Ultra-Luminous X-ray Sources: an Overview of Discussion on Their Origins and Nature

The subject of the nature and origins of ultra-luminous X-ray sources (ULXs) remains at the frontier of modern research. Existing data allows to fit a wide range of interpretations, including those based on stellar-mass black holes (sMBHs) and intermediate-mass black holes (IMBHs), accretion-powered pulsars, microquasars, and so on. The research of the ULXs is of cosmological and astrophysical importance, as they may become evidence of the existence of IMBHs that may be intimately connected to the formation of first active galactic nuclei engines at z~6.4. Although more recent research favors ULX interpretation based on stellar origins, the presence of IMBHs cannot be ruled out completely. In particular, hyper-luminous X-ray sources (HLXs), which comprise the brightest subset of the ULXs with X-ray luminosities LX 1041 erg s−1, are considered to be the strongest cases for harboring black holes of that type. This report will overview some of the observations and general properties of ULXs and will serve as an introduction to the discussion on the underlying physical models. In addition to ULX models based on black holes of both types, alternative interpretations will be reviewed. Within the sMBH framework, in particular, the importance of interpreting short timescale variations of ULXs is emphasized as a good diagnostic for revealing the underlying super-Eddington emission mechanisms.

Essay: Ultra-Luminous X-ray Sources: an Overview of Discussion on Their Origins and Nature

Detection of Population III Stars

It is suggested that two distinct Population III classes may have existed: population III.1 and population III.2. The former, consisting of stars of ∼ 100M⊙, and possibly going as high as 500M⊙, is believed to be formed in dark matter halos at z ≈ 10–30 which corresponds to the times of 0.1–0.48 Gyr after the Big Bang (Rydberg et al. 2013).

Note: Detection of Population III Stars

Galaxy Photometry


The aims of this project are as following:

  1. Reduce multi-band (BVR) CCD data of the M 51, M 63, M 106 (NGC 4258) and NGC 4725 galaxies obtained via 0.8-m (30-inch) telescope at the McDonald Observatory (MDO) in Austin, TX.
  2. Prepare scientific and color-combined frames.
  3. Discuss differences and similarities of galactic features appearing in the images that depend on the wavelength and the galaxy type.
  4. Conduct preliminary surface photometry of galaxies.

Project Report: Galaxy Photometry

Dynamical Mass Measurement of the Coma Cluster (Abell 1656)

Following (Zwicky 1937) we start with the virial theorem that relates the average kinetic energy ⟨K⟩ to the average gravitational potential energy ⟨U⟩ of bodies in a system (cluster, galaxy, etc) in the state of equilibrium: ⟨K⟩ = −1/2⟨U⟩, with brackets denoting an average value. We can measure radial velocities Vr of individual bodies in a system (of stars in a globular cluster or a galaxy, of galaxies in a cluster of galaxies) via spectroscopic means.

Note: Dynamical Mass Measurement of the Coma Cluster (Abell 1656)

Difficulties Involved in Observing Star and Planet Formation

It is known that star formation occurs in regions where dense molecular clouds undergo gravitational collapse. While observations of cold dusty disks and envelopes require long wavelength detectors to penetrate through obscuring material—from mid-infrared to radio—it is preferred to observe stars in the range between ultraviolet and near-infrared range (Hartmann 2003).

Note: Difficulties Involved in Observing Star and Planet Formation

What is a Galaxy?

Galaxies are enormous conglomerations of stars and interstellar material. The qualifying morphological properties of these objects, however, remain flexible due to two principal factors: continuity and irregularity.

Note: What is a Galaxy?

Basics of Calculus

This is a one-page note on the basics of calculus. Introduction to the study of change, Differential Calculus, Integral Calculus, Fundamental Theorem of Calculus, formula of Newton and Leibnitz. Full note in PDF.