Star clusters seen spewing out dust
Astronomers at UCLA have now confirmed that stars in a galaxy called II Zw 40 – roughly 33 million light-years away – are creating enormous amounts of dust. We know our Milky Way and other galaxies must contain gas and dust; the dark rift in the starry band of the Milky Way is due to dust. Long-standing astronomical theories say that stars produce dust by expelling the chemical elements fused deep within their interiors, thus enriching their host galaxies in elements heavier than hydrogen and helium. These heavier elements make up planets like Earth, and living things like human beings.
But actual observations of dust production by stars on galactic scales has been difficult. Now the UCLA team says it has evidence for it in galaxy II Zw 40. Their research was published online December 1, 2016 in the peer-reviewed Astrophysical Journal Letters.
Astronomy graduate student S. Michelle Consiglio is lead author on the paper, aided by her professor Jean Turner of UCLA, and two other collaborators. The researchers focused on II Zw 40 because it’s a starburst galaxy, that is, a galaxy with a high rate of star formation and so useful for testing theories of star formation. Turner commented in a statement:
This galaxy has one of the largest star-forming regions in the local universe.
Led by Consiglio, the astronomers obtained images of II Zw 40 using the ALMA telescope in Chile’s Atacama desert. The scientific work of this relatively new and very powerful telescope – whose array of 66 individual telescopes function as a single large observatory – began in 2011.
Consiglio and her team observed the central region of II Zw 40, a part of the galaxy known to be occupied by two young star clusters, each containing roughly a million stars. By imaging II Zw 40’s star clusters at different wavelengths, they constructed a map that traced the dust in the galaxy. The researchers then tested whether the location of the galaxy’s dust was consistent with the location of the galaxy’s star clusters. They found that it was. Consiglio and her team showed that II Zw 40’s dust was concentrated within roughly 320 light-years of the star clusters. Consiglio said:
The dust is all focused near the double cluster. The double cluster is a ‘soot factory’ polluting its local environment.
But, in this case, it’s a good kind of pollution, leading to the complex forms of nature we see around us on Earth. Turner said:
People have looked for [a] large-scale enrichment of galaxies, but they haven’t seen it before. We’re seeing galaxy-scale enrichment and we see clearly where it is coming from.
The researchers propose that the dust enrichment is so obvious in II Zw 40’s star clusters because they contain large numbers of very young, massive stars, which are the producers of dust.
Bottom line: UCLA astronomers show that stars are responsible for producing dust on galactic scales, a finding consistent with long-standing theory.