Planck star is a proposed new idea which, if it gains support, will change how we think about "black holes".
One can think of a Planck star as a slow-motion bounce that because of extreme time-dilation can take hundreds of billions of years to mature. When it finally does, the star breaks through its trapping horizon outer shell and dissipates in an explosion.
The concept arises in Loop gravity theory. As a general rule at extremely high densities a quantum correction appearing in Loop gravity causes gravity to repel rather than attract, so that "collapse to singularity" is replaced by BOUNCE. You can think of a Planck star as the final stage in the life of a massive star, even denser than a neutron star. In the Loop picture, it takes the place of the "singularity" in the classical BH picture.
A Planck star is so dense that it creates a trapping HORIZON around itself, analogous to the "event horizon" of a classical Schwarzschild black hole. It is an object so dense that
1. the local proper time is greatly SLOWED, an outside observer somehow able to witness it would see collapse and bounce happen with such glacial slowness that it would seem FROZEN to the outsider
2. but no outsider can witness this slow-motion bounce because the Planck star has created a trapped region around itself, from which light cannot escape. However the trapping horizon can emit Hawking radiation, and the Planck star will also eventually explode.
Radiation and eventual explosion.
Like the "event horizon" of a conventional black hole, the Planck star's outer trapping horizon emits HAWKING RADIATION. One can think of that as pairs of virtual particles one of which flies outward while the other falls inward giving up gravitational energy in the process. The total mass is reduced by Hawking radiation and the outer trapping horizon gradually shrinks.
Meanwhile the Planck star itself, which is at the center of this spherical trapping horizon, is gradually expanding and will eventually burst through it in an end-of-life explosion.
To get more detail, simply google "planck star". You will get an arxiv preprint of the "Planck stars" article posted by Rovelli and Vidotto. BTW Francesca Vidotto is a longtime PF member who used to post a lot here when she was still a student.
One can think of a Planck star as a slow-motion bounce that because of extreme time-dilation can take hundreds of billions of years to mature. When it finally does, the star breaks through its trapping horizon outer shell and dissipates in an explosion.
The concept arises in Loop gravity theory. As a general rule at extremely high densities a quantum correction appearing in Loop gravity causes gravity to repel rather than attract, so that "collapse to singularity" is replaced by BOUNCE. You can think of a Planck star as the final stage in the life of a massive star, even denser than a neutron star. In the Loop picture, it takes the place of the "singularity" in the classical BH picture.
A Planck star is so dense that it creates a trapping HORIZON around itself, analogous to the "event horizon" of a classical Schwarzschild black hole. It is an object so dense that
1. the local proper time is greatly SLOWED, an outside observer somehow able to witness it would see collapse and bounce happen with such glacial slowness that it would seem FROZEN to the outsider
2. but no outsider can witness this slow-motion bounce because the Planck star has created a trapped region around itself, from which light cannot escape. However the trapping horizon can emit Hawking radiation, and the Planck star will also eventually explode.
Radiation and eventual explosion.
Like the "event horizon" of a conventional black hole, the Planck star's outer trapping horizon emits HAWKING RADIATION. One can think of that as pairs of virtual particles one of which flies outward while the other falls inward giving up gravitational energy in the process. The total mass is reduced by Hawking radiation and the outer trapping horizon gradually shrinks.
Meanwhile the Planck star itself, which is at the center of this spherical trapping horizon, is gradually expanding and will eventually burst through it in an end-of-life explosion.
To get more detail, simply google "planck star". You will get an arxiv preprint of the "Planck stars" article posted by Rovelli and Vidotto. BTW Francesca Vidotto is a longtime PF member who used to post a lot here when she was still a student.
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