Free Astronomy Magazine November-December 2022

41 NOVEMBER-DECEMBER 2022 ASTRO PUBLISHING plained study leader Elena Sabbi of the Space Telescope Science Institute in Baltimore. “We have several mod- els that make predictions, and some of these predictions are contradic- tory. We want to determine what is regulating the process of star forma- tion, because these are the laws that we need to also understand what we see in the early Universe.” Researchers determined the motion of the stars in NGC 346 in two differ- ent ways. Using Hubble, Sabbi and her team measured the changes in the stars’ positions over 11 years. The stars in this region are moving at an average velocity of 3200 kilo- metres per hour, which means that in 11 years they move 320 million kilometres. This is about twice the distance between Earth and the Sun. But this cluster is relatively far away, inside a neighbouring galaxy. This means the observed motion is very small and therefore difficult to measure. These extraordinarily pre- cise observations were possible only because of Hubble’s exquisite reso- lution and high sensitivity. Also, Hubble’s three-decade-long history of observations provides a baseline for astronomers to follow minute celestial motions over time. The second team, led by Peter Zei- dler of AURA/STScI for the Euro- pean Space Agency, used the ground-based VLT’s Multi Unit Spectroscopic Explorer (MUSE) in- strument to measure radial velocity, which determines whether an ob- ject is approaching or receding from an observer. “What was really amazing is that we used two com- pletely different methods with dif- ferent facilities and basically we came to the same conclusion inde- pendently,” said Zeidler. “With Hubble, you can see the stars, but with MUSE we can also see the gas motion in the third dimension, and it confirms the theory that every- thing is spiralling inwards.” A stronomers have been be- mused to find young stars spiralling into the centre of a massive cluster of stars in the Small Magellanic Cloud, a satellite galaxy of the Milky Way. The outer arm of the spiral in this huge, oddly shaped stellar nursery — called NGC 346 — may be feeding star formation in a river-like motion of gas and stars. This is an efficient way to fuel star birth, researchers say. The Small Magellanic Cloud has a simpler chemical composition than the Milky Way, making it similar to the galaxies found in the younger Universe, when heavier elements were more scarce. Because of this, the stars in the Small Magellanic Cloud burn hotter and so run out of their fuel faster than in our Milky Way. Though a proxy for the early universe, at 200,000 light-years away the Small Magellanic Cloud is also one of our closest galactic neigh- bours. Learning how stars form in the Small Magellanic Cloud offers a new twist on how a firestorm of star birth may have occurred early in the history of the Universe, when it was undergoing a ‘baby boom’ about two to three billion years after the Big Bang (the Universe is now 13.8 billion years old). The new results show that the process of star formation there is similar to that in our own Milky Way. Only 150 light-years in diameter, NGC 346 boasts the mass of 50,000 Suns. Its intriguing shape and rapid star formation rate have puzzled as- tronomers. It took the combined power of the NASA/ESA Hubble Space Telescope and the European Southern Observatory’s Very Large Telescope (VLT) to unravel the be- haviour of this mysterious-looking stellar nesting ground. “Stars are the machines that sculpt the Universe. We would not have life without stars, and yet we don’t fully understand how they form,” ex- ! T he red spiral superimposed on NGC 346 traces the movement of stars and gas to- ward the center. Scientists say this spiraling motion is the most efficient way to feed star formation from the outside toward the center of the clus- ter. [NASA, ESA, A. James (STScI)]