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Large spiral galaxies are very efficient star factories

May 15 2019

The spiral system NGC 5371 is a very efficient star factory and contains almost no missing normal matter. © SDSS/Fraternali

Large spiral galaxies, like our nearest neighbour the Andromeda Galaxy, leave almost no gas or dust particles unused when forming stars. Astronomers have calculated this on the basis of the rotation speeds of more than one hundred nearby galaxies. The large galaxies achieve an efficiency of 80 to 100% and are therefore much more efficient than the maximum 20% that was attributed to the previous record holders: medium-sized spiral galaxies such as our Milky Way.

The new calculations also have implications for so-called missing normal matter. Scientists have long assumed that about 5% of the Universe consists of normal matter such as atoms and molecules and 95% of dark, unknown matter and dark, unknown energy. And of that 5% normal matter, most of it was also lost. According to the new calculations, however, there is hardly any normal matter missing in the large spiral galaxies.

Scientists are now adjusting the theory to the new findings. The fact that missing normal matter has now been found, is a boost. But the fact that large galaxies form stars much more efficiently than expected will cause headaches in the near future.

An example of a highly efficient spiral system is NGC 5371. The system is located at about one hundred million light years from the earth in the constellation of Hunting Dogs near the Great Bear. It is one of the heaviest of the more than one hundred galaxies studied. The system contains almost no missing normal matter and has used almost all the dust and gas to make stars. The Andromeda Galaxy, our nearest neighbour at 'only' 2.5 million light years away from us, also appears to be very efficient.

The study was carried out by Lorenzo Posti (University of Groningen and Université de Strasbourg, France), Filippo Fraternali (RUG) and Antonino Marasco (RUG and ASTRON) and will soon be published in the professional journal Astronomy and Astrophysics.

Article
Peak star formation efficiency and no missing baryons in massive spirals. By Lorenzo Posti (University of Groningen and Université de Strasbourg, France), Filippo Fraternali (RUG) & Antonino Marasco (RUG and ASTRON). Accepted for publication in Astronomy & Astrophysics. (free preprint: https://arxiv.org/abs/1812.05099

Contact : Lorenzo Posti, lorenzo.posti@astro.unistra.fr

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