Two researchers. Each looking at the same star. Stephanie Sallum (a UA graduate student) and Kate Follette (former UA graduate student now at Stanford University) were working independently of each other on their own Ph.D. projects. They were both observing LkCa15, a new star with a protoplanetary disk around it.
But LkCa15’s disk has a gap inside it. A relatively clear area where planets could be. And that’s what Sallum and Follete found. Despite being 450 light-years away from Earth and a dense, gaseous disk – the pair managed to capture the first photo of a planet in the making.
“This is the first time that we’ve imaged a planet that we can say is still forming,” says Sallum.
“No one has successfully and unambiguously detected a forming planet before,” Follette adds. “There have always been alternate explanations, but in this case we’ve taken a direct picture, and it’s hard to dispute that.”
Here’s the “direct picture” Follette is talking about.
Besides being a very young star with material left over from its formation, LkCa15 was a promising target because of what wasn’t there. Something had cleared the dust and gas from the star’s vicinity.
“It’s like a big doughnut,” said Follette. “This system is special because it’s one of a handful of disks 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.”
How they captured this image
You might assume only a space telescope like the Hubble could capture this image. Nope, it was ground based telescopes. Sallum and Follette used the Large Binocular Telescope (LBT) on Arizona’s Mount Graham to make the discovery.
LBT’s adaptive optics system helps the massive telescope overcome atmospheric turbulence. This mixing of hot and cold air gives you “a horrible-looking image,” according to Laird Close, a UA astronomy professor. “But it’s the same phenomenon that makes city lights and stars twinkle.”
Adaptive optics combined with new imaging techniques helped the researchers tease the crispest infrared images yet of LkCa15.
Using the Magellan Telescope in Chile, researchers were able to confirm what they saw with the LBT. Magellan also provided solid proof that it is forming planets they are seeing.
Magellan’s adaptive optics system MagAO looks for the planet’s “hydrogen alpha” spectral fingerprint. It’s a specific wavelength of light (glows dark red) researchers look for from forming planets and stars.
“We were able to separate the light of the faint planet from the light of the much brighter star and to see that they are both growing and glowing in this very distinct shade of red,” said Follette.
Without adaptive optics, this discovery wouldn’t be possible. What are they? They are deformable mirrors controlled by computers in real-time to offset the distortion caused by turbulence in Earth’s atmosphere. Usually, astronomers need a bright reference star to correct the distortion. But powerful lasers can also be shined into the Earth’s upper atmosphere. Thanks to adaptive optics, images from ground-based telescopes are almost as good as those taken from space-based telescopes.
The study was published today in the journal Nature.