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Mergers between galaxies trigger activity in their core by Staff Writers Groningen, Netherlands (SPX) May 29, 2020
Active galactic nuclei (AGNs) play a major role in galaxy evolution. Astronomers from the University of Groningen and Netherlands Institute for Space Research have now used a record-sized sample of galaxies to confirm that galaxy mergers have a positive effect on igniting AGNs. They were able to compile about ten times more images of merging galaxies than previous studies by using a machine-learning algorithm. The results were published on 27 May in the journal Astronomy and Astrophysics. One of the bigger questions in astronomy is how galaxies evolve from clouds of gas and dust to the beautiful spiral structures we see in our Galactic neighbourhood. So-called active galactic nuclei (AGNs) form interesting research objects to answer part of this question, because there appears to be co-evolution between AGNs and galaxies. AGNs harbour supermassive black holes that emit huge amounts of energy after accreting gas from their surroundings. Some have large enough magnetic or gravitational fields to spit out jets from their poles, stretching thousands of lightyears.
Seeds for stars On the other hand, AGN activity affects a galaxy's star formation. This could go either way. An AGN's jet pushes gas away as it propagates through the galaxy, forcing the gas to collide with other gas and thus creating clumps--seeds for new stars. But AGNs also emit energy, heating up the gas and thus preventing it to cool down and condense into clumps. Astronomers from the University of Groningen and SRON Netherlands Institute for Space Research have now compiled a sample with a record-number of galaxies to study one of the factors that allegedly has a positive effect on igniting AGNs: mergers between galaxies. And they found a correlation, counting both ways. There are about 1.4 times more AGNs in mergers than in non-mergers. And the other way around, the researchers find about 1.3 times more mergers in samples of galaxies with an AGN compared to samples of galaxies without an AGN.
Large sample 'This enables us to use a large sample of two telescope surveys with tens of thousands of galaxies. AGNs are relatively easy to recognize, based on their spectrum. But mergers must be classified from images, which is typically a human's job. With machine learning, we can now have computers do this for us.'
Research Report: Bland-Hawthorn, and M. S. Owers: Mergers Do Trigger AGNs out to z ~ 0.6.
Two More Rare, Explosive Events Captured as 'Cow' mystery strikes back Maunakea HI (SPX) May 27, 2020 The 'Cow' is not alone; with the help of W. M. Keck Observatory on Maunakea in Hawaii, astronomers have discovered two more like it - the 'Koala' and a similar mysterious bright object called CSS161010. This trio of fast blue optical transients (FBOTs) appear to be relatives, all belonging to a highly-luminous family that has a track record for surprising astronomers with their fast, powerful bursts of energy. The 'Koala,' which is a nickname derived from the tail end of its official name ZTF18abv ... read more
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