The biggest-ever survey of dense clumps in our Milky Way Galaxy, published in the Astrophysical Journal Supplement Series, has catalogued and mapped 6,194 early star-forming clouds – pockets shrouded in gas and dust where new stars are being born.
This is an artist’s rendition of the Milky Way, overlaid with results from the survey of early star-forming clouds. Each dot represents a dark cloud of dense gas and dust in the process of collapsing to give rise to a future cluster of stars. Image credit: R. Hurt / NASA / JPL-Caltech / SSC.
For this survey, which covers all parts of the galactic plane visible from the northern hemisphere, lead author Dr Yancy Shirley from the University of Arizona and his colleagues used the Sub-Millimeter Telescope at the Arizona Radio Observatory.
“When you look at the Milky Way on a clear summer night, you’ll notice it’s not a continuous stream of stars. Instead, you’ll notice all those little dark patches where there seem to be no stars. But those regions are not devoid of stars – they’re dark clouds containing dust and gas, the raw material from which stars and planets are forming in our Milky Way today,” Dr Shirley explained.
The survey is a major step forward in astronomy because it allows astronomers to study the earliest phases of star formation when the gas and dust in the star-forming clouds are just beginning to coalesce, before giving rise to clusters of stars.
“All the famous, major regions of star formation in our galaxy have been studied in great detail. But we know very little about what happens in those star-less clumps before proto-stars form, and where,” Dr Shirley said.
The survey provides the first unbiased map of Milky Way Galaxy that shows where all those regions are throughout the galaxy, in different galactic environments and at different evolutionary stages. This helps astronomers better understand how the properties of these regions change as star formation progresses.
“Starless clumps have only been detected in small numbers to date. Now, for the first time, we have seen this earliest phase of star formation, before a cluster actually forms, in large numbers in an unbiased way.”
The star formation rate in the Milky Way was higher in the past, and currently stars form on the order of about one solar mass per year. How long does it take to become a full-blown star?
“That is something we hope to be able to calculate by comparing the number of sources that are in that early phase to the number of sources that are in a later phase. The ratio between the two tells you how long each phase lasts. In our survey there seem to be fewer regions that have not yet begun forming stars than those that have, which tells us the earlier phase must be shorter. If that phase lasted much longer, there should be many more of those,” Dr Shirley explained.
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Bibliographic information: Yancy L. Shirley et al. 2013. The Bolocam Galactic Plane Survey. X. A Complete Spectroscopic Catalog of Dense Molecular Gas Observed toward 1.1 mm Dust Continuum Sources with 7fdg5 ≤ l ≤ 194°. ApJS 209, 2; doi: 10.1088/0067-0049/209/1/2
