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.

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On the White Dwarf Mass Limit and S. Chandrasekhar

Subrahmanyan Chandrasekhar (1910–1995) was born into a Brahmin family in Lahore, then India. At the age as early as 21, he was responsible for deriving a theoretical mass limit an ideal white dwarf star can achieve without collapsing in on itself, now referred to as the Chandrasekhar limit, and accepted at 1.39 M⊙. This was one of the most important discoveries in the 20th century as it paved the way for better understanding of the processes occurring during the collapses of degenerate stars that may lead to such phenomena as black holes—ingredients crucial for the development of our modern cosmological theories.

Note: On the White Dwarf Mass Limit and S. Chandrasekhar

Stellar-Mass Black Holes

Stellar-mass black holes are the result of a gravitational collapse of a massive star at the end of its life. The core of such star collapses to singularity – a point of infinite density and space-time curvature – that is cloaked in the event horizon. The gravitational force of the resulting black hole is so strong that no light or signal can escape its event horizon. This essay will address how astronomers search for stellar-mass black holes, will attempt to describe their characteristics, and will also discuss the current knowledge on Milky Way black hole candidates and their companion stars, and the connection between X-ray sources and black holes.

Essay: Stellar-Mass Black Holes