A black hole of inexplicable mass | Hacker News Reader

A black hole of inexplicable mass

phys.org

12 pointsdnetesn7 comments

A guess: The Big Bang resulted in lots of pieces some of which were black holes, of a wide variety of masses. In particular, the black holes of billions of solar masses weren't formed from collapsing stars and didn't grow to that size by accumulation but were born that size. And for dark matter, that's from many black holes of tiny masses.

Why couldn't it be a primordial black hole? Why isn't this possibility considered?

Primordial black holes should be far smaller. Super-massive black holes were thought to form through accumulation of matter ("feeding") only. This super-massive black hole is present in the early universe (given how far away it is), and exists much earlier than current theory predicted.

What are the hypotheses on which primordial black holes are thought to be smaller?

If the primordial distribution of matter is really inhomogeneous, for example with a gradient of density from the center of the "blob" to the rim, with the center being very "bloated", would that give birth to supermassive black holes (or maybe one) at the center and smaller ones among the rest of the soup?

> Depending on when exactly they formed, primordial black holes could have masses as low as 10^-7 ounces (10^-5 grams), or 100,000 times less than a paperclip, up to about 100,000 times greater than the Sun. [1]

Also, very small ones could have already evaporated.

> Hawking calculated that any primordial black hole with a mass greater than 10^12 pounds ([10^12 kilograms]; that’s far less than the mass of any planet, dwarf planet, and most named asteroids and comets in our solar system) could still be around today, while those less massive would have already disappeared. [1]

The theories for the likely formation of primordial black holes have been around since the seventies, and they all point to small black holes (compared to, for example, the supermassive black holes at the centers of galaxies). The Wikipedia page has a better history of the thinking around PBHs.[2]

What's remarkable about these new findings is that the age of these quasars being studied suggests that, though they are supermassive, and just like other quasars that are far younger, they appear "the same" and must be labeled "primordial" because of their age. (This is pointed out in the last paragraph of the original article.)

[1] https://www.astronomy.com/science/what-are-primordial-black-...

[2] https://en.wikipedia.org/wiki/Primordial_black_hole

Why didn't you read the article?

> By ruling out a number of alternative solutions, the results strongly support the idea that supermassive black holes started out with considerable masses from the get-go, in astronomy lingo: that they are "primordial" or "seeded large." Supermassive black holes did not form from the remnants of early stars, then grew massive very fast. They must have formed early with initial masses of at least a hundred thousand solar masses, presumably via the collapse of massive early clouds of gas.

Thanks. I thought I had read it, your quote is in the very end of it.

The whole remain of the article, from the title, keeps on saying it's "inexplicable", so I had skimmed it and wondered why they have so little imagination.

Reply on news.ycombinator.com