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If a black hole is created from light, can this black hole then move at the speed of light?


Will free-fall object into black hole exceed speed of light $c$ before hitting black hole surface?Speed of light originating from a star with gravitational pull close to black-hole strength?How can a black hole reduce the speed of light?If you shine a light away from the center of a Schwarzchild black hole, will it stay still?Can a black hole move at speed of light?Can light escape a black hole?Can a High Enough Temperature Create a Black Hole?can light go faster than light speed?If photons don't experience time then why can't they escape a black hole?if light is the fastest 'thing' then why can it not escape the pull of a black hole













23












$begingroup$


Imagine we managed to squeeze light into a very tiny region of space so that the energy concentration at that point becomes a black hole. Can this black hole then move at the speed of light?










share|cite|improve this question











$endgroup$
















    23












    $begingroup$


    Imagine we managed to squeeze light into a very tiny region of space so that the energy concentration at that point becomes a black hole. Can this black hole then move at the speed of light?










    share|cite|improve this question











    $endgroup$














      23












      23








      23


      3



      $begingroup$


      Imagine we managed to squeeze light into a very tiny region of space so that the energy concentration at that point becomes a black hole. Can this black hole then move at the speed of light?










      share|cite|improve this question











      $endgroup$




      Imagine we managed to squeeze light into a very tiny region of space so that the energy concentration at that point becomes a black hole. Can this black hole then move at the speed of light?







      black-holes mass speed-of-light mass-energy speed






      share|cite|improve this question















      share|cite|improve this question













      share|cite|improve this question




      share|cite|improve this question








      edited Mar 30 at 8:07









      Peter Mortensen

      1,95311323




      1,95311323










      asked Mar 29 at 11:00









      user6760user6760

      3,00312144




      3,00312144




















          2 Answers
          2






          active

          oldest

          votes


















          30












          $begingroup$

          No. I assume you're thinking that a black hole made from light would have a zero rest mass and could therefore travel at the speed of light. However the rest mass of any black hole is due not only to the mass that went into it but also the energy (e.g. photons) that went into it. The increase in mass due to the energy is given by Einstein's famous equation $E = mc^2$.



          So if we create the black hole from purely mass $m$ the rest mass of the black hole is just $m$.



          If we create the black hole from purely energy $E$, e.g. from photons with a total energy $E$, then the rest mass of the black hole is $E/c^2$.



          Or for completeness we could use a mixture of mass $m$ and energy $E$ in which case the rest mass would be $m + E/c^2$.



          So a black hole made from just photons would not have a zero rest mass and therefore could not travel at the speed of light.



          This conversion of photons to a mass isn't unique to a black hole. For example suppose we start with a hydrogen atom in the ground state, $1s$, and let it absorb a 10.2eV photon to excite it to the $2p$ state. This would increase the mass by $10.2textrmeV/c^2$ i.e. even though the photon is massless absorbing it increases the mass of the hydrogen atom. As a general rule mass is not a conserved quantity either in special or general relativity.






          share|cite|improve this answer









          $endgroup$












          • $begingroup$
            Comments are not for extended discussion; this conversation has been moved to chat.
            $endgroup$
            – ACuriousMind
            Mar 29 at 22:23


















          9












          $begingroup$

          No. Nothing with non-zero mass can move at lightspeed. A kugelblitz would behave just like a more conventional black hole formed from matter, due to the no-hair theorem.






          share|cite|improve this answer









          $endgroup$












          • $begingroup$
            'formed directly from matter'. If it's a black hole it has mass. If it has mass that means the photons collided and became electrons and positrons. = no lightspeed :(
            $endgroup$
            – Mazura
            Mar 29 at 22:10










          • $begingroup$
            Lightspeed - qualify by being in vacuum (I am thinking of Cherenkov radiation)?
            $endgroup$
            – Peter Mortensen
            Mar 30 at 3:23











          • $begingroup$
            @Mazura Yes, the black hole formed from photons has mass, but that doesn't necessarily mean that the photons produced matter. See chat.stackexchange.com/transcript/message/49710715#49710715
            $endgroup$
            – PM 2Ring
            Mar 30 at 10:49










          • $begingroup$
            @Peter Yes, by "lightspeed" I mean c, the speed of light in a perfect vacuum, 299792458 m/s.
            $endgroup$
            – PM 2Ring
            Mar 30 at 11:06











          Your Answer





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          2 Answers
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          2 Answers
          2






          active

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          active

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          active

          oldest

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          30












          $begingroup$

          No. I assume you're thinking that a black hole made from light would have a zero rest mass and could therefore travel at the speed of light. However the rest mass of any black hole is due not only to the mass that went into it but also the energy (e.g. photons) that went into it. The increase in mass due to the energy is given by Einstein's famous equation $E = mc^2$.



          So if we create the black hole from purely mass $m$ the rest mass of the black hole is just $m$.



          If we create the black hole from purely energy $E$, e.g. from photons with a total energy $E$, then the rest mass of the black hole is $E/c^2$.



          Or for completeness we could use a mixture of mass $m$ and energy $E$ in which case the rest mass would be $m + E/c^2$.



          So a black hole made from just photons would not have a zero rest mass and therefore could not travel at the speed of light.



          This conversion of photons to a mass isn't unique to a black hole. For example suppose we start with a hydrogen atom in the ground state, $1s$, and let it absorb a 10.2eV photon to excite it to the $2p$ state. This would increase the mass by $10.2textrmeV/c^2$ i.e. even though the photon is massless absorbing it increases the mass of the hydrogen atom. As a general rule mass is not a conserved quantity either in special or general relativity.






          share|cite|improve this answer









          $endgroup$












          • $begingroup$
            Comments are not for extended discussion; this conversation has been moved to chat.
            $endgroup$
            – ACuriousMind
            Mar 29 at 22:23















          30












          $begingroup$

          No. I assume you're thinking that a black hole made from light would have a zero rest mass and could therefore travel at the speed of light. However the rest mass of any black hole is due not only to the mass that went into it but also the energy (e.g. photons) that went into it. The increase in mass due to the energy is given by Einstein's famous equation $E = mc^2$.



          So if we create the black hole from purely mass $m$ the rest mass of the black hole is just $m$.



          If we create the black hole from purely energy $E$, e.g. from photons with a total energy $E$, then the rest mass of the black hole is $E/c^2$.



          Or for completeness we could use a mixture of mass $m$ and energy $E$ in which case the rest mass would be $m + E/c^2$.



          So a black hole made from just photons would not have a zero rest mass and therefore could not travel at the speed of light.



          This conversion of photons to a mass isn't unique to a black hole. For example suppose we start with a hydrogen atom in the ground state, $1s$, and let it absorb a 10.2eV photon to excite it to the $2p$ state. This would increase the mass by $10.2textrmeV/c^2$ i.e. even though the photon is massless absorbing it increases the mass of the hydrogen atom. As a general rule mass is not a conserved quantity either in special or general relativity.






          share|cite|improve this answer









          $endgroup$












          • $begingroup$
            Comments are not for extended discussion; this conversation has been moved to chat.
            $endgroup$
            – ACuriousMind
            Mar 29 at 22:23













          30












          30








          30





          $begingroup$

          No. I assume you're thinking that a black hole made from light would have a zero rest mass and could therefore travel at the speed of light. However the rest mass of any black hole is due not only to the mass that went into it but also the energy (e.g. photons) that went into it. The increase in mass due to the energy is given by Einstein's famous equation $E = mc^2$.



          So if we create the black hole from purely mass $m$ the rest mass of the black hole is just $m$.



          If we create the black hole from purely energy $E$, e.g. from photons with a total energy $E$, then the rest mass of the black hole is $E/c^2$.



          Or for completeness we could use a mixture of mass $m$ and energy $E$ in which case the rest mass would be $m + E/c^2$.



          So a black hole made from just photons would not have a zero rest mass and therefore could not travel at the speed of light.



          This conversion of photons to a mass isn't unique to a black hole. For example suppose we start with a hydrogen atom in the ground state, $1s$, and let it absorb a 10.2eV photon to excite it to the $2p$ state. This would increase the mass by $10.2textrmeV/c^2$ i.e. even though the photon is massless absorbing it increases the mass of the hydrogen atom. As a general rule mass is not a conserved quantity either in special or general relativity.






          share|cite|improve this answer









          $endgroup$



          No. I assume you're thinking that a black hole made from light would have a zero rest mass and could therefore travel at the speed of light. However the rest mass of any black hole is due not only to the mass that went into it but also the energy (e.g. photons) that went into it. The increase in mass due to the energy is given by Einstein's famous equation $E = mc^2$.



          So if we create the black hole from purely mass $m$ the rest mass of the black hole is just $m$.



          If we create the black hole from purely energy $E$, e.g. from photons with a total energy $E$, then the rest mass of the black hole is $E/c^2$.



          Or for completeness we could use a mixture of mass $m$ and energy $E$ in which case the rest mass would be $m + E/c^2$.



          So a black hole made from just photons would not have a zero rest mass and therefore could not travel at the speed of light.



          This conversion of photons to a mass isn't unique to a black hole. For example suppose we start with a hydrogen atom in the ground state, $1s$, and let it absorb a 10.2eV photon to excite it to the $2p$ state. This would increase the mass by $10.2textrmeV/c^2$ i.e. even though the photon is massless absorbing it increases the mass of the hydrogen atom. As a general rule mass is not a conserved quantity either in special or general relativity.







          share|cite|improve this answer












          share|cite|improve this answer



          share|cite|improve this answer










          answered Mar 29 at 12:17









          John RennieJohn Rennie

          279k44557804




          279k44557804











          • $begingroup$
            Comments are not for extended discussion; this conversation has been moved to chat.
            $endgroup$
            – ACuriousMind
            Mar 29 at 22:23
















          • $begingroup$
            Comments are not for extended discussion; this conversation has been moved to chat.
            $endgroup$
            – ACuriousMind
            Mar 29 at 22:23















          $begingroup$
          Comments are not for extended discussion; this conversation has been moved to chat.
          $endgroup$
          – ACuriousMind
          Mar 29 at 22:23




          $begingroup$
          Comments are not for extended discussion; this conversation has been moved to chat.
          $endgroup$
          – ACuriousMind
          Mar 29 at 22:23











          9












          $begingroup$

          No. Nothing with non-zero mass can move at lightspeed. A kugelblitz would behave just like a more conventional black hole formed from matter, due to the no-hair theorem.






          share|cite|improve this answer









          $endgroup$












          • $begingroup$
            'formed directly from matter'. If it's a black hole it has mass. If it has mass that means the photons collided and became electrons and positrons. = no lightspeed :(
            $endgroup$
            – Mazura
            Mar 29 at 22:10










          • $begingroup$
            Lightspeed - qualify by being in vacuum (I am thinking of Cherenkov radiation)?
            $endgroup$
            – Peter Mortensen
            Mar 30 at 3:23











          • $begingroup$
            @Mazura Yes, the black hole formed from photons has mass, but that doesn't necessarily mean that the photons produced matter. See chat.stackexchange.com/transcript/message/49710715#49710715
            $endgroup$
            – PM 2Ring
            Mar 30 at 10:49










          • $begingroup$
            @Peter Yes, by "lightspeed" I mean c, the speed of light in a perfect vacuum, 299792458 m/s.
            $endgroup$
            – PM 2Ring
            Mar 30 at 11:06















          9












          $begingroup$

          No. Nothing with non-zero mass can move at lightspeed. A kugelblitz would behave just like a more conventional black hole formed from matter, due to the no-hair theorem.






          share|cite|improve this answer









          $endgroup$












          • $begingroup$
            'formed directly from matter'. If it's a black hole it has mass. If it has mass that means the photons collided and became electrons and positrons. = no lightspeed :(
            $endgroup$
            – Mazura
            Mar 29 at 22:10










          • $begingroup$
            Lightspeed - qualify by being in vacuum (I am thinking of Cherenkov radiation)?
            $endgroup$
            – Peter Mortensen
            Mar 30 at 3:23











          • $begingroup$
            @Mazura Yes, the black hole formed from photons has mass, but that doesn't necessarily mean that the photons produced matter. See chat.stackexchange.com/transcript/message/49710715#49710715
            $endgroup$
            – PM 2Ring
            Mar 30 at 10:49










          • $begingroup$
            @Peter Yes, by "lightspeed" I mean c, the speed of light in a perfect vacuum, 299792458 m/s.
            $endgroup$
            – PM 2Ring
            Mar 30 at 11:06













          9












          9








          9





          $begingroup$

          No. Nothing with non-zero mass can move at lightspeed. A kugelblitz would behave just like a more conventional black hole formed from matter, due to the no-hair theorem.






          share|cite|improve this answer









          $endgroup$



          No. Nothing with non-zero mass can move at lightspeed. A kugelblitz would behave just like a more conventional black hole formed from matter, due to the no-hair theorem.







          share|cite|improve this answer












          share|cite|improve this answer



          share|cite|improve this answer










          answered Mar 29 at 11:19









          PM 2RingPM 2Ring

          3,64721123




          3,64721123











          • $begingroup$
            'formed directly from matter'. If it's a black hole it has mass. If it has mass that means the photons collided and became electrons and positrons. = no lightspeed :(
            $endgroup$
            – Mazura
            Mar 29 at 22:10










          • $begingroup$
            Lightspeed - qualify by being in vacuum (I am thinking of Cherenkov radiation)?
            $endgroup$
            – Peter Mortensen
            Mar 30 at 3:23











          • $begingroup$
            @Mazura Yes, the black hole formed from photons has mass, but that doesn't necessarily mean that the photons produced matter. See chat.stackexchange.com/transcript/message/49710715#49710715
            $endgroup$
            – PM 2Ring
            Mar 30 at 10:49










          • $begingroup$
            @Peter Yes, by "lightspeed" I mean c, the speed of light in a perfect vacuum, 299792458 m/s.
            $endgroup$
            – PM 2Ring
            Mar 30 at 11:06
















          • $begingroup$
            'formed directly from matter'. If it's a black hole it has mass. If it has mass that means the photons collided and became electrons and positrons. = no lightspeed :(
            $endgroup$
            – Mazura
            Mar 29 at 22:10










          • $begingroup$
            Lightspeed - qualify by being in vacuum (I am thinking of Cherenkov radiation)?
            $endgroup$
            – Peter Mortensen
            Mar 30 at 3:23











          • $begingroup$
            @Mazura Yes, the black hole formed from photons has mass, but that doesn't necessarily mean that the photons produced matter. See chat.stackexchange.com/transcript/message/49710715#49710715
            $endgroup$
            – PM 2Ring
            Mar 30 at 10:49










          • $begingroup$
            @Peter Yes, by "lightspeed" I mean c, the speed of light in a perfect vacuum, 299792458 m/s.
            $endgroup$
            – PM 2Ring
            Mar 30 at 11:06















          $begingroup$
          'formed directly from matter'. If it's a black hole it has mass. If it has mass that means the photons collided and became electrons and positrons. = no lightspeed :(
          $endgroup$
          – Mazura
          Mar 29 at 22:10




          $begingroup$
          'formed directly from matter'. If it's a black hole it has mass. If it has mass that means the photons collided and became electrons and positrons. = no lightspeed :(
          $endgroup$
          – Mazura
          Mar 29 at 22:10












          $begingroup$
          Lightspeed - qualify by being in vacuum (I am thinking of Cherenkov radiation)?
          $endgroup$
          – Peter Mortensen
          Mar 30 at 3:23





          $begingroup$
          Lightspeed - qualify by being in vacuum (I am thinking of Cherenkov radiation)?
          $endgroup$
          – Peter Mortensen
          Mar 30 at 3:23













          $begingroup$
          @Mazura Yes, the black hole formed from photons has mass, but that doesn't necessarily mean that the photons produced matter. See chat.stackexchange.com/transcript/message/49710715#49710715
          $endgroup$
          – PM 2Ring
          Mar 30 at 10:49




          $begingroup$
          @Mazura Yes, the black hole formed from photons has mass, but that doesn't necessarily mean that the photons produced matter. See chat.stackexchange.com/transcript/message/49710715#49710715
          $endgroup$
          – PM 2Ring
          Mar 30 at 10:49












          $begingroup$
          @Peter Yes, by "lightspeed" I mean c, the speed of light in a perfect vacuum, 299792458 m/s.
          $endgroup$
          – PM 2Ring
          Mar 30 at 11:06




          $begingroup$
          @Peter Yes, by "lightspeed" I mean c, the speed of light in a perfect vacuum, 299792458 m/s.
          $endgroup$
          – PM 2Ring
          Mar 30 at 11:06

















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