Previous infrared studies of the NGC 346 nebula have focused on stellar embryos heavier than five to eight times the mass of our Sun. With the help of the Web, it is possible to reach even lighter protostars, as small as a tenth of our sun
NGC 346, one of the most dynamic star-forming regions in nearby galaxies, is full of mystery. Now, however, some of the mystery has been lifted thanks to new findings from the James Webb Space Telescope
NCG 346 is located in the Small Magellanic Cloud (SMC), a dwarf galaxy close to our Milky Way. The Small Magellanic Cloud contains lower concentrations of elements heavier than hydrogen or helium, which astronomers call metals, than is seen in the Milky Way. Since dust grains in space are mainly composed of metals, scientists expected that the star formation region would have only small amounts of dust, and that it would be difficult to detect. But new Webb data reveals just the opposite.
Astronomers have studied this region because the conditions and amount of metals in the Small Magellanic Cloud are similar to those observed in galaxies billions of light-years away, at a time in the universe’s history known as ‘cosmic noon’, when star formation was at its peak. About 2 to 3 billion years after the Big Bang, galaxies formed stars at a dizzying rate. The echoes of that period of star formation still shape the galaxies we see around us today.
“A galaxy at cosmic noon will not have one NGC 346 like in the Small Magellanic Cloud, it will have thousands,” said Margaret Meixner, an astronomer at the University Space Research Association and the study team’s principal investigator. “But even if NGC 346 is now the one and only star-forming massive cluster in its galaxy, it offers us an excellent opportunity to study the conditions that existed at noon on the cosmic day.”
By looking at stars that are still forming, researchers can learn whether the star formation process in the SMC is different from what we see in our own Milky Way. Previous infrared studies of NGC 346 have focused on stellar embryos heavier than five to eight times the mass of our Sun. “With the Web, we can probe down to lighter protostars, as small as a tenth of our Sun, to see if their formation process is affected by the lower metal content,” said co-investigator Olivia Jones of the UK’s Astronomy Technology Center at the Royal Observatory Edinburgh. in the program
As stars form, they collect gas and dust, which appear as streaks in the Webb images, from the surrounding molecular cloud. The material is collected into an accretion disk that feeds the nascent central star. Astronomers have detected gas around protostars within NGC 346, but Webb’s near-infrared observations are the first time they’ve also detected dust in these disks.
“We see the building blocks, not only of stars, but also of planets,” said Guido de Marchi of the European Space Agency, a co-investigator on the research team. “And because the Small Magellanic Cloud has an environment similar to that of galaxies during the cosmic noon, rocky planets may have formed earlier in the universe’s history than we thought.”
The team also has spectroscopic observations from Webb’s NIRSpec instrument that they continue to analyze. These data are expected to provide new insights into the material accreting onto individual protostars, as well as the environment surrounding the protostars.
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