Rising stars provide a window into the early universe

Astronomers were baffled when they found young stars spiking at the center 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 massive, oddly shaped stellar nursery – called NGC 346 – may be fueling star formation in a river-like motion of gas and stars. The researchers 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, making it similar to galaxies found in the smaller universe, when heavier elements were much rarer. Because of this, the stars in the Small Magellanic Cloud burn hotter and run out of fuel faster than in our Milky Way. Despite being a proxy for the early universe, the Small Magellanic Cloud 200,000 light-years away is also one of our closest galactic neighbors.

Learning how stars form in the Small Magellanic Cloud offers a new twist on how a star-birth firestorm occurred early in the universe’s history, when it was going through a “baby boom” about 2 to 3 billion years after the Big Bang (the universe is now 13.8 billion years old). year).

The new results show that the process of star formation there is similar to that occurring in our own Milky Way.

NGC 346 is only 150 light-years across, and boasts a mass of 50,000 suns. Its intriguing shape and rapid star formation rate baffled astronomers. It took the combined power of the NASA/ESA Hubble Space Telescope (ESA) and the European Southern Observatory’s Very Large Telescope (VLT) to reveal the behavior of this mysterious star-nesting Earth.

“Stars are the machines that sculpt the universe. We wouldn’t have life without stars, yet we don’t fully understand how they form,” explained study leader Elena Sabi of the Space Telescope Science Institute in Baltimore. We have many models that make predictions, and some of these predictions are contradictory. We want to determine what regulates star formation, because these are the laws we also need to understand what we see in the early universe.”

Researchers have determined the motion of stars in NGC 346 in two different ways. Using Hubble, Sabi and her team measured changes in the star’s positions over the course of 11 years. The stars in this region move at an average speed of 3,200 kilometers per hour, which means that they move 320 billion kilometers in 11 years. This is about twice the distance between the Earth and the Sun.

But this cluster is relatively far away, within a neighboring galaxy. This means that the observed motion is very small and therefore difficult to measure. These extremely precise observations were only possible due to Hubble’s remarkable accuracy and high sensitivity. Also, Hubble’s three-decade history of observations provides a basis for astronomers to follow precise celestial movements over time.

The second team, led by Peter Zeidler of AURA/STScI for the European Space Agency, used VLT’s Multi Unit Spectroscopic Explorer (MUSE) instrument to measure radial velocity, which determines whether an object is approaching or receding from the observer.

“What was really amazing was that we used two completely different methods with different facilities and came to essentially the same result independently,” 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 this confirms the theory that everything is spiraling inward.”

But why vortex?

“The spiral is really a good natural way to fuel star formation from the outside toward the center of mass,” Zeidler explained. “It’s the most efficient way that stars and the gases that fuel more star formation can move toward the center.”

Half of the Hubble data for this study of NGC 346 is archival. The first notes were taken 11 years ago. It was recently replicated to track the movement of stars over time. Due to the telescope’s longevity, the Hubble data archive now contains more than 32 years of astronomical data, supporting unprecedented long-term studies.

“The Hubble archive is really a goldmine,” Sabi said. There are many interesting star-forming regions that Hubble has observed over the years. Given that Hubble performed very well, we can actually replicate these observations. This could enhance our understanding of star formation. “

Observations using the NASA/ESA/CSA James Webb Space Telescope should be able to resolve lower-mass stars, giving a more comprehensive view of the region. Over the course of Webb’s lifetime, astronomers will be able to repeat this experiment and measure the motion of low-mass stars. They will then be able to compare high-mass stars and low-mass stars to see the full extent of the dynamics of this nursery.

Source: NASA, ESA, A. James (STScI); CC BY 4.0

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