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For generations, scientists have speculated that carbon and its aromatic counterparts are abundant in the universe, even in space. However, this was all but a theory until astronomers were able to detect larger PAHs for the first time in space.

What are PAHs?

PAHs belongs to a group of carbon-based chemicals known as organic compounds. Carbon is a prolific element that is in almost everything we see and unlike other compounds, carbon has an endless cycle.

As carbon-based life forms we return to the soil when we die, that carbon gets picked up by plants, which will then be eaten by animals and insects, and so its cycle continues.

Polycyclic aromatic carbons or PAHs on the other hand are made when substances are burned. It naturally occurs in crude oil, coal, and gasoline and is present in products of fossil fuels like creosote, coal-tar pitch, and asphalt.

PAHs are found naturally in the environment. In the air, soil, and water and can persist for months or years.

Green Bank Telescope NRAO
(Photo: NRAO/AUI/NSF / Wikimedia Commons)
The Green Bank Telescope is the world’s largest, fully-steerable telescope. The GBT’s dish is 100-meters by 110-meters in size, covering 2.3 acres of space.

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PAHs in Space

For decades astronomers suspected that PAHs are abundant in space, however, detection has been scarce. Simpler molecules like single-ring carbons have been seen before.

But only until March 19 after publishing a report in the journal Science entitled, "Detection of two interstellar polycyclic aromatic hydrocarbons via spectral matched filtering" were astronomers able to detect larger PAHs for the first time in space according to Brett McGuire, lead author, and astrochemist from MIT.

Studying PAHs and other molecules could help scientists unravel the chemical precursors to life that might have begun in space.

McGuire says that carbon is a fundamental aspect of chemical reactions, especially reactions that lead to life's essential molecules and the discovery is a window into a vast reservoir.

Beginning in the 1980s, astronomers have been able to detect mysterious infrared glows coming from spots within the galaxy. Many suspected that the glow comes from PAHs but were unable to identify the sources.

Instead of searching infrared signals that often overlapped, McGuire and his team turned to radio waves, where different PAHs produce different frequencies. The team trained the Green Bank Telescope on TMC-1, a dark cloud roughly 430 lightyears from Earth.

Previously, McGuire discovered that dark cloud contained benzonitrile, single-carbon ring molecules which hinted that it was a good place to start looking for more complex molecules.

McGuire's team detected 1- and 2-cyanonaphthalene, two-ringed carbon molecules with 10 carbons, 8 hydrogens, and a nitrogen atom.

The team discovered that the cloud contained roughly 100,000 to one million times more PAHs than theoretical models predicted.

Alessandra Ricca, an astrochemist from SETI Institute who wasn't involved in the study says that the discovery is paramount to even more discoveries. The work is the first definitive detection of PAH molecules existing in the vacuums of space, as it was only a theory up until recently.

Ricca is developing a database of infrared PAH signals that the soon-to-launch James Webb Space Telescope can look for in efforts to understand the mysteries of carbon and its role in the universe.

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