PhD Opportunities

Transiting brown dwarfs in the era of PLATO

Supervisor: Dr David BrownLink opens in a new window

Anticipated start date: October 2026

Image Credit: NASA/JPL-Caltech

Brown dwarfs are sub-stellar objects ~13 to 80 times the mass of Jupiter. Their central temperature and pressure is high enough to initiate a short-lived deuterium-burning phase, distinguishing them from most gas giant planets, but is insufficient for main-sequence hydrogen fusion.

The first brown dwarf was only discovered in 1995Link opens in a new window, and they remain rather elusive objects due to their small sizes and low luminosities. However, brown dwarfs are expected to be ubiquitous, with an estimated 25-100 billion in our galaxyLink opens in a new window. These fascinating objects are key astrophysical laboratories; their uncertain origins (i.e. whether they are star-like or planet-like) make them vital for probing formation pathways, while their shared properties with giant exoplanets make them powerful proxies in atmospheric studies. Of particular interest are transiting brown dwarfs, since with spectroscopy and photometry we can precisely measure their masses and radii. This in turn allows us to test internal structure models.

While brown dwarfs orbiting main sequence stars are believed to form far from their stars, they have nonetheless been found in short period orbits with semi-major axes <1 AU. Compared to planets and stars, however, the number of brown dwarfs in this region of parameter space is very limited; thus, it has been dubbed the brown dwarf desertLink opens in a new window.

This project will explore the fascinating world of transiting brown dwarfs, and will use data from both space-based and ground-based observatories to study these mysterious objects.

Transiting BDs orbiting low-mass stars offer us valuable opportunities to measure the radius and mass (in combination with the radial-velocity technique) and orbital parameters of the system. The relatively small size of the star leads to a large transit signal on the order of ten percent. Furthermore, the relatively low mass results in a huge radial-velocity signal on the order of several kilometers per second. This makes high-precision measurements of a BD’s mass and radius possible. The mass and radius are key for exploring the physical properties of the BDs in order to improve our understanding of the mechanisms of formation and evolution of these mysterious sub-stellar objects.

The transiting brown dwarf (BD) population has grown at a remarkable rate over the past 4 years due in large part to NASA’s Transiting Exoplanet Survey Satellite (TESS ) mission (Ricker et al. 2015), which was launched in 2018. These discoveries have been especially important because of how well the TESS  mission has aided in the precise characterization of the fundamental properties, namely the radius, of these transiting BDs. Astronomers have traditionally defined the range of masses for BDs to be between 13 and 80 Jupiter masses (⁠⁠), but more thorough studies have determined the mass range to vary between at the lower end (Spiegel, Burrows & Milsom 2011) and (Baraffe et al. 2003) at the higher end. These thresholds vary by several Jupiter masses because of variations in the chemical composition of the BDs and possibly because of their formation conditions. Some studies even prefer a breakdown by mass density and show a substellar boundary as low as (Hatzes & Rauer 2015). Although a precise mass determination is important to confirm that an object is indeed a BD, a precise radius determination is just as crucial. One of the best ways we can precisely determine the radius of a BD is by searching for transiting BD systems. Of the 37 known transiting BD systems, we typically find them to have radii between 0.7 and 1.4 Jupiter radii (⁠⁠) (Carmichael et al. 2021; Grieves et al. 2021).

Be part of this exciting area of research.

Brown dwarfs are <...> and there are several areas that you could explore as part of this project, including:

• <Examples of possible avenues>

Please contact me directly to find out more and discuss how the project might be tailored to your particular interests and skill set.

If you have any questions about the projects listed on this page, or would like to know more, please get in touch by emailLink opens in a new window.

 

 

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