ALMA speeds up cosmic detective work

ALMA speeds up cosmic detective work

Read time: 3 minutes

Suppose someone stole money from the office of your school director. It must have been a teacher or a student – no one else was in the building when it happened. A clever detective finds fingerprints in the office. They don’t match the fingerprints of the director, so they must be the fingerprints of the thief. The detective then takes fingerprints from each and every teacher and student in the school. No two people have the same fingerprints, so now it is easy to find out who stole the money.

There are no thieves in outer space, but astronomers do similar detective work. And thanks to ALMA, the job can now be done much faster than they were used to.

Stars are born in giant clouds of gas and dust. There are lots of different gas molecules in the clouds. These molecules are in constant motion: they rotate like spinning tops, and they vibrate like springs. As a result, the molecules emit millimeter and submillimeter waves that can be studied by ALMA.

But different molecules behave differently. Oxygen molecules emit radiation at different wavelengths than ammonia molecules, for instance. Each type of molecule has its own radiation ‘fingerprint’. To know what kind of gas the cloud contains, you must first take the fingerprints of all possible molecules. That can be done in a chemical laboratory.

The problem is that the molecules also change their behavior when the temperature changes. It is as if your fingerprints are different in the winter and in the summer. That’s why the cosmic detective work – known as astrochemistry – is so difficult.

But now, astronomers have shown that the job can be done much faster. That’s because ALMA can observe and study many wavelengths at once. Thanks to new techniques, the laboratory measurements can also be done much more efficient.

As a result, many ‘unknown’ fingerprints can now be identified, so astronomers will get a much better idea of the composition and temperatures of cosmic gas clouds. That’s important, because these clouds give birth to new stars, planets, and – who knows – life.

The Orion Nebula is a large cloud of gas and dust where new stars and planets are being born. Scientists have compared ALMA observations of the Orion Nebula with laboratory ‘fingerprints’ of various gases.

This study was carried out by Suzanne Randall of the Headquarters of the European Southern Observatory (ESO) in Garching, Germany, and Anthony Remijan of the National Radio Astronomy Observatory in Charlottesville, Virginia. Suzanne and Anthony worked with other scientists from the United States. The results were published in a professional magazine called Journal of Molecular Spectroscopy.