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Gravitational Waves Might Reveal Primordial Black Hole Mergers Just After the Big Bang

Web_C0288811-Black_hole_merger_and_gravitational_waves-SPL — RUSSELL KIGHTLEY/SCIENCE PHOTO LIBRARY

Imagine the early universe: The first massive stars sparked to life and rapidly consumed their supply of hydrogen. These “metal poor” stars lived hard and died fast, burning quickly and then exploding as powerful supernovas. This first population of stars seeded the universe with heavier elements (i.e. elements heavier than helium, elements known as “metals” by astronomers) and their deaths created the first stellar-mass black holes.

But say if there were black holes bumbling around the universe before the first supernovae? Where the heck did they come from?

Quantum Fluctuations

Some models of universal evolution suggests that immediately after the Big Bang, some 13.82 billion years ago, quantum fluctuations created pockets of dense matter as the universe started to expand. As inflation occurred and the universe cooled, these density fluctuations formed the vast large-scale structure of the universe that we observe today. These cosmological models suggest the early quantum density fluctuations may have been dramatic enough to create black holes — known as primordial black holes — and these ancient Big Bang remnants may still exist to this day.

The theoretical models surrounding the genesis of primordial black holes, however, are hard to test as observing the universe immediately after the Big Bang is, needless to say, very difficult. But now we know gravitational waves exist and physicists have detected the space-time ripples generated by the collision and merger of stellar-mass black holes and neutron stars, astronomers have an observational tool at their disposal.

Simple Idea, Not-So-Simple Implementation

In a new study published in Physical Review Letters, researchers have proposed that if we have the ability to detect gravitational waves produced before the first stars died, we may be able to carry out astronomical archaeological dig of sorts to possibly find evidence of these ancient black holes.

“The idea is very simple,” said physicist Savvas Koushiappas, of Brown University, in a statement. “With future gravitational wave experiments, we’ll be able to look back to a time before the formation of the first stars. So if we see black hole merger events before stars existed, then we’ll know that those black holes are not of stellar origin.”

Primordial black holes were first theorized by Stephen Hawking and others in the 1970’s, but it’s still unknown if they exist or whether we could even distinguish the primordial ones from the garden variety of stellar-mass black holes (it’s worth noting, however, that primordial black holes would have a range of masses and not restricted to stellar masses). Now we can detect gravitational waves, however, this could change as gravitational wave detector sensitivity increases, scientists will probe more distant (and therefore more ancient) black hole mergers. And, if we can detect gravitational waves originating from black hole mergers younger than 65 million years after the Big Bang, the researchers say, those black holes wouldn’t have a stellar origin as the first stars haven’t yet died — they could have only been born from the quantum mess immediately after the birth of our universe.

Antimatter Angst: The Universe Shouldn’t Exist

veil-nebby — The Veil Nebula as seen by Hubble. Because it looks cool (NASA, ESA, Hubble Heritage Team)

The universe shouldn’t exist, according to new ultra-precise measurements of anti-protons.

But the fact that I’m typing this article and you’re reading it, however, suggests that we are here, so something must be awry with our understanding of the physics the universe is governed by.

The universe is the embodiment of an epic battle between matter and antimatter that occurred immediately after the Big Bang, 13.82 billion years ago. Evidently, matter won — because there are galaxies, stars, planets, you, me, hamsters, long walks on sandy beaches and beer — but how matter won is one of the biggest mysteries hanging over physics.

It is predicted that equal amounts of matter and antimatter were produced in the primordial universe (a basic prediction by the Standard Model of physics), but if that’s the case, all matter in the universe should have been annihilated when it came into contact with its antimatter counterpart — a Big Bang followed by a big disappointment.

This physics conundrum focuses on the idea that all particles have their antimatter twin with the same quantum numbers, only the exact opposite. Protons have anti-protons, electrons have positrons, neutrinos have anti-neutrinos etc.; a beautiful example of symmetry in the quantum world. But should one of these quantum numbers be very slightly different between matter and antimatter particles, it might explain why matter became the dominant “stuff” of the universe.

So, in an attempt to measure one of the quantum states of particles, physicists of CERN’s Baryon–Antibaryon Symmetry Experiment (BASE), located near Geneva, Switzerland, have made the most precise measurement of the anti-proton’s magnetic moment. BASE is a complex piece of hardware that can precisely measure the magnetic moments of protons and anti-protons in an attempt to detect an extremely small difference between the two. Should there be a difference, this might explain why matter is more dominant than antimatter.

However, this latest measurement of the magnetic moment of anti-protons has revealed that the magnetic moments of both protons and anti-protons are exactly the same to a record-breaking level of precision. In fact, the anti-proton measurement is even more precise than our measurements of the magnetic moment of a proton — a stunning feat considering how difficult anti-protons are to study.

“It is probably the first time that physicists get a more precise measurement for antimatter than for matter, which demonstrates the extraordinary progress accomplished at CERN’s Antiproton Decelerator,” said physicist Christian Smorra in a CERN statement. The Antiproton Decelerator is a machine that can capture antiparticles (created from particle collisions that occur at CERN’s Proton Synchrotron) and funnel them to other experiments, like BASE.

Antimatter is very tricky to observe and measure. Should these antiparticles come into contact with particles, they annihilate — you can’t simply shove a bunch of anti-protons into a flask and expect them to play nice. So, to prevent antimatter from making contact with matter, physicists have to create magnetic vacuum “traps” that can quarantine anti-protons from touching matter, thereby allowing further study.

A major area of research has been to develop ever more sophisticated magnetic traps; the slightest imperfections in a trap’s magnetic field containing the antimatter can allow particles to leak. The more perfect the magnetic field, the less chance there is of leakage and the longer antimatter remains levitating away from matter. Over the years, physicists have achieved longer and longer antimatter containment records.

In this new study, published in the journal Nature on Oct. 18, researchers used a combination of two cryogenically-cooled Penning traps that held anti-protons in place for a record-breaking 405 days. In that time they were able to apply another magnetic field to the antimatter, forcing quantum jumps in the particles’ spin. By doing this, they could measure their magnetic moments to astonishing accuracy.

According to their study, anti-protons have a magnetic moment of −2.792847344142 μ_N (where μ_N is the nuclear magneton, a physical constant). The proton’s magnetic moment is 2.7928473509 μ_N, almost exactly the same — the slight difference is well within the experiment’s error margin. As a consequence, if there’s a difference between the magnetic moment of protons and anti-protons, it must be much smaller than the experiment can currently detect.

These tiny measurements have huge — you could say: universal — implications.

“All of our observations find a complete symmetry between matter and antimatter, which is why the universe should not actually exist,” added Smorra. “An asymmetry must exist here somewhere but we simply do not understand where the difference is.”

Now the plan is to improve methods of capturing antimatter particles, pushing BASE to even higher precision, to see if there really is an asymmetry in magnetic moment between protons and anti-protons. If there’s not, well, physicists will need to find their asymmetry elsewhere.

Primordial Black Holes Might be Cosmic Gold Diggers

black-hole-gold — 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.

Alexander+Kusenko+2017+image_thmb — 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.

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

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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