The star TW Hydrae. an analogue of the Sun and other sun-like stars, in its very early stages already shows evidence of new planets forming at various radii in its protoplanetary disk. S. Andrews (Harvard-Smithsonian CfA); B. Saxton (NRAO/AUI/NSF); ALMA (ESO/NAOJ/NRAO)

This Is What It Looks Like When Solar Systems Form

After generations of speculations, we’ve finally got the images that tell us the full story.


Some 4.5 billion years ago, our Sun and Solar System were born from a collapsing cloud of gas, likely alongside many other stars.

Artist’s impression of a young star surrounded by a protoplanetary disk. There are many unknown properties about protoplanetary disks around Sun-like stars, but observations are catching up. (ESO/L. Calçada)

Over time, a protoplanetary disk forms, where imperfections will lead to young planets that eventually create full fledged solar systems.

A large number of protoplanetary systems have been imaged, but the state-of-the-art infrared imager designed for exoplanet disk pictures is SPHERE, which routinely obtains resolutions of ~10", or less than 0.003 degrees per pixel. (SHINE (SpHere INfrared survey for Exoplanets) collaboration / Arthur Vigan)

The details of how that work, however, have varied wildly depending on which stars we look at.

The young F-class star, HD 135344, exhibits a transitional structure showing both rings and a spiral shape to it. This star is more massive than our Sun, and right on the border of being or not being a T Tauri star. (T. Stolker et al., A&A, 595 (2016) A113)

Some stars, more massive than ours, show spiral shapes in their disks.

The observational structure of the young star MWC 758, at right, compared with a simulation involving a large outer planet, at left. This Herbig star is much more massive than our Sun ever was. (NASA, ESA, ESO, M. Benisty et al. (University of Grenoble), R. Dong (Lawrence Berkeley National Laboratory), and Z. Zhu (Princeton University))

The more massive they are, the more likely they are to show this structure, consistent with a large, outer, structure-driving planet.

The protoplanetary disk around the star HL Tauri in a young star cluster may well be the best analogue of a Sun-like star forming, with planets around it, that we’ve ever seen. (ALMA (ESO/NAOJ/NRAO)/NASA/ESA)

Others, lower in mass, show clear, symmetric rings.

Some stars, like HD 141569, show evidence of both ring-like structures and a disrupted, discontinuous presence. Most protoplanetary disks, like this one, are around closer, higher-mass stars. (C. Perrot et al., A&A, 590 (2016) L7)

Still others show a hybrid structure, where the rings exhibit some circularly-symmetric and some non-symmetric features.

The ESO’s Very Large Telescope (VLT) contains a new imaging instrument on it, SPHERE, which allows us to image exoplanets and protoplanetary disks around smaller, lower-mass stars at high resolution than ever before, and to do so rapidly as well. (ESO / Serge Brunier)

Owing to a new instrument on a remarkable telescope, the ESO’s Very Large Telescope, we can now image protoplanetary disks directly.

The SPHERE Common Path Infrastructure includes the main optical bench, connects the other sub-systems to the light path, and guarantees a static alignment of SPHERE to the VLT focus. The IRDIS instrument, in particular (at lower-left), is what enables these new, spectacular images. (ESO / SPHERE collaboration)

The SPHERE instrument, optimized for infrared exoplanet research, includes the IRDIS imager, designed for high-resolution viewing.

Eight young T Tauri stars, as imaged by SPHERE, show disks, rings, and symmetric, unperturbed structures. These 8 disks range in age from 1 to 15 million years, and are all around stars of 2 solar masses or less.(H. Avenhaus et al. (2018), https://arxiv.org/abs/1803.10882)

When it looked at T Tauri stars, very young stars of 2 solar masses or less, here’s what it saw.

The best ring-like fits around these stars, done automatically where the fits are good and manually where they are not.(H. Avenhaus et al. (2018), https://arxiv.org/abs/1803.10882)

Regardless of age or mass, symmetric and well-defined rings, disks, and gaps exist around every one.

All eight of these systems, imaged and processed and fitted to better understand what’s going on around these pre-main-sequence stars. The infant stages of planet formation are all in play here.(H. Avenhaus et al. (2018), https://arxiv.org/abs/1803.10882)

This should be exactly what our youthful Sun looked like.

The evolving protoplanetary disk, with large gaps, around the young star HL Tauri. ALMA image on the left, VLA image on the right. With the upcoming 30-meter class telescopes like GMT and ELT, new views of a protoplanetary disk like this, including in the optical, will become possible at last. (Carrasco-Gonzalez, et al.; Bill Saxton, NRAO/AUI/NSF)

Mostly Mute Monday tells the astronomical story of an image, object, class, or phenomenon in images, visuals, and no more than 200 words.

Starts With A Bang is now on Forbes, and republished on Medium thanks to our Patreon supporters. Ethan has authored two books, Beyond The Galaxy, and Treknology: The Science of Star Trek from Tricorders to Warp Drive.

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