Central OC Times

Astronomers at the University of California, Irvine have found that more white dwarf stars in the Milky Way galaxy could host habitable exoplanets than previously believed. This conclusion was reached by a research team led by Aomawa Shields, an associate professor of physics and astronomy at UC Irvine, who compared the climates of exoplanets orbiting different types of stars.

The study, published in The Astrophysical Journal, used a 3D global climate computer model typically applied to Earth's environment. The model revealed that exoplanets orbiting white dwarfs were warmer than those around main sequence stars like Kepler-62, despite similar stellar energy distributions.

Shields explained that "while white dwarf stars may still give off some heat from residual nuclear activity in their outer layers," they no longer undergo nuclear fusion at their cores. This characteristic has often led to these stars being overlooked as potential hosts for habitable planets. However, the simulations indicate that rocky planets within their orbits might possess more habitable surface areas than previously thought.

A critical factor influencing habitability is the rotational characteristics of the planets studied. The white dwarf's habitable zone is much closer to its star compared to other stars such as Kepler-62. This proximity results in a faster rotation period—10 hours for the white dwarf exoplanet versus 155 days for Kepler-62's planet.

Both planets are likely locked into synchronous orbits with permanent day and night sides. Shields noted that "the ultrafast white dwarf planet’s rotation stretches out the cloud circulation around the planet," while Kepler-62's slower orbital period leads to significant dayside cloud mass.

"We expect synchronous rotation of an exoplanet in the habitable zone of a normal star like Kepler-62 to create more cloud cover on the planet’s dayside," said Shields. This increased cloud cover reflects radiation away from the surface but can also result in cooling that reduces habitable area on certain planets.

The findings suggest new possibilities for researchers studying exoplanets and astrobiology, particularly with advancements like those offered by the James Webb Space Telescope. "These results suggest that the white dwarf stellar environment...may present new avenues for exoplanet and astrobiology researchers to pursue," said Shields.

Collaborators on this project included Eric Wolf from the University of Colorado Boulder; Eric Agol from the University of Washington; and Pier-Emmanuel Tremblay from Warwick University in England. Funding was provided by institutions such as the National Science Foundation and National Center for Atmospheric Research.

UC Irvine continues its Brilliant Future campaign aimed at enhancing university support through alumni engagement and philanthropic investments totaling $2 billion. The School of Physical Sciences plays a crucial role in this endeavor.

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