Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Quasars,white dwarf and neutron stars

  1. Jun 11, 2005 #1
    quasars are highly active but extremely distant galaxies, right?what kind of galaxies are they and do they represent an earlier stage of the lives of the conventional galaxies?i've a vague idea that quasars a galaxies in which the supermassive black holes at the centres are actively gobbling up matter. am i right?

    what exactly is the difference between a white dwarf and a neutron star in terms of composition. are neutron stars made of neutrons?where did the protons go. please clarify.
  2. jcsd
  3. Jun 11, 2005 #2
    Quasars a galaxies that seem to be radiating a lot more energy than normal galaxies. It is believed, but not confirmed, that this is due to black holes at their centres releasing gravitational energy as matter falls into it.

    Quavers, on the other hand, are a cheesy corn snack. They're floaty light.

    Yes, neutron stars are made of neutrons. White dwarves with more than 1.4 solar masses can collapse under their own gravity, becoming more and more dense. This gravity ultimately forces the electrons and protons in the star's atoms to forge neutrons. A typical neutron star may have many solar masses in a volume with a radius the size of a large city.
  4. Jun 11, 2005 #3
    I'm not up to date on the latest explanation of quasars, but I can help on the second problem.

    At core collapse, the mass of a neutron star core is so great that the electrostatic forces that keep the atoms apart is overcome. The electrons and protons combine to form neutrons (like normal beta decay in reverse) and as neutrons aren't repulsed from each other (as protons are) the neutrons form one big mass - like a huge atomic nuclei.
    The density of this is huge and the size remarkably small.

    A White dwarf is the remainder of a smaller star and here the atoms remain intact (although under enormous pressure). A white Dwarf is incredibly hot (100,000 deg) and will slowly cool down over billions of years.
    Last edited: Jun 11, 2005
  5. Jun 11, 2005 #4


    User Avatar
    Gold Member

    Neutrons actually are repulsed from one another. They are Fermions and they obey the Pauli exclusion principle - they resist being packed into the same quantum state as their identical neighbors. It is this repulsion that keeps the neutron star from further collapse, although as you pointed out, it is already a VERY degenerate form of matter.
  6. Jun 12, 2005 #5
    You hit the nail on the head. The most probable explanation for quasars is that they contained SMBHs gulping down matter. They represent an early stage in the evolution of galaxies; quasars were very numerous in the era known as the "http://www.jb.man.ac.uk/merlin/nam/dragns/cosmology.html [Broken]", that occurred between 1 billion and 3 billion years of the life of the Universe. In the local Universe, quasars are not so abundant, because they "shed their skin" to become normal galaxies
    Last edited by a moderator: May 2, 2017
  7. Jun 19, 2005 #6
    what are DRAGNs meteor?
    aren't neutrons on their own, a very unstable particle?then how do they remain stable within a neutron star?every galaxy seems to have a supermassive black hole at its core-so why are they active within the quasars only?
  8. Jun 20, 2005 #7


    User Avatar
    Gold Member

    I'm not Meteor, but here is a thumbnailed gallery. These objects are double-lobed emission events. If you believe that the redshift of the emitting object is entirely cosmological, and place these emitting objects at the distances suggested by these redshifts, you will find that the materials in the jets often moves at superluminal velocities - even 6-10x lightspeed. This is blithely explained as an optical illusion arising from the orientation of the jets almost directly at us.

  9. Jun 20, 2005 #8
    haha, I remember my high school physics teacher telling me someone had found something travelling faster than the speed of light. It was one of these things. I have always wanted to tell him he was wrong!
  10. Jun 20, 2005 #9


    User Avatar
    Science Advisor
    Gold Member

    Unless the axes of all those objects are exactly normal to our line of sight then there will be relativistic perspective effects producing the appearance of superluminal expansion.

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook