The Hubble Space Telescope has revealed a breathtaking view of the huge globular cluster NGC 1651, located 162,000 light-years away in the Large Magellanic Cloud. This dense ball of stars, also known as ESO 55-30 or LW 12, spans 120 light-years in diameter and is one of the most massive star clusters known.
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What are globular clusters?
Globular clusters are spherical collections of stars that are tightly bound together by gravity. They typically contain hundreds of thousands to millions of stars packed into a region just 10 to 300 light-years across. Some key facts about globular clusters:
- The Milky Way galaxy hosts over 150 globular clusters, with more possibly hidden behind its disk
- Globular clusters are among the oldest known objects in the Universe
- They are often associated with the most ancient parts of galaxies
These dense stellar cities provide astronomers with valuable insights into the early formation and evolution of galaxies. By studying their ages, compositions, and structures, scientists can piece together the history of the Universe.
NGC 1651: A colossal stellar city
First discovered in 1834 by astronomer John Herschel, NGC 1651 is a massive globular cluster residing in the constellation Mensa. It is part of the Large Magellanic Cloud (LMC), the biggest and brightest satellite galaxy of the Milky Way.
| Property | Value |
|---|---|
| Distance | 162,000 light-years |
| Diameter | 120 light-years |
| Alternate names | ESO 55-30, LW 12 |
| Constellation | Mensa |
| Host galaxy | Large Magellanic Cloud |
NGC 1651’s impressive size and luminosity make it stand out even among the LMC’s rich population of star clusters. Its great distance means that it appears much smaller in the sky than many of the Milky Way’s globular clusters, despite its large physical size.
Hubble’s unique view of NGC 1651
The incredibly sharp view of NGC 1651 was captured by the Hubble Space Telescope’s Wide Field Camera 3 (WFC3) in both visible and near-infrared light. The cluster’s stars completely fill Hubble’s field of view, showcasing the telescope’s ability to resolve individual stars within such a distant and compact object.
Astronomers explain that Hubble cannot zoom in on celestial targets like typical cameras:
“A common misconception is that Hubble and other large telescopes manage to observe wildly differently sized celestial objects by zooming in on them, as one would with a specialized camera here on Earth. However, whilst small telescopes might have the option to zoom in and out to a certain extent, large telescopes do not.” – Hubble astronomers
Instead, Hubble’s instruments each have a fixed field of view that determines the size of sky captured in a single exposure. WFC3’s ultraviolet/visible channel, for instance, sees an area only 1/12 the width of the full moon. Larger objects are imaged by stitching multiple exposures together into panoramic mosaics.
The reason Hubble can image both nearby star clusters and faraway galaxies is their varying distances from Earth – more distant objects appear smaller, so a physically large galaxy far away can look the same size as a much closer but intrinsically smaller globular cluster.
A galactic neighbor photobombs the image
Eagle-eyed viewers may notice a small spiral galaxy peeking into frame at the left edge of the cluster image. While certainly much more physically extended than NGC 1651, its extreme distance places it at a similar apparent size. Such “cameo appearances” by background galaxies are not uncommon in deep Hubble images, hinting at the vast scale of the Universe beyond the cluster.
Unraveling the mysteries of the early Universe
NGC 1651’s great age and well-resolved stellar population make it a valuable target for studies of stellar evolution and the early history of galaxies. Astronomers can measure the colors and brightness of its stars to construct a Hertzsprung-Russell diagram, a key tool for understanding how stars of different masses progress through their lifecycles. The distribution of stellar types within the cluster holds clues to the environments in which the first generations of stars formed over 13 billion years ago.
Globular clusters like NGC 1651 are relics of the early Universe, preserving information about the conditions that existed when galaxies first assembled. With Hubble and the next generation of telescopes, astronomers will continue probing these ancient stellar cities, uncovering new insights into the story of our cosmos.
As the renowned astronomer Carl Sagan once said:
“Imagination will often carry us to worlds that never were. But without it, we go nowhere.”
Hubble’s view of NGC 1651 sparks the imagination, inviting us to ponder our origins and our place in the grand tapestry of the Universe.
