Cosmic Dust Forms On Supernovae Blasts

Scientists claim to have solved a longstanding mystery as to how cosmic dust, the building blocks of stars and planets, forms across the Universe.

Cosmic dust contains tiny fragments or organic material and is spread out across the Universe. The dust is primarily formed in stars and is then blown off in a slow wind or a massive star explosion.

Up until now, astronomers have had little understanding as to why so much cosmic dust exists in the interstellar medium, with theoretical estimates suggesting it should be obliterated by supernova explosions.

A supernova is an event that occurs upon the violent death of a star and is one of the most powerful events in the Universe, producing a shockwave which destroys almost anything in its path.

Yet new research published in the Monthly Notices of the Royal Astronomical Society has observed the survival of cosmic dust around the closest supernova explosion detected to us, Supernova 1987A.

Observations using NASA’s research aircraft, the Stratospheric Observatory for Infrared Astronomy (SOFIA), have detected cosmic dust in a distinctive set of rings that form part of Supernova 1987A.

The results seem to suggest that there is rapid growth of cosmic dust within the rings, leading the team to believe that dust may actually be re-forming after it is destroyed in the wake of a supernova blast wave.

This immediacy – that the post-shock environment might be ready to form or re-form dust – had never been considered before, and may be pivotal in fully understanding how cosmic dust is both created and destroyed.

“We already knew about the slow-moving dust in the heart of 1987A,” said Dr. Mikako Matsuura, lead author on the paper from the School of Physics and Astronomy.

“It formed from the heavy elements created in the core of the dead star. But the SOFIA observations tell us something completely new.”

Cosmic dust particles can be heated from tens to hundreds of degrees causing them to glow at both infrared and millimeter wavelengths. Observations of millimeter-wave dust emission can generally be carried out from the ground using telescopes; however, observations in the infrared are almost impossible to interference from the water and carbon dioxide in the Earth’s atmosphere.

By flying above most of the obscuring molecules, SOFIA provides access to portions of the infrared spectrum not available from the ground.

Life Thrived On Earth 3.5 Billion Years Ago, Research Suggests

3.5 billion years ago Earth hosted life, but was it barely surviving, or thriving? A new study carried out by a multi institutional team with leadership including the Earth-Life Science Institute (ELSI) of Tokyo Institute of Technology (Tokyo Tech) provides new answers to this question. Microbial metabolism is recorded in billions of years of sulfur isotope ratios that agree with this study’s predictions, suggesting life throve in the ancient oceans. Using this data, scientists can more deeply link the geochemical record with cellular states and ecology.

Scientists want to know how long life has existed on Earth. If it has been around for almost as long as the planet, this suggests it is easy for life to originate and life should be common in the Universe. If it takes a long time to originate, this suggests there were very special conditions that had to occur. Dinosaurs, whose bones are presented in museums around the world, were preceded by billions of years by microbes. While microbes have left some physical evidence of their presence in the ancient geological record, they do not fossilize well, thus scientists use other methods for understanding whether life was present in the geological record.

Presently, the oldest evidence of microbial life on Earth comes to us in the form of stable isotopes. The chemical elements charted on the periodic are defined by the number of protons in their nuclei, for example, hydrogen atoms have one proton, helium atoms have two, carbon atoms contain six. In addition to protons, most atomic nuclei also contain neutrons, which are about as heavy as protons, but which don’t bear an electric charge. Atoms which contain the same number of protons, but variable numbers of neutrons are known as isotopes. While many isotopes are radioactive and thus decay into other elements, some do not undergo such reactions; these are known as “stable” isotopes. For example, the stable isotopes of carbon include carbon 12 (written as 12C for short, with 6 protons and 6 neutrons) and carbon 13 (13C, with 6 protons and 7 neutrons).

All living things, including humans, “eat and excrete.” That is to say, they take in food and expel waste. Microbes often eat simple compounds made available by the environment. For example, some are able to take in carbon dioxide (CO2) as a carbon source to build their own cells. Naturally occurring CO2 has a fairly constant ratio of 12C to 13C. However, 12CO2 is about 2 % lighter than 13CO2, so 12CO2 molecules diffuse and react slightly faster, and thus the microbes themselves become “isotopically light,” containing more 12C than 13C, and when they die and leave their remains in the fossil record, their stable isotopic signature remains, and is measurable. The isotopic composition, or “signature,” of such processes can be very specific to the microbes that produce them.

Besides carbon there are other chemical elements essential for living things. For example, sulfur, with 16 protons, has three naturally abundant stable isotopes, 32S (with 16 neutrons), 33S (with 17 neutrons) and 34S (with 18 neutrons). Sulfur isotope patterns left behind by microbes thus record the history of biological metabolism based on sulfur-containing compounds back to around 3.5 billion years ago. Hundreds of previous studies have examined wide variations in ancient and contemporary sulfur isotope ratios resulting from sulfate (a naturally occurring sulfur compound bonded to four oxygen atoms) metabolism. Many microbes are able to use sulfate as a fuel, and in the process excrete sulfide, another sulfur compound. The sulfide “waste” of ancient microbial metabolism is then stored in the geological record, and its isotope ratios can be measured by analyzing minerals such as the FeS2 mineral pyrite.

This new study reveals a primary biological control step in microbial sulfur metabolism, and clarifies which cellular states lead to which types of sulfur isotope fractionation. This allows scientists to link metabolism to isotopes: by knowing how metabolism changes stable isotope ratios, scientists can predict the isotopic signature organisms should leave behind. This study provides some of the first information regarding how robustly ancient life was metabolizing. Microbial sulfate metabolism is recorded in over a three billion years of sulfur isotope ratios that are in line with this study’s predictions, which suggest life was in fact thriving in the ancient oceans. This work opens up a new field of research, which ELSI Associate Professor Shawn McGlynn calls “evolutionary and isotopic enzymology.” Using this type of data, scientists can now proceed to other elements, such as carbon and nitrogen, and more completely link the geochemical record with cellular states and ecology via an understanding of enzyme evolution and Earth history.

Ancient Asteroid Impacts Played A Role In Creation Of Earth’s Future Continents

The heavy bombardment of terrestrial planets by asteroids from space has contributed to the formation of the early evolved crust on Earth that later gave rise to continents — home to human civilisation.

More than 3.8 billion years ago, in a time period called the Hadean eon, our planet Earth was constantly bombarded by asteroids, which caused the large-scale melting of its surface rocks. Most of these surface rocks were basalts, and the asteroid impacts produced large pools of superheated impact melt of such composition. These basaltic pools were tens of kilometres thick, and thousands of kilometres in diameter.

“If you want to get an idea of what the surface of Earth looked like at that time, you can just look at the surface of the Moon which is covered by a vast amount of large impact craters,” says Professor Rais Latypov from the School of Geosciences of the University of the Witwatersrand in South Africa.

The subsequent fate of these ancient, giant melt sheet remains, however, highly debatable. It has been argued that, on cooling, they may have crystallized back into magmatic bodies of the same, broadly basaltic composition. In this scenario, asteroid impacts are supposed to play no role in the formation of the Earth’s early evolved crust.

An alternative model suggests that these sheets may undergo large-scale chemical change to produce layered magmatic intrusions, such as the Bushveld Complex in South Africa. In this scenario, asteroid impacts may have played an important role in producing various igneous rocks in the early Earth’s crust and therefore they may have contributed to its chemical evolution.

There is no direct way to rigorously test these two competing scenarios because the ancient Hadean impact melts have been later obliterated by plate tectonics. However, by studying the younger impact melt sheet of the Sudbury Igneous Complex (SIC) in Canada, Latypov and his research team have inferred that ancient asteroid impacts were capable of producing various rock types from the earlier Earth’s basaltic crust. Most importantly, these impacts may have made the crust compositionally more evolved, i.e. silica-rich in composition. Their research has been published in a paper in Nature Communications.

The SIC is the largest, best exposed and accessible asteroid impact melt sheet on Earth, which has resulted from a large asteroid impact 1.85 billion years ago. This impact produced a superheated melt sheet of up to 5 km thick. The SIC now shows a remarkable magmatic stratigraphy, with various layers of igneous rocks.

“Our field and geochemical observations — especially the discovery of large discrete bodies of melanorites throughout the entire stratigraphy of the SIC — allowed us to reassess current models for the formation of the SIC and firmly conclude that its conspicuous magmatic stratigraphy is the result of large-scale fractional crystallization,” says Latypov.

“An important implication is that more ancient and primitive Hadean impact melt sheets on the early Earth and other terrestrial planets would also have undergone near-surface, large-volume differentiation to produce compositionally stratified bodies. The detachment of dense primitive layers from these bodies and their sinking into the mantle would leave behind substantial volumes of evolved rocks (buoyant crustal blocks) in the Hadean crust. This would make the crust compositionally layered and increasingly more evolved from its base towards the Earth’s surface.”

“These impacts made the crust compositionally more evolved — in other words, silica-rich in composition,” says Latypov. “Traditionally, researchers believe that such silica-rich evolved rocks — which are essentially building buoyant blocks of our continents — can only be generated deep in the Earth, but we now argue that such blocks can be produced at new-surface conditions within impact melt pools.”

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.

Planetary Collision That Formed The Moon Made Life Possible On Earth

Most of Earth’s essential elements for life — including most of the carbon and nitrogen in you — probably came from another planet.

Earth most likely received the bulk of its carbon, nitrogen and other life-essential volatile elements from the planetary collision that created the moon more than 4.4 billion years ago, according to a new study by Rice University petrologists in the journal Science Advances.

“From the study of primitive meteorites, scientists have long known that Earth and other rocky planets in the inner solar system are volatile-depleted,” said study co-author Rajdeep Dasgupta. “But the timing and mechanism of volatile delivery has been hotly debated. Ours is the first scenario that can explain the timing and delivery in a way that is consistent with all of the geochemical evidence.”

The evidence was compiled from a combination of high-temperature, high-pressure experiments in Dasgupta’s lab, which specializes in studying geochemical reactions that take place deep within a planet under intense heat and pressure.

In a series of experiments, study lead author and graduate student Damanveer Grewal gathered evidence to test a long-standing theory that Earth’s volatiles arrived from a collision with an embryonic planet that had a sulfur-rich core.

The sulfur content of the donor planet’s core matters because of the puzzling array of experimental evidence about the carbon, nitrogen and sulfur that exist in all parts of the Earth other than the core.

“The core doesn’t interact with the rest of Earth, but everything above it, the mantle, the crust, the hydrosphere and the atmosphere, are all connected,” Grewal said. “Material cycles between them.”

One long-standing idea about how Earth received its volatiles was the “late veneer” theory that volatile-rich meteorites, leftover chunks of primordial matter from the outer solar system, arrived after Earth’s core formed. And while the isotopic signatures of Earth’s volatiles match these primordial objects, known as carbonaceous chondrites, the elemental ratio of carbon to nitrogen is off. Earth’s non-core material, which geologists call the bulk silicate Earth, has about 40 parts carbon to each part nitrogen, approximately twice the 20-1 ratio seen in carbonaceous chondrites.

Grewal’s experiments, which simulated the high pressures and temperatures during core formation, tested the idea that a sulfur-rich planetary core might exclude carbon or nitrogen, or both, leaving much larger fractions of those elements in the bulk silicate as compared to Earth. In a series of tests at a range of temperatures and pressure, Grewal examined how much carbon and nitrogen made it into the core in three scenarios: no sulfur, 10 percent sulfur and 25 percent sulfur.

“Nitrogen was largely unaffected,” he said. “It remained soluble in the alloys relative to silicates, and only began to be excluded from the core under the highest sulfur concentration.”

Carbon, by contrast, was considerably less soluble in alloys with intermediate sulfur concentrations, and sulfur-rich alloys took up about 10 times less carbon by weight than sulfur-free alloys.

Using this information, along with the known ratios and concentrations of elements both on Earth and in non-terrestrial bodies, Dasgupta, Grewal and Rice postdoctoral researcher Chenguang Sun designed a computer simulation to find the most likely scenario that produced Earth’s volatiles. Finding the answer involved varying the starting conditions, running approximately 1 billion scenarios and comparing them against the known conditions in the solar system today.

“What we found is that all the evidence — isotopic signatures, the carbon-nitrogen ratio and the overall amounts of carbon, nitrogen and sulfur in the bulk silicate Earth — are consistent with a moon-forming impact involving a volatile-bearing, Mars-sized planet with a sulfur-rich core,” Grewal said.

Dasgupta, the principal investigator on a NASA-funded effort called CLEVER Planets that is exploring how life-essential elements might come together on distant rocky planets, said better understanding the origin of Earth’s life-essential elements has implications beyond our solar system.

“This study suggests that a rocky, Earth-like planet gets more chances to acquire life-essential elements if it forms and grows from giant impacts with planets that have sampled different building blocks, perhaps from different parts of a protoplanetary disk,” Dasgupta said.

“This removes some boundary conditions,” he said. “It shows that life-essential volatiles can arrive at the surface layers of a planet, even if they were produced on planetary bodies that underwent core formation under very different conditions.”

Dasgupta said it does not appear that Earth’s bulk silicate, on its own, could have attained the life-essential volatile budgets that produced our biosphere, atmosphere and hydrosphere.

“That means we can broaden our search for pathways that lead to volatile elements coming together on a planet to support life as we know it.”

Milky Way’s Neighbors Pick Up The Pace

After slowly forming stars for the first few billion years of their lives, the Magellanic Clouds, near neighbors of our own Milky Way galaxy, have upped their game and are now forming new stars at a fast clip. This new insight into the history of the Clouds comes from the first detailed chemical maps made of galaxies beyond the Milky Way.

Named for explorer Ferdinand Magellan, who led the first European expedition to circumnavigate the globe, the Large and Small Magellanic Clouds are the Milky Way’s nearest galactic neighbors — companion galaxies that will someday merge with our galaxy. The two galaxies are visible only from the Southern Hemisphere, where they look like bright, wispy clouds.

A Map to Stellar History

Although humans have gazed at the Clouds for millennia, this is the first time astronomers have made a detailed map of the chemical compositions of the stars within them. The project, carried out by the Sloan Digital Sky Survey (SDSS), was led by NOAO astronomer David Nidever, who is also a research professor of physics at Montana State University.

“We mapped the positions, movements, and chemical make-up of thousands of stars in the Magellanic Clouds,” said Nidever. “Reading these maps helps us reconstruct the history of when these galaxies formed their stars.”

The maps are the first major discovery to come out of the new southern operations of SDSS’s Apache Point Observatory Galaxy Evolution Experiment 2 (APOGEE-2) survey, which is being carried out on the Irénée du Pont Telescope at Las Campanas Observatory in Chile.

Making Maps from Stellar Spectra

To make the maps, the SDSS team collected spectra of as many stars as possible. Spectra, which spread out the light from a star in the form of a rainbow, encode the motions of stars, their temperature, the chemical elements they contain, and their stage in the stellar life cycle.

By measuring the chemical make-up of a galaxy’s stars, astronomers are able to infer their “star formation history,” a rough record of the rate at which stars formed over time. The reconstruction is possible because of the difference in the lifetimes of stars of different masses and the role more massive stars play in enriching galaxies with heavy elements.

As stars age, stars more massive than the Sun evolve and explode as supernovae, ejecting heavy elements out into the galaxy, while less massive stars live on. The ejected elements mix with the existing gas, enriching it. New generations of stars form from the enriched gas and inherit that chemical make-up. The process repeats, with the longer-lived lower mass stars surviving to record the enrichment history of the galaxy. By mapping the abundances of these stars, astronomers can “read” the star formation record of the galaxy.

Slow Start Followed by a Bang

The results show that the star formation history of the Large and Small Magellanic Clouds is completely different from that of our galaxy. “In the Milky Way, star formation began like gangbusters and later declined,” explained team member Sten Hasselquist from the University of Utah. “In contrast, in the Magellanic Clouds, stars formed extremely slowly at early times, at a rate only 1/50th of the star formation rate in the Milky Way, but that rate has skyrocketed in the last 2 billion years.”

Nidever thinks that the dramatic increase in the star formation rate is due to the interaction of the Magellanic Clouds with one another as they tumble toward the Milky Way. “The Clouds began their lives calmly in a relatively isolated part of the Universe, where there was no reason to form stars,” said Nidever. “But in the last few billion years, the close interactions that the Clouds have had with each other and with the Milky Way is causing the gas in the Clouds to transform into stars.”

Fireworks Ahead!

Over the next several billion years, the Magellanic Clouds will continue to merge with the Milky Way, as the gravitational force of the much more massive Milky Way pulls them in. As the merger progresses, star formation in the Clouds is expected to reach an even greater, fevered pitch, according to recent work. In about 2.5 billion years, the Large Magellanic Cloud will be entirely consumed by the Milky Way in a cosmic explosion of star formation. Our nearest neighbors may have gotten off to a slow start, but exciting times lie ahead!