Rocking shadows in protoplanetary discs

Stills from Rebecca Nealon protoplanetary disk simulation
This is a still from a simulation of a forming planetary disk, made by University of Warwick and Stephen Hawking Research Fellow Rebecca Nealon. The images show the rotating inner disk along the top half, and the shadow it casts on the outer disk in the lower half.
Rebecca Nealon / University of Warwick

Astronomers from the University of Warwick reveal a new phenomenon dubbed the “rocking shadow” effect that describes how discs in forming planetary systems are oriented, and how they move around their host star. The effect also gives clues as to how they might evolve with time. Dr Rebecca Nealon presented the new work this week at the 2022 National Astronomy Meeting at the University of Warwick.

Stars are born when a large cloud of gas and dust collapses in on itself. The leftover material that doesn’t make it into the star ends up circling around it, not unlike how water swirls around the drain before falling in. This swirling mass of gas and dust is called a protoplanetary disc, and it’s where planets like the Earth are born.

Protoplanetary discs are often thought to be shaped like dinner plates – thin, round and flat. However, recent telescope images from the Atacama Large Millimeter/Submillimeter Array (ALMA) show that this is not always the case. Some of the discs seen by ALMA have shadows on them, where the part of the disc closest to the star blocks some of the stellar light and casts a shadow onto the outer part of the disc. From this shadow pattern, it can be inferred that the inner part of the disc is oriented completely differently to the outer part, in what is called a broken disc.

In this research, the team used high performance computers to run three-dimensional simulations of a broken disc. The team then produced a mock observation, modelling what such a disc would look like if it were to be observed through a telescope, and how it would change over time.

As the inner disc moved through the gravitational pull of the central star, the shadow it cast moved across the outer disc. But instead of the shadow pattern moving around the disc like a clock-hand as expected, it rocked back and forth with a see-saw-like motion. So although the inside disc kept turning in the same direction, its shadow looked like it was rocking forwards and backwards. The team suggest this is caused by a geometric projection effect, which is likely to occur in all broken discs.

Movie made from the 3D simulation of a disk in a forming planetary system. The inner disk casts shadows on the outer disk, which rock back and forth. Credit: Rebecca Nealon / University of Warwick

Dr Nealon says: “JWST promises to give us a look at embryonic planetary systems in unprecedented detail, and with our new models we’ll be able to find out a lot more about the birth of planets.”


Media contacts

Dr Robert Massey
Royal Astronomical Society
Mob: +44 (0)7802 877699

Cait Cullen
Royal Astronomical Society


Science contacts

Dr Rebecca Nealon
Stephen Hawking Research Fellow
University of Warwick


Notes for editors

About NAM 2022

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About the Science and Technology Facilities Council

The Science and Technology Facilities Council (STFC) is part of UK Research and Innovation – the UK body which works in partnership with universities, research organisations, businesses, charities, and government to create the best possible environment for research and innovation to flourish. STFC funds and supports research in particle and nuclear physics, astronomy, gravitational research and astrophysics, and space science and also operates a network of five national laboratories, including the Rutherford Appleton Laboratory and the Daresbury Laboratory, as well as supporting UK research at a number of international research facilities including CERN, FERMILAB, the ESO telescopes in Chile and many more.

STFC's Astronomy and Space Science programme provides support for a wide range of facilities, research groups and individuals in order to investigate some of the highest priority questions in astrophysics, cosmology and solar system science. STFC's astronomy and space science programme is delivered through grant funding for research activities, and also through support of technical activities at STFC's UK Astronomy Technology Centre and RAL Space at the Rutherford Appleton Laboratory. STFC also supports UK astronomy through the international European Southern Observatory and the Square Kilometre Array Organisation.

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About the University of Warwick

The University of Warwick is one of the world’s leading research institutions, ranked in the UK’s top 10 and world top 80 universities. Since its foundation in 1965 Warwick has established a reputation of scientific excellence, through the Faculty of Science, Engineering and Medicine (which includes WMG and the Warwick Medical School).


Submitted by Robert Massey on Fri, 15/07/2022 - 09:58