The starburst galaxy M82, the size of the
carbon atoms and the observed spectral line
Credit: NASA, ESA, and The
Hubble Heritage Team (STScI/AURA)
An international team of astronomers under the guidance of graduate
student Leah Morabito of Leiden Observatory has for the first time
discovered the largest carbon atoms outside our Milky Way with the LOFAR
radio telescope. In the future astronomers will be able to measure how
cold and dense the gas around these atoms is that influences star
formation and the evolution of a galaxy. The results are published in
the journal Astrophysical Journal Letters on 28 October.
"Carbon atoms are about half a million times smaller than the
average thickness of a human hair, but they can be a billion times
larger in the cold and sparse gas. The outermost electron is then
orbiting the nucleus at a much larger distance," explains first author
Morabito. The outermost electron can be captured by an atom that is
missing an electron. A spectral line will then be visible in the light
spectrum. All spectral lines form the chemical fingerprint of an atom
such as carbon.
Astronomers predicted in the 70’s that the carbon spectral line
would be detectable outside our galaxy. This first observation took 40
years to be made. The line is hard to detect because it is too faint
when the gas that is surrounding the atoms is too warm or too dense. The
cold, sparse gas is present in starburst galaxies - galaxies in which
stars form at a high rate. For this reason the carbon spectral line is
easier to detect in galaxies of this type.
Most radio telescopes observe at frequencies at which the
carbon line can not be detected. Other telescopes are not sensitive
enough to detect the spectral lines of the carbon atoms at low
frequencies. The LOFAR radio telescope, that stretches from the
northeast of the Netherlands across Europe, is perfect for these kind of
observations because of its frequency range and sensitivity. Co-author
Raymond Oonk from Leiden Observatory en ASTRON: "LOFAR is an unique
telescope. This telescope opens up a new window on the universe."
The carbon atoms are present in the heart of the starburst
galaxy M82, where 10 times more stars are being born in the same period
as in our Milky Way. The cold and sparse gas in this area impacts star
formation, and the evolution of M82. "Since the co-discovery of the
hydrogen 21-cm line by Dutch, American and Australian astronomers, we
have been looking for a way to determine additional properties of the
cold gas such as its temperature and density. It is fantastic that we
now have found a way thanks to this carbon line. We can now collect more
and better observations, and compare them to predictions from
theoretical models," says co-author Huub Röttgering (Leiden
Observatory).
Discovery of Carbon Radio Recombination Lines in M82, Leah K. Morabito et al., Astrophysical Journal Letters, 28 oktober 2014. Arxiv: http://arxiv.org/pdf/1410.1544v1.pdf
