More information: Rapid growth of seed black holes in the early universe by supra-exponential accretion, Science DOI: 10.1126/science.1251053ABSTRACTMass accretion by black holes (BHs) is typically capped at the Eddington rate, when radiation’s push balances gravity’s pull. However, even exponential growth at the Eddington-limited e-folding time tE ~ few×0.01 Gyr, is too slow to grow stellar-mass BH seeds into the supermassive luminous quasars that are observed when the universe is 1 Gyr old. We propose a dynamical mechanism that can trigger supra-exponential accretion in the early universe, when a BH seed is trapped in a star cluster fed by the ubiquitous dense cold gas flows. The high gas opacity traps the accretion radiation, while the low-mass BH’s random motions suppress the formation of a slowly draining accretion disk. Supra-exponential growth can thus explain the puzzling emergence of supermassive BHs that power luminous quasars so soon after the Big Bang.Press release © 2014 Phys.org Journal information: Science This graphic shows the center of a newly formed star cluster (stars are in yellow), within which the seed black hole gets its super boost of gas (shown in blue). Explore further Citation: Research duo suggest possible explanation for rapid growth of seed black holes in early universe (2014, August 8) retrieved 18 August 2019 from https://phys.org/news/2014-08-duo-explanation-rapid-growth-seed.html Black hole that doesn’t emit x-rays discovered near massive star (Phys.org) —A pair of researchers, Tal Alexander of the Weizmann Institute of Science, in Israel and Priyamvada Natarajan with Yale University in the U.S. has come up with a possible explanation for the rapid growth of black holes believed to have existed in the early universe. In their paper published in the journal Science, the two propose that early black holes could have grown much more rapidly than those observed today due to dense gases that existed at the time that allowed for rapid growth in the absence of an accretion disk. This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. Black holes are thought to exist at the center of most if not all galaxies—but contrary to popular science fiction, they don’t simply suck in everything around them like a vacuum cleaner—if that were the case planet Earth would have been sucked into the black hole at the center of the Milky Way long ago. Materials are pulled into a black hole, but are slowed by the buildup of an accretion disk. That disk means that materials can only be pulled in along the plane of the disk. There is also the problem of materials colliding as they are pulled closer, generating enough energetic radiation to push other material away from the black hole. While this all makes sense in the modern era, it causes problems for space scientists seeking to figure out how everything got to where it is now—most theories point to super-massive black holes forming shortly after the Big Bang. But, how did they grow so big so fast?Alexander and Natarajan think they may have the answer—they note that shortly after the Big Bang, the universe was of course, much smaller and denser. Cold dense gas, they suggest, in the vicinity of a black hole would not have been susceptible to causing heat creation due to collisions. But perhaps more importantly, the gravity pull from other nearby stars could have caused black holes to move around in odd, erratic fashion, preventing the creation of an accretion disk. That in turn would mean material could be pulled into the black hole from every direction, greatly increasing the speed at which it would build in mass.A model the two built based on their ideas, suggests such a scenario could lead to a black hole starting with ten times the mass of our modern sun, growing to something ten billion times as big in just a billion years.
Journal information: Proceedings of the Royal Society B This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. Captain Scott’s century-old collections suggests marine life is capturing more carbon Explore further Captain Robert Falcon Scott was an officer with the British Royal Navy with an inclination for exploration. He led two expeditions in the Antarctic: The first was called the Discovery Expedition, the second was the Terra Nova Expedition. Falcon died during his return from the second expedition, but his efforts led to the discovery that Antarctica was once covered by forest—they also provided plant specimens for study by scientists back in England. One specimen was the cynobacterial mat—the main kind of vegetation covering the area where Falcon had based his camp. Once studied, the mats were pressed between sheets of paper and stored at the Natural History Museum. In this new effort, the researchers conducted a DNA analysis of the bacteria in the mats. Then they arranged to have researchers currently carrying out science experiments in nearly the same area in Antarctica collect new samples for study. After conducting a DNA analysis on the new samples, the results were compared with those from over a century ago. The researchers report that they found very little difference between the two.The sameness of the bacteria samples came as a surprise to the researchers, because they believed that it was likely that bacteria in Antarctica evolved as temperatures rose, or new species would have invaded. That neither has happened has caused the researchers to suggest that some organisms in Antarctica might be more resilient than expected. They also note that these findings do not contradict the belief that change is likely coming soon as temperatures continue to rise. It is possible, they also note, that the type of bacteria that live in Antarctica are unable to change and that is why they have not evolved. That would mean they will likely die once temperatures reach a certain point. © 2017 Phys.org More information: Using Captain Scott’s Discovery specimens to unlock the past: has Antarctic cyanobacterial diversity changed over the last 100 years? Proceedings of the Royal Society B (2017). rspb.royalsocietypublishing.or … .1098/rspb.2017.0833AbstractEvidence of climate-driven environmental change is increasing in Antarctica, and with it comes concern that this will propagate to impacts on biological communities. Recognition and prediction of change needs to incorporate the extent and timescales over which communities vary under extant conditions. However, few observations of Antarctic microbial communities, which dominate inland habitats, allow this. We therefore carried out the first molecular comparison of Cyanobacteria in historic herbarium microbial mats from freshwater ecosystems on Ross Island and the McMurdo Ice Shelf, collected by Captain R.F. Scott’s ‘Discovery’ Expedition (1902–1903), with modern samples from those areas. Using 16S rRNA gene surveys, we found that modern and historic cyanobacteria assemblages showed some variation in community structure but were dominated by the same genotypes. Modern communities had a higher richness, including genotypes not found in historic samples, but they had the highest similarity to other cyanobacteria sequences from Antarctica. The results imply slow cyanobacterial 16S rRNA gene genotype turnover and considerable community stability within Antarctic microbial mats. We suggest that this relates to Antarctic freshwater ‘organisms requiring a capacity to withstand diverse stresses, and that this could also provide a degree of resistance and resilience to future climatic-driven environmental change in Antarctica. A satellite image of Antarctica. Credit: USGS, via Wikipedia, Public Domain Citation: Bacteria samples collected in Antarctica a century ago nearly identical to present day samples (2017, June 21) retrieved 18 August 2019 from https://phys.org/news/2017-06-bacteria-samples-antarctica-century-identical.html (Phys.org)—A pair of researchers with the Natural History Museum of London and the University of Waikato have found that bacteria living in a part of Antarctica have not changed much over the past century. In their paper published in Proceedings of the Royal Society B, Anne Jungblut and Ian Hawes describe how they compared the DNA of cynobacterial mats collected during Captain Robert Falcon Scott’s Discovery Expedition from 1901 to 1904 with modern specimens and what they found.