Related Experiment Video
Updated: Jun 24, 2026

Automated, High-resolution Mobile Collection System for the Nitrogen Isotopic Analysis of NOx
Published on: December 20, 2016
Hydrogen 21-centimeter emission from a galaxy at cosmological distance
M A Zwaan1, P G van Dokkum, M A Verheijen
1School of Physics, University of Melbourne, Victoria 3010, Australia. mzwaan@physics.unimelb.edu.au
Abstract:
We have detected the neutral atomic hydrogen (HI) emission line at a cosmologically significant distance [redshift (z) = 0.18] in the rich galaxy cluster Abell 2218 with the Westerbork Synthesis Radio Telescope. The HI emission originates in a spiral galaxy 2.0 h65(-1) megaparsecs from the cluster core. No other significant detections have been made in the cluster, suggesting that the mechanisms that remove neutral gas from cluster galaxies are efficient. We infer that fewer than three gas-rich galaxies were accreted by Abell 2218 over the past 10(9) years. This low accretion rate is qualitatively consistent with low-density cosmological models in which clusters are largely assembled at z > 1.
Related Concept Videos
Rocket Propulsion in Empty Space - I
Rocket Propulsion In Empty Space - II
Escape Velocity
To calculate the escape velocity, it is assumed that no energy is lost to any frictional forces. In practice, a satellite launched from...
Schwarzschild Radius and Event Horizon
The minimum speed required to launch a projectile from the surface of an object to which it is gravitationally bound so that it eventually escapes the object’s gravitational field is called the escape velocity. The escape velocity is independent of the mass of the object. Merging the idea of escape velocity with the...
Escape Velocities of Gases
Radiation Pressure: Problem Solving
The average value of the rate of momentum transfer divided by the absorbing area represents the average force per...

