Using a novel technique, scientists have observed a “baby planet” being formed nearly 450 light years away. When new planets absorb nearby gases and dust they get hot. A strange light is emitted as a result and that has allowed researchers to watch a distant exoplanet as it is being formed. The plant is circling a star dubbed LkCa 15 and was discovered by astronomers Adam Kraus and Michael Ireland using the Keck II telescope. Named LkCa 15b, and in orbit in a system with two other planets (aptly named LkCa 15c and LkCa 15d), the protoplanet’s star has been observed with an unusual accretion disk that has a gap in it. This fact leads the astronomers to conclude that a planet is solidifying inside the disk, accreting dust and debris to add to its mass.
Researchers used telescopes in Chile and California to observe a deep red light that hydrogen atoms emit when they’re pulled across a planet’s magnetosphere when it absorbs nearby gases and dust. In the case of protoplanet LkCa 15 b, hydrogen atoms were heated up to nearly 10,000 degrees Celsius (18,000 Fahrenheit). The high temperatures caused them to transmit energy in the form of H-alpha (Hα) photons, which can be seen by telescopes on Earth.”Our new observations support that view. We are just now being able to image objects that are close to and much fainter than a nearby star,” said team member Stephanie Sallum, a Ph.D. student in astronomy at the University of Arizona, and lead author of the research. “That’s because of astronomers at the University of Arizona (UA) who have developed the instruments and techniques that make that difficult observation possible.”
“When you look through the Earth’s atmosphere, what you’re seeing is cold and hot air mixing in a turbulent way that makes stars shimmer,” said team member Professor Close of the University of Arizona. “To a big telescope, it’s a fairly dramatic thing, you see a horrible looking image.” The images have been made possible specifically because the Large Binocular Telescope was purpose-built using a novel imaging technique to overcome these atmospheric distortions, and that the MagAO instrument was able to capture the spectral fingerprint emitted at a specific wavelength of light that LkCa 15 and its planets emit as they grow. This is the first time we’ve imaged a planet that is definitely still in the process of forming,” said Professor Peter Tuthill from the School of Physics at the University of Sydney, and another contributing team member. “The difficulty had been that when you have indirect evidence, there are always alternate explanations that might fit the data.”
“This is the first time that we’ve imaged a planet that we can say is still forming,” said Stephanie Sallum, a UA graduate student who, with Kate Follette, a former UA graduate student now doing post-doctoral work at Stanford University, led the research. “No one has successfully and unambiguously detected a forming planet before,” Follette says. “There have always been alternate explanations, but in this case we’ve taken a direct picture, and it’s hard to dispute that.”
To make an already very impressive find even more impressive, of the 2,000 or so known exoplanets in the universe, only 10 have ever been imaged and they were all fully formed. The reason we selected this system is because it’s built around a very young star that has material left over from the star-formation process,” Follette said. “It’s like a big doughnut. This system is special because it’s one of a handful of discs that has a solar-system size gap in it. And one of the ways to create that gap is to have planets forming in there.”
The two graduates’ advisers verified the findings using Magellan’s adaptive optics system to capture the planet’s “hydrogen alpha” spectral fingerprint, the specific wavelength of light that LkCa15 and its planets emit as they grow. Cosmic objects are extremely hot as they’re forming and because they’re forming from hydrogen they all glow dark red, which is a particular wavelength of light referred to as H-alpha by scientists. “That single dark shade of red light is emitted by both the planet and the star as they undergo the same growing process,” Follette said. “We were able to separate the light of the faint planet from the light of the much brighter star and to see that they were both growing and glowing in this very distinct shade of red.” This new discovery could prove invaluable to astronomers studying how many trillions of tiny particles of dust can accrete to form massive planets, given that much of the mechanics prior to this observation were largely based on hypotheses and guesswork.
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