This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Astronomers have discovered a faint population of young stars extending far beyond the known edge of the nearby spiral galaxy Messier 74. The finding suggests the galaxy is nearly twice as large as previously measured.
The new study was published Sept. 4 in Astronomy & Astrophysics. Over time, galaxies grow by accumulating gas from their surroundings. Because this newer gas spins faster relative to the center, it cannot collapse all the way to the core.
Instead, it settles into the outer disk, where it eventually sparks the formation of new stars. Astronomers have observed this growth, but whether it is smooth and gradual or occurs in fast, episodic bursts remains unclear. Mergers or interactions with satellite galaxies can also trigger bursts of star formation in the outskirts of galactic disks, making them grow bigger.
One way to identify such growth is the "extended ultraviolet disk" (XUV disk): UV light tracing young stars beyond a galaxy's traditional boundary as seen in optical light. But astronomers are still debating how to define this "optical boundary," making XUV disks difficult to classify. Messier 74 (M74), located roughly 30 million light-years from Earth, was already known to be an interesting case.
It has a grand-design spiral structure but shows several signs of stellar population buildup. Its unusually messy, warped and extended HI (neutral hydrogen gas) disk points to a recent accumulation of gas. Four supernovae have been detected in the galaxy, and a 2007 study flagged it as hosting an XUV disk.
In the new study, researchers led by Ignacio Ruiz Cejudo of the Institute of Astrophysics of the Canary Islands used deep optical imaging to spot a faint stellar population on the outskirts of M74. Using extremely long-exposure images (5.4–6.5 hours per filter) from a new telescope called the Transient Survey Telescope (TST) at Teide Observatory, they were able to detect much fainter light than standard optical surveys like the Sloan Digital Sky Survey (SDSS). Their work revealed an extremely faint, distinctly blue stellar structure extending 30 kiloparsecs (around 97,800 light-years) from the galaxy's center, far beyond the previously known disk radius of about 14 kiloparsecs (around 45,600 light-years)—nearly doubling the galaxy's size.
Extract — continue reading at the source.
