Astronomers have recently discovered the presence of two planet-forming gas discs with tilted orbits. These planets-to-be are forming around two stars in the solar system HK Tauri, a binary system. Their results were published in the journal Nature on July 31, 2014.
Using the Atacama Large Millimeter/submillimeter Array (ALMA), astronomers were able to spot and observe these gas discs. This is the closest look humans have ever had at a planet before it has formed. The data that astronomers Eric L. N. Jensen and Rachael Akeson have gleaned from studying these gas discs may open a new understanding about how exoplanets form, and why exoplanets often have lopsided orbits.
Binary systems, solar systems with two stars instead of our one, are very common. It is interesting to see how planets form with the gravitational pulls of two stars.
Eric Jensen, one of the authors of the paper, and an astronomer at Swarthmore College in Pennsylvania, said, "ALMA has now given us the best view yet of a binary star system sporting protoplanetary discs - and we find that the discs are mutually misaligned!"
The HK Tauri system is about 450 light-years away from Earth. It is located within the Taurus constellation, and the stars are younger than five million years old. The binary stars are about 58 billion kilometers away from each other, 13 times greater than the distance between Neptune and the Sun.
One gas disc is orbiting HK Tauri B. Astronomers on Earth can get a good look at it because it blocks out the light of its star, the method currently most used to view exoplanets. The other star, HK Tauri A, also has a gas disc in orbit, but astronomers can't make it out as well because it does not block its star's light. However, even though they can't see the planetary object using visible light, they can see the gas disc because it shines in millimeter-wavelength light, which the ALMA tool can detect.
The ALMA interface allowed the team to measure the rotation of the gas disc orbiting around HK Tauri A for the first time. Using the new imaging, the astronomers were able to tell that the two proto-planets are lopsided; they are out of alignment with each other by at least 60 degrees.
Rachel Akeson, the other author of the study, and a member of the NASA Exoplanet Science Institute at the California Institute of Technology, said, "Although there have been earlier observations indicating that this type of misaligned system existed, the new ALMA observations of HK Tauri show much more clearly what is really going on in one of these systems."
The advanced imaging allowed by ALMA gives the astronomers an amazing chance to study a binary system as it grows. Akeson said, "Because we're seeing this in the early stages of formation with the protoplanetary discs still in place, we can see better how things are oriented."
