There’s a taste of the sublime in the photograph of this extrasolar worldby Philip Ball / July 3, 2018 / Leave a comment
“A planet in the throes of being born around another star.” Photo: ESO/A. Müller et al. Just occasionally, the astronomical sciences come up with sights that ought to awaken even in the most dulled sensibility a hint of Edmund Burke’s notion of the Sublime. If, as Burke said, such feelings stem from a sense of danger abrogated by distance and transformed into beauty, the live telescope imagesof comet Shoemaker-Levy 9 crashing into Jupiter and leaving an Earth-sized hole in 1994 did it for me. There’s a little taste of the same in the image just released by a team of astronomers of a planet in the throes of being born around another star. Sure, we already knew that “extrasolar” planets exist—there’s now a catalogue of thousands of them, seen mostly from the periodic, tiny dip in their parent star’s light as the planet passes in front of it, or from the wobble that a large enough planet induces in the star. We can deduce the masses, sizes and positions of these planets, and thereby have a sense of the tremendous diversity of other worlds beyond our solar system. We’ve even been able to measure the reflected light from a few such planets. But the object now seen by a team led by astronomers at the Max Planck Institute for Astronomy in Heidelberg, using a telescope at the European Southern Observatory (ESO) in Chile, is something else. It’s a planet in the process of formation, and the researchers have actually captured an image of it: a bright blob in the disk of hot gas and dust around a young dwarf star called PDS 70, in the constellation of Centaurus 370 light years away. We’re literally watching worlds in the making. For our own solar system, this process happened about four and a half billion years ago. A star will condense out of a cloud of interstellar gas and dust under the pull of its own gravity. The material falling inwards gets denser and hotter until eventually it ignites the process of nuclear fusion that will keep the star glowing for billions of years. “We can see a solar system taking shape, its planets starting to emerge from the chaos” During that collapse, material surrounding the central core becomes spun into a disk: the raw material of a planetary system. This too will gradually become clumpy as gravity concentrates randomly more dense patches. Some may collapse into dense bodies that coalesce into rocky planets like ours. Larger proto-planets might sweep up and hold onto a mantle of gas, becoming “gas giants” like Jupiter and Saturn. The planet seen by the ESO scientists, dubbed PDS 70b, is huge—several times bigger than Jupiter, which is what makes it visible at all. It is also intensely hot, with a surface temperature of around 1,000 oC. It sits within a “hole” in the star’s protoplanetary disk, where the forming planet has collected up much of the gas and dust along its orbit. Such a gap in a protoplanetary disk has been seen before, but only more blurrily and with no clear sign of a nascent planet within it. This model of planet formation is generally accepted, but until now it was pretty much all theory. The observation is one of the most striking fruits so far of an instrument called SPHERE, developed for ESO’s Very Large Telescope (yes, that’s the actual name) specifically to capture direct images of extrasolar planets. It has already delivered detailed images of dusty stellar disks, showing some of their concentric structure. But to see a solar system taking shape, its planets starting to emerge from the chaos, feels somehow more primordial, with all the blurry allure and sense of potential in those ultrasound images of a fetus in utero.