Mapping Dark Energy – Accelerating the Expansion of the Universe

On 21 June 2019 the Spektrum-Röntgen-Gamma (Spektr-RG / SRG) spacecraft will be launched from the Kazakh steppe, marking the start of an exciting journey. SRG will be carrying the German Extended ROentgen Survey with an Imaging Telescope Array (eROSITA) X-ray telescope and its Russian ART-XC partner instrument. A Proton rocket will carry the spacecraft from the Baikonur Cosmodrome towards its destination – the second Lagrange point of the Sun-Earth system, L2, which is 1.5 million kilometers from Earth.

In orbit around this equilibrium point, eROSITA will embark upon the largest-ever survey of the hot universe. The space telescope will use its seven X-ray detectors to observe the entire sky and search for and map hot sources such as galaxy clusters, active black holes, supernova remnants, X-ray binaries and neutron stars.

Walther Pelzer, executive board member for the Space Administration at the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR), says, “eROSITA’s X-ray ‘eyes’ are the best that have ever been launched as part of a space telescope. Their unique combination of light-collecting area, field-of-view and resolution makes them approximately 20 times more sensitive than the ROSAT telescope that flew to space in the 1990s. ROSAT also incorporated advanced technology that was ‘made in Germany’. With its enhanced capabilities, eROSITA will help researchers gain a better understanding of the structure and development of the universe, and also contribute towards investigations into the mystery of dark energy.”

The universe has been expanding continuously since the Big Bang. Until the 1990s, it was thought that this cosmic expansion would slow down and eventually come to a halt. Then, the astrophysicists Saul Perlmutter, Adam Riess and Brian Schmidt observed stellar explosions that were visible from a great distance and always emitted the same amount of light. They measured their distances and could hardly believe their findings.

“The Type 1a supernovae observed exhibited lower brightness levels than expected. It was clear that the universe was not slowing down as it expanded – quite the opposite, in fact. It is gathering speed and its components are being driven further and further apart at an ever-increasing rate,” explains Thomas Mernik, eROSITA Project Manager at the DLR Space Administration. With this discovery, the three researchers turned science upside and were awarded the Nobel Prize in Physics in 2011. Yet Perlmutter, Riess and Schmidt have left us with one crucial question: “What is the ‘cosmic fuel’ that powers the expansion of the universe? Since no one has yet been able to answer this question, and the ingredients of this catalyst are unknown, it is simply referred to as dark energy. eROSITA will now attempt to track down the cause of this acceleration,” explains Mernik.

Galaxy clusters – a key to dark energy

Very little is known about the universe. The ingredients that make up 4 percent of its energy density – ‘normal’ material such as protons and neutrons – is only a very small part of the ‘universe recipe’. What the other 96 percent is composed of remains a mystery. Today it is believed that 26 percent is dark matter. However, the largest share, estimated at 70 percent, is comprised of dark energy.

To track this down, scientists must observe something unimaginably large and extremely hot: “Galaxy clusters are composed of up to several thousand galaxies that move at different velocities within a common gravitational field. Inside, these strange structures are permeated by a thin, extremely hot gas that can be observed through its X-ray emissions. This is where eROSITA’s X-ray ‘eyes’ come into play. They allow us to observe galaxy clusters and see how they move in the universe, and above all, how fast they are travelling. We hope that this motion will tell us more about dark energy,” explains Thomas Mernik.

Scientists are not just interested in the movement patterns of galaxy clusters. They also want to count and map these structures. Up to 10,000 such clusters should be ‘captured’ by eROSITA’s X-ray ‘eyes’ – more than have ever been observed before. In addition, other hot phenomena such as active galactic nuclei, supernova remnants, X-ray binaries and neutron stars will be observed and identified.

eROSITA will scan the entire sky every six months for this purpose, and create a deep and detailed X-ray map of the universe over four years. It will thus produce the largest-ever cosmic catalog of hot objects and thus improve the scientific understanding of the structure and development of the universe.

The German telescope consists of two core components – its optics and the associated detectors. The former consists of seven mirror modules aligned in parallel. Each module has a diameter of 36 centimeters and consists of 54 nested mirror shells, whose surface is composed of a para-boloid and a hyper-boloid (Wolter-I optics).

“The mirror modules collect high-energy photons and focus them onto the CCD X-ray cameras, which were specially developed for eROSITA at our semiconductor laboratory in Garching. These form the second core component of eROSITA and are located at the focus of each of the mirror systems. The highly sensitive cameras are the best of their kind and, together with the mirror modules, form an X-ray telescope featuring an unrivaled combination of light-collecting area and field-of-view,” explains Peter Predehl, eROSITA principal investigator at MPE.

Thermal Analog Black Hole Agrees With Hawking Radiation Theory

A team of researchers at the Israel Institute of Technology has found that a thermal analog black hole they created agrees with the Hawking radiation theory. In their paper published in the journal Nature, the group describes building their analog black hole and using data from it to test its temperature. Silke Weinfurtner with the University of Nottingham has published a News and Views piece on the work done by the team in the same journal issue.

One of Stephen Hawking’s theories suggested that not all matter that approaches a black hole falls in—he argued that in some cases in which entangled pairs of particles arise, only one of them would fall in, while the other escaped. The escaping particles were named Hawking radiation. Hawking also predicted that the radiation escaping from a black hole would be thermal and that its temperature would depend on the size of the black hole. Testing the theory has been difficult because of the nature of black holes—any radiation escaping from them would be too faint to observe. To get around that problem, researchers have been working on creating black hole analogs in the lab. In this new effort, the researchers built one designed to absorb sound instead of light. With such an analog, pairs of phonons served as stand-ins for the entangled particles in a real black hole.

The experiment consisted of chilling a group of rubidium atoms and using lasers to create a Bose-Einstein condensate. The atoms were then forced to flow in a way that resembled the trapping that occurs with a real black hole. With such a flow, sound waves were unable to escape under normal circumstances. In their experiment, the researchers were able to force one of a pair of phonons to fall into the flow of atoms while the other was allowed to escape. As they did so, the researchers took measurements of both phonons, allowing them to estimate their temperature to .035 billionths of a kelvin. And in so doing, they found it agreed with Hawking’s prediction. They also found agreement that the radiation from such a system would be thermal.

The work does not prove the theory, of course; the only way to do that will be to develop technology capable of actually measuring the radiation from a real black hole—but it does give the theory more credence.

Did Ancient Supernovae Prompt Human Ancestors To Walk Upright?

Did ancient supernovae induce proto-humans to walk on two legs, eventually resulting in Homo sapiens with hands free to build cathedrals, design rockets and snap iPhone selfies?

A paper published today in the Journal of Geology makes the case: Supernovae bombarded Earth with cosmic energy starting as many as 8 million years ago, with a peak some 2.6 million years ago, initiating an avalanche of electrons in the lower atmosphere and setting off a chain of events that feasibly ended with bipedal hominins such as Homo habilis, dubbed “handy man.”

The authors believe atmospheric ionization probably triggered an enormous upsurge in cloud-to-ground lightning strikes that ignited forest fires around the globe. These infernos could be one reason ancestors of Homo sapiens developed bipedalism — to adapt in savannas that replaced torched forests in northeast Africa.

“It is thought there was already some tendency for hominins to walk on two legs, even before this event,” said lead author Adrian Melott, professor emeritus of physics & astronomy at the University of Kansas. “But they were mainly adapted for climbing around in trees. After this conversion to savanna, they would much more often have to walk from one tree to another across the grassland, and so they become better at walking upright. They could see over the tops of grass and watch for predators. It’s thought this conversion to savanna contributed to bipedalism as it became more and more dominant in human ancestors.”

Based on a “telltale” layer of iron-60 deposits lining the world’s sea beds, astronomers have high confidence supernovae exploded in Earth’s immediate cosmic neighborhood — between 100 and only 50 parsecs (163 light years) away — during the transition from the Pliocene Epoch to the Ice Age.

“We calculated the ionization of the atmosphere from cosmic rays which would come from a supernova about as far away as the iron-60 deposits indicate,” Melott said. “It appears that this was the closest one in a much longer series. We contend it would increase the ionization of the lower atmosphere by 50-fold. Usually, you don’t get lower-atmosphere ionization because cosmic rays don’t penetrate that far, but the more energetic ones from supernovae come right down to the surface — so there would be a lot of electrons being knocked out of the atmosphere.”

According to Melott and co-author Brian Thomas of Washburn University, ionization in the lower atmosphere meant an abundance of electrons would form more pathways for lightning strikes.

“The bottom mile or so of atmosphere gets affected in ways it normally never does,” Melott said. “When high-energy cosmic rays hit atoms and molecules in the atmosphere, they knock electrons out of them — so these electrons are running around loose instead of bound to atoms. Ordinarily, in the lightning process, there’s a buildup of voltage between clouds or the clouds and the ground — but current can’t flow because not enough electrons are around to carry it. So, it has to build up high voltage before electrons start moving. Once they’re moving, electrons knock more electrons out of more atoms, and it builds to a lightning bolt. But with this ionization, that process can get started a lot more easily, so there would be a lot more lightning bolts.”

The KU researcher said the probability that this lightning spike touched off a worldwide upsurge in wildfires is supported by the discovery of carbon deposits found in soils that correspond with the timing of the cosmic-ray bombardment.

“The observation is that there’s a lot more charcoal and soot in the world starting a few million years ago,” Melott said. “It’s all over the place, and nobody has any explanation for why it would have happened all over the world in different climate zones. This could be an explanation. That increase in fires is thought to have stimulated the transition from woodland to savanna in a lot of places — where you had forests, now you had mostly open grassland with shrubby things here and there. That’s thought to be related to human evolution in northeast Africa. Specifically, in the Great Rift Valley where you get all these hominin fossils.”

Melott said no such event is likely to occur again anytime soon. The nearest star capable of exploding into a supernova in the next million years is Betelgeuse, some 200 parsecs (652 light years) from Earth.

“Betelgeuse is too far away to have effects anywhere near this strong,” Melott said. “So, don’t worry about this. Worry about solar proton events. That’s the danger for us with our technology — a solar flare that knocks out electrical power. Just imagine months without electricity.”

New Clues About How Ancient Galaxies Lit Up The Universe

NASA’s Spitzer Space Telescope has revealed that some of the Universe’s earliest galaxies were brighter than expected. The excess light is a by-product of the galaxies releasing incredibly high amounts of ionising radiation. The finding offers clues to the cause of the Epoch of Reionisation, a major cosmic event that transformed the universe from being mostly opaque to the brilliant starscape seen today. The new work appears in a paper in Monthly Notices of the Royal Astronomical Society.

Researchers report on observations of some of the first galaxies to form in the universe, less than 1 billion years after the big bang (or a little more than 13 billion years ago). The data show that in a few specific wavelengths of infrared light, the galaxies are considerably brighter than scientists anticipated. The study is the first to confirm this phenomenon for a large sampling of galaxies from this period, showing that these were not special cases of excessive brightness, but that even average galaxies present at that time were much brighter in these wavelengths than galaxies we see today.

No one knows for sure when the first stars in our universe burst to life. But evidence suggests that between about 100 million and 200 million years after the Big Bang, the Universe was filled mostly with neutral hydrogen gas that had perhaps just begun to coalesce into stars, which then began to form the first galaxies. By about 1 billion years after the big bang, the Universe had become a sparkling firmament. Something else had changed, too: Electrons of the omnipresent neutral hydrogen gas had been stripped away in a process known as ionisation. The Epoch of Reionisation — the changeover from a universe full of neutral hydrogen to one filled with ionised hydrogen — is well documented.

Before this Universe-wide transformation, long-wavelength forms of light, such as radio waves and visible light, traversed the universe more or less unencumbered. But shorter wavelengths of light — including ultraviolet light, X-rays and gamma rays — were stopped short by neutral hydrogen atoms. These collisions would strip the neutral hydrogen atoms of their electrons, ionising them.

But what could have possibly produced enough ionizing radiation to affect all the hydrogen in the Universe? Was it individual stars? Giant galaxies? If either were the culprit, those early cosmic colonisers would have been different than most modern stars and galaxies, which typically don’t release high amounts of ionising radiation. Then again, perhaps something else entirely caused the event, such as quasars — galaxies with incredibly bright centres powered by huge amounts of material orbiting supermassive black holes.

“It’s one of the biggest open questions in observational cosmology,” said Stephane De Barros, lead author of the study and a postdoctoral researcher at the University of Geneva in Switzerland. “We know it happened, but what caused it? These new findings could be a big clue.”

To peer back in time to the era just before the Epoch of Reionisation ended, Spitzer stared at two regions of the sky for more than 200 hours each, allowing the space telescope to collect light that had travelled for more than 13 billion years to reach us.

As some of the longest science observations ever carried out by Spitzer, they were part of an observing campaign called GREATS, short for GOODS Re-ionization Era wide-Area Treasury from Spitzer. GOODS (itself an acronym: Great Observatories Origins Deep Survey) is another campaign that performed the first observations of some GREATS targets. The study also used archival data from the NASA / ESA Hubble Space Telescope.

Using these ultra-deep observations by Spitzer, the team of astronomers observed 135 distant galaxies and found that they were all particularly bright in two specific wavelengths of infrared light produced by ionising radiation interacting with hydrogen and oxygen gases within the galaxies. This implies that these galaxies were dominated by young, massive stars composed mostly of hydrogen and helium. They contain very small amounts of “heavy” elements (like nitrogen, carbon and oxygen) compared to stars found in average modern galaxies.

These stars were not the first stars to form in the Universe (those would have been composed of hydrogen and helium only) but were still members of a very early generation of stars. The Epoch of Reionisation wasn’t an instantaneous event, so while the new results are not enough to close the book on this cosmic event, they do provide new details about how the Universe evolved at this time and how the transition played out.

“We did not expect that Spitzer, with a mirror no larger than a Hula-Hoop, would be capable of seeing galaxies so close to the dawn of time,” said Michael Werner, Spitzer’s project scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California. “But nature is full of surprises, and the unexpected brightness of these early galaxies, together with Spitzer’s superb performance, puts them within range of our small but powerful observatory.”

The NASA / CSA / ESA James Webb Space Telescope, set to launch in 2021, will study the Universe in many of the same wavelengths observed by Spitzer. But where Spitzer’s primary mirror is only 85 centimetres in diameter, Webb’s is 6.5 metres — about 7.5 times larger — enabling Webb to study these galaxies in far greater detail. In fact, Webb will try to detect light from the first stars and galaxies in the Universe. The new study shows that due to their brightness in those infrared wavelengths, the galaxies observed by Spitzer will be easier for Webb to study than previously thought.

“These results by Spitzer are certainly another step in solving the mystery of cosmic reionisation,” said Pascal Oesch, an assistant professor at the University of Geneva and a co-author on the study. “We now know that the physical conditions in these early galaxies were very different than in typical galaxies today. It will be the job of the James Webb Space Telescope to work out the detailed reasons why.”

Spinning Black Hole Sprays Light-Speed Plasma Clouds Into Space

Astronomers have discovered rapidly swinging jets coming from a black hole almost 8000 light-years from Earth.

Published today in the journal Nature, the research shows jets from V404 Cygni’s black hole behaving in a way never seen before on such short timescales.

The jets appear to be rapidly rotating with high-speed clouds of plasma — potentially just minutes apart — shooting out of the black hole in different directions.

Lead author Associate Professor James Miller-Jones, from the Curtin University node of the International Centre for Radio Astronomy Research (ICRAR), said black holes are some of the most extreme objects in the Universe.

“This is one of the most extraordinary black hole systems I’ve ever come across,” Associate Professor Miller-Jones said.

“Like many black holes, it’s feeding on a nearby star, pulling gas away from the star and forming a disk of material that encircles the black hole and spirals towards it under gravity.

“What’s different in V404 Cygni is that we think the disk of material and the black hole are misaligned. “This appears to be causing the inner part of the disk to wobble like a spinning top and fire jets out in different directions as it changes orientation.”

V404 Cygni was first identified as a black hole in 1989 when it released a big outburst of jets and radiation.

Astronomers looking at archival photographic plates then found previous outbursts in observations from 1938 and 1956.

Associate Professor Miller-Jones said that when V404 Cygni experienced another very bright outburst in 2015, lasting for two weeks, telescopes around the world tuned in to study what was going on.

“Everybody jumped on the outburst with whatever telescopes they could throw at it,” he said.

“So we have this amazing observational coverage.”

When Associate Professor Miller-Jones and his team studied the black hole, they saw its jets behaving in a way never seen before.

Where jets are usually thought to shoot straight out from the poles of black holes, these jets were shooting out in different directions at different times.

And they were changing direction very quickly — over no more than a couple of hours.

Associate Professor Miller-Jones said the change in the movement of the jets was because of the accretion disk — the rotating disk of matter around a black hole.

He said V404 Cygni’s accretion disk is 10 million kilometres wide, and the inner few thousand kilometres was puffed up and wobbling during the bright outburst.

“The inner part of the accretion disk was precessing and effectively pulling the jets around with it,” Associate Professor Miller-Jones said.

“You can think of it like the wobble of a spinning top as it slows down — only in this case, the wobble is caused by Einstein’s theory of general relativity.”

The research used observations from the Very Long Baseline Array, a continent-sized radio telescope made up of 10 dishes across the United States, from the Virgin Islands in the Caribbean to Hawaii.

Co-author Alex Tetarenko — a recent PhD graduate from the University of Alberta and currently an East Asian Observatory Fellow working in Hawaii — said the speed the jets were changing direction meant the scientists had to use a very different approach to most radio observations.

“Typically, radio telescopes produce a single image from several hours of observation,” she said.

“But these jets were changing so fast that in a four-hour image we just saw a blur.

“It was like trying to take a picture of a waterfall with a one-second shutter speed.” Instead, the researchers produced 103 individual images, each about 70 seconds long, and joined them together into a movie.

“It was only by doing this that we were able to see these changes over a very short time period,” Dr Tetarenko said.

Study co-author Dr Gemma Anderson, who is also based at ICRAR’s Curtin University node, said the wobble of the inner accretion disk could happen in other extreme events in the Universe too.

“Anytime you get a misalignment between the spin of a black hole and the material falling in, you would expect to see this when a black hole starts feeding very rapidly,” Dr Anderson said.

“That could include a whole bunch of other bright, explosive events in the Universe, such as supermassive black holes feeding very quickly or tidal disruption events, when a black hole shreds a star.”

Unusual Galaxies Defy Dark Matter Theory

After drawing both praise and skepticism, the team of astronomers who discovered NGC 1052-DF2 – the very first known galaxy to contain little to no dark matter – are back with stronger evidence about its bizarre nature.

Dark matter is a mysterious, invisible substance that typically dominates the makeup of galaxies; finding an object that’s missing dark matter is unprecedented, and came as a complete surprise.

“If there’s one object, you always have a little voice in the back of your mind saying, ‘but what if you’re wrong?’ Even though we did all the checks we could think of, we were worried that nature had thrown us for a loop and had conspired to make something look really special whereas it was really something more mundane,” said team leader Pieter van Dokkum, Sol Goldman Family Professor of Astronomy at Yale University.

Now, van Dokkum’s team has not one, but two, new studies supporting their initial observations, demonstrating that dark matter is in fact separable from galaxies.

Team members include Roberto Abraham, Professor of Astronomy and Astrophysics at the University of Toronto, Aaron Romanowsky, Associate Professor of Physics and Astronomy at San Jose State University, Charlie Conroy, Professor of Astronomy at Harvard University, and Shany Danieli, a graduate student at Yale University.

“The fact that we’re seeing something that’s just completely new is what’s so fascinating,” said Danieli, who first spotted the galaxy about two years ago. “No one knew that such galaxies existed, and the best thing in the world for an astronomy student is to discover an object, whether it’s a planet, a star, or a galaxy, that no one knew about or even thought about.”

What Happened Before the Big Bang?

A team of scientists has proposed a powerful new test for inflation, the theory that the universe dramatically expanded in size in a fleeting fraction of a second right after the Big Bang. Their goal is to give insight into a long-standing question: what was the universe like before the Big Bang?

Although cosmic inflation is well known for resolving some important mysteries about the structure and evolution of the universe, other very different theories can also explain these mysteries. In some of these theories, the state of the universe preceding the Big Bang – the so-called primordial universe – was contracting instead of expanding, and the Big Bang was thus a part of a Big Bounce.

To help decide between inflation and these other ideas, the issue of falsifiability – that is, whether a theory can be tested to potentially show it is false – has inevitably arisen. Some researchers, including Avi Loeb of the Center for Astrophysics | Harvard & Smithsonian (CfA) in Cambridge, Mass., have raised concerns about inflation, suggesting that its seemingly endless adaptability makes it all but impossible to properly test.

“Falsifiability should be a hallmark of any scientific theory. The current situation for inflation is that it’s such a flexible idea, it cannot be falsified experimentally,” Loeb said. “No matter what value people measure for some observable attribute, there are always some models of inflation that can explain it.”

Now, a team of scientists led by the CfA’s Xingang Chen, along with Loeb, and Zhong-Zhi Xianyu of the Physics Department of Harvard University, have applied an idea they call a “primordial standard clock” to the non-inflationary theories, and laid out a method that may be used to falsify inflation experimentally. The study will appear in Physical Review Letters as an Editors’ Suggestion.

In an effort to find some characteristic that can separate inflation from other theories, the team began by identifying the defining property of the various theories – the evolution of the size of the primordial universe.

“For example, during inflation, the size of the universe grows exponentially,” Xianyu said. “In some alternative theories, the size of the universe contracts. Some do it very slowly, while others do it very fast.

“The attributes people have proposed so far to measure usually have trouble distinguishing between the different theories because they are not directly related to the evolution of the size of the primordial universe,” he continued. “So, we wanted to find what the observable attributes are that can be directly linked to that defining property.”

The signals generated by the primordial standard clock can serve such a purpose. That clock is any type of heavy elementary particle in the primordial universe. Such particles should exist in any theory and their positions should oscillate at some regular frequency, much like the ticking of a clock’s pendulum.

The primordial universe was not entirely uniform. There were tiny irregularities in density on minuscule scales that became the seeds of the large-scale structure observed in today’s universe. This is the primary source of information physicists rely on to learn about what happened before the Big Bang. The ticks of the standard clock generated signals that were imprinted into the structure of those irregularities. Standard clocks in different theories of the primordial universe predict different patterns of signals, because the evolutionary histories of the universe are different.

“If we imagine all of the information we learned so far about what happened before the Big Bang is in a roll of film frames, then the standard clock tells us how these frames should be played,” Chen explained. “Without any clock information, we don’t know if the film should be played forward or backward, fast or slow, just like we are not sure if the primordial universe was inflating or contracting, and how fast it did so. This is where the problem lies. The standard clock put time stamps on each of these frames when the film was shot before the Big Bang, and tells us how to play the film.”

The team calculated how these standard clock signals should look in non-inflationary theories, and suggested how they should be searched for in astrophysical observations. “If a pattern of signals representing a contracting universe were found, it would falsify the entire inflationary theory,” Xianyu said.

The success of this idea lies with experimentation. “These signals will be very subtle to detect,” Chen said, “and so we may have to search in many different places. The cosmic microwave background radiation is one such place, and the distribution of galaxies is another. We have already started to search for these signals and there are some interesting candidates already, but we need more data.”

Many future galaxy surveys, such as US-lead LSST, European’s Euclid and the newly approved project by NASA, SphereX, are expected to provide high quality data that can be used toward the goal.

Read more at: https://phys.org/news/2019-03-big.html#jCp