Astronomers using NASA’s Spitzer Space Telescope have identified three fastest-spinning ultracool dwarfs ever found: 2MASS J03480772-6022270, 2MASS J12195156+3128497, and 2MASS J04070752+1546457.
The faster a brown dwarf spins, the narrower the different-colored atmospheric bands on it likely become, as shown in this illustration. Some brown dwarfs glow in visible light, but they are typically brightest in infrared wavelengths, which are longer than what human eyes can see. Image credit: NASA / JPL-Caltech.
2MASS J03480772-6022270, 2MASS J12195156+3128497, and 2MASS J04070752+1546457 were first spotted by the ground-based Two Micron All Sky Survey (2MASS), which ran until 2001.
These brown dwarfs are all about the same diameter as Jupiter but between 40 and 70 times more massive.
They rotate once per 1.08, 1.14 and 1.23 hours, respectively, while the next-fastest known brown dwarfs rotate about once every 1.4 hours and Jupiter spins once every 10 hours.
Based on their size, that means the largest of the three brown dwarfs whips around at more than 100 km per second (60 miles per second).
“We seem to have come across a speed limit on the rotation of brown dwarfs,” said first author Megan Tannock, a Ph.D. candidate in the Department of Physics and Astronomy at the University of Western Ontario.
“Despite extensive searches, by our own team and others, no brown dwarfs have been found to rotate any faster. In fact, faster spins may lead to a brown dwarf tearing itself apart.”
Tannock and her colleagues first identified the rapid rotation rates of the three brown dwarfs using data from Spitzer.
They then corroborated their unusual findings through observations with the ground-based Gemini North and Magellan telescopes.
They did this by measuring alterations in the objects’ light caused by the Doppler effect and using a computer model to match those alterations to spin rates.
“Brown dwarfs, like planets with atmospheres, can have large weather storms that affect their visible brightness,” said co-author Dr. Stanimir Metchev, an astronomer at the Institute for Earth and Space Exploration at Western University.
“The observed brightness variations show how frequently the same storms are seen as the object spins, which reveals the brown dwarf’s spin period.”
Megan E. Tannock et al. 2021. Weather on Other Worlds. V. The Three Most Rapidly Rotating Ultra-Cool Dwarfs. AJ, in press; arXiv: 2103.01990