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White Dwarfs,Black Dwarfs & neutron star

by a.ratnaparkhi
Tags: black, dwarfs, neutron, star, white
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a.ratnaparkhi
#1
Jan7-11, 08:02 AM
P: 30
What are White Dwarfs & Black Dwarfs?
And what are Chandrasekhar's limits?
Also I wanna know about Neutron Star.
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Kracatoan
#2
Jan7-11, 08:21 AM
P: 119
White Dwarfs are the remnants of smaller stars, roughly < 3 Solar Masses, left over after their "death", ie the outer layers of the red giant cast off, leaving behind a highly dense white hot core of matter, the exact composition of which changes depending on the original star.

A Black dwarf is merely a white dwarf which has cooled down enough that it emits neglible light, but seeing as this takes so long, there are none in the Universe.

A neutron star is what happens when the star is so very massive it becomes a supernova, which compresses the core of the star so much, the protons and neutrons get pressed very close together. Normally they are kept apart by the Pauli Exclusion principle (this effect in stars is known as degeneracy pressure), but the immense pressures force them so close together, they essentially join and form neutrons, which are not as strongly effected by the principle at those pressure levels, so form a more stable structure.


The Chandrasekhar's limit is essentially the limit on the mass of white dwarfs. If the mass passes a certain limit, the Pauli Exclusion Principle can no longer support the star against the pressure caused by gravity and it becomes a neutron star. You get a similar limit for neutron stars, as if they are too massive you get a black hole.
Radrook
#3
Jan12-11, 11:16 AM
P: 334
The Chandrasekhar Limit limits the mass of electron-degenerate star core body to 1.4 solar masses. However, this refers to a non-rotating body since rotation sets up centrifugal counter forces which can counteract gravity and permit mass to exceed that limit. Only one white dwarf that I know of has been observed to exceed the Chandrasekhar limit. It was a product of the "Champagne Supernova" also designated as SNLS-03D3bb and its ability to exceed that limit was attribuited to fast rotation.

age123
#4
Nov27-12, 02:12 AM
P: 10
White Dwarfs,Black Dwarfs & neutron star

Hi all, im new here.
Just signed up. Was just starting to get interested in astronomy. About 12 years ago i was sleeping out on my trampoline with my dogs when i witnessed a cosmic event that i have never really been able to explain until now. I observed two starts that were about the same size but one was fading and then becoming brighter, It did this on and off a few times and then the other star which had not changed in intensity began firing small portions of itself towards the other star, however it did not decrease in intensity from what i could see. About 4-5 shots of this occured and then finally the start that was being dis-assembled exploded in a massive flash of light. I was quite literally scared stiff on the trampoline and was so shocked by what i had witnessed i didn't really tell anyone about it except my mum, for fear of being called a crazy person. I did however mention it to my mum who, a couple of days later had herd on the news that a super nova had been reported on and that she thinks that is what i saw. I was wondering if many other people had ever witnessed these types of events, and also if they could direct me to some reading material which explains how this occurs. I would also like to start reading about quantum mechanics if possible and anything on sub atomic particles. And if anyone can direct me to a good telescope to purchase as a beginner.
Thanks Adrian
Drakkith
#5
Nov27-12, 04:11 AM
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P: 11,878
I expect that you had a dream or hallucination or something like that. They are actually quite common. Supernovas do not look as you described.
age123
#6
Nov27-12, 04:48 AM
P: 10
Hi again. I am pretty sure i didn't dream it. But i guess your imagination can sometime get away from you. I looked up a few different alternatives. There are apparently a couple different types of super nova's which fit into different categories and act quite differently.
The type 1a super nova, which involves a white dwarf star which gradually pulls the other star that has gotten to close to each other into its magnetic field, as these two masses get closer the pol's attract each other causing a massive surge of energy and a explosion, and then there is another type of super nova known as a type m super nova where by the " dwarf star pulls pieces of the weaker star apart until it effectively draws all off its power. This is just a theory i found on a astronomy web site but i think they are quite confident that this is what happens. So as i explained i believe i saw this second type of reaction. I wanted to know if many people have seen these types of events. I read somewhere that super nova's occur about every 100 year in our galaxy. I saw all of this with my naked eye, so would it of been in our galaxy or another galaxy. Again thanks for your time, if you can assist in helping me out.
adrian
Drakkith
#7
Nov27-12, 04:58 AM
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Drakkith's Avatar
P: 11,878
I guarantee that what you described was NOT a supernova. You absolutely cannot see the separation between two stars near to each other at all with the naked eye. We can BARELY see these things with even our largest telescopes. It is not possible to witness part of the star being pulled apart unless it is a very close star and we are using the Hubble Space Telescope or something similar.

See here: http://en.wikipedia.org/wiki/Airy_disk
age123
#8
Nov27-12, 06:40 AM
P: 10
Sorry, maybe I should have described what I observed then, without explaining what I believe I saw after readin up on it. I sort of combined both my story and my current knowledge on the topic. Which appears to of upset you. I initially saw two star's. one was flickering very brightly, then very dull. This went on for a bit. Then the other star began shooting small specks at the star that was flickering. I remember thinking at the time that this was some time of intergalactic battle I was witnessing. It shot about 4-5 specs at the other star( the one that was flickering). Then the star that shot the specs at the flickering star exploded. I remember thinking, why did that star explode, it was the one doing all the shooting. Now, after doing some research, what I described sounds a lot like the current theory hypothesized about a type m super nova. As I said before, I witnessed it all with my naked eye. And if it wasn't a type m super nova, can anyone explain to me what it was. I would be very greatful to get some feed back on this as it has puzzled me since I was 16 years old. The Internet wasn't quite as informative as it is now, so I guess it is much easier to ask questions now. Thanks again. Sorry if I'm frustrating you. I just think since I have your attention, I would appreciate having a conversation with you about it. As I don't know anyone with this type of knowledge. I don't claim to know more than you, quite the opposite, I've only been reading a little on it yesterday and today, and I've found it fascinating. Please consider my story and try to explain what you think I may have observed! Thanks again. I really appreciate your time.
Adrian
age123
#9
Nov27-12, 06:47 AM
P: 10
Sorry if my previous two post were scattered, I was on my way to by a wetsuit, and was on the train, so i didn't really pay much attension to my spelling or grammar. Thanks again. Adrian
Bandersnatch
#10
Nov27-12, 07:01 AM
P: 709
Just to add to what Drakkith said, the only thing you can see when you witness a supernova is a star that gets brighter for a few days and then fades away.

It is absolutely not possible to see gravitationally bound binary star system as anything else than just a single star. You can check it yourself by looking at the brightest star in the sky(Sirius in the Canis Major constellation), or if you're located in the southern lattitudes, look at Alpha Centauri.
Syrius is a binary star with the secondary being a white dwarf and is ~8ly away.
Alpha Centauri is a binary with roughly similar size stars, and is ~4,5ly away. That's the closest star other than the sun you'll ever see, btw.

As for the explanation for your experience, we can only speculate due to not being able to reproduce it. I'd put my money on a meteor bolide falling to pieces in the atmosphere, and/or your mind playing tricks on you. Long term memories are notoriously unreliable, and we sometimes see what isn't there(and vice versa).
age123
#11
Nov27-12, 07:19 AM
P: 10
Ok thankyou for your answer. My memory of the event is a bit sketchy, but still quite vivid. I guess I will never know what it was, but it has definitely sparked a sudden interest in me that I am enjoying reading about. Thanks for your time. Adrian.


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