Figure 1: Integrated intensity distribution of CCH, superposed
on the 0.8 mm dust continuum map. The infalling rotating envelope
traced by CCH is broadened inward of the radius of about 150 au.Credit: Sakai et al. (RIKEN) . Click to enlarge
One of the big puzzles in astrophysics is how stars like the sun
manage to form from collapsing molecular clouds in star-forming regions
of the universe. The puzzle is known technically as the angular momentum
problem in stellar formation. The problem essentially is that the gas
in the star-forming cloud have some rotation, which gives each element
of the gas an amount of angular momentum. As they collapse inward,
eventually they reach a state where the gravitational pull of the
nascent star is balanced by the centrifugal force, so that they will no
longer collapse inward of a certain radius unless they can shed some of
the angular momentum. This point is known as the centrifugal barrier.
Now, using measurements taken by radio antennas, a group led by Nami
Sakai of the RIKEN Star and Planet Formation Laboratory has found clues
as to how the gas in the cloud can find their way to the forming star.
To gain a better understanding of the process, Sakai and her group
turned to the ALMA observatory, a network of 66 radio dishes located
high in the Atacama Desert of northern Chile. The dishes are connected
together in a carefully choreographed configuration so that they can
provide images on radio emissions from protostellar regions around the
sky.
The group chose to observe a protostar designated as L1527, located
in a nearby star-forming region known as the Taurus Molecular Cloud. The
protostar, located about 450 light years away, has a spinning
protoplanetary disk, almost edge-on to our view, embedded in a large
envelope of molecules and dust.
Previously, Sakai had discovered, from observations of molecules
around the same protostar, that unlike the commonly held hypothesis, the
transition from envelope to the inner disk--which later forms into
planets--was not smooth but very complex. "As we looked at the
observational data," says Sakai, "we realized that the region near the
centrifugal barrier--where particles can no longer infall--is quite
complex, and we realized that analyzing the movements in this transition
zone could be crucial for understanding how the envelope collapses. Our
observations showed that there is a broadening of the envelope at that
place, indicating something like a 'traffic jam' in the region just
outside the centrifugal barrier, where the gas heats up as the result of
a shock wave. It became clear from the observations that a significant
part of the angular momentum is lost by gas being cast in the vertical
direction from the flattened protoplanetary disk that formed around the
protostar."
Figure 2: Artist's impression of L1527
Credit: RIKEN
Credit: RIKEN
This behavior accorded well with calculations the group had done using a
purely ballistic model, where the particles behave like simple
projectiles that do not need to be influenced by magnetic or other
forces.
According to Sakai, "We plan to continue to use observations from the
powerful ALMA array to further refine our understanding of the dynamics
of stellar formation and fully explain how matter collapses onto the
forming star. This work could also help us to better understand the
evolution of our own solar system."
Paper and Research team
These observation results were published as Sakai et al. "Vertical
Structure of the Transition Zone from Infalling Rotating Envelope to
Disk in the Class 0 Protostar, IRAS04368+2557" in the Monthly Notices of
the Royal Astronomical Society in February 2017.
The research team members are:
Nami Sakai (The Institute of Physical and Chemical Research (RIKEN)),
Yoko Oya (The University of Tokyo), Aya E. Higuchi (RIKEN), Yuri Aikawa
(University of Tsukuba), Tomoyuki Hanawa (Chiba University), Cecilia
Ceccarelli (Laboratoire d'Astrophysique de Grenoble), B. Lefloch
(Laboratoire d'Astrophysique de Grenoble), Ana López-Sepulcre (The
University of Tokyo / Institut de Radioastronomie Millimétrique),
Yoshimasa Watanabe (The University of Tokyo), Takeshi Sakai (The
University of Electro-Communications), Tomoya Hirota (National
Astronomical Observatory of Japan), Emmanuel Caux (Universite de
Toulouse), Charlotte Vastel (Universite de Toulouse), Claudine Kahane
(Laboratoire d'Astrophysique de Grenoble), Satoshi Yamamoto (The
University of Tokyo)
This research was supported by a Grant-in-Aid from the Japan Society for the Promotion of Science and the Ministry of Education, Culture, Sports, Science and Technology, Japan (No. 25400223, 25108005, 16H03964).
This research was supported by a Grant-in-Aid from the Japan Society for the Promotion of Science and the Ministry of Education, Culture, Sports, Science and Technology, Japan (No. 25400223, 25108005, 16H03964).
Credit: Clem & Adri Bacri-Normier (wingsforscience.com)/ESO
ALMA
The Atacama Large Millimeter/submillimeter Array (ALMA), an
international astronomy facility, is a partnership of the European
Organisation for Astronomical Research in the Southern Hemisphere (ESO),
the U.S. National Science Foundation (NSF) and the National Institutes
of Natural Sciences (NINS) of Japan in cooperation with the Republic of
Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in
cooperation with the National Research Council of Canada (NRC) and the
National Science Council of Taiwan (NSC) and by NINS in cooperation with
the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space
Science Institute (KASI).
ALMA construction and operations are led by ESO on behalf of its Member
States; by the National Radio Astronomy Observatory (NRAO), managed by
Associated Universities, Inc. (AUI), on behalf of North America; and by
the National Astronomical Observatory of Japan (NAOJ) on behalf of East
Asia. The Joint ALMA Observatory (JAO) provides the unified leadership
and management of the construction, commissioning and operation of ALMA.
