Is a Primordial Black Hole Aiming at Us?

 Many mysteries about our universe haunt astronomers.  Among those, one of the most perplexing is what they call “dark matter.” By studying the gravitational interactions and motions of galaxies, astronomers learned that most of the matter in our universe, about 86%, is composed of stuff that has no connection to light. It doesn’t emit, reflect, or absorb any type of electromagnetic radiation, including light, hence the moniker dark matter.

Astronomers know it’s there. The evidence for it is overwhelming. Galaxies rotate so fast that they should fly apart unless there is a lot more mass than can be accounted for in stars, planets, gas clouds, and all the other stuff we can see. But they have no idea what it is.

Some astronomers have suggested that so-called primordial black holes (PBH) may be responsible for dark matter. Black holes are the extreme members of the cosmic zoo. Their gravity is so strong that nothing, not even light, the fastest thing in the universe, can escape. Normal black holes form when giant stars explode as a supernova, and the remaining core becomes so compressed by gravity that it collapses into a black hole. These are typically 5 to 10 times the mass of our sun. Black holes also do not emit or reflect any light.

PBHs form quite differently. When the universe began in the Big Bang, the density of matter was unimaginably high. Particles would constantly collide, sometimes sticking together. Usually, they would break apart in another collision a tiny fraction of a second later. Some areas of this infant universe were so dense that matter could clump together so tightly that they could form black holes millions of times smaller than a single proton. They may contain no more mass than a moon, a mountain, or even an elephant. Once formed, the extreme gravity holds them together regardless of how many collisions they may experience.

PBHs may well exist in such numbers that they could fill space. They might well be responsible for most or even all the dark matter that we know exists out there. Sarah Geller, a theoretical physicist at the University of California at Santa Cruz, co-authored a study of PBHs. They wondered how often one might pass through our solar system. "If there are lots of black holes out there, some of them must surely pass through our backyard every now and then," Geller said.

A primordial black hole interacting with Earth. Credit ESO/M Kornmesser

The researchers wondered "what might happen if a black hole punched through Earth's crust, or passed through our atmosphere, or left a crater on the moon," Geller said. "We even asked ourselves what would happen if one of these tiny black holes hit a human." After crunching the numbers, they realized that the chances of one hitting something as small as a person, or even our planet, were extremely tiny.

"We started thinking about the very precisely measured orbits of objects in the solar system," Geller said. "They could produce wobbles in the orbits of objects in the solar system that are big enough for us to measure." They estimate that one could pass through the inner parts of the solar system once every decade or so. The researchers aren’t claiming that PBHs exist, that they make up any of the dark matter, or that they are in or have passed through the solar system. But if they do exist in sufficient numbers that some or many have visited our planets, we can detect their gravitational pull.

Just to ease your mind, a separate study found that even if a PBH passed through your body, they are so tiny and so fast, they would likely cause no noticeable effect on your body.

Each month, I write an astronomy-related column piece for the Oklahoman newspaper. After it is published there, I post that same column to my blog page.

This is reprinted with permission from the Oklahoman and www.Oklahoman.com.

Where Did the Gold in Your Ring Come From?

 

Astronomers have a pretty good understanding of where the matter in our universe comes from. In the beginning, there was only hydrogen, helium, and a tiny smattering of lithium. Everything else, the oxygen we breathe, the carbon that makes up so much of our bodies, the silicon, magnesium, aluminum, and other elements that make up our planet, were all formed inside stars and released into the wider universe when stars explode.

Supernova Remnent Casseopeia A. Credit NASA

But there is one element that still has astronomers bumfuzzled: gold. There is too much of it. Supernova explosions can’t begin to account for the amount that we see because the gold is trapped in the neutron stars, the remnants of supernovas. Colliding neutron stars release prodigious amounts of gold, as do so-called magneto-rotational supernova. These rare supernovas spin so fast and generate such strong magnetic fields that they literally turn themselves inside out. This releases all of their trapped gold atoms. But while both produce extraordinary quantities of gold, they are extremely rare and cannot begin to account for all the gold we find here on Earth.

Chiaki Kobayashi is an astrophysicist at the University of Hertfordshire in the United Kingdom. She led the new study to determine the origin of gold. "There are two stages to this question," she said. "Number one: neutron star mergers are not enough. Number two: Even with the second source, magneto-rotational supernova, we still can't explain the observed amount of gold." Kobayashi and the other study authors accounted for the formation and relative abundance of all elements from carbon to uranium. All except for gold. Its abundance remains a mystery.

So, the next time you put on that gold ring or necklace, you can marvel that our Earth has as much gold as it does.

 

 Each month, I write an astronomy-related column piece for the Oklahoman newspaper. On the following day, I post that same column to my blog page.

 This is reprinted by permission from the Oklahoman and www.newsok.com.