Can Simple Mass Accretion Turn a Neutron Star Into a Black Hole?


by tvscientist
Tags: accretion, black, hole, mass, neutron, simple, star, turn
tvscientist
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#1
Sep6-11, 03:09 PM
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Can simple mass accretion turn a neutron star into a Black Hole, or does a BH require temperatures and pressures from the collapsed massive star?
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mathman
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Sep6-11, 03:41 PM
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If a neutron star accretes enough mass it will become a black hole. Temperature and pressure are only relevant to the extent that they affect the density.
tvscientist
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#3
Sep6-11, 04:06 PM
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Mathman

Thanks for the response. If mass accumulation can turn a neutron star into a BH, then a neutron star has both a lower and higher range of total mass. Do we have estimates of the total solar masses required to 1) produce a neutron star instead of a white dwarf; and two, turn a neutron star into a BH?

Chronos
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Sep6-11, 09:30 PM
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Can Simple Mass Accretion Turn a Neutron Star Into a Black Hole?


The theoretical upper mass limit for a white dwarf is the Chandrasekhar limit ~ 1.44 solar mass. Neutron stars have varying mass ranges. Most are between 1.2 and 1.4 solar mass, with a select few are in the 2 solar mass range. The theoretical upper limit is not known with any certainty, but, believed to closer to 2 solar masses than 3.
Bernie G
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#5
Apr1-12, 07:52 PM
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A great question; it will probably be resolved this decade. Possibly simple mass accretion can't turn a Neutron Star Into a Black Hole. Of the roughly 2000 observed neutron stars, none seems to have a mass greater than about 1.97 solar mass. Of the about 20 nearby observed black holes, the smallest seems to be at least 3 SM, and more probably 5 SM. Possibly a surface effect or more likely a core effect could be limiting the upper mass limit of neutron stars.
Nabeshin
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#6
Apr1-12, 09:36 PM
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Quote Quote by mathman View Post
If a neutron star accretes enough mass it will become a black hole. Temperature and pressure are only relevant to the extent that they affect the density.
Well that's not true. Remember pressure contributes directly into the stress energy tensor, and this is actually important for neutron star collapse. Since as the star collapses the pressure increases, it actually fuels the runaway collapse after a certain mass 'tipping point' has been reached.
Chronos
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Apr2-12, 01:51 AM
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There remains a serious question about the lower mass limit for black holes. Hardly any suspects are less than several solar masses. There should be many more if our stellar evolution models are correct - although it could be a detection limit thing.
Bernie G
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#8
Apr2-12, 11:01 AM
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On the other hand maybe neutron stars do collapse at about 1.99 SM. Could there be a lot more relatively nearby black holes that we just don't see because they have gobbled up all the nearby matter in their sphere of influence? Larger stars apparently gobble up nearby stars much faster because the relativistic gravity makes the orbits unstable.
Bernie G
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#9
Apr3-12, 11:33 AM
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Is there an equation to estimate the mass of unobserved neutron stars from the total mass of the about 2000 presently observed nearby neutrons stars? Is there a similar estimate for black holes?
Bernie G
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#10
Apr3-12, 07:56 PM
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"There should be many more if our stellar evolution models are correct ."

Solving this might lead to an answer. I think the figures presently are that there are about 2000 observed "nearby" neutron stars and about 20 observed "nearby" black holes, where "nearby" is within roughly 10,000 light years from earth. (Are these numbers correct?) 20 seems like too small a number, even taking into account that he average mass of these black holes is much more than the average mass of neutron stars. Might this be because over time the local nearby black holes have already swept up a greater percentage of their nearby material compared to neutron stars, and hence a greater percentage of these black holes are not observed?

Do you have a guesstimate of how many "nearby" black holes should be observed?
ImaLooser
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#11
Apr5-12, 02:52 AM
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Quote Quote by tvscientist View Post
Can simple mass accretion turn a neutron star into a Black Hole, or does a BH require temperatures and pressures from the collapsed massive star?
All neutron stars measured so far -- not very many -- have a mass between 1.4 and 1.97 AU(mass of Sun.) The smallest measured black holes are 4AU. The significance of this gap is not yet understood.

It IS known that neutron stars do collapse into black holes. It is called a type Ic supernova. They are rare but useful since each such collapse releases the same amount of energy, so it can be used as a "standard candle" to determine the distance to a galaxy.
Bernie G
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#12
Apr5-12, 11:01 PM
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"It IS known that neutron stars do collapse into black holes. It is called a type Ic supernova."

Are you sure about this? Do you have an internet reference that says this?
ImaLooser
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#13
Apr6-12, 06:07 AM
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Quote Quote by Bernie G View Post
"It IS known that neutron stars do collapse into black holes. It is called a type Ic supernova."

Are you sure about this? Do you have an internet reference that says this?
I recall reading that but don't recall where. A search turned up nothing, so my statement appears to have no foundation. It appears that a Ic is a supernova with no silicon or carbon absorption lines. A neutron star collapse would qualify, but that is not what it is generally believed to be.


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