Billions and Billions of Stars
We often say that life is too short but there are species that have a life span of less than one day. Other species, like house flies, are much more fortunate, as they can live up to four weeks. As much as we think that their sole purpose in life is to irritate humans, houseflies do not really care about that. All they want is to eat and breed. Our familiar ants can live to three months and humans live to one hundred years, more or less. But humans are not even close to the top of the lifespan pyramid. Whales and Galapagos tortoises can live up to two hundred years. No one really knows if they spend all that lifetime on artistic, scientific or other intellectual pursuits, and if they find the time to care about morality and religious beliefs. They probably just want to eat and breed and they can keep doing this for two hundred years.
An ant’s viewing range is no more than one meter. So an ant’s perspective reality is only a tiny portion of our human perspective reality. There is no way that an ant will ever know Paris or the Parthenon or Niagara Falls. The ant’s universe is limited to its colony and it is only a tiny fraction of the universe known to humans. But isn’t it likely that the universe that we humans can ever know is also a tiny portion of the entire universe? Isn’t it likely that our human perspective reality is limited, just like the ant’s perspective reality is limited, by our sensory range and by the limits of our intellectual capabilities? No one really knows the answer but we might speculate that, yes, it is more than likely that we can only know a tiny portion of the universe.
Scientists say that the Big Bang occurred 13.82 billion years ago. They do not even round the number to 14 billion, it is absolutely and precisely 13.82 billion years. So humans, with their 100 year lifespan and less than one hundred generations of accumulated scientific knowledge are able to discover evidence from 14 billion years ago. It really sounds strange and yet this is the object of much scientific research in physics and astronomy today. But the travel back to the time of the Big Bang can be fascinating, even if we think that some of it is fiction. We will not see any witches or dragons along the way but we will get acquainted with some incredible stories and sights of black holes, white dwarfs, red giants and quasars. These are the witches and dragons of the universe.
Back in 1919 a thirty-year old man named Edwin Hubble arrived at Mount Wilson in California to make some astronomical observations of the Milky Way, which at that time was considered to be the entire universe. Hubble was an unknown scientist at that time, with just a few years as a professional astronomer. He had studied mathematics and astronomy in Chicago and law at Oxford but his studies had been interrupted by his voluntary enlistment in the US Army during the first World War. Hubble’s arrival at Mount Wilson coincided with the completion of the Hooker telescope, the world’s largest at that time.
Hubble’s observations in 1923 showed that certain nebulae, those cloudy patches that we see up in the night sky, were too distant from our galaxy and were, in fact, galaxies of their own. Andromeda, the princess of all nebulae, was one of those galaxies. While the scientific community was still in shock and disbelief that our treasured Milky Way is not the entire universe, the New York Times published an article titled Finds spiral nebulae are stellar systems. Doctor Hubble confirms view that they are ‘island universes’ similar to our own.
Hubble’s seminal moment was still ahead of him. From the spectra of the emitted light he began to measure the velocities of all the known nebulae. After successive measurements of the same nebulae he made a startling discovery: the spectra of the nebulae displayed a redshift over time. A redshift happens when light is shifted to the red end of its spectrum, meaning that its frequency is reduced. Does this remind us of the Doppler effect? It sure does! The nebulae were moving away from us. This was a tremendous breakthrough in astronomy as it overturned the conventional view that the universe is static. This is how the theory of the expanding universe was established.
It is interesting to note that when Einstein developed his General Relativity, he found that his theory required the universe to be either expanding or contracting. He was puzzled by this result and he felt compelled to add a fudge factor in the equations in order to get rid of the problem, as the prevailing view at the time was that the universe is static. This fudge factor is known as the cosmological constant and it is usually denoted by the Greek capital lambda Λ. It is the energy density of the vacuum of space and it is meant to counteract the force of gravity. When Einstein learned of Hubble’s discovery, he realized that the expansion predicted by his own theory was real and the cosmological constant was redundant after all. Later in his life Einstein said that changing the equations was the biggest blunder of his life. British astrophysicist Stephen Hawking wrote in his book A Brief History of Time that Hubble’s discovery that the universe is expanding was one of the great intellectual revolutions of the 20th century.
Hubble remained active at Mount Wilson for the rest of his life. He was never awarded the Nobel prize in physics, as astronomers at that time were not eligible for the prize. The space telescope launched by NASA in 1990 on a low earth orbit was named after Edwin Hubble. It is known as the Hubble Telescope! After an initial problem with one of its mirrors, the telescope was repaired in 1993 and started producing spectacular images of distant stars, nebulae and galaxies.
General relativity predicted the existence of spacetime deformities around dense masses behaving like black holes, from which no light or any other radiation can escape. The idea goes back to 1783 when an English clergyman and natural philosopher named John Michell wrote a letter to Henry Cavendish, a scientist and prominent member of the Royal Society: “If the semi-diameter of a sphere of the same density as the Sun were to exceed that of the Sun in the proportion of 500 to 1, a body falling from an infinite height towards it would have acquired at its surface greater velocity than that of light, and consequently supposing light to be attracted by the same force in proportion to its inertial mass, with other bodies, all light emitted from such a body would be made to return towards it by its own proper gravity.”
In one amazing paragraph written two hundred and thirty years ago Michell described black holes and by all accounts he seems to have been the first person to do so. He called them dark stars. The theory was ignored for a long time, since it was not understood how light could be affected by gravity. Michell has been called “one of the greatest unsung scientists of all time”.
In addition to being the first person to propose the existence of black holes, Michell was the first to suggest that earthquakes travel in waves, the first to explain how to manufacture artificial magnets and the first to apply statistics to the study of the cosmos, recognizing that double stars were a product of mutual gravitation. Michell also invented an apparatus to measure the mass of the Earth. He has been called both the father of seismology and the father of magnetometry.
The first thing that comes to mind about a black hole is that since it does not emit any light it can never be observed. Well, if there is an unfalsifiable theory, this must be it! We have managed to come up with something that can never be discovered. We should perhaps recall Wittgenstein’s words “What can be said at all can be said clearly, and what we cannot talk about we must pass over in silence.”
Our philosophical skepticism aside, it was reported in May 2012 that the first visual proof of existence of black holes was achieved. A team from Johns Hopkins University made observations on the Hawaiian telescope Pan-STARRS 1 and recorded images of a supermassive black hole 2.7 million light years away that was in the process of swallowing a red giant! We do not know if they showed this on TV as live entertainment!
So, the red giant was trapped like a fly in a spider’s web and was then swallowed in one big gulp! The colorful description is really quite funny, but can it also be true? First of all, what is a red giant? It turns out that a red giant is a star in the latter part of its life, when most of its hydrogen, the most common element in the universe, has been converted to helium, in that familiar nuclear fusion that makes our own sun give us all that sunlight and warmth. Some of the most familiar stars in the night sky, like Aldebaran and Arcturus, are red giants. Another one is Betelgeuse, one of the four corners of the Orion constellation, a very familiar and visible star pattern on our sky. Astronomers say that our sun will also start to run out of hydrogen in about 5.4 billion years and will turn into a red giant.
There is no sure way of knowing how often these black hole feastings occur. Some astronomers say they are not frequent at all, just one per galaxy every 10,000 years or so. But on the cosmic time scale isn’t this like putting away three meals a day? This stuff is more exciting and entertaining than the best science fiction ever written but it is also serious business and we need to get serious.
Suvi Gezari was the Johns Hopkins team leader who made the observations. She and her colleagues used a number of different telescopes to watch the black hole devour the red giant that dared to come so close. This all happened in a galaxy two billion light years away. In other words, it happened two billion years ago and we just saw it in 2012. Things that are happening in the universe now will be seen a few billion years later, if there are still any intelligent beings watching the sky from somewhere.
Gezari’s team coordinated its observations with simultaneous observations from NASA’s Galaxy Evolution Explorer, which is an orbiting space telescope that makes observations at ultraviolet wavelengths to measure the history of star formation in the universe 80 percent of the way back to the Big Bang. Gezari and her team were able to analyze the constitution of debris matter from the consumed star. The material was found to be mostly helium with no hydrogen, a finding consistent with the red giant formation theory. This is actually how they determined that the devoured star was a red giant.
In any event, it may be premature to claim that the May 2012 astronomical report confirms the existence of black holes. It describes a celestial observation in a way that could be explained by the black hole hypothesis. But there could be other hypotheses, yet unproposed, that could explain the event just as well. The theory of black holes is very exciting stuff but it is still dark theory space.
The space between stars is not empty but filled with clouds of gas and dust. These clouds are mainly hydrogen, which is the most abundant element in nature. Clouds can also contain helium and small amounts of other elements, including lithium, which is gradually destroyed during the nuclear fusion. That is why the presence of lithium in the light spectrum is a good indicator of a star’s age.
If the cloud collides with other clouds or celestial objects, it may contract and develop a sufficient gravitational pull as it forms a mass of hydrogen at its center. The mass gets larger, the force of gravity increases and, as the mass gets even larger, the contraction becomes self sustaining. This is not a quick process and may take thousands of years. As more hydrogen collapses toward the center, the temperature and pressure at the core increase and at a certain temperature nuclear fusions begin to occur, creating helium and various other elements from the compression and fusion of hydrogen atoms. The process releases enormous energy. At some point the outward pressure from the fusion reactions will counterbalance the pull of gravity and prevent any further contraction. The star is now stable. It has reached maturity and is entering the Main Sequence of its life cycle. This is when the star is born!
Some cloud formations cannot achieve the large mass and high temperatures required for the fusion process and will not become stars. These are known as brown dwarfs. They will shine dimly, they may be attracted by a star and become a planet but will eventually die over hundreds of millions of years. Our sun is a yellow dwarf and is thought to be in the middle of its lifespan. When the hydrogen fuel that powers its nuclear reactions begins to run out, our sun will expand, cool down and become a red giant.
We do not need to worry just yet, as this will not be happening for another five billion years or so. Small stars like our sun will eventually die a relatively peaceful death, passing through a nebula phase and then a white dwarf phase. A white dwarf is basically a star near death, singing its swan song. Massive stars, on the other hand, experience a more violent death in an enormous explosion called a supernova. The remnants of a supernova may become either a rapidly spinning neutron star or a black hole.
When astronomers in the 1960s turned radio telescopes on the sky for the first time, they discovered sources of radio waves. These were spread out along the Milky Way. When astronomers turned visible light telescopes on those points in space, they found bright spots that might be distant stars. They named them quasi stellar radio sources, or quasars for short. Quasars are extremely bright, billions of times brighter than our sun, and they are also extremely distant. It is believed that they are compact regions that draw their energy from supermassive black holes near the center of their galaxy. Their light takes billions of years to reach the earth, which makes them possible sources of information about the early stages of the universe.
Famous American astronomer, educator and TV personality Carl Sagan once said that “A galaxy is composed of gas and dust and stars, billions upon billions of stars.” Sagan’s distinctive speech emphasized the letter b in “billions and billions” and the expression became a favorite catchphrase in astronomy discussions as well as a favorite target of comic performers. Sagan took all the comedy in good spirit and gave the title Billions and Billions to his final book. The title of this article is an hommage to the great astronomer and science popularizer Carl Sagan.
The truth is that some of the magnitudes in astronomy are just so difficult to grasp. Our Milky Way galaxy is said to contain 400 billion stars. These are not just any celestial objects but real stars, each with their own solar system. That is a big number, 400 billion stars, and yet our Milky Way is one of 200 billion galaxies, a number that is likely to increase as we improve our ability to look deep into space. If we assume that the Milky Way is an average sized galaxy, then we have 80 sextillion stars, or the number 8 followed by 22 zeros, or 80 billion trillion stars. No human mind can grasp these numbers and the cosmological vastness that spreads beyond our home planet. The cosmos is a wonderful world of fiction and at the same time a world of ultimate reality.
Much of the work in astronomy today centers around the Big Bang theory. Realistically, the concept of a beginning of the universe is troublesome. Does it make logical sense to say that it all started with a specific event? The first questions asked cannot be answered: What was there before? How is the law of conservation of energy fulfilled at time zero? Were the laws of physics created at that instant? How can our laws of physics guide us to an instant in time when they did not exist? There are too many logical contradictions and paradoxes.
However, if the Big Bang is the beginning of our part of the cosmos, the beginning of our visible universe, then, of course, the contradictions disappear. We can carry out a meaningful discussion, and we will, in this spirit, that the Big Bang is an event that created our visible galaxies, our own Milky Way and our solar system. The Big Bang has nothing to do with the beginning of the entire cosmos or the beginning of spacetime or the beginning of all existence. We note that the Encyclopedia Britannica is careful enough to define the Big Bang as “a widely held theory of the evolution of the universe”. Britannica does not even mention the “beginning” of the universe, the Big Bang is just an evolutionary event.
NASA scientists propose that the Big Bang did not occur at a single point in space as an explosion but as a simultaneous appearance of space everywhere in the universe. Before the Big Bang, space was no bigger than a point. In other words, space did not exist. The universe expanded from that zero-volume single point of origin. If we think of an inflating balloon, the radius of the balloon grows as the universe expands but all points on the surface of the balloon (the universe) recede from each other. NASA scientists believe that the Big Bang model does not need to consider questions such as “what is the universe expanding to?” or “what caused the Big Bang?”
The idea of an expanding universe is a logical contradiction, unless this is one of many universes. If “universe” means “everything there is”, where is the universe expanding to? We can solve this contradiction by defining the cosmos as everything there is and stating that the cosmos consists of many universes. The theory of expanding universe would then apply only to our own visible universe.
The Big Bang, according to NASA and other scientists, was an explosion that caused the creation of spacetime from a singular point at time zero. So, time must have been created as a unidirectional entity, with a future but without a past. If it had a past, there could be no zero point and no Big Bang. If spacetime just before the Big Bang were just a singular point, didn’t that point have to contain all the mass and energy that resulted in our vast universe? How can time be created at some instant? How can an event occur if time does not exist? The idea that everything, including spacetime, was created at one instant from a singularity is probably a good solution to a fine mathematical equation, but not a very good idea of physical reality.
The most troublesome part of all this is that nothing is verifiable or falsifiable. You can detect some weak cosmic radiation somewhere in space and then say “oh yes, these are remnants of the Big Bang, this confirms the theory”. Some cosmologists have gone as far as to suggest that the point of origin of the Big Bang was just a few millimetres across!
The problem here is that none of these ideas can be incorporated into our thinking in ways that the ideas can be experientially verified and validated in any way. Astronomy is a true science, like physics, but it seems that cosmology has made a full circle back to theology and metaphysics. In a world population of seven billion people there is always going to be a large number of grateful readers willing to accept exciting ideas without much proof. Some of this is as exciting as the best science fiction and as credible as science fiction.
The Big Bang is current orthodoxy in cosmology but our skeptical voice is not a voice in the wilderness. Quite a few scientists around the world are beginning to question the basic premises of the theory. There are extreme views on both sides, as there are moderate views. The idea that the Big Bang is not a creationist but an evolutionary event has great appeal and we might predict that this idea will define the path of future research.