Nanocosmos confirms there are PAHs in the interstellar medium

Image of the Heiles Cloud 2 as part of the massive Taurus Molecular Cloud (TMC). The magnifying glass shows the region, called TMC-1, where our line survey observations were made. Image captured at Grand Mesa Observatory in Colorado (USA). Image credit and copyright Terry Hancock and Tom Masterson.

First detection of a pure PAH (indene c-C9H8) in an unexpected place!

Polycyclic Aromatic Hydrocarbons (PAHs) are organic compounds formed by rings. Their bad reputation on Earth is due to their toxicity, as they are mostly the result of oil and coal combustion. However, in space they have another role that, despite waiting for confirmation, may be related even to the origin of life.

In the interstellar medium observations, there are infrared bands that, until now, were unidentified. The hypothesis (for more than 40 years) was that these bands were probably PAHs, but final confirmation was lacking.

The first milestone of this work is the confirmation, for the first time, of the presence of a pure PAH (indene) in the interstellar medium. The second milestone is that we have confirmed the discovery in an unexpected place: a cold dark cloud called TMC-I.

The TMC-1 cold dark cloud

It was originally thought that PAHs could form in circumstellar envelopes around evolved stars. These stars are in the final stages of their lives and expel much of their matter into the interstellar medium. In fact, twenty years ago benzene, (an aromatic ring present in many PAHs) was first detected in the hot and ultraviolet light illuminated regions around an evolved star. This made astronomers think that the formation of PAHs requires high temperatures and ultraviolet radiation. Therefore, the presence of PAHs in the interstellar medium would have an exogenous origin. That is, PAHs would form in circumstellar envelopes and would later be dragged into the interstellar medium by stellar winds.

However, the first detection has been carried out in an unexpected environment: the cold pre-stellar core TMC-1 in the Taurus Molecular Cloud complex, which is well protected from ultraviolet radiation. In this environment, in addition to the indene (c-C9H8), the presence of ethynyl cyclopropenylidene (c-C3HCCH) and cyclopentadiene (c-C5H6) has been detected. It should be noted that cyclopentadiene and indene, molecules formed by rings of five and six carbon atoms, are exceptionally abundant despite their large size.

With these observations, it is demonstrated not only the unambiguous presence of PAHs in the interstellar medium, but also that they are formed in situ and from less complex molecules. They are not dragged from other environments (e.g. on the surface of dust grains), but are formed according to what is called a bottom-up formation mechanism, that is, from smaller molecules that join in the gas phase.

Although some theories relate PAHs to the origin of life, more studies are still needed to confirm the role they could have played in the formation of nucleobases, which are part of the RNA. While astronomers gather more data that may or may not confirm this hypothesis, this NANOCOSMOS-ERC discovery is a major breakthrough in our current understanding to explain the formation mechanisms of complex molecules, which remain, for the most part, a mystery.

The Yebes 40m radio telescope

The TMC-1 observations have been carried out with the 40m radio telescope at Yebes Observatory (IGN, the Spanish National Geographic Institute). This was possible thanks to the Nanocosmos new receivers, built within the Nanocosmos-ERC project, funded by the European Research Council. Since they were installed, these high-sensitivity new receivers are providing valuable new information on the interstellar medium.

More information

Pure hydrocarbon cycles in TMC-1: Discovery of ethynyl cyclopropenylidene, cyclopentadiene and indene (Astronomy & Astrophysics, May 2021, DOI: 10.1051/0004-6361/202141156). Authors: J. Cernicharo, M. Agúndez, C. Cabezas, B. Tercero, N. Marcelino, J. R. Pardo, & P. de Vicente.

AstroPAH: A Newsletter on Astronomical PAHs (Leiden University, the Netherlands), issue 78, May 21, 2021. A new golden age era for Astrochemistry: Discovering PAHs with millikelvin sensitive radio astronomical molecular line surveys (by Prof. José Cernicharo, on behalf of the NANOCOSMOS ERC team).

CSIC press release: Hallados hidrocarburos policíclicos aromáticos en el medio interestelar

IGN press release: Hidrocarburos policíclicos aromáticos en el medio interestelar

El Mundo newspaper (May 22, 2021): ¿Por qué es importante el indeno hallado en el espacio por astrónomos españoles? (by Dr. Rafael Bachiller, director of the Observatorio Astronómico Nacional, IGN, Madrid).

Breaking: First Time Discovery of the PAH Indene in Space

The NANOCOSMOS team reports the first time detection of the simplest polycyclic aromatic hydrocarbon (PAH) carrying a five-membered ring—indene (c-C9H8) in Space (TMC-1 cold dark molecular cloud) with rotational spectroscopy. This major challenging breakthrough is the first step to understand the potential formation mechanisms of these species in the interstellar medium. Moreover, the team derives a high abundance of indene that needs to be explained through alternative and efficient chemical routes.

The team also reports the first time discovery in space of two other organic compounds, the c-C3HCCH (ethynyl cyclopropenylidene), and c-C5H6 (cyclopentadiene).

These discoveries are the result from the groundbreaking Yebes 40m Observatory sensitive survey with the new NANOCOSMOS Q-band receiver of the TMC-1 cold molecular cloud. This survey has led to the discovery of multiple molecular species since 2020 with more than 25 molecules, 15 of them for the first time in Space.

The best for NANOCOSMOS is yet to come. Stay tuned!

Pure hydrocarbon cycles in TMC-1: Discovery of ethynyl cyclopropenylidene, cyclopentadiene and indene (Accepted for publication in A&A Letters, 2021). Authors: J. Cernicharo, M. Agúndez, C. Cabezas, B. Tercero, N. Marcelino, J. R. Pardo, & P. de Vicente.

Why do we study chemical equilibrium in red giants?

You may have often read that “we are stardust.” It is a rather accurate expression, especially if we think that most of the elements that make us up (this scarce 5% of the baryonic matter of the universe) emerged from the core of a star and from a whole process of death and destruction. But what do we call stardust?

Nanocosmos has participated in this study, explained in the outreach article “Funambulist stars”, that you can continue reading by clicking here.

The documentary about NANOCOSMOS nominated for BICC awards

BICC is the acronym for “XXIX Bienal Internacional de Cine Científico Ronda-Madrid-México 2018”, the biennial international event for science movies. Our documentary “NANOCOSMOS: Un viaje a lo pequeño” has been selected as finalist in this contest within the category of “Science documentary”.

We are very proud to do our bit in science communication!  Even if we don’t get any prize, we acknowledge the jury for considering our movie for the contest.  We will stay tuned for the date of the ceremony. Let’s cross fingers!

Link to the BICC press release (in Spanish).

Horizon Europe: The New Search and Innovation Framework Programme: Challenges and Opportunities

Next week NANOCOSMOS will be in the workshop “Horizon Europe: The New Search and Innovation Framework Programme: Challenges and Opportunities“, organized in the Universidad Menéndez Pelayo (UIMP) by the Ministry of Science, Innovation and Universities and the Spanish Science Research Council (CSIC) . With several panels, this meeting joins some of the relevant scientific and industrial players around new opportunities and challenges in Horizon Europe for the period 2021-2027. The program of the meeting overviews the three major pillars of the Commission’s proposal, covering all forms of innovation, global challenges through research and innovation for the uptake of innovative solutions in industry and society, as well as investigator driven high quality research and infrastructures.  NANOCOSMOS will be represented by one of its Principal Investigators, José Cernicharo, in the panel “The ERC in Horizon Europe – A Reflection on Interdisciplinarity and Multipotentialities.”