Weighing the Milky Way? Yes we CAN!

© © Michiel Brentjens (2021)

Over the past few weeks students of the MSc course Radio Astronomy at Leiden University, taught by Michiel Brentjens and Timothy Shimwell, made radio telescopes out of paint cans. They used these "telescopes" to actually measure the orbital velocity of hydrogen in our Milky Way. The faster it orbits, the heavier our galaxy must be to prevent the gas from flying away. Our Milky Way has a maximum rotational speed of approximately 220 km/s, which is consistent with the paint can data!

A measurement like this requires accurate calibration to determine the properties of antenna and electronics in isolation. We are grateful that Dutch Microwave Absorber Solutions, based in nearby Zoeterwoude provided us with high tech microwave absorbing material to calibrate the data free of charge (the anthracite-coloured spikes).

This material is normally used in specialist laboratories for antenna-research, radar technology, and radio interference. Dutch Microwave Absorber Solutions is global market leader in sustainable, top-quality radio-absorbing materials and entirely "Made in NL".

An interesting aside is that these measurements were conducted within a few hundred meters of the "Pesthuispolder" site at which Johan Hamaker et al. conducted their first interferometry experiments for the WSRT more than half a century ago!