The life cycle of a Sun-like star (annotated)
Image of HIP 102152
Wide-field view of the region around Sun-like star HIP 102152
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ESO’s VLT provides new clues to help solve lithium mystery
An international team led by astronomers
in Brazil has used ESO’s Very Large Telescope to identify and study the
oldest solar twin known to date. Located 250 light-years from Earth, the
star HIP 102152 is more like the Sun than any other solar twin — except
that it is nearly four billion years older. This older, but almost
identical, twin gives us an unprecedented chance to see how the Sun will
look when it ages. The new observations also provide an important first
clear link between a star’s age and its lithium content, and in
addition suggest that HIP 102152 may be host to rocky terrestrial
planets.
Astronomers have only been observing the Sun with telescopes for 400
years — a tiny fraction of the Sun’s age of 4.6 billion years. It is
very hard to study the history and future evolution of our star, but we
can do this by hunting for rare stars that are almost exactly like our
own, but at different stages of their lives. Now astronomers have
identified a star that is essentially an identical twin to our Sun, but 4
billion years older — almost like seeing a real version of the twin
paradox in action [1].
Jorge Melendez (Universidade de São Paulo, Brazil), the leader of the team and co-author of the new paper explains: “For
decades, astronomers have been searching for solar twins in order to
know our own life-giving Sun better. But very few have been found since
the first one was discovered in 1997. We have now obtained
superb-quality spectra from the VLT and can scrutinise solar twins with
extreme precision, to answer the question of whether the Sun is special.”
The team studied two solar twins [2]
— one that was thought to be younger than the Sun (18 Scorpii) and one
that was expected to be older (HIP 102152). They used the UVES
spectrograph on the Very Large Telescope (VLT) at ESO's Paranal
Observatory to split up the light into its component colours so that the
chemical composition and other properties of these stars could be
studied in great detail.
They found that HIP 102152 in the constellation of Capricornus (The
Sea Goat) is the oldest solar twin known to date. It is estimated to be
8.2 billion years old, compared to 4.6 billion years for our own Sun. On
the other hand 18 Scorpii was confirmed to be younger than the Sun —
about 2.9 billion years old.
Studying the ancient solar twin HIP 102152 allows scientists to
predict what may happen to our own Sun when it reaches that age, and
they have already made one significant discovery. “One issue we wanted to address is whether or not the Sun is typical in composition,” says Melendez. “Most importantly, why does it have such a strangely low lithium content?”
Lithium, the third element in the periodic table, was created in the
Big Bang along with hydrogen and helium. Astronomers have pondered for
years over why some stars appear to have less lithium than others. With
the new observations of HIP 102152, astronomers have taken a big step
towards solving this mystery by pinning down a strong correlation
between a Sun-like star’s age and its lithium content.
Our own Sun now has just 1% of the lithium content that was present in the material from which it formed. Examinations of younger solar twins have hinted that these younger siblings contain significantly larger amounts of lithium, but up to now scientists could not prove a clear correlation between age and lithium content [3].
Our own Sun now has just 1% of the lithium content that was present in the material from which it formed. Examinations of younger solar twins have hinted that these younger siblings contain significantly larger amounts of lithium, but up to now scientists could not prove a clear correlation between age and lithium content [3].
TalaWanda Monroe (Universidade de São Paulo), the lead author on the new paper, concludes: “We
have found that HIP 102152 has very low levels of lithium. This
demonstrates clearly for the first time that older solar twins do indeed
have less lithium than our own Sun or younger solar twins. We can now
be certain that stars somehow destroy their lithium as they age, and
that the Sun's lithium content appears to be normal for its age.” [4]
A final twist in the story is that HIP 102152 has an unusual chemical
composition pattern that is subtly different to most other solar twins,
but similar to the Sun. They both show a deficiency of the elements
that are abundant in meteorites and on Earth. This is a strong hint that
HIP 102152 may host terrestrial rocky planets [5].
Notes
[1] Many people have heard of the twin paradox:
one identical twin takes a space journey and comes back to Earth
younger than their sibling. Although there is no time travelling
involved here, we see two distinctly different ages for these two very
similar stars — snapshots of the Sun’s life at different stages.
[2] Solar twins, solar analogues and solar-type stars
are categories of stars according to their similarity to our own Sun.
Solar twins are the most similar to our Sun, as they have very similar
masses, temperatures, and chemical abundances. Solar twins are rare but
the other classes, where the similarity is less precise, are much more
common.
[3] Previous studies have indicated that a star’s lithium content could also be affected if it hosts giant planets (eso0942, eso0118, Nature paper), although these results have been debated (ann1046).
[4] It is still unclear exactly how lithium is
destroyed within the stars, although several processes have been
proposed to transport lithium from the surface of a star into its deeper
layers, where it is then destroyed.
[5] If a star contains less of the elements that we
commonly find in rocky bodies, this indicates that it is likely to host
rocky terrestrial planets because such planets lock up these elements as
they form from a large disc surrounding the star. The suggestion that
HIP 102152 may host such planets is further reinforced by the radial
velocity monitoring of this star with ESO's HARPS spectrograph, which
indicates that inside the star’s habitable zone there are no giant
planets. This would allow the existence of potential Earth-like planets
around HIP 102152; in systems with giant planets existing close in to
their star, the chances of finding terrestrial planets are much less as
these small rocky bodies are disturbed and disrupted.
More information
This research was presented in a paper to
appear in “High precision abundances of the old solar twin HIP 102152:
insights on Li depletion from the oldest Sun”, by TalaWanda Monroe et
al. in the Astrophysical Journal Letters.
The team is composed of TalaWanda R. Monroe, Jorge Meléndez
(Universidade de São Paulo, Brazil [USP]), Iván Ramírez (The University
of Texas at Austin, USA), David Yong (Australian National University,
Australia [ANU]), Maria Bergemann (Max Planck Institute for
Astrophysics, Germany), Martin Asplund (ANU), Jacob Bean, Megan Bedell
(University of Chicago, USA), Marcelo Tucci Maia (USP), Karin Lind
(University of Cambridge, UK), Alan Alves-Brito, Luca Casagrande (ANU),
Matthieu Castro, José-Dias do Nascimento (Universidade Federal do Rio
Grande do Norte, Brazil), Michael Bazot (Centro de Astrofísica da
Universidade de Porto, Portugal) and Fabrício C. Freitas (USP).
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Links
Contacts
TalaWanda R. MonroeUniversidade de São Paulo
São Paulo, Brazil
Tel: +55 11 3091 2815
Email: tmonroe@usp.br
Jorge Meléndez
Universidade de São Paulo
São Paulo, Brazil
Tel: +55 11 3091 2840
Email: jorge.melendez@iag.usp.br
Richard Hook
ESO, Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org
