Stars are the engines that sculpt the universe, yet researchers still don’t fully understand how they form. Scientists turned to the Small Magellanic Cloud, a satellite galaxy of the Milky Way, to understand the frenzied “baby boom” of star birth that occurred early in the universe’s history. This nearby galaxy has a simpler chemical composition than the Milky Way, which makes it similar to galaxies found in the younger universe, when heavier elements were less abundant. As a result, it can serve as a proxy for the early universe. Two separate research studies – the first with the Hubble Space Telescope and the second with the European Southern Observatory’s Very Large Telescope – recently reached the same conclusion. Using different techniques, the independent teams discovered young stars spiraling into the center of a massive star cluster called NGC 346 in the Small Magellanic Cloud. This river-like movement of gas and stars is an efficient way to fuel star birth, astrophysicists say. The teams’ results show that the star formation process in the Small Magellanic Cloud is similar to that in our own Galaxy. The massive star cluster NGC 346, located in the Small Magellanic Cloud, has long fascinated astronomers with its unusual shape. Now researchers using two separate methods have determined that this shape is partly due to stars and gas spiraling through the center of this cluster in a river-like motion. Credit: NASA, ESA, Andi James (STScI)
NASA’s Hubble finds spiral stars, providing window into the early universe
Spirals are widespread in nature — from the vortex of a hurricane, to the pin-shaped protoplanetary disks around newborn stars, to the vast spheres of spiral galaxies throughout our universe. Now astronomers are discovering young stars spiraling at the center of a huge cluster of stars in the Small Magellanic Cloud, a satellite galaxy of the Milky Way. The outer spiral arm in this massive, oddly shaped stellar nursery called NGC 346 may be fueling star formation in a river-like movement of gas and stars. Scientists say this is an effective way to fuel the birth of stars. The Small Magellanic Cloud has a simpler chemical composition than the Milky Way. This makes it similar to galaxies found in the younger universe when heavier elements were rarer. Because of this, the stars in the Small Magellanic Cloud burn hotter and therefore run out of fuel more quickly than in our Milky Way. Although it can serve as a proxy for the early universe, the Small Magellanic Cloud is also one of our closest galactic neighbors, just 200,000 light-years away. The discovery of how stars form in the Small Magellanic Cloud offers a new twist on how a storm of star birth may have occurred early in the universe’s history, when it was in a “baby boom” about 2 to 3 billion years after the Big Bang. Big Bang (the universe is now 13.8 billion years old). According to the new findings, the star formation process there is similar to that in our own Milky Way. NGC 346 boasts the mass of 50,000 Suns, despite being only 150 light-years across. Its interesting shape and rapid rate of star formation have puzzled astronomers. It took the combined power of NASA’s Hubble Space Telescope and the European Southern Observatory’s Very Large Telescope (VLT) to reveal the behavior of this mysterious-looking stellar nesting ground. “Stars are the machines that sculpt the universe. We wouldn’t have life without stars, and yet we don’t fully understand how they form,” explained study leader Elena Sabi of the Space Telescope Science Institute in Baltimore. “We have a lot of models making predictions and some of those predictions are contradictory. We want to determine what regulates the star formation process, because these are the laws we need to also understand what we see in the early universe.” Scientists determined the motion of the stars in NGC 346 in two different ways. Using Hubble, Sabbi and her team measured changes in the stars’ positions over 11 years. Stars in this region move at an average speed of 2,000 miles per hour, resulting in a movement of 200 million miles in 11 years. This is about twice the distance between the Sun and the Earth. However, this cluster is relatively far away, in a neighboring galaxy. This means that the magnitude of the observed movement from our vantage point is very small and therefore difficult to measure. These extremely precise observations were only possible because of Hubble’s extraordinary resolution and high sensitivity. In addition, Hubble’s three-decade history of observations provides a basis for astronomers to track small celestial movements over time. The second team, led by Peter Zeidler of AURA/STScI for the European Space Agency (ESA), used the VLT’s ground-based Multi-Unit Spectroscopic Spectroscopy (MUSE) instrument to measure the radial velocity, which determines whether an object is approaching or recedes from an observer. “What was really surprising is that we used two completely different methods with different facilities and basically came to the same conclusion independently of each other,” Zeidler said. “With Hubble, you can see the stars, but with MUSE we can also see the movement of gas in the third dimension, and it confirms the theory that everything is spiraling inward.”
But why spiral?
“A spiral is really the good, natural way to fuel star formation from the outside to the center of the cluster,” Zeidler explained. “It’s the most efficient way that the stars and gas that fuel more star formation can move toward the center.” Half of the Hubble data for this study of NGC 346 is archival, with the first observations taken 11 years ago. These observations were recently repeated to trace the motion of the stars over time. Given the telescope’s longevity, more than 32 years of astronomical data are now contained in the Hubble data archive, which can feed unprecedented, long-term studies. “The Hubble archive really is a gold mine,” Sabbi said. “There are so many interesting star-forming regions that Hubble has observed over the years. Since Hubble performs so well, we can actually repeat these observations. This can really advance our understanding of star formation.” The teams’ findings appear today (September 8) in The Astrophysical Journal. Citation: “The Internal Line-of-Sight Kinematics of NGC 346: The Rotation of the Core Region” by Peter Zeidler, Elena Sabbi and Antonella Nota, September 8, 2022, The Astrophysical Journal.DOI: 10.3847/1538-4357/ac8 Observations with NASA’s James Webb Space Telescope should be able to analyze lower-mass stars in the cluster, giving a more holistic view of the region. During Webb’s lifetime, astronomers will be able to repeat this experiment and measure the motion of low-mass stars. Then they could compare high-mass stars and low-mass stars to finally learn the full extent of this nursery’s dynamics. The Hubble Space Telescope is an international collaborative project between NASA and ESA. NASA’s Goddard Space Flight Center in Greenbelt, Maryland operates the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Washington, DC
