ALMA catches 'intruder' redhanded in rarely detected stellar flyby event


Date:
January 13, 2022
Source:
National Radio Astronomy Observatory
Summary:
Scientists made a rare detection of a likely stellar flyby event in
the Z Canis Majoris (Z CMa) star system. An intruder -- not bound
to the system -- object came in close proximity to and interacted
with the environment surrounding the binary protostar, causing
the formation of chaotic, stretched-out streams of dust and gas
in the disk surrounding it.



FULL STORY ========================================================================== Scientists using the Atacama Large Millimeter/submillimeter Array (ALMA)
and the Karl G. Jansky Very Large Array (VLA) made a rare detection of a
likely stellar flyby event in the Z Canis Majoris (Z CMa) star system. An intruder - - not bound to the system -- object came in close proximity
to and interacted with the environment surrounding the binary protostar, causing the formation of chaotic, stretched-out streams of dust and gas
in the disk surrounding it.


========================================================================== While such intruder-based flyby events have previously been witnessed
with some regularity in computer simulations of star formation, few
convincing direct observations have ever been made, and until now,
the events have remained largely theoretical.

"Observational evidence of flyby events is difficult to obtain because
these events happen fast and it is difficult to capture them in
action. What we have done with our ALMA Band 6 and VLA observations is equivalent to capturing lightning striking a tree," said Ruobing Dong,
an astronomer at the University of Victoria in Canada and the principal investigator on the new study. "This discovery shows that close encounters between young stars harboring disks do happen in real life, and they
are not just theoretical situations seen in computer simulations. Prior observational studies had seen flybys, but hadn't been able to collect
the comprehensive evidence we were able to obtain of the event at Z CMa." Perturbations, or disturbances, like those at Z CMa aren't typically
caused by intruders, but rather by sibling stars growing up together in
space. Hau-Yu Baobab Liu, an astronomer at the Institute of Astronomy and Astrophysics at Academia Sinica in Taiwan and a co-author on the paper,
said, "Most often, stars do not form in isolation. The twins, or even
triplets or quadruplets, born together may be gravitationally attracted
and, as a result, closely approach each other. During these moments, some material on the stars' protoplanetary disks may be stripped off to form extended gas streams that provide clues to astronomers about the history
of past stellar encounters." Nicola's Cuello, an astrophysicist and Marie Curie Fellow at Universite' Grenoble Alpes in France and a co-author
on the paper added that in the case of Z CMa, it was the morphology,
or structure, of these streams that helped scientists to identify and
pinpoint the intruder. "When a stellar encounter occurs, it causes changes
in disk morphology -- spirals, warps, shadows, etc. - - that could be considered as flyby fingerprints. In this case, by looking very carefully
at Z CMa's disk, we revealed the presence of several flyby fingerprints."
These fingerprints not only helped scientists to identify the intruder
but also led them to consider what these interactions might mean for the
future of Z CMa and the baby planets being born in the system, a process
that so far has remained a mystery to scientists. "What we now know with
this new research is that flyby events do occur in nature and that they
have major impacts on the gaseous circumstellar disks, which are the
birth cradles of planets, surrounding baby stars," said Cuello. "Flyby
events can dramatically perturb the circumstellar disks around participant stars, as we've seen with the production of long streamers around Z CMa."
Liu added, "These perturbers not only cause gaseous streams but may also
impact the thermal history of the involved host stars, like Z CMa. This
can lead to such violent events as accretion outbursts, and also impact
the development of the overall star system in ways that we haven't yet
observed or defined." Dong said that studying the evolution and growth
of young star systems throughout the galaxy helps scientists to better understand our own Solar System's origin. "Studying these types of events
gives a window into the past, including what might have happened in the
early development of our own Solar System, critical evidence of which
is long since gone. Watching these events take place in a newly forming
star system provides us with the information needed to say, 'Ah-ha! This
is what may have happened to our own Solar System long ago.' Right now,
VLA and ALMA have given us the first evidence to solve this mystery,
and the next generations of these technologies will open windows on the Universe that we have yet only dreamed of." Recently, the National
Radio Astronomy Observatory (NRAO) received approval for its Central Development Laboratory (CDL) to develop a multi-million dollar upgrade
to ALMA's Band 6 receiver, and the Observatory's next-generation VLA
(ngVLA) received strong support from the astronomical community in the Astro2020 Decadal Survey. Technological advancements for both telescopes
will lead to better observations, and a potentially significant increase
in the discovery of difficult-to-see objects, like Z CMa's stellar
intruder. Both projects are funded in part by the National Science
Foundation (NSF). "These observations highlight the synergy that can come
from a newer instrument working in concert with a more seasoned one, and
how good a workhorse the ALMA Band 6 receiver is," said Dr. Joe Pesce, astrophysicist and ALMA Program Director at the NSF. "I look forward to
the even-better results the upgraded ALMA Band 6 receiver will enable." ========================================================================== Story Source: Materials provided by
National_Radio_Astronomy_Observatory. Note: Content may be edited for
style and length.


========================================================================== Related Multimedia:
*
Scientists_have_captured_an_intruder_object_disrupting_the_protoplanetary
disk--birthplace_of_planets--in_Z_Canis_Majors_(Z_CMa),_a_star_in_the
Canis_Majoris_constellation ========================================================================== Journal Reference:
1. Dong et. al. A likely flyby of binary protostar Z CMa Caught
in Action.

Nature Astronomy, 2022 DOI: 10.1038/s41550-021-01558-y ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/01/220113111405.htm
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