Four-and-a-half-billion years ago, a whirling cloud of cosmic dust condensed into the lump of rock we call home. For the first time, astronomers are now watching that same planet-forming process playing out around a distant star.
The star in question, LkCa15, sits 450 light years from Earth, seen at the centre of the image below It’s surrounded by a mess of gas and dust (shown in grey) called a protoplanetary disk. Cosmic dust clouds are a common sight around young stars, but LkCa15’s disk is pretty unusual: something has eaten away at its centre. According to a new analysis by astronomers at the University of Arizona, that something is a planet; namely, a planet in the process of forming right now.
Left: Composite image of LkCa 15, with blue showing the Magellan data taken at the H-alpha band, and green and red showing LBT data taken at infrared wavelengths. The greyscale is a previously published image of the disk. Right: Zoomed in composite image of LBT and Magellan observations, with several distinct objects marked.
As a protoplanetary disk evolves into distinct objects, astronomers suspect that a central clearing will begin to develop. Which is exactly what we see around LkCa15. So the UA team had a hunch that they were looking at something interesting. But the clincher came from crisp new images of the star, captured with UA’s Large Binocular Telescope and the Giant Magellan Telescope in Chile. These images show point sources of heat spiralling about the clearing, or, as the researchers put it, “multiple companions on Keplerian orbits".
What’s more, the star’s innermost “companion” (the blue red pixelated blob in the image above) is giving off hydrogen-alpha emissions. These emissions indicate very hot gas (roughly 9,700ºC, or 17,500ºF) falling “deep into the well of an accreting planet”.
“This is the first time we’ve imaged a planet that is definitely still in the process of forming,” said Peter Tuthill, co-author of a paper describing the find in this week’s edition of science journal Nature.
Telescopes are finally becoming powerful enough that astronomers can image objects close to (but much fainter than) neighbouring stars. As our instruments continue to improve, we can expect to witness many more births of planets. But for now, this is an utterly unique sight, and a testament to just how far astronomy has come. [Read the full scientific paper at Nature h/t UA News]
Image Credits: University of Arizona.