Advanced science, Environmental, International, Technical

Solar radiation management can help combat climate change

In the Environmental Physics course that I teach from time to time, a student once remarked that we really do not have to worry about the deleterious effects of climate change because technology would be able to solve all the problems we are facing. At that time, I thought this viewpoint is an extreme case of technological optimism. But today, as the likelihood of international consensus to stabilise atmospheric composition of greenhouse gases seems remote while the consequences of climate change are becoming more apparent and direr, many in the scientific community believe that the potential last-ditch effort to stave off the disastrous impacts of climate change is to appeal to technology, geoengineering in particular. Even the United Nation’s Intergovernmental Panel on Climate Change considers geoengineering as a necessary Plan B if global warming does not show any signs of slowing.

Geoengineering is deliberate, large-scale manipulation of the Earth’s environment to counteract anthropogenic climate change. It encompasses two different approaches using a variety of cutting-edge technologies to undo the effects of greenhouse gas emissions. They are removal and sequestration of carbon dioxide to lower its concentration in the atmosphere and offsetting global warming by targeting the overall amount of solar energy reaching the Earth. The removal technologies were discussed in an op-ed piece published in this newspaper on November 29, 2018.

Some of the offsetting options scientists are exploring are reflecting part of the sunlight back into space before it reaches the Earth’s surface, allowing more of the heat trapped by the Earth’s surface to escape into space, and increasing the reflectivity of roofs, Arctic ice, glaciers, pavements, croplands and deserts. Known as Solar Radiation Management (SRM), these options would slow down the rise in Earth’s temperature until carbon dioxide emissions can be reduced enough to prevent catastrophic repercussions of human-driven climate change.

The fraction of incoming sunlight that is reflected back to space could readily be changed by increasing the reflectivity of the low-level clouds. This could be achieved by spraying seawater in the air where they would evaporate to form sea salt, which would seed the clouds above the oceans making them thicker and more reflective. Several simulations have confirmed that the seeding mechanism, also known as Marine Cloud Brightening, would work with the likelihood to lower temperatures at a regional level.

Another proposed cloud-based approach involves thinning the high-altitude Cirrus clouds in the stratosphere by injecting ice nuclei into regions where the clouds are formed. These wispy clouds do not reflect much solar radiation back into space, and instead trap heat in the atmosphere by absorbing thermal radiation emitted by the Earth. While this method is not technically an example of SRM, thinning Cirrus clouds would provide more pathways for the trapped heat to escape into space, and thus, potentially cool the Earth. Currently, work in this field is limited to theoretical studies at research institutions. However, research shows that a cooling of about one degree Celsius is possible by thinning the clouds globally.

Scientists have known for a long time that volcanic eruptions could alter a planet’s climate for months on end, as millions of sunlight-reflecting minute particles (aerosols) are spread throughout the atmosphere. Indeed, the “cold and miserable” summer of 1816 in China, Europe and North America is attributed to the enormous eruption of the Indonesian volcano Tambora in 1815. Though the aerosol haze produced by the Tambora eruption reflected less than one percent of sunlight, it was enough to drop global temperatures by as much as two degrees by the summer of 1816.

The 1991 explosion of Mount Pinatubo in the Philippines cooled the Earth by about 0.5 degrees, while the average global temperatures were as much as one degree cooler for the next five years after the 1883 eruption of Krakatoa in Indonesia. Furthermore, the volcanic-induced cooling of the oceans caused by Krakatoa’s eruption was enough to offset rise in the ocean temperature and sea level for a few decades.

Inspired by these eruptions and the subsequent cooling effect of their sunlight-blocking plume of sulphate particles, scientists are suggesting injecting sulphate aerosols or hydrogen sulphide in the stratosphere. The geoengineering research programme at Harvard University is currently trying to model how clouds of such particles would behave.

One of the more practical SRM techniques that can be implemented easily is whitening surfaces like roofs, croplands and pavements to reflect more sunlight back into space. By absorbing less sunlight, they would negate some of the warming effect from greenhouse gas emissions. This is what greenhouse owners do with whitewash and blinds.

The small island of Bermuda in the North Atlantic is leading the way with white roof houses that not only reflect sunlight, but also keep the homes cooler during the hotter months. A study at the Lawrence Berkeley National Laboratory in California indicates that a 1,000 square foot of white rooftop has about the same one-time impact on global warming as reducing ten tons of carbon dioxide emissions.

Ice sheets are responsible for reflecting lots of sunlight into space. So less ice in the Arctic due to melting means less heat leaving the planet. Hence, scientists want to spread tiny glass beads around the Arctic in the hopes of making the polar ice more reflective and less prone to melting. Another idea is to cover deserts and glaciers with reflective sheets.

Perhaps the most challenging concept to control solar radiation entails deploying an array of reflecting mirrors at strategic points between the Sun and the Earth—just as we all do with sunscreens and sunblocks. Calculations by space scientists at the Lawrence Livermore National Laboratory in California indicate that a mirror roughly the size of Greenland would be able to block one to two percent of solar radiation from reaching the Earth. The idea of a sunscreen is still on the drawing board.

Finally, as we transition into a new era in which human activity is shaping the Earth more than the natural forces, technology could be seen as a way of humans reshaping the planet by limiting the adverse effects of climate change. Also, because international political efforts to curtail greenhouse gas emissions have been slow in coming, solar radiation management is a possible measure to be used if climate change trends become disruptive enough to warrant extreme and risky measures.

Quamrul Haider is a professor of physics at Fordham University, New York.

Advanced science, Bangladesh, Environmental, International, Life as it is, Political, Technical

We are hurtling towards a disastrous Climate Change (Part II)

In Part I, it was shown unambiguously that human activities from the period of industrial revolution (1720 – 1800) had been the root cause for the rise of global temperature by over 1ºC due to emission of greenhouse gases into the atmosphere. As industrial activities became more and more widespread, the greenhouse gas emission and its accumulation in atmosphere increased correspondingly and the global temperature went up even higher.

Climatologists, Geoscientists, Atmospheric Scientists and so forth had been warning the world leaders of signs of increase in global temperature over and above the natural increase right from the early 1970s. As time passed, their warning became louder and louder, but the leaders of industrialised countries deliberately ignored them or rejected their scientific evidence. United States of America is, in particular, the champion of such denial right from the beginning – presidents like Ronald Reagan, George H W Bush, George W Bush and recently Donald Trump are all rejectionists of man-made global climate change.

Despite incontrovertible scientific principle and evidence that increase in carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), chlorofluorocarbon (CFC) and other gases in atmosphere traps energy i.e. heat within earth’s atmosphere and thereby increase global temperature, the deniers reject all these arguments. Their short-sightedness and the damage they are inflicting on Earth are simply inexcusable.

The consequences of global increase in temperature are given below:

When air temperature increases, land surface temperature increases more than the sea temperature, as heat capacity of water is more than that of soil. What it means is that for the same amount of heat, water temperature will increase less (due to its high heat absorbing capacity) than that of soil. Similarly, when air temperature drops, land temperature drop would be more than sea temperature. Thus, sea temperature does not move up or down as much as the adjoining land mass temperature and that is why we get the moderating effect of sea.

This land-sea temperature differential is also the cause of rain, storm, snowfall etc. In the summer, land temperature increases substantially causing air to rise to high altitude and sea air being relatively cooler and heavier but laden with moisture moves towards land and gives rain. A higher temperature difference would give higher amount of rain, higher wind velocity (storm, tornado etc). Reciprocally, in the winter there would be severe snowfall, extreme cold spell etc. So, the climate change would exacerbate the nascent conditions.   

Melting of inland glaciers around the world, which would then be followed by Antarctic and Greenland ice sheets melting would cause sea-level to rise significantly. It is not only the extra volume of water from melting ice but also the thermal expansion of water due to rise in temperature that would cause sea-levels to rise and inundate large areas of land mass. It is estimated by the Inter-governmental panel on Climate Change (IPCC) that by the end of this century, the sea-level is likely to rise by at least 6ft (or even higher), if no remedial action is taken now i.e. if life continues as ‘business-as-usual’. But if action is taken urgently now to limit temperature rise to 1.50C, the sea-level rise may be contained within 3ft to 6ft.

Figure 1. Mangrove areas of Sundarbans in Bangladesh at present

In addition to that, worsening storm surge, frequent tropical storm and concentrated rainfall will affect large coastal areas and even inlands of a country, islands and low-lying areas. Bangladesh, a low-lying country, would be badly affected by sea-level rise. The average landmass there is only about 5ft above the sea level. Figure 1 shows the mangrove areas of Sundarbans in the southern part of the country at present and Figure 2 when sea level rises by the smallest estimated margin of about 3ft.  It can be seen that large areas have been inundated by the rising sea level. It is estimated that 1.3 billion people world-wide would be affected, which may require their permanent relocation or even mass migration.

Figure 2. Mangrove areas of Sundarbans in Bangladesh anticipated to be around 2050 AD.

It may be pointed out that sea-level rise does not just cause submersion of landmass, which might have been habitable area previously, but also damages arable land. Ingress of saline water precludes cultivation of crops, vegetation etc even in surrounding areas which are not inundated. 

Thawing permafrost speed up global warming, as permafrost is basically soil that stays below freezing (00C) for at least two years. Plants capture carbon dioxide (CO2) from the atmosphere by photosynthesis process and then this carbon is released when wood (in roots) decays in the soil or carbon is compressed in the natural process to form coal. In Arctic areas, wood decay or decomposition is very slow and hence these areas are regarded as carbon sink. However, decomposition increases as temperature increases causing enhanced carbon emission. The inventory of frozen carbon in permafrost is 1.5 trillion tons, which is nearly twice the amount of carbon in the atmosphere now!

Wildfires are caused due to global warming and these then contribute to further global warming. Wildfire thus has a positive (destructive) feedback effect. Trees and vegetation absorb CO2 and convert it to oxygen (O2), thus acting as sinks. Tropical forests in Indonesia, Malaysia, Brazil and in other parts of the world play a vital role in carbon sequestration. However, wildfires effectively convert the sink of carbon straight into source of carbon! The forest fires that are razing in the Amazon rain forest now, which is regarded as the lungs of the planet Earth, are extremely damaging. These forest fires are not natural wildfires; these are deliberate man-made fires to clear forest areas for agricultural use (deforestation). Man is making the planet uninhabitable. 

The effect of all these changes is causing severe disruption to the climate. Where there were moderate rainfalls, now there are severe rainfalls causing flash flood, bursting of dams, landslides etc. In 2018, there were devastating floods in Japan, North Korea and India. In 2019, bridges in North Yorkshire, England collapsed when full month’s rain fell in just four hours.

While some parts of the world were having tremendous amount of rainfall in short spell of time, others were baking in heat waves. France’s capital Paris experienced this summer (June 2019) the highest temperature of 46ºC and India experienced 50ºC. Pakistan experienced a deadly heat wave where highest recorded temperature was 54ºC!

There were unprecedented wildfires in Greece and Australia. Wildfires in the forest area called Paradise in California are devastating and becoming a regular event. Northern Finland (in Arctic Circle) and Siberia were used to be considered so cold that wildfires were thought to be incredible, but not anymore. Last year as well as this year, wildfires in those areas devastated large land mass.

In the year 2017, hurricane Irna, a category 5 storm, was the most powerful Atlantic storm in a decade to strike the Caribbean and Southern US. In addition, hurricane Harvey in Texas and hurricane Maria in Dominican Republic wrought havoc. Monsoon floods in Bangladesh and mudslides in Sierra Leone are devastating natural disasters in 2017.

The frequency and severity of these natural disasters are breaking all previous records. A natural disaster, which only 10 or 15 years ago would have been considered once in 100 years event, is now happening once or twice a decade and if runaway conditions are allowed to continue, those events may become regular events!

Donald Trump not only denies man-made climate change but also encourages activities which cause climate change. He and his right-wing coterie of extremist Republicans in America hold and promote the view that climate change is due to natural phenomenon. There is an Institute in America, called the Heartland Institute (which Trump endorses and supports) which claims to be one of the world’s “leading free market think-tanks” and promotes “free market solutions to social, economic and environmental problems”. It disputes scientific observations and knowledge on climate change (as is usual with right-wing cliques to denigrate scientific knowledge), criticises climate mitigation activities and promotes use of fossil fuels. 

When confronted with increased severity and more frequent incidences of droughts, forest and bush fires, floods, storms, tropical cyclones, cold spells etc, these climate change deniers assert these are just natural phenomena; nothing to do with human activities. Their denial is either based on sheer ignorance or moral depravity.

Dr A Rahman is an author and a columnist


Advanced science, Bangladesh, Environmental, International, Life as it is, Technical

Cyclone Fani and global climate change

The temperature of the Earth changes over geologic time. During periods of glaciation, it was about five degrees Celsius cooler and in the interglacial period about five degrees warmer. The last glaciation period was 100,000 years ago. Since then, there have been fluctuations of a few degrees, the period of 1430 to 1850 being one of particularly low temperatures in Europe. Although there were fluctuations from year to year, it seems evident that there has been a steady increase in average global temperature since the Industrial Revolution. According to the World Meteorological Organization, average global temperatures will reach a new milestone this year—one whole degree higher than temperatures before industrialisation.

In the early 1990s, when concern about climate change caused by the rise in temperature became widespread, the “signal” of anthropogenic effects hadn’t unambiguously emerged from the “noise” of natural climate variability. However, we now know that most of the climate-related changes observed over the past 50 years is attributable to human activities. In fact, by burning prodigious amounts of fossil fuels that emit carbon dioxide, which is the principal greenhouse gas, we humans have taken Earth’s atmosphere in general and global temperature in particular into a regime that our planet hasn’t seen for millions of years.

Although the interplay between carbon dioxide and temperatures is complex and not necessarily 100 percent predictive, nevertheless, the obvious correlation between the two variables suggests that we might expect a significant adverse climatic response to the industrial-era surge in fossil fuel derived atmospheric carbon dioxide. Undeniably, the effects of this interplay are manifested in the increase in the ferocity of storms, floods of biblical proportions, spike in the number of unusually hot days, melting of the glaciers, drought, desertification and deforestation, polar vortex, uncontrollable forest fires, degradation of the coral reefs, habitat loss and rise in the sea level, to mention a few.

Today, because of global warming, intense storms are occurring in many parts of the world. If they form in the Atlantic or Caribbean, they are known as hurricanes, and in the Pacific or China Sea as typhoons. If they develop off the coast of Indian Ocean or the Bay of Bengal, we call them cyclones. These storms are one of the most awe-inspiring displays of the raw power of nature. They are also among the deadliest and costliest natural disasters we have to contend with routinely.

After churning through the Bay of Bengal for several days, gathering immense amount of energy along the way, cyclone Fani roared through Bangladesh on May 4, 2019, leaving behind a massive trail of destruction—killing more than a dozen people, knocking out power, shredding roofs and leaving hundreds of thousands homeless. Classified by meteorologists as the equivalent of a Category 4 hurricane, it was one of the most intense cyclones in 20 years in the region.

Cyclones batter Bangladesh at regular intervals, mainly in April/May or October/November, when weather conditions align in a manner most favourable for storm origination and sustenance. As examples, cyclones Aila struck southern Bangladesh on May 27, 2009 and Sidr made landfall on November 14, 2007. The occurrence of these and other cyclones in close succession is a reminder of the country’s extreme vulnerability to the devastating effects of human-induced climate change.

The 1970 cyclone that hit Bangladesh on November 12 and raged the strongest on November 13 was the worst natural disaster we have witnessed so far. The resulting storm surge, more than 20 feet high and topped by huge tidal waves, washed over offshore islands and carried water from the sea many miles inland. The cyclone and flood destroyed the entire infrastructure of the country’s southern coast and killed an estimated half a million people, though some researchers estimate that the death count was close to a million. The failure of the Pakistani government to respond quickly to the crisis, among other things, contributed to the political turmoil that led to an independent Bangladesh in 1971.

Tropical cyclones are influenced by many factors, but the role of warm sea-surface temperatures is the primary source of energy for cyclones. In particular, a cyclone gets most of its energy from the latent heat of condensation and the moisture generated from the sea. Thus, for the genesis of cyclones, temperature of water near the surface of the sea must be higher than 27 degrees to a depth of at least 150 feet. Additionally, heat from the sea and Earth’s counter-clockwise rotation conspire to create the cyclone’s spin and propulsion. Furthermore, rising sea levels mean that surges produced by cyclones are much more powerful, thereby increasing the risk of inland flooding.

Moreover, cyclones need to be at least 300 miles from the equator, where a deflective force known as Coriolis force resulting from Earth’s rotation begins to take effect. When cyclones reach land, or cooler water, they lose energy as the conditions necessary to reinforce them are no longer present.

As a result of global warming, temperature near the surface of the Bay of Bengal varies from 27 degrees in January to more than 31 degrees in May. The unusually warm water, together with geographical and environmental factors, make the Bay of Bengal a hot spot for cyclonic activity.

Can changes in frequency and intensity of cyclones observed so far be attributed solely to anthropogenic global warming as against long-term periodic natural variations? Cyclones are affected by natural fluctuations too, driven by external factors, such as solar variability and volcanic eruptions, natural internal variations of the complex physical, chemical, and biological systems of Earth.

Additionally, research has shown that urbanisation significantly contributes to the amount of rainfall dumped, as evidenced by over 130 centimetres of rain that fell on the Houston region during hurricane Harvey in 2017. This is because the “roughness” of the city—as in the buildings and infrastructure—creates a drag on the storm system, causing it to slow down, resulting in more rain over the city area.

Climate models predict that global warming could spawn more bizarre and violent weather, notably cyclones and severe floods in the future. Indeed, while people are trying to come to grips with the effects of Fani, meteorologists have warned that Bangladesh is likely going to experience another cyclonic storm called Vayu some time later this month.

The models also predict that by the end of this century, global warming effects could increase a cyclone’s intensity by about 20 percent, making them more destructive than ever. The amount of rainfall would also increase substantially. Other estimates predict that a doubling of carbon dioxide concentration would result in a 40-50 percent increase in destructive cyclones.

So, what should we do to keep our planet in the so-called Goldilocks zone of the solar system? We have to make a concerted effort to end our dependence on fossil fuels. We have to replace them with non-polluting, renewable sources of energy. We have to develop more carbon-free energy technologies. We have to sequester carbon dioxide emissions using the available technology. More importantly, we have to shun the “business as usual” attitude. In short, we will have to build a sustainable future. Otherwise, climate change will cause our civilisation to collapse.

Quamrul Haider is a Professor of Physics at Fordham University, New York.

Advanced science, Astrophysics, Cultural, International, Technical

Mysterious dark matter and dark energy

Physics is traditionally viewed as a hard subject requiring a great deal of mathematical prowess, devotion and perseverance to muster the subject matter. To a large extent, it is definitely true. But it does also offer, in its turn, a great deal of satisfaction, excitement and sense of achievement.

The 21st century physics, spanning from quantum computing to super-thin layer material called graphene to ultra-efficient LED bulbs to efficient harnessing of renewable energies to black holes to dark matter and dark energy, the range of topics is endless and it will disappoint no one with its vast challenges and ensuing excitement.

In our day-to-day lives, we encounter matter comprising protons and neutrons bundled together at the centre, called nucleus, of an atom and electrons whizzing around the nucleus. Some decades ago, these protons, neutrons and electrons were thought to be the fundamental particles of all matter; but not anymore. Now, quarks (six types) are thought to be the fundamental matter particles, which are glued together by force particles to form protons and neutrons.

These atoms and molecules making up matter here on earth are what we are accustomed to. The laws of physics, or for that matter of natural sciences, were developed to explain the natural processes as we encounter in our lives.

The basic physical principles are like these: a body has a definite size comprising length, breadth and height; it has a mass and weight; it is visible when there is sufficient light. If we push a body, we impart momentum, which is the product of mass and velocity. As it has the mass, it has gravity, meaning it attracts every other body and every other body attracts this body. These are the basic properties of a body as described in classical physics.

But there is no reason to be dogmatic about these basic principles. These principles can change here on earth or in our galaxy or somewhere outside our galaxy. When they do change, we would feel that things have gone topsy-turvy.

We live on a very tiny planet, called Earth, which revolves round the star, called Sun. There are eight other planets, thousands of satellites, comets and asteroids, all held together by the gravity of the Sun. The Sun, though extremely bright and overwhelmingly powerful to us, is a small star in our galaxy, called the Milky Way. It is estimated that there are over a billion, yes, 1,000,000,000 stars, many of them are much bigger than the Sun, in our galaxy. Now our galaxy is by no means the biggest or dominant galaxy in the universe. Cosmologists estimate that there are around one billion galaxies in our universe! Some of these galaxies are hundreds or even thousands of times bigger or massive than our galaxy. There are massive black holes at the centres of most of the galaxies, exerting gravitational pull to keep the galaxy together. Some of these black holes are millions of times bigger than the Sun. Now we can have a feel of how big our universe is!

Physics, or more appropriately astrophysics, studies the processes of these vast expanse of celestial bodies. The Sun as well as our galaxy, the Milky Way having over a billion stars are not static. The stars are spinning, the galaxy is spiralling, and everything is in motion.

Strange glow from the centre of the Milky Way

It was estimated, purely on physical principles, that the stars at the edges of a galaxy should move slower than the central ones, as the force of gravity of the galaxy is weaker away from the centre. But astronomical observations show that stars orbit at more or less at the same speed regardless of their distance from the centre. That was a great surprise, indeed shock, to the astrophysicists. The way this puzzle was eventually tackled was by assuming that there are massive unseen matters that exert tremendous amount of gravitational pull to keep the outlying stars moving at nearly the same speed and that mysterious matter is called the dark matter.

There are other tell-tale signs that there is something amiss in the material accounting of the universe. A strange bright glow spread over the length of the Milky Way was thought to be due to ordinary pulsars (pulsating stars) along the length. But now it is thought that dark matter may be responsible for this glow! But how does it do that, physics does not know yet.

But is this dark matter a fudge to solve the apparent conflict of physical behaviour with observations? Not really, this is how science progresses. Well thought out ideas are advanced and those ideas are tested and cross-examined against observations and the idea or concept that passes the tests is taken as the valid scientific concept.

But how do we know dark matter is there, if we cannot see them. We cannot see them because dark matter does not interact with light or electromagnetic radiation such as visible light, infra-red, ultra violet, radio waves, gamma rays and so on. Light goes straight through the dark matter, as if it is not there.

It should, however, be pointed out that dark matter is not the same thing as black hole. A black hole is made up of everyday particles (matter particles and force particles) – electrons, protons, neutrons, atoms, molecules, photons etc. Its gravity has just become so strong (because of its mass and super-compacted size) that it pulls and crushes everything to its core and nothing can escape from its clutches, not even light! A beam of light coming close to a black hole is pulled right insight and that is the end of that light beam never to be seen again!

Dark energy expansion

Dark matter, although invisible, does exert gravitation pull and this gravitational pull that makes dark matter attractive to scientists. The Universe, although expanding, is not in danger of runaway expansion. There is something that is holding the whole thing together and that something may be the dark matter.

Immediately following the Big Bang, the then Universe expanded very rapidly, known as inflationary phase, for tens of millions of years followed by expansion for some billion years and then it stabilised for a few billion years and now it is again in the expansion phase. The present expansion is that the space itself is expanding and so every star and every galaxy is moving away from every other star or galaxy. What is giving these celestial bodies energy (repulsive in this case) to move away from each other? Scientists came up with the proposition that there must be some unknown, unseen energy, which is now called the dark energy.

On purely material and energy balance of the Universe, it is thought that our visible (and known) Universe accounts for only 4.9 percent of the total Universe, dark matter accounts for 26.8 percent and dark energy for 68.3 percent. So, we only know in the vast mind-boggling universe extending over 13.8 billion light years a meagre 5 percent and the remaining 95 percent is hidden or unknown to us!

Scientists all over the world are trying hard to find evidence of dark matter and dark energy. CERN’s Large Hadron Collider (LHC) is trying to find any remotest evidence of dark matter and energy. On theoretical basis, some scientists are proposing that dark energy may emanate from a fifth form of force, which is yet unknown. The four forces that we know are electromagnetic, weak nuclear, strong nuclear and gravitational forces. The fifth force may be a variant of gravitational force – a repulsive gravitational force – that comes into play in the vast intergalactic space.

When Einstein produced the general theory of relativity in 1915, he introduced, almost arbitrarily, a parameter, called the cosmological constant, into the theory to counter the effects of gravitational pull and make the Universe a static one. That cosmological constant effectively introduced the repulsive effects. It may be pointed out that the Universe was thought to be static at that time. But only a few years later when it was incontrovertibly shown that the Universe was, in fact, expanding, Einstein humbly admitted that it was his “biggest mistake”. Now, more than hundred years later, it is assumed that the cosmological constant may be considered to be the quantity to cater for the dark energy! Could Einstein’s “biggest mistake” be a blessing in disguise, it offers not only a correct presumption but also a saviour of modern cosmology?

  • Dr A Rahman is an author and a columnist

Advanced science, Astrophysics, Cultural, International, Life as it is, Religious, Technical

Isn’t black hole a black mystery?

A black hole – hitherto an invisible celestial body – was in cosmological vocabulary even before Einstein’s theory of relativity in 1915. But when the relativity theory predicted with full scientific rigour that a massive stellar body can have such a strong gravitational pull that nothing, no object, not even electromagnetic radiation such as light, can escape from it, the concept of a black hole became firmly established in scientific parlance. But it remained at that time only a mathematical curiosity, as no scientific evidence or mechanism of formation of a black hole was put forward. However, it became a realistic possibility after the detection of pulsars some decades later.   

The detection of pulsars (rotating neutron stars) by Jocelyn Bell Burnell, a research student at the University of Cambridge in 1967, gave renewed spurt to the concept of gravitational collapse and the formation of black holes. A normal star, when it comes to the end of its life due to lack of fusion fuel, collapses under its own gravity and becomes a neutron star. It may be mentioned that an atom consists of neutrons (neutral in charge) and positively charged protons and negatively charged electrons. If gravity becomes too strong, protons and electrons are pulled together to merge with each other, neutralise their charges and become neutrons and the whole star becomes a neutron star. (For the detection of neutron star, which was considered as “one of the most significant scientific achievements of the 20th century” by the Nobel Committee, her supervisor and another astronomer were awarded Nobel prize in Physics in 1974, but Jocelyn Bell was not even mentioned in the citation. However, years later, in 2018, she was awarded the Special Breakthrough Prize in Fundamental Physics. She donated the whole of the £2.3 million prize money to the Institute of Physics in the UK to help female, minority, and refugee students become physics researchers.

Not all stars eventually become neutron stars. If the mass of a star is less than 2.6 times the mass of the Sun, the gravity would not be strong enough to turn it into a neutron star. The gravitational pull in a neutron star ultimately becomes so strong that all its mass and its nearby matters are pulled to a small volume and the star becomes a black hole. A black hole can merge with another black hole to become a bigger and stronger black hole.

It is speculated that there are black holes of various sizes in most of the galaxies and in some galaxies, there are supermassive black holes at their centres. The nearest black hole from Earth is quite a few thousand light-years away; but they exert no influence on this planet. The supermassive black hole in our galaxy (the Milky Way) is about 26,000 light-years away.

Despite the name, a black hole is not all black. The gas and dust trapped around the edges of the black hole are compacted so densely and heated up so enormously that there are literally gigantic cauldrons of fire around the periphery of a black hole. The temperatures can be around billions of degrees!

The first direct visual evidence of a black hole had been produced on 10 April 2019 by a team of over 200 international experts working in a number of countries. The Event Horizon Telescope (EHT) was used to detect the existence of a colossal black hole in M87 galaxy, in the Virgo galaxy cluster. The computer simulation from data collected in the EHT is shown below. This black hole is located some 55 million light-years from the Earth and its estimated mass is 6.5 billion times that of the Sun! So, this black hole is truly a monster of a black hole.

Computer simulation of black hole from real data

Although it is a monstrous black hole, its size is quite small and it is enormously far away (520 million million million kilometres away) from Earth. To observe directly that elusive black body that far away, astronomers require a telescope with an angular resolution so sharp that it would be like spotting an apple on the surface of Moon from Earth and the aerial dish that would be required for such a detection would be around the size of Earth! Obviously, that is not possible.

Instead, the international team of experts devised a Very Long Baseline Interferometry (VLBI) technique, which involves picking up radio signals (wavelength 1.3 mm) by a network of radio telescopes scattered around the globe. The locations of these eight radio-telescopes are shown below. When radio signals from these radio-telescopes are joined up, taking into account their geographical locations, lapsed times for signal detection etc, and processed in a supercomputer, an image can gradually be built up of the bright part of the periphery of the black hole.

Locations of Event Horizon Telescopes (EHT)

The key feature of a black hole is its event horizon – the boundary at which even light cannot escape its gravitational pull. The size of the event horizon depends on the mass of the black hole. Once an object crosses the boundary of the event horizon, there is absolutely no chance of coming back. A lead astronomer from MIT working on this EHT team said, “Black hole is a one-way door out of this universe.”

The general theory of relativity also predicted that a black hole will have a “shadow” around it, which may be around three times larger than the event horizon size. This shadow is caused by gravitational bending of light by the black hole. If something gets nearer the shadow, it can possibly escape the gravitational pull of the black hole, if its speed is sufficiently high (comparable to the speed of light).

It is postulated that the “shadow” comprises a number of rings around the event horizon. The nearer a ring is to the event horizon, the more rigorous and compact it is with extreme pressure-temperature conditions. 

If, hypothetically, an unfortunate human being falls even into the outer ring of a “shadow”, he will be pulled towards the black hole initially slowly and then progressively strongly – his leg will be pulled more vigorously than his upper part and consequently, his body will be deformed into a long thin strip like a spaghetti. And when that spaghetti shape crosses the event horizon, it will be stretched so much that it will become a very thin and very long string of atoms!

Is wormhole the link between a black hole and a white hole?

The general perception of a black hole is that it is a monster vacuum cleaner where everything, even light, is sucked into it through a funnel and nothing, absolutely nothing, can come out. It absorbs enormous amount of matter and squashes them into tiny volumes. What happens to this gigantic amount of matter is a mystery, a black mystery.

There are two parallel streams of pure speculative thoughts. One is that when a black hole becomes too big – either by incessantly swallowing up matters from its surroundings or by merger with other black holes – a super-giant explosion, more like a big bang, may take place. So, a black hole may be the mother of a new big bang, a new generation of universe.

The other thought is that the funnel of a black hole is connected through a neck, called the wormhole, to a different spacetime and hence a different universe at the other end. All the materials that a black hole sucks up at the front end in this universe go through the wormhole to another reverse funnel where all the materials are spewed out into a different spacetime. That funnel is called the white hole. Thus, a black hole and a white hole is a conjugate pair – a connection between two universes!  But the question is, since there are billions of black holes in our universe, then there could be billions of corresponding wormholes and white holes and universes.

One universe is big enough or bad enough for human minds to contemplate, billions of universes will make humans go crazy.

Dr A Rahman is an author and a columnist