ One million, million, million, million, millionth of a second after the Big Bang the Universe was the size of a ...pea. 4/ DNA was first discovered in 1869 by Swiss Friedrich Mieschler. 5/ The molecular structure of DNA was first determined by Watson and Crick in 1953. 6/ The first synthetic human chromosome was constructed by US scientists in 1997. 7/ The thermometer was invented in 1607 by Galileo. 8/ Englishman Roger Bacon invented the magnifying glass in 1250. 9/ Alfred Nobel invented dynamite in 1866. 10/ Wilhelm Rontgen won the first Nobel Prize for physics for discovering X-rays in 1895. 11/ The tallest tree ever was an Australian eucalyptus - In 1872 it was measured at 435 feet tall. 12/ Christian Barnard performed the first heart transplant i...
Post a Comment
Read more