Astronomers using ALMA have uncovered chemical
“fingerprints” of methanol, dimethyl ether, and methyl formate in the
Large Magellanic Cloud. The latter two molecules are the largest organic
molecules ever conclusively detected outside the Milky Way. The
far-infrared image on the left shows the full galaxy. The zoom-in image
shows the star-forming region observed by ALMA. It is a combination of
mid-infrared data from Spitzer and visible (H-alpha) data from the
Blanco 4-meter telescope. Credit: NRAO/AUI/NSF; ALMA (ESO/NAOJ/NRAO); Herschel/ESA; NASA/JPL-Caltech; NOAO
The nearby dwarf galaxy known as the Large Magellanic Cloud (LMC) is a chemically primitive place.
Unlike the Milky Way, this semi-spiral collection of a few
tens-of-billions of stars lacks our galaxy’s rich abundance of heavy
elements, like carbon, oxygen, and nitrogen. With such a dearth of heavy
elements, astronomers predict that the LMC should contain a
comparatively paltry amount of complex carbon-based molecules. Previous
observations of the LMC seem to support that view.
New observations with the Atacama Large Millimeter/submillimeter
Array (ALMA), however, have uncovered the surprisingly clear chemical
“fingerprints” of the complex organic molecules methanol, dimethyl
ether, and methyl formate. Though previous observations found hints of
methanol in the LMC, the latter two are unprecedented findings and stand
as the most complex molecules ever conclusively detected outside of our
galaxy.
Astronomers discovered the molecules’ faint millimeter-wavelength
“glow” emanating from two dense star-forming embryos in the LMC, regions
known as “hot cores.” These observations may provide insights into the
formation of similarly complex organic molecules early in the history of
the universe.
“Even though the Large Magellanic Cloud is one of our nearest
galactic companions, we expect it should share some uncanny chemical
similarity with distant, young galaxies from the early universe,” said
Marta Sewiło, an astronomer with NASA’s Goddard Space Flight Center in
Greenbelt, Maryland, and lead author on a paper appearing in the Astrophysical Journal Letters.
Astronomers refer to this lack of heavy elements as “low
metallicity.” It takes several generations of star birth and star death
to liberally seed a galaxy with heavy elements, which then get taken up
in the next generation of stars and become the building blocks of new
planets.
“Young, primordial galaxies simply didn’t have enough time to become
so chemically enriched,” said Sewiło. “Dwarf galaxies like the LMC
probably retained this same youthful makeup because of their relatively
low masses, which severely throttles back the pace of star formation.”
“Due to its low metallicity, the LMC offers a window into these
early, adolescent galaxies,” noted Remy Indebetouw, an astronomer at the
National Radio Astronomy Observatory in Charlottesville, Virginia, and
coauthor on the study. “Star-formation studies of this galaxy provide a
stepping stone to understand star formation in the early universe.”
The astronomers focused their study on the N113 Star Formation Region
in the LMC, which is one of the galaxy’s most massive and gas-rich
regions. Earlier observations of this area with NASA’s Spitzer Space
Telescope and ESA’s Herschel Space Observatory revealed a startling
concentration of young stellar objects – protostars that have just begun
to heat their stellar nurseries, causing them to glow brightly in
infrared light. At least a portion of this star formation is due to a
domino-like effect, where the formation of massive stars triggers the
formation of other stars in the same general vicinity.
Sewiło and her colleagues used ALMA to study several young stellar
objects in this region to better understand their chemistry and
dynamics. The ALMA data surprisingly revealed the telltale spectral
signatures of dimethyl ether and methyl formate, molecules that have
never been detected so far from Earth.
Complex organic molecules, those with six or more atoms including
carbon, are some of the basic building blocks of molecules that are
essential to life on Earth and – presumably – elsewhere in the universe.
Though methanol is a relatively simple compound compared to other
organic molecules, it nonetheless is essential to the formation of more
complex organic molecules, like those that ALMA recently observed, among
others.
If these complex molecules can readily form around protostars, it’s
likely that they would endure and become part of the protoplanetary
disks of young star systems. Such molecules were likely delivered to the
primitive Earth by comets and meteorites, helping to jumpstart the
development of life on our planet.
The astronomers speculate that since complex organic molecules can
form in chemically primitive environments like the LMC, it’s possible
that the chemical framework for life could have emerged relatively early
in the history of the universe.
The National Radio Astronomy Observatory is a facility of the
National Science Foundation, operated under cooperative agreement by
Associated Universities, Inc.
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This research is presented in a paper titled “’The detection of hot
cores and complex organic molecules in the Large Magellanic Cloud,” by
M. Sewiło, et al., which appears in the Astrophysical Journal Letters.
The Atacama Large Millimeter/submillimeter Array (ALMA), an
international astronomy facility, is a partnership of the European
Organisation for Astronomical Research in the Southern Hemisphere (ESO),
the U.S. National Science Foundation (NSF) and the National Institutes
of Natural Sciences (NINS) of Japan in cooperation with the Republic of
Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in
cooperation with the National Research Council of Canada (NRC) and the
Ministry of Science and Technology (MOST) in Taiwan and by NINS in
cooperation with the Academia Sinica (AS) in Taiwan and the Korea
Astronomy and Space Science Institute (KASI).
ALMA construction and operations are led by ESO on behalf of its
Member States; by the National Radio Astronomy Observatory (NRAO),
managed by Associated Universities, Inc. (AUI), on behalf of North
America; and by the National Astronomical Observatory of Japan (NAOJ) on
behalf of East Asia. The Joint ALMA Observatory (JAO) provides the
unified leadership and management of the construction, commissioning and
operation of ALMA.
Charles Blue,
Public Information Officer
(434) 296-0314;
cblue@nrao.edu
