# Event Horizon and the Mass of a Black Hole

• I
Gold Member
I didnt understand a concept in black holes,So I ll try to make a vısualization to the process to explain my ideas properly.
Lets suppose we have a star with mass ##6M_ο##.We know that this star will turn to black hole,So Lets come to the end of the life of the star.It will explode as supernova, and the protons and electrons will make neutrons cause of the gravitational pressure.

Now in here , core (neutron) will reach a critical density which the star will turn the black hole,at this moment, the radius of this core will be equal to event horizon radius.And this radius value will determined by Schwarzschild radius.

Are these statements true ?

Gold Member

https://www.nasa.gov/audience/forstudents/5-8/features/nasa-knows/what-is-a-black-hole-58.html

and here:

https://www.space.com/37001-black-hole-born-from-collapsing-star-video-images.html

The event horizon is just a demarcation of where light can no longer escape the black hole. Once formed the collapsing star's matter collapses into a singularity with no discernable radius.
I looked the videos, second one is really interesting I was never heard such thing.

I understand that matter collapses and creates a singularity, then whats the difference between ##10M_ο## mass of star (A) and ##20M_ο## (B).Since both star A and B creates a black hole, they have singularity but their event horizon radius is different.How is that possible ? Is this means there's "different type of singularities" which affect the light in different way (Why event horizon radius is different , cause singularity is just singularity) ?

jedishrfu
Mentor
The event horizon is where light can no longer escape the clutches of the black hole so of course a more massive black hole will have a larger event horizon since its gravitational strength reaches farther out into the space around it.

Gold Member
since its gravitational strength reaches farther out into the space around it.

Since the mass collapses into singularity why does the mass of the star matters ? Cause in any case all mass will collape so singularity,

Lets suppose we have an earth and apple, they collapsed and formed black hole,I am saying they should have same radius cause they will form a singularity and singularities are same, but it is not, how ?

jedishrfu
Mentor
Mass doesn't vanish it just becomes a singularity. The mass tells space how to curve. The event horizon around the mass demarcates the point where light can no longer escape the black hole. The mass determines the size of the event horizon. Singularities are defined by the mass that created them and other properties such as charge and spin.

Even leaving General Relativity aside and using Newton's gravitation law you can see that the strength of gravity increases as the mass of one of the objects increases. It is the same in General Relativity.

https://en.wikipedia.org/wiki/Newton's_law_of_universal_gravitation

and here:

https://en.wikipedia.org/wiki/Black_hole

Gold Member
Mass doesn't vanish it just becomes a singularity. The mass tells space how to curve. The event horizon around the mass demarcates the point where light can no longer escape the black hole. The mass determines the size of the event horizon.

Even leaving General Relativity aside and using Newton's gravitation law you can see that the strength of gravity increases as the mass of one of the objects increases. It is the same in General Relativity.

https://en.wikipedia.org/wiki/Newton's_law_of_universal_gravitation
It make sense that If it has a bigger mass the event horizon would be bigger but still a bit awkward to me...

jedishrfu
Mentor
The problem with physics is you have to go back to the math to really understand whats what. For General Relativity, the math is really hard hence laymen and journalists use flawed analogies like rubber sheets to describe what is happening leading to confusion.

Gold Member
The problem with physics is you have to go back to the math to really understand whats what. For General Relativity, the math is really hard hence laymen and journalists use flawed analogies like rubber sheets to describe what is happening leading to confusion.
I totally agree with you.I am freshman physics student and GR is really hard to understand, the math is too complex etc.Without understanding them its hard for me to deal with such thing.Thank you for your help

I looked the videos, second one is really interesting I was never heard such thing.

I understand that matter collapses and creates a singularity, then whats the difference between ##10M_ο## mass of star (A) and ##20M_ο## (B).Since both star A and B creates a black hole, they have singularity but their event horizon radius is different.How is that possible ? Is this means there's "different type of singularities" which affect the light in different way (Why event horizon radius is different , cause singularity is just singularity) ?

Due to the Pauli exclusion principle, it's premature to suggest that all mass inside the event horizon ever reaches a true state of "singularity" or anything approaching 'infinite density at a point". Be careful with that particular assumption. It's a pretty safe bet however that a larger mass object will have a larger event horizon.

Gold Member
Due to the Pauli exclusion principle, it's premature to suggest that all mass inside the event horizon ever reaches a true state of "singularity" or anything approaching 'infinite density at a point". Be careful with that particular assumption. It's a pretty safe bet however that a larger mass object will have a larger event horizon.
I see your point.I didnt and I cannot read the literature about this since I dont know the math and physics but from books about this issues or etc, I state that assumption,In simply way I guess we dont know how black holes form and hence whats there inside..Its pretty amazing.

William Blake
I also strangled for couple of months on this topic but then started from scratch once again to clear my concepts, bro kindly start from this article and then proceed to have a better understanding
http://www.astro.cardiff.ac.uk/research/gravity/tutorial/?page=5super

Regards
William Blake
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Gold Member
I also strangled for couple of months on this topic but then started from scratch once again to clear my concepts, bro kindly start from this article and then proceed to have a better understanding
http://www.astro.cardiff.ac.uk/research/gravity/tutorial/?page=5super