What makes starburst galaxies so fertile?

What makes starburst galaxies so fertile?

Read time: 3 minutes

If you’re tending a school or home garden, you know the problem. Some parts of the garden may produce lots of flowers or vegetables, while other parts remain pretty barren. In your garden, this may be due to variations in the soil, or to the use of different seeds.

Something similar happens in the Universe. In some galaxies, new stars are born in huge numbers, while other galaxies produce only a handful of new stars each year. What makes the ‘starburst galaxies’ so special? Thanks to new ALMA observations, astronomers now start to find the answer to this question.

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Stars are born from huge clouds of gas and dust. So you might think that the explanation is obvious: if there’s more gas and dust, there will be more stars in the end. But ALMA has shown that the answer is a bit more interesting.

ALMA was trained at star forming regions in the Sculptor galaxy. Sculptor is a starburst galaxy where stars are born about a thousand times faster than in our own Milky Way galaxy. By observing at different wavelengths, astronomers were able to map the distribution and the motions of about forty different types of molecules in the gas clouds.

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Some of these molecules can only exist in regions where the gas has a very high temperature and density. So the ALMA observations not only revealed the composition of the gas, but also the properties of the gas clouds.

It turns out that the Sculptor galaxy not only contains more gas and dust, but that the galaxy’s star forming regions are also much denser and more turbulent than similar gas clouds in the Milky Way.

If gas clouds in starburst galaxies have such different properties, even the process of star formation may be different. In the future, the astronomers hope to learn if this also leads to the birth of different kinds of stars.

After all, if the soil in your school garden is very fertile, your carrots will be bigger than average, right?


What?
The Sculptor galaxy, also known as the Silver Dollar galaxy or NGC 253, is a spiral galaxy at a distance of some 11.5 million light-years in the direction of the southern constellation Sculptor. It’s a bit smaller than our own Milky Way, but the birth rate of new stars in Sculptor is about a thousand times higher. The galaxy also harbours a few ‘super star clusters’, containing many millions of massive stars.

Who?
The ALMA observations of the Sculptor galaxy were carried out by an international team of astronomers, led by Adam Leroy of the National Radio Astronomy Observatory in Charlottesville, Virginia. Adam has since moved to Ohio State University in Columbus. He presented the new ALMA results at the 2015 annual meeting of the American Association for the Advancement of Science, which was held in San Jose, California, in February 2015. The observations of the Sculptor galaxy have also been published in The Astrophysical Journal.