{"id":337988,"date":"2025-12-09T00:49:06","date_gmt":"2025-12-09T00:49:06","guid":{"rendered":"https:\/\/www.newsbeep.com\/us\/337988\/"},"modified":"2025-12-09T00:49:06","modified_gmt":"2025-12-09T00:49:06","slug":"the-primordial-black-hole-saga-part-2-not-your-normal-black-holes","status":"publish","type":"post","link":"https:\/\/www.newsbeep.com\/us\/337988\/","title":{"rendered":"The Primordial Black Hole Saga: Part 2 – Not Your Normal Black Holes"},"content":{"rendered":"

(This is Part 2 of a series on primordial black holes. Check out Part 1 here!<\/a>)<\/p>\n

At the same time that Vera Rubin was turning cosmology upside down with conclusive evidence for the existence of dark matter, Stephen Hawking was doing\u2026Stephen Hawking things. Which at the time largely concerned minor questions like the ultimate origins to the universe and the true nature of black holes.<\/p>\n

In his work Hawking realized that black holes aren\u2019t exactly, precisely, totally, 100% black. They\u2019re a little\u2026gray. Or maybe dusty maroon. Or maybe something else, but definitely not black. Due the complex relationship between a black hole\u2019s event horizon and the quantum fields that soak all of spacetime (which for now we\u2019ll just call magic and move on, but feel free to ask and I\u2019ll do a whole episode on it) that black holes slowly emit radiation.<\/p>\n

Now this isn\u2019t a lot of radiation. For a typical solar mass black hole, we\u2019re talking a rate of around one photon a year. Which\u2026okay it\u2019s not nothing which is the important part.<\/p>\n

But what does all this have to do with dark matter?<\/p>\n

From all available evidence we suspect that dark matter is matter. It\u2019s not a new force or change to how gravity operates. And the easiest way to make dark matter is for it to just exist. Like normal matter that\u2019s not exactly very bright. Of which we have plenty of examples in the nearby universe. Planets and asteroids and bits of dust aren\u2019t particularly glowy, all things considered. And black holes, even the radiating kind, are\u2026well they\u2019re close enough to black that they might as well be invisible.<\/p>\n

So case closed! You just take a galaxy or cluster or whatever and fill it up with a bunch of black holes, and boom, you\u2019ve soled the dark matter mystery. Can\u2019t see the black holes, but they still have gravity, and the rest of cosmology can proceed.<\/p>\n

Except for one teensy tiny little problem: the universe can\u2019t make enough black holes.<\/p>\n

There\u2019s only one bona fide confirmed way to manufacture black holes, and that\u2019s through the deaths of massive stars. You take a giant star, let it run long enough that it fuses iron in its core, ad before you know it, it turns inside out and you\u2019ve got a supernova explosion on your hands. And in the brief instant right before total catastrophe, the pressures in the core reach such insane levels that nothing can stop total and complete collapse, aka the formation of a black hole.<\/p>\n

So to make black holes you need stars, and to make stars you need stuff. But there\u2019s only so much stuff in the universe.<\/p>\n

We know this through a completely different calculation that doesn\u2019t involve dark matter at all. It\u2019s called Big Bang nucleosynthesis, and it\u2019s our understand of how the universe worked when it was only a few minutes old. At that time, when the entire observable cosmos was smaller than a light-year or so, the temperatures and pressures were so high that nuclear fusion could take place. This made protons and neutrons bind together to make deuterium, helium, and a little bit of lithium.<\/p>\n

But the universe was also expanding, and once it got too big it got too cold for the fusion party to keep going. This locked in the total amount of matter available for the entire future history of the universe. And what\u2019s most amazing about this story is that it predicts the ratio of hydrogen to helium in the universe to be 75% hydrogen and 25 % helium (which everything else being a rounding error). <\/p>\n

And that\u2019s\u2026what we see in the real universe. So that\u2019s nice.<\/p>\n

What big bang nucleosynthesis also tells us is that the total amount of normal matter, the kind of matter made out of protons and neutrons, can be no more than 4 or 5 percent of the total amount of stuff available in the universe.<\/p>\n

It\u2019s just locked in from the very beginning. So you can\u2019t have the dark matter be black holes, because for there to be enough black holes you first need a lot of stars, and to have a lot of stars you need a lot of material, and to have a lot of material you need a lot of protons and neutrons, and all of our calculations and estimates and theories and observations and experiments all tell us that there aren\u2019t enough protons and neutrons.<\/p>\n

So black holes are not the dark matter.<\/p>\n

Unless you\u2019re Stephen Hawking. Or, at least thinking like he did in the 1970\u2019s, because he\u2019s dead now and not up to much thinking anymore.<\/p>\n

Hawking didn\u2019t set out to solve the dark matter mystery. He knew it was happened and was curious about the new developments, but never made it the focus of his research. Instead he was interested in finding ways to test his new discovery that black holes emit radiation.<\/p>\n

His calculation suggested that smaller black holes emit more radiation than larger ones. And that REALLY small black holes pop off like mini-supernovas in flashes of intense energy. But once again, the known process of building black holes kills all the joy: stars have to be big enough to fuse iron to trigger black hole formation, which means the smallest black holes are going to be a few times the mass of the Sun.<\/p>\n

And those black holes will eventually evaporate in about\u202610^100 years. Astronomers are patient people but good luck getting funding for an experiment that will have to run for many multiples of the present age of the universe.<\/p>\n

Case closed. Unless there\u2019s another way to build black holes.<\/p>\n

To be continued…<\/p>\n","protected":false},"excerpt":{"rendered":"(This is Part 2 of a series on primordial black holes. Check out Part 1 here!) At the…\n","protected":false},"author":2,"featured_media":337989,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[49],"tags":[199,79],"class_list":{"0":"post-337988","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-physics","8":"tag-physics","9":"tag-science"},"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/posts\/337988","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/comments?post=337988"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/posts\/337988\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/media\/337989"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/media?parent=337988"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/categories?post=337988"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/tags?post=337988"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}