22 | New Scientist | 5 October 2019
W
E KNOW the universe
doesn’t revolve around
us. But parts of it
do, like household dust. This
continuously reproducing filth
is comprised of skin cells, hair,
clothing fibres, dirt from outside,
dust mites, bacteria and chemicals
that can stick to any of these items.
As a child, one of my weekly
chores was dusting the house. If
you had told 12-year-old me that,
at 37, I would find dusting one of
the most comforting things I do
at home, I would have been very
concerned about exactly how
awful adulthood is. But perhaps
I might have worried less if I had
also been told that with adulthood
would come knowledge of cosmic
dust, which is all over the universe
and absolutely does not revolve
around us.
Space dust is part of a
fascinating life cycle of structure
formation in the universe: the
emergence of stars and planets,
as well as their deaths. In the very
early universe, gravity caused
hydrogen and helium gas to
collapse into objects that often
became densely packed enough to
ignite nuclear hydrogen burning,
which leads to star formation. The
nuclear chain reactions that occur
in stars produce elements heavier
than hydrogen and helium, like
carbon, nitrogen and oxygen.
Even heavier elements, like neon
and titanium, are made in the
supernova explosions that can
occur at the end of a star’s life.
These explosions blow stardust
made of these elements – most
commonly silicon and carbon –
out into the universe. Some of it
leads to solar system formation,
producing the extrasolar planets
we are increasingly capable of
observing. In the case of our
local star, the sun, that solar
system sprouted life on the
third-innermost planet, Earth.Some of the dust helps form
the next-generation stars that
burn a little differently than their
forebears because some of the
elements they contain are heavier.
One thing cosmic dust does have
in common with household dust is
that it can be annoying. An ongoing
issue in astronomy observations
is figuring out how to learn about
objects – from planets to stars –
that are obscured by cosmic dust
in what we call our line of sight,
the path of light travelling from
that object to our telescope. Light
passing through cosmic dust
interacts with its particles. The
dust will sometimes absorb andscatter the light, dimming the
object’s brightness, although this
can also offer valuable insight
into the size of the dust particles.
Like household dust, cosmic
dust can lead to misinterpretations
of what we are viewing. Your
black television stand can end
up looking grey if you don’t clean
it. Similarly, cosmic dust can get
mistaken for something else.
Just five years ago, researchers on
the BICEP2 experiment revealed
they had detected gravitational
waves, ripples in space-time,
from the universe’s first second
of existence. It turned out that
instead they had seen dust.
The mistaken announcementoccurred because they hadn’t
properly subtracted dust out of
their data. In other words, dust
can really get in the way of taking
a good, clean picture.
At the same time, studying
cosmic dust is a critical part of
understanding how objects form
in the cosmos. While most of the
matter in the universe is probably
in the form of dark matter, most
of the visible matter is in the form
of interstellar dust, not in compact
objects like stars and planets.
Thus, insight into large-scale
structures like galaxies requires an
understanding of dust dynamics.
One galaxy we would really like to
understand is ours, the Milky Way.
But we face challenges in trying to
comprehend it because of the way
dust obscures our view, so looking
at other examples is important.
It is good to have neighbours.
The Milky Way is part of what
is known as the Local Group,
a collection of galaxies whose
largest members are our own
and Andromeda. By looking at the
patterns of dust in Andromeda, we
can gain exciting insight into our
own corner of the universe. Ant
Whitworth at Cardiff University
in the UK recently led a team in
doing just that, using data from
the Herschel Space Observatory.
Herschel, named after British
astronomers and siblings Caroline
and William Herschel, was a
European Space Agency telescope
that specialised in looking at
the universe in the part of the
electromagnetic spectrum that
straddles infrared and radio
waves – exactly where space dust
is most visible to our instruments.
With their data, Whitworth and
his team affirmed a previously
noted tension between theoretical
models of interstellar dust and
observations. Dust continues to
give humanity trouble, whether at
NA home or in the galaxy next door. ❚SA/ESA/STS
CI/
SC
IENCE
PHOT
O^ LIBRAR
YThis column appears
monthly. Up next week:
Graham Lawton“ Like household dust,
cosmic dust can lead
to misinterpretations
of what we are
viewing”The universe is rather dusty Whether in our homes or the
depths of space, dust is everywhere – and it can be very annoying,
writes Chanda Prescod-WeinsteinField notes from space-time
What I’m reading
This month, a study
group I am in is reading
Biocultural Creatures
by Samantha Frost.What I’m watching
I really liked the first
episode of Stumptown!What I’m working on
What happens if there
is more than one dark
matter particle?Chanda’s week
Chanda Prescod-Weinstein
is an assistant professor of
physics and astronomy, and
a core faculty member in
women’s studies at the
University of New Hampshire.
Her research in theoretical
physics focuses on cosmology,
neutron stars and particles
beyond the standard modelViews Columnist