Astronomers of the Universitat de València and the National Radio Astronomy Observatory (NRAO-Virginia, USA) have determined the 3D structure of the molecular emission of a supernova. This means that they have been able to observe in three dimensions the remains of the star after its explosion, something that has not been possible until now. The results of this research have been published in 'The Astrophysical Journal Letters' magazine.
The supernovae -as it is known the explosive end of the short but blazing life of the massive stars- are one of the most amazing phenomena of Universe. Even though supernovae correspond to the death of a star, they also provoke the birth of new elements and the formation of molecules that abound in the cosmos.
Among the remains of a star that exploded in February 1987, there is a dense bunch of molecules and dust formed after the cooling of it. A group of astronomers contemplated this phenomenon in the 1987A Supernova located at the Large Magellanic Cloud, which is a tiny galaxy located at the outskirts of the Milk Way, 163.000 light-years from the Earth.
During the next 30 years, the observations of the remains of this explosion have revealed previously unknown details of the star’s death and they have showed how the atoms that were formed there (carbon, oxygen and nitrogen, among others) ended up spilled in the Space, thus forming new molecules and dust. These microscopic particles could originate new generations of stars and planets some day.
Astronomers of the Universitat de València, Fran Abellán and Jon Marcaide, together with Rémy Indebetouw, of the University of Virginia and NRAO, in collaboration with scientists from different countries, have now used the ALMA (Atacama Large Millimetre / submillimetre Array) radio telescope to study the centre of the SN 1987A. ALMA's ability to observe incredibly minute details has allowed researchers to generate an impressive three-dimensional image of newly formed molecules inside the supernova remnant. The results of this research are published in The Astrophysical Journal Letters magazine.
The mapping of the new molecules and the capture of the high resolution 3D image of this "dust factory" allow a better understanding of the relationship between the remnant of this supernova and its host galaxy. "For the first time we have observed that supernova explosions are capable of creating immense amounts of dust and molecules that are released into the interstellar medium. Due to this, and even though supernovae are relatively rare phenomena in our cosmic neighbourhood, we now know that the appearance and composition of galaxies are largely determined by the supernovae that have occurred in them,” explains Fran Abellán (Department of Astronomy and Astrophysics of the Universitat de València), first writer of the article. "In addition, supernovae such as SN 1987A can strike and heat the surrounding gas by triggering the creation of new stars and even planets, which would be rich in elements such as carbon, oxygen and silicon, which are essential components for life as we know it," he says.
Rémy Indebetouw states that "when the supernova exploded, more than 30 years ago, astronomers knew much less about how these phenomena alter the interstellar space and how the hot and bright debris of a exploded star end up cooling and forging new molecules. Thanks to ALMA, we can finally see how cold 'star dust' is formed and better understand the original star and the way in which supernovae create the basic components of the planets."
Supernova: from the death of a star to the birth of dust
Before the current observations of SN 1987A, few conclusions could be drawn from these explosive cosmic phenomena. It was known for sure that massive stars (about 10 times the mass of our Sun) were extinguished quite spectacularly. When the fuel of these stars runs out, there is not enough heat or energy left to fight against the force of gravity, and the outer areas of the star, which are sustained until then by the power of fusion, implode with tremendous force. The rebound effect of this collapse causes an explosion that releases material into space.
Supernovae are quite common in the observable universe. Nevertheless, since they appear once every 50 years in galaxies the size of the Milk Way, astronomers have few opportunities to study them from their detonation until the moment in which they get cold and form new molecules. Although to be fair SN 1987A is not in our galaxy, it is close enough to us so that ALMA and other telescopes can study it in detail.
Production of a 3D image of SN 1987A with ALMA
Scientists have observed SN 1987A for several decades with the help of radio astronomy, optical and even X-ray observatories, but they have always had difficulties to analyse their centre due to the presence of dust remaining around them. The ability of ALMA to capture millimetre wavelengths has allowed to observe through dust and gas, and to analyse the abundance and location of newly formed molecules, especially silicon monoxide (SiO) and carbon monoxide (CO), which shine more strongly in the submillimetric spectrum that ALMA observes.
In addition to producing the first three-dimensional image of SN 1987A, ALMA has revealed fascinating details about how physical conditions have changed over time and continue to change. These observations also provide information on the physical instabilities of the supernova.
New discoveries in SN 1987A
The previous observations made with ALMA had revealed that SN 1987A produced a huge amount of dust. The new observations provide more details on how the supernova generated all that dust and on the molecular emission of SiO and CO.
"The results we have obtained give us information about the form of the explosion, and they give it to us in an unexpected way through the emission of molecules that have been formed in the last 25 years and which until recently we hadn’t suspected that it could be formed. Five years ago, when we made the proposal that led us to these discoveries, we had no idea that we could detect the molecular emission, that it was going to be so strong, and that we could do tomography and determine the three-dimensional structure of something that is surrounding the black hole or the neutron star,” the full university professor of Astronomy and Astrophysics Joan Marcaide continues. "The curious thing is that once the extraordinary takes place we get used to it immediately and we lose even the capacity for surprise," he concludes.
New questions and future researches
While the new ALMA observations have revealed important data on SN 1987A, many questions still remain unanswered, such as: Are any other molecules still to be discovered? How will the three-dimensional structure of SN 1987A continue to evolve over time?
Future observations of ALMA at different wavelengths may also help to determine what type of compact object resides at its centre: whether a pulsar or a neutron star. Although the presence of an object of this kind has been predicted inside SN 1987A, the signals necessary to confirm it have not yet been detected.
Additional information
This research was presented in two articles. The first one was entitled ‘Very deep inside the SN 1987 A core ejecta: Molecular structures seen in 3D’, by F. J. Abellán et al., is published in The Astrophysical Journal Letters. On the other hand, ‘ALMA spectral survey of supernova 1987A—molecular inventory, chemistry, dynamics an explosive nucleosynthesis’ will be soon published in the Monthly Notices magazine of the Royal Astronomical Society.
Reference:
Very Deep inside the SN 1987A Core Ejecta: Molecular Structures Seen in 3D
F. J. Abellán1, R. Indebetouw2,3, J. M. Marcaide1, M. Gabler4, C. Fransson5, J. Spyromilio6, D. N. Burrows7, R. Chevalier2, P. Cigan8, B. M. Gaensler9, H. L. Gomez8, H.-Th. Janka4, R. Kirshner10, J. Larsson11, P. Lundqvist5, M. Matsuura8, R. McCray12, C.-Y. Ng13, S. Park14, P. Roche15, L. Staveley-Smith16,17, J. Th. van Loon18, J. C. Wheeler19, and S. E. Woosley20
Published 2017 June 22 • © 2017. The American Astronomical Society. All rights reserved.
The Astrophysical Journal Letters, Volume 842, Number 2
http://iopscience.iop.org/article/10.3847/2041-8213/aa784c/meta
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