Observing with a cutting-edge telescope led Professor of Astronomy Eric Jensen and a colleague to an exciting discovery: weird and wild, planet-forming disks of gas around the two young stars of the binary system HK Tauri. Their observations offer the clearest picture ever of such phenomena and could shed light on the birth and orbit of planets beyond our solar system.
The findings, appearing in the international science research journal Nature this week, surprised Jensen. But not as much as the speed at which he and co-author Rachel Akeson were able to gather no-doubt-about-it data.
“As we sat there analyzing it the first time, I could just see it — the disks are misaligned!” he says. “It was, ‘Holy cow, it’s right there.’”
“It may not be anything earth-shattering,” he adds, “but you’re sitting there in that moment thinking, ‘I’m the only person in the world who knows this right now.’ Kind of cool.”
Jensen credits the Atacama Large Millimeter/Submillimeter Array (ALMA), a revolutionary telescope in northern Chile composed of 66 high-precision antennae, with offering “an unprecedented view” of a main star and its binary companion with mutually misaligned protoplanetary disks.
Since the disks are raw material that can clump together to form planets, “we could be seeing the formation of a solar system that may never settle down,” says Jensen.
Unlike the sun, most stars form in binary pairs — two stars in orbit around each other, says the European Southern Observatory. Binary stars are common and pose several questions, including how and where planets develop in such complex environments.
The two young stars in the HK Tauri system, located about 450 light-years from Earth in the constellation of Taurus, are less than five million years old and separated by about 58 billion kilometers (or 13 times the distance of Neptune from the sun).
This system’s companion star, HK Tau B, appears fainter to astronomers on Earth because its disk of dust and gas blocks much of the starlight, says the National Radio Astronomy Observatory (NRAO). But the disk itself can be easily seen through the starlight that it scatters at optical and near-infrared wavelengths.
The disk around the main star, HK Tau A, is tilted in such a way that the light from its host star shines through, making it difficult for astronomers to see the disk. But this was not a problem for ALMA, which detects the millimeter-wavelength light emitted by the dust and gas.
By seeing the early stages of formation, with the protoplanetary disks still in place, the astronomers got a better glimpse of how things are oriented, says Akeson, of the NASA Exoplanet Science Institute at the California Institute of Technology.
“You can simply see gas better than you can see planets,” she says.
Jensen did similar work for his Ph.D. thesis 20 years ago, which he remembers as “like pulling teeth.” It took hundreds of times longer to make the observations than it did with ALMA, and he had to pore over data to conclude that something may be happening.
“This was like another world,” he says. “It’s exciting to think what technology will come next.”
Moving forward, the astronomers want to examine whether their remarkable discovery is common throughout our home galaxy, the Milky Way.
“The biggest question colleagues have is how many more of these are there,” Jensen says. “Do other systems look like this? My guess is that they do, but we’ll just have to see.”
The director of Swarthmore’s Aydelotte Foundation for the Advancement of the Liberal Arts, Jensen relishes the chance to collaborate on research with students.
Although his most recent findings occurred while Jensen was on sabbatical, he filled students in while working closely with them on other projects in the Science Center.
“I couldn’t wait to share my latest results with them and hear their thoughts,” he says. “It speaks to the relationships that can form between students and faculty while working on research. There’s always that teacher-student aspect, but as they become more advanced, students kind of evolve into colleagues.”
While surveying a series of binary stars with the Atacama Large Millimeter/submillimeter Array (ALMA), astronomers uncovered a striking pair of wildly misaligned planet-forming disks around the young binary star HK Tau. These results provide the clearest picture ever of protoplanetary disks around a double-star and could reveal important details about the birth and eventual orbit of planets in a multi-star system.