But around some stars it gets odder. Nevermind the common stories about the planets with liquid iron – that’s just heat. NewScientist (8 October 2016) reports on malformed stars and their attendant planets’ behavior:
Earth’s tilt gives our planet its seasons. But hot, massive “early-type” stars can spin almost 100 times faster than the sun, creating a midriff bulge. The gas around the star’s equator is then further from its centre, so it cools more than other parts of the star’s surface, while the poles remain hot and dense.
John Ahlers at the University of Idaho in Moscow wondered how this might change the seasons on an orbiting planet. If its orbit is angled, it would be directly over the star’s chilled equator twice in each orbit, and would have two summers and two winters a year.
Ahlers found that difference could mean the planet’s surface would oscillate rapidly between a boiling hellscape and a frozen tundra (arxiv.org/abs/1609.07106).
Altair, as seen from Mt. Wilson Observatory
Image credit: NASA/JPL/Caltech/Steve Golden
To some extent, it’s simply the thought that being closer to star’s surface actually results in a cooler disposition for the planet. And I wonder how the bulge impacts the orbital dynamics of the hypothetical planet.
In 2001, NASA/JPL provided a description of the star Altair, giving us an idea of the conditions of a midriff bulge:
Altair is a perfect example — it rotates at least once every 10.4 hours, and the new Palomar observations reveal the diameter at its equator is at least 14 percent greater than at its poles. For a star that spins slowly, this effect is miniscule. For example, our Sun rotates once every 30 days and has an equator only .001 percent greater in diameter than its poles.
By measuring Altair’s size at separate positions along its edge, van Belle and his colleagues determined that Altair rotates at a speed of at least 210 kilometers per second (470,000 miles per hour) at the equator. Future studies may pin down the speed more precisely.
For those who are interested, the speed of light (c) is 6.706×108.MPH, so Altair’s equatorial velocity at its surface is nowhere near c.
And I’ll tell you, searching on stars midriff bulge returns some mighty odd images.
