The Milky Way Could Be Spreading Life From Star to Star

For almost two centuries, scientists have theorized that life may be distributed throughout the Universe by meteoroids, asteroids, planetoids, and other astronomical objects. This theory, known as Panspermia, is based on the idea that microorganisms and the chemical precursors of life are able to survive being transported from one star system to the next.

Expanding on this theory, a team of researchers from the Harvard Smithsonian Center for Astrophysics (CfA) conducted a study that considered whether panspermia could be possible on a galactic scale. According to the model they created, they determined that the entire Milky Way (and even other galaxies) could be exchanging the components necessary for life.

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Narrowing Down the Mass of the Milky Way

Since the birth of modern astronomy, scientists have sought to determine the full extent of the Milky Way galaxy and learn more about its structure, formation and evolution. At present, astronomers estimate that it is 100,000 to 180,000 light-years in diameter and consists of 100 to 400 billion stars – though some estimates say there could be as many as 1 trillion.

And yet, even after decades of research and observations, there is still much about our galaxy astronomers do not know. For example, they are still trying to determine how massive the Milky Way is, and estimates vary widely. In a new study, a team of international scientists presents a new method for weighing the galaxy based the dynamics of the Milky Way’s satellites galaxies.

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We’re in the Milky Way’s Second Life. Star Formation was Shut Down for Billions of Years

Since the birth of modern astronomy, scientists have sought to determine the full extent of the Milky Way galaxy and learn more about its structure, formation and evolution. According to current theories, it is widely believed that the Milky Way formed shortly after the Big Bang (roughly 13.51 billion years ago). This was the result of the first stars and star clusters coming together, as well as the accretion of gas directly from the Galactic halo.

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Astronomers Have Found Grease in Space

Over the course of many centuries, scientists learned a great deal about the types of conditions and elements that make life possible here on Earth. Thanks to the advent of modern astronomy, scientists have since learned that these elements are not only abundant in other star systems and parts of the galaxy, but also in the medium known as interstellar space.

Consider carbon, the element that is essential to all organic matter and life as we know it. This life-bearing element is also present in interstellar dust, though astronomers are not sure how abundant it is. According to new research by a team of astronomers from Australia and Turkey, much of the carbon in our galaxy exists in the form of grease-like molecules.

Their study, “Aliphatic Hydrocarbon Content of Interstellar Dust“, recently appeared in the Monthly Notices of the Royal Astronomical Society. The study was led by Gunay Banihan, a professor from the Department of Astronomy and Space Sciences of Erge University in Turkey, and included members from multiple departments from the University of New South Wales in Sydney (UNSW).

A new study by a team of Turkish and Australian astronomers has found evidence of grease-like molecules in interstellar dust. Credit: ESO/R. Fosbury (ST-ECF)

For the sake of their study, the team sought to determine exactly how much of our galaxy’s carbon is bound up in grease-like molecules. At present, it is believed that half of the interstellar carbon exists in pure form, whereas the rest in bound up in either grease-like aliphatic molecules (carbon atoms that form open chains) and mothball-like aromatic molecules (carbon atoms that form planar unsaturated rings).

To determine how plentiful grease-like molecules are compared to aromatic ones, the team created material with the same properties as interstellar dust in a laboratory. This consisted of recreating the process where aliphatic compounds are synthesized in the outflows of carbon stars. They then followed up on this by expanding the carbon-containing plasma into a vacuum at low temperatures to simulate interstellar space.

As Prof. Tim Schmidt, from the Australian Research Council Centre of Excellence in Exciton Science in the School of Chemistry at UNSW Sydney and a co-author on the paper, explained:

“Combining our lab results with observations from astronomical observatories allows us to measure the amount of aliphatic carbon between us and the stars.”

Using magnetic resonance and spectroscopy, they were then able to determine how strongly the material absorbed light with a certain infrared wavelength. From this, the team found that there are about 100 greasy carbon atoms for every million hydrogen atoms, which works out to about half of the available carbon between stars. Expanding that to include all of the Milky Way, they determined that about 10 billion trillion trillion tonnes of greasy matter exists.

Artist’s impression of the Milky Way Galaxy. Credit: NASA/JPL-Caltech/R. Hurt (SSC-Caltech)

To put that in perspective, that’s enough grease to fill about 40 trillion trillion trillion packs of butter. But as Schmidt indicated, this grease is far from being edible.

“This space grease is not the kind of thing you’d want to spread on a slice of toast! It’s dirty, likely toxic and only forms in the environment of interstellar space (and our laboratory). It’s also intriguing that organic material of this kind – material that gets incorporated into planetary systems – is so abundant.”

Looking ahead, the team now wants to determine the abundance of the other type of non-pure carbon, which is the mothball-like aromatic molecules. Here too, the team will be recreating the molecules in a laboratory environment using simulations. By establishing the amount of each type of carbon in interstellar dust, they will be able to place constraints on how much of this elements is available in our galaxy.

This in turn will allow astronomers to determine exactly how much of this life-giving element is available, and could also help shed light on how and where life can take hold!

Further Reading: RAS, MNRAS

Globular Clusters Might not be as Old as Astronomers Thought. Like, Billions of Years Younger

Globular clusters have been a source of fascination ever since astronomers first observed them in the 17th century. These spherical collections of stars are among the oldest known stars in the Universe, and can be found in the outer regions of most galaxies. Because of their age and the fact that almost all larger galaxies appear to have them, their role in galactic evolution has remained something of a mystery.

Previously, astronomers were of the opinion that globular clusters were some of the earliest stars to have formed in the Universe, roughly 13 billion years ago. However, new research has indicated that these clusters may actually be about 4 billion years younger, being roughly 9 billion years old. These findings may alter our understanding of how the Milky Way and other galaxies formed, and how the Universe itself came to be.

The study, titled “Reevaluating Old Stellar Populations“, recently appeared online and is being evaluated for publication in The Monthly Notices for the Royal Astronomical Society. The study was led by Dr. Elizabeth Stanway, an Associate Professor in the Astronomy group at the University of Warwick, UK, and was assisted by Dr. J.J. Eldridge, a Senior Lecturer at the University of Auckland, New Zealand.

Within larger galaxies, like the Milky Way, globular clusters are part of the galactic halo. Between 150 and 180 are estimated to be part of the Milky Way alone. Credit: ESO

For the sake of their study, Dr. Stanway and Dr. Eldridge developed a series of new research models designed to reconsider the evolution of stars. These models, known as Binary Population and Spectral Synthesis (BPASS) models, had previously proven effective in exploring the properties of young stellar populations within the Milky Way and throughout the Universe.

Using these same models, Dr. Stanway and Dr. Eldridge studied a sample of globular clusters in the Milky Way and nearby quiescent galaxies. They also took into account the details of binary star evolution within globular clusters and used them to explore the colors of light and spectra from old binary populations. In short, binary star system evolution consists of one star expanding into a giant while the gravitational force of the smaller star strips away the atmosphere of the giant.

What they found was that these binary systems were about 9 billion years old. Since these stars are thought to have formed at the same time as the globular clusters themselves, this demonstrated that globular clusters are not as old as other models have suggested. As Dr. Stanway said of the BPASS models she and Dr. Eldridge developed:

“Determining ages for stars has always depended on comparing observations to the models which encapsulate our understanding of how stars form and evolve. That understanding has changed over time, and we have been increasingly aware of the effects of stellar multiplicity – the interactions between stars and their binary and tertiary companions.

An artist’s impression of a millisecond pulsar and its companion. The presence of binaries in globular clusters is a good means of providing age estimates of those clusters. Credit: ESA & Francesco Ferraro (Bologna Astronomical Observatory)

If correct, this study could open up new pathways of research into how massive galaxies and their stars are formed. However, Dr. Stanway admits that much work still lies ahead, which includes looking at nearby star systems where individual stars can be resolved – rather than considering the integrated light of a cluster. Nevertheless, the study could have immense significant for our understanding of how and when galaxies in our Universe formed.

“If true, it changes our picture of the early stages of galaxy evolution and where the stars that have ended up in today’s massive galaxies, such as the Milky Way, may have formed,” she said. “We aim to follow up this research in the future, exploring both improvements in modelling and the observable predictions which arise from them.”

An integral part of cosmology is understanding when the Universe came to be the way it is, not just how. By determining how old globular clusters are, astronomers will have another crucial piece of the puzzle as to how and when the earliest galaxies formed. And these, combined with observations that look to the earliest epochs of the Universe, could just yield a complete model of cosmology.

Further Reading: University of Warwick, arXiv

Thanks to a Massive Release from Gaia, we now Know Where 1.7 BILLION Stars are in the Milky Way

On December 19th, 2013, the European Space Agency’s (ESA) Gaia spacecraft took to space with one of the most ambitious missions ever. Over the course of its planned 5-year mission (which was recently extended), this space observatory would map over a billion stars, planets, comets, asteroids and quasars in order to create the largest and most precise 3D catalog of the Milky Way ever created.

The first release of Gaia data, which took place in September 2016, contained the distances and motions of over two million stars. But the second data release, which took place on April 25th, 2018, is even more impressive. Included in the release are the positions, distance indicators and motions of more than one billion stars, asteroids within our Solar System, and even stars beyond the Milky Way.

Whereas the first data release was based on just over a year’s worth of observations, the new data release covers a period of about 22 months – which ran from July 25th, 2014, to May 23rd, 2016. Preliminary analysis of this data has revealed fine details about 1.7 billion stars in the Milky Way and how they move, which is essential to understanding how our galaxy evolved over time.

ESA’s Gaia is currently on a five-year mission to map the stars of the Milky Way. Image credit: ESA/ATG medialab; background: ESO/S. Brunier.

As Günther Hasinger, the ESA Director of Science, explained in a recent ESA press release:

The observations collected by Gaia are redefining the foundations of astronomy. Gaia is an ambitious mission that relies on a huge human collaboration to make sense of a large volume of highly complex data. It demonstrates the need for long-term projects to guarantee progress in space science and technology and to implement even more daring scientific missions of the coming decades.

The precision of Gaia‘s instruments has allowed for measurements that are so accurate that it was possible to separate the parallax of stars – the apparent shift caused by the Earth’s orbit around the Sun – from their movements through the galaxy. Of the 1.7 billion stars cataloged, the parallax and velocity (aka. proper motion) of more than 1.3 billion were measured and listed.

For about 10% of these, the parallax measurements were so accurate that astronomers can directly estimate distances to the individual stars. As Anthony Brown of Leiden University, who is also the chair of the Gaia Data Processing and Analysis Consortium Executive Board, explained:

The second Gaia data release represents a huge leap forward with respect to ESAs Hipparcos satellite, Gaias predecessor and the first space mission for astrometry, which surveyed some 118 000 stars almost thirty years agoThe sheer number of stars alone, with their positions and motions, would make Gaias new catalogue already quite astonishing. But there is more: this unique scientific catalogue includes many other data types, with information about the properties of the stars and other celestial objects, making this release truly exceptional.

In addition to the proper motions of stars, the catalog provides information on a wide range of topics that will be of interest to astronomers and astrophysicists. These include brightness and color measurements of nearly all of the 1.7 billion stars cataloged, as well as information on how the brightness and color change for half a million variable stars over time.

It also contains the velocities along the line of sight of seven million stars, the surface temperatures of about 100 million, and the effect interstellar dust has on 87 million. The Gaia data also contains information on objects in our Solar System, which includes the positions of 14,000 known asteroids (which will allow for the precise determination of their orbits).

Beyond the Milky Way, Gaia obtained more accurate measurements of the positions of half a million distant quasars – bright galaxies that emit massive amounts of energy due to the presence of a supermassive black hole at their centers. In the past, quasars have been used as a reference frame for the celestial coordinates of all objects in the Gaia catalogue based on radio waves.

However, this information will now be available at optical wavelengths for the first time. This, and other developments made possible by Gaia, could revolutionize how we study our galaxy and the Universe. As Antonella Vallenari, from the Istituto Nazionale di Astrofisica (INAF), the Astronomical Observatory of Padua, Italy, and the deputy chair of the Data Processing Consortium Executive Board, indicated:

The new Gaia data are so powerful that exciting results are just jumping at us. For example, we have built the most detailed Hertzsprung-Russell diagram of stars ever made on the full sky and we can already spot some interesting trends. It feels like we are inaugurating a new era of Galactic archaeology.

The Hertzsprung-Russell diagram, which is named after the two astronomers who devised it in the early 20th century, is fundamental to the study of stellar populations and their evolution. Based on four million stars that were selected from the catalog (all of which are withing five thousand light-years from the Sun), scientist were able to reveal many fine details about stars beyond our Solar System for the first time.

Along with measurements of their velocities, the Gaia Hertzsprung-Russell diagram enables astronomers to distinguish between populations of stars that are of different ages, are located in different regions of the Milky Way (i.e. the disk and the halo), and that formed in different ways. These include fast moving stars that were previously thought to belong to the halo, but are actually part of two stellar populations.

“Gaia will greatly advance our understanding of the Universe on all cosmic scales,” said Timo Prusti, a Gaia project scientist at ESA. “Even in the neighborhood of the Sun, which is the region we thought we understood best, Gaia is revealing new and exciting features.”

For instance, for a subset of stars within a few thousand light-years of the Sun, Gaia measured their velocity in all three dimensions. From this, it has been determined that they follow a similar pattern to stars that are orbiting the galaxy at similar speeds. The cause of these patterns will be the subject of future research, as it is unclear whether its caused by our galaxy itself or are the result of interactions with smaller galaxies that merged with us in the past.

Last, but not least, Gaia data will be used to learn more about the orbits of 75 globular clusters and 12 dwarf galaxies that revolve around the Milky Way. This information will shed further light on the evolution of our galaxy, the gravitational forces affecting it, and the role played by dark matter. As Fred Jansen, the Gaia mission manager at ESA, put it:

Gaia is astronomy at its finest. Scientists will be busy with this data for many years, and we are ready to be surprised by the avalanche of discoveries that will unlock the secrets of our Galaxy.

The third release of Gaia data is scheduled to take place in late 2020, with the final catalog being published in the 2020s. Meanwhile, an extension has already been approved for the Gaia mission, which will now remain in operation until the end of 2020 (to be confirmed at the end of this year). A series of scientific papers describing what has been learned from this latest release will also appear in a special issue of Astronomy & Astrophysics.

From the evolution of stars to the evolution of our galaxy, the second Gaia data release is already proving to be a boon for astronomers and astrophysicists. Even after the mission concludes, we can expect scientists will still be analyzing the data and learning a great deal more about the structure and evolution of our Universe.

Further Reading: ESA

Did the Milky Way Steal These Stars or Kick Them Out of the Galaxy?

Despite thousands of years of research and observation, there is much that astronomers still don’t know about the Milky Way Galaxy. At present, astronomers estimate that it spans 100,000 to 180,000 light-years and consists of 100 to 400 billion stars. In addition, for decades, there have been unresolved questions about how the structure of our galaxy evolved over the course of billions of years.

For example, astronomers have long suspected that galactic halo came from – giant structures of stars that orbit above and below the flat disk of the Milky Way – were formed from debris left behind by smaller galaxies that merged with the Milky Way. But according to a new study by an international team of astronomers, it appears that these stars may have originated within the Milky Way but were then kicked out.

The study recently appeared in the journal Nature under the title “Two chemically similar stellar overdensities on opposite sides of the plane of the Galactic disk“. The study was led by Margia Bergmann, a researcher from the Max Planck Institute for Astronomy, and included members from the Australian National University, the California Institute of Technology, and multiple universities.

Artist’s impression of the Milky Way Galaxy. Credit: NASA/JPL-Caltech/R. Hurt (SSC-Caltech)

For the sake of their study, the team relied on data from the W.M. Keck Observatory to determine the chemical abundance patterns from 14 stars located in the galactic halo. These stars were located in two different halo structures – the Triangulum-Andromeda (Tri-And) and the A13 stellar overdensities – which are bout 14,000 light years above and below the Milky Way disc.

As Bergemann explained in a Keck Observatory press release:

“The analysis of chemical abundances is a very powerful test, which allows, in a way similar to the DNA matching, to identify the parent population of the star. Different parent populations, such as the Milky Way disk or halo, dwarf satellite galaxies or globular clusters, are known to have radically different chemical compositions. So once we know what the stars are made of, we can immediately link them to their parent populations.”

The team also obtained spectra from one additional using the European Southern Observatory’s Very Large Telescope (VLT) in Chile. By comparing the chemical compositions of these stars with the ones found in other cosmic structures, the scientists noticed that the chemical compositions were almost identical. Not only were they similar within and between the groups being studies, they closely matched the abundance patterns of stars found within the Milky Way’s outer disk.

Computer model of the Milky Way and its smaller neighbor, the Sagittarius dwarf galaxy. Credit: Tollerud, Purcell and Bullock/UC Irvine

From this, they concluded that these stellar population in the Galactic Halo were formed in the Milky Way, but then relocated to locations above and below the Galactic Disk. This phenomena is known as “galactic eviction”, where structures are pushed off the plane of the Milky Way when a massive dwarf galaxy passes through the galactic disk. This process causes oscillations that eject stars from the disk, in whichever the dwarf galaxy is moving.

“The oscillations can be compared to sound waves in a musical instrument,” added Bergemann. “We call this ‘ringing’ in the Milky Way galaxy ‘galactoseismology,’ which has been predicted theoretically decades ago. We now have the clearest evidence for these oscillations in our galaxy’s disk obtained so far!”

These observations were made possible thanks to the High-Resolution Echelle Spectrometer (HiRES) on the Keck Telescope. As Judy Cohen, the Kate Van Nuys Page Professor of Astronomy at Caltech and a co-author on the study, explained:

“The high throughput and high spectral resolution of HIRES were crucial to the success of the observations of the stars in the outer part of the Milky Way. Another key factor was the smooth operation of Keck Observatory; good pointing and smooth operation allows one to get spectra of more stars in only a few nights of observation. The spectra in this study were obtained in only one night of Keck time, which shows how valuable even a single night can be.”

360-degree panorama view of the Milky Way (an assembled mosaic of photographs) by ESO. Credit: ESO/S. Brunier

These findings are very exciting for two reasons. On the one hand, it demonstrates that halo stars likely originated in the Galactic think disk – a younger part of the Milky Way. On the other hand, it demonstrates that the Milky Way’s disk and its dynamics are much more complex than previously thought. As Allyson Sheffield of LaGuardia Community College/CUNY, and a co-author on the paper, said:

“We showed that it may be fairly common for groups of stars in the disk to be relocated to more distant realms within the Milky Way – having been ‘kicked out’ by an invading satellite galaxy. Similar chemical patterns may also be found in other galaxies, indicating a potential galactic universality of this dynamic process.”

As a next step, the astronomers plan to analyze the spectra of additional stars in the Tri-And and A13 overdensities, as well as stars in other stellar structures further away from the disk. They also plan to determine masses and ages of these stars so they can constrain the time limits of when this galactic eviction took place.

In the end, it appears that another long-held assumption on galactic evolution has been updated. Combined with ongoing efforts to probe the nuclei of galaxies – to see how their Supermassive Black Holes and star formation are related – we appear to be getting closer to understanding just how our Universe evolved over time.

Further Reading: W.M. Keck Observatory, Nature

Amazing High Resolution Image of the Core of the Milky Way, a Region with Surprisingly Low Star Formation Compared to Other Galaxies

Compared to some other galaxies in our Universe, the Milky Way is a rather subtle character. In fact, there are galaxies that are a thousands times as luminous as the Milky Way, owing to the presence of warm gas in the galaxy’s Central Molecular Zone (CMZ). This gas is heated by massive bursts of star formation that surround the Supermassive Black Hole (SMBH) at the nucleus of the galaxy.

The core of the Milky Way also has a SMBH (Sagittarius A*) and all the gas it needs to form new stars. But for some reason, star formation in our galaxy’s CMZ is less than the average. To address this ongoing mystery, an international team of astronomers conducted a large and comprehensive study of the CMZ to search for answers as to why this might be.

The study, titled “Star formation in a high-pressure environment: an SMA view of the Galactic Centre dust ridge” recently appeared in the Monthly Notices of the Royal Astronomical Society. The study was led by Daniel Walker of the Joint ALMA Observatory and the National Astronomical Observatory of Japan, and included members from multiple observatories, universities and research institutes.

A false color Spitzer infrared image of the Milky Way’s Central Molecular Zone (CMZ). Credit: Spitzer/NASA/CfA

For the sake of their study, the team relied on the Submillimeter Array (SMA) radio interferometer, which is located atop Maunakea in Hawaii. What they found was a sample of thirteen high-mass cores in the CMZ’s “dust ridge” that could be young stars in the initial phase of development. These cores ranged in mass from 50 to 2150 Solar Masses and have radii of 0.1 – 0.25 parsecs (0.326 – 0.815 light-years).

They also noted the presence of two objects that appeared to be previously unknown young, high-mass protostars. As they state in their study, all of this indicated that stars in CMZ had about the same rate of formation as those in the galactic disc, despite their being vast pressure differences:

“All appear to be young (pre-UCHII), meaning that they are prime candidates for representing the initial conditions of high-mass stars and sub-clusters. We compare all of the detected cores with high-mass cores and clouds in the Galactic disc and find that they are broadly similar in terms of their masses and sizes, despite being subjected to external pressures that are several orders of magnitude greater.”

To determine that the external pressure in the CMZ was greater, the team observed spectral lines of the molecules formaldehyde and methyl cyanide to measure the temperature of the gas and its kinetics. These indicated that the gas environment was highly turbulent, which led them to the conclusion that the turbulent environment of the CMZ is responsible for inhibiting star formation there.

A radio image from the NSF’s Karl G. Jansky Very Large Array showing the center of our  galaxy. Credit: NSF/VLA/UCLA/M. Morris et al.

As they state in their study, these results were consistent with their previous hypothesis:

“The fact that >80 percent of these cores do not show any signs of star-forming activity in such a high-pressure environment leads us to conclude that this is further evidence for an increased critical density threshold for star formation in the CMZ due to turbulence.”

So in the end, the rate of star formation in a CMZ is not only dependent on their being a lot of gas and dust, but on the nature of the gas environment itself. These results could inform future studies of not only the Milky Way, but of other galaxies as well – particularly when it comes to the relationship that exists between Supermassive Black Holes (SMBHs), star formation, and the evolution of galaxies.

For decades, astronomers have studied the central regions of galaxies in the hopes of determining how this relationship works. And in recent years, astronomers have come up with conflicting results, some of which indicate that star formation is arrested by the presence of SMBHs while others show no correlation.

In addition, further examinations of SMBHs and Active Galactic Nuclei (AGNs) have shown that there may be no correlation between the mass of a galaxy and the mass of its central black hole – another theory that astronomers previously subscribed to.

As such, understanding how and why star formation appears to be different in galaxies like the Milky Way could help us to unravel these other mysteries. From that, a better understanding of how stars and galaxies evolved over the course of cosmic history is sure to emerge.

Further Reading: CfA, MNRAS

It Turns Out, Andromeda is Younger Than Earth… Sort Of

Since ancient times, astronomers have looked up at the night sky and seen the Andromeda galaxy. As the closest galaxy to our own, scientists have been able to observe and scrutinize this giant spiral galaxy for millennia. By the 20th century, astronomers realized that Andromeda was the Milky Way’s sister galaxy and was moving towards us. In 4.5 billion years, it will even merge with our own to form a supergalaxy.

However, it seems astronomers were wrong about the Andromeda galaxy in one major respect. According to recent study led by a team of French and Chinese astronomers, this giant spiral galaxy formed from a major merger that occurred less than 3 billion years ago. This means that Andromeda, as we know it today, is effectively younger than our very own Solar System, which has it beat by about 1.5 billion years!

The study, titled “A 2-3 billion year old major merger paradigm for the Andromeda galaxy and its outskirts“, recently appeared in the Monthly Notices of the Royal Astronomical Society. Led by Francois Hammer, the Principle Investigator of the Galaxies, Etoiles, Physique et Instrumentation (GEPI) department at the Paris Observatory, the team included members from the Chinese Academy of Sciences and the University of Strasbourg.

For the sake of their study, the relied on data gathered by recent surveys that noted considerable differences between the Andromeda and Milky Way galaxies. The first of these studies, which took place between 2006 and 2014, demonstrated all Andromeda has a wealth of young blue stars in its disk (less than 2 billion years old) that undergo random motions over large scales. This is contrast to the stars in the Milky Way’s disk, which are subject only to simple rotation.

In addition, deep observations conducted between 2008 and 2014 with the French-Canadian telescope in the Hawaiian Islands (CFHT) indicated some interesting things about Andromeda’s halo. This vast region, which is 10 times the size of the galaxy itself, is populated by gigantic currents of stars. The most prominent of which is called the “Giant Stream”, a warped disk that has shells and clumps at its very edges.

Using this data, the French-Chinese collaboration then created a detailed numerical model of Andromeda using the two most powerful computers available in France – the Paris Observatory’s MesoPSL and the National Center for Scientific Research’s (CNRS) IDRIS-GENCI supercomputer. With the resulting numerical model, the team was able to demonstrate that these recent observations could be explained only by a recent collision.

Basically, they concluded that between 7 and 10 billion years ago, Andromeda consisted of  two galaxies that had slowly achieved a encountering orbit. After optimizing the trajectories of both galaxies, they determined that they would have collided 1.8 to 3 billion years ago. This collision is what gave birth to Andromeda as we know it today, which effectively makes it younger than our Solar System – which formed almost 4.6 billion years ago.

What’s more, they were able to calculate mass distributions for both parent galaxies that merged to formed Andromeda, which indicated that the larger galaxy was four times the size of the smaller. But most importantly, the team was able to reproduce in detail all the structures that compose Andromeda today – including the bulge, the bar, the huge disk, and the presence of young stars.

The presence of young blue stars in its disk, which has remained unexplained until now, is attributable to a period of intense star formation that took place after the collision. In addition, structures like the “Giant Stream” and the shells of the halo belonged to the smaller parent galaxy, whereas the diffuse clumps and the warped nature of the halo were derived from the larger one.

Their study also explains why the features attributed to the smaller galaxy have an under-abundance in heavy elements compared to the others – i.e. it was less massive so it formed fewer heavy elements and stars. This study is immensely significant when it comes to galactic formation and evolution, mainly because it is the first numerical simulation that has succeeded in reproducing a galaxy in such detail.

It is also of significance given that such a recent impact it could have left materials in the Local Group. In other words, this study could have implications that range far beyond our galactic neighborhood. It is also a good example of how increasingly sophisticated instruments are leading to more detailed observations which, when combined with increasingly sophisticated computers and algorithms, are leading to more detailed models.

One can only wonder if future extra-terrestrial intelligence (ETI) will draw similar conclusions about our own galaxy once it merges with Andromeda, billions of years from now. The collision and resulting features are sure to be of interest to anyone advanced species that’s around to study it!

Further Reading: Paris Observatory, Monthly Notices of the Royal Astronomical Society search and more info website

Astronomers Find One of the Oldest Stars in the Milky Way

According to modern cosmological models, the Universe began in a cataclysm event known as the Big Bang. This took place roughly 13.8 billion years ago, and was followed by a period of expansion and cooling. During that time, the first hydrogen atoms formed as protons and electrons combined and the fundamental forces of physics were born. Then, about 100 million years after the Big Bang, that the first stars and galaxies began to form.

The formation of the first stars was also what allowed for the creation of heavier elements, and therefore the formation of planets and all life as we know it. However, until now, how and when this process took place has been largely theoretical since astronomers did not know where the oldest stars in our galaxy were to be found. But thanks to a new study by a team of Spanish astronomers, we may have just found the oldest star in the Milky Way!

The study, titled “J0815+4729: A chemically primitive dwarf star in the Galactic Halo observed with Gran Telescopio Canarias“, recently appeared in The Astrophysical Journal Letters. Led by David S. Aguado of the Instituto de Astrofisica de Canarias (IAC), the team included members from the University of La Laguna and the Spanish National Research Council (CSIC).

Artist’s impression of the Milky Way Galaxy. Credit: NASA/JPL-Caltech/R. Hurt (SSC-Caltech)

This star is located roughly 7,500 light years from the Sun, and was found in the halo of the Milky Way along the line of sight to the Lynx constellation. Known as J0815+4729, this star is still in its main sequence and has a low mass, (around 0.7 Solar Masses), though the research team estimates that it has a surface temperature that is about 400 degrees hotter – 6,215 K (5942 °C; 10,727 °F) compared to 5778 K (5505 °C; 9940 °F).

For the sake of their study, the team was looking for a star that showed signs of being metal-poor, which would indicate that it has been in its main sequence for a very long time. The team first selected J0815+4729 from the Sloan Digital Sky Survey-III Baryon Oscillation Spectroscopic Survey (SDSS-III/BOSS) and then conducted follow-up spectroscopic investigations to determine its composition (and hence its age).

This was done using the Intermediate dispersion Spectrograph and Imaging System (ISIS) at the William Herschel Telescope (WHT) and the Optical System for Imaging and low-intermediate-Resolution Integrated Spectroscopy (OSIRIS) at Gran Telescopio de Canarias (GTC), both of which are located at the Observatorio del Roque de los Muchachos on the island of La Palma.

Consistent with what modern theory predicts, the star was found in the Galactic halo – the extended component of our galaxy that reaches beyond the galactic disk (the visible portion). It is in this region that the oldest and most metal-poor stars are believed to be found in galaxies, hence why the team was confident that a star dating back to the early Universe would be found here.

The William Herschel Telescope, part of the Isaac Newton group of telescopes, located on Canary Island. Credit: ing.iac.es

As Jonay González Hernández – a professor from the University of La Laguna, a member of the IAC and a co-author on the paper – explained in an IAC press release:

“Theory predicts that these stars could use material from the first supernovae, whose progenitors were the first massive stars in the galaxy, around 300 million years after the Big Bang. In spite of its age, and its distance away from us, we can still observe it.”

Spectra obtained by both the ISIS and OSIRIS instruments confirmed that the star was poor in metals, indicating that J0815+4729 has only one-millionth of the calcium and iron that the Sun contains. In addition, the team also noticed that the star has a higher carbon content than our Sun, accounting for almost 15% percent of its solar abundance (i.e. the relative abundance of its elements).

In short, J0815+4729 may be the most iron-poor and carbon-rich star currently known to astronomers. Moreover, finding it was rather difficult since the star is both weak in luminosity and was buried within a massive amount of SDSS/BOSS archival data. As Carlos Allende Prieto, another IAC researcher and a co-author on the paper, indicated:

“This star was tucked away in the database of the BOSS project, among a million stellar spectra which we have analysed, requiring a considerable observational and computational effort. It requires high-resolution spectroscopy on large telescopes to detect the in the star, which can help us to understand the first supernovae and their progenitors.”

In the near future, the team predicts that next-generation spectrographs could allow for further research that would reveal more about the star’s chemical abundances. Such instruments include the HORS high-resolution spectrograph, which is presently in a trial phase on the Gran Telescopio Canarias (GTC).

“Detecting lithium gives us crucial information related to Big Bang nucleosynthesis,” said Rafael Rebolo, the director of the IAC and a coauthor of the paper. “We are working on a spectrograph of high-resolution and wide spectral range in order to measure the detailed chemical composition of stars with unique properties such as J0815+4719.”

These future studies are sure to be a boon for astronomers and cosmologists. In addition to being a chance to study stars that formed when the Universe was still in its infancy, they could provide new insight into the early stages of the universe, the formation of the first stars, and the properties of the first supernovae. In other words, they would put us a step closer to know how the Universe as we know it formed and evolved.

Further Reading: IAC, The Astrophysical Journal Letters