Session H8: Galactic and Planetary Astrophysics

The influence of Dynamical state on Scatter in Galaxy Cluster Mass-Observable Relations

Clusters of galaxies, as the most massive bound objects in the universe, are sensitive probes of the cosmological parameters. Determination of cluster mass is crucial and often relies on scaling relations between cluster mass and observables, such as X-ray temperature, X-ray luminosity, etc. Therefore, systematic bias and scatter in these relations have to be studied carefully both for cosmological purposes and for understanding complicated cluster physics. The dynamical state of clusters is one possible source of scatter, because most clusters are formed only recently by merging small galaxies or groups and many of the unrelaxed ones still show disturbed morphology in high-resolution X-ray images. In our work, we simulate galaxy clusters in cosmological simulations with dark matter particles and gas. We follow the actual cluster merging histories to quantify the dynamical state of clusters. To compare with observations more directly, we also produce mock Chandra images and extract X-ray observables in the same way observers do. There analyses allow us to examine to contribution of dynamical state on scatter in cluster mass-observable relations.   

Can Cluster Evaporation Explain the Missing Thermal Energy in Galaxy Clusters?

Resent observations of a number of galaxy clusters using the Sunyaev-Zel'dovich effect indicate that about 1/3 of baryonic mass is missing from the hot intracluster medium (ICM), which is significantly larger than the fraction of stars and cool gas, which account for only about $10\%$. Here we address the question whether the remaining $22\%\pm 10\%$ can be accounted for by thermal evaporation of gas from clusters. We have found that evaporation can occur only from the cluster ``surface'', $r\sim r_{vir}$, and not from it's interior. We evaluated particle diffusion through the magnetized ICM for several scenarios of ISM turbulence and found that diffusivity is suppressed by at least a factor of 100 or more, compared to the Spitzer value. Thus, only particles from radii $r\agt 0.9r_{vir}$ can evaporate. Diffusion of particles from inside the cluster, $r\alt 0.9r_{vir}$, takes longer than the Hubble time. This lowers the cluster-averaged fraction of the evaporated hot gas to few percent or less. However, if the missing hot component {\em is indeed} due to evaporation, this strongly constrains the magnetic field structure in the cluster envelope, namely either (i) the gas is completely unmagnetized ($B\alt 10^{-21}$ gauss) in the cluster halo or (ii) the magnetic fields in the ICM are rather homogeneous and non-turbulent.   

Why are the earth spin and its axis 24hours, tilted by 23.5degree?

The spins of planets have become a long subject of physics as well as the planetary science, and a lot of researches have been done mostly on the basis of the origin of the solar system, where the rotation rates of planets have been believed to be important clues to lead to the answer of question of planetary formations. Most studies reported in recent years discuss the rotation rate of a planet on the basically same kind of model where spin angular momentum was accreted from a disk of planetesimals at the early stage of planet formations. It is demonstrated that the earth spin is driven by a force induced from the gravitation and orbital motion of the earth-moon system, which leads the earth spin to be calculated from the fundamental quantities by almost an exact number, $23^{h}38^{m}58^{s}$ without any adjusting constants. It is also demonstrated that the earth spin axis which is tilted by 23.5deg. with respect to the earth orbit can be derived from the gravitation of the sun acting on the earth. The calculated number, 23.487deg., is astonishingly close to the observation. The spin of the sun is also obtained by the same way as the earth by reducing the many body system into a two body system. The calculation results in an approximated number which validates our theory, analysis, and calculations. A possible experiment to measure the force driving the earth spin is discussed.   

Dark matter places planets

Consider that the dark matter density (d) drops off as 1/r$^2$ from an oscillating, standing wave producing sun. The wave velocity is proportional to the reciprocal of the square root of d. The planet distances r=r$_{0}$exp(0.625N) provides good values (N an integer equals 7 for Mercury). r$_{0}$ is sun's radius when relation applied to sun.$_{ }$1.25 m/s falls out of the calculations as the starting velocity for the waves from the sun. The relation also holds for satellites of oscillating gaseous planets. On earth a preliminary surface velocity is 5 m/s. See Physics Essays 12(1):3-10 (1999). Standing waves provide solar system stability. One can use the relation to get some history of the solar system and of the individual planets. For example the sun had a somewhat larger radius when the planets were placed. Apparently planets like Saturn used to be hotter with larger radii. These are determined from present satellite locations etc. One can arrive at reasonable layering of the gaseous planets considering that ring systems are due to ongoing layer oscillations. Sharp cutoffs of the rings indicate high Q oscillations instead of just gravity are involved. The data indicate that dark matter is not just a far away phenomenon but is involved on earth and is much more dense here than previously surmised.   

Ordinary Dark Matter versus Mysterious Dark Matter in Galactic Rotation

To theoretically describe the measured rotational velocity curves of spiral galaxies, there are two different approaches and conclusions. (1) ORDINARY DARK MATTER. We assume Newtonian gravity/dynamics and successfully find (via computer) mass distributions in bulge/disk configurations that duplicate the measured rotational velocities. There is ordinary dark matter within the galactic disk towards the cooler periphery which has lower emissivity/opacity. There are no mysteries in this scenario based on verified physics. (2) MYSTERIOUS DARK MATTER. Others INaccurately assume the galactic mass distributions follow the measured light distributions, and then the measured rotational velocity curves are NOT duplicated. To alleviate this discrepancy, speculations are invoked re ``Massive Peripheral Spherical Halos of Mysterious Dark Matter.'' But NO matter has been detected in this UNtenable Halo configuration. Many UNverified ``Mysteries'' are invoked as necessary and convenient. CONCLUSION. The first approach utilizing Newtonian gravity/dynamics and searching for the ordinary mass distributions within the galactic disk simulates reality and agrees with data.