World’s Largest Digital Sky Survey Issues Biggest Astronomical Data Release Ever

The Space Telescope Science Institute (STScI) in Baltimore, Maryland, in conjunction with the University of Hawai’i Institute for Astronomy (IfA), is releasing the second edition of data from Pan-STARRS—the Panoramic Survey Telescope & Rapid Response System—the world’s largest digital sky survey. This second release contains over 1.6 petabytes of data (a petabyte is 1015 bytes or one million gigabytes), making it the largest volume of astronomical information ever released. The amount of imaging data is equivalent to two billion selfies, or 30,000 times the total text content of Wikipedia. The catalog data is 15 times the volume of the Library of Congress.

The Pan-STARRS observatory consists of a 1.8-meter telescope equipped with a 1.4-billion-pixel digital camera, located at the summit of Haleakalā, on Maui. Conceived and developed by the IfA, it embarked on a digital survey of the sky in visible and near-infrared light in May 2010. Pan-STARRS was the first survey to observe the entire sky visible from Hawai’i multiple times in many colors of light. One of the survey’s goals was to identify moving, transient, and variable objects, including asteroids that could potentially threaten the Earth. The survey took approximately four years to complete, scanning the sky 12 times in five filters. This second data release provides, for the first time, access to all of the individual exposures at each epoch of time. This will allow astronomers and public users of the archive to search the full survey for high-energy explosive events in the cosmos, discover moving objects in our own solar system, and explore the time domain of the universe.

Dr. Heather Flewelling, a researcher at the Institute for Astronomy in Hawai’i, and a key designer of the PS1 database, stated that “Pan-STARRS DR2 represents a vast quantity of astronomical data, with many great discoveries already unveiled. These discoveries just barely scratch the surface of what is possible, however, and the astronomy community will now be able to dig deep, mine the data, and find the astronomical treasures within that we have not even begun to imagine.”

“We put the universe in a box and everyone can take a peek,” said database engineer Conrad Holmberg.

The four years of data comprise 3 billion separate sources, including stars, galaxies, and various other objects. This research program was undertaken by the PS1 Science Consortium—a collaboration among 10 research institutions in four countries, with support from NASA and the National Science Foundation (NSF). Consortium observations for the sky survey were completed in April 2014. The initial Pan-STARRS public data release occurred in December 2016, but included only the combined data and not the individual exposures at each epoch of time.

“The Pan-STARRS1 Survey allows anyone access to millions of images and catalogs containing precision measurements of billions of stars, galaxies, and moving objects,” said Dr. Ken Chambers, Director of the Pan-STARRS Observatories. “While searching for Near Earth Objects, Pan-STARRS has made many discoveries from ‘Oumuamua passing through our solar system to lonely planets between the stars; it has mapped the dust in three dimensions in our galaxy and found new streams of stars; and it has found new kinds of exploding stars and distant quasars in the early universe. We hope people will discover all kinds of things we missed in this incredibly large and rich dataset.”

The Space Telescope Science Institute hosts the storage hardware, the computers that handle the database queries, and the user-friendly interfaces to access the data. The survey data resides in the Mikulski Archive for Space Telescopes (MAST), which serves as NASA’s repository for all of its optical and ultraviolet-light observations, some of which date to the early 1970s. It includes all of the observational data from such space astrophysics missions as Hubble, Kepler, GALEX, and a wide variety of other telescopes, as well as several all-sky surveys. Pan-STARRS marks the nineteenth mission to be archived in MAST.

Ancient Crystals Offer Evidence Of The Start of Earth’s Core Solidifying

A quartet of researchers from the University of Rochester and the University of California has found evidence of the starting period for the solidification of Earth’s core. In their paper published in the journal Nature Geoscience, Richard Bono, John Tarduno, Francis Nimmo and Rory Cottrell describe their analysis of ancient crystals found in eastern Canada, what they found, and why they believe their results offer clues about the formation of Earth’s inner core. Peter Driscoll, with the Carnegie Institution for Science, has written a News and Views piece on the study in the same journal issue.

Planetary scientists have found strong evidence that suggests the Earth has an inner and an outer core. The inner core is believed to be solid, while the outer core is made up of molten material. Prior evidence has also indicated that the entire core was once liquid, but as the interior cooled, the innermost part began to crystallize. It is at this point that scientists disagree—some suggest the start of solidification began as far back as 2.5 billion years ago. Others believe it was much more recent—perhaps as recent as just 500 million years ago. In this new effort, the researchers have found evidence that supports the latter theory.

The work by the researchers involved carefully analyzing plagioclase and clinopyroxene crystals, which have been dated to approximately 565 million years ago. The crystals are important because they contain bits of metal called inclusions. The inclusions are very small and needle-shaped and aligned themselves with the Earth’s magnetic field as they became embedded in the crystal. Since the Earth’s magnetic field is generated by activity in the inner core, the inclusions are a means of determining the state of the core during the time when the crystals formed. The researchers report that their analysis showed that the magnetic field was significantly weaker than it is today, suggesting that solidification of the core must have occurred soon thereafter or the magnetic field would have collapsed altogether. The reason it did not, theory suggests, is because as the inner core solidified, he magnetic field became stronger.

Extratropical Volcanoes Influence Climate More Than Assumed

The eruption of Mount Pinatubo in 1991 had a significant impact on climate, decreasing global mean temperature by about 0.5°C. Like the famous eruptions of Krakatau (1883) and Tambora (1815), Pinatubo is located in the tropics, which has been considered an important factor underlying its strong climate forcing. However, an international research group led by the GEOMAR has now published a study in the journal Nature Geoscience that shows that explosive extratropical eruptions can have a strong impact on the climate, too.

In recent decades, extratropical eruptions including Kasatochi (Alaska, U.S., 2008) and Sarychev Peak (Russia, 2009) have injected sulfur into the lower stratosphere. The climatic forcing of these eruptions has, however, been weak and short-lived. So far, scientists have largely assumed this to be a reflection of a general rule—that extratropical eruptions lead to weaker forcing than their tropical counterparts. Researchers from the GEOMAR Helmholtz Centre for Ocean Research Kiel, the University of Oslo, the Max Planck Institute for Meteorology in Hamburg together with colleagues from Switzerland, the U.K. and the U.S. now contradict this assumption in the international journal Nature Geoscience.

“Our investigations show that many extratropical volcanic eruptions in the past 1,250 years have caused pronounced surface cooling over the Northern Hemisphere, and in fact, extratropical eruptions are actually more efficient than tropical eruptions in terms of the amount of hemispheric cooling in relation to the amount of sulfur emitted by the eruptions,” says Dr. Matthew Toohey from GEOMAR, first author of the current study.

Large-scale cooling after volcanic eruptions occurs when volcanoes inject large quantities of sulfur gases into the stratosphere, a layer of the atmosphere that starts at about 10 to 15 kilometers height. There, the sulfur gases produce a sulfuric aerosol haze that persists for months or years. The aerosols reflect a portion of incoming solar radiation, which can no longer reach the lower layers of the atmosphere and the Earth’s surface.

Until now, the assumption was that aerosols from volcanic eruptions in the tropics have a longer stratospheric lifetime because they have to migrate to mid or high latitudes before they can be removed. As a result, they would have a greater effect on the climate. Aerosols from eruptions at higher latitudes would be removed from the atmosphere more quickly.

The recent extratropical eruptions, which had minimal but measurable effects on the climate, fit this picture. However, these eruptions were much weaker than that of Pinatubo. To quantify the climate impact of extratropical vs. tropical eruptions, Dr. Toohey and his team compared new, long-term reconstructions of volcanic stratospheric sulfur injection from ice cores with three reconstructions of Northern Hemisphere summer temperature from tree rings dating back to 750 CE. Surprisingly, the authors found that extratropical explosive eruptions produced much stronger hemispheric cooling in proportion to their estimated sulfur release than tropical eruptions.

To understand these results, Dr. Toohey and his team performed simulations of volcanic eruptions in the mid to high latitudes with sulfur amounts and injection heights equal to that of Pinatubo. They found that the lifetime of the aerosol from these extratropical explosive eruptions was only marginally smaller than for tropical eruptions. Furthermore, the aerosol was mostly contained within the hemisphere of eruption rather than globally, which enhanced the climate impact within the hemisphere of eruption.

The study goes on to show the importance of injection height within the stratosphere on the climate impact of extratropical eruptions. “Injections into the lowermost extratropical stratosphere lead to short-lived aerosol, while those with stratospheric heights similar to Pinatubo and the other large tropical eruptions can lead to aerosol lifetimes roughly similar to the tropical eruptions,” says co-author Prof. Dr. Kirstin Krüger from the University of Oslo.

The results of this study will help researchers to better quantify the degree to which volcanic eruptions have impacted past climate variability. It also suggests that future climate will be affected by explosive extratropical eruptions. “There have been relatively few large explosive eruptions recorded in the extratropics compared to the tropics in recent centuries, but they definitely do happen,” says Dr. Toohey. The strongest Northern Hemisphere cooling episode of the past 2500 years was initiated by an extratropical eruption in 536 CE. This new study explains how the 536 CE eruption could have produced such strong cooling.

Active Galaxies Point To New Physics Of Cosmic Expansion

Investigating the history of our cosmos with a large sample of distant ‘active’ galaxies observed by ESA’s XMM-Newton, a team of astronomers found there might be more to the early expansion of the universe than predicted by the standard model of cosmology.

According to the leading scenario, our universe contains only a few percent of ordinary matter. One quarter of the cosmos is made of the elusive dark matter, which we can feel gravitationally but not observe, and the rest consists of the even more mysterious dark energy that is driving the current acceleration of the universe’s expansion.

This model is based on a multitude of data collected over the last couple of decades, from the cosmic microwave background, or CMB – the first light in the history of the cosmos, released only 380,000 years after the big bang and observed in unprecedented detail by ESA’s Planck mission – to more ‘local’ observations. The latter include supernova explosions, galaxy clusters and the gravitational distortion imprinted by dark matter on distant galaxies, and can be used to trace cosmic expansion in recent epochs of cosmic history – across the past nine billion years.

A new study, led by Guido Risaliti of Università di Firenze, Italy, and Elisabeta Lusso of Durham University, UK, points to another type of cosmic tracer – quasars – that would fill part of the gap between these observations, measuring the expansion of the universe up to 12 billion years ago.

Quasars are the cores of galaxies where an active supermassive black hole is pulling in matter from its surroundings at very intense rates, shining brightly across the electromagnetic spectrum. As material falls onto the black hole, it forms a swirling disc that radiates in visible and ultraviolet light; this light, in turn, heats up nearby electrons, generating X-rays.

Three years ago, Guido and Elisabeta realised that a well-known relation between the ultraviolet and X-ray brightness of quasars could be used to estimate the distance to these sources – something that is notoriously tricky in astronomy – and, ultimately, to probe the expansion history of the universe.

Astronomical sources whose properties allow us to gauge their distances are referred to as ‘standard candles’.

The most notable class, known as ‘type-Ia’ supernova, consists of the spectacular demise of white dwarf stars after they have over-filled on material from a companion star, generating explosions of predictable brightness that allows astronomers to pinpoint the distance. Observations of these supernovas in the late 1990s revealed the universe’s accelerated expansion over the last few billion years.

“Using quasars as standard candles has great potential, since we can observe them out to much greater distances from us than type-Ia supernovas, and so use them to probe much earlier epochs in the history of the cosmos,” explains Elisabeta.
With a sizeable sample of quasars at hand, the astronomers have now put their method into practice, and the results are intriguing.

Digging into the XMM-Newton archive, they collected X-ray data for over 7000 quasars, combining them with ultraviolet observations from the ground-based Sloan Digital Sky Survey. They also used a new set of data, specially obtained with XMM-Newton in 2017 to look at very distant quasars, observing them as they were when the universe was only about two billion years old. Finally, they complemented the data with a small number of even more distant quasars and with some relatively nearby ones, observed with NASA’s Chandra and Swift X-ray observatories, respectively.

“Such a large sample enabled us to scrutinise the relation between X-ray and ultraviolet emission of quasars in painstaking detail, which greatly refined our technique to estimate their distance,” says Guido.

The new XMM-Newton observations of distant quasars are so good that the team even identified two different groups: 70 percent of the sources shine brightly in low-energy X-rays, while the remaining 30 percent emit lower amounts of X-rays that are characterised by higher energies. For the further analysis, they only kept the earlier group of sources, in which the relation between X-ray and ultraviolet emission appears clearer.

“It is quite remarkable that we can discern such level of detail in sources so distant from us that their light has been travelling for more than ten billion years before reaching us,” says Norbert Schartel, XMM-Newton project scientist at ESA.

After skimming through the data and bringing the sample down to about 1600 quasars, the astronomers were left with the very best observations, leading to robust estimates of the distance to these sources that they could use to investigate the universe’s expansion.

“When we combine the quasar sample, which spans almost 12 billion years of cosmic history, with the more local sample of type-Ia supernovas, covering only the past eight billion years or so, we find similar results in the overlapping epochs,” says Elisabeta.

“However, in the earlier phases that we can only probe with quasars, we find a discrepancy between the observed evolution of the universe and what we would predict based on the standard cosmological model.”
Looking into this previously poorly explored period of cosmic history with the help of quasars, the astronomers have revealed a possible tension in the standard model of cosmology, which might require the addition of extra parameters to reconcile the data with theory.

“One of the possible solutions would be to invoke an evolving dark energy, with a density that increases as time goes by,” says Guido.

Incidentally, this particular model would also alleviate another tension that has kept cosmologists busy lately, concerning the Hubble constant – the current rate of cosmic expansion. This discrepancy was found between estimates of the Hubble constant in the local universe, based on supernova data – and, independently, on galaxy clusters – and those based on Planck’s observations of the cosmic microwave background in the early universe.

“This model is quite interesting because it might solve two puzzles at once, but the jury is definitely not out yet and we’ll have to look at many more models in great detail before we can solve this cosmic conundrum,” adds Guido.

The team is looking forward to observing even more quasars in the future to further refine their results. Additional clues will also come from ESA’s Euclid mission, scheduled for a 2022 launch to explore the past ten billion years of cosmic expansion and investigate the nature of dark energy.

“These are interesting times to investigate the history of our universe, and it’s exciting that XMM-Newton can contribute by looking at a cosmic epoch that had remained largely unexplored so far,” concludes Norbert.

Missing-Link In Planet Evolution Found

For the first time ever, astronomers have detected a 1.3 km radius body at the edge of the solar system. Kilometer-sized bodies like the one discovered have been predicted to exist for more than 70 years. These objects acted as an important step in the planet formation process between small initial amalgamations of dust and ice and the planets we see today.

The Edgeworth-Kuiper Belt is a collection of small celestial bodies located beyond Neptune’s orbit. The most famous Edgeworth-Kuiper Belt Object is Pluto. Edgeworth-Kuiper Belt Objects are believed to be remnants left over from the formation of the solar system. While small bodies like asteroids in the inner solar system have been altered by solar radiation, collisions, and the gravity of the planets over time; objects in the cold, dark, lonely Edgeworth-Kuiper Belt preserve the pristine conditions of the early solar system. Thus astronomers study them to learn about the beginning of the planet formation process.

Edgeworth-Kuiper Belt objects with radii from 1 kilometer to several kilometers have been predicted to exist, but they are too distant, small, and dim for even world-leading telescopes, like the Subaru Telescope, to observe directly. So a research team led by Ko Arimatsu at the National Astronomical Observatory of Japan used a technique known as occultation: monitoring a large number of stars and watching for the shadow of an object passing in front of one of them. The Organized Autotelescopes for Serendipitous Event Survey (OASES) team placed two small 28 cm telescopes on the roof of the Miyako open-air school on Miyako Island, Miyakojima-shi, Okinawa Prefecture, Japan, and monitored approximately 2000 stars for a total of 60 hours.

Analyzing the data, the team found an event consistent with a star appearing to dim as it is occulted by a 1.3 km radius Edgeworth-Kuiper Belt Object. This detection indicates that kilometer sized Edgeworth-Kuiper Belt Objects are more numerous than previously thought. This supports models where planetesimals first grow slowly into kilometer sized objects before runaway growth causes them to merge into planets.

Arimatsu explains, “This is a real victory for little projects. Our team had less than 0.3 percent of the budget of large international projects. We didn’t even have enough money to build a second dome to protect our second telescope! Yet we still managed to make a discovery that is impossible for the big projects. Now that we know our system works, we will investigate the Edgeworth-Kuiper Belt in more detail. We also have our sights set on the still undiscovered Oort Cloud out beyond that.”

The study is published in Nature Astronomy.

Seeing Double Could Help Resolve Dispute About How Fast The Universe Is Expanding

The question of how quickly the universe is expanding has been bugging astronomers for almost a century. Different studies keep coming up with different answers — which has some researchers wondering if they’ve overlooked a key mechanism in the machinery that drives the cosmos.

Now, by pioneering a new way to measure how quickly the cosmos is expanding, a team led by UCLA astronomers has taken a step toward resolving the debate. The group’s research is published today in Monthly Notices of the Royal Astronomical Society.

At the heart of the dispute is the Hubble constant, a number that relates distances to the redshifts of galaxies — the amount that light is stretched as it travels to Earth through the expanding universe. Estimates for the Hubble constant range from about 67 to 73 kilometers per second per megaparsec, meaning that two points in space 1 megaparsec apart (the equivalent of 3.26 million light-years) are racing away from each other at a speed between 67 and 73 kilometers per second.

“The Hubble constant anchors the physical scale of the universe,” said Simon Birrer, a UCLA postdoctoral scholar and lead author of the study. Without a precise value for the Hubble constant, astronomers can’t accurately determine the sizes of remote galaxies, the age of the universe or the expansion history of the cosmos.

Most methods for deriving the Hubble constant have two ingredients: a distance to some source of light and that light source’s redshift. Looking for a light source that had not been used in other scientists’ calculations, Birrer and colleagues turned to quasars, fountains of radiation that are powered by gargantuan black holes. And for their research, the scientists chose one specific subset of quasars — those whose light has been bent by the gravity of an intervening galaxy, which produces two side-by-side images of the quasar on the sky.

Light from the two images takes different routes to Earth. When the quasar’s brightness fluctuates, the two images flicker one after another, rather than at the same time. The delay in time between those two flickers, along with information about the meddling galaxy’s gravitational field, can be used to trace the light’s journey and deduce the distances from Earth to both the quasar and the foreground galaxy. Knowing the redshifts of the quasar and galaxy enabled the scientists to estimate how quickly the universe is expanding.

The UCLA team, as part of the international H0liCOW collaboration, had previously applied the technique to study quadruply imaged quasars, in which four images of a quasar appear around a foreground galaxy. But quadruple images are not nearly as common — double-image quasars are thought to be about five times as abundant as the quadruple ones.

To demonstrate the technique, the UCLA-led team studied a doubly imaged quasar known as SDSS J1206+4332; they relied on data from the Hubble Space Telescope, the Gemini and W.M. Keck observatories, and from the Cosmological Monitoring of Gravitational Lenses, or COSMOGRAIL, network — a program managed by Switzerland’s Ecole Polytechnique Federale de Lausanne that is aimed at determining the Hubble constant.

Tommaso Treu, a UCLA professor of physics and astronomy and the paper’s senior author, said the researchers took images of the quasar every day for several years to precisely measure the time delay between the images. Then, to get the best estimate possible of the Hubble constant, they combined the data gathered on that quasar with data that had previously been gathered by their H0liCOW collaboration on three quadruply imaged quasars.

“The beauty of this measurement is that it’s highly complementary to and independent of others,” Treu said.

The UCLA-led team came up with an estimate for the Hubble constant of about 72.5 kilometers per second per megaparsec, a figure in line with what other scientists had determined in research that used distances to supernovas — exploding stars in remote galaxies — as the key measurement. However, both estimates are about 8 percent higher than one that relies on a faint glow from all over the sky called the cosmic microwave background, a relic from 380,000 years after the Big Bang, when light traveled freely through space for the first time.

“If there is an actual difference between those values, it means the universe is a little more complicated,” Treu said.

On the other hand, Treu said, it could also be that one measurement — or all three — are wrong.

The researchers are now looking for more quasars to improve the precision of their Hubble constant measurement. Treu said one of the most important lessons of the new paper is that doubly imaged quasars give scientists many more useful light sources for their Hubble constant calculations. For now, though, the UCLA-led team is focusing its research on 40 quadruply imaged quasars, because of their potential to provide even more useful information than doubly imaged ones.

Sixteen other researchers from 13 institutions in seven countries contributed to the paper; the research was supported in part by grants from NASA, the National Science Foundation and the Packard Foundation.

Star Material Could Be Building Block Of Life

An organic molecule detected in the material from which a star forms could shed light on how life emerged on Earth, according to new research led by Queen Mary University of London.

The researchers report the first ever detection of glycolonitrile (HOCH2CN), a pre-biotic molecule which existed before the emergence of life, in a solar-type protostar known as IRAS16293-2422 B.

This warm and dense region contains young stars at the earliest stage of their evolution surrounded by a cocoon of dust and gas — similar conditions to those when our Solar System formed.

Detecting pre-biotic molecules in solar-type protostars enhances our understanding of how the solar system formed as it indicates that planets created around the star could begin their existence with a supply of the chemical ingredients needed to make some form of life.

This finding, published in the journal Monthly Notices of the Royal Astronomical Society: Letters, is a significant step forward for pre-biotic astrochemistry since glycolonitrile is recognised as a key precursor towards the formation of adenine, one of the nucleobases that form both DNA and RNA in living organisms.

IRAS16293-2422 B is a well-studied protostar in the constellation of Ophiuchus, in a region of star formation known as rho Ophiuchi, about 450 light-years from Earth.

The research was also carried out with the Centro de Astrobiología in Spain, INAF-Osservatorio Astrofisico di Arcetri in Italy, the European Southern Observatory, and the Harvard-Smithsonian Center for Astrophysics in the USA.

Lead author Shaoshan Zeng, from Queen Mary University of London, said: “We have shown that this important pre-biotic molecule can be formed in the material from which stars and planets emerge, taking us a step closer to identifying the processes that may have led to the origin of life on Earth.”

The researchers used data from the Atacama Large Millimeter/submillimetre Array (ALMA) telescope in Chile to uncover evidence for the presence of glycolonitrile in the material from which the star is forming — known as the interstellar medium.

With the ALMA data, they were able to identify the chemical signatures of glycolonitrile and determine the conditions in which the molecule was found. They also followed this up by using chemical modelling to reproduce the observed data which allowed them to investigate the chemical processes that could help to understand the origin of this molecule.

This follows the earlier detection of methyl isocyanate in the same object by researchers from Queen Mary. Methyl isocyanate is what is known as an isomer of glycolonitrile — it is made up of the same atoms but in a slightly different arrangement, meaning it has different chemical properties.

The research was partially funded by Queen Mary University of London and the UK Science and Technology Facilities Council.