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09/01/2017
Heavy Stuff and a Forgotten Star
CHAPTER 84 Dark and Bright Stuff in the Sky
I ended last month's column saying that I had to go to the bathroom. Actually, after posting the column, I did go to the bathroom, where I picked up my July 2017 issue of Scientific American. In it was an article that stimulated the writing of about half the material in this month's column. The article, "Black Holes from the Beginning of Time", was written by Juan Garcia-Bellido and Sébastien Clesse, based at the University of Madrid and at RWTH Aachen University in Germany, respectively. Currently, two of the biggest unsolved problems in the worlds of astronomy and theoretical physics are the identities of dark matter and dark energy, which together make up about 95 percent of our universe. Only about 5 percent is ordinary matter that makes up ourselves and the stuff we can see and feel. Garcia-Bellido and Clesse propose the possibility that the dark matter that makes up approximately 85 percent of the mass of our universe might be collections of black holes formed early in the evolution of our universe. Very early, as we shall see.
The possibility of the existence of dark matter goes back to the 1800s, with Lord Kelvin proposing the existence of such a thing. Others along the way also speculated on its existence. Last December marked the death of Vera Rubin, a woman who, working with Kent Ford, back in the 1970s, was studying the motion of stars in the Andromeda Galaxy and noticed something strange. The stars and other stuff at the outer edges of the galaxy were moving at roughly the same speed as the stars near the center of the galaxy. This was not supposed to happen according to Isaac Newton, whose laws of motion still hold even though his view of gravity got messed up by Einstein. It took a couple years but Rubin, and I imagine others by that time, concluded that galaxies in general do not have enough mass to hold them together and that the stars making up galaxies should just fly apart into space. This nailed down the idea that there must be some form of dark matter that we can't see that holds the galaxies together.
All manner of astronomical studies, including studies of the cosmic background radiation left over from the Big Bang, have led to the conclusion that dark matter is the dominant form (85 percent) of matter that makes up our universe. Over the years, the theoretical physics community has come to favor dark matter as being an invisible form of matter known as WIMPs, weakly interacting massive particles. So far, however, attempts to detect a WIMP have come up short. No luck even with super high energy machines such as the Large Hadron Collider that recently gave us the Higgs boson, which gives us humans and everything else mass. Don't ask me to explain why.
Could it be that maybe WIMPs don't exist? What's something else that is invisible? A black hole, and it's got lots of mass. Here's where things really get weird. Garcia-Bellido and Clesse propose that dark matter consists of black holes and not just old fashioned black holes that form when stars blow up or when existing black holes swallow stars or other black holes. No, what they propose is the formation of zillions of "primordial black holes" (PBHs) way back only seconds after the Big Bang during the period of inflation. I won't attempt to understand the argument but they propose that in this fraction of a second period there were quantum fluctuations that produced PBHs ranging in size from a mere one hundredth the mass of our Sun up to 10,000 times the mass of our Sun. Later on, the big PBHs could gobble up stuff to become supermassive black holes and attract material to form galaxies with haloes of the smaller PBHs surrounding the galaxies. We can't see these primordial black holes so let's call them dark matter.
Garcia-Bellido and Clesse make the point that we actually may be able to get some degree of experimental confirmation of this explanation of dark matter. They suggest that future experiments on the detection of gravity waves resulting from collisions of black holes may allow us to learn something as to the number and density of black holes. You may remember the excitement not too long ago when members of the so-called LIGO teams detected a gravity wave that was generated over a billion years ago when two black holes collided. Since then, a few more such waves have been detected and soon a third LIGO facility in Europe will be added to the two in the USA in a joint effort. Additionally, a LIGO project in space will be launched sometime in the future. Who knows, if all these projects get together, gravity waves may be a dime a dozen. If so, the number of black holes colliding might be taken as support for the idea that galaxies are surrounded by haloes of black holes in numbers sufficient to support the suggestion that they are indeed the dark matter holding our galaxies together.
In case you did not appreciate the segue from my bathroom trip in the last column to primordial black holes, let's try another bathroom segue. In that column I discussed how the job of cleaning out outhouses in India frequently falls to Dalits, members of what was known as the Untouchable caste before India did away with the caste system. I found in the Spring issue of the magazine Distillations an article titled "A Forgotten Star" by Sam Kean. The forgotten star is Meghnad Saha, who was born in India in 1893, when the caste system was such that in school some students refused to eat in the same room with him because of his lowly caste. I never heard of Saha but Kean likens him to the Darwin of astronomy.
Saha had a checkered career in school, being taken out of school by his father, who thought school not to be worthwhile. After being readmitted, Saha was then thrown out because he participated in some sort of a protest. However, each time someone came to his aid and he finally graduated and entered college. In college, he studied thermodynamics, quantum physics and German. As a young professor he made his name by translating some of Einstein's papers into English and later, after World War I ended, his knowledge of German changed his life. German journals again were making their way to India and Saha found a paper in one of the journals about how electrons are stripped from atoms as the atoms are heated up. Well, Saha had made top marks in astronomy in high school and he connected that German paper with a question related to astronomy.
For decades, astronomers had classified stars into different groupings based on their spectra. When starlight was filtered through a prism the resulting spectra had thin dark lines and the different patterns of dark lines formed the basis for classifying stars in groups. However, nobody knew what the groups meant or why the lines were there in the first place. Saha, after reading the German paper, realized that it was chemistry. As elements are heated up, the positions of the dark lines in the spectra are shifted and as more electrons are stripped on heating the number of lines changes. What astronomers were doing in their groupings was really classifying them by temperature.
Sadly, India lacked high quality astronomical facilities and Saha could not pursue studies to confirm or expand his fundamental findings. Later, he reverted to his confrontational style of politics and engaged in controversies with the likes of Mahatma Ghandi, who apparently wasn't fond of science, which he considered an imperialist institution. Saha was elected to the India's parliament in 1952.
The magazine Distillations, where I found the article on Saha, is a publication of the Chemical Heritage Foundation dedicated to preserving the history of chemistry. Accordingly, one might expect an eclectic mix of papers in their journal. The article following the one on Saha deals with the history and science of the women's sports bra! Another article traces Richard Nixon's contributions to the environment, one of them being the creation of the Environmental Protection Agency. I hate to think of what an article in Distillations decades from now might say about our current leader's contributions to the environment. One of the predictions of those scientists involved in the field of climate change/global warming is that number of storms and their intensity will increase as the world warms up. While the epic flooding in Texas can't be definitively pinned on climate change, is it just a coincidence that only a few weeks ago major flooding in Nepal, India and Bangladesh killed over a thousand people? Or that another hurricane is already headed towards the Caribbean area?
Having had to contend here in New Jersey with a flooded basement in past storms in which the rainfall measured just 5 to 8 inches, I can't imagine over 50 inches of rain. And combining that with threats of tornadoes is more than anyone should have to bear. Will the future icon of the Texas disaster be a first responder, namely the policeman who died after ignoring the pleas of his wife to stay home with the response "I've got work to do"? That works for me.
Next column on or about October 1, hopefully.
Allen F. Bortrum
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