PR Video noirlab2410a
Cosmoview Episode 80: Gemini South Reveals Origin of Unexpected Differences in Giant Binary Stars
PR Video noirlab2410b
Cosmoview Episodio 80: Desde Chile descubren causas de la diversidad estelar en estrellas binarias
It is estimated that up to 85% of stars exist in binary star systems, some even in systems with three or more stars. These stellar pairs are born together out of the same molecular cloud from a shared abundance of chemical building blocks, so astronomers would expect to find that they have nearly identical compositions and planetary systems. However, for many binaries that isn’t the case. While some proposed explanations attribute these dissimilarities to events occurring after the stars evolved, a team of astronomers have confirmed for the first time that they can actually originate from before the stars even began to form.
Led by Carlos Saffe of the Institute of Astronomical, Earth and Space Sciences (ICATE-CONICET) in Argentina, the team used the Gemini South telescope in Chile, one half of the International Gemini Observatory,
supported in part by the U.S. National Science Foundation and operated
by NSF NOIRLab. With the new, precise Gemini High Resolution Optical
SpecTrograph (GHOST)
the team studied the different wavelengths of light, or spectra, given
off by a pair of giant stars, which revealed significant differences in
their chemical make-up. “GHOST’s extremely high-quality spectra offered unprecedented resolution,” said Saffe, “allowing us to measure the stars’ stellar parameters and chemical abundances with the highest possible precision.”
These measurements revealed that one star had higher abundances of
heavy elements than the other. To disentangle the origin of this
discrepancy, the team used a unique approach.
Previous studies have proposed three possible explanations for
observed chemical differences between binary stars. Two of them involve
processes that would occur well into the stars’ evolution: atomic diffusion,
or the settling of chemical elements into gradient layers depending on
each star’s temperature and surface gravity; and the engulfment of a
small, rocky planet, which would introduce chemical variations in a
star’s composition.
The third possible explanation looks back at the beginning of the
stars’ formation, suggesting that the differences originate from
primordial, or pre-existing, areas of nonuniformity within the molecular
cloud. In simpler terms, if the molecular cloud has an uneven
distribution of chemical elements, then stars born within that cloud
will have different compositions depending on which elements were
available at the location where each formed.
So far, studies have concluded that all three explanations are probable; however, these studies focused solely on main-sequence
binaries. The ‘main-sequence’ is the stage where a star spends most of
its existence, and the majority of stars in the Universe are
main-sequence stars, including our Sun. Instead, Saffe and his team
observed a binary consisting of two giant stars. These stars possess extremely deep and strongly turbulent external layers, or convective zones. Owing to the properties of these thick convective zones, the team was able to rule out two of the three possible explanations.
The continuous swirling of fluid within the convective zone would
make it difficult for material to settle into layers, meaning giant
stars are less sensitive to the effects of atomic diffusion — ruling out
the first explanation. The thick external layer also means that a
planetary engulfment would not change a star’s composition much since
the ingested material would rapidly be diluted — ruling out the second
explanation. This leaves primordial inhomogeneities within the molecular
cloud as the confirmed explanation. “This is the first time
astronomers have been able to confirm that differences between binary
stars begin at the earliest stages of their formation,” said Saffe.
“Using the precision-measurement capabilities provided by the
GHOST instrument, Gemini South is now collecting observations of stars
at the end of their lives to reveal the environment in which they were
born,” says Martin Still, NSF program director for the International Gemini Observatory. “This
gives us the ability to explore how the conditions in which stars form
can influence their entire existence over millions or billions of
years.”
Three consequences of this study are of particular significance.
First, these results offer an explanation for why astronomers see binary
stars with such different planetary systems. “Different planetary
systems could mean very different planets — rocky, Earth-like, ice
giants, gas giants — that orbit their host stars at different distances
and where the potential to support life might be very different,” said Saffe.
Second, these results pose a crucial challenge to the concept of
chemical tagging — using chemical composition to identify stars that
came from the same environment or stellar nursery — by showing that
stars with different chemical compositions can still have the same
origin.
Finally, observed differences previously attributed to planetary
impacts on a star’s surface will need to be reviewed, as they might now
be seen as having been there from the very beginning of the star’s life.
“By showing for the first time that primordial differences really
are present and responsible for differences between twin stars, we show
that star and planet formation could be more complex than initially
thought,” said Saffe. “The Universe loves diversity!”
More information
The team is composed of C. Saffe (ICATE-CONICET/UNSJ, Argentina), P. Miquelarena (ICATE-CONICET/UNSJ, Argentina), J. Alacoria (ICATE-CONICET, Argentina), E. Martioli (LNA/MCTI, Brasil), M. Flores (ICATE-CONICET/UNSJ, Argentina), M. Jaque Arancibia (Universidad de La Serena, Chile), R. Angeloni (International Gemini Observatory/NSF NOIRLab, Chile), E. Jofré (OAC/CONICET, Argentina), J. Yana Galarza (Carnegie Institution for Science, CA), E. González (UNSJ, Argentina), and A. Collado (ICATE-CONICET/UNSJ, Argentina).
NSF NOIRLab (U.S. National Science Foundation National Optical-Infrared Astronomy Research Laboratory), the U.S. center for ground-based optical-infrared astronomy, operates the International Gemini Observatory (a facility of NSF, NRC–Canada, ANID–Chile, MCTIC–Brazil, MINCyT–Argentina, and KASI–Republic of Korea), Kitt Peak National Observatory (KPNO), Cerro Tololo Inter-American Observatory (CTIO), the Community Science and Data Center (CSDC), and Vera C. Rubin Observatory (operated in cooperation with the Department of Energy’s SLAC National Accelerator Laboratory). It is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with NSF and is headquartered in Tucson, Arizona. The astronomical community is honored to have the opportunity to conduct astronomical research on I’oligam Du’ag (Kitt Peak) in Arizona, on Maunakea in Hawai‘i, and on Cerro Tololo and Cerro Pachón in Chile. We recognize and acknowledge the very significant cultural role and reverence that these sites have to the Tohono O’odham Nation, to the Native Hawaiian community, and to the local communities in Chile, respectively.
Links
- Read the paper: Disentangling the origin of chemical differences using GHOST
- Photos of the Gemini South telescope
- Videos of the Gemini South telescope
- Other Gemini South news
- Other discoveries made with GHOST
- Check out other NOIRLab Science Releases
Contacts:
Carlos Saffe
Institute of Astronomical, Earth and Space Sciences, Argentina
Email: saffe.carlos@gmail.com
Josie Fenske
Jr. Public Information Officer
NSF NOIRLab
Email: josie.fenske@noirlab.edu
