PhD in the Spotlight: Lucas Ellerbroek
On 14 March Lucas Ellerbroek (b. 1984) will be awarded his doctorate at the University of Amsterdam (UvA). As part of his doctoral research at the Anton Pannekoek Institute (API), Ellerbroek researched the development of massive stars. He discovered that the star HD163296 discharged clouds at regular intervals of 16 years during its development.
You were looking at young stars?
‘Yes, I researched the birth of massive stars, which are heavier than the sun. Stars like that take millions of years to develop. We still don’t know much about this, because lots of clouds and vapour envelop stars as they grow, reducing our visibility of them. I used the Very Large Telescope in Chile to research the development of HD163296. This star is located around 400 light years from us and is still young: around four million years old. I found that it discharges a cloud from two sides every 16 years, with a circumference of a few hundred million kilometres. This occurred in 1969, in 1985 and in 2001. It’s likely to happen again in 2017. I also looked for photographic material about the star on the Internet and in archives. During the discharges, the star was less clearly visible. That makes sense, because that’s when the jet is in front of the star.’
What do those clouds tell us?
‘They probably indicate a growth spurt for the star, both in terms of mass and shape. They might be due to a small planet rotating around the star in an unusual trajectory, disrupting its constant growth. The series of clouds are in any case a clear indication that stars grow in staggered phases rather than as a gradual process. The question now is whether other stars also discharge jets at regular intervals. If we know more about how stars develop, we can also better understand the development of our own planet.’
Are you the first to have observed these jets?
‘No, but I’m the first to have measured how regularly they are discharged. I
managed it partly because I was able to use a new spectrograph, the X-shooter,
which my supervisor Lex Kaper came up with. A telescope can see only a small
part of the spectrum. The X-shooter sees the whole spectrum, from ultraviolet to
infrared light. After my degree in theoretical physics, I was eager to carry out
observational research. Then I was invited to apply for this job as a trainee
research assistant. I went to Chile four times to make observations through the
Very Large Telescope. That’s quite an unusual opportunity for astronomy trainee
research assistants. It was fantastic: researching stars using the telescope in
Chili is the most direct way of observing them. I felt like a kind of detective.
In that respect I was really lucky.’
Are you planning to go back to Chile more often?
‘I don’t know yet. I’m now teaching astronomy at a secondary school, and after the summer I’ll see what I’m going to do next. Completing my doctorate was certainly a learning experience in any case. What I found is that you sometimes have to be really business-like. If you want feedback from an overseas expert, you can email them, but it’s even better to visit. I was once on holiday in Paris and one afternoon I visited a professor to ask him to read my paper. That worked. If someone is standing right in front of you, you don’t say no. For me, that networking was probably the most enjoyable part of doing research.’
Author: Carin Röst
