Scientists from Japan have for the first time found conclusive evidence of the presence of a particular complex organic molecule in regions with less dense gas clouds. Photo credit: Tokyo University of Science
How did organic matter come to earth? Cosmic detectives trace the origin of complex organic molecules
Scientists confirm the presence of acetonitrile in a distant interstellar gas cloud with a radio telescope.
How did organic matter get to earth in the first place? One way to think about this question is to observe 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, for the first time, scientists from Japan have found conclusive evidence of the presence of a particular complex organic molecule in such a region.
The origin of life on earth is a subject that piqued man’s curiosity, probably before recorded history began. But how did the organic matter that make up life come about on our planet? Although this is still the subject of debate among scientists and practitioners in related fields, one approach to answering this question is to find and study complex organic molecules (COMs) in space.
The 45-meter radio telescope at Nobeyama Radio Observatory in Japan. Photo credit: Dr. Mitsunori Araki from Tokyo University of Science
Many scientists have reported that they find all kinds of COMs in molecular cloud-gigantic regions of interstellar space that contain different kinds of gases. This is commonly done with radio telescopes that measure and record radio frequency waves to obtain a frequency profile of the incident radiation called a spectrum. Molecules in space usually rotate in different directions and send or absorb radio waves at very specific frequencies when their speed changes. Current physical and chemical models enable us to approximate the composition of a radio telescope by analyzing the intensity of the incident radiation at these frequencies.
In a recently published study in Monthly releases from the Royal Astronomical SocietyDr. Mitsunori Araki of Tokyo University of Science, along with other scientists from across Japan, tackled a difficult question in the search for interstellar COMs: How can we claim the presence of COMs in the less dense regions of molecular clouds? Since molecules in space are mainly excited by collisions with hydrogen molecules, COMs in the low density regions of molecular clouds emit fewer radio waves, making them difficult for us to detect. Dr. However, Araki and his team took a different approach based on a special organic molecule called acetonitrile (CH)3CN).
Using radio wave absorption to detect acetonitrile in the molecular cloud of Sgr B2 (M) in the center of our galaxy. Photo credit: Dr. Mitsunori Araki from Tokyo University of Science
Acetonitrile is an elongated molecule that has two independent modes of rotation: around its long axis, like a top, or as if it were a pencil spinning around your thumb. The latter type of rotation tends to slow down spontaneously due to the emission of radio waves, and of course it becomes less energetic or “cold” in the low density regions of molecular clouds.
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 could prove it. He explains: “In regions with a low density of molecular clouds, the proportion of acetonitrile molecules that spin like a top should be higher. From this it can be concluded that an extreme state should exist in which many of them would spin in this way. However, our research team was the first to predict its existence, select astronomical bodies that could be observed, and actually begin exploring. ”
The observation setup. Photo credit: Mr. Daitoshi Ishihara / National Astronomical Observatory of Japan
Instead of opting for radio wave emissions, they focused on the absorption of radio waves. The “cold” state of the low-density region, when populated by acetonitrile molecules, should have a predictable impact on the radiation emanating from and passing through celestial bodies such as stars. In other words, the spectrum of a radiating body that we perceive on Earth to be “behind” a low density region would be filtered by acetonitrile molecules that spin in a predictable manner like a top before it reaches our telescope on Earth. Therefore, Dr. Araki and his team carefully selected radiant bodies that could be used as appropriate “background light” to determine whether the shadow of “cold” acetonitrile appeared in the measured spectrum. To do this, they used the 45-meter radio telescope from Nobeyama Radio Observatory, Japan to study this effect in a low-density region around the “Sagittarius Molecular Cloud Sgr B2 (M),” one of the largest molecular clouds in the world of the center of our galaxy.
After carefully analyzing the measured spectra, the scientists concluded that the analyzed region is rich in acetonitrile molecules that spin like a top. Indeed, the proportion of molecules rotating in this way was the highest ever recorded. Dr. Araki is enthusiastic about the results and remarks: “By taking into account the special behavior of acetonitrile, its amount can be precisely determined in the low density range around Sgr B2 (M). Since acetonitrile is a representative COM in space, knowing its amount and distribution in space can help us to further study the overall distribution of organic matter. ”
Ultimately, this study can not only provide clues as to where the molecules that correspond to us come from, but can also serve as data for the time humans will manage to venture outside the solar system.
Reference: “Observations and analyzes of absorption lines including J. = K. Rotation levels of CH3CN: The Envelope of the Shooter B2 (M) “by Mitsunori Araki, Shuro Takano, Nobuhiko Kuze, Yoshiaki Minami, Takahiro Oyama, Kazuhisa Kamegai, Yoshihiro Sumiyoshi and Koichi Tsukiyama, August 10, 2020, Monthly releases from the Royal Astronomical Society.
DOI: 10.1093 / mnras / staa1754
Dr. Mitsunori Araki received her PhD in chemistry from the Graduate University of Advanced Studies in Japan in 1999. After working as a Research Fellow and Assistant Professor at various universities in Japan, he moved to Tokyo University of Science in 2009 and since 2014. He was Principal Investigator for astrochemical research projects. His research interests mainly revolve around complex organic molecules in space. His goal is to find new such molecules and to clarify their cosmic origins, both through experiments with synthesized molecules in the laboratory and through direct observations with radio telescopes.
