Astronomers at Western University have discovered a group of three brown dwarfs that complete a full rotation about once every hour, making them the fastest rotating stars of this type known to date.
The brown dwarfs , in fact, are failed stars. They form like stars, but are less massive and more like giant planets like Jupiter, Saturn, Uranus, and Neptune.
The brown dwarfs now discovered rotate at their equator with speeds of about 360,000 kilometers per hour, that is, 10 times faster than Jupiter.
At 360,000 kilometers per hour, the brown dwarfs’ relatively weak gravity barely holds them together. If they rotate faster, they could be destroyed.
That rotational speed is about 10 times faster than normal, and about 30 percent faster than the fastest rotations previously measured on these types of objects.
Stars, brown dwarfs, and planets generally rotate around their axis once every 10 hours and even more slowly.
For example, the Earth rotates around its axis once every 24 hours, while Jupiter and Saturn take about 10 hours. The Sun rotates around its axis on average every 27 days.
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First identified by NASA’s Spitzer Space Telescope, brown dwarfs were later studied by telescopes on the ground, including Gemini North, confirming this surprising speed of rotation.
They were discovered spinning faster than anything else found before thanks to the work of astronomers at Western University in Canada, who used NASA’s Spitzer Space Telescope to preliminarily measure their rotational speeds.
The finding was later confirmed with follow-up observations from the Gemini North Telescope in Maunakea, Hawai’i, and the Carnegie Institution for Science’s Baade Magellan Telescope in Chile.
Speed limit The leader of the research team, Megan Tannock, specialized in brown dwarfs, said in a statement that “it seems that we have run into a speed limit in the rotation of brown dwarfs, since, despite the searches Thoroughly conducted by our own team and others, no faster rotating brown dwarf has been found. “
The astronomers were able to confirm these rapid rotations by measuring alterations in the light of the brown dwarfs caused by the Doppler effect, and using a computational model to match those alterations to the spin speeds.
As each brown dwarf rotates, the light from the hemisphere spinning toward us appears blue-shifted, while the light from the hemisphere moving away from us appears red-shifted due to the Doppler effect.
The Doppler effect , named for the Austrian physicist Christian Andreas Doppler, is the apparent frequency change of a wave produced by the relative motion of the source with respect to its observer.
The Doppler effect makes the absorption lines in the spectrum of the brown dwarf appear widened (stretched towards both the red end of the spectrum and the blue end of the spectrum). By matching this enlargement with a computer model, the astronomers determined how fast each brown dwarf spins.
The results of this research will be published in a future edition of The Astronomical Journal, but they are already available in the ArXiv repository.
Reference Weather on Other Worlds. V. The Three Most Rapidly Rotating Ultra-Cool Dwarfs . Megan E. Tannock et al. arXiv: 2103.01990 [astro-ph.SR]