[NTD News, Beijing time, July 03, 2024] American astronomers have used NASA’s James Webb Space Telescope (JWST) to deeply analyze the composition of the Crab Nebula, hoping to understand its origin and composition. The Crab Nebula was discovered by ancient people about 1,000 years ago.
In 1054 AD, Chinese astronomers observed a supernova explosion in the Crab Nebula near the constellation Taurus, about 6,500 light-years from Earth. The explosion was so bright that it could be seen during the day.
The Crab Nebula was the first object identified as the result of a supernova explosion. It is known for its crab-like appearance and has been one of the most studied objects since its discovery. Today, the Crab Nebula is no longer shining as brightly; it is a faint supernova remnant.
Astronomers have discovered that when a supernova explodes, most or even almost all of its material can be thrown outward at extremely high speeds to form a nebula. The Crab Nebula is composed of gas, dust, and high-speed outflow winds (flows in the interstellar medium). At its center is a rapidly rotating and highly magnetized neutron star (pulsar). This neutron star continuously ejects winds of high-energy particles to the surroundings, forming the bright pulsar wind nebula (PWN).
A neutron star is a neutron ball with a diameter of about 10 kilometers and an extremely high density. It is thought to be produced by the core of a star collapsing under the influence of gravity during a supernova explosion. It has a mass equivalent to that of an ordinary star (usually about 1.5 times the mass of the Sun). Neutron stars that regularly emit pulses of radiation are also called “pulsars.”
In the past, astronomers calculated the total kinetic energy of the Crab Nebula explosion based on the number and speed of the ejecta. However, the total energy of the explosion was relatively low (less than one-tenth of a normal supernova). Therefore, it was previously believed that the progenitor stars of the Crab Nebula were caused by “electron capture type” (ECSN) supernova explosions, rather than typical “iron core collapse” supernova explosions.
It is generally believed that an “electron capture type” supernova explosion is a rare explosion in which the supernova core is mainly composed of oxygen, neon, and magnesium, rather than a typical iron core. After these oxygen, neon, and magnesium atoms become too dense in the core, they begin to absorb surrounding electrons, causing the core pressure to rapidly decrease. This ultimately causes the core to rapidly collapse and produce a stellar explosion.
However, there are some inconsistencies between predictions of electron capture supernovae and past observations of the Crab Nebula. Theoretically, it is predicted that the abundance of iron-nickel (Ni/Fe) in the core of its supernova should be much higher than that of the core of the sun.
To reduce the uncertainty in observing the progenitor stars of the Crab Nebula, the astronomical research team at Princeton University in the United States used the mid-infrared instrument (MIRI) and near-infrared camera (NIRCam) in the JWST space telescope. They used these instruments’ spectroscopic capabilities to target two regions within the inner filaments of the Crab Nebula for multiple detections and observations, hoping to shed light on its origins.
The research results were published in the Astrophysical Journal Letters on June 20.
They began with a smaller imaging sample of argon, neon, and oxygen at MIRI nuclear magnetic resonance (MRS). This instrument uses 4 different filters and a variety of different imaging filters to make the image of the Crab Nebula more three-dimensional and clear during the synthesis process. It also makes the image have different colors, which helps astronomers identify its appearance better.
Additionally, the team used MIRI’s spectroscopic analysis capabilities to sample iron (Fe), sulfur (S), dust, and PWN emission lines. This allowed them to create a more reliable estimate of the nickel-iron abundance ratio.
The MIRI and NIRCam composite image of the Crab Nebula shows red-orange representing sulfur, blue showing iron, and yellow-white and green showing dust emission. NIRCam observed that the smoky white color comes from the Pulsar Wind Nebula (PWN).
The team also used the JWST telescope to map warm dust emissions. This was combined with data from the Herschel Space Observatory on cooler dust grains to create a comprehensive picture of the high-resolution dust distribution. The image’s outermost filaments contain relatively warm dust, while cooler grains are generally closer to the center.
They also used the JWST telescope to detect the iron-nickel ratio in two selected areas of the Crab Nebula and observe the distribution of these materials throughout space. The results show that the iron-nickel richness ratio is between 0.156 and 0.277, which is 2.8 to 5.2 times higher than the iron-nickel richness ratio of the sun (0.053). This data is, however, far lower than the 50 to 75 times estimated by scientists in the past.
The data observed by the JWST telescope this time reveal unprecedented details of the Crab Nebula and our understanding of the abundance of iron and nickel ejected from the PWN pulsar nebula. Scientists compared the revised values with the electron capture supernova synthesis model and found that the abundance of iron and nickel in the Crab Nebula is consistent with the theory of “low-mass iron core collapse” explosion or “electron capture supernova” explosion.
“Low-mass iron core collapse” stems from astronomers’ new understanding of iron core collapse supernovae. Astronomers now believe that lower-mass stars may also produce low-energy iron core-collapse explosions.
Tea Temim, an astronomer at Princeton University in the United States, told NASA, “The data collected by the JWST telescope on the Crab Nebula has expanded and may explain the formation of the Crab Nebula. The current observation of the gas composition in space shows that supernovae do not require electron capture to explode, so they can be explained by low-mass iron core collapse supernovae.”
“Where you see dust in the Crab Nebula is interesting because it is different from other supernova remnants, such as Cassiopeia,” said astronomer Nathan Smith of the University of Arizona’s Steward Observatory. “The dust in objects A and 1987A is usually located in the center, but the dust in the Crab Nebula is found in the dense fibers of the outer shell.”
Martin Laming, co-author of the paper and the U.S. Naval Research Laboratory, said, “Currently, the Webb telescope’s spectroscopic data covers two small regions of the Crab Nebula, so it is important to study more debris and determine any spatial changes. “It would be interesting if we could identify other elements such as cobalt or germanium.”
Scientists said that they will continue to study the data collected by the JWST telescope in the future and combine it with other observations to understand the formation process of the Crab Nebula and other celestial objects.
(Reprinted from The Epoch Times/Editor: Ye Ping)
Unveiling the Secrets of the Crab Nebula: James Webb Telescope Reveals New Insights
The Crab Nebula: A Supernova’s Legacy
The Crab Nebula, a celestial spectacle located about 6,500 light-years away in the constellation Taurus, has captivated astronomers for centuries. First observed in 1054 AD by Chinese astronomers, this nebula is the remnant of a supernova explosion, a cataclysmic event that marked the death of a massive star. Its distinctive crab-like appearance, a testament to the chaotic aftermath of the stellar explosion, has earned it its name.
Understanding the Crab Nebula’s Composition: Unveiling its Origins
The Crab Nebula is a complex tapestry woven from gas, dust, and high-speed winds. Residing at its heart is a rapidly rotating neutron star, a celestial object with an incredibly dense core, packed with neutrons. This neutron star, also known as a pulsar, continuously ejects high-energy particles, creating a pulsar wind nebula (PWN) that illuminates the surrounding space.
The Mystery of the Crab Nebula’s Energy
Previously, astronomers calculated the Crab Nebula’s total kinetic energy based on the speed and quantity of the ejected material. However, the energy measured was significantly lower than expected for a typical supernova. This led scientists to believe that the Crab Nebula’s progenitor star underwent an "electron capture" supernova explosion, a rare event where the star’s core is primarily composed of oxygen, neon, and magnesium.
However, discrepancies existed between the predictions of electron capture supernovae and observations of the Crab Nebula. These discrepancies involved the abundance of iron-nickel (Ni/Fe) in the nebula’s core, which theoretical models predicted to be much higher than observed.
James Webb Telescope Delivers New Insights
To clarify the mysteries surrounding the Crab Nebula’s formation, a team of astronomers at Princeton University employed the James Webb Space Telescope (JWST) to analyze its composition in unprecedented detail. Using the Mid-Infrared Instrument (MIRI) and Near-Infrared Camera (NIRCam) on board the JWST, they focused on two regions within the inner filaments of the Crab Nebula.
The team used MIRI’s spectroscopic capabilities to accurately analyze the abundance of iron (Fe), sulfur (S), dust, and PWN emission lines. They also utilized MIRI’s nuclear magnetic resonance (MRS) to observe argon, neon, and oxygen, creating a three-dimensional composite image with enhanced clarity.
A Glimpse into the Crab Nebula’s Inner Workings
The JWST data revealed a fascinating picture. Red-orange hues represent sulfur, while blue indicates iron. Yellow-white and green indicate dust emission, while smoky white portrays the Pulsar Wind Nebula (PWN).
The team also used the JWST to map the distribution of warm dust, combining these observations with data from the Herschel Space Observatory to obtain a comprehensive picture of the Crab Nebula’s dust distribution. The image reveals that the outermost filaments contain relatively warm dust, while cooler dust grains are found closer to the center.
New Data Challenges Existing Theories
One of the most significant findings from the JWST observations was the iron-nickel ratio in the two selected areas of the Crab Nebula. This ratio was found to be between 0.156 and 0.277, which is significantly higher than the sun’s iron-nickel ratio (0.053). This discovery contradicts previous estimates suggesting a much higher iron-nickel ratio.
The JWST data also indicated that the abundance of iron and nickel in the Crab Nebula aligns with the theory of "low-mass iron core collapse" explosions or "electron capture supernovae." This suggests that the Crab Nebula’s progenitor star may have experienced a less energetic iron core collapse than initially thought.
A New Perspective on Supernovae: Expanding Our Understanding
This new insight, derived from JWST observations, indicates that supernovae may not always require electron capture to explode. The possibility of low-mass iron core collapse explosions opens up new avenues for understanding stellar evolution.
The Future of the Crab Nebula’s Exploration
Future studies will combine the JWST’s data with other observations to provide a more complete picture of the Crab Nebula’s formation. Scientists are particularly eager to analyze other elements like cobalt and germanium, which could provide further clues about the nebula’s complex history.
The Crab Nebula, an object once shrouded in mystery, has become a beacon of understanding, illuminating new pathways in our journey to comprehend the universe. With each new observation, we refine our understanding of the celestial wonders that surround us, pushing the boundaries of our knowledge and awe.