Several individual stars have been found in the Milky Way's halo with measured ages very close to the 13.80-billion-year age of the Universe. In 2007, a star in the galactic halo, HE 1523-0901, was estimated to be about 13.2 billion years old. As the oldest known object in the Milky Way at that time, this measurement placed a lower limit on the age of the Milky Way. This estimate was made using the UV-Visual Echelle Spectrograph of the Very Large Telescope to measure the relative strengths of spectral lines caused by the presence of thorium and other elements created by the R-process.
Age and cosmological history
Milky Way
Milky Way | Age and cosmological history
Several individual stars have been found in the Milky Way's halo with measured ages very close to the 13.80-billion-year age of the Universe. A star, HD 140283, is 14.5 ± 0.7 billion years old. A star in the galaxy, HD 140283, is 14.5 ± 0.7 billion years old. Several individual stars have been found in the Milky Way's halo with measured ages very close to the 13.80-billion-year age of the Universe.
where is the solar system located in our galaxy
user
The Solar System, is located in the Milky Way's galactic habitable zone.
assistant
what is the milky way?
user
It is the galaxy that contains our Solar System.
assistant
can you tell me the names of the stars that form a part of this galaxy?
user
The Milky Way may contain ten billion white dwarfs, a billion neutron stars, and a hundred million stellar black holes.
assistant
can this galaxy be seen from earth in the northern hemisphere?
user
The Milky Way is visible from Earth as a hazy band of white light, some 30° wide, arching across the night sky.  As viewed from Earth, the visible region of the Milky Way's galactic plane occupies an area of the sky that includes 30 constellations.
assistant
how would you describe its size?
user
The Milky Way is the second-largest galaxy in the Local Group with its stellar disk approximately in diameter and, on average, approximately thick. The Milky Way is approximately 890 billion times the mass of the Sun.
assistant
name the structural parts of this.
user
Sorry. I cannot find the answer based on the context.
assistant
what is the estimated age of this galaxy?
user
With this technique, the age of the globular cluster M4 was estimated as . Age estimates of the oldest of these clusters gives a best fit estimate of 12.6 billion years, and a 95% confidence upper limit of 16 billion years. In November 2018, astronomers reported the discovery of one of the oldest stars in the universe. About 13.5 billion-years-old, 2MASS J18082002-5104378 B is a tiny ultra metal-poor (UMP) star made almost entirely of materials released from the Big Bang, and is possibly one of the first stars. The discovery of the star in the Milky Way galaxy suggests that the galaxy may be at least 3 billion years older than previously thought.
Milky Way | Age and cosmological history
In 2004, a team of astronomers focused on the cluster to estimate the age of the Milky Way Galaxy. The team consisted of Luca Pasquini, Piercarlo Bonifacio, Sofia Randich, Daniele Galli, and Raffaele G. Gratton. They used the UV-Visual Echelle Spectrograph of the Very Large Telescope at Cerro Paranal to measure the beryllium content of two stars in the cluster. This allowed them to deduce the time elapsed between the rise of the first generation of stars in the entire Galaxy and the first generation of stars in the cluster. This, added to the estimated age of the stars in the cluster, gives an estimate for the age for the Galaxy: about 13.6 billion years, which is nearly as old as the universe itself.
NGC 6397 | Estimating the age of the Milky Way
Several individual stars have been found in the Milky Way's halo with measured ages very close to the 13.80-billion-year age of the Universe. In 2007, a star in the galactic halo, HE 1523-0901, was estimated to be about 13.2 billion years old. As the oldest known object in the Milky Way at that time, this measurement placed a lower limit on the age of the Milky Way. This estimate was made using the UV-Visual Echelle Spectrograph of the Very Large Telescope to measure the relative strengths of spectral lines caused by the presence of thorium and other elements created by the R-process.
Milky Way | Age and cosmological history
Globular clusters are among the oldest objects in the Milky Way, which thus set a lower limit on the age of the Milky Way. The ages of individual stars in the Milky Way can be estimated by measuring the abundance of long-lived radioactive elements such as thorium-232 and uranium-238, then comparing the results to estimates of their original abundance, a technique called nucleocosmochronology. These yield values of about for CS 31082-001 and for BD +17° 3248. Once a white dwarf is formed, it begins to undergo radiative cooling and the surface temperature steadily drops. By measuring the temperatures of the coolest of these white dwarfs and comparing them to their expected initial temperature, an age estimate can be made.
Milky Way | Age and cosmological history
ca. 14 billion years. Sandage performed photometric studies of globular clusters, and calculated their age to be at least 25 billion years. This led him to speculate that the universe did not merely expand, but actually expanded and contracted with a period of 80 billion years. The current cosmological estimates of the age of the universe, in contrast, are typically of the order of 14 billion years. As part of his studies concerning the formation of galaxies in the early universe, he co-wrote the paper now referred to as ELS after the authors Olin J. Eggen, Donald Lynden-Bell and Sandage, first describing the collapse of a proto-galactic gas cloud into our present Milky Way Galaxy.
Allan Sandage | Career
The line strengths yield abundances of different elemental isotopes, from which an estimate of the age of the star can be derived using nucleocosmochronology. Another star, HD 140283, is 14.5 ± 0.7 billion years old.
Milky Way | Age and cosmological history
The oldest stars in a galaxy can only set a minimum age for the galaxy (when star formation began) but by no means determine the actual age.
Stellar age estimation | Membership in a star cluster or system
The steady state theory postulated spontaneous creation of matter to keep the average density constant as the universe expands, and therefore most galaxies still have an age less than 1/H. However, if H had been 550 (km/s)/Mpc, our Milky Way galaxy would be exceptionally large compared to most other galaxies, so it could well be much older than an average galaxy, therefore eliminating the age problem.
Cosmic age problem | Early years
The age of the universe based on the best fit to Planck 2015 data alone is billion years (the estimate of billion years uses Gaussian priors based on earlier estimates from other studies to determine the combined uncertainty). This number represents an accurate "direct" measurement of the age of the universe (other methods typically involve Hubble's law and the age of the oldest stars in globular clusters, etc.). It is possible to use different methods for determining the same parameter (in this case – the age of the universe) and arrive at different answers with no overlap in the "errors".
Age of the universe | Assumption of strong priors
Since around 1997–2003, the problem is believed to be solved by most cosmologists: modern cosmological measurements lead to a precise estimate of the age of the universe (i.e. time since the Big Bang) of 13.8 billion years, and recent age estimates for the oldest objects are either younger than this, or consistent allowing for measurement uncertainties.
Cosmic age problem | Introduction
Studies at the Palomar Observatory some 40 years ago led astronomers to believe that the galaxy erupted with star formation billions of years after its galactic neighbors. Galaxies resembling I Zwicky 18's youthful appearance are typically found only in the early universe. Early observations with the Hubble Space Telescope suggested an age of 500 million years old for I Zwicky 18. The Hubble Space Telescope, however, later found faint, older stars contained within the galaxy, suggesting its star formation started at least one billion years ago and possibly as much as ten billion years ago. The galaxy, therefore, may have formed at the same time as most other galaxies.
I Zwicky 18 | Age
The presence of dark energy implies that the universe was expanding more slowly at around half its present age than today, which makes the universe older for a given value of the Hubble constant. The combination of the three results above essentially removed the discrepancy between estimated globular cluster ages and the age of the universe. More recent measurements from WMAP and the Planck spacecraft lead to an estimate of the age of the universe of 13.80 billion years with only 0.3 percent uncertainty (based on the standard Lambda-CDM model), and modern age measurements for globular clusters and other objects are currently smaller than this value (within the measurement uncertainties).
Cosmic age problem | Late 1990s: probable solution
The estimated age is now about 13.7 billion years, but before the Hubble Telescope, scientists predicted an age ranging from 10 to 20 billion years.
Hubble Space Telescope | Age of the universe
The estimated bolometric luminosity of this galaxy is a trillion (10) times the solar luminosity (the luminosity of the Sun) and it has a mass of approximately . The spectrum of this object indicates that most of its energy is being emitted by stars with three solar masses or less. Hence, as larger stars will exist for shorter periods, this galaxy has an age of more than 300 million years. The period of initial active star formation in this galaxy may have lasted less than 100 million years, during which the galaxy likely participated in the reionization event.
HUDF-JD2 | Introduction
Thus, in 1958 Sandage published the first reasonably accurate measurement of the Hubble constant, at 75 (km/s)/Mpc, which is close to modern estimates of 68–74 (km/s)/Mpc. The age of the Earth (actually the Solar System) was first accurately measured around 1955 by Clair Patterson at 4.55 billion years, essentially identical to the modern value. For H ~ 75 (km/s)/Mpc, the inverse of H is 13.0 billion years; so after 1958 the Big Bang model age was comfortably older than the Earth. However, in the 1960s and onwards, new developments in the theory of stellar evolution enabled age estimates for large star clusters called globular clusters: these generally gave age estimates of around 15 billion years, with substantial scatter.
Cosmic age problem | 1950–1970
Pedreros et al. estimated its age to be (1.24 ± 0.15) × 10 years from ZAMS fitting the cluster (Pedreros, 1987) and the UBVI CCD photometric study of the cluster by Carraro et al. estimated its age to be 100 ± 10 million years.
NGC 5316 | Introduction
In addition, knowing the age of one member of a star system can help determine the age of that system. In a star system, stars almost always form at the same time as each other, and given the age of one star, the age of all of the others can be known. However, this method does not work for galaxies. These units are much larger, and are not merely a one-off creation of stars which allows their age to be determined in this fashion. The creation of stars in a galaxy takes place over billions of years, even though star production may long since have ceased (see elliptical galaxy).
Stellar age estimation | Membership in a star cluster or system
It is estimated that Earth-like planets in the Milky Way started forming 9 billion years ago, and that their median age is 6.4 ± 0.7 Ga. Moreover, 75% of stars in the galactic habitable zone are older than the Sun. This makes the existence of potential planets with evolved intelligent life more likely than not to be older than that of the Earth (4.54 Ga). This creates an observational dilemma since interstellar travel, (even of the "slow" kind that is nearly within the reach of present Earth technology) could in theory, if this had arisen elsewhere, take from only 5 million to 50 million years to colonize the galaxy.
Neocatastrophism | The problem
A substantial majority of cosmologists therefore believe the age problem is now resolved. New Research from teams, including one led by Nobel laureate Adam Riess of the Space Telescope Science Institute in Baltimore, have found the universe to be between 12.5 and 13 billion years old, disagreeing with the Planck findings. Whether this stems merely from errors in data gathering, or is related to the as yet unexplained aspects of physics, such as Dark Energy or Dark Matter, has yet to be confirmed.
Cosmic age problem | Late 1990s: probable solution
Following the 1920 Great Debate between the astronomers Harlow Shapley and Heber Curtis, observations by Edwin Hubble showed that the Milky Way is just one of many galaxies. The Milky Way is a barred spiral galaxy with an estimated visible diameter between 170,000 and 200,000 light-years (ly). It is estimated to contain 100–400 billion stars and at least that number of planets. The dark matter halo around the Milky Way may span as much as 2 million light years. The Solar System is located at a radius of about 27,000 light-years from the Galactic Center, on the inner edge of the Orion Arm, one of the spiral-shaped concentrations of gas and dust.
Milky Way | Introduction
The star (and the Milky Way) must have formed soon after the Big Bang. Another result is the first measurement of the beryllium content of two stars in a Milky Way globular cluster. With this measurement, astronomers found that the first generation of stars in our galaxy must have formed soon after the end of the 200-million-year "Dark Age" following the Big Bang.
European Southern Observatory | Age of the universe
In physical cosmology, the age of the universe is the time elapsed since the Big Bang. Today astronomers have derived two different measurements of the age of the universe: a measurement based on the observations of a distant, infant state of the universe, whose results are an age of around 13.8 billion years (as of 2015) , billion years within the Lambda-CDM concordance model as of 2018; and a measurement based on the observations of the local, modern universe which suggest a younger universe. The uncertainty of the first kind of measurement has been narrowed down to 20 million years, based on a number of studies which all gave extremely similar figures for the age.
Age of the universe | Introduction
The cosmic age problem is a historical problem in astronomy concerning the age of the universe. The problem was that at various times in the 20th century, some objects in the universe were estimated to be older than the time elapsed since the Big Bang, as estimated from measurements of the expansion rate of the universe known as the Hubble constant, denoted H. (This is more correctly called the Hubble parameter, since it generally varies with time). If so, this would represent a contradiction, since objects such as galaxies, stars and planets could not have existed in the extreme temperatures and densities shortly after the Big Bang.
Cosmic age problem | Introduction
Ages for star clusters can be estimated by comparing the Hertzsprung–Russell diagram for the cluster with theoretical models of stellar evolution. Using this technique, ages for the Pleiades of between 75 and 150 million years have been estimated. The wide spread in estimated ages is a result of uncertainties in stellar evolution models, which include factors such as convective overshoot, in which a convective zone within a star penetrates an otherwise non-convective zone, resulting in higher apparent ages. Another way of estimating the age of the cluster is by looking at the lowest-mass objects. In normal main-sequence stars, lithium is rapidly destroyed in nuclear fusion reactions.
Pleiades | Age and future evolution
With the Very Large Telescope, astronomers have made an independent determination of the age of the universe and shed new light on the earliest stages of the Milky Way. For the first time, they measured the amount of the radioactive isotope uranium-238 in a star born when the Milky Way was still forming. Like carbon dating over longer timescales, the uranium clock measures the age of a star. It shows that this star is 12.5 billion years old. Because the star cannot be older than the universe itself, the universe must be older than this. This agrees with known cosmology, which gives an age of the universe of 13.8 billion years.
European Southern Observatory | Age of the universe
In 2015, the Planck Collaboration estimated the age of the universe to be billion years, slightly higher but within the uncertainties of the earlier number derived from the WMAP data. By combining the Planck data with external data, the best combined estimate of the age of the universe is old. In the table below, figures are within 68% confidence limits for the base ΛCDM model. Legend:
Age of the universe | Planck
NASA's Wilkinson Microwave Anisotropy Probe (WMAP) project's nine-year data release in 2012 estimated the age of the universe to be years (13.772 billion years, with an uncertainty of plus or minus 59 million years). However, this age is based on the assumption that the project's underlying model is correct; other methods of estimating the age of the universe could give different ages. Assuming an extra background of relativistic particles, for example, can enlarge the error bars of the WMAP constraint by one order of magnitude. This measurement is made by using the location of the first acoustic peak in the microwave background power spectrum to determine the size of the decoupling surface (size of the universe at the time of recombination).
Age of the universe | WMAP
However, in the late 1970s to early 1990s, the age problem re-appeared: new estimates of the Hubble constant gave higher values, with Gerard de Vaucouleurs estimating values 90–100 (km/s)/Mpc, while Marc Aaronson and co-workers gave values around 80-90 (km/s)/Mpc. Sandage and Tammann continued to argue for values 50-60, leading to a period of controversy sometimes called the "Hubble wars". The higher values for H appeared to predict a universe younger than the globular cluster ages, and gave rise to some speculations during the 1980s that the Big Bang model was seriously incorrect.
Cosmic age problem | 1975–1990
The first observation that one can make from this formula is that it is the Hubble parameter that controls that age of the universe, with a correction arising from the matter and energy content. So a rough estimate of the age of the universe comes from the Hubble time, the inverse of the Hubble parameter. With a value for formula_1 around , the Hubble time evaluates to formula_5 = billion years. To get a more accurate number, the correction factor "F" must be computed. In general this must be done numerically, and the results for a range of cosmological parameter values are shown in the figure.
Age of the universe | Cosmological parameters
The age problem was eventually thought to be resolved by several developments between 1995-2003: firstly, a large program with the Hubble Space Telescope measured the Hubble constant at 72 (km/s)/Mpc with 10 percent uncertainty. Secondly, measurements of parallax by the Hipparcos spacecraft in 1995 revised globular cluster distances upwards by 5-10 percent; this made their stars brighter than previously estimated and therefore younger, shifting their age estimates down to around 12-13 billion years. Finally, from 1998-2003 a number of new cosmological observations including supernovae, cosmic microwave background observations and large galaxy redshift surveys led to the acceptance of dark energy and the establishment of the Lambda-CDM model as the standard model of cosmology.
Cosmic age problem | Late 1990s: probable solution
The space velocity of this group relative to the Sun is 59 km/s. The estimated age of this group is 2 Gyr, suggesting a corresponding age for this star.
HR 1614 | Introduction
The ages of the younger two align with the ages of the shells around the galaxy proper. This suggests that the younger clusters and shells formed in bouts of starburst star formation following the merger of the galaxy with another. Also, there are thousands of distant galaxies in the background of PGC 6240.
PGC 6240 | Introduction
For Big Bang models with zero cosmological constant and positive matter density, the actual age must be somewhat younger than this Hubble time; typically the age would be between 66% and 90% of the Hubble time, depending on the density of matter. Hubble's early estimate of his constant was 550 (km/s)/Mpc, and the inverse of that is 1.8 billion years. It was believed by many geologists such as Arthur Holmes in the 1920s that the Earth was probably over 2 billion years old, but with large uncertainty. The possible discrepancy between the ages of the Earth and the universe was probably one motivation for the development of the Steady State theory in 1948 as an alternative to the Big Bang; in the (now obsolete) steady state theory, the universe is infinitely old and on average unchanging with time.
Cosmic age problem | Early years
The light travel time to this surface (depending on the geometry used) yields a reliable age for the universe. Assuming the validity of the models used to determine this age, the residual accuracy yields a margin of error near one percent.
Age of the universe | WMAP
Comparison of the observed or calculated physical properties of each star with theoretical stellar evolutionary tracks allows the age of the star to be estimated. The estimated ages of the components Aa, Ab, and B, are respectively Myr, Myr, and Myr. Within their large margins of error, these can all be considered to be consistent with each other, although it is harder to reconcile them with the 2-3 Myr estimated age of the σ Orionis cluster as a whole.
Sigma Orionis | Ages
Astronomers calculate the age of the universe by assuming that the Lambda-CDM model accurately describes the evolution of the Universe from a very uniform, hot, dense primordial state to its present state and measuring the cosmological parameters which constitute the model. This model is well understood theoretically and supported by recent high-precision astronomical observations such as WMAP and Planck. Commonly, the set of observations fitted includes the cosmic microwave background anisotropy, the brightness/redshift relation for Type Ia supernovae, and large-scale galaxy clustering including the baryon acoustic oscillation feature. Other observations, such as the Hubble constant, the abundance of galaxy clusters, weak gravitational lensing and globular cluster ages, are generally consistent with these, providing a check of the model, but are less accurately measured at present.
Universe | Age and expansion
Further revisions of the Hubble constant by Sandage and Gustav Tammann in the 1970s gave values around 50–60 (km/s)/Mpc, and an inverse of 16-20 billion years, consistent with globular cluster ages.
Cosmic age problem | 1950–1970
The Milky Way's central black hole, known as Sagittarius A*, has a mass four million times greater than the Sun. As of March 2016, GN-z11 is the oldest and most distant observed galaxy with a comoving distance of 32 billion light-years from Earth, and observed as it existed just 400 million years after the Big Bang. Previously, as of July 2015, EGSY8p7 was the most distant known galaxy, estimated to have a light travel distance of 13.2 billion light-years away.
Outline of galaxies | Introduction
The Sun is from the Galactic Center. This value is estimated using geometric-based methods or by measuring selected astronomical objects that serve as standard candles, with different techniques yielding various values within this approximate range. In the inner few kpc (around 10,000 light-years radius) is a dense concentration of mostly old stars in a roughly spheroidal shape called the bulge. It has been proposed that the Milky Way lacks a bulge formed due to a collision and merger between previous galaxies, and that instead it only has a "pseudobulge" formed by its central bar. However, confusion in the literature between the (peanut shell)-shaped structure created by instabilities in the bar, versus a possible bulge with an expected half-light radius of 0.5 kpc, abounds.
Milky Way | Galactic Center
To best avoid the problem, it is common to show two sets of uncertainties; one related to the actual measurement and the other related to the systematic errors of the model being used. An important component to the analysis of data used to determine the age of the universe (e.g. from Planck) therefore is to use a Bayesian statistical analysis, which normalizes the results based upon the priors (i.e. the model). This quantifies any uncertainty in the accuracy of a measurement due to a particular model used.
Age of the universe | Assumption of strong priors
Calculating the age of the universe is accurate only if the assumptions built into the models being used to estimate it are also accurate. This is referred to as strong priors and essentially involves stripping the potential errors in other parts of the model to render the accuracy of actual observational data directly into the concluded result. Although this is not a valid procedure in all contexts (as noted in the accompanying caveat: "based on the fact we have assumed the underlying model we used is correct"), the age given is thus accurate to the specified error (since this error represents the error in the instrument used to gather the raw data input into the model).
Age of the universe | Assumption of strong priors
Matter continues to draw together under the influence of gravity, to form galaxies. The stars from this time period, known as Population II stars, are formed early on in this process, with more recent Population I stars formed later. Gravitational attraction also gradually pulls galaxies towards each other to form groups, clusters and superclusters. Hubble Ultra Deep Field observations has identified a number of small galaxies merging to form larger ones, at 800 million years of cosmic time (13 billion years ago). (This age estimate is now believed to be slightly overstated). Using the 10-metre Keck II telescope on Mauna Kea, Richard Ellis of the California Institute of Technology at Pasadena and his team found six star forming galaxies about 13.2 billion light-years away and therefore created when the universe was only 500 million years old.
Chronology of the universe | Galaxies, clusters and superclusters
Very little star formation occurs in these galaxies; the lack of star formation in elliptical galaxies appears to start at the center and then slowly propagates outward. Its age is estimated to be 8.1 ± 1.7 billion years. An image taken by the Hubble Space Telescope in 2015 shows a characteristically smooth profile, with no spiral arms. However, IC 2006 has a ring surrounding it. The ring appears to rotate in a direction opposite to the rest of the body, but this may be explained by a polar ring with an elliptical shape.
IC 2006 | Introduction
Current cosmological models of the early universe are based on the Big Bang theory. About 300,000 years after this event, atoms of hydrogen and helium began to form, in an event called recombination. Nearly all the hydrogen was neutral (non-ionized) and readily absorbed light, and no stars had yet formed. As a result, this period has been called the "dark ages". It was from density fluctuations (or anisotropic irregularities) in this primordial matter that larger structures began to appear. As a result, masses of baryonic matter started to condense within cold dark matter halos. These primordial structures would eventually become the galaxies we see today.
Galaxy | Formation
NGC 5286 may be one of the oldest globular clusters in the galaxy, with an estimated age of 12.54 billion years. It is not perfectly spherical, but has a projected ellipticity of 0.12. The velocity dispersion of stars at the center of the cluster is . Based upon the motions of stars at the core of this cluster, it may host an intermediate mass black hole with less than 1% of the cluster's mass. The upper limit for the mass estimate of this object is 6,000 times the mass of the Sun.
NGC 5286 | Introduction
A study published in 2013 used the Fine Guidance Sensors of NASA's Hubble Space Telescope to measure a precise parallax (and therefore distance and luminosity) for the star. This information was used to estimate an age for the star of 14.46 ± 0.8 billion years. Due to the uncertainty in the value, this age for the star may or may not conflict with the calculated age of the Universe as determined by the final 2015 Planck satellite results of 13.799 ± 0.021 billion years. Once dubbed the "Methuselah Star" by the popular press due to its age, if the assumptions of stellar evolution are correct in the report, the star must have formed soon after the Big Bang and is one of the oldest stars known.
HD 140283 | Age and significance
Compared to the Milky Way, the Andromeda Galaxy appears to have predominantly older stars with ages >7 years. The estimated luminosity of Andromeda Galaxy, , is about 25% higher than that of our own galaxy. However, the galaxy has a high inclination as seen from Earth and its interstellar dust absorbs an unknown amount of light, so it is difficult to estimate its actual brightness and other authors have given other values for the luminosity of the Andromeda Galaxy (some authors even propose it is the second-brightest galaxy within a radius of 10 mega-parsecs of the Milky Way, after the Sombrero Galaxy, with an absolute magnitude of around -22.21 or close).
Andromeda Galaxy | Luminosity estimates
The Greek philosopher Democritus (450–370 BCE) proposed that the bright band on the night sky known as the Milky Way might consist of distant stars. Aristotle (384–322 BCE), however, believed the Milky Way to be caused by "the ignition of the fiery exhalation of some stars that were large, numerous and close together" and that the "ignition takes place in the upper part of the atmosphere, in the region of the World that is continuous with the heavenly motions." The Neoplatonist philosopher Olympiodorus the Younger (–570 CE) was critical of this view, arguing that if the Milky Way is sublunary (situated between Earth and the Moon) it should appear different at different times and places on Earth, and that it should have parallax, which it does not.
Galaxy | Milky Way
SPT0418-47 is a young, extremely distant galaxy, discovered in 2020, surprisingly similar to the Milky Way, and looks like it was when the universe was only 1.4 billion years old. It is surprisingly non-chaotic and contradicts the theory that all galaxies in the early Universe were turbulent and unstable. It is located at a distance of about twelve billion light years from the Milky Way, where the planet Earth is located.
SPT0418-47 | Introduction
Among the dimmest stars in the cluster are groups of white dwarfs that are 6 billion years old and another group that appear to be 4 billion years old. The ages are out of sync with those of the cluster's normal stars, which are 8 billion years old. This seeming contradiction in age for this cluster has been studied and a solution proposed with age of about 8 billion years.
NGC 6791 | Age studies
In physical cosmology, the present time in the chronology of the universe is estimated at 13.8 billion years after the singularity determining the arrow of time. In terms of the metric expansion of space, it is in the dark-energy-dominated era, after the universe's matter content has become diluted enough for metric expansion to be dominated by vacuum energy (dark energy). It is also in the universe's Stelliferous Era, after enough time for superclusters to have formed (at about 5 billion years), but before the accelerating expansion of the universe has removed the local supercluster beyond the cosmological horizon (at about 150 billion years).
Present | Cosmology
As of March 2016, GN-z11 is the oldest and most distant observed galaxy with a comoving distance of 32 billion light-years from Earth, and observed as it existed just 400 million years after the Big Bang. Research released in 2016 revised the number of galaxies in the observable universe from a previous estimate of 200 billion () to a suggested two trillion () or more and, overall, as many as an estimated stars (more stars than all the grains of sand on planet Earth). Most of the galaxies are 1,000 to 100,000 parsecs in diameter (approximately 3,000 to 300,000 light years) and separated by distances on the order of millions of parsecs (or megaparsecs).
Galaxy | Introduction
The search for such very iron-poor stars has shown they are almost all anomalies in globular clusters and the Galactic Halo. This accords with a narrative that they are rare survivors of their generation. If so, the apparent visual data of the oldest of these enables us to longstop-date the reionization (first star formation) phase of the Universe independently of theories and evidence of the first few million years after the Big Bang. Most stars from Population II and Population III are no longer observable. Theories exist allowing for an older age of the universe than conventionally accepted, which can still accommodate the observed redshift of early objects and earlier radiation.
HD 140283 | Age and significance
In our Galaxy, globular clusters are distributed roughly spherically in the galactic halo, around the Galactic Centre, orbiting the centre in highly elliptical orbits. In 1917, the astronomer Harlow Shapley made the first reliable estimate of the Sun's distance from the galactic centre based on the distribution of globular clusters. Until the mid-1990s, globular clusters were the cause of a great mystery in astronomy, as theories of stellar evolution gave ages for the oldest members of globular clusters that were greater than the estimated age of the universe. However, greatly improved distance measurements to globular clusters using the Hipparcos satellite and increasingly accurate measurements of the Hubble constant resolved the paradox, giving an age for the universe of about 13 billion years and an age for the oldest stars of a few hundred million years less.
Star cluster | Globular cluster
The estimated age based upon the chromospheric activity level is 397 years, per Gray et al. (2015). Marsden et al. (2014) gave a larger age estimate of 1.2 billion years, but with a margin of error that overlaps the younger value. Age estimates of the Ursa Major group are around 300 million years old.
MT Pegasi | Introduction
The star's age, as measured by ESO's Very Large Telescope, is 13.2 billion years. This makes it among the oldest stars and nearly as old as the estimated age of the universe itself (13.8 billion years as measured by Planck). The measurement uncertainty in the age estimate is 0.7 to 2.7 billion years, depending upon the assumptions made to estimate the uncertainty, although the uncertainty in the relative age of this and other stars using the same method is smaller. HE 1523-0901 is the first star whose age was determined using the decay of the radioactive elements uranium and thorium in tandem with measurements of several neutron capture elements.
HE 1523-0901 | Age
Nucleocosmochronology or nuclear cosmochronology is a technique used to determine timescales for astrophysical objects and events. It compares the observed ratios of abundances of heavy radioactive and stable nuclides to the primordial ratios predicted by nucleosynthesis theory in order to calculate the age of formation of astronomical objects. Nucleocosmochronology has been employed to determine the age of the Sun ( billion years) and of the Galactic thin disk ( billion years), among others. It has also been used to estimate the age of the Milky Way itself, as exemplified by a recent study of Cayrel's Star in the Galactic halo, which due to its low metallicity, is believed to have formed early in the history of the Galaxy.
Nucleocosmochronology | Introduction
Only about 10 of these extremely early objects are currently known. More recent observations have shown these ages to be shorter than previously indicated. The most distant galaxy observed as of October 2016, GN-z11, has been reported to be 32 billion light-years away, a vast distance made possible through spacetime expansion ("z" = 11.1; comoving distance of 32 billion light-years; lookback time of 13.4 billion years).
Chronology of the universe | Galaxies, clusters and superclusters
If one has accurate measurements of these parameters, then the age of the universe can be determined by using the Friedmann equation. This equation relates the rate of change in the scale factor "a"("t") to the matter content of the universe. Turning this relation around, we can calculate the change in time per change in scale factor and thus calculate the total age of the universe by integrating this formula. The age "t" is then given by an expression of the form where formula_1 is the Hubble parameter and the function "F" depends only on the fractional contribution to the universe's energy content that comes from various components.
Age of the universe | Cosmological parameters
Betelgeuse in particular is expected to die in a supernova explosion within the next million years. As well as the scenarios of supermassive stars violently casting off their outer layers before their deaths, other examples can be found of the properties of stars which illustrate their age. For example, Cepheid variables have a characteristic pattern in their lightcurves, the rate of repetition of which is dependent on the luminosity of the star. Since Cepheid variables are a relatively short evolutionary stage in the lifecycle of stars, and knowing the mass of the star allows for the star to be tracked in its evolutionary path, one can estimate the age of the Cepheid variable.
Stellar age estimation | Stellar age estimation of stars
As the star spends only about 1% of its total lifetime as a red giant, this is an accurate method of determining age.
Stellar age estimation | Luminosity increase and the Hertzsprung–Russell diagram
Fitting the main sequence, and pre-main sequence gives a cluster age of 1 million years or less. There is no clear main sequence turnoff, although the most massive stars are modelled best with an age of 2.5 million years, but are compatible with an age around one million years. A small number of stars, for example Sher 25, apparently show much greater ages and it has been suggested that there is either ongoing star formation, or an earlier burst of star formation. Other studies have estimated ages up to 2 million years, but the existence of the most massive and luminous stars provide a hard upper limit of 2.5 million years on the possible age.
HD 97950 | Age
Most of these clusters are 15 million years old or less. The current burst of galactic star formation is estimated to have lasted 30 million years. External to the ring, the stars are generally older than within the ring structure, suggesting a previous epoch of star formation.
NGC 4314 | Introduction
It is best observed around August. M30 is located at a distance of about 27,100 light-years from Earth, and is about 93 light-years across. The estimated age is roughly 12.93 billion years and it has a combined mass of about 160,000 times the mass of the Sun. The cluster is following a retrograde orbit through the inner galactic halo, suggesting that it was acquired from a satellite galaxy rather than forming within the Milky Way. It is currently located at a distance of about from the center of the galaxy, compared to an estimated for the Sun. The M30 cluster has passed through a dynamic process called core collapse and now has a concentration of mass at its core of about a million times the Sun's mass per cubic parsec.
Messier 30 | Introduction
A different method by Harlow Shapley based on the cataloguing of globular clusters led to a radically different picture: a flat disk with diameter approximately 70 kiloparsecs and the Sun far from the center. Both analyses failed to take into account the absorption of light by interstellar dust present in the galactic plane, but after Robert Julius Trumpler quantified this effect in 1930 by studying open clusters, the present picture of our host galaxy, the Milky Way, emerged.
Galaxy | Milky Way
The age of the universe as estimated from the Hubble expansion and the CMB is now in good agreement with other estimates using the ages of the oldest stars, both as measured by applying the theory of stellar evolution to globular clusters and through radiometric dating of individual Population II stars. The prediction that the CMB temperature was higher in the past has been experimentally supported by observations of very low temperature absorption lines in gas clouds at high redshift. This prediction also implies that the amplitude of the Sunyaev–Zel'dovich effect in clusters of galaxies does not depend directly on redshift.
Big Bang | Other lines of evidence
One means for this to occur is by acquiring gas from an external source, which then undergoes star formation. An alternative is by a merger with a second galaxy. Neither scenario has been ruled out. The age of the lower mass, counter-rotating population is younger by about than the primary star population of the galaxy.
NGC 3593 | Introduction
The outer ring appears to be fairly young, at about 0.13 billion years old, while the core is much older, at 5.5 billion years old. The age of the inner ring is, as yet, undetermined. This makes the galaxy even more unusual, possibly making it one of a kind. The details of the formation of Hoag-type objects are still largely unknown. It has been suggested that the near-perfect core of Hoag's Object formed from a sort of "bar instability" where the central bar structure decays into a rounder core. It may also be due to another galaxy. In the case of LEDA 1000714, because its two rings have significantly different ages, the galaxy's morphology may have come from an anomalous collision with another galaxy, however more data is needed to draw conclusions.
LEDA 1000714 | Structure
Ordinary matter gathers where dark matter is denser, and in those places it collapses into clouds of mainly hydrogen gas. The first stars and galaxies form from these clouds. Where numerous galaxies have formed, galaxy clusters and superclusters will eventually arise. Large voids with few stars will develop between them, marking where dark matter became less common. The exact timings of the first stars, galaxies, supermassive black holes, and quasars, and the start and end timings and progression of the period known as reionization, are still being actively researched, with new findings published periodically. As of 2019, the earliest confirmed galaxies date from around 380–400 million years (for example GN-z11), suggesting surprisingly fast gas cloud condensation and stellar birth rates, and observations of the Lyman-alpha forest and other changes to the light from ancient objects allows the timing for reionization, and its eventual end, to be narrowed down.
Chronology of the universe | Earliest structures and stars emerge
The distance the light from the edge of the observable universe has travelled is very close to the age of the universe times the speed of light, , but this does not represent the distance at any given time because the edge of the observable universe and the Earth have since moved further apart. For comparison, the diameter of a typical galaxy is 30,000 light-years (9,198 parsecs), and the typical distance between two neighboring galaxies is 3 million light-years (919.8 kiloparsecs). As an example, the Milky Way is roughly 100,000–180,000 light-years in diameter, and the nearest sister galaxy to the Milky Way, the Andromeda Galaxy, is located roughly 2.5 million light-years away.
Universe | Size and regions
In March 2019, observations from Hubble and data from the European Space Agency's Gaia space observatory were combined to determine that the Milky Way Galaxy weighs approximately 1.5 trillion solar units and has a radius of 129,000 light years.
Hubble Space Telescope | Mass and size of Milky Way
If they match well, the assumed age of the isochrone is close to the actual age of the cluster.
Stellar isochrone | Introduction
Following theoretical developments of the Friedmann equations by Alexander Friedmann and Georges Lemaître in the 1920s, and the discovery of the expanding universe by Edwin Hubble in 1929, it was immediately clear that tracing this expansion backwards in time predicts that the universe had almost zero size at a finite time in the past. This concept, initially known as the "Primeval Atom" by Lemaitre, was later elaborated into the modern Big Bang theory. If the universe had expanded at a constant rate in the past, the age of the universe now (i.e. the time since the Big Bang) is simply the inverse of the Hubble constant, often known as the "Hubble time".
Cosmic age problem | Early years
The rotational period is about 240 million years at the radius of the Sun. The Milky Way as a whole is moving at a velocity of approximately 600 km per second with respect to extragalactic frames of reference. The oldest stars in the Milky Way are nearly as old as the Universe itself and thus probably formed shortly after the Dark Ages of the Big Bang.
Milky Way | Introduction
The star's spectral type is therefore written as . Age determination of this star shows some variation based on the method used. Statistically, for stars hosting a debris disk, the luminosity of this star suggests an age of about 20–150 million years. Comparison with stars having similar motion through space gives an age in the range 30–160 million years. Given the star's position on the Hertzsprung–Russell diagram of luminosity versus temperature, it has an estimated age in the range of 30–1,128 million years. λ Boötis stars like this are generally young, with a mean age of a billion years. More accurately, asteroseismology also suggests an age of approximately a billion years.
HR 8799 | Stellar properties
The galaxy has a comoving distance (light travel distance multiplied by the Hubble constant, caused by the metric expansion of space) of about 30 billion light years from Earth. EGS-zs8-1 was born 670 million years after the Big Bang, during the period of reionization, and it's 15 percent the size of the Milky Way. The galaxy was found to be larger than its other neighbors in that period when the universe was still very young. Its mass at the time the light was emitted is estimated to have been about 15% of the Milky Way's current mass. The galaxy was making new stars at roughly 80 times the rate of the current Milky Way, or equivalent to 800 worth of material turning to stars every year.
EGS-zs8-1 | Description
It is now generally believed to be a member of that galaxy. It is estimated to be 6.5 Gyr old.
Palomar 12 | Introduction
The problem of determining the age of the universe is closely tied to the problem of determining the values of the cosmological parameters. Today this is largely carried out in the context of the ΛCDM model, where the universe is assumed to contain normal (baryonic) matter, cold dark matter, radiation (including both photons and neutrinos), and a cosmological constant. The fractional contribution of each to the current energy density of the universe is given by the density parameters Ω, Ω, and Ω. The full ΛCDM model is described by a number of other parameters, but for the purpose of computing its age these three, along with the Hubble parameter formula_1, are the most important.
Age of the universe | Cosmological parameters
used the Hubble Space Telescope to find that the dominant population of this galaxy has an age of ~7 Gyr. Using its Hess diagram, they found that its evolutionary history may be similar to that of the Pegasus Dwarf Irregular Galaxy. Both galaxies are classified as Ir V in the DDO system. Also in 1999, Antonello et al. found five cepheids of Population II in IC 1613, giving self-evident support for the existence of a very old stellar population component of IC 1613. In 1999, King, Modjaz, & Li discovered the first nova ever detected in IC 1613.
IC 1613 | Introduction
As stars grow older, their luminosity increases at an appreciable rate. Given the mass of the star, one can use this rate of increase in luminosity in order to determine the age of the star. This method only works for calculating stellar age on the main sequence, because in advanced evolutionary stages of the star, such as the red giant stage, the standard relationship for the determination of age no longer holds. However, when one can observe a red giant star with a known mass, one can calculate the main-sequence lifetime, and thus the minimum age of star is known given that it is in an advanced stage of its evolution.
Stellar age estimation | Luminosity increase and the Hertzsprung–Russell diagram
Various methods and tools are involved in stellar age estimation, an attempt to identify within reasonable degrees of confidence what the age of a star is. These methods include stellar evolutionary models, membership in a given star cluster or system, fitting the star with the standard spectral and luminosity classification system, and the presence of a protoplanetary disk, among others. Nearly all of the methods of determining age require knowledge of the mass of the star, which can be known through various methods. No individual method can provide accurate results for all types of stars.
Stellar age estimation | Introduction
Given a cosmological model with certain values of the cosmological density parameters, it is possible to integrate the Friedmann equations and derive the age of the universe. By comparing this to actual measured values of the cosmological parameters, we can confirm the validity of a model which is accelerating now, and had a slower expansion in the past.
Accelerating expansion of the universe | Age of the universe
Exceptional stellar properties which allow for an estimation of age are not confined to advanced evolutionary stages. When a roughly solar-mass star exhibitis T Tauri variability, astronomers can locate the age of the star as being before the beginning of the main sequence phase of the star's life. Additionally, more massive pre-main-sequence stars could be Herbig Ae/Be stars. If a red dwarf star is emitting immense stellar flares and x-rays, the star can be calculated to be in an early stage of its main-sequence lifetime, after which it will become less variable and become stable.
Stellar age estimation | Stellar age estimation of stars
This found that the horizontal branch stars, like other dwarf spheroidal galaxies were predominantly red. From this, and the abundance of blue horizontal branch stars, along with 99 RR Lyrae stars detected in 2005, lead to the conclusion there was an extended epoch of star formation. The estimated age is approximately 10 Gyr. The Hubble telescope also found a globular cluster in Andromeda I, being the least luminous galaxy where such a cluster was found.
Andromeda I | Introduction
They have ages between 5 and 9 million years. The star formation rate in the central region of NGC 7741 is 0.022 per year per square kpc. The total stellar mass of NGC 7741 is estimated to be . NGC 7741 belongs to a small galaxy group known as the NGC 7741 group. Other members of the group are the galaxies UGC 12732, and UGC 12791.
NGC 7741 | Introduction
While the inner section of the galaxy shows a symmetrical two-arm structure, it has a single outer spiral arm that wraps 180° around the nucleus, giving the galaxy an overall asymmetric, lopsided appearance. The outer spiral arm has a red component that indicates a significant age. However, the existence of this structure is difficult to explain. The galaxy shows indications of recent starburst activity that may have terminated around 15 million years ago. The active central nucleus shows weak LINER behavior, and it may be an intermediate form between a LINER and an H II region. The luminosity of the X-ray source at the nucleus is in the 0.3–7 keV band.
NGC 1637 | Introduction
The presence of RR Lyrae variables shows that the galaxy has an old stellar population that is up to 10 billion years in age. The neutral hydrogen in this galaxy occupies in a volume similar to its optical extent, and is distributed in a squashed, uneven ring. The galaxy is not rotating and the hydrogen is moving about in random clumps. The proportion of elements with higher atomic numbers than helium is only about 1-2% of the ratio in the Sun. This indicates a much less complete conversion of gas into stars than in the Milky Way galaxy. The Leo A galaxy shows sign of increased star formation some time within the last 1-4 billion years, although the current level is low.
Leo A | Introduction
In the 14th century, the Syrian-born Ibn Qayyim proposed the Milky Way galaxy to be "a myriad of tiny stars packed together in the sphere of the fixed stars." Actual proof of the Milky Way consisting of many stars came in 1610 when the Italian astronomer Galileo Galilei used a telescope to study the Milky Way and discovered that it is composed of a huge number of faint stars. In 1750 the English astronomer Thomas Wright, in his "An Original Theory or New Hypothesis of the Universe", speculated (correctly) that the galaxy might be a rotating body of a huge number of stars held together by gravitational forces, akin to the Solar System but on a much larger scale.
Galaxy | Milky Way
Along with other factors, the presence of a protoplanetary disk sets a maximum limit on the age of stars. Stars with protoplanetary disks are typically young, having moved onto the main sequence only a relatively short time ago. Over time, this disk would coalesce to form planets, with leftover material being deposited into various asteroid belts and other similar locations. However, the presence of pulsar planets complicates this method as a determinant of age.
Stellar age estimation | Presence of a protoplanetary disk
The "distance" of a far away galaxy depends on how it is measured. With a redshift of 1, light from this galaxy is estimated to have taken around 7.7 billion years to reach Earth. However, since this galaxy is receding from Earth, the present comoving distance is estimated to be around 10 billion light-years away. In context, Hubble is observing this galaxy as it appeared when the Universe was around 5.9 billion years old.
UDF 423 | Distance measurements
Its estimated age is about 135000 years.
Erdmanns Cave | Description
This starburst may also be accompanied by the formation of galactic relativistic jets as matter falls into the central black hole. It is thought that the Milky Way undergoes a starburst of this sort every 500 million years. In addition to the paradox of youth, there is also a "conundrum of old age" associated with the distribution of the old stars at the Galactic Center. Theoretical models had predicted that the old stars—which far outnumber young stars—should have a steeply-rising density near the black hole, a so-called Bahcall–Wolf cusp. Instead, it was discovered in 2009 that the density of the old stars peaks at a distance of roughly 0.5 parsec from Sgr A*, then falls inward: instead of a dense cluster, there is a "hole", or core, around the black hole.
Galactic Center | Stellar population
Compared with the Milky Way galaxy, GN-z11 is of the size, has 1% of the mass, and was forming new stars approximately twenty times as fast. With a stellar age estimated at 40 million years, it appears the galaxy formed its stars relatively rapidly. The fact that a galaxy so massive existed so soon after the first stars started to form is a challenge to some current theoretical models of the formation of galaxies.
GN-z11 | Discovery
The galaxy has an unusually young star population, with populations throughout the galactic disc having an age of ~0.04 - 0.1 Gyr.
NGC 612 | Physical characteristics
Optical long slit spectrography of the galaxy showed a strong age gradient along the semimajor axis of NGC 720, which has been explained on the grounds of two distinct population components. At the centre of the galaxy lie stars whose age is estimated to be 13 billion years (Gyrs) old up to 0.73 kpc, where stars with solar metallicity age (5 Gyrs) dominate. These older stars form a small bulge-like spheroid. At distances over 1 kpc dominate stars with age at 2,5 Gyrs. Based on the Mg2 gradient and its mass, it is proposed that NGC 720 underwent an unequal mass galaxy merger about 4 Gyrs ago.
NGC 720 | Characteristics
The age of Alicante 8 is estimated to be around 16–20 million years. The observed red supergiants are type II supernova progenitors. The cluster is heavily obscured and have not been detected in the visible light. It lies close to other groupings of red supergiants known as RSGC1, Stephenson 2, RSGC3, Alicante 7, and Alicante 10. The mass of the open cluster is estimated at 10–20 thousand solar masses, which makes it one of the most massive open clusters in the Galaxy.
Alicante 8 | Introduction
It has an estimated age of 158.5 million years and a mass of . The magnitude 8.3 supergiant star BD +60°2532 is a probable member of M52. The stellar population includes 18 candidate slowly pulsating B stars, one of which is a δ Scuti variable, and three candidate γ Dor variables. There may also be three Be stars. The core of the cluster shows a lack of interstellar matter, which may be the result of supernovae explosions early in the cluster's history.
Messier 52 | Introduction
Its age is estimated to be years, based on its measured expansion rate of 31 km·s.
Helix Nebula | General information
It is at the edge of Fornax Cluster. Near the galaxy is bright foreground star that makes deep observations more difficult, so the galaxy's apparent magnitude is 12.6. Its size on night sky is 2.5' x 2.2' which is, along with it distance, proportional to real size of 45,000 light-years. IC 1993 is one of the 25 galaxies known to have rings or partial rings. Most resemble local collisional ring galaxies in morphology, size, and clumpy star formation. Clump ages range from to yr, and clump masses go up to several × solar masses, based on color evolution models. The clump ages are consistent with the expected lifetimes of ring structures if they are formed by collisions.
IC 1993 | Introduction
It is believed to have formed directly from the remnants of the first-generation stars that reached the end of their longevity and exploded as supernovae early in the history of known matter.
HE 1523-0901 | Age