NASA's Hubble Space Telescope detects whirling stars, providing insight into the early universe

The massive star cluster NGC 346, located in the Small Magellanic Cloud, has long intrigued astronomers with its unusual shape. Now researchers using two separate methods have determined that this shape is partly due to stars and gas spiraling into the center of this cluster in a river-like motion. The red spiral superimposed on NGC 346 traces the movement of stars and gas toward the center. Scientists say this spiraling motion is the most efficient way to feed star formation from the outside toward the center of the cluster. Credit: NASA, ESA, Andi James (STScI)

Nature loves spirals, from a hurricane's vortex to pinwheel-shaped protoplanetary disks encircling young stars to the immense worlds of spiral galaxies that span our cosmos. Astronomers are now perplexed by the discovery of newborn stars spiraling into the heart of a huge star cluster in the Small Magellanic Cloud, a satellite galaxy of the Milky Way. The spiral's outer arm in this massive, unusually shaped stellar nursery known as NGC 346 may be fueling star production in a river-like motion of gas and stars. According to the experts, this is an effective technique to fuel star creation. Because the Small Magellanic Cloud has a simpler chemical makeup than the Milky Way, it is similar to galaxies seen in the earlier cosmos, when heavy metals were sparse. As a result, the stars in the Small Magellanic Cloud burn hotter and deplete their fuel quicker than the stars in our Milky Way. The Small Magellanic Cloud, albeit a proxy for the early cosmos, is also one of our nearest galactic neighbors at 200,000 light-years away.

Learning how stars develop in the Small Magellanic Cloud provides a fresh perspective on how a firestorm of star formation may have occurred early in the universe's history, about 2 to 3 billion years after the big bang (the universe is now 13.8 billion years old). According to the latest findings, the mechanism of star creation there is comparable to that of our own Milky Way. NGC 346 is only 150 light-years across yet has the mass of 50,000 Suns. Astronomers have been perplexed by its interesting structure and high pace of star production. The combined power of NASA's Hubble Space Telescope and the European Southern Observatory's Very Large Telescope (VLT) was required to decipher the activity of this enigmatic-looking stellar nesting ground.

According to the study's primary author, Elena Sabbi of the Space Telescope Science Institute in Baltimore, stars are the machines that shape the cosmos. We couldn't live without stars, yet we still don't know how they develop. We have various models that make predictions, and some of them contradict each other. We want to figure out what principles govern star formation since these are the laws we need to interpret what we see in the early cosmos.

The movement of the stars in NGC 346 was established in two methods by researchers. Sabbi and her colleagues used Hubble to track the movement of the stars during an 11-year period. The stars in this region move at an average velocity of 2,000 miles per hour, which implies they move 200 million miles every 11 years. This is approximately twice the distance between the Sun and Earth. However, this cluster is rather distant, located within a nearby galaxy. This indicates that the quantity of observable motion is very little and hence impossible to quantify. Only Hubble's exquisite resolution and high sensitivity enabled these extraordinarily precise observations. In addition, Hubble's three-decade history of observations offers a foundation for astronomers to track minute celestial motions throughout time.

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

What was truly astonishing, according to Zeidler, was that we employed two entirely distinct methodologies with separate facilities and practically arrived to the same conclusion, independently of one other. Hubble can detect stars, but MUSE can sense gas motion in the third dimension, which validates the hypothesis that everything is spiraling inwards. A spiral is a nice, natural mechanism to feed star formation from the edge of the cluster toward the center. It's the most effective path for stars and gas, which fuels additional star formation, to flow to the center.

Half of the Hubble data used in this NGC 346 investigation is archived. The initial measurements were collected 11 years ago. They were recently repeated in order to chart the movement of the stars through time. Because of the telescope's lifespan, the Hubble data archive currently has more than 32 years of astronomical data, allowing for unparalleled long-term investigations.

According to Sabbi, the Hubble archive is a gold mine. Hubble has spotted numerous fascinating star-forming areas throughout the years. We can really repeat these measurements since Hubble is working so well. This has the potential to significantly increase our understanding of star formation.

The findings of the teams will be published in The Astrophysical Journal on September 8th. NASA's James Webb Space Telescope observations should be able to resolve lower-mass stars in the cluster, providing a more comprehensive view of the region. Astronomers will be able to repeat this experiment and measure the velocity of low-mass stars over Webb's lifetime. They might then compare the high-mass stars to the low-mass stars to determine the entire range of this nursery's dynamics.

Journal Information: Peter Zeidler et al, The Internal Line-of-Sight Kinematics of NGC 346: The Rotation of the Core Region, The Astrophysical Journal (2022). DOI: 10.3847/1538-4357/ac8004