# Can Relativistic Mass Create a Black Hole?

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• Aerodyn
In summary, the statement that relativistic mass is used to determine whether an object is a black hole is wrong.
Aerodyn
Hello dear colleagues from the physics forum,

Following question came to my mind, can you tell me which statement (s) is/are wrong?.

Since relativistic mass is weighed with the Lorentz factor for an external observer, it is expected an increase with speed.

Such mass (m1) would tend to infinity with v=c, but before infinity it would go through the mass required to create a black hole. In addition, since the external observer would see the fast object contracted due to its speed, he would see a smaller object with a higher mass, which definitely would increase its density, creating the best conditions for a good black hole soup.

So the external observer would see m1 creating a black hole. What if now m1 decides to slow down until v=0? Would the external observer see m1 escaping from a black hole?

Thank you very much for four support on understanding this strange phenomenaAerodyn

Aerodyn said:
can you tell me which statement (s) is/are wrong?
This:

Aerodyn said:
Such mass (m1) would tend to infinity with v=c, but before infinity it would go through the mass required to create a black hole. In addition, since the external observer would see the fast object contracted due to its speed, he would see a smaller object with a higher mass, which definitely would increase its density, creating the best conditions for a good black hole soup.
The relevant quantity for determining whether an object is a black hole is not its relativistic mass, so the entire quote above is wrong. Whether or not an object is a black hole is invariant, independent of any choice of reference frame. Since relativistic mass is not an invariant, but frame-dependent, it obviously cannot be what determines whether an object is a black hole.

The rest of your post is also wrong since it follows from the above error.

dextercioby and FactChecker
Also, relativistic mass is not used by most scientists for the last many decades. It basically fell out of favor even within Einstein's lifetime.

dextercioby and vanhees71
Aerodyn said:
can you tell me which statement (s) is/are wrong?.
A simple way to see that your reasoning fails is to note that, as seen by a neutrino emitted by the Sun, you are doing 99.99999...% of the speed of light. Do you feel like a black hole?

This kind of mistake is one of the reasons relativistic mass fell out of favour. It leads to too many problems by kind of implying that relativistic physics is just Newtonian physics with a few Lorentz gammas thrown in. It is not. The source of gravity in relativity is a thing called the stress-energy tensor, which includes rest mass and various other forms of energy, but its behaviour is significantly more complex than just relativistic mass, I'm afraid.

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