beecee Posted June 10, 2019 Share Posted June 10, 2019 (edited) https://phys.org/news/2019-06-astronomers-mass-small-black-hole.html If astronomers want to learn about how supermassive black holes form, they have to start small—really small, astronomically speaking. In fact, a team including University of Michigan astronomer Elena Gallo has discovered that a black hole at the center of a nearby dwarf galaxy, called NGC 4395, is about 40 times smaller than previously thought. Their findings are published in the journal Nature Astronomy. Currently, astronomers believe that supermassive black holes sit at the center of every galaxy as massive as or larger than the Milky Way. But they're curious about black holes in smaller galaxies such as NGC 4395 as well. Knowing the mass of the black hole at the center of NGC 4395—and being able to measure it accurately—can help astronomers apply these techniques to other black holes. more at link............. the paper: https://www.nature.com/articles/s41550-019-0790-3 A 10,000-solar-mass black hole in the nucleus of a bulgeless dwarf galaxy: Abstract: The motions of gas and stars in the nuclei of nearby galaxies have demonstrated that massive black holes are common1 and that their masses correlate with the stellar velocity dispersion σ★ of the bulge2,3,4. This correlation suggests that massive black holes and galaxies influence each other’s growth5,6,7. Dynamical measurements are less reliable when the sphere of influence is unresolved; thus, it remains unknown whether this correlation exists in galaxies much smaller than the Milky Way. Light echoes from photoionized clouds around accreting black holes8,9, in combination with the velocity of these clouds, yield a direct mass measurement that circumvents this difficulty. Here we report an exceptionally low reverberation delay of 83 ± 14 min between variability in the accretion disk and Hα emission from the nucleus of the dwarf galaxy NGC 4395. Combined with the Hα velocity dispersion σline = 426 ± 1 km s−1, this lag determines a mass of about 10,000 M⊙ for the black hole (MBH). This mass is among the smallest central black hole masses reported, near the low end of expected masses for heavy ‘seeds’10,11,12, and the best direct mass measurement for a galaxy of this size. Despite the lack of a bulge, NGC 4395 is consistent with the MBH–σ★ relation, indicating that the relation need not originate from hierarchical galaxy assembly nor from black hole feedback. Edited June 10, 2019 by beecee Link to comment Share on other sites More sharing options...
Recommended Posts