Beautiful butterflies of stars

Here is a stunning collection of images of the Butterfly Nebula to celebrate new beginnings! This beautiful double lobed nebula forms briefly in a star's life after it has exhausted its fuel supply and casts off its outermost shells into shells of ionised gas as it dies.

The Butterfly Nebula NGC 6302. Credit: (Hubble, Webb, ALMA)

One could even say that stars like to go out in style with a fanfare. Nebulae such as these are supposedly called planetary nebulae, but have no relation to planets at all, so I tend not to use this term as it generates confusion. Instead, these form when stars between around 0.8 to 8 times the mass of the Sun shed the majority of their mass at the end of their lives. Stars can live for millions of years, yet this nebula phase can last as short as 20,000 years, a mere fleeting blink of an eye in cosmic terms. The Butterfly Nebula is bipolar, meaning it has two lobes, which spread out like the wings of a butterfly. The central star between the lobes is mostly blocked out by a band of dusty gas, in the shape of a doughnut with the star in the centre. Potentially, this doughnut of dust may be responsible for the nebula's lobed shape, as it prevents gas flowing outward from the star equally in a radial direction.

The first two images (left to right) were taken by the Hubble telescope. The first image shows the nebula in the optical wavelength, within the range human eyes can see. The second image was taken in infrared, a wavelength of light longer than human eyes can detect. There appear to be more background stars in the infrared image because longer infrared wavelength light is better able to pass through dust and gas than optical light, which is either scattered or blocked, giving the illusion in the first image that there are no background stars. The final image is taken by the current favourite tool in astronomy, the mighty Webb telescope (perhaps I am being biased here, but it does seem pretty popular at the moment), which is celebrating its 3rd year in the sky observing. This image zooms right into the centre of the nebula, revealing a star shrouded in dust at the centre. Sometimes, astronomers combine images taken by multiple telescopes in different wavelengths, as in this image, which has been supplemented with data from the Atacama Large Millimetre/submillimetre Array, a network of radio dishes in the Chilean desert which I hope to visit some day. 

Multiwavelength studies of the same stellar region can be very useful for astronomers, providing an insight into different details and stages of star formation. For example, long wavelength radio astronomy is best suited to cool regions of the interstellar medium and probing the birthplaces of stars. Getting shorter in wavelength, infrared is suited to slightly hotter radiation, such as observing young protostars and seeing how they sculpt their surrounding molecular clouds with stellar winds. Optical wavelengths are shorter still, and probe (most) stars when they are in what is known as the main sequence stage of their lives- the longest phase of their evolution, where they are burning hydrogen fuel, particularly the case for stars similar to the sun. Instruments such as the Chandra telescope can probe ultraviolet astronomy, such as the radiation emanating from very hot massive stars which can destroy surrounding molecules in the interstellar medium and halt future star formation, or to yet shorter wavelengths such as x-ray, which can be used to observe the remnants of violent stellar explosions, binary star systems, galaxy clusters or matter around black holes. 

While they are exquisite to look at, there is some fascinating science going on behind the pixels too.  Having done some digging, I discovered this research project was an international collaboration between scientists ranging from experts in spectroscopy observation to theoretical astrochemistry to stellar physics to nebular dynamics. Astronomers have found unexpected molecules in these stellar chemical laboratories. Astrochemistry, a close friend of astrophysics, probes the chemical processes going on around stellar regions, and is a rapidly growing field. Molecular behaviour informs our understanding of the physical processes going on around these pretty structures, with chemical signatures acting as a fingerprint of the history, present and possibly even the future of a stellar region. The possible chemistry that can occur is highly influenced by the star's temperature, as different molecules survive at different temperatures, and some are destroyed in intense UV radiation such as that present around this central star. Intriguingly, astronomers found unexpected detections of carbon molecules around the dying star, in a stellar environment where such molecules were not predicted to exist. However, extreme environments such as those around very hot stars (hundreds of thousands of degrees Celcius) can change the possible chemistry that can occur. There is great diversity in the complex molecules that can exist in space, and studies such as these may help astronomers expand their understanding of the environments in which carbon based molecules can form. This in turn has implications for habitable zones around stars, given that carbon is currently thought to be a fundamental building block for life. Following on from the previous article about my degree in Planetary Science and Life in the Universe at Cambridge last year, it can be seen that modern astronomy is becoming increasingly interdisciplinary, with astrophysics/chemistry/biology working together to unravel the secrets of the origins of matter and life in the universe.

Annotated and zoomed in, caption taken from Western News: There is a bright source at the centre of the image, labeled ‘dying star’. This is surrounded by greenish nebulosity and several looping lines in cream, orange and pink. One of these lines appears to form a ring oriented vertically and nearly edge-on around the bright source at the centre. This ring is labeled in several different places to indicate the near and far sides of a structure called the torus, a dust lane running along the torus and an area where the torus is ionised. Other lines trace out a figure eight shape. These lines are labeled to indicate the inner bubble as well as where the bubble intersects with the torus. Moving outward from these complex lines and green nebulosity, there is a section of red light on either side of the object, labeled ‘outer bubble’. The upper-right and lower-left corners of this image show a purple streak pointing out of the image. These purple streaks are labeled ‘jet’. Credit: ESA/Webb, NASA & CSA, M. Matsuura, ALMA (ESO/NAOJ/NRAO), N. Hirano, M. Zamani (ESA/Webb)