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

In summary, it is believed that if a neutron star accretes enough mass, it can become a black hole. The temperature and pressure only affect the density, not the formation of a black hole. The theoretical upper mass limit for a white dwarf is 1.44 solar mass, while most neutron stars have a mass between 1.2 and 1.4 solar mass. The upper limit for neutron stars is not certain, but is believed to be closer to 2 solar masses. There is a question about the lower mass limit for black holes, and it is possible that there are more undetected black holes in the nearby universe. It is known that neutron stars can collapse into black holes, but it is not commonly believed
  • #1
tvscientist
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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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  • #2
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.
 
  • #3
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?
 
  • #4
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.
 
  • #5
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.
 
  • #6
mathman said:
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.
 
  • #7
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.
 
  • #8
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.
 
  • #9
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?
 
  • #10
"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?
 
  • #11
tvscientist said:
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.
 
  • #12
"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?
 
  • #13
Bernie G said:
"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.
 

1. Can a neutron star turn into a black hole?

Yes, it is possible for a neutron star to turn into a black hole through a process called mass accretion. This occurs when a neutron star is in a binary system with another star and accretes mass from its companion, leading to an increase in its mass and the potential to become a black hole.

2. How much mass does a neutron star need to turn into a black hole?

A neutron star needs to accrete at least 20% of its original mass to have a chance of turning into a black hole. This means that it would need to gain about 0.2 solar masses in order to reach the critical mass required for black hole formation.

3. Is mass accretion the only way for a neutron star to become a black hole?

No, mass accretion is not the only way for a neutron star to turn into a black hole. It is also possible for a neutron star to collapse into a black hole if its internal structure changes, such as through a change in its temperature or magnetic field strength.

4. What happens to the matter that is accreted by the neutron star?

The matter that is accreted by the neutron star is compressed and heated as it falls onto the surface of the star. This can lead to the emission of X-rays and gamma rays, making accreting neutron stars visible to telescopes. If enough matter is accreted, it can also contribute to the growth of the neutron star's mass and potentially lead to black hole formation.

5. How long does it take for a neutron star to turn into a black hole through mass accretion?

The timescale for a neutron star to become a black hole through mass accretion depends on the rate of accretion and the mass of the star's companion. It can take anywhere from a few million years to billions of years for a neutron star to gain enough mass to become a black hole.

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