When it comes to observing protoplanetary disks, the Atacama Large Millimetre/sub-millimetre Array (ALMA) is probably the champion. ALMA was the first telescope to peer inside the almost inscrutable protoplanetary disks surrounding young stars and watch planets forming. ALMA advanced our understanding of the planet-forming process, though our knowledge of the entire process is still in its infancy.

According to new observations, it looks like chaos and disorder are part of the process. Astronomers using ALMA have watched as a star got too close to one of these planet-forming disks, tearing a chunk away and distorting the disk’s shape.

What effect will it have on planetary formation?

A team of researchers led by Ruobing Dong, an astronomer at the University of Victoria in Canada, made the discovery. Their paper is titled “A likely flyby of binary protostar Z CMa caught in action.” They published their paper in the journal Nature Astronomy.

Astronomers know that when a star forms, the left-over material resides in a disk around the star called a protoplanetary disk. Planets form from that material. We know that they form via accretion, but there’s a lot of questions around how exactly that happens.

ALMA was the first to observe this process in any detail. In 2014 astronomers using ALMA imaged the disk around the young star HL-Tauri in greater detail than ever before. The image showed gaps in the disk, which scientists interpreted as “lanes” where planets are forming, sweeping up gas and dust and leaving a gap in the process.

This is the sharpest image ever taken by ALMA — sharper than is routinely achieved in visible light with the NASA/ESA Hubble Space Telescope. It shows the protoplanetary disc surrounding the young star HL Tauri. These new ALMA observations reveal substructures within the disc that have never been seen before and even show the possible positions of planets forming in the dark patches within the system. Image Credit: ALMA
This is the sharpest image ever taken by ALMA as of 2014— sharper than is routinely achieved in visible light with the NASA/ESA Hubble Space Telescope. It shows the protoplanetary disc surrounding the young star HL Tauri. These new ALMA observations reveal substructures within the disc that have never been seen before and even display the possible positions of planets forming in the dark patches within the system. Image Credit: ALMA

ALMA still spends some of its time peering into protoplanetary disks. In this new study, a team of researchers used ALMA and the Very Large Array (VLA) to examine the disk around the Z Canis Majoris (Z CMa) star system. They spotted the aftermath of a stellar interloper’s path through the star’s disk. The interloper wasn’t part of Z CMa, and its path through the system left an imprint. It warped Z CMa’s disk structure and created a stretched-out gas and dust stream.

Z CMa is a pre-main-sequence group of stars about 3750 light-years away in the constellation Canis Major. Astronomers thought that Z CMa was a binary pair, but this study identified two additional probable stars in the system. The stars in Z CMa are young, only about 300,000 years old. At that age, planets haven’t formed yet. The stars are still in their mass-accretion phase themselves.

These images from the study show the Z CMa system as seen through different telescopes, and at different wavelengths. The main binary pair is in the center and the streamer is clearly visible stretching down and to the right. The streamer of gas and dust is about 2000 AU long. Image Credit: Dong et al 2022. https://www.mansbrand.com/look-up-and-watch-asteroid-1994-pc1-fly-past-earth-this-week/

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