Tracing the cosmic origin of complex organic molecules with their radiofrequency footprint
Scientists confirm the presence of acetonitrile in a distant interstellar
gas cloud using a radio telescope

Date:
August 25, 2020
Source:
Tokyo University of Science
Summary:
How did organic matter reach the Earth in the first place? One
way to ponder this question is by observing the distribution
and abundance of complex organic molecules in interstellar gas
clouds. However, detecting such molecules in the less dense regions
of these gas clouds has been challenging. Now, scientists have
found concluding evidence for the presence of a particular complex
organic molecule in such a region for the first time.



FULL STORY ==========================================================================
The origin of life on Earth is a topic that has piqued human curiosity
since probably before recorded history began. But how did the organic
matter that constitutes lifeforms even arrive at our planet? Though this
is still a subject of debate among scholars and practitioners in related fields, one approach to answering this question involves finding and
studying complex organic molecules (COMs) in outer space.


==========================================================================
Many scientists have reported finding all sorts of COMs in molecular
clouds - - gigantic regions of interstellar space that contain various
types of gases.

This is generally done using radio telescopes, which measure and record radiofrequency waves to provide a frequency profile of the incoming
radiation called spectrum. Molecules in space are usually rotating in
various directions, and they emit or absorb radio waves at very specific frequencies when their rotational speed changes. Current physics and
chemistry models allow us to approximate the composition of what a radio telescope is pointed at, via analysis of the intensity of the incoming radiation at these frequencies.

In a recent study published in Monthly Notices of the Royal Astronomical Society, Dr Mitsunori Araki from Tokyo University of Science, along
with other scientists from across Japan, tackled a difficult question
in the search for interstellar COMs: how can we assert the presence of
COMs in the less dense regions of molecular clouds? Because molecules
in space are mostly energized by collisions with hydrogen molecules,
COMs in the low-density regions of molecular clouds emit less radio
waves, making it difficult for us to detect them. However, Dr Araki and
his team took a different approach based on a special organic molecule
called acetonitrile (CH3CN).

Acetonitrile is an elongated molecule that has two independent ways of rotating: around its long axis, like a spinning top, or as if it were
a pencil spinning around your thumb. The latter type of rotation tends
to spontaneously slow down due to the emission of radio waves and, in
the low-density regions of molecular clouds, it naturally becomes less energetic or "cold." In contrast, the other type of rotation does not
emit radiation and therefore remains active without slowing down. This particular behavior of the acetonitrile molecule was the basis on which
Dr Araki and his team managed to detect it. He explains: "In low-density regions of molecular clouds, the proportion of acetonitrile molecules
rotating like a spinning top should be higher. Thus, it can be inferred
that an extreme state in which a lot of them would be rotating in this
way should exist. Our research team was, however, the first to predict
its existence, select astronomical bodies that could be observed,
and actually begin exploration." Instead of going for radio wave
emissions, they focused on radio wave absorption. The "cold" state of
the low-density region, if populated by acetonitrile molecules, should
have a predictable effect on the radiation that originates in celestial
bodies like stars and goes through it. In other words, the spectrum of a radiating body that we perceive on Earth as being "behind" a low-density
region would be filtered by acetonitrile molecules spinning like a top
in a calculable way, before it reaches our telescope on earth. Therefore,
Dr Araki and his team had to carefully select radiating bodies that could
be used as an appropriate "background light" to see if the shadow of
"cold" acetonitrile appeared in the measured spectrum. To this end, they
used the 45 m radio telescope of the Nobeyama Radio Observatory, Japan,
to explore this effect in a low-density region around the "Sagittarius molecular cloud Sgr B2 (M)," one of the largest molecular clouds in the vicinity of the center of our galaxy.

After careful analysis of the spectra measured, the scientists concluded
that the region analyzed was rich in acetonitrile molecules rotating like
a spinning top; the proportion of molecules rotating this way was actually
the highest ever recorded. Excited about the results, Dr Araki remarks:
"By considering the special behavior of acetonitrile, its amount in the low-density region around Sgr B2(M) can be accurately determined. Because acetonitrile is a representative COM in space, knowing its amount and distribution though space can help us probe further into the overall distribution of organic matter." Ultimately, this study may not only
give us some clues about where the molecules that conform us came from,
but also serve as data for the time when humans manage to venture outside
the solar system.


========================================================================== Story Source: Materials provided by Tokyo_University_of_Science. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Mitsunori Araki, Shuro Takano, Nobuhiko Kuze, Yoshiaki Minami,
Takahiro
Oyama, Kazuhisa Kamegai, Yoshihiro Sumiyoshi, Koichi Tsukiyama.

Observations and analysis of absorption lines including J =
K rotational levels of CH3CN: the envelope of Sagittarius
B2(M). Monthly Notices of the Royal Astronomical Society, 2020;
497 (2): 1521 DOI: 10.1093/mnras/ staa1754 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200825110612.htm

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