This past summer, Piper Lentz analyzed data of dwarf stars to advance investigations into the possibilities of life beyond our universe. A senior Astronomy and Physics double major at Amherst College, she has spent the past three years working under Professor Bardalez Gagliuffi in the Binary Worlds Lab. When Piper joined the summer after her freshman year, the lab had five members; now, it has grown to 11. At first, her research focused on fitting exoplanet orbits. However, this past summer, Professor Gagliuffi connected Piper with University of California San Diego professor Chris Theissen to tackle a new project: determining whether the spectra of ultracool dwarfs can predict their likelihood of hosting exoplanets.
Ultracool dwarfs (UCDs) are small stars that are relatively cold and dim; they are typically around 100 times fainter than our Sun. Every star has a unique spectrum, which describes the brightness of a celestial body at different wavelengths. A spectrum can be viewed through a telescope that observes this separation of wavelengths, similar to a glass prism dividing light into multiple colors. This is how Piper’s team has studied UCDs in their research.
This graph, created by Dr. Theissen, depicts the spectra for two different UCDs.
TRAPPIST-1 is a UCD proven to host exoplanets. The purple line shows the spectrum for a standard UCD that is 2600 Kelvin. The black line depicts TRAPPIST-1’s spectrum, which is less bright at longer wavelengths. TRAPPIST-1’s spectrum shows that it has a low surface gravity. The team hypothesized that the low surface gravity in this UCD is caused by the presence of orbiting exoplanets.
Using this idea, Piper’s team wishes to determine whether other UCDs with the same spectrum anomaly have exoplanets lowering its surface gravity and pulling and deforming the star.
Diagram showing the exoplanet deforming the UCD with its gravitational pull (Hana Zavadska, NASA, NASA/GSFC/ASU, modified by Piper)
Over the summer, Piper researched each of the 839 UCDs in her sample and determined which stars were part of a multiple-star system, where two or more stars are gravitationally bound together, and which were single-star systems. Grouping these types of systems together could skew the results and detract from statistical robustness, which is why Piper’s work was extremely important. She found that of the 839 sample UCDs, 93 were part of a multiple-star system. After categorizing the UCD’s, Dr. Theissen is using Piper’s findings to study each star that contains the same peculiarity found in TRAPPIST-1 and see if they also host exoplanets. Afterward, they will run statistical tests to determine if the spectrum peculiarity can predict the presence of orbiting exoplanets among UCDs.
Studies have suggested that as stars get cooler, there is a higher frequency of orbiting Earth-like exoplanets. Researching a method for finding UCDs that host exoplanets is critical for continuing these investigations. TRAPPIST-1 has exoplanets within the habitable zone, which means they are the necessary distance from the star for liquid water to exist.
If the spectrum of a UCD can find stars hosting exoplanets, we can better identify other potential habitable planets. This would be especially helpful because of limitations in observing UCDs by telescope. These stars are hard to see due to their temperature and small size. Compared with the stars themselves, their exoplanets are even harder to examine. Instead of attempting to see the exoplanets through telescopes, astronomers can identify UCDs with the same spectrum features as TRAPPIST-1 to search for habitable exoplanets. If any of these planets are in the habitable zone, there is a chance for life beyond Earth.
Currently, the team anxiously awaits the final results of the research. Once published, Piper Lentz and the team’s research just might help determine locations of life elsewhere in the universe.
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