In this article, I do not intend to question or verify the scientific facts surrounding the 13.75 billion years (Gy), the most recently established age of the Universe. I only intend to provide a summary of the various measurement methods astronomers applied lately to determine the ages of galaxies, and how they derive the age of the Universe from that. Although these methods may well have been known in scientific circles for a long time, a summary of those procedures could be of some interest to many people.
Astronomers and cosmologists have recently used several methods to measure astrophysical objects and events in order to determine the distances of these objects and events from us. This has ultimately enabled them to calculate the ages of stars and galaxies, and ultimately the age of the physical Universe. Although the distance measurements that are described below may have been achieved using similar methods, the objects and events selected below differ greatly.
The distance measuring methods upon which the various calculations of the age of the Universe relied are the following:
- Measurements of redshift of the light from galaxies. From this measurement, scientists postulated a cosmic expansion and, with the aid of the Hubble Constant, calculated the age of the Universe.
- Measurements of the rate of decay of the radioactive nuclei of elements, using the technique of nucleo-cosmochronology of the Type II Supernovae (>8 MSolar).
- Measurements of the recession of galaxies, using the Type Ia Supernovae (<4MSolar).
- Measurements of the age of our galaxy, using the spectral analysis of stars in the globular clusters.
- Measurements of the temperature of the Oldest White Dwarfs, the end-state of main sequence stars <4Solar, (and which will be similar to the future of our Sun), after their planetary nebula stage.
Note: Since the above methods of measurements were used, a more accurate and up-to-date age of 13.7 Gy for the Universe has been confirmed recently, through the beryllium analysis of the globular clusters. See: How Old is the Milky Way? (ESO Press Release, 20-04-2013). (A description of this latest method of measurement is excluded from this article.)
I used the following sources of information for this article:
- The World Treasury of Physics, Astronomy and Mathematics, edited by Timothy Ferris (1991).
- A free publication from the National Academy of Scientific Paper, by J.W. Truran and D.N. Schramm, Department of Astronomy, University of Chicago, USA.
- Cosmic Enigmas, by J. Silk, Professor of Theoretical Physics, University of California, USA.
- The Extravagant Universe, by R. P. Kirshner, Professor of Science, Harvard University, USA.
- The Physical Universe, by Frank Shu, Professor of Astronomy, University of California, USA.
- Hertzsprung-Russel Diagram, courtesy of Mr D. Eicher, editor of the Astronomy Magazine (modified by Francis F. Kish).
- The Hertzsprung-Russell Diagram
- The Cosmic Expansion Method
- The Nucleo-cosmochronology—using the Type II Supernovae
- The Recession of Galaxies, using the Type Ia Supernovae
- The Spectral Analysis of Stars in the Globular Clusters
- The Age of the Oldest White Dwarfs
1) THE HERTZSPRUNG-RUSSELL DIAGRAM
Stars play a principal role in all manner of measurement procedures to determine the ages of galaxies and, from that, the age of the Universe. Therefore, it is appropriate to highlight the salient aspects of the Hertzsprung-Russell Diagram (HR-D) that entail the very basis of and represent those measurement procedures in a visual form.
The HR-D is widely used in astronomy, engineering and in statistical work.
Astronomers use two types of diagrams, the theoretical and observational HR-D.
a) The Theoretical HR-D
There are various ways by which the properties of stars can be represented on the theoretical HR-D. However, the simplest and most common way to represent them is by their luminosity and effective surface temperature. The relationship between these two properties also determines their colour. The diagram shows a diagonally located ‘main sequence’ band of chemically homogeneous, core-hydrogen-burning stars that have similar mass and shine steadily throughout their life, like our Sun. In this article, I will mainly refer to this theoretical HR-D.
Note: A modified copy of this theoretical HR-D (modified by Francis F. Kish) is attached to this article.
The peculiarities of the theoretical HR-D are that:
- virtually all stars begin their life cycle on the diagonal ‘main sequence’ band by converting, through fusion reaction, their core hydrogen into helium
- all stars are represented by their mass, with reference to the MSolar, and their mass determines their relative position; thus, the heavier a star, the higher its position on the ‘main sequence’
- the stars on the ‘main sequence’ have, on average, the lowest mass; hence, they are called dwarfs (e.g. our Sun)
- after a star exhausts its primary fuel of core hydrogen, it begins to leave the ‘main sequence’
- the older a star, the earlier it begins to drift to the right; astronomers can estimate the age of a star from this turn-off point
- after a star leaves the ‘main sequence’, its subsequent event depends on its mass—most single stars will turn into giants, supergiants, or planetary nebulae and end up as White Dwarfs (similarly to our Sun and including all those stars that were originally binary stars, which, after their first explosion into planetary nebulae and reaching White Dwarf stage, will accrete enough energy to explode once again into Type Ia Supernovae and end up as planetary nebulae with a White Dwarf end-stage).
- stars between 4 MSolar (mass of our Sun) and 8 MSolar will, after their supergiant stage, turn into Type II Supernovae and end up as neutron stars, pulsars or sometimes even black holes
- stars larger than 8 MSolar will, after their supergiant stage, turn into Type II Supernovae and end up as neutron stars, pulsars or sometimes even black holes
- irrespective of the age of the Universe, all cosmic events remain in their general sequence as shown in the HR-D.
b) The Observational HR-D
To compare the results of the theoretical calculations with the observed stars and star clusters, astronomers first have to prepare the observational counterpart of the theoretical HR-D. These observations include measuring the luminosity of a star, from its apparent brightness, and the distance to the star. It also requires the determination of the effective temperature of a star.
Note by F. Shu: ‘Because of our observations into the far distances of space, we appear to see only the large galaxies, as the small ones become invisible, and during such times, much evolution of the stellar populations may have taken place, thus they become incomparable with local examples. This incompatibility represents a fundamental and unresolved obstacle for observational cosmology.’
2) THE COSMIC EXPANSION METHOD
Before I begin describing the cosmic expansion, which is the earliest method used to determine the age of the Universe, it may help to recapitulate the two important theories that are associated intimately with this measurement method, namely:
- The Cosmological Redshift
- The Hubble Constant.
a) The Cosmological Redshift
For a long time, astronomers have been able to make distance measurements within our galaxy with great ease, and even of nearby bright spiral galaxies. However, for galaxies that are more distant this has been more difficult and, in addition, there is the problem that as we look to more and more distant clusters of galaxies, we are examining them as they appeared in their earlier past.
For example, if the light from the furthest recognisable galaxy began its journey to us, say, 500 million years ago this represents a difficulty in our observations because those distant objects underwent already a considerable evolutionary phase. Thus, in these cases, we lack a valid basis to compare our observations with nearby examples obtained from younger age galaxies (see the note on the observational HR-D above). Consequently, as Kirshner indicates ‘…just at distances where the effects of cosmology (the subtle changes in brightness) begin to be important, the uncertainties in the measurements (of redshift) begin to grow large.’ It is important to emphasise that galaxies redshift because of ‘space-time curvature’, and not because they have velocities along the radial line of sight or in any other observed direction. Hence the recession ‘velocity’ is a misnomer. And since we have no velocity in its true sense, then we cannot think of the redshift as a Doppler shift either.
The concept of the cosmological redshift is a product of the Einstein-relativistic theory, as interpreted by Friedman-Lemaitre for the radius of curvature for a matter-dominated, closed Universe. One may symbolise this concept by the wavelength of light, be it from radio waves to gamma rays that we receive through space-time. Irrespective of whether wavelength of light represents waveform or radiant energy, it will grow in direct proportion to an expansion factor, which is the meaning of redshift.
In other words, the cosmic expansion stretches out the wavelength of every photon or any other massless particle in direct proportion to the expansion factor during an elapsed time. Therefore, formally, the redshift is just a number, whose symbol of z = (Wavelength Observed / Wavelength Emitted) – 1; for small redshifts, the speed of light (c) times the redshift (z) gives a ‘velocity’.
As we know already from the above, the redshift does not tell us how fast the galaxies are moving away from us, and/or from one another, but it measures the expansion of space itself that has taken place while the light from a galaxy is approaching towards us. Astronomers often use the redshift z as a synonymous indicator of both distance and elapsed time:
- the statement that an object lies at z = x means that an object lies at a distance associated with redshift x
- an event that occurred at redshift z = y means the event occurred a time ago associated with redshift y.
b) The Hubble Constant
Many fundamental questions, such as finding the age of the Universe, are closely associated with the need for a more precise cosmic-distance scale, such as the Hubble constant. The Hubble constant is also known as the Hubble Law, although it is neither a law nor a constant as it varies very slowly over time. In this article, we will call it a ‘constant’.
The Hubble constant was built around Einstein’s theory of relativity and has three important aspects:
- the velocity of light is constant
- there is no absolute system of reference in existence
- the remnants of the Big Bang are accelerating in a curved space, away from a centre of the observer.
Hubble measured initially some 40 galaxies as moving away at a speed proportional to their distance from the observer. This became known as the Hubble constant of v = H0 x D, where:
- v is the galaxy’s radial outward velocity
- D is the galaxy’s distance from Earth
- H0 is the current value of the Hubble constant.
From this equation the inverse of 1/H0= the Age of the Universe.
The Hubble constant is determined first by spectroscopic observations of several, distant galaxies’ redshift i.e. their radial velocities, coupled with the precise distance measurements of those galaxies from Earth. Through averaging out many such readings the present-day value of H0 was determined. The units of Hubble constant are km/sec.Mpc
We can, however, calculate the age of the Universe more easily by using the alternative numerical values for the Hubble constant proposed by F. Shu as being 20 km/sec million light years.
Thus, one million light years = 3 × 105 km/sec x 106 yr
Therefore, H0-1 = 3 x 1011 km sec-1 yr / 20 km sec-1 = 15 x 1010 yr; i.e. the age of the Universe = 15 Gy approximately.
c) The Cosmic Expansion
The inflationary period of the Universe, which was closer to the Big Bang, is from where the cosmic expansion believed to have begun. The initial exponential expansion, i.e. inflation, is intended to provide for us the meaning of space-time and everything in it through the mathematical equations of the Standard Cosmological Model. The theory of the cosmic expansion is therefore primarily part of the Standard Cosmological Model. Principally, the expansion of the Universe is now explained by some versions of the Big Bang theory of cosmology as being opposed to the rival ‘steady-state’ theory.
As mentioned before, experts tell us, that the expansion of the Universe occurs not because galaxies move in any direction away from one another, but because space itself is expanding and that the galaxies thus have no other choice than to move along with this expansion. They also note that the internal dimensions of galaxies do not change with the expansion of space. Therefore, in Big Bang theories, cosmic expansion and a finite age of the Universe go hand in hand. ‘Since the Universe is constantly expanding, its size depends on its age.’ (J. Barrow)
Hence, the age of the Universe is the interval between the Big Bang to the present, and its age, therefore, can be established from the rate of its expansion. At present, the natural time scale of the Universe is its expansion time of about 13.75 Gy and its natural distance scale is 13.75 billion light years. From this, it is easy to see the difficulties astronomers face when trying to get reliable distance measurements using the theory of the accelerating cosmic expansion.
- There is the problem posed by a ‘disappearing’ Universe, i.e. due to its accelerating expansion we see less and less of it.
- When astronomers in the 1990’s produced an audit for the ‘total energy’ of the Universe, they realised there was a dilemma posed by the small amount of visible, gravitating material that was found. They reasoned that they could accept the ‘dark matter’ hypothesis, but that this would make the Universe younger than the stars in globular clusters. As Kirshner said, ‘Another wild idea entered into the cosmic picture, that the initial hot-dark matter of neutrinos is now accompanied by cold-dark matter, all based on evidence of things invisible.’ (Kirshner)
When Einstein was surprised to find that the Universe was expanding, he applied a ‘quick-fix’ to solve that problem by inventing the idea of a ‘cosmological constant’, which he later on just as quickly deleted, saying ‘Who needs it?’ As Kirshner puts it: ‘You cannot fight facts even when they are wrong.’
Now the astronomers seem to be in a similar dilemma as Einstein was, i.e.: they suspect that they might still need the cosmological constant. So, they have resurrected the ‘cosmological constant’, which we call today ‘dark energy’, (highly hypothetical still), to counter-balance the inward pull (or pressure), of gravitating matter. Otherwise, one may be tempted to question the properties surrounding the Big Bang theory or even the relativity theory itself. Thus, once again, the ‘cosmological constant’ has an important role in complementing the cosmic expansion, whose measurements with the latest ‘modification’ now would fit in neatly with the age of the oldest globular clusters and the age of the Universe.
d) The Bases for the Theory of the Cosmic Expansion
The Theory of Cosmic Expansion is supported by several hypotheses:
- the hypothesis of the inflationary period, following the Big Bang of the Universe
- the hypothesis of the cosmological constant and/or the dark energy
- the hypothesis of redshift of galaxies, which indicates the apparent velocities at which the galaxies are moving away from us (it is not yet certain that the redshift is caused by an increase in galactic distances)
- the Hubble constant, which was regarded at the time of writing this article as a fairly reliable cosmic-distance scale, at least for comparison purposes with other distance scales
- the apparent magnitude of galaxies (but with some modifications), which seems to agree with the cosmic expansion theory
- the number counts of galaxies against their redshift; this method may work in a static Universe, as shown by observations, but, as some cosmologists say, in an expanding model this theory appears to have some weak points.
In opposition to the above reasoning about the cosmic microwave background radiation—of which the true causes of the observed fact of radiation are still being questioned by some cosmologists—there are hypotheses that moments after the Big Bang heavy elements were synthesised by thermonuclear reactions.
To enable such reaction to proceed fast enough, as the adversaries continue, to offset the rapid decrease of density caused by the inflation of the early Universe, the matter in the Universe must have started to form at very high temperatures, associated with a similarly strong thermal radiation field. As the Universe expanded, both matter and radiation would cool, and eventually the temperature would drop too low for further nuclear reactions.
Matter would have continued to cool as each photon red-shifted by the cosmic expansion. Astronomers detected the traces of the above described thermal radiation of the early Universe and identified it erroneously as the cosmic microwave background radiation.
Note by F. Shu: ‘One point should be made clear: The free-expansion model must represent more of an overestimate if the Universe is bound than if it is not. Gravity plays little role in slowing down the expansion of an unbound Universe; so 1/H0 must be a good estimate for the age of such a Universe.’ One may justifiably conclude from this remark that the Hubble constant could vary further, due to the present indecision on whether the Universe is bound or unbound.
3) NUCLEO-COSMOCHRONOLOGY—USING TYPE II SUPERNOVAE
The nucleo-cosmochronology method is synonymous with nuclear chronometers, and analogous to radioactive dating. It uses the rate of radioactive decay, which is written in the chemical elements, the building blocks of the whole Universe. From these objects and events, astronomers collect chronological data and calculate the ages of the supernovae—from which they then calculate the ages of our Galaxy and the Universe, as it is now generally accepted that these three events have similar age.
a) The Nucleo-cosmochronology Method
The nucleo-cosmochronology method uses radioactive dating of heavy elements in supernovae of our galaxy to estimate the life-formation activities in astrophysical objects and events. Heavy elements are formed by the capture of neutrons by the nuclei of iron and neighbouring elements. This capture can occur in two places, namely:
- in the envelop of Red Giant stars, which is called the ‘slow process’ (s)
- in the supernova remnant, just outside the neutron star or the black hole. This is called the “rapid process” (r) and all elements heavier than bismuth are believed to be formed this way. The elements that are the most suitable nucleo-chronometers are formed by this ‘r’ process. Through determining the age of these elements, astronomers can calculate the age of the oldest supernovae, the galaxy and the age of the Universe.
b) The Measuring Method
The measuring method is a dating process that involves analysing samples of meteorites and finding a suitable pair of longest-lived nuclei that were in abundance in the earliest times of the galaxy. Chronometer elements used are 232 Thorium/ 230 Uranium and also 235 Uranium/ 244 Plutonium. In their production ratio, one element’s decay enriches the other element in a pair. This production ratio has to be mathematically calculated because several atomic masses need to contribute to the abundance of each of these nucleo-chronometers to reduce the effect of the variation from the average abundance. Behind this dating process lies the assumption that all the elements were created in one event; an assumption which, although it may assist to give astronomers an idealised model, is still incorrect. However, from using the above chronometers, the present age of the Galaxy and the Universe is calculated to be 12.5 +/- 3 Gy approximately (Star CS31082-001, Cayrel, 2001).
c) Type II Supernovae
When a massive star leaves the ‘main sequence’ (on the HR-D) to become a supergiant larger than 8 MSolar, it is surrounded by fusion reaction within its gaseous outer shells until its innermost silicon shell is fused to a massive iron core (larger than 1.4 MSolar), which collapses in less than one second. When this compressed core of the super giant reaches a density of 400 million tons per cm3, it begins to rebound, creating thermal shock waves throughout its shells, until a colossal explosive force, at approximately 5% the speed of light and accompanied with brightness of an entire galaxy, blows off all its outer shells.
This phenomenon is called the Type II Supernova, whose gaseous ejecta become its glowing remnants called the planetary nebula. The emission lines of these nebulae, in addition to lines from H, He, C, Oand Fe, also show lines from elements heavier than iron (i.e. containing more than 26 protons in their nuclei). The high-energy shock waves in these supernova explosions are the only place in the Universe where heavy-metal elements, among them gold, silver, iron, nickel, chromium, titanium, vanadium copper, uranium and lead are made in bulk, and spread by its remnants in the interstellar medium throughout the galaxies. These are the elements that make up stars, planets and all forms of carbon-based biological life in the Universe.
d) The End-stage of Type II Supernovae
Type II Supernovae end up with a compressed stellar core, called neutron stars, which may be regarded as one gigantic atomic nucleus and have greater gravitational-potential energy than a White Dwarf. They may also become rapidly spinning neutron stars, called pulsars (which, by the way, ‘rotate and do not pulsate’; F. Shu), and/or black holes. Pulsars are also known as variable radio stars. A pulsar has a very brief period of pulsations, produces narrow beams of electromagnetic radiation and sweeps around itself in a similar way to a spinning search-light. This end-stage means that the greatest ultimate energy source common in all stars is gravity. Type II Supernovae are considered to be the most reliable nuclear chronometers or cosmic yardsticks for establishing the age of the Universe.
4) THE RECESSION OF GALAXIES—USING TYPE Ia SUPERNOVAE
a) The Measuring Method
The search for still higher and reliable luminous objects to confirm previous distance measurements (as described above), led astronomers to the Type Ia Supernovae in the elliptical and spiral galaxies. The luminosities of these Type Ia Supernovae indicated the most consistent, peak absolute magnitude, regardless of their environment. Many astronomers view the Type Ia Supernovae the best cosmic candles for measuring distances from galaxies, and consider them starting points from where they can determine the age of the Universe. The reason for this is that these supernovae can be more accurately judged for their apparent brightness than, say, measurements made using the ‘Cosmic Expansion’ method.
As a matter of interest, the observations of these luminous objects were the first that highlighted the hypothesis of the ‘expanding Universe’ with the concept of the Hubble redshift. The ‘recession of galaxy’ measurement is based on the application of the Hubble constant, i.e. the more recession a galaxy has, the more redshift it will indicate.
Light from supernovae of distant galaxies is analysed through different wavelengths and compared with data received from already known galaxies; hence, the distance to any of these galaxies can easily be determined on a statistical basis. Such analysis of distant supernovae resulted in the average value of H0= 70 km/s.Mpc (+/-10%), which made the host galaxies and the age of the Universe 12 to 13.5 Gy approximately. (personal communication, Professor J. Mould, Mt Stromlo Observatory, ACT, June 1999)
b) White Dwarfs—The End-stage of Solitary Stars
When a low-mass solitary star (like our Sun) leaves the ‘main sequence’ (on the HR-D), it becomes a gaseous red supergiant star.
Note by F. Shu: ‘White Dwarfs resemble terrestrial metal in many respects. They shine because they have non-zero internal temperature, as relics from a more fiery past. They resemble glowing embers. Its degeneracy pressure and not thermal pressure, which holds it up against self-gravity; this is why it can come into true thermodynamic equilibrium with the cold Universe. Their state will form a crystal lattice and solidify.’
c) Type Ia Supernovae, the End-stage of Binary Stars
Initially, when a low-mass star is close-coupled with a companion binary star (which applies to most of the stars), that binary star at its end-stage begins to transfer its mass and will raise the White Dwarf’s mass to 1.4 MSolar, the Chandrasekhar limit. At this point, the White Dwarf is no longer stable against gravitational collapse, due to its radius decrease and its consequent density-pressure and temperature increase. A new fusion reaction of carbon and oxygen into iron will begin in its core, and the White Dwarf will explode against the force of gravity and essentially be entirely consumed in a gigantic thermonuclear reaction.
This phenomenon is called the Type Ia Supernova, which may be likened to the explosion of a hydrogen bomb of approximately the size of the Earth, but with the mass of the Sun. The reason why iron is such a common metal on planet Earth (whose core is made up of iron) is that the main product of Type Ia Supernovae is iron, and these keep dumping iron into the interstellar space at a rate of about 1 MSolarwith every explosion.
Carbon, the sixth element of the Periodic Table, may have a bad reputation for its implication with ‘green-house’ gases, it has still a longer and synonymous association with biological life. After all, ‘carbon-based life’ is understood to mean life on Planet Earth, as we know it; and ‘organic molecule’ means carbon-based molecule even if no living organism is involved.
However, Carbon, the fourth most abundant element in the Universe, has not been around since the Big Bang beginning of time, because initially only Hydrogen, Helium and traces of Lithium were formed. All other elements, including Carbon, were forged later, mostly by nuclear fusion reaction inside stars, and distributed slowly into interstellar space by Type Ia Supernovae explosions.
d) The End-stage of Type I Supernovae
Although Type I Supernovae end up as planetary nebulae, there are three important points to consider, namely:
- The process to becoming a White Dwarf is not complete, and this is indicated often with a dashed line on the HR-D.
- The White Dwarfs of Type Ia Supernovae are ‘probably’ blown apart and, consequently, do not leave solid core remnants.
- The White Dwarfs of Type Ib and Ic Supernovae, however, are expected to become terrestrial-metal-like remnants of about 1.4 MSolar with non-zero core temperature.
Note by F. Shu: ‘The amount of energy released by such a supernova explosion is about 1044 Jules, being as much energy as the Sun radiates out during its entire 9 Gy lifetime.’
Note by Kirshner: ‘If there are something like 10 billion galaxies in the observable Universe, then since a century is: 3 billion seconds, a supernova per century per galaxy means there are about three of Type Ia Supernova occurrences at every second in the Universe. The problem isn’t a shortage of supernovae, it’s that we can’t look far enough in all directions.’
5) THE SPECTRAL ANALYSIS OF STARS IN THE GLOBULAR CLUSTERS
Globular Clusters usually are found on the perimeter of galactic disks. They are a spherically symmetrical collection of the oldest stars in the Universe. Globular Clusters appear like sparkling diamonds on a black velvet and clusters such as the Omega Centauri offer spectacular views through high-powered telescopes. These clusters may contain a million stars, and span some 150 light years across. The mass of a star in a typical globular cluster is 0.7 MSolar.
Knowing that the life cycle of a star depends on its mass, and that the brighter it is the shorter its life is, astronomers suggest that the oldest globular clusters may be around for over 10 Gy.
One of the uncertainties in determining the age of a globular cluster is the luminosity of its stars. However, from the most luminous stars on the ‘main sequence’ of the HR-D, astronomers can easily calculate the upper limit for the age of a cluster, where all the stars are assumed to have the same age, and hence to have the same luminosity.
Since all the stars that are located on the ‘horizontal branch’ on the HR-D have the same time-averaged luminosity, such as the star clusters, the Cepheids and the RR Lyrae, they are good distance indicators. As the age of RR Lyrae in a globular cluster is proportional to the reciprocal of their luminosity, astronomers can determine the distance to the globular clusters in a more accurate way. The horizontal branch of these stars is located way above the location of the Blue-Giants; therefore they are not shown on the attached HR-D. From average distance measurements, Chaboyer calculates that the age of the Universe is approximately 14.6 (+/- 1.7) Gy (Chaboyer, 1997). Other data proposed for the age of the Universe vary within wide ranges.
6) THE AGE OF THE OLDEST WHITE DWARFS
As described above for the end-stage of a low-mass solitary star, the mass of the hot stellar core of a White Dwarf ionizes the gas that becomes the glowing planetary nebula. In this case, astronomers look for the faintest White Dwarfs to obtain the longest cooling period, which will also represent the oldest White Dwarf. Using this method, and analysing the data obtained with the Hubble Space Telescope from the M4 Globular Cluster, Hansen calculated an age for the Universe of approximately 12.8 (+/- 1.1) Gy (Hansen, 2004).
Should we accept the different ages of the Universe whose measurement methods are detailed above, an average age of the Universe would result in the following entities and events:
- Cosmic Expansion: 15 Gy
- Type II Supernovae: 12.5 (+/- 3) Gy
- Type Ia Supernovae:13.5 Gy
- Globular Clusters: 14.6 (+/- 1.7) Gy
- White Dwarfs: 12.8 (+/- 1.1) Gy
Total = 68.4 / 5 = 13.68 Gy average Age of the Universe
It is truly impressive, and as a science writer remarked: ‘…this has never been stated before, that using five different measurement methods of astrophysical entities and events should yield such a surprising result of 13.68 Gy for the age of the Universe.’ This result is all the more surprising, because it is consistent with the most recent and officially acknowledged 13.7 Gy for the age of the Universe, which has been obtained through the beryllium analysis (ESO Press Release).