Primordial Black Holes Might be Cosmic Gold Diggers

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Neutron stars might have black hole parasites in their cores (NASA’s Goddard Space Flight Center)

When the universe’s first black holes appeared is one of the biggest mysteries in astrophysics. Were they born immediately after the Big Bang 13.8 billion years ago? Or did they pop into existence after the first population of massive stars exploded as supernovas millions of years later?

The origin of primordial black holes isn’t a trivial matter. In our modern universe, the majority of galaxies have supermassive black holes in their cores and we’re having a hard time explaining how they came to be the monsters they are today. For them to grow so big, there must have been a lot of primordial black holes formed early in the universe’s history clumping together to form progressively more massive black holes.

Now, in a new study published in Physical Review Letters, Alexander Kusenko and Eric Cotner, who both work at the University of California, Los Angeles (UCLA), have arrived at an elegant theory as to how the early universe birthed black holes.

Primordial beginnings

Immediately after the Big Bang, the researchers suggest that a uniform energy field pervaded our baby universe. In all the superheated chaos, long before stars started to form, this energy field condensed as “Q balls” and clumped together. These clumps of quasi-matter collapsed under gravity and the first black holes came to be.

These primordial black holes have been singled out as possible dark matter candidates (classed as massive astrophysical compact halo objects, or “MACHOs”) and they may have coalesced to quickly seed the supermassive black holes. In short: if these things exist, they could explain a few universal mysteries.

But in a second Physical Review Letters study, Kusenko teamed up with Volodymyr Takhistov (also from UCLA) and George Fuller, at UC San Diego, to investigate how these primordial black holes may have triggered the formation of heavy elements such as gold, platinum and uranium — through a process known as r-process (a.k.a. rapid neutron capture process) nucleosynthesis.

It is thought that energetic events in the universe are responsible for the creation for approximately half of elements heavier than iron. Elements lighter than iron (except for hydrogen, helium and lithium) were formed by nuclear fusion inside the cores of stars. But the heavier elements formed via r-process nucleosynthesis are thought to have been sourced via supernova explosions and neutron star collisions. Basically, the neutron-rich debris left behind by these energetic events seeded regions where neutrons could readily fuse, creating heavy elements.

These mechanisms for heavy element production are far from being proven, however.

“Scientists know that these heavy elements exist, but they’re not sure where these elements are being formed,” Kusenko said in a statement. “This has been really embarrassing.”

A cosmic goldmine

So what have primordial black holes got to do with nucleosynthesis?

If we assume the universe is still populated with these ancient black holes, they may collide with spinning neutron stars. When this happens, the researchers suggest that the black holes will drop into the cores of the neutron stars.

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Alexander Kusenko/UCLA

Like a parasite eating its host from the inside, material from the neutron star will be consumed by the black hole in its core, causing the neutron star to shrink. As it loses mass, the neutron star will spin faster, causing neutron-rich debris to fling off into space, facilitating (you guessed it) r-process nucleosynthesis, creating the heavy elements we know and love — like gold. The whole process is expected to take about 10,000 years before the neutron star is no more.

So, where are they?

There’s little evidence that primordial black holes exist, so the researchers suggest further astronomical work to study the light of distant stars that may flicker by the passage of invisible foreground black holes. The black holes’ gravitational fields will warp spacetime, causing the starlight to dim and brighten.

It’s certainly a neat theory to think that ancient black holes are diving inside neutron stars to spin them up and create gold in the process, but now astronomers need to prove that primordial black holes are out there, possibly contributing to the dark matter budget of our universe.

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Did Dark Matter Reionize the Universe?

Did dark matter characterize our early Universe?

Immediately after the Big Bang, 13.72 billion (±120 million) years ago, the Universe was filled with energy. Nothing but energy. No protons, electrons, quarks or photons; just energy. Even the fundamental forces of nature (gravity, weak, strong, electromagnetic) were a confused mess and could not be distinguished, but that issue didn’t last for long. 10-43 seconds after the Big Bang the grand unification epoch began, when gravity is thought to have separated from the soup. Shortly after, the strong force separated from the electroweak force in a period called the electroweak epoch.
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Mystery Blob Detected 12.9 Billion Light Years Away

The Himiko object, the most massive object ever discovered in the early universe (M. Ouchi et al.)

Take a good look, this is one of the most mysterious, massive objects ever discovered in the cosmos. We don’t really know what it is, but this thing is huge, spanning 55,000 light years across (the approximate radius of our Milky Way). What makes this all the more intriguing is the fact that this object formed only 800 million years after the Big Bang and it is 10 times more massive than the next biggest object observed in the early Universe. But what is it?
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The Universe Could Soon Be 6,000 Years Old… In Texas

Yesterday, some strange stuff went down in Texas. It may not be a surprising development, especially if you have been following Phil Plait’s articles at Bad Astronomy, but it is still… strange. I don’t usually discuss creationism on Astroengine.com as I’ve always considered much of the wrangling to be an evolution/intelligent design “debate” (debate? Really? Which century are we in again?). To be honest, I’m glad I work and write in a field that can sidestep a lot of creationist bunkum. But hold up there, it’s not that simple. It would appear that some individuals in the Texan educational board have taken it upon themselves to give schools “the option” to teach, in astronomy classes, an ‘alternative’ to Big Bang theory. OK, that’s cool, what alternative scientific theory can be put forward?

That’s the problem, there isn’t a scientific alternative. Big Bang theory is solid, and with the help of WMAP we know the Big Bang occurred 13.73 billion years ago (+/-120 million years). Unfortunately, one member of the Texas Educational Board wants the state’s science classes to teach creationism alongside cosmology, meaning students will have one of the most confusing and damaging cosmology lessons I can possibly imagine.

Guess what kids, the Universe is somewhere between 6,000 to 13,730,000,000 years old. Yes, it’s looking like creationism will be taught alongside cosmology
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