loading page

The number of things
  • Columbia astronomy grads,
  • Emily Sandford,
  • Zephyr Penoyre
Columbia astronomy grads
Columbia University Department of Astronomy
Emily Sandford
Columbia University Department of Astronomy

Corresponding Author:esandford@astro.columbia.edu

Author Profile
Zephyr Penoyre
Columbia University Department of Astronomy
Author Profile


We ask a simple question: how many things are there in the universe? More specifically we ask how numerous, in a given volume, are objects of a specific mass. By collecting and collating data from across astrophysical disciplines we can build a picture of the universe, spanning all scales from planets to clusters of galaxies. Any realtionships within and between objects and scales highlight where the physics that goes into forming specific objects is universal and where it is scale and object dependence.
The most basic view of the universe is of a uniform power spectrum of density pertubations, and gravity being the dominant force leading individual objects to collapse and form. Thus number density per unit mass \(\left( \frac{dN}{dVdM} \right)\)should follow a simple relationship \((\propto M^{-2})\). This is broadly true across a huge range of scales (see figure \ref{125409}) ,  and any deviations bely the more nuanced interaction of other physical processes which we will discus in more detail.
Words words words.