Amino Acid Ingredients Found in Distant Galaxy
Using the giant dish at Arecibo, Puerto Rico, radio astronomers have discovered evidence of hydrogen cyanide and methanimine, two carbon compounds that can combine with water to make the amino acid glycine. Because proteins are composed of amino acids, the new results make distant space seem a bit more hospitable to life.
Except that life is highly unlikely to exist in the tempestuous galaxy named Arp 220, which is about 250 million light years distant, says Robert Minchin, a post-doctoral fellow at Arecibo. “This is often referred to as a prototype of a massive star-forming galaxy. It is currently undergoing a huge burst of star formation, so a huge amount of radiation is coming off.” Still, Minchin says the discovery of hydrogen cyanide and methanimine is exciting: “Just add water!” and you have one component of life as we know it. Minchin worked in a group directed by Christopher Salter, a senior research associate at Arecibo, which is managed by Cornell University.
The detections of hydrogen cyanide and methanimine, coming on top of a previous detection of water at Arp 220, mark the first firm, extra-galactic report of the complete makings for any amino acid, Minchin says. “We have seen all the ingredients for the simplest amino acid; that’s the reason it’s exciting; it’s the start of a building block of life.”
But there are no traces of glycine to date, he adds. “We’d love to see it, but it is a more complicated molecule” and therefore is harder to detect on the spectrograph.
The highly luminous Arp 220 is highly conducive to spectrography, which detects the presence of “chemical species” – ions, atoms or molecules – by studying radiation patterns caused by either emission or absorption. The emission spectrum, the source of the methanimine (CH2NH) detection, is radiation released by the chemical species. The absorption spectrum, used to detect hydrogen cyanide (HCN), shows radiation that was blocked by a chemical species. In both cases, a stronger light source makes for stronger, clearer signals.
Having detected the precursors for glycine, the researchers next plan to look at another 21 galaxies, selected to match or contrast with Arp 220’s characteristics. That sort of mix-and-match may suggest what, if anything, is peculiar about Arp 220 that enables it to make the amino-acid precursors in detectable quantities – or it may show that these two compounds are common components of many types of galaxies.
Hydrogen cyanide is frequently seen in the Milky Way, especially around star-forming regions. And although methanimine has tentatively been detected in the nearby NGC 253 galaxy, Arp 220 “is by far the farthest, and firmest, detection to date,” Minchin says.
“This is a wonderful result, particularly since it concerns compounds of carbon, an essential element of life,” says Max Bernstein, a member of the Astrochemistry Lab at NASA Ames Research Center who is interested in the carbon chemistry of space environments, especially molecules that resemble those in living things and thus may be important for making planets habitable . “Of course we knew that there was carbon in other galaxies,” he adds, “and we had indications (from infrared emissions) that at least some of the molecules were similar to those we know, but there is just nothing like the detection of specific, familiar carbon compounds to really drive home the fact that the carbon chemistry in other galaxies is like that in our own.”
The exact origin of the emissions within Arp 220 is unknown, says Minchin, who expects that radio intereferometry studies using the Merlin array in the United Kingdom may narrow that question down. (Interferometry compares electromagnetic radiation collected at multiple telescopes to obtain a precise picture of the source’s location and velocity.) “The most likely source is in the star-formation regions, which is where a lot of complicated molecules are seen in our own galaxy.”
Louis Allamandola, a physicist and astrochemist at the NASA Ames Research Center, focuses on laboratory studies on the chemistry, composition, and spectroscopy of interstellar matter with emphasis on complex organics and interstellar and solar system ices. “Galaxies contain everything,” he says, so “I don’t think it is the nature of the molecules which make this detection special, it is the astronomical object.” Arp 220 is “a very unusual and exceptionally energetic object … that is now thought to be a collision between two galaxies the size of the Milky Way. This collision is dissipating an enormous amount of energy.”
And as Minchin concedes, the massive amount of energy at Arp 220 makes it an extremely unlikely location for life. “The conditions are very hostile for life to develop,” says Allamandola. “You’d expect life to turn up in galaxies that are slightly more stable than this one.”
It’s helpful to remember the bigger picture of astrobiology, says Bernstein. “There are many of these necessary-but-not-sufficient conditions for habitability. There must be carbon, for sure, but also it has been noted that our position in our galaxy (not too close to the center), the position of our planet in our solar system (not too close to the sun), the kind of star we orbit (not too big and thus short-lived), the fact that we have a companion (the moon), etc., may all be necessary but not sufficient conditions for life.”
Still, it doesn’t hurt the odds to find a vast storehouse of two amino-acid building blocks in a remote galaxy.