Discovery of new type of space dust excites astrophysicists

Infant galaxies in the early Universe may have developed much faster than previously thought, suggest new observations of ‘space dust’ from the James Webb Space Telescope.

The NASA mission is already rewriting much of what we thought we knew about the Universe and has now discovered a new ‘building block’ which could have created the first planets.

An international team observed the chemical signature of carbon-rich dust grains which existed just one billion years after the birth of the Universe. Similar signatures have only been observed in the much more recent Universe, attributed to complex, carbon-based molecules known as polycyclic aromatic hydrocarbons (PAHs).

It is not thought likely, however, that PAHs would have developed within the first billion years of cosmic time and raises the possibility of the existence of a different species of carbon-based molecule: possibly minuscule graphite or diamond-like grains produced by the earliest stars or supernovae.

“This discovery implies that infant galaxies in the early Universe developed much faster than we ever anticipated," said senior author Dr Renske Smit of Liverpool John Moores University's Astrophysics Research Institute. 

Cosmic dust is crucial to the evolution of the Universe, as dust clouds ultimately form the birthplaces for new stars and planets. Certain molecules will very consistently interact with specific wavelengths of light, allowing astronomers to tell the composition of dust by the wavelengths of light that it blocks.

The wavelength in this observation was around 217.5 nanometres – usually associated with dust seen on our own Milky way and ‘younger’ galaxies up to redshift ~ 3 [1]).  

Dr Joris Witstok, lead author from the University of Cambridge, said that according to current models, molecules of this type should not have formed by 1 billion years after the Big Bang. But he added that the feature observed by the team actually peaked at 226.3 nanometres a tiny difference but perhaps sufficient to indicate a different type of dust.  

“This slight shift in wavelength suggests we may be seeing a different mix of grains, for example graphite or diamond-like grains,” adds Witstok. “This could also potentially be produced on short timescales by Wolf-Rayet stars or supernova ejecta.”

With the advent of the James Webb Telescope, astronomers are now able to make very detailed observations of the light from individual dwarf galaxies, as Irene Shivaei of the University of Arizona stresses: “This discovery was made possible by the unparalleled sensitivity improvement in near-infrared spectroscopy provided by Webb, and specifically its Near-Infrared Spectrograph.”

The results have been published today in Nature.

Notes

[1] The Universe is expanding. The expansion is taking place at the fundamental spacetime level, which means that light travelling through the Universe is ‘stretched’ as the Universe expands. The earlier in the Universe the light originated, the more it will have been stretched by now. Practically speaking, this stretching of light means its wavelength becomes longer. This effect is known as cosmological redshift, because the colour red has the longest wavelength of all light visible to human eyes. Because of this, cosmological time is often not measured in years, but is indicated by the redshift of the observed light. The very local Universe — where the light we observe was emitted recently and has not been notably redshifted — has a low redshift. Conversely, redshift 7 corresponds to light that was emitted about 13 billion years ago, in the very early Universe.