An article published in “The Astrophysical Journal” reports the results of a study that has identified an important part of the planetary formation process. A team of researchers led by Indrani Das of the Academia Sinica Institute of Astronomy and Astrophysics (ASIAA) has discovered a transition zone where gas becomes a part of a planet-forming disk using the ALMA radio telescope. This zone was called ENDTRANZ (Envelope Disk Transition Zone) and was located around the protostar L1527 IRS.

The image (Courtesy Indrani Das/ASIAA) shows an artist’s concept of the zone called ENDTRANZ, colored in red, part of a forming star system.

Protostars form within gas clouds, surrounded by envelopes that gradually collapse under the force of gravity. In these envelopes, the gas moves chaotically and slowly, whereas the motion is more orderly in the circumstellar disk. So far, it was unclear how the transition from chaos to order occurred, and theoretical models suggested a quick transition, but new observations offer a different picture.

The authors of this new study attempted to simulate the collapse of a gas envelope using FEOSAD (Formation and Evolution Of a Star And Its Circumstellar Disk), a software developed specifically to study the coevolution of gas, dust, and volatile compounds in circumstellar disks.

Thanks to the FEOSAD simulations, the researchers identified the possibility of a gradual transition in a region they called ENDTRANZ. The gas falling toward the protostar exhibits a specific angular momentum distribution. The gas mass and angular momentum are redistributed during the formation of stars and the dusty gas disk surrounding them.

To test whether this simulation matches reality, the researchers used data from the ALMA Large Program eDisk (Embedded Disks in Planet Formation) and discovered the “signature” of the angular momentum predicted in the simulations in the system in formation cataloged as L1527 IRS. About 450 light-years from Earth, it’s made of a protostar surrounded by a disk of gas and dust and an envelope. The ENDTRANZ found in that system spans approximately 16 times the distance between the Earth and the Sun.

This discovery was possible thanks to the power and sensitivity of the ALMA radio telescope. Over the course of over a decade, this instrument has enabled significant progress in understanding the processes of star and planet formation. The wealth of data collected has allowed to test the validity of simulations created with software such as FEOSAD and, in this case, to identify ENDTRANZ. This could represent a new phase in the study of star and planet formation. It certainly opens the door to the search for ENDTRANZ around other protostars.