Hawking radiation
Hawking radiation is predicted to be extremely faint and is many orders of magnitude below the current best telescopes' detecting ability.
[3][4] A black hole can form when enough matter or energy is compressed into a volume small enough that the escape velocity is greater than the speed of light.
[5]: 37–43 In 1971 Soviet scientists Yakov Zeldovich and Alexei Starobinsky proposed that rotating black holes ought to create and emit particles, reasoning by analogy with electromagnetic spinning metal spheres.
In 1972, Jacob Bekenstein developed a theory and reported that the black holes should have an entropy proportional to their surface area.
[7] Initially Stephen Hawking argued against Bekenstein's theory, viewing black holes as a simple object with no entropy.
[8]: 425 After meeting Zeldovich in Moscow in 1973, Hawking put these two ideas together using his mixture of quantum field theory and general relativity.
A quantum fluctuation in the electromagnetic field can result in a photon outside of the black hole horizon paired with one on the inside.
To find the appropriate boundary conditions, consider a stationary observer just outside the horizon at position The local metric to lowest order is which is Rindler in terms of τ = t/4M.
Forming a black hole is the most efficient way to compress mass into a region, and this entropy is also a bound on the information content of any sphere in space time.
The form of the result strongly suggests that the physical description of a gravitating theory can be somehow encoded onto a bounding surface.
Page concluded that primordial black holes could survive to the present day only if their initial mass were roughly 4×1011 kg or larger.
A 2008 calculation using the particle content of the Standard Model and the WMAP figure for the age of the universe yielded a mass bound of (5.00±0.04)×1011 kg.
[18] Post-1998 science modifies these results slightly; for example, the modern estimate of a solar-mass black hole lifetime is 1067 years.
However, since the universe contains the cosmic microwave background radiation, in order for the black hole to dissipate, the black hole must have a temperature greater than that of the present-day blackbody radiation of the universe of 2.7 K. A study suggests that M must be less than 0.8% of the mass of the Earth[23] – approximately the mass of the Moon.
In that case, the source of all the outgoing photons can be identified: a microscopic point right at the moment that the black hole first formed.
Tracing the future of this matter, it is compressed onto the final singular endpoint of the white hole evolution, into a trans-Planckian region.
The reason for these types of divergences is that modes that end at the horizon from the point of view of outside coordinates are singular in frequency there.
[citation needed] The key point is that similar trans-Planckian problems occur when the modes occupied with Unruh radiation are traced back in time.
In a model with large extra dimensions (10 or 11), the values of Planck constants can be radically different, and the formulas for Hawking radiation have to be modified as well.
[32] The quantum effects are centered at a set of discrete and unblended frequencies highly pronounced on top of the Hawking spectrum.
[33] In June 2008, NASA launched the Fermi space telescope, which is searching for the terminal gamma-ray flashes expected from evaporating primordial black holes.
