Particle emission from galactic objects due to interactions with primordial black holes
Final Report Abstract
In the first ~ 10^-32 seconds of the existence of the Universe, density fluctuations can lead to the formation of black holes, referred to as primordial black holes (PBHs). PBHs at above 10^15 g can still exist today and they are one of the candidates to explain the nature of dark matter. Different methods have lead to constraints on the PBHs' contribution to the dark matter at below ~ 10^16 g and above ~ 10^26 g. At masses between these two masses, nothing is known about the abundance of PBHs. Therefore, a method was proposed to detect these PBHs: if a PBH traverses a stellar object, it looses energy which will finally be radiated. In the project, however, we find that such a signature is unobservable. Either, the radiated signal is too weak (at masses below ~ 10^20 g), or the rate of such interactions is too low (at masses above ~ 10^20 g). Observation time needed for a possible detection lie far above several tens of years, even in the most optimistic calculations. Realistic observation time provided by current instruments are typically below a month. Our central result is therefore that interactions of PBHs with stellar objects do not lead to any detectable signal. In the search for alternative methods, we find that in the already constrained mass range, for masses above 10^28 g, the PBHs could be captured and induce supernova explosions. Here, PBHs are already constrained to contribute with less than 10% to the dark matter, but even at that level, as much as ~ 10^5 PBHs can be captured within the life time of the Universe. We further investigated the possibility that classical astrophysical processes can lead to what is so-far accepted as dark matter signatures: the excess of electrons and positrons at high energies. We find that this signature can be well-described by the explosion of massive stars, i.e. M > 15 solar masses. We found out that the signatures we wanted to find in order to set limits on the abundance of PBHs in the Universe were far too weak to be detected. Therefore, we looked for alternatives in two ways: • We investigated if existing limits could be further improved by our method - and we find that this could be possible if a PBH at masses above ~ 10^28 g can induce a supernova explosion. • The recently observed spectrum of high-energy electrons and positrons was interpreted as a signature of dark matter by many authors. We investigated the possibility if classical physics can also produce the signature and found that supernova explosions of massive stars (M > 15 • Mʘ) can easily explain the observations. o March 01, 2009 - Public lecture at Gothenburg University o April 04 and April 07, 2009 - Public lectures at the "Universeum" (a science museum in Gothenburg) o September 30, October 01 and October 07 - Further popular science talks in the Gothenburg area o August 10, 2009 - Press release on PRL article: http://www.science.gu.se/aktuellt/nyheter/Nyheter+Detalj/Mystiskt_partikelflode_inte_mork_ materia.cid888354 o August 10, 2009 - interview with the Swedish radio "P4": http://www.sr.se/cgi-bin/goteborg/program/index.asp?programID=3542
Publications
- "No observational constraints from hypothetical collisions of hypothetical dark halo primordial black holes with galactic objects", The Astrophysical Journal
M. A. Abramowicz, J. K. Becker, P. L. Biermann, A. Garzilli, F. Johansson and L. Qian
(See online at https://doi.org/10.1088/0004-637X/705/1/659) - "Cosmic ray electrons and positrons from supernova explosions of massive stars", Physical Review Letters, 103:061101 (2009)
P. L. Biermann, J. K. Becker, A. Meli, W. Rhode, E. S. Seo, T. Stanev
(See online at https://dx.doi.org/10.1103/PhysRevLett.103.061101) - "On the detectability of primordial black holes in the Galaxy", 31st International Cosmic Ray Conference, Lodz, Poland (2009)
Julia K. Becker, M. A. Abramowicz and P. L. Biermann
