Number of short-lived gamma-ray bursts resulting from neutron star mergers in dwarf galaxies |  Urania

Evidence of the formation of heavy elements has been discovered when neutron stars merge in dwarf galaxies.

Composition of heavier elements
Understanding the origin of the elements is one of the main goals of astronomical research. Significant progress has been made in this field in recent years, mainly due to the discovery of neutron star mergers in 2017. Neutron stars They are the dense remains of massive stars that ended their lives in a spectacular explosion. These cosmic objects are full of neutrons and are maintained primarily by neutron decay pressure, the force acting between neutrons close together. Neutrons play a major role in the process of forming heavy elements in the so-called practicalThey are quickly captured by atomic nuclei, creating heavy elements. The natural place for this process is the collision of two atomic nuclei, which is observed in each of them Gravitational wavesWhat Gamma rays In event marked GW170817.

GW170817 is an event that stunned astronomers because it allowed them to link the origin of short gamma ray bursts (sGRBs) to the merger of neutron stars. Gamma ray bursts (GRBs) They are short-lived bursts of gamma radiation emissions that come in two different types. Long gamma-ray bursts, which account for about 70% of all gamma-ray bursts, typically last longer than two seconds and are considered to be associated with the formation of… Streams During the death of some massive stars. In contrast, short GRBs typically last less than 2 seconds, and have long been thought to be associated with neutron star mergers, even before GW170817 was confirmed. However, GW170817 did not solve all the cosmic mysteries. For example, this event was observed in an ancient passive galaxy, while there are other places in the universe where important elements of the r process have been observed, e.g. Dwarf galaxies. Authors condition It is set out to understand whether sGRBs may be associated with dwarf galaxies and where neutron star mergers trigger R processes in these systems.

Difficult task – studying faint galaxies
Previous studies of galaxies hosting sGRBs have been unable to study the smallest galaxies due to very limited observational data. One of the most difficult problems is distinguishing between whether these faint galaxies are naturally faint (such as low-mass dwarf galaxies) or whether they are just ordinary galaxies that are very distant. For the 11 weaker sGRB host galaxies, researchers used new techniques to solve this problem.

To separate the host galaxy distance (defined by Redshift) on its mass (expressed as stellar mass, i.e. the total mass of all stars in a given galaxy), the researchers adjusted data from Hubble Space Telescope, Very large telescope I Spitzera Using new and advanced models. They use two new technologies that were specifically developed to handle limited and very noisy data sets. The first new technology related Bayesian analysis, which relies on prior knowledge from both theory and observation, and which generally limits its results best to plausible physical values. The second innovative technique is to include information about the size of the galaxy in the modeling. It has been shown that galaxies show a relationship between their mass and size, so researchers found that including information about galaxy size provides better constraints on stellar mass and redshift than using just flux data!

Finally, the authors also examined whether these sGRBs were unique compared to the rest of the sample. There is no evidence of any differences in the characteristics of the flares that appear when the jets interact with the surrounding medium. However, sGRBs in these dwarf galaxies have been found to occur at smaller distances from their host galaxies compared to the total population. This may be due to smaller “kicks” – the speed with which the compact object produced in the explosion that caused it – is ejected than previously expected, keeping the resulting binary and r-process elements within the dwarf galaxy. This is the first evidence that neutron star mergers can occur in dwarf galaxies and enrich their host galaxies with strong r-process elements, which agrees well with current observations of r-process-rich dwarf galaxies.

Agnieszka Novak

more information:

Source: Astrobits

Pictured: Brief gamma-ray bursts in host galaxies over cosmic time. Source: WM Keck Observatory/Adam Makarenko

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