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



The Next CEO of Stack OverflowWill 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










21












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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











$endgroup$
















    21












    $begingroup$


    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











    $endgroup$














      21












      21








      21


      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 yesterday









      Peter Mortensen

      1,95111323




      1,95111323










      asked 2 days ago









      user6760user6760

      2,96412144




      2,96412144




















          2 Answers
          2






          active

          oldest

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          29












          $begingroup$

          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
            2 days ago


















          8












          $begingroup$

          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
            2 days ago










          • $begingroup$
            Lightspeed - qualify by being in vacuum (I am thinking of Cherenkov radiation)?
            $endgroup$
            – Peter Mortensen
            yesterday











          • $begingroup$
            @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
            yesterday










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











          Your Answer





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          2 Answers
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          2 Answers
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          active

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          29












          $begingroup$

          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
            2 days ago















          29












          $begingroup$

          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
            2 days ago













          29












          29








          29





          $begingroup$

          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 2 days ago









          John RennieJohn Rennie

          279k44557804




          279k44557804











          • $begingroup$
            Comments are not for extended discussion; this conversation has been moved to chat.
            $endgroup$
            – ACuriousMind
            2 days ago
















          • $begingroup$
            Comments are not for extended discussion; this conversation has been moved to chat.
            $endgroup$
            – ACuriousMind
            2 days ago















          $begingroup$
          Comments are not for extended discussion; this conversation has been moved to chat.
          $endgroup$
          – ACuriousMind
          2 days ago




          $begingroup$
          Comments are not for extended discussion; this conversation has been moved to chat.
          $endgroup$
          – ACuriousMind
          2 days ago











          8












          $begingroup$

          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
            2 days ago










          • $begingroup$
            Lightspeed - qualify by being in vacuum (I am thinking of Cherenkov radiation)?
            $endgroup$
            – Peter Mortensen
            yesterday











          • $begingroup$
            @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
            yesterday










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















          8












          $begingroup$

          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
            2 days ago










          • $begingroup$
            Lightspeed - qualify by being in vacuum (I am thinking of Cherenkov radiation)?
            $endgroup$
            – Peter Mortensen
            yesterday











          • $begingroup$
            @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
            yesterday










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













          8












          8








          8





          $begingroup$

          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 2 days ago









          PM 2RingPM 2Ring

          3,1332922




          3,1332922











          • $begingroup$
            '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
            2 days ago










          • $begingroup$
            Lightspeed - qualify by being in vacuum (I am thinking of Cherenkov radiation)?
            $endgroup$
            – Peter Mortensen
            yesterday











          • $begingroup$
            @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
            yesterday










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
















          • $begingroup$
            '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
            2 days ago










          • $begingroup$
            Lightspeed - qualify by being in vacuum (I am thinking of Cherenkov radiation)?
            $endgroup$
            – Peter Mortensen
            yesterday











          • $begingroup$
            @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
            yesterday










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















          $begingroup$
          '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
          2 days ago




          $begingroup$
          '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
          2 days ago












          $begingroup$
          Lightspeed - qualify by being in vacuum (I am thinking of Cherenkov radiation)?
          $endgroup$
          – Peter Mortensen
          yesterday





          $begingroup$
          Lightspeed - qualify by being in vacuum (I am thinking of Cherenkov radiation)?
          $endgroup$
          – Peter Mortensen
          yesterday













          $begingroup$
          @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
          yesterday




          $begingroup$
          @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
          yesterday












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




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

















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