53 research outputs found
The galaxy halo formation in the absence of violent relaxation and a universal density profile of the halo center
While N-body simulations testify for a cuspy profile of the central region of
the dark matter haloes, observations favor a shallow, cored density profile of
the central region of, at least, some spiral galaxies and dwarf spheroidals. We
show that a central profile, very close to the observed one, inevitably forms
in the center of dark matter haloes if we make a supposition about a moderate
energy relaxation of the system during the halo formation. If we assume the
energy exchange between dark matter particles during the halo collapse to be
not too intensive, the profile is universal: it depends almost not at all on
the properties of the initial perturbation and is very akin, but not identical,
to the Einasto profile with small Einasto index . We estimate the
size of the 'central core' of the distribution, i.e., the extent of the very
central region with a respectively gentle profile, and show that the cusp
formation is unlikely, even if the dark matter is cold. The obtained profile is
in a good agreement with observational data for, at least, some types of
galaxies, but clearly disagrees with N-body simulations.Comment: 8 pages, 4 figure
Electric charge estimation of a new-born black hole
Though a black hole can theoretically possess a very big charge (), the charge of the real astrophysical black holes is usually
considered to be negligible. This supposition is based on the fact that an
astrophysical black hole is always surrounded by some plasma, which is a very
good conductor. However, it disregards that the black holes have usually some
angular momentum, which can be interpreted as its rotation of a sort. If in the
plasma surrounding the hole there is some magnetic field, it leads to the
electric field creation and, consequently, to the charge separation.
In this article we estimate the upper limit of the electric charge of stellar
mass astrophysical black holes. We have considered a new black hole formation
process and shown that the charge of a new-born black hole can be significant
( {Coulombs}). Though the obtained charge of an astrophysical
black hole is big, the charge to mass ratio is small , and it is not enough to affect significantly either the gravitational
field of the star or the dynamics of its collapse.Comment: 11 pages, 1 figure, accepted to International Journal of Modern
Physics
Extragalactic dark matter and direct detection experiments
Recent astronomical data strongly suggest that a significant part of the dark
matter, composing the Local Group and Virgo Supercluster, is not incorporated
into the galaxy haloes and forms diffuse components of these galaxy clusters.
Apparently, a portion of the particles from these components may penetrate into
the Milky Way and make an extragalactic contribution to the total dark matter
containment of our Galaxy.
We find that the particles of the diffuse component of the Local Group are
apt to contribute to the total dark matter density near the Earth.
The particles of the extragalactic dark matter stand out because of their high
speed ( {km/s}), i.e. they are much faster than the galactic dark
matter. In addition, their speed distribution is very narrow (
{km/s}). The particles have isotropic velocity distribution (perhaps, in
contrast to the galactic dark matter). The extragalactic dark matter should
give a significant contribution to the direct detection signal. If the detector
is sensitive only to the fast particles ( {km/s}), the signal may even
dominate.
The density of other possible types of the extragalactic dark matter (for
instance, of the diffuse component of the Virgo Supercluster) should be
relatively small and comparable with the average dark matter density of the
Universe. However, these particles can generate anomaly high energy collisions
in direct dark matter detectors.Comment: 5 pages, 2 figure
Dark matter annihilation at cosmological redshifts: possible relic signal from annihilation of weakly interacting massive particles
We discuss the possibility to observe the products of dark matter
annihilation that was going on in the early Universe. Of all the particles that
could be generated by this process we consider only photons, as they are both
uncharged and easily detectable. The earlier the Universe was, the higher the
dark matter concentration and the annihilation rate (proportional to )
were. However, the emission from the very early Universe cannot reach us
because of the opacity. The main part of the signal was generated at the moment
the Universe had just become transparent for the photons produced by the
annihilation. Thus, the dark matter annihilation in the early Universe should
have created a sort of relic emission. We obtain its flux and the spectrum.
If weakly interacting massive particles (WIMPs) constitute dark matter, it is
shown that we may expect an extragalactic gamma-ray signal in the energy range
0.5 - 20 {MeV} with a maximum near 8 {MeV}. We show that an experimentally
observed excess in the gamma-ray background at 0.5 - 20 {MeV} could be created
by the relic WIMPs annihilation only if the dark matter structures in the
universe had appeared before the universe became transparent for the
annihilation products (). We discuss in more detail physical
conditions whereby this interpretation could be possible.Comment: 8 pages, 3 figure
Dark matter annihilation in the gravitational field of a black hole
In this paper we consider dark matter particle annihilation in the
gravitational field of black holes. We obtain exact distribution function of
the infalling dark matter particles, and compute the resulting flux and spectra
of gamma rays coming from the objects. It is shown that the dark matter density
significantly increases near a black hole. Particle collision energy becomes
very high affecting relative cross-sections of various annihilation channels.
We also discuss possible experimental consequences of these effects.Comment: 9 pages, 1 figur
On collisions with unlimited energies in the vicinity of Kerr and Schwarzschild black hole horizons
Two particle collisions close to the horizon of the rotating nonextremal
Kerr's and Schwarzschild black holes are analyzed. For the case of multiple
collisions it is shown that high energy in the centre of mass frame occurs due
to a great relative velocity of two particles and a large Lorentz factor. The
dependence of the relative velocity on the distance to horizon is analyzed, the
time of movement from the point in the accretion disc to the point of
scattering with large energy as well as the time of back movement to the Earth
are calculated. It is shown that they have reasonable order.Comment: 6 pages, 1 figure. arXiv admin note: significant text overlap with
arXiv:1105.154
The tactics of the treating congenital deformities of the feet associated with the amniotic band syndrome
Amniotic constriction is an anomaly in the development of the amnion, in which tissue soft tissue tissues are formed in the amniotic cavity, stretched between the walls of the uterus. In most cases, they do not harm the fetus and do not interfere with normal childbirth, but sometimes amniotic bands can entangle, bind and squeeze the fetus or cord and cause wrinkles (furrows) on the limbs, leading to their amputation. Often amniotic constrictions are combined with such a defect as congenital equino-varus and flat-valgus deformation of the foot. To avoid loss of correction at the stages of amniotic clubfoot treatment and not to get vascular and neurological complications before the pediatric orthopedic surgeon, it becomes clear what to treat first. Therefore, the goal of this work was to show the tactics of sequential treatment of congenital clubfoot and congenital vertical ram associated with the amniotic band syndrome.ΠΠΌΠ½ΠΈΠΎΡΠΈΡΠ΅ΡΠΊΠΈΠ΅ ΠΏΠ΅ΡΠ΅ΡΡΠΆΠΊΠΈ β ΡΡΠΎ Π°Π½ΠΎΠΌΠ°Π»ΠΈΡ ΡΠ°Π·Π²ΠΈΡΠΈΡ Π°ΠΌΠ½ΠΈΠΎΠ½Π°, ΠΏΡΠΈ ΠΊΠΎΡΠΎΡΠΎΠΉ Π² Π°ΠΌΠ½ΠΈΠΎΡΠΈΡΠ΅ΡΠΊΠΎΠΉ ΠΏΠΎΠ»ΠΎΡΡΠΈ ΠΎΠ±ΡΠ°Π·ΡΡΡΡΡ ΡΠΊΠ°Π½Π΅Π²ΡΠ΅ ΠΌΡΠ³ΠΊΠΎΡΠΊΠ°Π½ΡΠ΅ ΡΡΠΆΠΈ, Π½Π°ΡΡΠ½ΡΡΡΠ΅ ΠΌΠ΅ΠΆΠ΄Ρ ΡΡΠ΅Π½ΠΊΠ°ΠΌΠΈ ΠΌΠ°ΡΠΊΠΈ. Π Π±ΠΎΠ»ΡΡΠΈΠ½ΡΡΠ²Π΅ ΡΠ»ΡΡΠ°Π΅Π² ΠΎΠ½ΠΈ Π½Π΅ Π½Π°Π½ΠΎΡΡΡ Π²ΡΠ΅Π΄Π° ΠΏΠ»ΠΎΠ΄Ρ ΠΈ Π½Π΅ ΠΏΡΠ΅ΠΏΡΡΡΡΠ²ΡΡΡ Π½ΠΎΡΠΌΠ°Π»ΡΠ½ΡΠΌ ΡΠΎΠ΄Π°ΠΌ, Π½ΠΎ ΠΈΠ½ΠΎΠ³Π΄Π° Π°ΠΌΠ½ΠΈΠΎΡΠΈΡΠ΅ΡΠΊΠΈΠ΅ ΡΡΠΆΠΈ ΠΌΠΎΠ³ΡΡ ΠΎΠΏΡΡΡΠ²Π°ΡΡ, ΡΠ²ΡΠ·ΡΠ²Π°ΡΡ ΠΈ ΡΠ΄Π°Π²Π»ΠΈΠ²Π°ΡΡ ΠΏΠ»ΠΎΠ΄ ΠΈΠ»ΠΈ ΠΏΡΠΏΠΎΠ²ΠΈΠ½Ρ ΠΈ ΠΏΡΠΈΠ²ΠΎΠ΄ΠΈΡΡ ΠΊ ΠΎΠ±ΡΠ°Π·ΠΎΠ²Π°Π½ΠΈΡ ΡΠΊΠ»Π°Π΄ΠΎΠΊ-Π²ΡΡΠΆΠ΅Π½ΠΈΠΉ (Π±ΠΎΡΠΎΠ·Π΄) Π½Π° ΠΊΠΎΠ½Π΅ΡΠ½ΠΎΡΡΡΡ
, ΠΏΡΠΈΠ²ΠΎΠ΄Ρ ΠΊ ΠΈΡ
Π°ΠΌΠΏΡΡΠ°ΡΠΈΠΈ. ΠΠ΅ΡΠ΅Π΄ΠΊΠΎ Π°ΠΌΠ½ΠΈΠΎΡΠΈΡΠ΅ΡΠΊΠΈΠ΅ ΠΏΠ΅ΡΠ΅ΡΡΠΆΠΊΠΈ ΡΠΎΡΠ΅ΡΠ°ΡΡΡΡ Ρ ΡΠ°ΠΊΠΈΠΌ ΠΏΠΎΡΠΎΠΊΠΎΠΌ, ΠΊΠ°ΠΊ Π²ΡΠΎΠΆΠ΄Π΅Π½Π½Π°Ρ ΡΠΊΠ²ΠΈΠ½ΠΎ-Π²Π°ΡΡΡΠ½Π°Ρ ΠΈ ΠΏΠ»ΠΎΡΠΊΠΎ-Π²Π°Π»ΡΠ³ΡΡΠ½Π°Ρ Π΄Π΅ΡΠΎΡΠΌΠ°ΡΠΈΡ ΡΡΠΎΠΏΡ. Π§ΡΠΎΠ±Ρ ΠΈΠ·Π±Π΅ΠΆΠ°ΡΡ ΠΏΠΎΡΠ΅ΡΠΈ ΠΊΠΎΡΡΠ΅ΠΊΡΠΈΠΈ Π½Π° ΡΡΠ°ΠΏΠ°Ρ
Π»Π΅ΡΠ΅Π½ΠΈΡ Π°ΠΌΠ½ΠΈΠΎΡΠΈΡΠ΅ΡΠΊΠΎΠΉ ΠΊΠΎΡΠΎΠ»Π°ΠΏΠΎΡΡΠΈ ΠΈ Π½Π΅ ΠΏΠΎΠ»ΡΡΠΈΡΡ ΡΠΎΡΡΠ΄ΠΈΡΡΡΡ
ΠΈ Π½Π΅Π²ΡΠΎΠ»ΠΎΠ³ΠΈΡΠ΅ΡΠΊΠΈΡ
ΠΎΡΠ»ΠΎΠΆΠ½Π΅Π½ΠΈΠΉ, ΠΏΠ΅ΡΠ΅Π΄ Π΄Π΅ΡΡΠΊΠΈΠΌ ΠΎΡΡΠΎΠΏΠ΅Π΄ΠΎΠΌ Π²ΡΡΠ°Π΅Ρ Π²ΠΎΠΏΡΠΎΡ ΠΎ ΡΠΎΠΌ, ΡΡΠΎ Π»Π΅ΡΠΈΡΡ ΠΏΠ΅ΡΠ²ΡΠΌ. ΠΠΎΡΡΠΎΠΌΡ ΡΠ΅Π»ΡΡ Π΄Π°Π½Π½ΠΎΠΉ ΡΠ°Π±ΠΎΡΡ ΡΡΠΎΡΠ»ΠΎ ΠΏΠΎΠΊΠ°Π·Π°ΡΡ ΡΠ°ΠΊΡΠΈΠΊΡ ΠΏΠΎΡΠ»Π΅Π΄ΠΎΠ²Π°ΡΠ΅Π»ΡΠ½ΠΎΠ³ΠΎ Π»Π΅ΡΠ΅Π½ΠΈΡ Π²ΡΠΎΠΆΠ΄Π΅Π½Π½ΠΎΠΉ ΠΊΠΎΡΠΎΠ»Π°ΠΏΠΎΡΡΠΈ ΠΈ Π²ΡΠΎΠΆΠ΄Π΅Π½Π½ΠΎΠ³ΠΎ Π²Π΅ΡΡΠΈΠΊΠ°Π»ΡΠ½ΠΎΠ³ΠΎ ΡΠ°ΡΠ°Π½Π°, Π°ΡΡΠΎΡΠΈΠΈΡΠΎΠ²Π°Π½Π½ΡΡ
Ρ ΡΠΈΠ½Π΄ΡΠΎΠΌΠΎΠΌ Π°ΠΌΠ½ΠΈΠΎΡΠΈΡΠ΅ΡΠΊΠΈΡ
ΠΏΠ΅ΡΠ΅ΡΡΠΆΠ΅ΠΊ
Light curve and neutrino spectrum emitted during the collapse of a nonrotating, supermassive star
The formation of a neutrino pulse emitted during the relativistic collapse of
a spherical supermassive star is considered. The free collapse of a body with
uniform density in the absence of rotation and with the free escape of the
emitted neutrinos can be solved analytically by quadrature. The light curve of
the collapsing star and the spectrum of the emitted neutrinos at various times
are calculated.Comment: 17 pages, 2 figures, published in Astronomy Report
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