Dutch students warn space mission of noisy white dwarfs

The gravitational wave background from orbiting white dwarf stars will be louder than the noise from binary black holes. This is what two Dutch master’s students and their supervisors predict in two articles in anticipation of the LISA space mission. Until now, this mission did not take into account noisy white dwarfs. Fortunately, noise can be filtered and even provide new information.

The papers, titled “On the uncertainty of the white dwarf astrophysical gravitational wave background” and “The probability that white dwarf binaries dominate the astrophysical gravitational wave background in the MHz band” were published in Astronomy and astrophysics.

LISA, the laser interferometer space antenna, is planned to be launched by the European Space Agency (ESA) in the mid-2030s. Among other things, the Netherlands is building the “eyes”, the software, the guidance mechanism and LISA reading electronics.

LISA will measure gravitational waves from compact binary stars, double white dwarfs, merging supermassive black holes and other exotic objects in the universe. As a byproduct, LISA will also capture background noise from trillions of black holes that merged long ago.

Gijs Nelemans is an astronomer at Radboud University (Nijmegen, Netherlands). He is involved in the Dutch contribution to LISA. With now-graduate master’s students Seppe Staelens and Sophie Hofman, he developed models to see if the background of white dwarfs could be captured in the same way as the background of black holes.

Staelens, who came to Nijmegen as part of a student exchange from Louvain (Belgium) and who is now a doctoral student. student in Cambridge (UK), started with simple models. Hofman, who just graduated and is interning in the industry, then expanded the models.

Models have shown that the background of white dwarfs is louder than that of black holes. “Our supervisor thought that LISA would never be able to detect the collective signal from white dwarfs,” says Staelens. “And now our models show that white dwarfs eclipse black holes. Ha!”

Astronomers see the background noise of white dwarfs as an opportunity to study the evolution of stars like our sun in distant galaxies. “With telescopes you can only study white dwarfs in our own Milky Way, but with LISA we can listen to white dwarfs in other galaxies,” says Nelemans.

“Moreover, in addition to the background noise of black holes and the noise of white dwarfs, perhaps other exotic processes in the early universe can be detected.”

Hofman adds: “I think it’s really cool that with my master’s research we are contributing to the expected discovery of such an important mission as LISA.”