More than 500,000 stars glow in shades of red, white, and blue in a spectacular new image captured by NASA’s Hubble Space Telescope. Released in celebration of the United States’ 250th anniversary, the image features Messier 3 (M3), one of the Milky Way’s largest globular clusters.
Globular clusters are dense, spherical groups of stars held together by gravity. Their stars formed from the same cloud of gas at roughly the same time, making them some of the oldest stellar populations in the galaxy. Astronomers have identified about 150 globular clusters orbiting in the outer regions of the Milky Way.
Messier 3 Stands Out Among Globular Clusters
M3 is remarkable not only because of its enormous size but also because of its location and stellar population. It lies relatively far from the center of the Milky Way and contains more than 240 RR Lyrae variable stars, more than any other known globular cluster in our galaxy.
These ancient variable stars are especially valuable to astronomers because their brightness changes in a predictable way. By comparing how bright they truly are with how bright they appear from Earth, scientists can accurately determine their distance. The process is similar to estimating how far away a car is at night by knowing the brightness of its headlights.
Ancient Stars That Appear Young
The cluster also contains about 70 identified candidates for a rare type of star known as a blue straggler. These unusually bright, blue stars appear much younger than the older, redder stars that dominate globular clusters.
In fact, M3 was the first globular cluster where blue stragglers were discovered. Astronomers believe these stars likely gained material from nearby companion stars through gravitational interactions. That extra mass effectively rejuvenated them, causing them to shine hotter, bluer, and appear younger than they actually are.
A Possible Cosmic Merger
Scientists think M3’s unusual properties may be the result of an ancient merger. The cluster contains two distinct populations of stars, suggesting it may have formed when two globular clusters combined into one.
Those two clusters are thought to have originally belonged to the same dwarf galaxy before that smaller galaxy was eventually absorbed by the Milky Way.
Hubble Helps Reconstruct the Milky Way’s History
Hubble has observed M3, also known as NGC 5272, multiple times over the years, allowing astronomers to study its complex structure and unusual stellar population in greater detail.
In this latest image, blue represents shorter wavelengths of visible light, while red corresponds to longer visible wavelengths along with some near-infrared light. The colors are assigned using standard Hubble image processing methods to accurately represent the wavelengths recorded through the telescope’s filters. Because a star’s color is closely tied to its temperature, the blue stars in the image are hotter, while the red stars are cooler.
The image is part of a Hubble Treasury program that aims to observe roughly half of the Milky Way’s known globular clusters. By studying these ancient stellar systems, astronomers hope to build a detailed timeline of how our galaxy formed and evolved.
After more than three decades in operation, Hubble remains one of NASA’s flagship observatories. Working alongside missions such as the James Webb Space Telescope and the upcoming Nancy Grace Roman Space Telescope, it continues to help scientists assemble an increasingly complete picture of the universe.
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