Posted on July 5, 2022 by Erika Le Bourdais
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Myriam Prasow-Émond, an iREx student at the Université de Montréal, presented her master’s thesis in the spring of 2022. Here she summarizes the research projects she carried out as part of her master’s degree.
When the first exoplanets were discovered in the early 1990s, astronomers were very surprised: they were orbiting pulsar stars, that is, neutron stars that rotate very fast. Therefore, it was already established that exoplanets can exist in extreme environments, which led us to explore the environment of X-ray binaries, which are equally extreme. The first component of an X-ray binary is a compact object, that is, an object that is only a few kilometers wide but has a mass several times that of the Sun: white dwarfs, neutron stars or black holes. of stellar mass. The second component is the so-called donor star, which transfers part of its matter to the compact object, a process that emits a large amount of energy in the form of X-ray radiation, hence the binary name “rays X “.
Simplified representation of an X-ray binary. The latter consists of a compact object (white na, neutron star or black hole) that accumulates matter from a donor star, which emits a large amount of X-ray radiation. Credit: Myriam Prasow-Émond.
For more than 50 years, the scientific community believed that X-ray binaries were simply binaries (that is, they contained only two objects). Now, for the first time, we are looking for companions for X-ray binaries using direct imaging techniques, which are typically used to search for and study young, hot, distant exoplanets orbiting “normal” stars near Earth. To observe the selected X-ray binaries, we used the WM Keck Observatory in Hawaii and its near-infrared instrument NIRC2. We took pictures of their surroundings in hopes of finding bright fountains. But we had to be careful! Not all sources are necessarily a companion. To make sure that a source is not an unrelated background star, we can, for example, wait a few months or a few years and verify that the source actually orbits the X-ray binary, as the Earth orbits the around the Sun.
High contrast image (direct imaging technique) of the X-ray track RX J1744.7-2713, taken with the NIRC2 instrument at the WM Keck Observatory. The 21 sources detected, ie possible companions, are labeled with letters. The X symbol in the center indicates the approximate position of the X-ray binary. Credit: Prasow-Émond et al. (2022).
In short, my master’s thesis aims to bring together two completely different subjects in astronomy, namely exoplanets and compact objects such as black holes. In total, we found more than one source in nine X-ray binaries (see an example in the image on the right) and our analyzes show us that several of them could be accompanying. Thus, these findings tell us that stars and exoplanets can potentially exist and survive in the extreme environments created by X-ray binaries.
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Myriam worked on her M.Sc. degree at the University of Montreal between 2020 and 2022, under the supervision of Julie Hlavacek-Larrondo. His thesis will be available soon.
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