The James Webb Space Telescope has made an astounding discovery in a galaxy
hanging out in the early Universe, less than 1.5 billion years after the Big
Bang.
From light that traveled for over 12 billion years from a galaxy known as
SPT0418-47, astronomers teased out the spectral signal of complex molecules
– the polycyclic aromatic hydrocarbons (PAHs) that make up some of the dust
grains in the clouds that drift between the stars, soaking up the light and
re-emitting it at infrared wavelengths.
This dust suggests a rapid rate of star formation, which is typical for a
galaxy from this early era of the universe. But the dust is not evenly
distributed, and that suggests that this star creation may be traced to
multiple areas within the galaxy, according to a team led by astronomer
Justin Spilker of Texas A&M University.
And the capacity to perform such a comprehensive survey of such a distant
galaxy is honestly pretty danged mind-blowing.
"Here we present James Webb Space Telescope observations that detect the
3.3-micrometer PAH feature in a galaxy observed less than 1.5 billion years
after the Big Bang.
According
to the researchers, star formation predominates infrared emission throughout
the galaxy rather than black hole accretion because of the high equivalent
width of the PAH feature.
"Our observations demonstrate that differences in emission from PAH
molecules and large dust grains are a complex result of localized processes
within early galaxies."
Despite its lofty tone,
polycyclic aromatic hydrocarbons
are not extremely uncommon. They are as prevalent as soot on Earth. because
of the soot on them. They belong to a group of organic compounds that can
develop when organic matter is compressed and heated and contain a ring of
carbon atoms. Coal includes PAHs; so does smoke, smog, and crude oil.
As far as we know, the majority of the PAHs in the universe have
non-biological origins, but the origins of PAHs can also be non-biological.
And there are a lot of them out there.
Previous work estimates roughly 15 percent of all carbon between the stars in galaxies
like ours is wrapped up in PAHs. They are regarded as a pretty accurate
tracer of star formation, with the majority of that material
drifting between the stars
as dust in the interstellar medium.
Although we have found
PAHs in other galaxies, it is much more difficult to find them in very distant galaxies. These
molecules absorb light and re-emit it in infrared wavelengths, and previous
infrared telescopes had vastly limited sensitivity and coverage. However, we
now have the JWST, the most powerful space telescope ever built, strongest
in infrared wavelengths.
But on its own, that isn't nearly enough. To make such an in-depth
observation, JWST had to make use of gravitational lensing, a peculiarity of
physics. This is a gravitational curvature of space-time that occurs around
massive objects in the Universe. Imagine a bowling ball put on a trampoline:
In reaction to the weight, the trampoline's fabric expands and warps.
Space-time does something similar around massive objects such as galaxies
and galaxy clusters, but there's a bonus. Because space-time is distorted
and stretched, any light moving through it likewise becomes deformed,
amplified, and occasionally duplicated. By effectively using these lenses as
a form of cosmic magnifying glass, we can greatly increase the power of our
telescopes.
Between us and SPT0418-47 is another galaxy, at a distance of around 3
billion light-years, providing that lensing oomph. This means when JWST took
observations of the galaxy as part of the
TEMPLATES
Early Release Science program, it was able to get enough detail that Spilker
and his colleagues could tease out the spectral signature of the light
emitted by PAHs at a mid-infrared wavelength of 3.3 micrometers.
This constitutes the most distant detection to date of complex aromatic
molecules, and although there's a lot we still don't know – the reason for
the uneven distribution of PAHs throughout the galaxy is unknown – it bodes
excitingly well for future studies of the evolution of galaxies in the early
Universe.
The research has been published in
Nature.
