Brown Dwarfs - Blog Posts

The Importance of Deuterium

Deuterium is an isotope of hydrogen with one extra proton. The ratio of deuterium to hydrogen (D/H) is an indicator of mass in isolated substellar objects. Brown dwarfs that have more than 12 times the mass of Jupiter are theoretically warm enough to fuse deuterium, causing smaller atmospheric D/H ratios. In Solar System objects the D/H ratio can be altered by temperature, material transport, or atmospheric escape. In Rowland+ 2024 (accepted ApJL), we were able to detect deuterium for the first time outside of our solar system in WISE 0855, the coldest known brown dwarf.

The overall D/H ratio is inferred by detecting both deuterated methane (CH3D) and normal methane (CH4) in the atmosphere of WISE 0855. From the data we also estimate that WISE 0855 has two times more mass than Jupiter. Both the deueterium abundance and mass are consistent with theoretical expectations. Deuterium is not exclusive to gravitationally bound companions and can be used to infer mass in both brown dwarfs and exoplanets. I was super excited to be apart of this paper and also previous work demonstrating we could detect CH3D is most cold brown dwarfs.

I really enjoyed doing this interview for the Brown Dwarf Podcast. It was such a pleasure talking with Phoenix.

A Rogue World, not a Failed Star

At the scientific conference Cool Stars 22 hosted on the UC San Diego campus, there were numerous talks about stellar and substellar research. The last session on Friday was titled Brown Dwarfs and Giant Exoplanets: Future Prospects and Thirty Years of Discovery. The first talk was an invited review by Davy Kirkpatrick, a prolific brown dwarf researcher that has enabled my own research and the work of others. It was an overview starting from the discovery era into the characterization era we are in right now thanks to JWST.

I appreciated him openly saying that brown dwarf researchers need to stop letting people refer to brown dwarfs as "failed stars" and be careful when talking to media. This is crucial because brown dwarfs are not a typical astrophysical object people are exposed to. Many people know what galaxies, planets, and asteroids are and these objects have been repeatedly depicted in science fiction for decades. Many people may not have an image in their mind when they read the phrase "brown dwarf".

A brown dwarf is a Jupiter-sized (sized in radius, not mass) object that is mainly hydrogen and helium gas. Brown dwarfs are not massive enough to fuse hydrogen for energy like stars, but some of the most massive brown dwarfs can still fuse deuterium. They start out with whatever heat they were born with and cool down slowly over time. Brown dwarfs range in temperature from about 4400 to 35° C ( 2700 to 280 Kelvin). This temperature range extends from the bottom tail of the coolest stars to average room temperature. Such a massive spread in temperature leads to a large variety in the types of gases and clouds we see within their atmospheres.

Brown dwarfs are unique and dynamic worlds that exist outside of the context of not being able to fuse hydrogen like stars. Astronomers commonly see water vapor, methane, carbon monoxide, ammonia, or carbon dioxide in their atmospheres. Some warm brown dwarfs have clouds with sand-like material and the coldest ones could potentially host water clouds like the ones we see on Earth. Brown dwarfs even have weather. These objects are very successful at repeatedly challenging our understanding of how atmospheric chemistry works.

In my own head, I frequently imagine brown dwarfs as planet-like worlds. Essentially Jupiter with a different, but cooler color scheme. Maybe with less cloud coverage for the hottest brown dwarfs. I wonder what it would be like to live in a society among the cloud decks or even orbiting around a brown dwarf. If those beings had vision, they would very likely need to see in the infrared given the absence of a host star.

While doing my own work I would like to romanticize brown dwarfs a bit more and get back in touch with the wonder that led me to the field in the first place. One way I'm hoping to do that is by participating as an advisory board member for the in development planetarium show Rogue Objects. The planetarium show is being developed by Janani Balasubramanian who is an artist in residence with the Brown Dwarf New York City Research Group. I had an absolutely wonderful time chatting with them last year about what we thought brown dwarfs looked like and how they related to the everyday experiences of people.

The People Behind JWST

I was featured in an article about the people who support and use JWST. I was so excited to share more of my personal experience working with the data. Link to article here.

Another video that highlights some of my work and hopes for JWST are here in this TikTok posted by the SETI Institute. The interview was done by Franck Marchis.