2024-04-08 07:39:45
There are many “wandering” planets in space that do not have a parent star. These free-floating planets free-floating planets, FFP), including pairs of Jupiter-sized worlds orbiting each other, are sufficiently mysterious to scientists. But the new study likely rules out one way these so-called Jupiter-mass binaries (JuMBOs) could have formed.
Astronomers discovered FFP more than 20 years ago using the UK’s Infrared Telescope Facility in Hawaii. Since then, observers have spotted hundreds of such roving astronomical bodies, with the biggest catch last year. The find consists of more than 500 free-floating planets in the trapezoidal Orion Nebula, the birthplace of stars.
Notably, 80 of these worlds, ranging in mass from 0.7 to 13 times the mass of Jupiter, formed pairs of planets that orbit each other.
These enigmatic formations have puzzled the astronomical community. For one thing, how exactly JuMBO and FFP in general are formed is a mystery. One idea is that such planets, binary or otherwise, form when clouds of gas and dust break up under their own gravity. It’s like a scaled-down version of star formation.
Another hypothesis is that such planets are pulled away from tightly packed parent planetary systems by the gravitational force of a particularly large object, such as a passing star.
“Flying through the stars is one way to create [FFP]”, says Dong Lai, professor of astrophysics at Cornell University (USA) and lead author of the new study. In fact, after a marathon of discoveries last year, another group of researchers estimated that the probability of JuMBOs being knocked off their parent stars by a passing star is about one-fifth less than the probability of other FFPs being knocked off their parent stars.
To find out what process formed JuMBO and other FFPs, Lai and Fangyuan Yu, a student at Shanghai Jiao Tong University in China, created tens of thousands of simulations of a planetary system with a pair of Jupiter-mass planets orbiting a Sun-like star.
In each simulation, the researchers allowed a second star of a similar size to approach the FFP—and calculated the fraction of simulations in which both planets were ejected from orbit. In all simulations, Lai and Yu varied several parameters—such as the masses of the planets, their relative distance, and the speed of the passing star relative to the parent star—to see how these factors affect the JuMBO’s “ejection” frequency.
They found that JuMBOs are more likely to form if the planets initially orbit close together, or if they have a mass up to 4 times that of Jupiter. However, even in the most likely scenario, the probability of the pairs of planets being “thrown out” at the same time was still incredibly small – less than 1 percent.
In contrast, the probability of single planets being “ejected” during interstellar flybys was typically hundreds of times greater, resulting in single FFPs. Indeed, Lai believes that such guest stars could have contributed to the formation of FFPs in the Orion Nebula.
Lai and Yu’s results, which are not yet peer-reviewed, were submitted to The Astrophysical Journal and are available as pre-publication on arXiv.
Lai and Yu believe their research makes the “cloud collapse” model a much more likely explanation for how JuMBO formed. In any case, Lai believes that the simulations are a kind of physics experiment that can help future observations with telescopes like the Vera C. Rubin Observatory being built in Chile.
For example, the results of their simulations will be useful for understanding what happens to planetary systems in dense star clusters — and for identifying exotic planetary systems, such as “captured” planets, Lai says.
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2024-04-08 07:39:45