This week, Nature published
a research article that challenges the theory of stellar evolution. "I think
that, over the coming months, stellar astrophysicists will have to redo their
calculations," said Gilles Fontaine, a physics professor at Université de
Montréal and one of the authors of the article, titled "A large
oxygen-dominated core from the seismic cartography of a pulsating white
dwarf."
Its lead author is Noemi
Giammichele, who recently completed her doctorate in 2016 under the joint supervision of
Fontaine and his colleague Pierre Bergeron, both of whom co-authored the
article along with six other researchers. The piece reports on a study of data
collected by the Kepler Space Telescope.
"We were able to map
the interior of a pulsating white dwarf star with precision, as if we'd sliced
it into cross-sections to study its composition," said Giammichele, now a
post-doctoral fellow at Université de Toulouse, in France. The map showed the
star's vibrations sometimes reach all the way to its centre.
White dwarfs "are the
core remnants of nearly 97% of the stars in the Universe," explained
Robert Lamontagne, head of media relations at UdeM's Centre for Research in
Astrophysics.
"As stars slowly die,
inexorably cooling down in the form of white dwarfs, they experience periods of
instability in which they vibrate. These deep vibrations – or starquakes – are
the key to seeing right into the very interior of these stellar remnants."
From a distance of 1,375
light-years from Earth, white dwarf KIC08626021 emits light that is barely
visible by telescopes on Earth. The Kepler, however, can focus on it over an
extended period, resulting in significantly more detailed images. Because the
Montreal researchers were able to access the space telescope, the authors were
able to take a close look at this small star – about the size of the Earth –
and its vibrations.
Nearly 300 experts worldwide
specialize in studying white dwarfs. Giammichele's initial goal was to verify a
theory on this final stage of a star's life cycle. The theory proved correct,
but the team's observations led to a number of surprising discoveries.
When examining this
particular star, located at the edges of the Cygnus and Lyra constellations,
the researchers discovered that its carbon and oxygen core was twice as big as
the theory predicted. "This is a major discovery that will force us to
re-evaluate our view of how stars die," said Fontaine. "That said,
more work must be done to confirm whether this observation holds true for other
stars. It may just be an anomaly."
"We must try to
reproduce these results with other celestial bodies before we can make any
conclusions," Giammichele agreed.
Although KIC08626021 was the
first pulsating white dwarf identified by the Kepler telescope, approximately
60 more have since been discovered, she added. "I have enough data to
spend the next 20 years analyzing them one by one."
The new article is
Fontaine's fourth in Nature, one of the world's top scientific magazines, and
its publication closes a circle in his career. In 1978, the professor glimpsed
the potential for determining the internal structure of a pulsating white dwarf
through a solid understanding of the theory of stellar evolution. "But
there was still a long way to go," he recalled.
"First, we had no
access to high-quality images because terrestrial telescopes gave us very
imprecise images of these bodies. Then we had to create the analytical tools,
the software, etc. And last but not least, we had to find the right person to
pursue this lead."
Fontaine praised his former
student, who developed an innovative approach to achieve her goals. As a
graduate of Polytechnique Montréal with a master's in mechanical engineering,
Giammichele applied methods used for calculating the aerodynamics of airplane wings
to astrophysics.
"I believe this
approach is what allowed us to move forward," said Fontaine, adding that
five of the other co-authors studied under him as well.
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For her part, Giammichele is
pleased that one of the five articles comprising her doctoral thesis will now
reach a broader audience. "What I want to do now, in terms of my career,
is keep doing research," she said. "That's what I like most: figuring
out how to solve problems."
This article was initially
published on Phys.org. You can read the article here.