Tyler O'Neal, Staff Editor APPLICATIONS

Using hydrodynamical simulations from the Constrained Local UniversE project, Instituto de Astrofísica de Canarias' Arianna di Cintio shows that satellite galaxies can carry on forming stars when they pass close to their parent galaxies

Historically most scientists thought that once a satellite galaxy has passed close by its higher mass parent galaxy its star formation would stop because the larger galaxy would remove the gas from it, leaving it shorn of the material it would need to make new stars. However, for the first time, a team led by the researcher at the Instituto de Astrofísica de Canarias (IAC), Arianna di Cintio, has shown using numerical simulations that this is not always the case.

Using sophisticated supercomputer simulations of the whole of the Local Group of galaxies, including the Milky Way, the Andromeda galaxy, and their respective satellite galaxies, the researchers have shown that the satellites not only can retain their gas but also can experience many new episodes of star formation just after passing close to the pericentre of their parent galaxy (the mínimum distance they reach from its center). Image of the simulated local group used for the article. Left, image of dark matter; on the right, gas distribution. The three main galaxies of the Local Group (MW, M31 and M33) are indicated.

The satellite galaxies of the Local Group show a wide variety of star formation histories, whose origin has not previously been fully understood. Using hydrodynamic simulations within the project Constrained Local UniversE (CLUES) the authors studied the star formation histories of satellite galaxies similar to those of the Milky Way in a cosmological context.

While in the majority of the cases the gas of the satellite is sucked out by the parent galaxy due to gravitational action and transfers itself to the larger galaxy, interrupting star formation in the satellite, in a process known as accretion; in some 25% of the sample, they found that star formation was enhanced by this interactive process.

The results show that the peaks of star formation are correlated with the close pass of the satellite around the parent galaxy, and occasionally by the interaction of two satellites. The researchers identified two key features to the star formation: the satellite must enter the parent galaxy with a large reserve of cold gas, and a minimum distance not too small, so that stars may form due to compression of the gas. On the contrary, galaxies that pass too close to the parent galaxy, or to a parent galaxy with little gas, are stripped of their gas and thereby lose the possibility of forming new stars.

"The passage of satellites also coincide with peaks in the star formation of their parent galaxies, which suggests that this mechanism causes bursts of stars equally in both parent galaxies and satellites, in agreement with recent studies of the history of star formation in our own Galaxy", explains Arianna di Cintio, the lead author on the paper.

"This is very important when we try to understand how star formation is produced in the smaller dwarf galaxies of our Local Group, an unresolved question", she adds.

This finding will shed light on the episodes of star formation which are observed in the dwarf galaxies of the Local Group, such as Carina and Fornax, giving an attractive explanation of their existence. It also requires a revision of the theoretical models used to explain the formation of stars in dwarf galaxies.

German scientists develop a new fisheries management planning tool; fewer cod stocks are expected

Tyler O'Neal, Staff Editor APPLICATIONS

The future of cod stocks in the North Sea and the Barents Sea may be much easier to predict than before. This is the result of an international research project led by the Helmholtz-Zentrum Hereon and its Institute of Coastal Systems - Analysis and Modeling. For the first time, the team has succeeded in predicting the development of stocks for ten years in advance, taking into account both changes due to climate and fishing. Traditionally, fisheries experts provide catch recommendations for about a year in advance, based on which fishing quotas are negotiated and set internationally. This involves first estimating the size of current cod stocks and then calculating how much cod can be caught in the coming year without endangering the stocks as well as harvesting the stock optimally. The climatic change, long-term changes in water temperature, circulation, and mixing, which have a decisive influence on how well cod reproduce, are not included in this prediction so that the development of stocks can only be predicted in the short term. Cod stocks will probably decrease in the future CREDIT Photo: David Young via Fotolia

The warm North Sea causes stress

As the experts around climate modeler, Vimal Koul und Corinna Schrum of Hereon now have taken temperature into account in their calculations. For the North Sea, the climate forecast continues to predict temperatures at a high level, so that cod stocks are unlikely to recover or reach earlier levels. As a result, catches are expected to remain low. Things look better for the Barents Sea, where stocks can be managed sustainably.

For the researchers, the challenge was that climate models cannot calculate how much fish there will be in the oceans in the future. They only provide information about expected temperatures. "So we first had to develop a program that translates water temperature into fish quantities," says Vimal Koul. Among other things, this took into account the ocean temperature in the North Atlantic. The researchers were then able to run their prediction model. The model starts with today's conditions - the current temperature conditions and the current carbon dioxide content of the atmosphere, and can then calculate how the situation will change as carbon dioxide concentrations increase. The future temperatures are then translated into expected fish abundance and stock sizes.

To test how reliably the model works, it was first compared with real fish data from the 1960s to the present. As it turned out, it was able to correctly estimate fish stocks for the ten-year periods since the early 1960s. In this respect, the researchers led by Vimal Koul can assume that the current view of the coming ten years is also correct.

Fishing intensity is taken into account

Another interesting aspect of the study is that the team of climate modelers, fisheries biologists, and oceanographers took four different fishing scenarios into account. This allowed them to determine how cod stocks would fare if they were fished at different levels - from intensive to sustainable. In this respect, the results of the current study are very practical. "The 10-year estimates will help the fishing industry better plan catches in the future - so that cod stocks are fished sustainably and gently despite climate changes," says Vimal Koul. The new 10-year calculation model could also help fishing companies in their strategic planning - by providing a secure basis for investments in new vessels or processing facilities.

MMS data reveal a mechanism for accelerating heavy ions in galactic cosmic rays

Tyler O'Neal, Staff Editor APPLICATIONS

Scientists have used data from the Southwest Research Institute-led Magnetospheric Multiscale (MMS) mission to explain the presence of energetic heavy elements in galactic cosmic rays (GCRs). GCRs are composed of fast-moving energetic particles, mostly hydrogen ions called protons, the lightest and most abundant elements in the universe. Scientists have long debated how trace amounts of heavy ions in GCRs are accelerated.

The supernova explosion of a dying star creates massive shockwaves that propagate through the surrounding space, accelerating ions in their path to very high energies, creating GCRs. How heavy ions are energized and accelerated is important because they affect the redistribution of mass throughout the universe and are essential for the formation of even heavier and more chemically complex elements. They also influence how we perceive astrophysical structures. Scientists at SwRI developed this conceptual image of heavy ion dynamics based on MMS observations. The colored trajectory lines illustrate how alpha particles (He++) behave as they encounter an extreme shock. Strong magnetic fields effectively change their trajectory, placing them in the acceleration zones. This process explains how trace heavy elements could be accelerated into galactic cosmic rays by supernova events.

"Heavy ions are thought to be insensitive to an incoming shockwave because they are less abundant, and the shock energy is overwhelmingly consumed by the preponderance of protons. Visualize standing on a beach as waves move the sand under your feet, while you remain in place," said SwRI's Dr. Hadi Madanian, the lead author of the paper about this research published in Astrophysical Journal Letters. "However, that classical view of how heavy ions behave under shock conditions is not always what we have seen in high-resolution MMS observations of the near-Earth space environment."

Shock phenomena also occur in the near-Earth environment. The Sun's magnetic field is carried through interplanetary space by the supersonic solar wind flow, which is obstructed and diverted by the Earth's magnetosphere, a bubble of protection around our home planet. This interaction region is called the bow shock due to its curved shape, comparable to the bow waves that occur as a boat travels through water. The Earth's bow shock forms at a much smaller scale than supernova shocks. However, at times, conditions of this small shock resemble those of supernova remnants. The team used high-resolution in-situ measurements from the MMS spacecraft at the bow shock to study how heavy ions are accelerated.

"We observed intense amplification of the magnetic field near the bow shock, a known property associated with strong shocks such as supernova remnants. We then analyzed how different ion species behaved as they encountered the bow shock," Madanian said. "We found that these enhanced fields significantly modify the trajectory of heavy ions, redirecting them into the acceleration zone of the shock."

While this behavior was not expected to occur for heavy ions, the team identified direct evidence for this process in alpha particles, helium ions that are four times more massive than protons and have twice the charge.

"The superb resolution of MMS observations has given us a much clearer picture of how a shockwave energizes the heavy elements. We will be able to use this new understanding to improve our computer models of cosmic ray acceleration at astrophysical shocks," said David Burgess, a professor of mathematics and astronomy at the Queen Mary University of London and a co-author of the paper. "The new findings have significant implications for the composition of cosmic rays and the observed radiation spectra from astrophysical structures."