An Astronomical Bonanza
CHAPTER 86 My Gold Ring and Neutron Stars
I'm not much when it comes to jewelry but for the past 66 or so years I've worn my gold wedding ring. In all that time it never occurred to me to ask what was the ultimate source of that gold? I certainly would not have guessed that I would find the likely answer in work related to Einstein and the detection of a gravitational wave. In my column of February 29, 2016 (see archives), I wrote about the mind boggling detection in 2015 of a gravitational wave lasting less than a second, said gravity wave resulting from the merging of two black holes over a billion years ago. The detection of this gravity wave by the so-called LIGO project confirmed Einstein's prediction of gravity waves in spacetime over a century ago. Last month the 2017 Nobel Prize in Physics was awarded to three of the key players in the LIGO project, Kip Thorne and Barry Barish of Cal Tech and Rainer Weiss of MIT.
I first wrote about LIGO in a column posted on May 9, 2000 and you can read that in the archives if you want details of the unbelievable precision of the measurements needed to catch a gravity wave. Recently, the two LIGO facilities in Livingston, Louisiana and in Hanford, Washington were joined by a sister facility called VIRGO near Pisa in Italy. A mere 130 million years ago, two neutron stars in another galaxy came together and on August 17 of this year a gravity wave from that smashup was detected by all three VIRGO and LIGO facilities. The addition of a third member to this group provides astronomers with a much better idea as to the direction in the sky from whence such waves originate. The result has galvanized the astronomical community and at least 70 major telescopes on Earth and in space have been pointed at the source of this wave.
A neutron star, the remnant of a collapsed star, is truly an odd object. Although it may have a diameter of only about 10 miles, it may have a mass a couple times that of our Sun. If its mass is around 3 times that of the Sun it will collapse into another weirdo, a black hole. How can something be so dense? Let's look at a hydrogen atom, in which an electron whirls around a proton, an extremely tiny positively charged particle, the diameter of which is some 60,000 times less than that of hydrogen atom. Suppose than the proton "captures" the electron. Now we have a neutron, which takes up a minute fraction of the space that the atom did. Get a whole bunch of neutrons together when a star explodes and you have a neutron star, which is mostly neutrons. In the vastness of space you might not expect two of these city-sized neutron stars to collide but they do. And the gravity wave that was detected was quite different from the wave detected earlier from the black hole collision. The neutron star wave was some 200 seconds long whereas the wave from the black hole collision was a mere chirp, a fraction of a second.
OK, so we've now detected several gravity waves from black holes colliding. What's so special about this one? It's what happened next. Just two seconds after the arrival of the gravity wave, NASA's Fermi spacecraft detected a gamma ray burst. Gamma rays are a very high energy form of light and bursts of gamma rays have been observed for years. The source of these bursts has been speculated as possibly coming from collisions of neutron stars. Could it be? Was that cosmic wave and the gamma ray burst from the same event? The communication network within the astronomical community is to be marveled at. Within minutes messages were flying. The LIGO/VIRGO team came up with an area to search for a flare-up resulting from neutron stars merging and soon all the major telescopes on earth and in space that could were searching and they found it! There was a new dot where there was none in a picture taken of an area by the Hubble telescope some time earlier. I'm sure there must be many telescopes focused on the site today watching what happens as the debris from the collision spreads out in the surrounding space. This is the first neutron star merger ever seen and it's being studied in all forms of light, X-rays, radio waves, gamma rays, etc.
Hey what about my gold ring? Another major finding. It's well known that we are all made of star stuff. Hydrogen (and helium and probably some lithium) were around from the Big Bang and other elements such as carbon, oxygen, and other common elements in our bodies were formed in supernovas arising from explosions of stars. However, what about those heavier elements such as gold, platinum or uranium and those other elements lying at the bottom of the periodic table? With the astronomical world focused on the neutron star collision, there were spectral data collected that can tell what elements were there and, sure enough, there is gold in them there collisions, an estimated earth-size amount or more! And other heavier elements as well. And all that gold and uranium and stuff can be incorporated into planets that form in that galaxy, or maybe planets that have already formed given that we are looking at what happened 130 million years ago. So I now know that it is most likely that the gold in my ring came from the collision of two neutron stars, I'm thinking billions of years ago.
Another result from the effort is a measure of how fast the universe is expanding. Here I'm not an solid ground in my understanding but I'll take the word of the experts. Apparently, the amplitude of the gravity wave gives the astronomers a measure of the distance to the site of the collision and from the red shift of light similar to the Doppler effect they have figured out the expansion rate as 70 kilometers per second per megaparsec. A megaparsec is 3.3 million light years. I went to an abstract in Nature that deals with this effort and was totally overwhelmed with the number of authors. I'm not sure if that paper is the one but on the Discover magazine website it states one of the dozens of papers already published has 3500 authors!! I don't know how they can winnow down such numbers to decide to whom to give the Nobel Prize for these discoveries!
The work has also provided the best evidence that gravity waves travel at the speed of light and it's the first time we've known the location of the source of a gravity wave. Of course, there have only been a handful of gravity waves detected to date. Considering the monumental findings in this work it's surprising that one of the researchers, Salvatore Vitale, expressed a degree of sadness. Quoting Vitale on the LIGO Caltech website: "Those few days were among the most beautiful days of my life. ... It's also been sad, I don't know if I'll ever live a moment like that again in my life." Thinking back over my scientific career, I haven't been burdened by such a monumental experience. The closest I came was probably being a member of the team that put the first LEDs on a working telephone in the Bell System.
While writing this column about the detection of the elusive gravity wave I couldn't help thinking about how unusually large and costly "instruments" are used to find and study elusive objects. For example, the Large Hadron Collider that was used to detect the Higgs boson is some 17 miles in circumference diameter. The LIGO facilities have the miles long perpendicular tunnels. Another elusive object is the neutrino. While you've been reading this column millions or zillions of neutrinos have passed through you without you noticing them. Recently, I've seen a number of articles describing work on these little fellows. One of the articles was "The Unbearable Lightness of Neutrinos" by Adrian Cho in the June 30 issue of Science, which discusses the Karlsruhe Tritium Neutrino experiment (KATRIN) at the Karlsruhe Institute of Technology in Germany.
I won't attempt to describe the details of the science involved but the goal of the KATRIN project is to try weigh a neutrino. For a long time there was a question as to whether the neutrino even had a mass but apparently the physics community is convinced that it does. As you might expect, the apparatus to carry out the experiment to weigh a neutrino is something unique, to say the least. It involves a huge chamber made of stainless steel that looks like a dirigible and is about a tenth the size of the ill-fated Hindenburg. What really got me was a picture of the chamber being towed through a village in Germany called Leopoldshafen on its way to Karlsruhe. There's a crowd of people there leading the procession with the zeppelin-like chamber bigger than the houses with just two inches clearance for the chamber to pass through! It's worth a trip to the library to look up the picture on page 1326 of the July 30 issue of Science to appreciate the monumental task of getting this thing to its destination.
What really got me was why the chamber was in this village. The chamber was manufactured in the town of Deggendorf, which is some 400 kilometers from Karlsruhe. Now, I'm wondering if the Germans thought of this ahead of time. There was no road from Deggendorf to Karlsruhe that could handle the more than 200 ton, house-size chamber! So, what did they do? They sailed the chamber down the Danube River to the Black Sea, where it was placed on a ship that carried it on a journey of over 5,000 miles through the Mediterranean Sea and then around Spain up to the Rhine River into Germany and Leopoldshafen, where a special truck carried it to Karlsruhe. The cost of the journey was stated to be some 600,000 Euros which is close to $700,000 in US dollars! Boy, I hope they manage to weigh a neutrino!
Next column on or about December 1, hopefully.
Allen F. Bortrum