Phd in the Spotlight: Thijs Coenen
Thijs Coenen (b. 1980) will be awarded his doctorate degree at the University of Amsterdam (UvA) on 20 November. While conducting his research at the Anton Pannekoek Institute (API), he discovered two new radio pulsars using the Low Frequency Array (LOFAR), a new radio telescope in the Netherlands. With this discovery, he demonstrated the LOFAR telescope's suitability for finding pulsars.
What is a radio pulsar?
´A radio pulsar is a very compact, rapidly spinning neutron star located many light years away from the earth that emits radio frequency radiation. A neutron star weighs a little more than the sun while it only has a diameter of approximately 20 kilometres. In other words, it is an enormous mass concentrated into a small area, which is why conditions in a radio pulsar are so different to those on earth. There are around 2,000 radio pulsars that we know of, the first of which was discovered in 1967. Radio pulsars emit radio frequency radiation. LOFAR, whose centre is located near Exloo in Drenthe, is able to detect this radiation. The telescope largely consists of a great number of simple antennas which, with the help of software, have been transformed into a large telescope. LOFAR was designed to detect long wavelengths such as those emitted by pulsars. I used LOFAR to discover two new pulsars.'
Did that come as a surprise?
'Yes, it did. Many people didn't think it possible in a country as overpopulated as the Netherlands. Everyone's electronic equipment and appliances would cause too much interference for the telescope to work properly. Also, my research started when the telescope was being built, which was sometimes problematic. It's good news that I discovered new radio pulsars. It shows that the LOFAR telescope can certainly be used to locate radio pulsars, also in the Netherlands. It means we can expand our knowledge of radio pulsars, a phenomenon we don't know that much about yet. Because it's impossible for us on earth to simulate the conditions in a neutron star, our research is dependent on telescopes.
Tell us about your discovery of the radio pulsars.
'I set out on two major quests to find pulsars. First I scoured the northern part of the sky and then I concentrated in more detail on a smaller section along the surface of the Milky Way. During both searches I came across dozens of already discovered pulsars, but during the second I found two new ones. The discovery certainly gave me cause to celebrate. Though I did also get it wrong on occasion. Searches for radio pulsars are going on elsewhere too. The first time I discovered a new radio pulsar, I emailed my colleagues in my enthusiasm. I found out soon afterwards that the Green Bank Telescope in West Virginia had discovered that same radio pulsar just before I did. After that experience, I became more careful.'
Have the neutron stars been named after you or after someone else?
'They are always named in accordance with their celestial coordinates. The pulsars we discovered are named PSR J0140+5621 and PSR J0613+3731. There are a few pulsars with names, such as the Crab pulsar, so named because it is located in the Crab Nebula. I wouldn't dare name a dead star after a person. After all, a neutron star is the remains of a star destroyed in the blast of a supernova.'
Would you like to continue studying radio pulsars after you receive your PhD?
'Definitely. Although I love it in Amsterdam, I may go abroad. New telescopes are being built in Australia and South Africa, projects I would love to be involved in. The pulsars I discovered are pretty ordinary as far as pulsars go. But we expect pulsars to exist that orbit black holes. Discovering one of those would indeed be something.'
Author: Carin Röst