As the world discusses the magnitude of the energy of hydrogen bombs, C Sivaram writes about celestial explosions, which release as much energy as the sun would emit in its entire lifetime of 10 billion years.
The first hydrogen bomb (H-bomb) was detonated by the US on November 1, 1952 in Enewetak Atoll in the Marshall Islands. The Russians soon followed a few months later, while Britain detonated its first H-bomb in November 1958, followed by France and China.
The development of thermonuclear bombs made it possible to build warheads five times lighter, but several hundred times more powerful than the nuclear fission devices dropped on Hiroshima and Nagasaki.
In the latter, the nuclear fission chain reaction set up in the isotopes of the heavy elements, i.e., uranium 235 (U 235) and plutonium trigger the explosive release of nuclear energy. Actually, the so-called hydrogen bomb uses heavier isotopes of hydrogen, that is deuterium and tritium, which undergo nuclear fusion reactions to form helium, but at temperatures exceeding 100 million degrees. So, the deuterium-tritium mixture has to be heated up first to such high temperatures by triggering or exploding nuclear fission bomb, the nuclear fission reactions occurring spontaneously, once a critical mass of U 235 or plutonium is assembled.
The process
The fission bomb first heats up the heavy hydrogen isotopes (kept in a surrounding container) to some hundred million degrees. The nuclear fusion reactions then occur causing the isotopes to combine to form helium. As the fusion reactions occur only at such high temperatures, they are dubbed thermonuclear reactions. Such reactions release several times more energy than the fission reactions, where uranium splits up into lighter elements like the nuclei of barium and krypton.
On March 1, 1954 at Bikini Atoll in the Pacific, the US tested its first deliverable hydrogen bomb. The ‘Bravo’ test had an explosive force of several thousand Hiroshima-type bombs and it vapourised the test island, parts of two others and left a mile-wide crater in the lagoon floor. The Bikini and Enewetak Atolls were used for 66 nuclear tests in 10 years. In October 1961, Russia carried out the biggest nuclear explosion on Earth, a 50-megaton hydrogen bomb, several thousand times more powerful than the Hiroshima bomb. The Russian physicists had bypassed the American billion dollar tritium bomb and gone straight to the cheaper and simpler lithium hydride bomb. The Chinese thermonuclear device used lithium deuteride.
It’s ironic that despite all talk on curbing nuclear arms, in about 50 years, the US carried out one test every two weeks, while Russia carried out one test in every three weeks. So, in the first 50 years after the first bomb was dropped, more than 2,500 tests were carried out by the main nuclear powers, which is one test every week. So, before the nuclear atmospheric test ban treaty in 1963, more than 500 massive nuclear explosions were carried out totally. Even after the treaty, China conducted 23 atmospheric tests, but France had more than 40 atmospheric tests in 10 years.
When North Korea conducted its recent test, the blast had been detected by a global seismic network, called international monitoring system, that aims to make sure that no nuclear explosion on Earth goes undetected. More number of sophisticated monitoring systems are being developed to find even ‘difficult to detect’ events.
Up in the space
In the 1970s, the United States used Vela satellites to try and spot whether any country was carrying out secretive nuclear blasts. The satellites had sensors to detect gamma ray flashes from the terrestrial nuclear explosions. Ironically, this group of satellites spotted many gamma ray flashes coming from all over the sky and not from the Earth. They had accidentally detected several tremendously powerful celestial explosions. These so-called gamma ray bursts were a mystery for two decades, when finally in the 1990s, it was realised that they were occurring at a place billions of light years away. In a few seconds, these gamma ray bursts release as much energy as the sun would emit in its entire lifetime of 10 billion years.
For reference, the sun emits an amount of energy that is equivalent to the energy that all our power stations, when put together, would produce in several million years. And these objects emit in one second what the Sun would release in 10 billion years! If one of these objects was at a distance of even 2,000 light years from us, the planet would be fried. The flux falling on Earth would be far greater than the combined energy released by all the nuclear arsenals of mankind.
The sun, of course, also produces its vast outpourings of energy from nuclear fusion reactions at its core; about 600 million tonnes of hydrogen being consumed every second. However, this is not an explosive release of energy. Actually, the rate is very slow considering the large volume of the core. But there are stellar nuclear explosions all around. Compact stars, known as white dwarfs, accumulate hydrogen from a companion star.
When this reaches a critical mass, the accreted hydrogen undergoes a thermonuclear explosion (literally a celestial H-bomb) and seen as a nova. If a white dwarf, by accreting matter, becomes more massive than the Chandrasekhar limit, maximum mass theoretically possible for a stable white dwarf star, it can undergo a titanic thermonuclear explosion called a type Ia supernova. It would be one billion times more luminous than the sun and release as much energy in a few weeks, as the sun radiates in its entire lifetime.
Neutron stars
More compact objects called neutron stars, forming part of so-called X-ray binaries, which may consist of a neutron star and white dwarf, undergo thermonuclear flashes lasting several seconds or even minutes. The accumulated helium (or carbon), from their companion stars, is detonated on the neutron star surface as a tremendous thermonuclear explosion, releasing in a few minutes what the sun would radiate in a thousand years. Massive stars can in their final stages collapse catastrophically, leading to a Type II supernova, which can lead to the formation of a neutron star.
Apart from being a tremendous thermonuclear celestial bomb, a Type II supernova is literally a neutron (and a neutrino) bomb. The neutron bomb (as an ultimate nuclear device) is presumably still under secretive testing on Earth. Most of the energy is released as neutrons, rather than as a destructive blast destroying everything. Beryllium and lithium undergo reactions, which can double the incoming neutrons. So, these are used as “blankets” to improvise on nuclear devices.
However, a Type II supernova produces an intense flux of neutrons, perhaps producing all the heaviest elements like gold and uranium in a few seconds through the so-called rapid neutron capture or “r process”. It also releases 1058 neutrinos. The supernova in 1987, from a neighbouring galaxy, released such a burst of neutrinos that they were detected on Earth.
Yes, one nuclear test was carried out on Earth every week during the Cold War. But, every second, a massive star is collapsing somewhere in our Universe, as a tremendous thermonuclear celestial bomb releasing as much energy in a short time as the sun would emit in its entire lifetime of 10 billion years!
