ZTF J1813+4251 is a 51-minute-orbital-period, fully eclipsing binary system consisting of a star with a temperature comparable to that of the Sun but a density 100 times greater, accreting onto a white dwarf star.
A cataclysmic variable occurs when the two stars draw close, over billions of years, causing the white dwarf to start accreting material away from its partner star.
This process can give off enormous, variable flashes of light that, centuries ago, astronomers assumed to be a result of some unknown cataclysm.
ZTF J1813+4251, which is located about 3,000 light-years away in the constellation of Hercules, is a cataclysmic variable with the shortest orbit detected to date.
“Of more than a thousand known cataclysmic variables, where a white dwarf is accreting from a hydrogen-rich star, only a dozen have orbital periods below 75 minutes,” said MIT astronomer Kevin Burdge and colleagues.
In the study, the astronomers simulations of what ZTF J1813+4251 is likely doing today and how it should evolve over the next hundreds of millions of years.
They conclude that the stars are currently in transition, and that the Sun-like star has been circling and donating much of its hydrogen atmosphere to the voracious white dwarf.
The Sun-like star will eventually be stripped down to a mostly dense, helium-rich core.
In another 70 million years, the stars will migrate even closer together, with an ultrashort orbit reaching just 18 minutes, before they begin to expand and drift apart.
Decades ago, scientists predicted that such cataclysmic variables should transition to ultrashort orbits.
This is the first time such a transitioning system has been observed directly.
“This is a rare case where we caught one of these systems in the act of switching from hydrogen to helium accretion,” Dr. Burdge said.
“People predicted these objects should transition to ultrashort orbits, and it was debated for a long time whether they could get short enough to emit detectable gravitational waves.”
“We got doubly lucky to find a system that answers a big open question, and is one of the most beautifully behaved cataclysmic variables known.”
The discovery is described in a paper in the journal Nature.
K.B. Burdge et al. A dense 0.1-solar-mass star in a 51-minute-orbital-period eclipsing binary. Nature, published online October 6, 2022; doi: 10.1038/s41586-022-05195-x
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