New Model Explains What We See When A Massive Black Hole Devours A Star

A star that wanders too close to the supermassive black hole in the center of its galaxy will be torn apart by the black hole’s gravity in a violent cataclysm called a tidal disruption event (TDE), producing a bright flare of radiation. A new study led by theoretical astrophysicists at the University of Copenhagen’s Niels Bohr Institute and UC Santa Cruz provides a unified model that explains recent observations of these extreme events.

The breakthrough study, published in Astrophysical Journal Letters, provides a new theoretical perspective for a fast-growing research field.

“Only in the last decade or so have we been able to distinguish TDEs from other galactic phenomena, and the new model will provide us with the basic framework for understanding these rare events,” said coauthor Enrico Ramirez-Ruiz, professor and chair of astronomy and astrophysics at UC Santa Cruz and Niels Bohr Professor at the University of Copenhagen.

In most galaxies, the central black hole is quiescent, not actively consuming any material and therefore not emitting any light. Tidal disruption events are rare, only happening about once every 10,000 years in a typical galaxy. When an unlucky star gets torn apart, however, the black hole is “overfed” with stellar debris for a while and emits intense radiation.

“It is interesting to see how materials get their way into the black hole under such extreme conditions,” said first author Jane Lixin Dai, assistant professor at the University of Copenhagen, who led the study. “As the black hole is eating the stellar gas, a vast amount of radiation is emitted. The radiation is what we can observe, and using it we can understand the physics and calculate the black hole properties. This makes it extremely interesting to go hunting for tidal disruption events.”

While the same physics is expected to happen in all tidal disruption events, about two dozen of which have been observed so far, the observed properties of these events have shown great variation. Some emit mostly x-rays, while others emit mostly visible and ultraviolet light. Theorists have been struggling to understand this diversity and assemble different pieces of the puzzle into a coherent model.

In the new model, it is the viewing angle of the observer that accounts for differences in the observations. Galaxies are oriented randomly with respect to the line of sight of observers on Earth, who see different aspects of a tidal disruption event depending on its orientation.

“It is like there is a veil that covers part of a beast,” Ramirez-Ruiz explained. “From some angles we see an exposed beast, but from other angles we see a covered beast. The beast is the same, but our perceptions are different.”

The model developed by Dai and her collaborators combines elements from general relativity, magnetic fields, radiation, and gas hydrodynamics. It shows what astronomers can expect to see when viewing tidal disruption events from different angles, allowing researchers to fit different events into a coherent framework.

Survey projects planned for the next few years are expected to provide much more data on tidal disruption events and will help greatly expand this field of research, according to Dai. These include the Young Supernova Experiment (YSE) transient survey, led by the DARK Cosmology Centre at the Niels Bohr Institute and UC Santa Cruz, and the Large Synoptic Survey Telescopes being built in Chile.

“We will observe hundreds to thousands of tidal disruption events in a few years. This will give us a lot of ‘laboratories’ to test our model and use it to understand more about black holes,” Dai said.

In addition to Dai and Ramirez-Ruiz, the coauthors include Jonathan McKinney, Nathaniel Roth, and Cole Miller at the University of Maryland, College Park. State-of-the-art computational tools were employed to solve the puzzle, and the simulations were carried out by Dai and Roth on the recently acquired large computer cluster made possible by a grant from the Villum Foundation for Jens Hjorth, head of DARK Cosmology Centre, as well as clusters funded by the U.S. National Science Foundation and NASA.

Hawaii’s Kilauea Volcano Belches Another Plume Of Ash

As an explosive eruption on the Kilauea volcano sent another plume of ash high into the air, and as more residents were evacuated from a nearby subdivision, officials at the U.S. Geological Survey (USGS) warned against toasting marshmallows over the Hawaiian volcano’s vents.

The USGS said early Tuesday an eruption had sent ash 4,500 metres into the air, warning that the ash was drifting northwest and liable to affect anyone in the summit area.

The wind is also carrying thin strands of volcanic glass fibres that could injure eyes and lungs, officials said.

The eruption came hours after Hawaii County officials knocked on doors on several streets in the Leilani Estates subdivision alerting residents to flee fast-moving lava flowing from one of the world’s most active volcanos. Hundreds have left the area since more intense eruptions began on May 3.

Multiple fissures continue to spew hot lava flows, which have blocked roads and damaged dozens of buildings on Hawaii’s Big Island.

One fountain of lava rose more than 60 metres at times on Monday, the USGS said.

Back in Hawaii, the Pacific Tsunami Warning Centre on Oahu said a 4.4 magnitude earthquake shook the Hilina region of the volcano, southwest of the estates, on Monday. Officials said it wasn’t strong enough to generate a tsunami.

Lava has oozed over two wells at the Puna geothermal power plant, but county officials said the flow stopped. Officials said there was no release of any dangerous hydrogen sulfide gas after lava crept over the plugged wells.

Residents fear the wells may be explosive. Officials have said the power plant is safe, but lava has never engulfed a geothermal plant anywhere in the world, creating a measure of uncertainty.

As of Friday, lava had destroyed 82 structures, including 37 homes. About 2,000 people have been ordered to leave the area since Kilauea began erupting on May 3.

So far, no deaths have been blamed on the eruption, though a man’s leg was shattered when he was hit by a spatter of super-dense lava.

Land Rising Above The Sea 2.4 Billion Years Ago Changed Planet Earth

Chemical signatures in shale, the Earth’s most common sedimentary rock, point to a rapid rise of land above the ocean 2.4 billion years ago that possibly triggered dramatic changes in climate and life.

In a study published in the May 24 issue of the journal Nature, researchers report that shale sampled from around the world contains archival quality evidence of almost imperceptible traces of rainwater that caused weathering of land from as old as 3.5 billion years ago.

Notable changes in the ratios of oxygen 17 and 18 with more common oxygen 16, said lead author Ilya Bindeman, a geologist at the University of Oregon, allowed researchers to read the chemical history in the rocks.

In doing so, they established when newly surfaced crust was exposed to weathering by chemical and physical processes, and, more broadly, when the modern hydrologic process of moisture distillation during transport over large continents started.

The evidence is from analyses of three oxygen isotopes, particularly the rare but stable oxygen 17, in 278 shale samples drawn from outcrops and drill holes from every continent and spanning 3.7 billion years of Earth’s history. The analyses were done in Bindeman’s Stable Isotope Laboratory.

Based on his own previous modeling and other studies, Bindeman said, total landmass on the planet 2.4 billion years ago may have reached about two-thirds of what is observed today. However, the emergence of the new land happened abruptly, in parallel with large-scale changes in mantle dynamics.

Isotopic changes recorded in the shale samples at that time also coincides with the hypothesized timing of land collisions that formed Earth’s first supercontinent, Kenorland, and high-mountain ranges and plateaus.

“Crust needs to be thick to stick out of water,” Bindeman said. “The thickness depends on its amount and also on thermal regulation and the viscosity of the mantle. When the Earth was hot and the mantle was soft, large, tall mountains could not be supported. Our data indicate that this changed exponentially 2.4 billion years ago. The cooler mantle was able to support large swaths of land above sea level.”

Temperatures on the surface when the new land emerged from the sea would have likely been hotter than today by several tens of degrees, he said.

The study found a stepwise change in triple-isotopes of oxygen around that time frame. That, the scientists said, resolves previous arguments for a gradual or stepwise emergence of land between 1.1 and 3.5 billion years ago. At 2.4 billion years ago, Bindeman said, the newly emerged land began to consume carbon dioxide from the atmosphere amid chemical weathering.

The timing also coincides with the transition from the Archean Eon, when simple prokaryotic life forms, archaea and bacteria, thrived in water, to the Proterozoic Eon, when eukaryotes, such as algae, plants and fungi, emerged.

“In this study, we looked at how weathering proceeded over 3.5 billion years,” Bindeman said. “Land rising from water changes the albedo of the planet. Initially, Earth would have been dark blue with some white clouds when viewed from space. Early continents added to reflection. Today we have dark continents because of lots of vegetation.”

Exposure of the new land to weathering, he said, may have set off a sink of greenhouse gases such carbon dioxide, disrupting the radiative balance of the Earth that generated a series of glacial episodes between 2.4 billion and 2.2 billion years ago. That, he said, may have spawned the Great Oxygenation Event in which atmospheric changes brought significant amounts of free oxygen into the air. Rocks were oxidized and became red. Archean rocks are gray.

In the absence of much land, he said, photons from the sun interacted with water and heated it. A bright surface, provided by emerging land, would reflect sunlight back into space, creating additional torque on radiative-greenhouse balance and a change in climate.

“What we speculate is that once large continents emerged, light would be reflected back into space and initiate runaway glaciation,” Bindeman said. “Earth would have seen its first snowfall.”

Shales are formed by the weathering of crust.

“They tell you a lot about the exposure to air and light and precipitation,” Bindeman said. “The process of forming shale captures organic products and eventually helps to generate oil. Shales provide us with a continuous record of weathering.”

Mars Rocks May Harbor Signs Of Life From 4 Billion Years Ago

Iron-rich rocks near ancient lake sites on Mars could hold vital clues that show life once existed there, research suggests.

These rocks — which formed in lake beds — are the best place to seek fossil evidence of life from billions of years ago, researchers say.

A new study that sheds light on where fossils might be preserved could aid the search for traces of tiny creatures — known as microbes — on Mars, which it is thought may have supported primitive life forms around four billion years ago.

A team of scientists has determined that sedimentary rocks made of compacted mud or clay are the most likely to contain fossils. These rocks are rich in iron and a mineral called silica, which helps preserve fossils.

They formed during the Noachian and Hesperian Periods of Martian history between three and four billion years ago. At that time, the planet’s surface was abundant in water, which could have supported life.

The rocks are much better preserved than those of the same age on Earth, researchers say. This is because Mars is not subject to plate tectonics — the movement of huge rocky slabs that form the crust of some planets — which over time can destroy rocks and fossils inside them.

The team reviewed studies of fossils on Earth and assessed the results of lab experiments replicating Martian conditions to identify the most promising sites on the planet to explore for traces of ancient life.

Their findings could help inform NASA’s next rover mission to the Red Planet, which will focus on searching for evidence of past life. The US space agency’s Mars 2020 rover will collect rock samples to be returned to Earth for analysis by a future mission.

A similar mission led by the European Space Agency is also planned in coming years.

The latest study of Mars rocks — led by a researcher from the University of Edinburgh — could aid in the selection of landing sites for both missions. It could also help to identify the best places to gather rock samples.

The study, published in Journal of Geophysical Research, also involved researchers at NASA’s Jet Propulsion Laboratory, Brown University, California Institute of Technology, Massachusetts Institute of Technology and Yale University in the US.

Dr Sean McMahon, a Marie Sklodowska-Curie fellow in the University of Edinburgh’s School of Physics and Astronomy, said: “There are many interesting rock and mineral outcrops on Mars where we would like to search for fossils, but since we can’t send rovers to all of them we have tried to prioritise the most promising deposits based on the best available information.”

‘Vog’ From Kilauea Volcano Blankets Marshall Islands, 3700km Away

Haze from the Kilauea volcano eruption in Hawaii blanketed the Marshall Islands 3,700 kilometres (2,300 miles) away on Sunday, as officials warned it would continue moving west.

The haze, a phenomenon known as “vog” or volcanic smog, is spreading across Micronesia, the US National Weather Service based in Guam said.

The volcano on Hawaii’s Big Island is now in its fourth week of eruptions.

Meteorologists advised residents on the Marshall Islands with respiratory problems to stay indoors while airlines and shipping companies were warned to be aware of “lower visibilities”.

The Guam weather office said haze produced by Kilauea would spread westward and reach Kosrae, Pohnpei and possibly Chuuk in the Federated States of Micronesia over the next few days.

Kilauea is the world’s most active volcano and one of five on Hawaii’s Big Island.

It started erupting on 3 May, prompting about 2,000 people to flee from their mountainside homes.

Scientists believe the volcanic activity may be a precursor to a major eruption similar to the one that shook the island in the mid-1920s.

Scientists Introduce Cosmochemical Model For Pluto Formation

Southwest Research Institute scientists integrated NASA’s New Horizons discoveries with data from ESA’s Rosetta mission to develop a new theory about how Pluto may have formed at the edge of our solar system.

“We’ve developed what we call ‘the giant comet’ cosmochemical model of Pluto formation,” said Dr. Christopher Glein of SwRI’s Space Science and Engineering Division. The research is described in a paper published online today in Icarus. At the heart of the research is the nitrogen-rich ice in Sputnik Planitia, a large glacier that forms the left lobe of the bright Tombaugh Regio feature on Pluto’s surface. “We found an intriguing consistency between the estimated amount of nitrogen inside the glacier and the amount that would be expected if Pluto was formed by the agglomeration of roughly a billion comets or other Kuiper Belt objects similar in chemical composition to 67P, the comet explored by Rosetta.”

In addition to the comet model, scientists also investigated a solar model, with Pluto forming from very cold ices that would have had a chemical composition that more closely matches that of the Sun.

Scientists needed to understand not only the nitrogen present at Pluto now — in its atmosphere and in glaciers — but also how much of the volatile element potentially could have leaked out of the atmosphere and into space over the eons. They then needed to reconcile the proportion of carbon monoxide to nitrogen to get a more complete picture. Ultimately, the low abundance of carbon monoxide at Pluto points to burial in surface ices or to destruction from liquid water.

“Our research suggests that Pluto’s initial chemical makeup, inherited from cometary building blocks, was chemically modified by liquid water, perhaps even in a subsurface ocean,” Glein said. However, the solar model also satisfies some constraints. While the research pointed to some interesting possibilities, many questions remain to be answered.

“This research builds upon the fantastic successes of the New Horizons and Rosetta missions to expand our understanding of the origin and evolution of Pluto,” said Glein. “Using chemistry as a detective’s tool, we are able to trace certain features we see on Pluto today to formation processes from long ago. This leads to a new appreciation of the richness of Pluto’s ‘life story,’ which we are only starting to grasp.”

Peruvian Scientists Use DNA To Trace Origins Of Inca Emperors

Researchers in Peru believe they have traced the origins of the Incas —the largest pre-Hispanic civilization in the Americas—through the DNA of the modern-day descendants of their emperors.

From their ancient capital Cusco, the Incas controlled a vast empire called Tahuantinsuyo, which extended from the west of present-day Argentina to the south of Colombia.

They ruled for more than two hundred years before being conquered by the invading Spanish in the 16th century.

The empire included the mountain-top citadel of Machu Picchu in modern-day Peru—now a UNESCO World Heritage Site and a major tourist attraction.

After becoming fascinated by the Inca culture, their organizational skills and their mastery of engineering, researchers Ricardo Fujita and Jose Sandoval of Lima’s University of San Martin de Porresit became interested in the genetic profile of their descendants.

They said the aim of the study, the first of its kind, was to reveal whether there was a unique Inca patriarch.

“It’s like a paternity test, not between father and son but among peoples,” Fujita told AFP.

The scientists wanted to verify two common legends about the origin of the Incas.

One attributes them to a couple from around Lake Titicaca, in Peru’s Puno region. The other identifies the first Incas as the Ayar brothers from the Pacaritambo mountain in the Cusco region.

DNA samples were taken from inhabitants of both places.

“After three years of tracking the genetic fingerprints of the descendants, we confirm that the two legends explaining the origin of the Inca civilization could be related,” said Fujita.

Genetic similarities

“They were compared with our genealogical base of more than 3,000 people to reconstruct the genealogical tree of all individuals,” said Fujita.

“We finally reduced this base to almost 200 people sharing genetic similarities close to the Inca nobility.”

The study released some preliminary results in April, in the review Molecular Genetics and Genomics.

“The conclusion we came to is that the Tahuantinsuyo nobility is descended from two lines, one in the region of Lake Titicaca, the other around the mountain of Pacaritambo in Cusco. That confirms the legends,” said Sandoval.

But it also confirms that the two legends were linked.

“Probably the first migration came from the Puno region and was established in Pacaritambo for a few decades before heading to Cusco and founding Tahuantinsuyo,” he said.

But the work of the researchers does not stop there. Now they want to go further back in time.

For that, they have to test the DNA of ancient relics, such as mummies, “to form the most complete picture of the origin of the most important pre-Hispanic civilization,” said Fujita.

The task looks complicated because the Spanish Conquistadores, who arrived 1532, destroyed Inca mummies that families venerated, as they sought to convert people to Christianity.

The researchers are now looking for where the Incas’ most direct descendants are buried in order to trace their history.

The DNA analysis would add to archeological and anthropological research to understand the exact origin of the people.

“In this case, we use … genetics, the transmission of molecular features across the generations,” said Fujita.