Jellyfish Nebula
| Polish version is here |
The constellation of Gemini is most closely associated with Castor and Pollux, two bright stars that represent the heads of the mythological brothers. But it is also worth looking at the part of the sky that corresponds to their feet. Two of the stars in this region are Mu Geminorum (μ Gem) and Eta Geminorum (η Gem). The first is now known as Tejat, formerly Tejat Posterior, meaning the Rear Foot. The latter is called Propus, formerly Tejat Prior, which means the Front Foot.
Between these two stars lies a fascinating region of the Milky Way. It contains clouds of gas associated with the H II region S249, the faint emission nebula IC 444 and, most notably, the Jellyfish Nebula, known to astronomers as IC 443 or Sh2-248, among other interesting objects. At first glance, its filamentary structure might look like that of a normal emission nebula illuminated by radiation from nearby stars. But what we are actually seeing is the remnant of the violent death of a massive star.
IC 443 was discovered photographically by German astronomer Max Wolf on September 25, 1892. IC 443 lies about 5,000-6,000 light-years from Earth. Published distance estimates vary, partly because the region is complex and the exact spatial relationships between its individual components are difficult to determine. At this distance, IC 443 has a physical diameter of about 70 light-years.
The Jellyfish Nebula is a supernova remnant, probably from a Type II supernova. Such explosions happen at the end of the life of a massive star, when nuclear reactions in the star's core can no longer produce enough pressure to balance gravity. The core then collapses in a very short time, while the outer layers of the star are ejected at enormous speeds. This creates a shock wave that travels through the surrounding interstellar medium. The gas is compressed and heated, causing it to glow.
The date of the explosion that formed IC 443 has long been debated. Estimates of the remnant's age vary from about 3,000 years to 35,000 years, depending on the model used. More recent models suggest an age of around 8,000-9,000 years. The uncertainty remains considerable because IC 443 is expanding through a highly nonuniform environment rather than into empty space. The shock wave encounters clouds of very different densities, so different parts of the nebula evolve at very different rates.
In fact, the present-day appearance of IC 443 is not simply the result of the original explosion. Instead, its shape has been strongly influenced by thousands of years of interaction between the shock wave and the inhomogeneous interstellar medium, a process that is still continuing today. The nebula is expanding into a region containing molecular clouds, neutral hydrogen, and material left behind by earlier stages in the evolution of massive stars. In some directions, the shock wave can move relatively freely, while in others it is suddenly slowed by dense gas.
Observations
January 30, 2025, around 09:00 PM - Jaworzno
urban conditions, high level of light pollution
It was quite chilly that night, but the sky was perfectly clear. Despite the cold, conditions like these make observing a real pleasure. Even under heavily light-polluted city skies, I managed to image the Jellyfish Nebula (Photo 1).
As seen from Earth, the Jellyfish Nebula spans about 50 arcminutes, making it noticeably larger than the disk of the full Moon. However, this does not mean it is an easy target for observation. Its light is spread out over a large area, and its individual filaments have a low surface brightness. Visually, IC 443 remains an object that requires a dark sky, a suitable filter, and a telescope with a large aperture. Much more detail can be captured photographically, especially by stacking many long exposures.
For a long time, astronomers searched for the dense, fast-spinning stellar core, or pulsar, that should have been left behind by the supernova that gave rise to the nebula. Observations made with the Chandra telescope led to the identification of such an object on the southern edge of the nebula. It is a young neutron star designated CXOU J061705.3+222127. The diffuse X-ray emission around this object suggests the direction of its motion.
Photo 1 Parameters:
- Total exposure time: 130 minutes (stack of 130 RAW frames at 60s each, using an appropriate number of dark, bias, and flat frames)
- ISO: 1600
- Maksutov-Cassegrain telescope (100/1400), prime focus exposure
- A filter was used to reduce the effects of artificial light pollution and atmospheric glow
- Mount: equatorial mount with tracking, aligned using the drift method and controlled by a custom-built system.
Further readings:
- Asaoka I., Aschenbach B., An X-ray study of IC 443 and the discovery of a new supernova remnant by ROSAT, Astronomy and Astrophysics, vol. 284, 1994, pp. 573-582
- Rho J., Petre R., Mixed-Morphology Supernova Remnants, The Astrophysical Journal Letters, vol. 503, nr 2, 1998, pp. L167-L170
- Chevalier R.A., Supernova Remnants in Molecular Clouds, The Astrophysical Journal, vol. 511, nr 2, 1999, pp. 798-811
- Olbert C.M., et al., A Bow Shock Nebula around a Compact X-Ray Source in the Supernova Remnant IC 443, The Astrophysical Journal Letters, vol. 554, nr 2, 2001, pp. L205-L208
Marek Ples