In the last couple of decades, it\u2019s become increasingly clear that massive galaxies like our own Milky Way host supermassive black holes (SMBHs) in their centres. How they became so massive and how they affect their surroundings are active questions in astronomy. Astronomers working with the James Webb Space Telescope have discovered an SMBH in the early Universe that is accreting mass at a very low rate, even though the black hole is extremely massive compared to its host galaxy.<\/p>\n
What\u2019s going on with this SMBH, and what does it tell astronomers about the growth of these gargantuan black holes?<\/p>\n
<\/p>\n The black hole, named GN-1001830, was discovered as part of JADES (JWST Advanced Deep Extragalactic Survey). It is one of the most massive SMBHs discovered by the JWST in the early Universe. While most present-day SMBHs account for about 0.1 % of the mass of their host galaxies, this one accounts for about 40% of its host galaxy\u2019s mass.<\/p>\n The puzzling thing is that GN-1001830 is consuming the gas it needs to grow at a very low rate and is basically dormant. Is it taking a break? Did it experience accelerated bursts of growth in the past? <\/p>\n The findings are in new research published in Nature titled \u201cA dormant overmassive black hole in the early Universe.\u201d The lead author is Ignas Juod\u017ebalis. Juod\u017ebalis is a grad student at the Kavli Institute for Cosmology at the University of Cambridge. <\/p>\n \u201cThe early universe managed to produce some absolute monsters, even in relatively tiny galaxies.\u201d<\/p>\n Ignas Juod\u017ebalis, Kavli Institute for Cosmology, University of Cambridge<\/cite><\/p><\/blockquote>\n<\/figure>\n The JWST has found many SMBHs already in place, only a few hundred million years after the Big Bang. Some of them are overmassive yet dormant, like GN-1001830. Researchers have developed multiple different models to explain them. <\/p>\n One model is the \u2018heavy seed\u2018 model, where primordial gas clouds directly collapsed into black holes that grew to become SMBHs. Another model proposes light seeds that experience powerful bursts of accretion. Both models hold promise, but there\u2019s no certainty. \u201cYet, current datasets are unable to differentiate between these various scenarios,\u201d Juod\u017ebalis and his co-authors write in their research article.<\/p>\n These overmassive black holes that appear to be dormant are testing astrophysicists\u2019 understanding of how SMBHs form and grow. It\u2019s likely that they go through bursts of growth, and in between those bursts, they lie dormant. One of the problems is that it\u2019s very difficult to spot an SMBH that isn\u2019t actively accreting gas. They\u2019re visible when accreting because the accretion disk heats up and emits light.<\/p>\n This one was only spotted because it\u2019s so massive.<\/p>\n \u201cEven though this black hole is dormant, its enormous size made it possible for us to detect,\u201d said lead author Juod\u017ebalis. \u201cIts dormant state allowed us to learn about the mass of the host galaxy as well. The early universe managed to produce some absolute monsters, even in relatively tiny galaxies.\u201d <\/p>\n The Eddington Limit (also known as Eddington Luminosity) is an important factor in the growth of SMBHs. It is a theoretical upper limit on the mass and luminosity of stellar objects, explaining the luminosity we observe in accreting black holes. The Eddington limit is reached when the outward pressure of radiation exceeds the object\u2019s gravitational power, and it can\u2019t accrete more matter. Objects can also exceed this limit, and when that happens, it\u2019s called Super Eddington accretion. Some researchers suggest that Super Eddington accretion was more common in the early Universe and that it explains not only this overmassive black hole but all of the other massive black holes the JWST has discovered in the Universe\u2019s early times.<\/p>\n \u201cIt\u2019s possible that black holes are \u2018born big\u2019, which could explain why Webb has spotted huge black holes in the early universe,\u201d said co-author Professor Roberto Maiolino from the Kavli Institute and Cambridge\u2019s Cavendish Laboratory. \u201cBut another possibility is they go through periods of hyperactivity, followed by long periods of dormancy.\u201d<\/p>\n \u201cIt\u2019s likely that the vast majority of black holes out there are in this dormant state.\u201d<\/p>\n Professor Roberto Maiolino, Kavli Institute and Cambridge\u2019s Cavendish Laboratory<\/cite><\/p><\/blockquote>\n<\/figure>\n The research is based on the detection of broad H-alpha emissions from the SMBH. Those emissions showed that the overmassive black hole has an estimated mass of approximately 4 \u00d7 10? (40 million) solar masses. That\u2019s extremely massive for an object only about 800 million years after the Big Bang. For comparison, Sagittarius A*, the SMBH in the Milky Way, has an estimated mass of about 4.3 million solar masses. <\/p>\n The SMBH in question is one of the most overmassive objects the JWST has found. Its mass is almost 50% of the stellar mass of its host galaxy. That\u2019s about 1,000 times more massive than the relation in local galaxies. <\/p>\n The researchers conducted computer simulations to probe the issue. Their research suggests that the SMBH\u2019s periods of hyperactivity likely exceed the Eddington Limit. The SMBH\u2019s long periods of dormancy and inactivity can last for 100 million years, where the accretion rate is only 0.02 times the Eddington Limit, and are punctuated by episodes of Super Eddington accretion that last for about five or ten million years.<\/p>\n \u201cIt sounds counterintuitive to explain a dormant black hole with periods of hyperactivity, but these short bursts allow it to grow quickly while spending most of its time napping,\u201d said Maiolino.<\/p>\n Since these SMBHs spend far more time dormant than they do active, they\u2019re more likely to be spotted during dormancy. However, they\u2019re far more difficult to spot when they\u2019re not actively accreting and emitting radiation from their accretion rings. That\u2019s part of what makes this detection so valuable. <\/p>\n These results are agnostic when it comes to heavy or light seeds. Instead, they\u2019re all about Super Eddington episodes. \u201cIt is tempting to speculate that our result favours light seed models. However, the same result would also hold if the models had started with heavy seeds. The key feature that allows the properties of GN-1001830 to be matched is the fact that accretion goes through super-Eddington phases, regardless of the seeding mechanism,\u201d the authors explain. <\/p>\n \u201cThis was the first result I had as part of my PhD, and it took me a little while to appreciate just how remarkable it was,\u201d said Juod\u017ebalis. \u201cIt wasn\u2019t until I started speaking with my colleagues on the theoretical side of astronomy that I was able to see the true significance of this black hole.\u201d<\/p>\n \u201cIt\u2019s likely that the vast majority of black holes out there are in this dormant state\u2014I\u2019m surprised we found this one\u2014but I\u2019m excited to think that there are so many more we could find,\u201d said Maiolino.<\/p>\n\n
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