Tag Archives: Universe

You can now hold the whole (simulated) universe in the palm of your hand

A team of international researchers led by members at the National Institutes of Natural Sciences in Tokyo wants to put the universe in the palm of your hand.

Image credits IAA-CSIC.

The Universe is a really big place, which can make understanding it a bit difficult. What would definitely help in this regard would be a simulation encompassing it in its entirety — which is exactly what the researchers did. Named Uchuu (“Outer Space” in Japanese), this is the largest and most realistic simulation of the Universe to date, consisting of 2.1 trillion particles spread across a simulated cube whose side is 9.63 billion light-years.

A digital new world

The simulated universe is the product of a collaboration between researchers from Japan, Spain, the U.S.A., Argentina, Australia, Chile, France, and Italy. ATERUI II, the most powerful supercomputer dedicated to astronomy in the world, was used to produce Uchuu, an effort that still took a full year.

“To produce Uchuu we have used […] all 40,200 processors (CPU cores) available exclusively for 48 hours each month. Twenty million supercomputer hours were consumed, and 3 Petabytes of data were generated, the equivalent of 894,784,853 pictures from a 12-megapixel cell phone,” explains Tomoaki Ishiyama, an associate professor at Chiba University who developed the code used to generate Uchuu.

The intended purpose behind Uchuu is to give astronomers a new tool to understand the results of Big Data galaxy surveys. This type of research simply generates immense quantities of data and making heads and tails of it all can become quite difficult.

But Uchuu’s sheer scale can, counterintuitively, help researchers parse this data much more easily. The side of the simulated square, of 9.63 billion light-years, is around three-quarters of the estimated distance between the Earth and the farthest galaxies we can currently observe. This provides the context for researchers to study the evolutionary history of the Universe on a scale that was previously impossible.

Obviously, the software isn’t perfect, nor does it simulate an entire Universe in complete detail. It focuses on the large-scale structures that defined its history and evolution. The team explains that they focused on the large-scale structures formed by dark matter (known as ‘halos’) which control processes such as the formation of galaxies, instead of relatively smaller structures such as stars.

This focus on the large scale comes down to technical constraints. Uchuu aims to simulate almost 13.8 billion years of the history of the Universe, roughly from the Big Bang up to today.

“Uchuu is like a time machine: we can go forward, backward and stop in time, we can ‘zoom in’ on a single galaxy or ‘zoom out’ to visualize a whole cluster, we can see what is really happening at every instant and in every place of the Universe from its earliest days to the present, being an essential tool to study the Cosmos,” explains Julia F. Ereza, a Ph.D. student at the Institute of Astrophysics of Andalusia (Instituto de Astrofísica de Andalucía / IAA-CSIC), who uses Uchuu for their research.

The end of this process is, essentially, a recording of all the computations ATERUI II performed during this time. This shows the evolution of dark matter haloes in a 100-terabyte catalog, one which you can download and browse at your own leisure — if you have the disk space to spare, which most of us here don’t.

But fear not! The catalog is also publically available on the cloud thanks to the IAA-CSIC (link at the bottom of the page). Future releases will include catalogues of virtual galaxies and gravitational lensing maps.

Cecilia Payne would overcome the adversity that faced women in academia at the turn of the century to blaze a trail through physics and become one of the most important figures in astrophysics.

Who is Cecilia Payne-Gaposchkin: The Woman Who Knew The Stars

It’s almost staggering to think that before 1925 humanity knew very little about the composition of the stars. In fact, we would develop the theories of quantum mechanics, special and general relativity before we knew what lay beneath the surface of the Sun.

The first scientist to develop an accurate theory of the composition of the stars was Cecilia Payne-Gaposchkin. Born Cecilia Helena Payne in a small English market town in Buckinghamshire in 1900, in doing so she would also develop the first accurate picture of the abundance of the elements hydrogen and helium throughout the Universe.

But, these remarkable discoveries were not met with the appreciation one would expect. Payne-Gaposchkin would be discouraged from publishing her findings by a male contemporary. The setback would be just one more obstacle for Cecilia to overcome.

Cecilia Payne-Gaposchkin (1900-1979)

Facing the prejudice and misogyny that typified society in general, and science and academia in particular, during the early 20th Century, Payne-Gaposchkin would show a resolve that led to her becoming the world’s foremost expert on variable stars and enable her to lay the groundwork for astrophysics. 

Through sheer grit and determination, she would redefine our understanding of the composition of the stars and the Universe in general. Not bad for a scientist whose lectures weren’t even listed in her University’s course catalogue, who also had her wages by the same institute paid under ‘equipment costs.’

From Botany to Astronomy

The reward of the young scientist is the emotional thrill of being the first person in the history of the world to see something or to understand something. Nothing can compare with that experience.

Cecilia Payne-Gaposchkin

Things could have been very different for Cecilia Payne-Gaposchkin. Her interest in science first manifested as a fascination with the natural world and botany. A hint towards her future as an astronomer and astrophysicist shone through when Cecilia was just ten and she watched, transfixed, as a meteor traversed the night sky.

Payne’s interest in nature was encouraged by her mother, Emma Leonora Helena Payne, after her father Edward passed away when she was just four years old. The death of her father, who drowned in a canal under questionable circumstances, left young Cecilia devastated and her mother to raise the future astronomer and her two siblings alone.

Emma strongly encouraged the education of her three children, of which Cecilia was the eldest, introducing them to literature at an early age. Cecilia’s traits as a scientist would be further bolstered by her experience at her first school ran by Elizabeth Edwards which strongly encouraged the memorization of facts and figures.

Beyond this, Ms Edwards would actively teach her pupils, including the girls, geometry and algebra. Young Cecilia revelled in the solving of quadratic equations.

“My mother had told me of the Riviera-trapdoor spiders and mimosa and orchids, and I was dazzled by a flash of recognition. For the first time, I knew the leaping of the heart, the sudden enlightenment, that were to become my passion.”

At the age of twelve, Cecilia was forced to move schools when her family relocated from Wendover to London. Her new school, St Mary’s College, Paddington, could not have been less like Ms Edward’s. Like her female contemporaries, at the Church of England school with its strong emphasis on religion and ‘traditional values’ Cecilia would be offered little in the way of educational stimulation and even less encouragement to embark on a career in science.

In fact, it was here that a male teacher would confidently tell Payne-Gaposchkin she would never achieve a career in science. A prediction that may well go down in history as one of the worst ever made by an educator.

The Milky Way’s Trifid Nebula home to many Cepheid variable stars. Cecilia Payne-Gaposchkin would overcome adversity to become one of the foremost experts on such stars (ESO/VVV consortium/D. Minniti)

Fortunately, at the age of 17, Payne-Gaposchkin would be asked to transfer to St. Paul’s Girls School in London. Though the move initially troubled her, it is here where her teachers would allow Cecilia to study elements of physics such as mechanics, dynamics, electricity and magnetism, light, and thermodynamics.

At St. Pauls she was encouraged by her teachers to pursue science, enabling her to obtain a scholarship to Newnham College in 1919 where she would study the slightly odd but eclectic mix of botany, chemistry, and astronomy.

Attending the college, part of Cambridge University, Payne-Gaposchkin soon became bored with botany. Her tutors taught the subject stiffly and rigidly, relaying information she already knew, thus providing Cecilia with little stimulation. She recalled, in particular, an incident in which she discovered a group of desmids whilst studying algae under a microscope. Asking her tutor for help in identifying the organisms, he simply responded that it was not within the remit of her studies so she should just ignore it.

Her decision to switch to astronomy as her major was solidified when she attended a lecture given by Cambridge’s renowned astronomer Sir Arthur Eddington.

Eddington had found fame journeying to the island of Príncipe off the west coast of Africa to examine a solar eclipse that would provide verification for Einstein’s theory of general relativity. The lecture was on the same subject and for Payne, it ignited her desire to study nature beyond the surface of our planet.

Cecilia approached Eddington asking for a research project. He set her the problem of integrating the properties of a model star, starting from initial conditions at the centre and working outward. 

“The problem haunted me day and night. I recall a vivid dream that I was at the center of Betelgeuse, and that, as seen from there, the solution was perfectly plain; but it did not seem so in the light of day.”

Betelgeuse would come to occupy Cecila Payne-Gaposchkin’s thoughts thanks to a problem set by Eddington (ESO/DIGITIZED SKY SURVEY 2/DAVIDE DE MARTIN)

Disappointed at not being able to solve the problem she took her calculations to Eddington incomplete. She need not have worried. Eddington revealed to her with a jovial smile that he had not been able to solve the conumdrum either and had spent years trying!

Building the foundations of Astrophysics

Do not undertake a scientific career in quest of fame or money. There are easier and better ways to reach them. Undertake it only if nothing else will satisfy you; for nothing else is probably what you will receive. Your reward will be the widening of the horizon as you climb. And if you achieve that reward you will ask no other.

Cecilia Payne-Gaposchkin

Eddington was just taken with Payne-Gaposchkin as she was with astronomy, seeing great potential in the young woman. Unfortunately, transferring to the class of Ernest Rutherford, Cecilia discovered that not all of Eddington’s colleagues would be as supportive.

Rutherford, who would go onto perform experiments that would reveal the structure of the atom, was extremely cruel to Payne–the only woman in his class–encouraging the other, exclusively male, students to mock and taunt her, something they did with relish.

Payne-Gaposchkin weathered the storm. She had already experienced what it was like to exist in a male-dominated world and had already overcome too much to fold under mere mockery.

And the indignities would nor end there. Despite completing her coursework, women were forbidden to obtain degrees in the United Kingdom in 1923. Thus Payne-Gaposchkin would have no paperwork to verify her academic achievements. Her chances of obtaining a master’s degree or PhD in the UK were slim to none.

It was upon attending a meeting of the Royal Astronomical Society that Cecilia’s options improved markedly. Its new director Harlow Shipley regaled Payne-Gaposchkin with tales of the opportunities that would await her were she to relocate across the Atlantic to the United States.

Cecilia needed little further encouragement. She was awarded the Pickering Fellowship through Harvard College, taking the small financial aid offered by the only scholarship exclusively for women at the time and using it to move to America. Her association with Havard would continue for many years and prove to be extremely fruitful. Indeed, she would come to consider Boston her second home.

Whilst working under the auspices of Shapely at Harvard College Observatory she continued her studies, finalising what would go on to be her doctoral thesis–Stellar Atmospheres.

Cecilia Payne-Gaposchkin and two astronomers who would have a major influence on her early career. Eddington (centre) would inspire her to embark on the study of astronomy and Ruessell (right) would encourage her not to publish her most important discovery in her doctoral thesis.

In the work, Payne-Gaposchkin would be the first person to suggest that hydrogen was the most abundant element in the universe and the primary constituent of stars. At that time scientists had believed that the Sun and other stars had a chemical composition similar to that of the Earth’s crust. American physicist Henry Norris Russell has pioneered the idea that if earth’s temperature was raised to that of the Sun’s it would have a spectral signature the same as our star.

Payne-Gaposchkin’s finding bucked this idea and arose from the fact she had a much better understanding of atomic spectra than her contemporaries. Unfortunately, American Russell strongly disagreed with her conclusion and persuaded her to leave it out of her thesis.

Payne later reflected on her regret with regards to being persuaded not to publish her findings. It was not a mistake that Payne would never be convinced to make again.

“I was to blame for not having pressed my point. I had given in to Authority when I believed I was right. That is another example of How Not To Do Research. I note it here as a warning to the young. If you are sure of your facts, you should defend your position.”

For what it is worth, Russell too would go on to regret his decision to pressure Cecilia. Russell published a 1929 paper that credited Cecilia as Payne’s earlier work and her discoveries.

It must be one of the most heinous injustices in the history of astronomy that Russell is still to this day often wrongly credited with Payne-Gaposchkin’s discovery.

Russian-American astronomer Otto Struve later recognised the genius of Payne-Gaposchkin’s thesis, describing it as “the most brilliant PhD thesis ever written in astronomy.”

To The Stars and Beyond

The reward of the old scientist is the sense of having seen a vague sketch grow into a masterly landscape.

Cecilia Payne-Gaposchkin

In 1934 on a visit to Germany for an astronomy meeting Cecilia met a young  Russian astronomer, Sergei Gaposchkin. The astronomer was an exile from his country of birth due to his political convictions, and Cecilia found his struggles to be an echo of her own. She was determined to help Sergei find a secure and consistent place to practice science.

Indeed, obtaining Sergei a visa as a stateless person, Cecilia found him a research position at Harvard. To the surprise of their colleagues, the two were married in late 1934. Initial doubts that the marriage wouldn’t last were ill-founded.

Cecilia Payne-Gaposchkin and Sergei Gaposchkin would go on to have three children and remained married until her death in 1979. The two would also form a solid partnership in research, authoring several papers and books together. They even started their own farm–though it’s undeniable that Sergei enjoyed the life of a farmer much more than Cecilia did.

The discovery of the abundances of hydrogen and helium in the Universe and the composition of the stars would not be Payne-Gaposchkin’s only substantial contribution to astronomy and the burgeoning field of astrophysics.

The evolution of the light echo around V838 Monocerotis a variable star. Cecilia Payne was one of the prominant experts on this variety of star. (ESO)

Following the completion of her doctorate, Payne-Gaposchkin would begin to study high luminosity stars in order to understand the composition of the Milky Way. The period marked the beginning of Payne-Gaposchkin’s fascination with variable stars–stars which display periodic brightness fluctuations over radically different periods of time– and novae. This specialization led to the book Stars of High Luminosity, published in 1930.

Cecilia and Sergei undertook an audacious investigation of variable stars, during the ’30s and ’40s, they would make nearly 1.3 million observations of variable stars, with Payne-Gaposchkin’s mind for memorizing facts and figures making her almost a walking compendium of such objects. One of their papers published in 1938 would be the ‘go-to’ tome on variable stars for decades.

During the 1960s, Cecilia and Sergei would shift their attention to the small irregular galaxies situated by the Milky Way–the Magellanic Clouds–and the variable stars located within it. They would make another staggering contribution to astronomy during this study, cataloguing over 2 million visual estimates of these star’s magnitudes.

In 1956, Payne-Gaposchkin would finally be awarded the title of professor, making her the first woman in Harvard’s history to receive such an accolade. She would also be made the chair of a department at Harvard, also the first woman to be recognised in this way. Whilst no one could disagree that the accolade was insultingly well overdue, it was a small positive step in the right direction, finally opening the door for female professors across the US.

The Legacy of Cecilia Payne- Gaposchkin

Payne-Gaposchkin’s most dramatic scientific contribution was the discovery that hydrogen is millions of times more abundant than any other element in the universe. Every high school student knows that Newton discovered gravity, that Darwin discovered evolution, even that Einstein discovered relativity. But when it comes to the composition of our universe, the textbooks simply say that the most prevalent element in the universe is hydrogen. And no one ever wonders how we know…”

Jeremy Knowles, dean of the Harvard University’s Faculty of Arts and Sciences (2002)

Despite waiting so long to be named a professor, Payne-Gadoschkin’s life would not be short on accolades. In 1934, the American Astronomical Society recognized her significant contribution to astronomy by awarding her Annie J. Cannon Prize.

In 1936 she would become a member of the American Philosophical Society, and the 1940s and 1950s marked the award of several honorary doctorates, that should not be viewed as merely consolation prizes for the actual doctorate that she had strived for and had been denied her.

Continuing her trailblazing progress for women in the sciences, in 1976 she would become the first woman to receive the Henry Russell Prize from the American Astronomical Society. The astronomer, who would publish over 150 papers and several books during her career, would receive a further honour in 1977 when the astroid 1974 CA–occupying the asteroid belt between Jupiter and Mars–was renamed 2039 Payne-Gaposchkin.

Amongst the thousands of asteroids between Mars and Jupiter lies 2039 Payne-Gaposchkin a testament to the woman who discovered the composition of the stars.
(Emer O Boyle, Meadhbh O’Connor)

After her semi-retirement in 1966, Payne-Gaposchkin would continue to lecture inspiring the next generation of astronomers. Her final academic paper was published in 1977, just months before her death in December of that year.

During the course of her life, Cecilia Payne- Gaposchkin would change our understanding of the Universe in a way that was no less profound than her colleagues in physics did. Without doubt, her name, therefore, should be listed alongside luminaries such as Copernicus, Newton, and Einstein.

Yet, because of her gender, her genius was barely recognised during her lifetime and her name is still sadly omitted from many textbooks and is nowhere near as prominent as the names of her male counterparts or as her achievements demand.

It is abundantly clear, by becoming the first person to known the true composition of the universe, her star shines just as bright if not brighter as any other scientist. And without her, we still may not know why.

This NASA/ESA Hubble Space Telescope image shows the massive galaxy cluster MACSJ 1206. Embedded within the cluster are the distorted images of distant background galaxies, seen as arcs and smeared features. These distortions are caused by the dark matter in the cluster, whose gravity bends and magnifies the light from faraway galaxies, an effect called gravitational lensing. This phenomenon allows astronomers to study remote galaxies that would otherwise be too faint to see. (NASA, ESA, G. Caminha (University of Groningen), M. Meneghetti (Observatory of Astrophysics and Space Science of Bologna), P. Natarajan (Yale University), the CLASH team, and M. Kornmesser (ESA/Hubble))

Could this be the oldest galaxy in the universe?

Back in the day of GN-z11, galaxies were made of stronger stuff and it just doesn’t understand young whipper-snappers like the Milky Way. Such is the life of older galaxies. In this case, the oldest that we know of. So distant, in fact, it defines the very boundary of the observable universe itself.

The oldest known galaxy is a whopping 13.4 billion light years from Earth (Photo: Pixabay)

Professor Nobunari Kashikawa from the Department of Astronomy at the University of Tokyo sought the most distant galaxy one can observe in order to find out how and when it came to be. In his quest, he and his team were able to more accurately find the distance to the aging galaxy.

While it has been known for a while that GN-z11 was the oldest known galaxy, measuring the distance to it turned out to be quite the challenge.

“From previous studies, the galaxy GN-z11 seems to be the farthest detectable galaxy from us, at 13.4 billion light years, or 134 nonillion kilometers (that’s 134 followed by 30 zeros),” said Kashikawa. “But measuring and verifying such a distance is not an easy task.”

In order to measure the distance, Kashikawa measured the redshift, or how much light has shifted toward the red end of the spectrum as galaxies move away from each other with the universal expansion. The farther away the galaxy is, the more redshift. Using the Keck I telescope, the astronomers were able to get a decent fix on GN-z11.

“We looked at ultraviolet light specifically, as that is the area of the electromagnetic spectrum we expected to find the redshifted chemical signatures,” said Kashikawa. “The Hubble Space Telescope detected the signature multiple times in the spectrum of GN-z11. However, even the Hubble cannot resolve ultraviolet emission lines to the degree we needed. So we turned to a more up-to-date ground-based spectrograph, an instrument to measure emission lines, called MOSFIRE.”

When working with distances at these enormous scales, it just isn’t sensible to use our familiar units of kilometers and miles, or even multiples of them. Instead, astronomers use a value known as the redshift number denoted by z.

Using MOSFIRE (Multi-Object Spectrometer For Infra-Red Exploration), the team captured the emission lines from GN-z11 in detail, which allowed them to make a much better estimation on its distance than was possible from previous data, confirming the galaxy’s ‘farthest’ status.

The study was published in the journal Nature Astronomy on December 14.

Physicists perform the most detailed simulation of the Universe yet

Images showing various disk galaxies from the simulated TNG50 universe. Credit: D. Nelson, TNG team.

How did the universe evolve from a point of singularity, known as the Big Bang, into a massive structure whose boundaries seem limitless? New clues and insight into the evolution of the universe have recently been provided by an international team of physicists, who performed the most detailed large-scale simulation of the universe to date.

Formation and evolution of a massive galaxy in the TNG50 simulation. The resulting TNG50 galaxy is similar in mass and shape to the Andromeda galaxy (M31). After a turbulent beginning, the galaxy experiences no major disturbances and can settle down into an equilibrium state. Credit: D. Nelson, TNG team.

The researchers made their own universe in a box — a cube of space spanning more than 230 million light-years across. Previous cosmological simulations were either very detailed but spanned a small volume or less detailed across large volumes. The new simulation, known as TNG50, managed to combine the best of two worlds, producing a large-scale replica of the cosmos while, at the same time, allowing for unprecedented computational resolution.

The level of detail is incredible, matching what was once only possible to do in simulations of individual galaxies. TNG50, in fact, tracks 20 billion particles representing dark matter, stars, cosmic gas, magnetic fields, and supermassive black holes.

However, this kind of fine detail came at a cost. It took more than 16,000 cores on the Hazel Hen supercomputer in Stuttgart operating in tandem, non-stop for a year to perform the required calculations. For reference, it would have taken 15,000 years to complete the simulation on a single processor, making TNG50 one of the most computationally demanding astrophysical simulations to date.

In two recently published studies led by Annalisa Pillepich and Dylan Nelson, from the Max Planck Institute for Astronomy and Max Planck Institute for Astrophysics, respectively, the researchers shared their most important findings.

“Numerical experiments of this kind are particularly successful when you get out more than you put in. In our simulation, we see phenomena that had not been programmed explicitly into the simulation code. These phenomena emerge in a natural fashion, from the complex interplay of the basic physical ingredients of our model universe,” Nelson said in a statement.

One example of such emerging behavior if the formation of “disk” galaxies, like the Milky Way. While disk galaxies seem very ordered and flat, by rewinding their evolution, researchers could see that such structures emerge from chaotic and disorganized turbulent clouds of gas.

“In practice, TNG50 shows that our own Milky Way galaxy with its thin disk is at the height of galaxy fashion: over the past 10 billion years, at least those galaxies that are still forming new stars have become more and more disk-like, and their chaotic internal motions have decreased considerably. The Universe was much more messy when it was just a few billion years old!” Pillepich said in a statement.

The outflow of as gas from a galaxy. Left to right: false-color representations of the velocity, temperature, density, and heavy element content of the galaxy. The galaxy itself is the tiny blue drop in the second frame from the left or the yellow firmament in the third column. Credit: D. Nelson, TNG team.

Another emerging phenomenon captured by the simulation was represented by high-speed outflows and winds of gas emanating from galaxies. These outflows and winds are the result of supernovae and supermassive black hole activity.

These galactic outflows were initially chaotic — just like early galactic structures — but, over time, they became more focused on the paths of least resistance. In the modern universe, these winds slow down as they make their way away from the gravitational well of the dark matter halo, and can eventually stall and fall back onto their parent galaxies. The astronomers liken the process to a galactic fountain of recycled gas.

By this process, gas is redistributed from the center of the galaxy to its outskirts. In time, this contributes to the transformation of the galaxy into a thin disk. But this can also work both ways: galactic structures also shape galactic fountains.

In the future, the astronomers will release all the simulation’s data to the scientific community at large so that new discoveries might come out of the TNG50 universe.

The two studies will be published in the December 2019 issue of the Monthly Notices of the Royal Astronomical Society

Illustration of planetary nebula NGC 7027 and helium hydride molecules. Credit: NASA.

Astronomers finally find the earliest molecule in the Universe

Illustration of planetary nebula NGC 7027 and helium hydride molecules. Credit: NASA.

Illustration of planetary nebula NGC 7027 and helium hydride molecules. Credit: NASA.

About 100,000 years after the Big Bang, a blink of an eye on the universe’s timescale, the primordial atoms helium and hydrogen combined to form the first molecule, helium hydride. Physicists believe that this molecule’s formation helped the young universe cool down, allowing stars to form. Helium hydride should still be present in some parts of the modern universe but it has never been detected in space — until now.

“The lack of evidence of the very existence of helium hydride in interstellar space was a dilemma for astronomy for decades,” said Rolf Guesten of the Max Planck Institute for Radio Astronomy, in Bonn, Germany, and lead author of the study published in the journal Nature this week.

The discovery was made by NASA’s Stratospheric Observatory for Infrared Astronomy, or SOFIA, the world’s largest airborne observatory. Flying up to 13,700 meters (45,000 feet), SOFIA makes observations above the interfering layers of Earth’s atmosphere, taking off and landing for each observation. Inside a modified Boeing 747SP jetliner, scientists fitted state-of-the-art instruments such as the German Receiver at Terahertz Frequencies (GREAT) instrument that can be tuned to the frequency of helium hydride, similar to tuning an FM radio to the right station, and search for it in space.

NASA researchers pointed SOFIA’s instruments onto a planetary nebula located 3,000 light-years away called NGC 7027. Since the 1970s, scientists had suspected that this is one of the best places to look for helium hydride but until now they were lacking the proper tools.

“This molecule was lurking out there, but we needed the right instruments making observations in the right position — and SOFIA was able to do that perfectly,” said Harold Yorke, director of the SOFIA Science Center, in California’s Silicon Valley.

Finding evidence of the primordial molecule validates our current models of how the universe came to existence. According to the theory, after the universe started to cool down, hydrogen atoms interacted with helium hydride, leading to the creation of molecular hydrogen — the substance primarily responsible for the formation of the first stars. Once the first stars appear, they could forge heavier elements that would eventually disperse into the universe forming asteroids, planetoids, and planets.

“It was so exciting to be there, seeing helium hydride for the first time in the data,” said Guesten. “This brings a long search to a happy ending and eliminates doubts about our understanding of the underlying chemistry of the early universe.

Scientists measure all the starlight ever produced in the Universe

Astrophysicists have measured all the photons ever emitted by the trillions and trillions of stars forged during the Universe’s 13.7-billion-long history. Unpeeling the history of star formation is a major breakthrough with ramifications in other areas of research, such as galactic evolution or the search for dark matter. Ultimately, work like this brings scientists closer to understanding the most fundamental processes, all the way back to the Big Bang.

A map of the night’s sky showing the location of 739 blazars used in the study to measure starlight in the universe. Credit: NASA/DOE/Fermi LAT Collaboration.

Scientists estimate that there are about two trillion galaxies, which hold a trillion-trillion stars. In order to measure how much starlight has been emitted, Marco Ajello and colleagues at the Clemson College of Science turned to data from NASA’s Fermi Gamma-ray Space Telescope. Launched in 2008, the Fermi Telescope has so far provided invaluable information pertaining to gamma rays (the most energetic form of electromagnetic radiation) and their interaction with the extragalactic background light (EBL) — a ‘cosmic fog’ composed of all the ultraviolet, visible and infrared light emitted by stars or from dust in their vicinity.

The results suggest that the total number of photons that have been emitted into space by stars is about 4×1084 — that’s 4 followed by 84 zeroes. It’s a staggering number beyond our comprehension, but one that will help scientists greatly to understand how stars and galaxies evolve.

“From data collected by the Fermi telescope, we were able to measure the entire amount of starlight ever emitted. This has never been done before,” said Ajello, who is lead author of the paper. “Most of this light is emitted by stars that live in galaxies. And so, this has allowed us to better understand the stellar-evolution process and gain captivating insights into how the universe produced its luminous content.”

Despite the huge number of photons out there, the Universe is largely dim due to its sheer vastness. According to the researchers, starlight other than that coming from our own and Milky Way is as dim as a 60-watt light bulb viewed from 2.5 miles away.

The study hinged on observations of energetic particles emitted by blazars, which are galaxies with supermassive black holes that are capable of releasing collimated jets of electromagnetic radiation. When such jets happen to be directly pointed at Earth, our instruments are able to detect their source even from billions of light-years away. Gamma rays produced by the jets interact with the cosmic fog, producing an imprint that astrophysicists can use to measure the fog’s density. What’s more, this density can be measured for various times in the history of the universe.

“Gamma-ray photons traveling through a fog of starlight have a large probability of being absorbed,” said Ajello, an assistant professor in the department of physics and astronomy. “By measuring how many photons have been absorbed, we were able to measure how thick the fog was and also measure, as a function of time, how much light there was in the entire range of wavelengths.”

Clemson University astrophysicist Marco Ajello. Credit: Pete Martin / Clemson University.

Clemson University astrophysicist Marco Ajello. Credit: Pete Martin / Clemson University.

By directly measuring the density of this cosmic fog, the authors of the new study were able to eliminate the need to estimate light emissions by far-away galaxies. In total, 739 blazars were included in the study.

“By using blazars at different distances from us, we measured the total starlight at different time periods,” said postdoctoral fellow Vaidehi Paliya. “We measured the total starlight of each epoch—one billion years ago, two billion years ago, six billion years ago, etc. – all the way back to when stars were first formed. This allowed us to reconstruct the EBL and determine the star-formation history of the universe in a more effective manner than had been achieved before.”

“Scientists have tried to measure the EBL for a long time. However, very bright foregrounds like the zodiacal light (which is light scattered by dust in the solar system) rendered this measurement very challenging,” said co-author Abhishek Desai, a graduate research assistant in the department of physics and astronomy. “Our technique is insensitive to any foreground and thus overcame these difficulties all at once.”

According to the study’s results, star formation peaked around 11 billion years ago — but it is still going strong. The Milky Way adds seven new stars every year, for instance.

Understanding star formation is important for astronomy research. For instance, this analysis will enable research in the future to target the earliest days of stellar evolution, using the upcoming James Webb Space Telescope, which should come online in 2021. And because the measurement is very sensitive to the expansion of the Universe, Ajello believes that their data can be used to measure the Hubble Constant more precisely.

“The first billion years of our universe’s history are a very interesting epoch that has not yet been probed by current satellites,” Ajello said in a statement. “Our measurement allows us to peek inside it. Perhaps one day we will find a way to look all the way back to the Big Bang. This is our ultimate goal.”

The findings were reported in the journal Science.

The universe’s rate of expansion is in dispute – and we may need new physics to solve it


File 20180730 106514 bm50kc.jpg?ixlib=rb 1.1
Colorful view of the universe as seen by Hubble in 2014.
NASA, ESA, H. Teplitz and M. Rafelski (IPAC/Caltech), A. Koekemoer (STScI), R. Windhorst (Arizona State University), and Z. Levay (STScI)


Next time you eat a blueberry (or chocolate chip) muffin consider what happened to the blueberries in the batter as it was baked. The blueberries started off all squished together, but as the muffin expanded they started to move away from each other. If you could sit on one blueberry you would see all the others moving away from you, but the same would be true for any blueberry you chose. In this sense galaxies are a lot like blueberries.

Since the Big Bang, the universe has been expanding. The strange fact is that there is no single place from which the universe is expanding, but rather all galaxies are (on average) moving away from all the others. From our perspective in the Milky Way galaxy, it seems as though most galaxies are moving away from us – as if we are the centre of our muffin-like universe. But it would look exactly the same from any other galaxy – everything is moving away from everything else.

To make matters even more confusing, new observations suggest that the rate of this expansion in the universe may be different depending on how far away you look back in time. This new data, published in the Astrophysical Journal, indicates that it may time to revise our understanding of the cosmos.

Hubble’s challenge

Cosmologists characterise the universe’s expansion in a simple law known as Hubble’s Law (named after Edwin Hubble – although in fact many other people preempted Hubble’s discovery). Hubble’s Law is the observation that more distant galaxies are moving away at a faster rate. This means that galaxies that are close by are moving away relatively slowly by comparison.

The relationship between the speed and the distance of a galaxy is set by “Hubble’s Constant”, which is about 44 miles (70km) per second per Mega Parsec (a unit of length in astronomy). What this means is that a galaxy gains about 50,000 miles per hour for every million light years it is away from us. In the time it takes you to read this sentence a galaxy at one million light years’ distance moves away by about an extra 100 miles.

The Hubble Space Telescope as seen from the departing Space Shuttle Atlantis, flying STS-125, HST Servicing Mission 4.

This expansion of the universe, with nearby galaxies moving away more slowly than distant galaxies, is what one expects for a uniformly expanding cosmos with dark energy (an invisible force that causes the universe’s expansion to accelerate ) and dark matter (an unknown and invisible form of matter that is five times more common than normal matter). This is what one would also observe of blueberries in an expanding muffin.

The history of the measurement of Hubble’s Constant has been fraught with difficulty and unexpected revelations. In 1929, Hubble himself thought the value must be about 342,000 miles per hour per million light years – about ten times larger than what we measure now. Precision measurements of Hubble’s Constant over the years is actually what led to the inadvertent discovery of dark energy. The quest to find out more about this mysterious type of energy, which makes up 70% of the energy of the universe, has inspired the launch of the world’s (currently) best space telescope, named after Hubble.

Cosmic showstopper

Now it seems that this difficulty may be continuing as a result of two highly precise measurements that don’t agree with each other. Just as cosmological measurements have became so precise that the value of the Hubble constant was expected to be known once and for all, it has been found instead that things don’t make sense. Instead of one we now have two showstopping results.

On the one side we have the new very precise measurements of the Cosmic Microwave Background – the afterglow of the Big Bang – from the Planck mission, that has measured the Hubble Constant to be about 46,200 miles per hour per million light years (or using cosmologists’ units 67.4 km/s/Mpc).

On the other side we have new measurements of pulsating stars in local galaxies, also extremely precise, that has measured the Hubble Constant to be 50,400 miles per hour per million light years (or using cosmologists units 73.4 km/s/Mpc). These are closer to us in time.

Both these measurements claim their result is correct and very precise. The measurements’ uncertainties are only about 300 miles per hour per million light years, so it really seems like there is a significant difference in movement. Cosmologists refer to this disagreement as “tension” between the two measurements – they are both statistically pulling results in different directions, and something has to snap.

New physics?

So what’s going to snap? At the moment the jury is out. It could be that our cosmological model is wrong. What is being seen is that the universe is expanding faster nearby than we would expect based on more distant measurements. The Cosmic Microwave Background measurements don’t measure the local expansion directly, but rather infer this via a model – our cosmological model. This has been tremendously successful at predicting and describing many observational data in the universe.

So while this model could be wrong, nobody has come up with a simple convincing model that can explain this and, at the same time, explain everything else we observe. For example we could try and explain this with a new theory of gravity, but then other observations don’t fit. Or we could try and explain it with a new theory of dark matter or dark energy, but then further observations don’t fit – and so on. So if the tension is due to new physics, it must be complex and unknown.

A less exciting explanation could be that there are “unknown unknowns” in the data caused by systematic effects, and that a more careful analysis may one day reveal a subtle effect that has been overlooked. Or it could just be statistical fluke, that will go away when more data is gathered.

It is presently unclear what combination of new physics, systematic effects or new data will resolve this tension, but something has to give. The expanding muffin picture of the universe may not work anymore, and cosmologists are in a race to win a “great cosmic bake-off” to explain this result. If new physics is required to explain these new measurements, then the result will be a showstopping change of our picture of the cosmos.

Thomas Kitching, Reader in Astrophysics, UCL

This article was originally published on The Conversation. Read the original article.


We’ve just found the earliest traces of hydrogen, showing when the first-ever stars ignited

MIT and Arizona State University researchers are hot on the heels of the Universe’s first stars: they’ve traced the faint signals of hydrogen gas energized by stellar radiation just 180 million years after the Big Bang.


Image via Pixabay.

Where does everything come from? That’s one of the questions people have been burning to answer since times immemorial. It’s a hugely complicated question, but science can offer some bits and pieces to start cobbling the answer together. A paper published today by MIT and Arizona State University researchers uncovered a fundamental one such piece: the earliest evidence of hydrogen gas and the earliest evidence of stars igniting that we’ve ever seen.

The gas from whence we came

Using a table-sized radio antenna plopped down in a remote part of western Australia, dubbed EDGES (Experiment to Detect Global EoR Signature), the team managed to pick up trace signals generated by hydrogen gas, just 180 million years after the Big Bang. This is the earliest evidence we’ve ever seen for the presence of hydrogen in the early universe — a very important find, considering hydrogen is the simplest, and thus first, atom out there. The team was also able to determine that by this time, the gas bore traces of the first stars in the world.

“This is the first real signal that stars are starting to form, and starting to affect the medium around them,” says study co-author Alan Rogers, a scientist at MIT’s Haystack Observatory.

“What’s happening in this period is that some of the radiation from the very first stars is starting to allow hydrogen to be seen. It’s causing hydrogen to start absorbing the background radiation, so you start seeing it in silhouette, at particular radio frequencies.”

The EDGES instrument was designed to pick up radio signals generated during a time in the universe’s history known as the Epoch of Reionization, or EoR. It’s during this time that we think the first sources of light (such as stars) sprang up in the world, from a sort of cosmic primordial soup made up mostly of hydrogen gas. Not much else was happening before this time, mostly due to a lack of energy to change objects in the universe: hydrogen, for example, was virtually invisible, as its energy state made it indistinguishable from the surrounding cosmic background radiation.


The dark Horsehead Nebula in the constellation Orion. Hydrogen corresponds to red.
Image credits Ken Crawford.

But the birth of these sources of light and energy ionized the hydrogen gas, changing its energy state, and making it release energy as radio waves — and that’s exactly what EDGES was designed to pick up.

However, not all went according to plan. When the team looked at the frequency range the antenna was designed to pick up, between 100 to 200 megahertz, they hardly picked up any signal.


One explanation they came up with is that the theoretical models which we used to calculate what emissions this early hydrogen would give off overestimated the gas’ temperature. So they re-crunched the numbers, this time assuming that the hydrogen and its environment were at about the same, lower temperature. They decided their best bet was to search the 50 to 100 megahertz frequency range, so they returned their antenna and flipped the switch again.

“As soon as we switched our system to this lower range, we started seeing things that we felt might be a real signature,” Rogers says.

The device picked up a flattened absorption profile (i.e. a dip in the radio wave-spectrum) centered around 78 megahertz. Rogers adds that the frequency corresponds to “roughly 180 million years after the Big Bang”, adding that “this has got to be the earliest” detection of a signal from hydrogen we yet have. To put things into perspective, we know that the universe is at least 11 billion years old, and most estimates place its age upwards of 13.5 billion years.

The radio profile matches theoretical predictions of a star-hydrogen interaction. These early stellar bodies poured ultraviolet radiation out into the void, ionizing any surrounding body of hydrogen. As a result, the gas began to absorb background radiation, which changed the spin on its single electron. Ultimately, this change made the atoms emit, rather than absorb, radiation, at a characteristic wavelength of 21 centimeters, or a frequency of 1,420 megahertz — becoming, in effect, ‘visible’ for the first time.

Red-shift affected these waves, so by the time it reached present-day Earth, it was somewhere in the range of 100 megahertz.

But the dip in the radio spectrum was also stronger and deeper than the models predicted — suggesting that the hydrogen was indeed colder than previously assumed. The team estimates that the hydrogen gas and the universe as a whole must have been twice as cold as previously estimated, at about 3 kelvins, or -270.15 degrees Celsius / -454 degrees Fahrenheit.

The edges of discovery

Haystack EDGES.

Image credits MIT / Haystack Observatory.

The research is likely the best window we’ll have into the universe’s early history for a long time to come. It took an incredible scientific effort to obtain these results. It took years of hard work for engineers and scientists to design, re-design, and re-calibrate the EDGES instrument to even have a hope of picking up on these signals. Peter Kurczynski, program director for Advanced Technologies and Instrumentation in the Division of Astronomical Sciences at the National Science Foundation, the organization that built EDGES, compares it to “being in the middle of a hurricane and trying to hear the flap of a hummingbird’s wing.”

“Sources of noise can be a thousand times brighter than the signal they are looking for,” he explains.

It was built in the middle of Australia’s nowhere (which has to be at least nowhere squared) because it was the most remote place they could get to — and that limited interference from man-made radio signals, which would easily overpower any of the signals the antenna was designed to pick up on.

“It is unlikely that we’ll be able to see any earlier into the history of stars in our lifetimes,” lead author Judd Bowman of ASU says. “This project shows that a promising new technique can work and has paved the way for decades of new astrophysical discoveries.”

It’s also the first actual glimpse we get into this period of the universe, a particularly important one — these were, after all, the universe’s early days. The foundation of everything we see today was laid down during that Epoch.

The paper, “An absorption profile centred at 78 megahertz in the sky-averaged spectrum” has been published in the journal Nature.

Plasma lamp.

Scientists just found half of the universe’s missing matter, and strengthened the Standard Model in the process

The missing matter in our universe has been found — and it’s exactly where we thought it would be.


Image via Pixabay.

Chances are you’re familiar with dark matter, that ‘stuff’ which can exert gravity but doesn’t yet seem to do much else. It makes up around 27% of all the universe. We also have dark energy, which makes up about 68% of everything, and then there’s the normal, regular matter you or me are made of. This latter variety only makes up 5% of the known universe, which may come as a surprise, since it literally makes up our whole world.

We’re still trying to understand dark matter and dark energy, but in the meantime, scientists have put another scientific mystery to rest: accounting for all ‘normal’ matter.

Where my matter at?

Simply put, scientists couldn’t account for half of all matter that has to be out there, that 5% that we can actually see and interact with. Our working theory was that this matter could be found as very diffuse strands of plasma spread between galaxies. Given the huge spans of space involved here, even a very wispy gas could add up to a huge amount, as much as that contained by all visible galaxies combined.

Problem is, if that matter keeps floating around in such a thin and insubstantial form, how do we actually detect it?

Two groups of astronomers have developed a method that allows them to do just that. A research team at the Institute of Space Astrophysics (IAS) in Orsay, France, and one from the University of Edinburgh, used data from the Planck satellite to see the effect this matter has on the cosmic background radiation, CBR.

To do so they relied on a physical phenomenon known as the Sunyaev-Zel’dovich effect. The boiled down version is that when CBR passes through hot plasma (which is ionized gas) this latter one brightens just enough for us to capture it. Using data from the Sloan Digital Sky Survey, each team chose pairs of galaxies believed to be connected by baryon strands (baryons are elemental particles of ‘normal’ matter). To make the individual strands more visible, they then stacked the Planck signals for these areas. The French team worked with about 260,000 pairs of galaxies, while their Scottish counterparts worked with over a million pairs.

Plasma lamp.

Image via Wikipedia.

Both reached a similar result. The IAS team calculated that the baryon gasses are three times denser than the baseline mass of matter in the universe, while the Edinburgh team calculated them to be six times denser than the baseline. While the numbers differ a bit (we’re talking super small values here, so the differences between the team are minute), both were dense enough for filaments to form. Overall, the extra matter in this filaments is enough to account for the missing half of normal matter in the universe.

It also shows that the physical models we use to explain the world around us are sound. The theory of matter filaments is decades old, but scientists have simply lacked the technological means to test it up to now. Finding the filaments, and a way to detect them in the future could even help us navigate in inter-galactic space — if we ever get so far.

The two papers “A Search for Warm/Hot Gas Filaments Between Pairs of SDSS Luminous Red Galaxies” (IAS) and “Missing baryons in the cosmic web revealed by the Sunyaev-Zel’dovich effect” (Edinburgh) have both been published in the preprint server ArXiv.

What shape is the Universe, really?

The Universe is flat, according to modern research. But what does that mean?

Geometry, Topology, and the Big Bang

The detailed, all-sky picture of the infant universe created from nine years of WMAP data. The image reveals 13.77 billion year old temperature fluctuations (shown as color differences) that correspond to the seeds that grew to become the galaxies. Image credits: NASA / WMAP

Thinking about the shape of the Universe is in itself a bit absurd. When you consider the shape of anything, you view it from outside – yet how could you view the universe from outside? When discussing this, astronomers generally approach two concepts:

  1. The local geometry. This concerns the geometry of the observable universe, along with its curvature.
  2. The global geometry. This concerns the topology, everything that is, as opposed to everything we can observe.

If we can observe the entire universe and we’re not limited somehow by its geometry or another characteristic, then the two coincide. But there’s a good chance that the two don’t coincide, and our observations are limited somehow by an intrinsic characteristic of the universe – we can’t really know, at least not now.

Most people would expect the universe in its entirety to be symmetrically round – a sphere-like shape, sort of like the Earth. Speaking of the Earth, let’s consider it for a while. We know the Earth is not flat, but what does that mean? Geometrically, it means that parallel lines on its surface aren’t really parallel. All lines, even if they do start parallel, would end up uniting at one of the Poles, and the distance between them will not be constant. As below:

Three possible shapes of the Universe: closed, open and flat from top to bottom. Image credits: NASA.

So a flat Universe would mean that drawn parallel lines remain parallel – and herein lies the key. Broadly speaking and simplifying things, scientists noted that the light from several galaxies remains parallel to each other, across large distances of the universe. The Baryon Oscillation Spectroscopic Survey (BOSS) telescope gave some very strong evidence that the observable universe is indeed flat, and the implications are puzzling.

“One of the reasons we care is that a flat universe has implications for whether the universe is infinite,” said David Schlegel, a member of the Physics Division of the U.S. Department of Energy’s Lawrence Berkeley National Laboratory. “That means – while we can’t say with certainty that it will never come to an end – it’s likely the universe extends forever in space and will go on forever in time. Our results are consistent with an infinite universe.”

Here’s an excellent video which details why the Universe is probably flat:

Finite vs Infinite

Another debate about the universe which involves its shape is infinity. The universe is really big, we know that, but is it really infinite?

Since ancient times, humans have asked themselves that. In the 18th century, German astronomer Heinrich Wilhelm Olbers came up with a paradox: if the Universe is infinite, then the sky wouldn’t be dark. Why? Because in any direction you’d look, there would be infinite space and eventually, you’d encounter a star which would send its light. The night sky doesn’t completely light up so voila, the universe isn’t infinite. Unfortunately, it’s not as simple as that. There could be a number of explanations for Olber’s paradox, and none are simple. The universe is expanding rapidly, so distant stars are red-shifted into obscurity. Or light from other stars simply hasn’t reached us yet – again, we can’t really know. What we do know is that objects more than about 13.7 billion years old (the latest figure) are too far away for their light ever to reach us. So we pretty much know the age of the Universe, but what about its size?

You could say “Why don’t we just look in all directions and see how big it is?” but alas, once more – it’s not so simple.

Universe in an expanding sphere. The galaxies farthest away are moving fastest and hence experience length contraction and so become smaller to an observer in the centre. Image credits: Drschawrz

The diameter of the observable Universe is 91 billion light-years. The distance the light from the edge of the observable universe has traveled is very close to the age of the Universe times the speed of light, 13.8 billion light-years, 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. Because we cannot observe space beyond the edge of the observable universe, we can’t know directly whether the Universe is inifinite or not. Modern measurements, including those from the Cosmic Background Explorer (COBE), Wilkinson Microwave Anisotropy Probe (WMAP), and Planck maps of the CMB, suggest that the Universe is infinite in extent, but it’s still an ongoing debate.

But what about the Big Bang?

A representation of the evolution of the universe over 13.77 billion years. The far left depicts the earliest moment we can now probe, when a period of “inflation” produced a burst of exponential growth in the universe. Image credits: NASA / WMAP

Most people have some kind of basic idea about what happened during the Big Bang, and this is where the most misconceptions lie. Because that’s when space came into existence, most people imagine it expanding in all directions equally – but that’s likely not how things went down. Before the Big Bang, there was no space or time. So, there is nothing “outside” the Big Bang in which the universe to expand to. The Universe simply expanded from a very small volume into a huge volume, and this expansion is occurring even today – but there’s no guarantee that the expansion took place symmetrically, in all directions.

So let’s get back to the local and global geometry. What our scientific observations are detecting is the local geometry, the observable universe (we can only observe the “observable” – hence the name). Our observations, as thorough and well thought as they may be, can’t be exhaustive.

The overall shape of the Universe

So, in the end, we’re left with a potentially flat, potentially infinite universe, but what is its global shape? Unfortunately, we don’t really know. Even if lines are parallel and the observable universe is flat, it doesn’t mean that the whole universe is flat. It could be a Möbius strip for all we know—a shape where space bends and distorts, but lines stay parallel, ultimately connecting one end of space to another.

At the end of the day, there are three distinct possibilities, all with their own distinct implications:

  • Universe with zero curvature. A flat universe. Not necessarily infinite, and not necessarily looking like a sheet of paper. It could also have a shape like a torus.
  • Universe with positive curvature.  A sphere-like shape.
  • Universe with negative curvature. You can think of it locally as a three-dimensional analog of an infinitely extended saddle shape.

We don’t know which one is true. What we do know is that the observable universe is flat – and that in itself is a remarkable finding.

Universe has 2 trillion galaxies, 20 times more than we thought, new study claims

We may have dramatically underestimated what lies in the Universe.

Image via NASA/HUBBLE.

Try for a moment to ponder this: there are two trillion galaxies in the universe. The Milky Way alone has over 100 million stars. Can you even wrap your head around that? The sheer number of stars in the Universe is mind-bending, as is the possibility for life. We’ve just started scratching the surface.

“It boggles the mind that over 90% of the galaxies in the universe have yet to be studied,” commented Christopher Conselice of the University of Nottingham, who led this study. he said in a statement.

ESA’s Gaia observatory sends back first star chart showing a billion new stars

The team working with the Gaia space telescope has just released the first batch of the data they’ve recorded — and it’s huge. The craft has seen over a billion stars and measured the distance to and sideways motion of two million of them.

Gaia’s first star map.

Gaia is ESA’s space observatory launched in December 2013 — the best craft of its kind humanity has ever constructed. Its mapping efforts are still several years to completion but the data it beamed back is on a scale far greater than anything we’ve had access to before. On Wednesday, ESA released a huge set of data comprising 1.1 billion light sources. Out of these, roughly 400 million are objects never before recorded.

“You’re imaging the whole sky in basically [Hubble] space telescope quality and because you can now resolve all the stars that previously maybe looked as though they were merged as one star at low resolution – now we can see them,” explained Anthony Brown from Leiden University, Netherlands.

“Gaia is going to be a revolution,”  said Gerry Gilmore from Cambridge University, UK, was one of the mission’s proposers. “It’s as if we as astronomers have been bluffing up until now. We’re now going to see the truth.”

The treasure trove of data is so huge that scientists say they won’t to be able to analyze all of it — so they’re appealing to the public to join in and discover the great unknown.  A web page has been created where anyone can play with Gaia data and look for novel phenomena.

Gaia’s goal was to improve on the work of Hipparcos, the first high-precision astrometry satellite, launched in 1989. At the time Hipparcos’ catalogue of the Milky Way became the go-to chart of this corner of the Universe, detailing the precise position, brightness, distance to and proper motion of 100,000 stars. Gaia increased that number twenty-fold — and this is only the first part of the data.

Astrometry is the art of calculating the position and movement of celestial bodies hundreds, thousands, even millions of light years away starting from distances we can measure — the distance between two points on Earth’s orbit, for example. As our planet orbits the Sun, relatively nearby stars seem to move against the seemingly fixed stars farther away. So, we can use the parallax angle to calculate the distance to these target stars.

Because the ratio between the distances we know and those we’re calculating is so huge these angles are tiny — under one arcsecond (1/60 of a degree) for the nearest stars. Parallax measurements are used as references to correct more indirect techniques of measuring these huge distances, so Gaia is programmed to take repeated measurements for each star to reduce errors to under seven micro-arcseconds — an error the size of a one euro coin on a Moon-Earth distance.

The craft carries two sets of optical telescopes, which project their light on a one-billion-pixel camera detector connected to a trio of instruments. This technological fortitude allows Gaia to pick out stars more accurately than anything we’re ever constructed before. It uses all this information to measure details such as the temperature and composition of the stars, which can be used to determine their age.

Getting an accurate reading over such distances is tricky, so repeated viewings of each point are required.

All in all, the mission is expected to take five years to complete but once over it’s estimated Hipparcos’ 100,000-strong catalogue will expand to over one billion objects. But after seeing the data it became apparent that Gaia is picking up many more faint light sources that we’ve anticipated, so that number could climb as high as two to three billion objects.

Not all of these will be actual stars. Quasars, planets, distant galaxies — they’re all here. In particular, by looking at how the stars Gaia picked up “wobble” through the sky, astronomers can predict the existence of worlds orbiting them.

“Gaia is going to be extremely useful for exoplanets, and especially systems that have the Jupiter kind of planets,” said Esa’s Gaia project scientist, Timo Prusti.

“The numbers are going to be impressive; we expect 20,000. The thing is, you need patience because the exoplanets are something where you have to collect five years of data to see the deviation in the movements.”

Another goal of the Gaia mission is to measure the radial velocity of stars — the movement they make towards or away from the craft as they move around the galaxy. Compare this with the stars’ proper motion, and it will give us a glimpse into the dynamics of the Milky Way.

Image credits ESA.

Before the mission’s launch, scientists had hoped to get radial velocity data on about 150 million stars. Soon after the satellite’s launch, however, scientists realized that there was a lot of stray light reaching the camera, which impaired its observation of the faintest stars and their colors. Engineers think this is caused in part by the way sunlight bends past the 10m-diameter shade that Gaia uses to keep its telescopes shaded. They say that the more time the mission runs, the closer Gaia will get to its target.

“Clearly, with the stray light we lost sensitivity. On the other hand, it happens to be that there are more stars than were thought before. So we’re still talking about 100 million radial velocities,” Timo Prusti told BBC News.

The Universe expands equally in all directions — and this is bad news for Einstein’s equations

Researchers analyzed the background radiation left over from the Big Bang to put an end to a long standing debate: Is our Universe expanding the same in all directions, or does this vary depending on where you look?

The microwave sky as seen by Planck.

Finding out if our Universe is a homogeneous body or not is a really important topic in physics. A lot of really heavy-duty math hinges on us knowing this bit of information — mathematical systems such as Einstein’s field equations (EFE,) a set of 10 equations in his theory of relativity that explain the behavior of gravitation as space-time gets distorted by energy or matter.

A team from the University College London analyzed the cosmic microwave background (CMB,) the left-over radiation from the Big Bang, to find out just that. They found that there isn’t any preferential direction of expansion and the Universe just pushes out evenly all over. This goes along nicely with our current cosmological models — but throws a wrench into the mathematical systems behind EFE.

Homogeneous space

There’s basically two ways our Universe can behave. Either it is homogeneous and isotropic, meaning that its properties are the same no matter which directions you measure them in, or anisotropic, when these properties vary with the direction you measure them in.

Let’s start from a small scale example. On an molecular level, graphite is made up of layers of carbon atoms one on top of the other — kind of like a sandwich. If you apply an electrical current parallel to these layers — along the slices of bread — it’s a really good conductor, because there’s nothing to stop electrons from flowing freely. But if you run the current perpendicular to the layers — through the slices — it’s roughly 20 times more resistant. So its resistivity to electrical current is dependent on which direction you measure it — this is anisotropy.

Certain observations lend weight to the theory that the Universe might be anisotropic — matter, for instance, isn’t evenly distributed throughout it. Star systems, galaxies, and galaxy clusters are clumps of matter seemingly randomly thrown about the Universe, and some researchers have suggested that this caused by some kind of force or directional flow has pushing them into position.

“This, they assume, arises because the Universe was born as a homogeneous soup of subatomic particles in the Big Bang,” explains Adrian Cho for Science magazine. “As the Universe underwent an exponential growth spurt called inflation, tiny quantum fluctuations in that soup expanded to gargantuan sizes, providing density variations that would seed the galaxies.”

Our cosmological models are build from the assumption that these variations only matter on the very small scale (when you’re talking about a whole Universe, “tiny” means clusters of galaxies) but even out as you look at the big picture. But in the early 2000s, NASA’s Wilkinson Microwave Anisotropy Probe (WMAP) mapped ‘bumps’ in the CMB that the homogeneity/isotropy theory couldn’t explain. There’s one region in our Universe so baffling scientists have actually called it the Axis of Evil, which also flies in the face of homogeneity. But an anisotropic Universe could quite comfortably explain both.

Microwaveable answers

To settle the debate once and for all, the University College London team tuned in on the CMB, residual radiation left over from the birth of the Universe. They modeled what an anisotropic Universe would look like, then compared real recordings to their model. As team member Daniela Saadeh told Universe Today:

“We analysed the temperature and polarisation of the cosmic microwave background (CMB), a relic radiation from the Big Bang, using data from the Planck mission. We compared the real CMB against our predictions for what it would look like in an anisotropic universe. After this search, we concluded that there is no evidence for these patterns and that the assumption that the Universe is isotropic on large scales is a good one.”

CMB patterns measured by the Planck mission — top.
CMB patterns modeled for an anisotropic Universe — bottom.
They don’t really fit.
Image credits (top) ESA and the Planck Collaboration, (bottom) D. Saadeh et. al.

They calculated that there’s a 1-in-121,000 chance that the Universe has a preferred direction of expansion, which are pretty good odds in favor of the isotropy theory,

“For the first time, we really exclude anisotropy,” Saadeh told Cho at Science. “Before, it was only that it hadn’t been probed.”

So our cosmological models are safe for now. But as Universe Today points out, EFE can only really be solved in an anisotropic Universe. Solutions to these equations were proposed by Italian mathematician Luigi Bianchi in the late 19th century and allow for an anisotropic Universe. However, if that assumption is proved wrong, the solutions are left up in the air.

On the other hand, proving that the Universe is isotropic means we don’t have to re-think everything we know about cosmology, which is pretty convenient.

“In the last 10 years there has been considerable discussion around whether there were signs of large-scale anisotropy lurking in the CMB,” Saadeh said.

“If the Universe were anisotropic, we would need to revise many of our calculations about its history and content. Planck high-quality data came with a golden opportunity to perform this health check on the standard model of cosmology and the good news is that it is safe.”

The results have been accepted for publication in an upcoming edition of Physical Review Letters under the title “How isotropic is the Universe?”. Until then, you can access the pre-print version at arXiv.org.:

First stars formed much later than we thought

The European Space Agency’s Planck satellite has revealed some information which may force us to rethink the evolution of the early Universe.

Visualization of the CMB. Image via NASA.

Our telescopes and other observation tools allow us to see a lot of the Universe today, but we’re so used to it in its current state that it can be hard to imagine how it looked like 13.8 billion years ago. Everything was still in its infancy, without the multitude of stars and galaxies we see today. Back then, everything was a thick, hot haze, a primordial soup of particles – mostly electrons, protons, neutrons and photons.

As the cosmos expanded, it started to cool down a bit and became more rarefied. Astrophysicists believe that the universe became transparent some 380,000 years after its birth, meaning that photons could finally travel through the universe freely. Today, we can still observe some of this ‘fossil light,’ and its distribution yields information about the history, composition, and geometry of the Universe.

This distribution is called the Cosmic Microwave Background, or CMB for short. The release of the CMB indicates the first moment in the Universe when matter was in an electrically neutral state – in other words, when electrons merged with protons to form atoms. After that, matter as we know it started to emerge, but it still took a few hundred million years for the first stars to form. These in turn started to brake down matter into electrons and protons once again, while also sending light (photons) in all directions. It didn’t take long and most — virtually all, except for a few isolated places — matter became ionized.

“The CMB can tell us when the epoch of reionisation started and, in turn, when the first stars formed in the Universe,” explains Jan Tauber, Planck project scientist at ESA.

Astronomers have conducted observations on galaxies with supermassive black holes, finding that the reionization took place when the Universe was 900 million years old. But when this process started (and therefore, when the first stars were formed) is much harder to pinpoint.

The key is still in the CMB.

Cosmic reionisation.
Credit: ESA – C. Carreau

“It is in the tiny fluctuations of the CMB polarisation that we can see the influence of the reionisation process and deduce when it began,” adds Tauber.

The new analysis conducted by Tauber and his team isn’t conceptually different from previous efforts, but it uses a more advanced technology from Planck’s other detector, the High-Frequency Instrument (HFI).

“The highly sensitive measurements from HFI have clearly demonstrated that reionisation was a very quick process, starting fairly late in cosmic history and having half-reionised the Universe by the time it was about 700 million years old,” says Jean-Loup Puget from Institut d’Astrophysique Spatiale in Orsay, France, principal investigator of Planck’s HFI.

This new analysis also showed that these stars were the only sources needed to account for reionizing atoms in the cosmos and that half of this process was completed when the Universe had reached an age of 700 million years.

“These results are now helping us to model the beginning of the reionisation phase,” he concluded.

It’s still a work in progress and the exact ionization age will remain a matter of debate, but the fact that we can infer so much about the early history of the Universe is simply mind blowing.

Journal References:

  1. Matthieu Tristram and Collaboration. Planck intermediate results. XLVII. Planck constraints on reionization history. Astronomy & Astrophysics, 2016; DOI: 10.1051/0004-6361/201628897
  2. Planck Collaboration. Planck intermediate results. XLVI. Reduction of large-scale systematic effects in HFI polarization maps and estimation of the reionization optical depth. Astronomy & Astrophysics, 2016; DOI: 10.1051/0004-6361/201628890

The Universe is expanding faster than we thought, new Hubble study finds

Astronomers working with the Hubble telescope have discovered that the Universe is expanding 5-9% faster than expected, and this is intriguing.

This illustration shows the three steps astronomers used to measure the universe’s expansion rate to an unprecedented accuracy, reducing the total uncertainty to 2.4 percent. Astronomers made the measurements by streamlining and strengthening the construction of the cosmic distance ladder, which is used to measure accurate distances to galaxies near and far from Earth. Credit: NASA, ESA, A. Feild (STScI), and A. Riess (STScI/JHU)

Even though it’s a well documented phenomenon, universal expansion is still baffling. The entire universe, every single thing that we know of is moving apart – and it’s accelerating! That’s just crazy when you think about it. The fact that we can measure how fast it’s expanding is even crazier.

In theory, you could measure the expansion of the universe could by taking a standard ruler and measuring the distance between two cosmologically distant points, waiting a certain time, and then measuring the distance again, but in practice, you’re never going to have a cosmological ruler, and time isn’t really on your side either. So astronomers are using other indirect methods, which of course come with an associated error. Such an error was corrected this time, and it came as quite a surprise.

“This surprising finding may be an important clue to understanding those mysterious parts of the universe that make up 95 percent of everything and don’t emit light, such as dark energy, dark matter, and dark radiation,” said study leader and Nobel Laureate Adam Riess of the Space Telescope Science Institute and The Johns Hopkins University, both in Baltimore, Maryland.

He an his team refined the measurement and managed to reduce the uncertainty to only 2.4 percent. They measured about 2,400 Cepheid stars (stars that pulsate radially) in 19 galaxies and compared the observed brightness of the stars. Cepheid stars pulsate at rates that correspond to their true brightness, which can be compared with their apparent brightness as seen from Earth to accurately determine their distance.

The new constant value they found 73.2 kilometers per second per megaparsec. (A megaparsec equals 3.26 million light-years.) This means that the distance between cosmic objects will double in another 9.8 billion years. We still don’t know what is the cause for the initial error, but one of the likely culprits is dark energy, already known to be accelerating the universe. Another possible explanation is an unexpected characteristic of dark matter. Dark matter is the backbone of the universe upon which galaxies built themselves up into the large-scale structures seen today.

“If we know the initial amounts of stuff in the universe, such as dark energy and dark matter, and we have the physics correct, then you can go from a measurement at the time shortly after the big bang and use that understanding to predict how fast the universe should be expanding today,” said Riess. “However, if this discrepancy holds up, it appears we may not have the right understanding, and it changes how big the Hubble constant should be today.”


The Universe expands much faster than we thought, and current models can’t explain why

Scientists have completed the most precise measurement of the Universe’s rate of expansion to date,  but the result just isn’t compatible with speed calculations from residual Big Bang radiation. Should the former results be confirmed by independent techniques, we might very well have to rewrite the laws of cosmology.

Data from galaxies such as M101, seen here, allow scientists to gauge the speed at which the universe is expanding.
Image credits X-ray: NASA/CXC/SAO; Optical: Detlef Hartmann; Infrared: NASA/JPL-Caltech

“I think that there is something in the standard cosmological model that we don’t understand,” says astrophysicist Adam Riess, a physicist at Johns Hopkins University in Baltimore, Maryland, who co-discovered dark energy in 1998 and led the latest study.

This discrepancy might even mean that dark energy — thought to be responsible for observed acceleration in the expansion of the Universe — has steadily been gaining in strength since the dawn of time. Should the results be confirmed, they have the potential of “becoming transformational in cosmology” said Kevork Abazajian, cosmologist at the University of California, Irvine.

In our current cosmological model, the Universe is the product of a tug of war of sorts between dark matter and dark energy. Dark matter uses its gravitational pull to slow down expansion, while dark energy is pushing everything apart, making it accelerate. Riess and others suggest that dark energy’s strength has been constant throughout the history of the Universe.

Most of what we know about dark matter-dark energy interaction and how each of them affects the Universe comes from studying remanent Big Bang radiation, known as the cosmic microwave background. The most exhaustive study on this subject was done by the European Space Agency’s Planck observatory. Those measurements essentially give researchers a picture of the Universe when it was really young — 400.000 years of age. Based on them, they can determine how the Universe evolved up to now, including the rate of expansion at any point in its history. Knowing where it was and where it is now, they can also predict those two parameters in the future.

But here’s the thing: they don’t add up to the observed rate of expansion. These predictions are invalidated by direct measurements of the current rate of cosmic expansion — also known as the Hubble constant. This constant is calculated by observing how rapidly nearby galaxies move away from the Milky Way using stars of known intrinsic brightness called ‘standard candles’. Until now the errors were small enough that the disagreement could be ignored, but Riess and his team warn that the discrepancy is too great to ignore any longer.

Riess’s team studied two types of standard candles in 18 galaxies using hundreds of hours of observing time on the Hubble Space Telescope.

“We’ve been going gangbusters with this,” says Riess.

They managed to measure constant with an uncertainty of 2.4%, down from a previous best result of 3.3%. Based on this value, they found that the actual rate of expansion is about 8% faster than what the Planck data predicts, Riess reports.

If both the new Hubble constant and the earlier Planck team measurements are accurate, then there’s a problem with our current model. Either we misunderstood dark energy, or we got it right but it just got stronger as time progressed. Planck researcher François Bouchet of the Institute of Astrophysics in Paris says he doubts that the problem is in his team’s measurement, but that the new findings are “exciting” regardless of what the solution turns out to be.

However, when working on such (forgive the pun) astronomical scales, a lot of things can go wrong. One last possibility is that standard candles aren’t that reliable when it comes to precision measurements, says Wendy Freedman, astronomer at the University of Chicago in Illinois. In 2001 she led the first precision measurement of the Hubble constant. She and her team are working on an alternative method based on a different class of stars. We’ll just have to wait and see.

The full paper, titled “A 2.4% Determination of the Local Value of the Hubble Constant” has been published on the arXiv online repository on and can be read here.

The entire Universe in one Logarithmic Map

Don’t you just love it when art and science get together? Here, artist Pablo Carlos Budassi managed what seems impossible: representing the entire Universe in one picture.

Using lots and lots of telescope, satellite images and photos snapped from NASA’s rovers, he painstakingly stitched many of the prominent features in the known Universe. He started from our solar system and then moved on in logarithmic progression. Logarithms are useful for understanding large numbers or distances, and here each consecutive map ring represents several orders of magnitude.

A similar, though much less artistically appealing map was created by astronomers atPrinceton back in 2005.

dark age universe

The oldest galaxy we’ve come across might re-write the way we think the early cosmos evolved

NASA’s Hubble Space Telescope and the Spitzer Space Telescope jointly used their instruments to identify the oldest galaxy yet seen. Dubbed EGS8p7, this unusually luminous galaxy was formed just 600 million years after the Big Bang. When you peer that far into space and time, you’re bound to find some freaky stuff. EGS8p7 did no disappoint. Already, the 13.2 billion-year-old galaxy is raising questions about how we think the Universe evolved during its infancy.

dark age universe

Here lies Galaxy EGS8p7. Top right: as seen by Hubble; bottom right: Spitzer’s view in infrared. Image: NASA

Shortly after the Big Bang, everything was a mess – a really hot mess of charged protons and electrons. These particles chaotically dispersed throughout the early universe in such a way that photons could not travel freely, hence there was no light. This lasted for some 400,000 years post-Big Bang until the the universe cooled to the level that protons and electrons combined to form neutral hydrogen. This enabled the first light in the cosmos, that from the Big Bang, to finally shine. However, there was no other sources of light since stars hadn’t formed yet – this was the dark ages. Then, roughly 500 million years later the universe entered the age of reionization when the first galaxies lit up.

Here’s where  EGS8p7 falls into all of this, though. When hydrogen gas is heated by ultraviolet rays, it produces a telltale spectral emission called Lyman-alpha line. Typically, when you see this spectral signature it’s a sign of star formation inside a newborn galaxy. Such was the case of EGS8p7, but at the same time the timeline of the galaxy is off with the current theory, particularly the age of reionization. Theoretically, we shouldn’t be able to register a Lyman-alpha line in such an ancient galaxy. Something does not compute.

“The surprising aspect about the present discovery is that we have detected this Lyman-alpha line in an apparently faint galaxy at a redshift of 8.68, corresponding to a time when the universe should be full of absorbing hydrogen clouds,” Richard Ellis of the California Institute of Technology and co-author of the paper.

universe evolution

“The galaxy we have observed, EGS8p7, which is unusually luminous, may be powered by a population of unusually hot stars, and it may have special properties that enabled it to create a large bubble of ionized hydrogen much earlier than is possible for more typical galaxies at these times,” added Sirio Belli, a Caltech graduate student part of the project.

Adi Zitrin, another co-author, says that the physics behind the theory of the early universe evolution isn’t essentially wrong. The discovery of EGS8p7 just adds another dimension. It means things are a bit more complex than previously thought and, most likely, reionization may not have happened in a unified matter. This particular ancient galaxy may have formed in a blind spot allowing it to shine despite its surroundings.

Pushing the limit: scientists discover oldest known stars

Astronomers have discovered the oldest known stars lurking in a super-luminous galaxy – they may very well be among the very first objects that formed in the history of the Universe.

Artist’s impression of the first stars, 400 million years after the Big Bang. Image via Wikipedia.

These stars — known as Population III stars — were created with primordial material from the Big Bang from hydrogen and helium, with only traces of lithium. Until recently, Population III stars were only discussed theoretically, but in recent years, astronomers have uncovered several, confirming their existence. What’s interesting about these ones is not only that they are extremely old, but that they are found in a very luminous part of the universe, whereas the theory claimed that they should be in faint, blue galaxies. This may provide even more valuable clues regarding their birth – as well as the birth of the Universe.

“We may be witnessing, for the first time, direct evidence for the occurrence of waves of PopIII-like star formation which could happen from an original star cluster outwards (resulting from strong feedback which can delay PopIII star formation),” the researchers reported.

Astronomers found an ancient galaxy that harbors the earliest stars that were formed out of helium, hydrogen and lithium. CR7 is 13.7 billion year-old and the most luminous galaxy to be found to date.
(Photo : ESO/M. Kornmesser)

The discovery was made by researchers from Portugal, who didn’t hesitate to give a nod to their favorite football player, Cristiano Ronaldo (often nicknamed CR7).

“The discovery challenged our expectations from the start, as we didn’t expect to find such a bright galaxy,” Dr. David Sobral, an astrophysicist at the University of Lisbon in Portugal and leader of the team of astronomers who made the discovery, said in a written statement. “Then, by unveiling the nature of CR7 piece by piece, we understood that not only had we found by far the most luminous distant galaxy, but also started to realize that it had every single characteristic expected of Population III stars.”

The finding also seems to confirm that the much newer Population I and Population II stars were built on the corpses of much older stars, which had a very reduced lifespan of a few million years, compared to current stars, which generally live for billions of years.

Scientists were also very eager to uncover Pop III stars, because they basically consisted only of hydrogen and helium, and they created all the other elements we see around us today.

“I have always wondered where we came from,” Jorryt Matthee, a Ph.D. student at Leyden University in the Netherlands and one of the astronomers involved in the discovery, said in the statement. “Even as a child I wanted to know where the elements come from: the calcium in my bones, the carbon in my muscles, the iron in my blood…With this discovery, remarkably, we are starting to actually see such objects for the first time.”

Journal References.


Astronomers discover farthest galaxy yet

A team of astronomers from Yale and the University of California-Santa Cruz have looked back in time, discovering a galaxy that was formed when the Universe was only 5% of its current age. This is now the farthest, and youngest galaxy known to date.

The galaxy EGS-zs8-1 sets a new distance record. It was discovered in images from the Hubble Space Telescope’s CANDELS survey.
Credit: NASA, ESA, P. Oesch and I. Momcheva (Yale University), and the 3D-HST and HUDF09/XDF teams

When we look at something through a telescope, we don’t see it as it is now, we see it as it was when light coming from it started its journey towards us. It takes light from the Sun 8 minutes to reach us, so when we view the Sun from Earth, we see it as it was 8 minutes ago. But it took light from that galaxy billions of years to reach us, so astronomers are effectively taking a glimpse in the past.

The galaxy, named EGS-zs8-1 is one of the brightest ones we know, and it emerged just 670 million years after the Big Bang. The light from it took 13 billion years to reach us, but because the Universe is continuously expanding, it’s estimated that the galaxy is now over 30 billion light years away from us.

“It has already built more than 15% of the mass of our own Milky Way today,” said Pascal Oesch, a Yale astronomer and lead author of a study published online May 5 in Astrophysical Journal Letters. “But it had only 670 million years to do so. The universe was still very young then.” The new distance measurement also enabled the astronomers to determine that EGS-zs8-1 is still forming stars rapidly, about 80 times faster than our galaxy.

This finding is even more remarkable as only a handful galaxies from the early stages of the Universe were accurately measured in terms of distance to the Milky Way.

“Every confirmation adds another piece to the puzzle of how the first generations of galaxies formed in the early universe,” said Pieter van Dokkum, the Sol Goldman Family Professor of Astronomy and chair of Yale’s Department of Astronomy, who is second author of the study. “Only the largest telescopes are powerful enough to reach to these large distances.”

The moment at which this galaxy was captured in time was a very significant one for our Universe – it was a time when the hydrogen between galaxies was transitioning from a neutral state to an ionized state.

“It appears that the young stars in the early galaxies like EGS-zs8-1 were the main drivers for this transition, called reionization,” said Rychard Bouwens of the Leiden Observatory, co-author of the study.

The discoveries excited astronomers who believe that they will make many more similar discoveries in the future.

“Our current observations indicate that it will be very easy to measure accurate distances to these distant galaxies in the future with the James Webb Space Telescope,” said co-author Garth Illingworth of the University of California-Santa Cruz. “The result of JWST’s upcoming measurements will provide a much more complete picture of the formation of galaxies at the cosmic dawn.”

Journal Reference: P. A. Oesch, P. G. van Dokkum, G. D. Illingworth, R. J. Bouwens, I. Momcheva, B. Holden, G. W. Roberts-Borsani, R. Smit, M. Franx, I. Labbé, V. González, D. Magee. A SPECTROSCOPIC REDSHIFT MEASUREMENT FOR A LUMINOUS LYMAN BREAK GALAXY ATz= 7.730 USING KECK/MOSFIRE. The Astrophysical Journal, 2015; 804 (2): L30 DOI: 10.1088/2041-8205/804/2/L30