Scientists inch closer than ever to signal from cosmic dawn

By: Thomas Schmitt Attorney on November 27, 2019 / comment : 0 Astronomy, Astrophysics, Universe

Around 12 billion years ago, the universe emerged from a great cosmic dark age as the first stars and galaxies lit up. With a new analysis of data collected by the Murchison Widefield Array (MWA) radio telescope, scientists are now closer than ever to detecting the ultra-faint signature of this turning point in cosmic history.

The Murchison Widefield Array radio telescope, a portion of which is pictured here, is searching  for a signal emitted during the formation of the first stars in the universe [Credit: Goldsmith/MWA Collaboration/Curtin University]

In a paper on the preprint site ArXiv and soon to be published in the Astrophysical Journal, researchers present the first analysis of data from a new configuration of the MWA designed specifically to look for the signal of neutral hydrogen, the gas that dominated the universe during the cosmic dark age. The analysis sets a new limit -- the lowest limit yet -- for the strength of the neutral hydrogen signal.

"We can say with confidence that if the neutral hydrogen signal was any stronger than the limit we set in the paper, then the telescope would have detected it," said Jonathan Pober, an assistant professor of physics at Brown University and corresponding author on the new paper. "These findings can help us to further constrain the timing of when the cosmic dark ages ended and the first stars emerged."

The research was led by Wenyang Li, who performed the work as a Ph.D. student at Brown. Li and Pober collaborated with an international group of researchers working with the MWA.

Despite its importance in cosmic history, little is known about the period when the first stars formed, which is known as the Epoch of Reionization (EoR). The first atoms that formed after the Big Bang were positively charged hydrogen ions -- atoms whose electrons were stripped away by the energy of the infant universe. As the universe cooled and expanded, hydrogen atoms reunited with their electrons to form neutral hydrogen. And that's just about all there was in the universe until about 12 billion years ago, when atoms started clumping together to form stars and galaxies. Light from those objects re-ionized the neutral hydrogen, causing it to largely disappear from interstellar space.

The goal of projects like the one happening at MWA is to locate the signal of neutral hydrogen from the dark ages and measure how it changed as the EoR unfolded. Doing so could reveal new and critical information about the first stars -- the building blocks of the universe we see today. But catching any glimpse of that 12-billion-year-old signal is a difficult task that requires instruments with exquisite sensitivity.

When it began operating in 2013, the MWA was an array of 2,048 radio antennas arranged across the remote countryside of Western Australia. The antennas are bundled together into 128 "tiles," whose signals are combined by a supercomputer called the Correlator. In 2016, the number of tiles was doubled to 256, and their configuration across the landscape was altered to improve their sensitivity to the neutral hydrogen signal. This new paper is the first analysis of data from the expanded array.

Neutral hydrogen emits radiation at a wavelength of 21 centimeters. As the universe has expanded over the past 12 billion years, the signal from the EoR is now stretched to about 2 meters, and that's what MWA astronomers are looking for. The problem is there are myriad other sources that emit at the same wavelength -- human-made sources like digital television as well as natural sources from within the Milky Way and from millions of other galaxies.

"All of these other sources are many orders of magnitude stronger than the signal we're trying to detect," Pober said. "Even an FM radio signal that's reflected off an airplane that happens to be passing above the telescope is enough to contaminate the data."

To home in on the signal, the researchers use a myriad of processing techniques to weed out those contaminants. At the same time, they account for the unique frequency responses of the telescope itself.

"If we look at different radio frequencies or wavelengths, the telescope behaves a little differently," Pober said. "Correcting for the telescope response is absolutely critical for then doing the separation of astrophysical contaminants and the signal of interest."

Those data analysis techniques combined with the expanded capacity of the telescope itself resulted in a new upper bound of the EoR signal strength. It's the second consecutive best-limit-to-date analysis to be released by MWA and raises hope that the experiment will one day detect the elusive EoR signal.

"This analysis demonstrates that the phase two upgrade had a lot of its desired effects and that the new analysis techniques will improve future analyses," Pober said. "The fact that MWA has now published back-to-back the two best limits on the signal gives momentum to the idea that this experiment and its approach has a lot of promise."

Source: Brown University [November 27, 2019]

Black hole nurtures baby stars a million light years away

By: Thomas Schmitt Attorney on November 25, 2019 / comment : 0 Astronomy, Astrophysics, Universe

Black holes are famous for ripping objects apart, including stars. But now, astronomers have uncovered a black hole that may have sparked the births of stars over a mind-boggling distance, and across multiple galaxies.

Credit: X-ray: NASA/CXC/INAF/R. Gilli et al.; Radio NRAO/VLA; Optical: NASA/STScI

If confirmed, this discovery, made with NASA's Chandra X-ray Observatory and other telescopes, would represent the widest reach ever seen for a black hole acting as a stellar kick-starter. The black hole seems to have enhanced star formation more than one million light-years away. (One light-year is equal to 6 trillion miles.)

"This is the first time we've seen a single black hole boost star birth in more than one galaxy at a time," said Roberto Gilli of the National Institute of Astrophysics (INAF) in Bologna, Italy, lead author of the study describing the discovery. "It's amazing to think one galaxy's black hole can have a say in what happens in other galaxies millions of trillions of miles away."

A black hole is an extremely dense object from which no light can escape. The black hole's immense gravity pulls in surrounding gas and dust, but particles from a small amount of that material can also get catapulted away instead at nearly the speed of light. These fast-moving particles form two narrow beams or "jets" near the poles of the black hole.

The supermassive black hole scientists observed in the new study is located in the center of a galaxy about 9.9 billion light-years from Earth. This galaxy has at least seven neighboring galaxies, according to observations with the European Southern Observatory's Very Large Telescope (VLT) and the Large Binocular Telescope (LBT).

Using the National Science Foundation's Karl Jansky Very Large Array, scientists had previously detected radio-wave emission from a jet of high-energy particles that is about a million light-years long. The jet can be traced back to the supermassive black hole, which Chandra detected as a powerful source of X-rays produced by hot gas swirling around the black hole. Gilli and colleagues also detected a diffuse cloud of X-ray emission surrounding one end of the radio jet. This X-ray emission is most likely from a gigantic bubble of hot gas heated by the interaction of the energetic particles in the radio jet with surrounding matter.


As the hot bubble expanded and swept through four neighboring galaxies, it could have created a shock wave that compressed cool gas in the galaxies, causing stars to form. All four galaxies are approximately the same distance, about 400,000 light-years, from the center of the bubble. The authors estimate that the star formation rate is between about two to five times higher than typical galaxies with similar masses and distance from Earth.

"The story of King Midas talks of his magic touch that can turn metal into gold," said co-author Marco Mignoli, also of INAF in Bologna, Italy. "Here we have a case of a black hole that helped turn gas into stars, and its reach is intergalactic."

Astronomers have seen many cases where a black hole affects its surroundings through "negative feedback"—in other words, curtailing the formation of new stars. This can occur when the black hole's jets inject so much energy into the hot gas of a galaxy, or galaxy cluster, that the gas can't cool down enough to make large numbers of stars.

In this newly discovered collection of galaxies, astronomers have found a less common example of "positive feedback," where the black hole's effects increase star formation. Moreover, when astronomers previously encountered positive feedback, it either involved increases in the star formation rate of 30% or less, or it occurred over scales of only about 20,000 to 50,000 light-years on a nearby companion galaxy. Whether the feedback is positive or negative depends on a delicate balance between the heating rate and cooling rate of a cloud. That is because clouds that are initially cooler when hit by a shock wave are more prone to experience positive feedback, and form more stars.

"Black holes have a well-earned reputation for being powerful and deadly, but not always," said co-author Alessandro Peca, formerly at INAF in Bologna and now a Ph.D. student at the University of Miami. "This is a prime example that they sometimes defy that stereotype and can be nurturing instead."

The researchers used a total of six days of Chandra observing time spread out over five months.

"It's only because of this very deep observation that we saw the hot gas bubble produced by the black hole," said co-author Colin Norman of the Johns Hopkins University in Baltimore, Maryland. "By targeting objects similar to this one, we may discover that positive feedback is very common in the formation of groups and clusters of galaxies."

A paper describing these results has been published in the most recent issue of the journal Astronomy and Astrophysics.

Source: Chandra X-ray Center [November 26, 2019]

Planets around a black hole?

By: Thomas Schmitt Attorney on November 24, 2019 / comment : 0 Astronomy, Astrophysics, Universe

Theoreticians in two different fields defied the common knowledge that planets orbit stars like the Sun. They proposed the possibility of thousands of planets around a supermassive black hole.

Artist's impression of planets orbiting a supermassive black hole [Credit: Kagoshima University]

"With the right conditions, planets could be formed even in harsh environments, such as around a black hole," says Keiichi Wada, a professor at Kagoshima University researching active galactic nuclei which are luminous objects energized by black holes.

According to the latest theories, planets are formed from fluffy dust aggregates in a protoplanetary disk around a young star. But young stars are not the only objects that possess dust disks. In a novel approach, the researchers focused on heavy disks around supermassive black holes in the nuclei of galaxies.

"Our calculations show that tens of thousands of planets with 10 times the mass of the Earth could be formed around 10 light-years from a black hole," says Eiichiro Kokubo, a professor at the National Astronomical Observatory of Japan who studies planet formation. "Around black holes there might exist planetary systems of astonishing scale."

Some supermassive black holes have large amounts of matter around them in the form of a heavy, dense disk. A disk can contain as much as a hundred thousand times the mass of the Sun worth of dust. This is a billion times the dust mass of a protoplanetary disk.

In a low temperature region of a protoplanetary disk, dust grains with ice mantles stick together and evolve into fluffy aggregates. A dust disk around a black hole is so dense that the intense radiation from the central region is blocked and low temperature regions are formed. The researchers applied the planet formation theory to circumnuclear disks and found that planets could be formed in several hundred million years.

Currently there are no techniques to detect these planets around black holes. However, the researchers expect this study to open a new field of astronomy.

The study is published in The Astrophysical Journal.

Author: Hitoshi Yamaoka | Source: National Astronomical Observatory of Japan [November 25, 2019]

The simultaneous merging of giant galaxies

By: Thomas Schmitt Attorney on November 20, 2019 / comment : 0 Astronomy, Astrophysics, Universe

An international research team led by scientists from Gottingen and Potsdam proved for the first time that the galaxy NGC 6240 contains three supermassive black holes. The unique observations, published in the journal Astronomy & Astrophysics, show the black holes close to each other in the core of the galaxy. The study points to simultaneous merging processes during the formation of the largest galaxies in the universe.

The irregular galaxy NGC 6240. New observations show that it harbours not two but three supermassive black holes at its core. The northern black hole (N) is active and was known before. The zoomed-in new high-spatial resolution image shows that the southern component consists of two supermassive black holes (S1 and S2). The green colour indicates the distribution of gas ionized by radiation surrounding the black holes. The red lines show the contours of the starlight from the galaxy and the length of the white bar corresponds to 1000 light years [Credit: P Weilbacher (AIP), NASA, ESA, the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration,   and A Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University)]

Massive Galaxies like the Milky Way typically consist of hundreds of billions of stars and host a black hole with a mass of several million up to several 100 million solar masses at their centres. The galaxy known as NGC 6240 is known as an irregular galaxy due to its particular shape. Until now, astronomers have assumed that it was formed by the collision of two smaller galaxies and therefore contains two black holes in its core. These galactic ancestors moved towards each other at velocities of several 100 km/s and are still in the process of merging. The galaxy system which is around 300 million light years away from us - close by cosmic standards - has been studied in detail at all wavelengths, and has so far been regarded as a prototype for the interaction of galaxies.

"Through our observations with extremely high spatial resolution we were able to show that the interacting galaxy system NGC 6240 hosts not two - as previously assumed - but three supermassive black holes in its centre," reports Professor Wolfram Kollatschny from the University of Gottingen, the lead author of the study. Each of the three heavyweights has a mass of more than 90 million Suns. They are located in a region of space less than 3000 light-years across, i.e. in less than one hundredth of the total size of the galaxy. "Up until now, such a concentration of three supermassive black holes had never been discovered in the universe," adds Dr Peter Weilbacher of the Leibniz Institute for Astrophysics Potsdam (AIP). "The present case provides evidence of a simultaneous merging process of three galaxies along with their central black holes."

The discovery of this triple system is of fundamental importance for understanding the evolution of galaxies over time. Until now it has not been possible to explain how the largest and most massive galaxies, which we know from our cosmic environment in the "present time", were formed just by normal galaxy interaction and merging processes over the course of the previous 14 billion years approximately, ie the age of our universe. "If, however, simultaneous merging processes of several galaxies took place, then the largest galaxies with their central supermassive black holes were able to evolve much faster," Peter Weilbacher summarizes. "Our observations provide the first indication of this scenario."

For the unique high-precision observations of the galaxy NGC 6240 using the 8 metre VLT, a telescope operated by the European Southern Observatory in Chile, the 3D MUSE spectrograph was used in spatial high-resolution mode together with four artificially generated laser stars and an adaptive optics system. Thanks to the sophisticated technology, images are obtained with a sharpness similar to that of the Hubble Space Telescope but additionally contain a spectrum for each image pixel. These spectra were decisive in determining the motion and masses of the supermassive black holes in NGC 6240.

The scientists assume that the observed, imminent merging of the supermassive black holes in a few million years will also generate very strong gravitational waves. In the foreseeable future, signals of similar objects can be measured with the planned satellite-based gravitational wave detector LISA and further merging systems can be discovered.

Source: University of Gottingen [November 21, 2019]

Blowtorch jets from a black hole drive starbirth

By: Thomas Schmitt Attorney on November 19, 2019 / comment : 0 Astronomy, Astrophysics, Universe

Supermassive black holes, weighing millions or even billions of times our Sun's mass, are still only a tiny fraction of the mass of the galaxies they inhabit. But in some cases, the central black hole is the tail wagging the dog. It seems that black holes can run hot or cold when it comes to either enhancing or squelching star birth inside a cluster of galaxies.

Phoenix Cluster [Credit: X-ray: NASA/CXC/MIT/M.McDonald et al;  Radio: NRAO/VLA; Optical: NASA/STScI]

Typically, giant black holes, pumping out energy via jets, keep interstellar gas too warm to condense and form stars. Now, astronomers have found a cluster of galaxies, called the Phoenix cluster, where stars are forming at a furious rate because of the black hole's influence. This stellar turboboost is apparently linked to less energetic jets from a central black hole that do not pump up the gas temperature. Instead, the gas loses energy as it glows in X-rays. The gas cools to where it can form large numbers of stars at a breathtaking rate. Where our Milky Way forms one star per year on average, newborn stars are popping out of this cool gas at a rate of about 500 solar masses per year in the Phoenix cluster.

Unraveling this mystery required the combined power of NASA's Hubble Space Telescope, NASA's Chandra X-ray Observatory, and the Very Large Array (VLA) radio observatory near Socorro, New Mexico.

The VLA radio data reveals jets blasting out from the vicinity of the central black hole. These jets inflated bubbles in the hot gas that are detected in X-rays by Chandra. Hubble resolves bright blue filaments of newborn stars in cavities between the hot jet and gas clouds. As the black hole has grown more massive and more powerful, its influence has been increasing.

Astronomers have confirmed the first example of a galaxy cluster where large numbers of stars are being born at its core. Using data from NASA space telescopes and a National Science Foundation radio observatory, researchers have gathered new details about how the most massive black holes in the universe affect their host galaxies.

Galaxy clusters are the largest structures in the cosmos that are held together by gravity, consisting of hundreds or thousands of galaxies embedded in hot gas, as well as invisible dark matter. The largest supermassive black holes known are in galaxies at the centers of these clusters.

For decades, astronomers have looked for galaxy clusters containing rich nurseries of stars in their central galaxies. Instead, they found powerful, giant black holes pumping out energy through jets of high-energy particles and keeping the gas too warm to form many stars.

Now, scientists have compelling evidence for a galaxy cluster where stars are forming at a furious rate, apparently linked to a less effective black hole in its center. In this unique cluster, the jets from the central black hole instead appear to be aiding in the formation of stars. Researchers used new data from NASA's Chandra X-ray Observatory and Hubble Space Telescope, and the NSF's Karl Jansky Very Large Array (VLA) to build on previous observations of this cluster.

"This is a phenomenon that astronomers had been trying to find for a long time," said Michael McDonald, astronomer at the Massachusetts Institute of Technology (MIT), who led the study. "This cluster demonstrates that, in some instances, the energetic output from a black hole can actually enhance cooling, leading to dramatic consequences."


The black hole is in the center of a galaxy cluster called the Phoenix Cluster, located about 5.8 billion light years from Earth in the Phoenix Constellation. The large galaxy hosting the black hole is surrounded by hot gas with temperatures of millions of degrees. The mass of this gas, equivalent to trillions of Suns, is several times greater than the combined mass of all the galaxies in the cluster.

This hot gas loses energy as it glows in X-rays, which should cause it to cool until it can form large numbers of stars. However, in all other observed galaxy clusters, bursts of energy driven by such a black hole keep most of the hot gas from cooling, preventing widespread star birth.

"Imagine running an air conditioner in your house on a hot day, but then starting a wood fire. Your living room can't properly cool down until you put out the fire," said co-author Brian McNamara of the University of Waterloo in Canada. "Similarly, when a black hole's heating ability is turned off in a galaxy cluster, the gas can then cool."

Evidence for rapid star formation in the Phoenix Cluster was previously reported in 2012 by a team led by McDonald. But deeper observations were required to learn details about the central black hole's role in the rebirth of stars in the central galaxy, and how that might change in the future.

By combining long observations in X-ray, optical, and radio light, the researchers gained a ten-fold improvement in the data quality compared to previous observations. The new Chandra data reveal that hot gas is cooling nearly at the rate expected in the absence of energy injected by a black hole. The new Hubble data show that about 10 billion solar masses of cool gas are located along filaments leading towards the black hole, and young stars are forming from this cool gas at a rate of about 500 solar masses per year. By comparison, stars are forming in the Milky Way galaxy at a rate of about one solar mass per year.

The VLA radio data reveal jets blasting out from the vicinity of the central black hole. These jets likely inflated bubbles in the hot gas that are detected in the Chandra data. Both the jets and bubbles are evidence of past rapid growth of the black hole. Early in this growth, the black hole may have been undersized, compared to the mass of its host galaxy, which would allow rapid cooling to go unchecked.

"In the past, outbursts from the undersized black hole may have simply been too weak to heat its surroundings, allowing hot gas to start cooling," said co-author Matthew Bayliss, who was a researcher at MIT during this study, but has recently joined the faculty at the University of Cincinnati. "But as the black hole has grown more massive and more powerful, its influence has been increasing."

The cooling can continue when the gas is carried away from the center of the cluster by the black hole's outbursts. At a greater distance from the heating influence of the black hole, the gas cools faster than it can fall back towards the center of the cluster. This scenario explains the observation that cool gas is located around the borders of the cavities, based on a comparison of the Chandra and Hubble data.

Eventually the outburst will generate enough turbulence, sound waves and shock waves (similar to the sonic booms produced by supersonic aircraft) to provide sources of heat and prevent further cooling. This will continue until the outburst ceases and the build-up of cool gas can recommence. The whole cycle may then repeat.

"These results show that the black hole has temporarily been assisting in the formation of stars, but when it strengthens its effects will start to mimic those of black holes in other clusters, stifling more star birth," said co-author Mark Voit of Michigan State University in East Lansing, Michigan.

The lack of similar objects shows that clusters and their enormous black holes pass through the rapid star formation phase relatively quickly.

A paper describing these results was published in a recent issue of The Astrophysical Journal, and a preprint is available online.

Source: ESA/Hubble Information Centre [November 19, 2019]

The measurements of the expansion of the universe don't add up

By: Thomas Schmitt Attorney on November 18, 2019 / comment : 0 Astronomy, Astrophysics, Universe

Physicists use two types of measurements to calculate the expansion rate of the universe, but their results do not coincide, which may make it necessary to touch up the cosmological model. "It's like trying to thread a cosmic needle," explains researcher Licia Verde of the University of Barcelona, co-author of an article on the implications of this problem.

Solving the discordant data on the expansion rate of the universe is like trying to thread a /cosmic needle/ where its hole is the H0 value measured today and the thread is brought by the model from the furthest Universe we can observe: the cosmic microwave background [Credit: NASA/JPL-Caltetch/ESA and the Planck Collaboration/SINC]

More than a hundred scientists met this summer at the Kavli Institute for Theoretical Physics at the University of California (USA) to try to clarify what is happening with the discordant data on the expansion rate of the universe, an issue that affects the very origin, evolution and fate of our cosmos. Their conclusions have been published in Nature Astronomy journal.

"The problem lies in the Hubble constant (H0), a parameter which value -it is actually not a constant because it changes with time- indicates how fast the Universe is currently expanding," points out cosmologist Licia Verde, an ICREA researcher at the Institute of Cosmos Sciences of the University of Barcelona (ICC-UB) and the main author of the article.

"There are different ways of measuring this quantity," she explains, "but they can be divided into two major classes: those relying on the Late Universe (the closest to us in space and time) and those based on the Early Universe, and they do not give exactly the same result."

A classic example of measurements in the late universe are those provided by the regular pulsations of cepheid stars, which the astronomer Henrietta Swan Leavitt already observed a century ago and which helped Edwin Hubble calculate distances between galaxies and prove in 1929 that the Universe is expanding.

The current analysis of the variable brightness of cepheids with space telescopes such as the Hubble, along with other direct observations of objects in our cosmic environment and more distant supernovae, indicate that the H0 value is approximately 73.9 kilometres per second per megaparsec (an astronomical unit equivalent to about 3.26 million light years).

However, measurements based on the early Universe provide an average H0 value of 67.4 km/s/Mpc. These other records, obtained with data from the European Space Agency's Planck Satellite and other instruments, are obtained indirectly on the basis of the success of the standard cosmological model (Lambda-CDM model), which proposes a Universe made up of 5 % atoms or ordinary matter, 27 % dark matter (made up of particles, as yet detected, that provide additional gravitational attraction so that galaxies can form and clusters of galaxies are held together) and 68 % dark energy, which is responsible for accelerating the expansion of the Universe.

"In particular, these measurements of the primordial Universe focus on the farthest light that can be observed: the cosmic microwave background, produced when the Universe was only 380,000 years old, in the so-called recombination era (where protons recombined with electrons to form atoms)," says Licia Verde.

Time Line of the Universe [Credit: NASA/WMAP Science Team]

The researcher highlights a relevant fact: "There are very different and independent ways (with totally different instruments and scientific tools) to measure the H0 on the basis of the early Universe, and the same goes for the late Universe. What is interesting is that all the measurements of one type are in mutual agreement with one another, at an exquisite precision of 1 or 2 %, as are those of the other type, with the same great precision; but when we compare the measurements of one class with those of the other, the discrepancy arises."

"It looks like a small difference, only 7%, but it is significant considering that we are talking about precisions of 1 or 2% in the value of the Hubble constant," as emphasised by Licia Verde, who jokes: "It is like trying to thread a 'cosmic needle' where its hole is the H0 value measured today and the thread is brought by the model from the furthest Universe we can observe: the cosmic microwave background."

In addition, she points out some of the consequences of the discrepancy: "The lower the H0 is, the older the Universe is. Its current age is calculated at about 13.8 billion years considering that the Hubble constant is 67 or 68 km/s/Mpc; but if its value were 74 km/s/Mpc, our universe would be younger: it would be approximately 12.8 billion years old."

Modifying the model in the early Universe

The authors point out in their study that this anomaly does not seem to depend on the instrument or method used for measuring, or on human equipment or sources. "If there are no errors in the data or measurements, could it be a problem with the model?" the researcher asks.

"After all, the H0 values of the primordial Universe class are based on the standard cosmological model, which is very well established, very successful, but which we can try to change a little to solve the discrepancy," says the expert. "However, we cannot tamper with the characteristics of the model that work very well".

If the data continue to confirm the problem, theoretical physicists seem to agree that the most promising route for solving it is to modify the model just before the light observed of the cosmic microwave background was formed, i.e. just before recombination (in which there was already 63 % dark matter, 15 % photons, 10 % neutrinos and 12 % atoms). One of the ideas proposed is that, shortly after the Big Bang, an intense episode of dark energy could have occurred that expanded the Universe faster than previously calculated.

"Although it is still highly speculative, with this fine-tuned model, the H0 value obtained with measurements based on the primordial Universe could coincide with local measurements," notes Licia Verde, who concludes: "It won't be easy, but in this way we could thread the cosmic needle without breaking what works well in the model."

Author: Enrique Sacristan | Source: Spanish Foundation for Science and Technology (FECYT) [November 18, 2019]

Zeroing in on baby exoplanets could reveal how they form

By: Thomas Schmitt Attorney on November 18, 2019 / comment : 0 Astronomy, Astrophysics, Universe

Twenty-four years ago, Swiss astronomers Michel Mayor and Didier Queloz discovered the first planet orbiting a sun-like star outside our solar system—a milestone recognised by this year's Nobel prize in physics. Today we know of thousands more 'exoplanets," and researchers are now trying to understand when and how they form.

The way that a young exoplanet interacts with its star's disc of dust and gas determines the type of exoplanet that will ultimately form [Credit: NASA/JPL-Caltech/D. Berry]

The known exoplanets are certainly an eclectic bunch. They range in size from small rocky planets, like Earth, to gas giants that are many times bigger than Jupiter.

Some have meandering orbits, whereas others orbit not one star but two. Some have the modest mass and temperatures that are thought necessary to support life, while some are hellish balls of heat and crushing gravity. Some exoplanets appear to orbit their stars alone, while others orbit along with several other planets, like Earth in our solar system.

The vast majority of those we've discovered so far, however, are Earth- to Jupiter-sized planets that orbit very close to their host stars—often closer than Mercury orbits the sun. Astronomers are trying to understand how these close-orbiting planets came into existence by studying examples in different—preferably early—stages of formation.

Hot Jupiters are gas giants that orbit their parent stars more closely than Mercury orbits our sun. One such exoplanet , Osiris, orbits its parent star so closely that its atmosphere is continually evaporating [Credit - NASA/European Space Agency/Alfred Vidal-Madjar (Institut d'Astrophysique de Paris, CNRS)]

But young, faint exoplanets are hard to make out amid the glare of a highly active parent star. As a group led by Dr. Jerome Bouvier at the Grenoble Institute of Planetology and Astrophysics in France asks on its website: "Have you ever tried to listen to Sibelius next to a jackhammer?"

To see through the noise, Dr. Bouvier and colleagues are employing some of the world's most powerful telescope arrays, such as the European Southern Observatory's Very Large Telescope Interferometer on the Paranal mountain in Chile. Meanwhile, computer simulations of how a young planet disturbs the disc of gas and dust surrounding its nascent star will help them know how to spot young exoplanets in real space.

Close-orbiting

The researchers hope that their project, SPIDI, will lead to the discovery of close-orbiting exoplanets as they are forming, when they are about a million years old. "One million years—that corresponds to about two days on the scale of a human lifetime," said Dr. Bouvier.

The darkest exoplanet known to date is TrES-2b, which is found 750 light years away from our solar system. It is so black that it reflects even less light than coal, and astronomers haven’t yet figured out why that is [Credit - NASA/JPL-Caltech/T. Pyle]

One and a half years in, the project is still too new to have delivered any results. But by measuring the properties of close-orbiting exoplanets in their baby phases, the researchers aim to understand how they are born.

The project will probably not shed light on the formation of exoplanets with other types of orbit, however. And the type of orbit is important, because it determines the conditions on an exoplanet's surface—and potentially whether it is habitable.

Each type of exoplanet and exoplanet orbit could be studied individually. But Professor Richard Alexander of the University of Leicester in the UK believes that by studying different types of exoplanets orbiting different stars there is less chance of missing important processes that help make up the big picture of planetary formation.

PSO J318.5-22, thought to be 12 million years old, is one of the only confirmed free floating exoplanets, meaning it does not orbit a star. These planets ‘gone rogue’ are suspected of being ejected from a star’s orbit because of competing gravitational forces or through impact with another body [Credit - N. Metcalfe & Pan-STARRS 1 Science Consortium]

"To use a very poor analogy: if you could only see one part of an elephant—its trunk, say—you would end up with a very different understanding of elephants to someone who could only see its toes," he said. "By looking at different types of (exoplanet) systems, we're trying our best to step back and look at the whole of the "planet-formation elephant," rather than just one part of it."

Star's disc

Somehow, the way that a young exoplanet interacts with its star's disc of dust and gas determines the type of exoplanet that will ultimately form. Prof. Alexander's project, BuildingPlanS, involves developing computer simulations that predict the effect of different formation processes.

These simulations can be tested against observations to see whether the processes they describe are accurate.

The approach is paying off. In one recent study, led by Prof. Alexander's colleague Dr. Dipierro at the University of Leicester, UK, the computer simulations suggested that a ring observed in the disc of a star called Elias 24 is the path cleared by an orbiting, as-yet unidentified, gas-giant planet.

Kepler-16b is the first confirmed example of a planet that orbits a binary star system - two stars that orbit each other. This means the planet has two suns, which it orbits every 228 days [Credit – NASA/JPL-Caltech]

To really learn something new about planetary formation, however, the researchers want to predict something that has not yet been observed. "Then we can use new observations to test the physics directly, and maximise the understanding we gain from all this new knowledge," said Prof. Alexander.

Astrophysicists know that, in the very beginning, planets form as dust and gas accumulate under gravity. But this earliest phase of planet formation is especially hard to study.

The trouble is that the dust and the gas around young stars each evolve in very complex ways, and studying how they form planets together requires a lot of expertise and computing power. Traditionally, therefore, dust and gas have been simulated as separate processes.

Knotted

But as Dr. Mario Flock of the Max Planck Institute for Astronomy in Heidelberg, Germany, points out, the two processes cannot be truly separated. For instance, the presence of dust can reduce turbulence in the gas, while the turbulence of the gas impacts the size and fragmentation of the dust grains.

Some exoplanets orbit pulsars - the dead remains of massive stars. PSR 1267+12 B, also named Poltergeist, is one such planet. It is part of a three-planet system that survived a supernova explosion and is now orbiting a pulsar in the constellation of Virgo [Credit - NASA/JPL-Caltech/R. Hurt (SSC)]

In a project called UFOS, Dr. Flock and colleagues are starting to unite gas and dust simulations for the first time, to accurately describe some of the earliest stages of planetary formation. Their hope is to explain some of the features seen in very young stellar disks—spirals and rings—as the footprints of embryonic dust grains clumping together.

The biggest challenge here, says Dr. Flock, is finding the right scales of time and space over which gas and dust interact with the most influence. "That requires huge expertise in magneto-hydrodynamics, dust coagulation, numerical tools and high-performance computing.

"If we succeed to link the sites of grain growth and planet formation with current observations—that would be the highest goal," he continued. "It would help us to understand what's currently happening in systems we observe now."

Author: Jon Cartwright | Source: Horizon: The EU Research & Innovation Magazine [November 18, 2019]

How to observe a 'black hole symphony' using gravitational wave astronomy

By: Thomas Schmitt Attorney on November 17, 2019 / comment : 0 Astronomy, Astrophysics, Universe

Shrouded in mystery since their discovery, the phenomenon of black holes continues to be one of the most mind-boggling enigmas in our universe.

A snapshot of the 3D gravitational waveform from a general relativistic simulation of binary black holes. Gravitational waves from such binary mergers are routinely observed by LIGO. With space missions such as LISA, the evolution of these binaries can be monitored years in advance, allowing multi-frequency constraints on astrophysical formations and tests of general relativity [Credit: Jani, K., Kinsey, M., Clark, M. Center for Relativistic Astrophysics, Georgia Institute of Technology]

In recent years, many researchers have made strides in understanding black holes using observational astronomy and an emerging field known as gravitational wave astronomy, first hypothesized by Albert Einstein, which directly measures the gravitational waves emitted by black holes.

Through these findings on black hole gravitational waves, which were first observed in 2015 by the Laser Interferometer Gravitational-Wave Observatories (LIGO) in Louisiana and Washington, researchers have learned exciting details about these invisible objects and developed theories and projections on everything from their sizes to their physical properties.

Still, limitations in LIGO and other observation technologies have kept scientists from grasping a more complete picture of black holes, and one of the largest gaps in knowledge concerns a certain type of black hole: those of intermediate-mass, or black holes that fall somewhere between supermassive (at least a million times greater than our sun) and stellar (think: smaller, though still 5 to 50 times greater than the mass of our sun).

That could soon change thanks to new research out of Vanderbilt on what's next for gravitational wave astronomy. The study, led by Vanderbilt astrophysicist Karan Jani and featured today as a letter in Nature Astronomy, presents a compelling roadmap for capturing 4- to 10-year snapshots of intermediate-mass black hole activity.

"Like a symphony orchestra emits sound across an array of frequencies, the gravitational waves emitted by black holes occur at different frequencies and times," said Jani. "Some of these frequencies are extremely high-bandwidth, while some are low-bandwidth, and our goal in the next era of gravitational wave astronomy is to capture multiband observations of both of these frequencies in order to 'hear the entire song,' as it were, when it comes to black holes."


Jani, a self-proclaimed "black hole hunter" who Forbes named to its 2017 30 Under 30 list in Science, was part of the team that detected the very first gravitational waves. He joined Vanderbilt as a GRAVITY postdoctoral fellow in 2019.

Along with collaborators at Georgia Institute of Technology, California Institute of Technology and the Jet Propulsion Laboratory at NASA, the new paper, "Detectability of Intermediate-Mass Black Holes in Multiband Gravitational Wave Astronomy," looks at the future of LIGO detectors alongside the proposed Laser Interferometer Space Antenna (LISA) space-mission, which would help humans get a step closer to understanding what happens in and around black holes.

"The possibility that intermediate mass black holes exist but are currently hidden from our view is both tantalizing and frustrating," said Deidre Shoemaker, co-author of the paper and professor in Georgia Tech's School of Physics. "Fortunately, there is hope as these black holes are ideal sources for future multiband gravitational wave astronomy."

LISA, a mission jointly led by the European Space Agency and NASA and planned for launch in the year 2034, would improve detection sensitivity for low-frequency gravitational waves. As the first dedicated space-based gravitational wave detector, LISA would provide a critical measurement of a previously unattainable frequency and enable the more complete observation of intermediate-mass black holes. In 2018, Vanderbilt physics and astronomy professor Kelly Holley-Bockelmann was appointed by NASA as the inaugural chair of the LISA Study Team.

"Inside black holes, all known understanding of our universe breaks down," added Jani. "With the high frequency already being captured by LIGO detectors and the low frequency from future detectors and the LISA mission, we can bring these data points together to help fill in many gaps in our understanding of black holes."

Author: Spencer Turney | Source: Vanderbilt University [November 18, 2019]

Nearly extreme black holes which attempt to regrow hair become bald again

By: Thomas Schmitt Attorney on November 15, 2019 / comment : 0 Astronomy, Astrophysics, Universe

The black holes of Einstein's theory of relativity can be completely described by just three parameters: their mass, spin angular momentum, and electric charge. Since two black holes that share these parameters cannot be distinguished, regardless of how they were made, black holes are said to "have no hair": they have no additional attributes that can be used to tell them apart.

An artist's conception of a spinning black hole with accretion flow and a jet [Credit: NASA/JPL-Caltech]

In the early 1970s the late Jacob Bekenstein provided a proof for the nonexistence of hair made of scalar fields given a set of assumptions on the properties of the latter. Researcher Lior Burko of Theiss Research said, "Since Bekenstein's proof, several papers found examples for scalar hair, and all these examples violate one or another of the assumptions made by Bekenstein. But in all cases, the hair was made of the scalar field itself."

Recently, it was shown that black holes that are charged by the maximum possible electric charge ("extreme black holes") can have an additional property, permanent hair that is made of a massless scalar field, and that this newly found hair can be observed from a great distance. "A massless scalar hair does not violate any of the assumptions underlying Bekenstein's proof. It was a big surprise for me when this new hair was found by Angelopoulos, Aretakis, and Gajic, so I wanted to look at it in greater detail. It is hair in a different sense than the kinds of hair that were found before. It is not the scalar field itself, but a certain integral on a derivative of the scalar field that is to be calculated on the surface of the black hole, on its event horizon," said Burko. The new hair can be observed at a great distance, by calculating a different quantity there.

"The measurement at a great distance that Angelopoulos, Aretakis, and Gajic found is strictly speaking precise only at infinitely late time," added Burko. "These would be observers who are very distant from the black hole, and who make the measurements in the infinite future. We wanted to see what happens at late but finite times, to see the time dependence of the measurement and how it approaches its asymptotic value. Another special thing about this new hair is that it is applies only for exactly extreme black holes, and we wanted to understand what happens when the black hole is nearly extreme, but not exactly extreme."

Burko and his colleagues Gaurav Khanna of the University of Massachusetts Dartmouth and his former student Subir Sabharwal, currently with the Eastamore Group, showed in a paper just published in Physical Review Research that measurements from a great distance are approaching the hair value, with the difference between them decaying with inverse time. But then they went beyond the original model used by Angelopoulos, Aretakis, and Gajic, and generalized the hair to black holes that rotate at the maximum possible spin rate or just close to it.

"In addition to a maximal value of charge, there is also a limit for how fast a black hole can spin. Black holes that spin at the maximal allowed rate are therefore also called extreme black holes. We describe both maximally charged and maximally spinning black holes by the name extreme black holes, as there are many similarities between the two. The new hair was originally found for a very useful toy model for black holes, specifically black holes that are spherically symmetric and electrically charged. But black holes in reality are neither. Instead, we wanted to find out if this hair can be found also for spinning black holes," said Burko. "In the movie Interstellar the monster black hole is nearly extreme. We wanted to see if Gargantua has hair."

The team used very intensive numerical simulations to generate their results. The simulations involved using dozens of the highest-end Nvidia graphics-processing-units (GPUs) with over 5,000 cores each, in parallel. "Each of these GPUs can perform as many as 7 trillion calculations per second; however, even with such computational capacity the simulations took many weeks to complete" said Khanna.

The team showed that for the nearly extreme spinning black holes the hair is a transient behavior. At intermediate times nearly extreme black holes behave like extreme black holes would, but at late times they behave like regular, non-extreme black holes. "Nearly extreme black holes can pretend that they are extreme for only so long. But eventually their non-extremality becomes manifest," Burko summarized. "Nearly extreme black holes that attempt to regrow hair will lose it and become bald again." The team also discusses the observational features, e.g., with gravitational waves observatories such as LIGO/VIRGO or LISA, of the smoking-gun detection of nearly extreme black holes.

Source: Theiss Research [November 15, 2019]

Astrophysicists find when galaxies rotate, size matters

By: Thomas Schmitt Attorney on November 15, 2019 / comment : 0 Astronomy, Astrophysics, Universe

A team of astrophysicists analysed 1418 galaxies and found that small ones are likely to spin on a different axis to large ones. The rotation was measured in relation to each galaxy's closest "cosmic filament" -- the largest structures in the universe.

A simulation showing a section of the Universe at its broadest scale. A web of cosmic filaments forms a lattice of matter, enclosing vast voids [Credit: Tiamat simulation, Greg Poole]

Filaments are massive thread-like formations, comprising huge amounts of matter -- including galaxies, gas and, modelling implies, dark matter. They can be 500 million light years long but just 20 million light years wide. At their largest scale, the filaments divide the universe into a vast gravitationally linked lattice interspersed with enormous dark matter voids.

"It's worth noticing that the spine of cosmic filaments is pretty much the highway of galactic migration, with many galaxies encountering and merging along the way," says lead researcher Charlotte Welker, an ASTRO 3D researcher working initially at the International Centre for Radio Astronomy Research (ICRAR) and now at McMaster University in Canada.

ASTRO 3D is the ARC Centre of Excellence in All Sky Astrophysics, based in Australia. The filaments are why the universe looks a little like a honeycomb, or a cosmic Aero chocolate bar.

Using data gathered by an instrument called the Sydney-AAO Multi-object Integral-field spectrograph (SAMI) at Australia's Anglo-Australian Telescope (AAT), Dr Welker, second author and ASTRO 3D principal investigator Professor Joss Bland-Hawthorn from the University of Sydney, and colleagues from Australia, the US, France and Korea studied each of the target galaxies and measured its spin in relation to its nearest filament.

They found that smaller ones tended to rotate in direct alignment to the filaments, while larger ones turned at right angles. The alignment changes from the first to the second as galaxies, drawn by gravity towards the spine of a filament, collide and merge with others, thus gaining mass. It is a phenomenon that Dr Welker likens to roller-skating in the company of a friend.

"The flip can be sudden," she says. "Merging with another galaxy can be all it takes. Imagine you are skating after a friend and catching up. If you grab your friend's hand while you are still moving faster, you will both start rotating on a vertical axis -- a spin perpendicular to your horizontal path. However, if a small cat -- a much lighter bit of matter -- runs after your friend and jumps on her she probably won't start spinning. It would take a lot of cats leaping on her at once to change her rotation."

Co-author Scott Croom from the University of Sydney, also an ASTRO 3D principal investigator, says the result offers insight into the deep structure of the Universe.

"Virtually all galaxies rotate, and this rotation is fundamental to how galaxies form," he says. "For example, most galaxies are in flat rotating disks, like our Milky Way. Our result is helping us to understand how that galactic rotation builds up across cosmic time."

He adds that a new instrument, called Hector, set to be installed at the Anglo Australian Telescope next year, will enable a significant expansion of research in the field. "Hector will be able to carry out surveys five times larger than SAMI," he says. "With this we will be able to dig into the details of this spin alignment to better understand the physics behind it."

The Milky Way, by the way, has a spin well aligned with its nearest cosmic filament, but belongs to a class of intermediate size galaxies that, over all, show no clear tendency towards parallel or perpendicular spins.

"It's like saying that there is no preference for tea or coffee among a group of people," says Dr Welker. "Individuals may still prefer either tea or coffee, but overall there is no general tendency towards coffee in the group."

The study is published in Monthly Notices of the Royal Astronomical Society.

Source: ARC Centre of Excellence for All Sky Astrophysics in 3D (ASTRO 3D) [November 15, 2019]

Two cosmic peacocks show violent history of the magellanic clouds

By: Thomas Schmitt Attorney on November 13, 2019 / comment : 0 Astronomy, Astrophysics, Universe

Two peacock-shaped gaseous clouds were revealed in the Large Magellanic Cloud (LMC) by observations with the Atacama Large Millimeter/submillimeter Array (ALMA). A team of astronomers found several massive baby stars in the complex filamentary clouds, which agrees well with computer simulations of giant collisions of gaseous clouds. The researchers interpret this to mean that the filaments and young stars are telltale evidence of violent interactions between the LMC and the Small Magellanic Cloud (SMC) 200 million years ago.

ALMA images of two molecular clouds: N159E-Papillon Nebula (left) and N159W South (right). Red and green show the distributions of molecular gas with different velocities mapped by 13CO emissions. The blue region in N159E-Papillon Nebula shows the ionized hydrogen gas observed with the Hubble Space Telescope. The blue part in N159W South shows the emissions from dust particles obtained with ALMA [Credit: ALMA (ESO/NAOJ/NRAO)/ Fukui et al./Tokuda et al./NASA-ESA Hubble Space Telescope]

Astronomers know that stars are formed in collapsing clouds in space. However, the formation processes of giant stars, 10 times or more massive than the Sun, are not well understood because it is difficult to pack such a large amount of material into a small region. Some researchers suggest that interactions between galaxies provide a perfect environment for massive star formation. Due to the colossal gravity, clouds in the galaxies are stirred, stretched, and often collide with each other. A huge amount of gas is compressed in an unusually small area, which could form the seeds of massive stars.

A research team used ALMA to study the structure of dense gas in N159, a bustling star formation region in the LMC. Thanks to ALMA's high resolution, the team obtained a detailed map of the clouds in two sub-regions, N159E-Papillon Nebula and N159W South.

Interestingly, the cloud structures in the two regions look very similar: fan-shaped filaments of gas extending to the north with the pivots in the southernmost points. The ALMA observations also found several massive baby stars in the filaments in the two regions.

Artist’s impression of the formation process of peacock-shaped clouds. After the collision of two clouds (left), complicated filamentary structures with a pivot in the bottom are formed in the boundary region (center), and a massive star is formed in the dense part with the ionized region shown in blue (right) [Credit: NAOJ]

"It is unnatural that in two regions separated by 150 light-years, clouds with such similar shapes were formed and that the ages of the baby stars are similar," says Kazuki Tokuda, a researcher at Osaka Prefecture University and the National Astronomical Observatory of Japan. "There must be a common cause of these features. Interaction between the LMC and SMC is a good candidate."

In 2017, Yasuo Fukui, a professor at Nagoya University and his team revealed the motion of hydrogen gas in the LMC and found that a gaseous component right next to N159 has a different velocity than the rest of the clouds. They suggested a hypothesis that the starburst is caused by a massive flow of gas from the SMC to the LMC, and that this flow originated from a close encounter between the two galaxies 200 million years ago.

The pair of peacock-shaped clouds in the two regions revealed by ALMA fits nicely with this hypothesis. Computer simulations show that many filamentary structures are formed in a short time after a collision of two clouds, which also backs this idea.

"For the first time, we uncovered a link between massive star formation and galaxy interactions in very sharp detail," says Fukui, the lead author of one of the research papers. "This is an important step in understanding the formation process of massive star clusters in which galaxy interactions have a big impact."

The findings are published in The Astrophysical Journal.

Source: National Institutes of Natural Sciences [November 14, 2019]

New study proposes light signature for detecting black hole mergers

By: Thomas Schmitt Attorney on November 13, 2019 / comment : 0 Astronomy, Astrophysics, Universe

Gravitational wave detectors are finding black hole mergers in the universe at the rate of one per week. If these mergers occur in empty space, researchers cannot see associated light that is needed to determine where they happened. However, a new study in The Astrophysical Journal Letters, led by scientists at the American Museum of Natural History and the City University of New York (CUNY), suggests that researchers might finally be able to see light from black hole mergers if the collisions happen in the presence of gas.

In this artist’s conception of a supermassive black hole at the heart of a galaxy, dust and gas form a swirling disk as they fall onto the hole, attracted by its gravity. A new study suggests researchers may be able to see light from the effect black hole mergers have on the gas in the disk [Credit: NASA/JPL-Caltech]

"With a light signature, astronomers could easily pinpoint the cosmic location of these mergers and study them in much more detail than is presently possible," said paper author Barry McKernan, a research associate in the Museum's Department of Astrophysics as well as a professor at the Borough of Manhattan Community College, CUNY, and a faculty member at CUNY's Graduate Center.

Black holes form when massive stars die. Much like dense objects sinking into a river on Earth, black holes tend to sink into regions of galaxies where gravity is strongest. It is believed that large numbers of black holes build up in the centers of galaxies, where a much larger, single, supermassive black hole lurks.

If individual small black holes pass close enough to each other as they orbit, their mutual gravity allows them to pair off and orbit each other, while also orbiting the central supermassive black hole. But a second random close encounter with another small black hole can easily break apart such a pairing.

"So the black holes dance, forming and breaking partnerships, but rarely getting close enough to each other to merge," said paper coauthor K.E. Saavik Ford, who is also a research associate in the Museum's Department of Astrophysics as well as a professor at the Borough of Manhattan Community College, CUNY, and a faculty member at CUNY's Graduate Center. "If a merger does happen, it will occur in the dark, with no associated light."

This picture changes if a large mass of gas falls onto the central supermassive black hole. This will result in a bright gas disk that envelops many of the black holes swarming around the central supermassive black hole and changes their orbits. Once inside the disk, the gas tugs on the black holes, causing them to spiral closer to the central supermassive black hole. If the smaller black holes pass close enough to each other, gas very quickly drives them together causing a merger and a burst of gravitational waves that can be detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO) in the United States and the European-based Virgo detector.

The new work by McKernan, Ford, and collaborators at the California Institute of Technology, Jet Propulsion Laboratory, University of Edinburgh, Columbia University, and University of Florida, suggests that it may be possible to see the effect of black hole mergers on the gas disk. The idea: once the black holes merge, they typically experience a kick at high speed (about 50 kilometers per second/112,000 miles per hour). Nearby gas attempts to follow the merger product, but smacks into neighboring disk gas causing a shock collision. If the gas disk is thin enough to let the light escape, the shock glow may be detectable with telescope sky surveys. The likelihood of detecting the shock glow against an already bright disk is best for large mass black hole mergers, around smaller-mass central black holes. The timescale during which the glow is released may help astronomers distinguish the black hole merger from random variations in the disk gas.

"LIGO has opened up this whole new way of letting us 'hear' how two black holes merge into one; and if we are correct, there may well now be a way we can see these otherwise invisible events happen," said co-author Nicholas Ross of the University of Edinburgh. "This would have deep implications for how we study black holes and for observational cosmology."

Co-author Matthew Graham of Caltech adds: "We've got lots of telescopes, such as ZTF [Zwicky Transient Facility], now covering large regions of the sky every night. If there is an optical counterpart, we should see it; if we don't find any then that also tells us something interesting."

Source: American Museum of Natural History [November 13, 2019]

Mysteries behind complex interstellar carbon molecules finally answered

By: Thomas Schmitt Attorney on November 12, 2019 / comment : 0 Astronomy, Astrophysics, Universe

Scientists have long been puzzled by the existence of so-called "buckyballs" - complex carbon molecules with a soccer-ball-like structure - throughout interstellar space. Now, a team of researchers from the University of Arizona has proposed a mechanism for their formation in a study published in the Astrophysical Journal Letters.

Artist's conception showing spherical carbon molecules known as buckyballs coming out from a planetary nebula —  material shed by a dying star. Researchers at the University of Arizona have now created these molecules under laboratory conditions thought to mimic those in their "natural" habitat in space [Credit: NASA/JPL-Caltech]

Carbon 60, or C60 for short, whose official name is Buckminsterfullerene, comes in spherical molecules consisting of 60 carbon atoms organized in five-membered and six-membered rings. The name "buckyball" derives from their resemblance to the architectural work of Richard Buckminster Fuller, who designed many dome structures that look similar to C60. Their formation was thought to only be possible in lab settings until their detection in space challenged this assumption.

For decades, people thought interstellar space was sprinkled with lightweight molecules only: mostly single atoms, two-atom molecules and the occasional nine or 10-atom molecules. This was until massive C60 and C70 molecules were detected a few years ago.

Researchers were also surprised to find that that they were composed of pure carbon. In the lab, C60 is made by blasting together pure carbon sources, such as graphite. In space, C60 was detected in planetary nebulae, which are the debris of dying stars. This environment has about 10,000 hydrogen molecules for every carbon molecule.

"Any hydrogen should destroy fullerene synthesis," said astrobiology and chemistry doctoral student Jacob Bernal, lead author of the paper. "If you have a box of balls, and for every 10,000 hydrogen balls you have one carbon, and you keep shaking them, how likely is it that you get 60 carbons to stick together? It's very unlikely."

Bernal and his co-authors began investigating the C60 mechanism after realizing that the transmission electron microscope, or TEM, housed at the Kuiper Materials Imaging and Characterization Facility at UArizona, was able to simulate the planetary nebula environment fairly well.

The TEM, which is funded by the National Science Foundation and NASA, has a serial number of "1" because it is the first of its kind in the world with its exact configuration. Its 200,000-volt electron beam can probe matter down to 78 picometers - scales too small for the human brain to comprehend - in order to see individual atoms. It operates under a vacuum with extremely low pressures. This pressure, or lack thereof, in the TEM is very close to the pressure in circumstellar environments.

"It's not that we necessarily tailored the instrument to have these specific kinds of pressures," said Tom Zega, associate professor in the UArizona Lunar and Planetary Lab and study co-author. "These instruments operate at those kinds of very low pressures not because we want them to be like stars, but because molecules of the atmosphere get in the way when you're trying to do high-resolution imaging with electron microscopes."

The team partnered with the U.S. Department of Energy's Argonne National Lab, near Chicago, which has a TEM capable of studying radiation responses of materials. They placed silicon carbide, a common form of dust made in stars, in the low-pressure environment of the TEM, subjected it to temperatures up to 1,830 degrees Fahrenheit and irradiated it with high-energy xenon ions.

Then, it was brought back to Tucson for researchers to utilize the higher resolution and better analytical capabilities of the UArizona TEM. They knew their hypothesis would be validated if they observed the silicon shedding and exposing pure carbon.

"Sure enough, the silicon came off, and you were left with layers of carbon in six-membered ring sets called graphite," said co-author Lucy Ziurys, Regents Professor of astronomy, chemistry and biochemistry. "And then when the grains had an uneven surface, five-membered and six-membered rings formed and made spherical structures matching the diameter of C60. So, we think we're seeing C60."

This work suggests that C60 is derived from the silicon carbide dust made by dying stars, which is then hit by high temperatures, shockwaves and high energy particles , leeching silicon from the surface and leaving carbon behind. These big molecules are dispersed because dying stars eject their material into the interstellar medium - the spaces in between stars - thus accounting for their presence outside of planetary nebulae. Buckyballs are very stable to radiation, allowing them to survive for billions of years if shielded from the harsh environment of space.

"The conditions in the universe where we would expect complex things to be destroyed are actually the conditions that create them," Bernal said, adding that the implications of the findings are endless.

"If this mechanism is forming C60, it's probably forming all kinds of carbon nanostructures," Ziurys said. "And if you read the chemical literature, these are all thought to be synthetic materials only made in the lab, and yet, interstellar space seems to be making them naturally."

If the findings are any sign, it appears that there is more the universe has to tell us about how chemistry truly works.

Author: Rachel Abraham | Source: University of Arizona [November 13, 2019]