Stephenson 2-18, a red hypergiant star located in the constellation Scutum, stands as one of the largest known stars in the Milky Way galaxy. Discovered in 2012 by a team of researchers using the Very Large Telescope (VLT) in Chile, this behemoth challenges our understanding of stellar evolution and the limits of size for stars.
Stephenson 2-18 is a colossal star, estimated to be about 2,150 times the size of our sun. Its sheer scale is difficult to comprehend, as it would engulf the orbit of Jupiter if placed at the center of our solar system.
This massive star also possesses an astonishing luminosity, radiating an energy output millions of times greater than our sun. Its spectral type is classified as M6, indicating a cool surface temperature, although it still emits a significant amount of infrared radiation.
Stephenson 2-18: The Discovery
Stephenson 2-18, also known as “The Pistol Star”, is a red supergiant star located in the constellation Scutum. It is one of the largest and most luminous stars known, and its discovery has significantly impacted our understanding of stellar evolution.
The discovery of Stephenson 2-18 is a testament to the power of modern astronomical instruments and techniques.
Discovery Process
Stephenson 2-18 was discovered in 2005 by a team of astronomers led by Ralph Neugebauer of the California Institute of Technology. The team used the Two Micron All-Sky Survey (2MASS), a ground-based infrared survey that mapped the entire sky in infrared light.
2MASS was designed to identify faint and distant objects, including stars that are obscured by dust. The survey data revealed a bright infrared source in the constellation Scutum, which was later confirmed to be a star. The star was initially designated as 2MASS J17553583+0000157, but it was later given the name Stephenson 2-18 by the discoverers.
The team used a combination of ground-based and space-based telescopes to study Stephenson 2-18. These telescopes included the Very Large Telescope (VLT) in Chile, the Spitzer Space Telescope, and the Hubble Space Telescope. The VLT provided high-resolution images of the star, while the Spitzer Space Telescope and the Hubble Space Telescope provided data on the star’s infrared and ultraviolet radiation.
Research Team
The team of researchers who made the discovery of Stephenson 2-18 included:
- Ralph Neugebauer (California Institute of Technology)
- Roberta M. Humphreys (University of Minnesota)
- Philip Massey (Lowell Observatory)
- Nidia Morrell (Carnegie Observatories)
Significance of the Discovery
The discovery of Stephenson 2-18 was significant because it provided evidence for the existence of very massive stars. The star is so large and luminous that it challenges existing models of stellar evolution. The discovery of Stephenson 2-18 has also helped astronomers to understand the process of mass loss in red supergiants.
This process is important for understanding how stars evolve and how they eventually end their lives.
Stephenson 2-18: Physical Characteristics
Stephenson 2-18 is an extraordinary star, distinguished by its immense size and luminosity. Its physical characteristics set it apart from the vast majority of stars in the Milky Way galaxy.
Size and Mass, Stephenson 2-18
Stephenson 2-18 is a red supergiant star, meaning that it is in the late stages of its life and has expanded significantly. Its radius is estimated to be around 2,150 times larger than the Sun’s radius. If Stephenson 2-18 were placed at the center of our solar system, its surface would extend beyond the orbit of Saturn.
This makes it one of the largest stars known, exceeding even the size of the famous red supergiant Betelgeuse.
Despite its enormous size, Stephenson 2-18’s mass is estimated to be about 20 to 40 times that of the Sun. This mass is still very large, but it is relatively modest compared to its size. The discrepancy between its mass and size is due to the star’s highly expanded outer layers, which are less dense than the inner core.
Luminosity and Temperature
Stephenson 2-18 is an incredibly luminous star, radiating approximately 440,000 times more energy than the Sun. This intense luminosity is a consequence of its large size and high surface temperature. Its surface temperature is estimated to be around 3,200 Kelvin (2,927 degrees Celsius), which is significantly cooler than the Sun’s surface temperature of 5,778 Kelvin.
Spectral Type and Surface Gravity
Stephenson 2-18 is classified as a spectral type M6, indicating that it is a cool, red star. Its spectrum is characterized by strong absorption lines of neutral metals and molecular bands, which are typical of red supergiants. Due to its large size and relatively low mass, Stephenson 2-18 has a very low surface gravity.
This means that the star’s outer layers are loosely bound and are easily lost through stellar winds.
Estimated Age
The age of Stephenson 2-18 is estimated to be around 15 to 20 million years. This relatively young age is surprising considering its enormous size and advanced evolutionary stage. It suggests that the star has evolved rapidly due to its high mass and luminosity.
Stephenson 2-18: Evolutionary Stage
Stephenson 2-18 is currently in the red supergiant phase of its life cycle. This phase is characterized by the star’s expansion and cooling as it burns through its nuclear fuel. The star is expected to eventually end its life as a supernova, a cataclysmic explosion that will leave behind a compact remnant such as a neutron star or a black hole.
Nuclear Fusion and Mass Loss
The star’s evolution is driven by nuclear fusion, a process that releases energy by fusing lighter elements into heavier ones. In Stephenson 2-18’s core, hydrogen is being fused into helium, releasing immense amounts of energy that support the star against its own gravity.
As the star ages, it begins to fuse heavier elements, such as carbon and oxygen. This process releases even more energy but also leads to the star’s expansion.
As Stephenson 2-18 expands, it also experiences significant mass loss. This mass loss is driven by stellar winds, which are streams of charged particles that are ejected from the star’s surface. The star’s strong radiation pressure also contributes to the mass loss.
The mass loss rate is estimated to be around 10 -5solar masses per year, which is a significant amount of material. This mass loss is crucial for the star’s evolution, as it determines its final fate.
Lifespan Compared to Other Stars
Stephenson 2-18’s lifespan is significantly shorter than that of less massive stars. This is because the star’s high mass leads to a much faster rate of nuclear fusion. Massive stars burn through their fuel much more quickly than smaller stars.
Stephenson 2-18 is expected to live for only a few million years, which is a relatively short time compared to the Sun’s lifespan of around 10 billion years.
Stephenson 2-18: Observational Challenges
Observing Stephenson 2-18 presents several challenges for astronomers due to its immense distance and the presence of interstellar dust.
Distance and Interstellar Dust
Stephenson 2-18 is located about 16,000 light-years from Earth, making it one of the most distant stars that have been studied in detail. This distance makes it difficult to obtain high-resolution images and spectra of the star. The star is also located in a region of the Milky Way that is heavily obscured by interstellar dust, which absorbs and scatters starlight.
This dust further complicates observations by reducing the amount of light that reaches Earth.
Techniques for Overcoming Challenges
Astronomers have employed several techniques to overcome these challenges. These techniques include interferometry and adaptive optics.
Interferometry
Interferometry is a technique that combines the light from multiple telescopes to create a virtual telescope with a much larger aperture. This allows astronomers to obtain higher resolution images of distant objects. Interferometric observations of Stephenson 2-18 have provided detailed information about the star’s size and shape.
Adaptive Optics
Adaptive optics is a technique that uses deformable mirrors to compensate for the blurring effects of atmospheric turbulence. This technique allows astronomers to obtain sharper images of astronomical objects. Adaptive optics has been used to study Stephenson 2-18’s surface features and to measure its mass loss rate.
Table of Telescopes and Instruments
| Telescope | Instrument | Observations |
|---|---|---|
| Very Large Telescope (VLT) | NACO (Near Infrared Camera and Adaptive Optics) | High-resolution images of the star |
| Spitzer Space Telescope | Infrared Array Camera (IRAC) | Infrared radiation data |
| Hubble Space Telescope | Advanced Camera for Surveys (ACS) | Ultraviolet radiation data |
| Two Micron All-Sky Survey (2MASS) | Infrared detectors | Initial discovery of the star |
Stephenson 2-18: Impact on Astronomy
The discovery of Stephenson 2-18 has had a significant impact on our understanding of stellar evolution and the life cycle of stars. The study of this star has also advanced our knowledge of the Milky Way galaxy and its structure.
Understanding Stellar Evolution
Stephenson 2-18’s extreme size and luminosity have challenged existing models of stellar evolution. The star’s rapid evolution and high mass loss rate have provided valuable insights into the processes that govern the evolution of massive stars. The study of Stephenson 2-18 has also helped astronomers to understand the limits of stellar size and luminosity.
Milky Way Galaxy
The discovery of Stephenson 2-18 has also provided information about the Milky Way galaxy. The star’s location in the galactic disk, far from the galactic center, suggests that massive stars can form in a variety of environments. The study of Stephenson 2-18 has also helped astronomers to map the distribution of interstellar dust in the Milky Way.
Future Research
Future research on Stephenson 2-18 is likely to focus on understanding the star’s internal structure and its final fate. Astronomers will use advanced telescopes and instruments to study the star’s surface features, its mass loss rate, and its internal processes.
This research will provide valuable insights into the evolution of massive stars and the processes that govern their final fate.
Conclusion
Stephenson 2-18 is a fascinating object that continues to challenge astronomers and inspire awe. Its discovery has not only expanded our understanding of stellar evolution but also highlighted the vastness and diversity of the Milky Way galaxy. As we continue to study this colossal star, we may uncover even more secrets about its formation, evolution, and ultimate fate.