Dust, did someone say dust? When I hear about an astronomy article talking about dust, I always get drawn to read about it. Since my early career in astronomy, I have always been interested in dust because of its complexity and because we know it is responsible for many events in our Universe. It is found in star-forming regions, shielding the molecular gas that collapses to form stars. It is also found in debris disks around recently formed stars and is likely the seed for planet formation. Here on Earth, dust is responsible for the formation of clouds, and we have heard so many times that we are made of dust. However, the study of dust is quite complex, not only understanding its composition but also how it forms and how it survives many of the most violent events in the Universe.
The most recent observation of NGC 6946, made with the James Webb telescope, provides relevant information that can reveal how dust forms and how much of it exists in our Universe. In this case, a group of astronomers[1] explore the theory that Supernovae (SNe) explosions are a possible source of dust in the Universe. In their journal article published in the Monthly Notices of the Royal Astronomical Society and entitled “JWST observations of dust reservoirs in type IIP supernovae 2004et and 2017eaw,” Melissa Shahbandeh and a group of scientists took advantage of the great sensitivity of JWST in the long infrared bands to observe distant supernovae more than a year after their explosion, where it is more likely to measure the dust produced by these events.
The two supernovae studied by the team are 2004et, which exploded 18 years ago, and SN 2017eaw, which exploded five years ago. Both are Type IIP (or II Plateau) supernovae, which are likely the result of the rapid collapse of massive stars, which after exploding, remain bright with constant luminosity for an extended period of time of at least 100 days after maximum.
The image below is an observation of NGC 6946 from the Astronomy Section Rochester Academy of Science (ASRAS)[2], which shows the galaxy when the supernovae SN2004ET were discovered in 2004 by Stefano Moretti.
Source Image: https://www.rochesterastronomy.org/sn2004/sn2004et.html
When comparing this image with another image of the galaxy taken in 2008 with the Nicholas U. Mayall 4-meter Telescope at Kitt Peak National Observatory, we can clearly see how the bright source visible in the 2004 image has now disappeared.
Source image: https://webbtelescope.org/contents/media/images/2023/115/01H3D2YW8KJRXPEVYEXYCRRX1B?news=true
Why were they looking for dust in the remnants of supernovae? The main reason is to try to explain the amount of dust observed in distant galaxies[3]. Due to their distance, we know these are young galaxies and therefore could not produce all that dust through the most accepted mechanism, which is the envelopes of evolved low-mass star ejecta -- this stage of evolution happens at longer lifetimes than the ages of the observed galaxies. Also, because of its low temperature, as compared to stars, dust emits light in the infrared (IR) wavelengths. JWST does not only observe at these wavelengths but also can resolve the IR emission arising from supernovae in other galaxies, which is a great way to test this theory.
Melissa Shahbandeh[1] and a group of astronomers analyzed observations of these two well-known SNe remnants taken with the JWST/MIRI detector [4]. From these observations, the group determined that the remnants of these supernovae have considerable amounts of dust and therefore that SNe are potentially a significant source of dust in the Universe.
Reference [4]
In order to come up with this conclusion, they first explore several physical scenarios by considering where in the ejecta the peak of the IR observations is and its temperature. In this case, the temperature can be obtained by identifying the shape of the IR light that best fits the observations. The location and temperature can then help to determine if the dust was formed by condensing the material that the SN explosion ejected, or if it was pre-existing at the time of the SN explosion. Using dust models[5], they explore different parameters for the composition, size, and temperature of the dust, driving a lower limit for the dust mass produced by these two supernovae, which is between half to 15 times the mass of Jupiter.
This diagram is derived from the diagram of the dust production in SNe in references [5] and [1]
They also concluded that the observed dust temperatures, ∼100–150 K, indicate the dust was most likely produced after the SN explosion and survived the typical reverse shocks that occur in these supernovae[4]. However, since we only can see warm dust with the IR light that MIRI can observe, it is possible to conclude that the SNe will also produce colder dust as the ejecta continues to expand. If further observations detect that these SNs end up producing more than 1 times the mass of the sun in dust, then scientists might be able to explain the observed amount of dust in the early Universe. This, of course, is just a small piece of the puzzle in understanding the role that dust plays in many phenomena of our Universe, and more observations in IR and other light will be necessary to understand it.
References:
[1] Melissa Shahbandeh, Arkaprabha Sarangi, Tea Temim, Tamás Szalai, Ori D Fox, Samaporn Tinyanont, Eli Dwek, Luc Dessart, Alexei V Filippenko, Thomas G Brink 2023, Monthly Notices of the Royal Astronomical Society, Volume 523, Issue 4, Pages 6048–6060, https://doi.org/10.1093/mnras/stad1681
[2] https://www.rochesterastronomy.org/sn2004/sn2004et.html
[3] Maiolino, R., Schneider, R., Oliva, E. et al. A supernova origin for dust in a high-redshift quasar. Nature 431, 533–535 (2004). https://doi.org/10.1038/nature02930
[4]https://webbtelescope.org/contents/media/images/2023/115/01H3D0HJG0A3EXG56K45AY35EK?news=true
[5] Fox O. D., Chevalier R. A., Dwek E., Skrutskie M. F., Sugerman B. E. K., & Leisenring J. M. 2010, ApJ , 725, 1768 https://doi.org/10.1088/0004-637X/725/2/1768