Upcoming Asteroid Flyby Will Help NASA Planetary Defense Network

Upcoming Asteroid Flyby Will Help NASA Planetary Defense Network:

For the first time, NASA will use an actual space rock for an observational campaign to test NASA's network of observatories and scientists who work with planetary defense. The asteroid, named 2012 TC4, does not pose a threat to the Earth, but NASA is using it as a test object for an observational campaign because of its close flyby on Oct. 12, 2017.

NASA has conducted such preparedness drills rehearsing various aspects of an asteroid impact, such as deflection, evacuation and disaster relief, with other entities in the past. Traditionally, however, these exercises involved hypothetical impactors, prompting Vishnu Reddy of the University of Arizona's Lunar and Planetary Laboratory to propose a slightly more realistic scenario, one that revolves around an actual close approach of a near-Earth asteroid, or NEA. 

"The question is: How prepared are we for the next cosmic threat?" said Reddy, an assistant professor of planetary science at the Lunar and Planetary Laboratory. "So we proposed an observational campaign to exercise the network and test how ready we are for a potential impact by a hazardous asteroid."

NASA's Planetary Defense Coordination Office, or PDCO, the federal entity in charge of coordinating efforts to protect Earth from hazardous asteroids, accepted Reddy's idea to conduct an observational campaign as part of assessing its Earth-based defense network and identified the upcoming close approach of 2012 TC4 as a good opportunity to conduct the exercise. Reddy will assist Michael Kelley, who serves as a program scientist with NASA PDCO and as the lead on the exercise. 

The goal of the TC4 exercise is to recover, track and characterize 2012 TC4 as a potential impactor in order to exercise the entire system from observations, modeling, prediction and communication. 

Measuring between 30 and 100 feet, roughly the same size as the asteroid that exploded over Chelyabinsk, Russia, on Feb. 15, 2013, TC4 was discovered by the Pan-STARRS 1 telescope on Oct. 5, 2012, at Haleakala Observatory on Maui, Hawaii. Given its orbital uncertainty, the asteroid will pass as close as 6,800 kilometers (4,200 miles) above the Earth’s surface.

"This is a team effort that involves more than a dozen observatories, universities and labs across the globe so we can collectively learn the strengths and limitations of our planetary defense capabilities," said Reddy, who is coordinating the campaign for NASA PDCO. 

Since its discovery in 2012, the uncertainty in the asteroid's orbit has slowly increased, as it would for any asteroid as time passes. Therefore, the first order of business will be to "recover" the object — in other words, nail down its exact path. Reddy and his collaborators hope that depending on its predicted brightness, the asteroid would be visible again to large ground-based telescopes in early August. 

"One of the strengths of UA research is partnering with federal agencies or industry to work together in solving some of the grand challenges we face," said Kimberly Andrews Espy, the UA's senior vice president for research. "This project is a perfect example of matching UA capabilities — from our world-class imaging to our expertise in space sciences — with an external need."

The UA is home to the Catalina Sky Survey, one of the most prolific asteroid discoverers, and the Spacewatch project that recovers and tracks faint NEAs. Both teams will take part in the planetary defense exercise.

Credit: arizona.edu

Possible First Exomoon Detected

Possible First Exomoon Detected:

A signal has been spotted that might be the first moon detected outside our solar system, and researchers are gearing up to use the Hubble Space Telescope to confirm it. David Kipping at Columbia University in New York and his colleagues have been using the Kepler Space Telescope to search for moons around other worlds for years, but they haven’t found any yet. “We’ve had candidates in the past and investigated them, and most of them have evaporated,” said Kipping.

The candidate moon is known as Kepler-1625 b I and is observed around a star that lies some 4,000 light-years from Earth. On account of its large size, team members have dubbed it a "Nept-moon".

Kepler-1625 b is a candidate planet that Kepler, NASA’s flagship exoplanet mission, had previously observed. Periodic dips in the host star’s brightness indicated that a massive object was crossing the line of sight from the star to Earth; but the dips were lopsided, suggesting that perhaps instead of one object there were two: a Jupiter-sized planet with a Neptune-sized moon in tow. If this were indeed an ‘exomoon’, it would have been a long-awaited discovery. But it was still a big if.

“It wasn’t something we were planning on announcing, because at this point it’s only a candidate,” said Kipping, who would have preferred to be more cautious with the news. “It really only takes the slightest misstep in our language to miscommunicate the reality of what we have.”

If Kipping and his team are able to verify this detection, as well as being the first exomoon we’ve ever seen, it would be a much larger moon than we’ve ever seen before. This indicates that there may be even more types of moon than the many we’ve already observed.

“It would be analogous to the first exoplanet detections, which defied our prejudices from the solar system as well,” says Duncan Forgan at the University of St Andrews in the UK.

A paper about the candidate moon is published on the arXiv pre-print site.

Credit: newscientist.com, nature.com

Astrophysicists Map Out the Light Energy Contained Within the Milky Way

Astrophysicists Map Out the Light Energy Contained Within the Milky Way:

For the first time, a team of scientists have calculated the distribution of all light energy contained within the Milky Way, which will provide new insight into the make-up of our galaxy and how stars in spiral galaxies such as ours form. The study is published in the journal Monthly Notices of the Royal Astronomical Society.

This research, conducted by astrophysicists at the University of Central Lancashire (UCLan), in collaboration with colleagues from the Max Planck Institute for Nuclear Physics in Heidelberg, Germany and from the Astronomical Institute of the Romanian Academy, also shows how the stellar photons, or stellar light, within the Milky Way control the production of the highest energy photons in the Universe, the gamma-rays. This was made possible using a novel method involving computer calculations that track the destiny of all photons in the galaxy, including the photons that are emitted by interstellar dust, as heat radiation.

Previous attempts to derive the distribution of all light in the Milky Way based on star counts have failed to account for the all-sky images of the Milky Way, including recent images provided by the European Space Agency's Planck Space Observatory, which map out heat radiation or infrared light.

Lead author Prof Cristina Popescu from the University of Central Lancashire, said: "We have not only determined the distribution of light energy in the Milky Way, but also made predictions for the stellar and interstellar dust content of the Milky Way.”

By tracking all stellar photons and making predictions for how the Milky Way should appear in ultraviolet, visual and heat radiation, scientists have been able to calculate a complete picture of how stellar light is distributed throughout our Galaxy. An understanding of these processes is a crucial step towards gaining a complete picture of our Galaxy and its history.

The modelling of the distribution of light in the Milky Way follows on from previous research that Prof Popescu and Dr Richard Tuffs from the Max Planck Institute for Nuclear Physics conducted on modelling the stellar light from other galaxies, where the observer has an outside view.

Commenting on the research, Dr Tuffs, one of the co-authors of the paper, said: “It has to be noted that looking at galaxies from outside is a much easier task than looking from inside, as in the case of our Galaxy.”

Scientists have also been able to show how the stellar light within our Galaxy affects the production of gamma-ray photons through interactions with cosmic rays. Cosmic rays are high-energy electrons and protons that control star and planet formation and the processes governing galactic evolution. They promote chemical reactions in interstellar space, leading to the formation of complex and ultimately life-critical molecules.

Dr Tuffs added: "Working backwards through the chain of interactions and propagations, one can work out the original source of the cosmic rays."

The research, funded by the Leverhulme Trust, was strongly interdisciplinary, bringing together optical and infrared astrophysics and astro-particle physics. Prof Popescu notes: “We had developed some of our computational programs before this research started, in the context of modelling spiral galaxies, and we need to thank the UK's Science and Technology Facility Council (STFC) for their support in the development of these codes. This research would also not have been possible without the support of the Leverhulme Trust, which is greatly acknowledged.”

Credit: ras.org.uk

Asteroid 2017 NB7 to Fly By Earth on August 6

Asteroid 2017 NB7 to Fly By Earth on August 6:

A newly discovered Amor-type asteroid, designated 2017 NB7 is slated to pass by Earth on Sunday, Aug. 6 at a safe distance of 6.8 lunar distances (LD), or 2.6 million kilometers. The near-Earth object (NEO) will fly by our planet at approximately 10:43 UTC with a relative velocity of 5.98 km/s.

2017 NB7 was detected on July 1, 2017 by the Mount Lemmon Survey (MLS), which uses a 1.52 m cassegrain reflector telescope at Mount Lemmon Observatory in Arizona. MLS is one of the most prolific surveys when it comes to discovering new NEOs. It has detected more than 50,000 minor planets to date.

Astronomers reveal that 2017 NB7 has a diameter between 36 and 110 meters, and an absolute magnitude of 23.6. The asteroid has a semimajor axis of approximately 1.6 AU and orbits the sun every two years.

Besides 2017 NB7, one more space rock is expected to give fly by Earth on Aug. 6. The asteroid 2017 OJ7, which is 41-130 meters in diameter, will miss our planet at a much larger distance of nearly 30 LD (11.5 million kilometers).

Currently, there are 1,803 Potentially Hazardous Asteroids (PHAs) detected, however none of them is on a collision course with our planet. PHAs are asteroids larger than 100 meters that can come closer to Earth than 19.5 LD.

Astronomers Discover ‘Heavy Metal’ Supernova Rocking Out

Astronomers Discover ‘Heavy Metal’ Supernova Rocking Out:

Many rock stars don’t like to play by the rules, and a cosmic one is no exception. A team of astronomers has discovered that an extraordinarily bright supernova occurred in a surprising location. This “heavy metal” supernova discovery challenges current ideas of how and where such super-charged supernovas occur.

Supernovas are some of the most energetic events in the Universe. When a massive star runs out of fuel, it can collapse onto itself and create a spectacular explosion that briefly outshines an entire galaxy, dispersing vital elements into space.

In the past decade, astronomers have discovered about fifty supernovas, out of the thousands known, that are particularly powerful. These explosions are up to 100 times brighter than other supernovas caused by the collapse of a massive star.

Following the recent discovery of one of these “superluminous supernovas”, a team of astronomers led by Matt Nicholl from the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Mass., has uncovered vital clues about where some of these extraordinary objects come from.

Cambridge University’s Gaia Science Alerts team discovered this supernova, dubbed SN 2017egm, on May 23, 2017 with the European Space Agency’s Gaia satellite. A team led by Subo Dong of the Kavli Institute for Astronomy and Astrophysics at Peking University used the Nordic Optical Telescope to identify it as a superluminous supernova.

SN 2017egm is located in a spiral galaxy about 420 million light years from Earth, making it about three times closer than any other superluminous supernova previously seen. Dong realized that the galaxy was very surprising, as virtually all known superluminous supernovas have been found in dwarf galaxies that are much smaller than spiral galaxies like the Milky Way.

Building on this discovery, the CfA team found that SN 2017egm’s host galaxy has a high concentration of elements heavier than hydrogen and helium, which astronomers call “metals”. This is the first clear evidence for a metal-rich birthplace for a superluminous supernova. The dwarf galaxies that usually host superluminous supernovas are known to have a low metal content, which was thought to be an essential ingredient for making these explosions.

“Superluminous supernovas were already the rock stars of the supernova world,” said Nicholl. “We now know that some of them like heavy metal, so to speak, and explode in galaxies like our own Milky Way.”

“If one of these went off in our own Galaxy, it would be much brighter than any supernova in recorded human history and would be as bright as the full Moon,” said co-author Edo Berger, also of the CfA. “However, they’re so rare that we probably have to wait several million years to see one.”

The CfA researchers also found more clues about the nature of SN 2017egm. In particular, their new study supports the idea that a rapidly spinning, highly magnetized neutron star, called a magnetar, is likely the engine that drives the incredible amount of light generated by these supernovas.

While the brightness of SN 2017egm and the properties of the magnetar that powers it overlap with those of other superluminous supernovas, the amount of mass ejected by SN 2017egm may be lower than the average event. This difference may indicate that the massive star that led to SN 2017egm lost more mass than most superluminous supernova progenitors before exploding. The spin rate of the magnetar may also be slower than average.

These results show that the amount of metals has at most only a small effect on the properties of a superluminous supernova and the engine driving it. However, the metal-rich variety occurs at only about 10% of the rate of the metal-poor ones. Similar results have been found for bursts of gamma rays associated with the explosion of massive stars. This suggests a close association between these two types of objects.

From July 4th, 2017 until September 16th, 2017 the supernova is not observable because it is too close to the Sun. After that, detailed studies should be possible for at least a few more years.

“This should break all records for how long a superluminous supernova can be followed”, said co-author Raffaella Margutti of Northwestern University in Evanston, Illinois. “I’m excited to see what other surprises this object has in store for us.”

The CfA team observed SN 2017egm on June 18th with the 60-inch telescope at the Smithsonian Astrophysical Observatory’s Fred Lawrence Whipple Observatory in Arizona.

A paper by Matt Nicholl describing these results was recently accepted for publication in The Astrophysical Journal Letters, and is available online. In addition to Berger and Margutti, the co-authors of the paper are Peter Blanchard, James Guillochon, and Joel Leja, all of the CfA, and Ryan Chornock of Ohio University in Athens, Ohio.

A copy of the paper is available online.

Credit: cfa.harvard.edu

Gravity Waves Detected in Sun's Interior Reveal Rapidly Rotating Core

Gravity Waves Detected in Sun's Interior Reveal Rapidly Rotating Core:

Scientists using the ESA/NASA SOHO solar observatory have found long-sought gravity modes of seismic vibration that imply the Sun’s core is rotating four times faster than its surface. Just as seismology reveals Earth’s interior structure by the way in which waves generated by earthquakes travel through it, solar physicists use ‘helioseismology’ to probe the solar interior by studying sound waves reverberating through it. On Earth, it is usually one event that is responsible for generating the seismic waves at a given time, but the Sun is continuously ‘ringing’ owing to the convective motions inside the giant gaseous body.

Higher frequency waves, known as pressure waves (or p-waves), are easily detected as surface oscillations owing to sound waves rumbling through the upper layers of the Sun. They pass very quickly through deeper layers and are therefore not sensitive to the Sun’s core rotation.

Conversely, lower frequency gravity waves (g-waves) that represent oscillations of the deep solar interior have no clear signature at the surface, and thus present a challenge to detect directly.

In contrast to p-waves, for which pressure is the restoring force, buoyancy (gravity) acts as the restoring force of the gravity waves.

“The solar oscillations studied so far are all sound waves, but there should also be gravity waves in the Sun, with up-and-down, as well as horizontal motions like waves in the sea,” says Eric Fossat, lead author of the paper describing the result, published in Astronomy & Astrophysics.

“We’ve been searching for these elusive g-waves in our Sun for over 40 years, and although earlier attempts have hinted at detections, none were definitive. Finally, we have discovered how to unambiguously extract their signature.”

Eric and his colleagues used 16.5 years of data collected by SOHO’s dedicated ‘Global Oscillations at Low Frequencies’ (GOLF) instrument. By applying various analytical and statistical techniques, a regular imprint of the g-modes on the p-modes was revealed.

In particular, they looked at a p-mode parameter that measures how long it takes for an acoustic wave to travel through the Sun and back to the surface again, which is known to be 4 hours 7 minutes. A series of modulations was detected in this p-mode parameter that could be interpreted as being due to the g-waves shaking the structure of the core.

The signature of the imprinted g-waves suggests the core is rotating once every week, nearly four times faster than the observed surface and intermediate layers, which vary from 25 days at the equator to 35 days at the poles.

“G-modes have been detected in other stars, and now thanks to SOHO we have finally found convincing proof of them in our own star,” adds Eric. “It is really special to see into the core of our own Sun to get a first indirect measurement of its rotation speed. But, even though this decades long search is over, a new window of solar physics now begins.”

The rapid rotation has various implications, for example: is there any evidence for a shear zone between the differently rotating layers? What do the periods of the g-waves tell us about the chemical composition of the core? What implication does this have on stellar evolution and the thermonuclear processes in the core?

“Although the result raises many new questions, making an unambiguous detection of gravity waves in the solar core was the key aim of GOLF. It is certainly the biggest result of SOHO in the last decade, and one of SOHO’s all-time top discoveries,” says Bernhard Fleck, ESA’s SOHO project scientist.

ESA’s upcoming solar mission, Solar Orbiter will also ‘look’ into the solar interior but its main focus is to provide detailed insights into the Sun’s polar regions, and solar activity. Meanwhile ESA’s future planet-hunting mission, Plato, will investigate seismic activity in stars in the exoplanet systems it discovers, adding to our knowledge of relevant processes in Sun-like stars.

Credit: ESA

NASA Continues to Study Pulsars, 50 Years After Their Chance Discovery

NASA Continues to Study Pulsars, 50 Years After Their Chance Discovery:

A little bit of “scruff” in scientific data 50 years ago led to the discovery of pulsars – rapidly spinning dense stellar corpses that appear to pulse at Earth. Astronomer Jocelyn Bell made the chance discovery using a vast radio telescope in Cambridge, England. Although it was built to measure the random brightness flickers of a different category of celestial objects called quasars, the 4.5-acre telescope produced unexpected markings on Bell’s paper data recorder every 1.33730 seconds. The pen traces representing radio brightness revealed an unusual phenomenon.

“The pulses were so regular, so much like a ticking clock, that Bell and her supervisor Anthony Hewish couldn’t believe it was a natural phenomenon,” said Zaven Arzoumanian of NASA's Goddard Space Flight Center in Greenbelt, Maryland. “Once they found a second, third and fourth they started to think differently.”

The unusual stellar objects had been previously predicted but never observed. Today, scientists know of over 2,000 pulsars. These rotating “lighthouse” neutron stars begin their lives as stars between about seven and 20 times the mass of our sun. Some are found to spin hundreds of times per second, faster than the blades of a household blender, and they possess enormously strong magnetic fields.

Technology advances in the past half-century allowed scientists to study these compact stellar objects from space using different wavelengths of light, especially those much more energetic than the radio waves received by the Cambridge telescope. Several current NASA missions continue to study these natural beacons.

The Neutron star Interior Composition Explorer, or NICER, is the first NASA mission dedicated to studying pulsars. In a nod to the anniversary of Bell’s discovery, NICER observed the famous first pulsar, known today as PSR B1919+21.

NICER launched to the International Space Station in early June and started science operations last month. Its X-ray observations – the part of the electromagnetic spectrum in which these stars radiate both from their million-degree solid surfaces and from their strong magnetic fields – will reveal how nature’s fundamental forces behave within the cores of these objects, an environment that doesn’t exist and can’t be reproduced anywhere else. "What's inside a pulsar?" is one of many long-standing astrophysics questions about these ultra-dense, fast-spinning, powerfully magnetic objects.

The “stuff” of pulsars is a collection of particles familiar to scientists from over a century of laboratory studies on Earth – neutrons, protons, electrons, and perhaps even their own constituents, called quarks. However, under such extreme conditions of pressure and density, their behavior and interactions aren’t well understood. New, precise measurements, especially of the sizes and masses of pulsars are needed to pin down theories.

“Many nuclear-physics models have been developed to explain how the make-up of neutron stars, based on available data and the constraints they provide,” said Goddard’s Keith Gendreau, the principal investigator for NICER. “NICER’s sensitivity, X-ray energy resolution and time resolution will improve these by more precisely measuring their radii, to an order of magnitude improvement over the state of the art today.”

The mission will also pave the way for future space exploration by helping to develop a Global Positioning System-like capability for the galaxy. The embedded Station Explorer for X-ray Timing and Navigation Technology, or SEXTANT, demonstration will use NICER’s X-ray observations of pulsar signals to determine NICER's exact position in orbit.

“You can time the pulsations of pulsars distributed in many directions around a spacecraft to figure out where the vehicle is and navigate it anywhere,” said Arzoumanian, who is also the NICER science lead. “That’s exactly how the GPS system on Earth works, with precise clocks flown on satellites in orbit.”

Scientists have tested this method using computer and lab simulations. SEXTANT will demonstrate pulsar-based navigation for the first time in space.

NICER-SEXTANT is the first astrophysics mission dedicated to studying pulsars, 50 years after their discovery. “I think it is going to yield many more scientific discoveries than we can anticipate now,” said Gendreau.

NICER-SEXTANT is a two-in-one mission. NICER is an Astrophysics Mission of Opportunity within NASA's Explorer program, which provides frequent flight opportunities for world-class scientific investigations from space utilizing innovative, streamlined, and efficient management approaches within the heliophysics and astrophysics science areas. NASA's Space Technology Mission Directorate supports the SEXTANT component of the mission, demonstrating pulsar-based spacecraft navigation.

Credit: NASA

Cutting-edge Adaptive Optics Facility Sees First Light

Cutting-edge Adaptive Optics Facility Sees First Light:

The Unit Telescope 4 (Yepun) of ESO’s Very Large Telescope (VLT) has now been transformed into a fully adaptive telescope. After more than a decade of planning, construction and testing, the new Adaptive Optics Facility (AOF) has seen first light with the instrument MUSE, capturing amazingly sharp views of planetary nebulae and galaxies. The coupling of the AOF and MUSE forms one of the most advanced and powerful technological systems ever built for ground-based astronomy.

The Adaptive Optics Facility (AOF) is a long-term project on ESO’s Very Large Telescope (VLT) to provide an adaptive optics system for the instruments on Unit Telescope 4 (UT4), the first of which is MUSE (the Multi Unit Spectroscopic Explorer). Adaptive optics works to compensate for the blurring effect of the Earth’s atmosphere, enabling MUSE to obtain much sharper images and resulting in twice the contrast previously achievable. MUSE can now study even fainter objects in the Universe.

“Now, even when the weather conditions are not perfect, astronomers can still get superb image quality thanks to the AOF,” explains Harald Kuntschner, AOF Project Scientist at ESO.

Following a battery of tests on the new system, the team of astronomers and engineers were rewarded with a series of spectacular images. Astronomers were able to observe the planetary nebulae IC 4406, located in the constellation Lupus (The Wolf), and NGC 6369, located in the constellation Ophiuchus (The Serpent Bearer). The MUSE observations using the AOF showed dramatic improvements in the sharpness of the images, revealing never before seen shell structures in IC 4406.

The AOF, which made these observations possible, is composed of many parts working together. They include the Four Laser Guide Star Facility (4LGSF) and the very thin deformable secondary mirror of UT4. The 4LGSF shines four 22-watt laser beams into the sky to make sodium atoms in the upper atmosphere glow, producing spots of light on the sky that mimic stars. Sensors in the adaptive optics module GALACSI (Ground Atmospheric Layer Adaptive Corrector for Spectroscopic Imaging) use these artificial guide stars to determine the atmospheric conditions.

One thousand times per second, the AOF system calculates the correction that must be applied to change the shape of the telescope’s deformable secondary mirror to compensate for atmospheric disturbances. In particular, GALACSI corrects for the turbulence in the layer of atmosphere up to one kilometer above the telescope. Depending on the conditions, atmospheric turbulence can vary with altitude, but studies have shown that the majority of atmospheric disturbance occurs in this “ground layer” of the atmosphere.

“The AOF system is essentially equivalent to raising the VLT about 900 meters higher in the air, above the most turbulent layer of atmosphere,” explains Robin Arsenault, AOF Project Manager. “In the past, if we wanted sharper images, we would have had to find a better site or use a space telescope — but now with the AOF, we can create much better conditions right where we are, for a fraction of the cost!”

The corrections applied by the AOF rapidly and continuously improve the image quality by concentrating the light to form sharper images, allowing MUSE to resolve finer details and detect fainter stars than previously possible. GALACSI currently provides a correction over a wide field of view, but this is only the first step in bringing adaptive optics to MUSE. A second mode of GALACSI is in preparation and is expected to see first light early 2018. This narrow-field mode will correct for turbulence at any altitude, allowing observations of smaller fields of view to be made with even higher resolution.

“Sixteen years ago, when we proposed building the revolutionary MUSE instrument, our vision was to couple it with another very advanced system, the AOF,” says Roland Bacon, project lead for MUSE. “The discovery potential of MUSE, already large, is now enhanced still further. Our dream is becoming true.”

One of the main science goals of the system is to observe faint objects in the distant Universe with the best possible image quality, which will require exposures of many hours. Joël Vernet, ESO MUSE and GALACSI Project Scientist, comments: “In particular, we are interested in observing the smallest, faintest galaxies at the largest distances. These are galaxies in the making — still in their infancy — and are key to understanding how galaxies form.”

Furthermore, MUSE is not the only instrument that will benefit from the AOF. In the near future, another adaptive optics system called GRAAL will come online with the existing infrared instrument HAWK-I, sharpening its view of the Universe. That will be followed later by the powerful new instrument ERIS.

“ESO is driving the development of these adaptive optics systems, and the AOF is also a pathfinder for ESO’s Extremely Large Telescope,” adds Arsenault. “Working on the AOF has equipped us — scientists, engineers and industry alike — with invaluable experience and expertise that we will now use to overcome the challenges of building the ELT.”

Credit: ESO

New Simulations Could Help in Hunt for Massive Mergers of Neutron Stars, Black Holes

New Simulations Could Help in Hunt for Massive Mergers of Neutron Stars, Black Holes:

Now that scientists can detect the wiggly distortions in space-time created by the merger of massive black holes, they are setting their sights on the dynamics and aftermath of other cosmic duos that unify in catastrophic collisions. Working with an international team, scientists at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) have developed new computer models to explore what happens when a black hole joins with a neutron star – the superdense remnant of an exploded star.

The simulations, carried out in part at Berkeley Lab’s National Energy Research Scientific Computing Center (NERSC), are intended to help detectors home in on the gravitational-wave signals. Telescopes, too, can search for the brilliant bursts of gamma-rays and the glow of the radioactive matter that these exotic events can spew into surrounding space.

In separate papers published in a special edition of the scientific journal Classical and Quantum Gravity, Berkeley Lab and other researchers present the results of detailed simulations.

One of the studies models the first milliseconds (thousandths of a second) in the merger of a black hole and neutron star, and the other details separate simulations that model the formation of a disk of material formed within seconds of the merger, and of the evolution of matter that is ejected in the merger.

That ejected matter likely includes gold and platinum and a range of radioactive elements that are heavier than iron.

Any new information scientists can gather about how neutron stars rip apart in these mergers can help to unlock their secrets, as their inner structure and their likely role in seeding the universe with heavy elements are still shrouded in mystery.

“We are steadily adding more realistic physics to the simulations,” said – Foucart, who served as a lead author for one of the studies as a postdoctoral researcher in Berkeley Lab’s Nuclear Science Division.

“But we still don’t know what’s happening inside neutron stars. The complicated physics that we need to model make the simulations very computationally intensive.”

Foucart, who will soon be an assistant professor at the University of New Hampshire, added, “We are trying to move more toward actually making models of the gravitational-wave signals produced by these mergers,” which create a rippling in space-time that researchers hope can be detected with improvements in the sensitivity of experiments including Advanced LIGO, the Laser Interferometer Gravitational-Wave Observatory.

In February 2016, LIGO scientists confirmed the first detection of a gravitational wave, believed to be generated by the merger of two black holes, each with masses about 30 times larger than the sun.

The signals of a neutron star merging with black holes or another neutron star are expected to generate gravitational waves that are slightly weaker but similar to those of black hole–black hole mergers, Foucart said.

Daniel Kasen, a scientist in the Nuclear Science Division at Berkeley Lab and associate professor of physics and astronomy at UC Berkeley who participated in the research, said that inside neutron stars “there may be exotic states of matter unlike anything realized anywhere else in the universe.”

In some computer simulations the neutron stars were swallowed whole by the black hole, while in others there was a fraction of matter coughed up into space. This ejected matter is estimated to range up to about one-tenth of the mass of the sun.

While much of the matter gets sucked into the larger black hole that forms from the merger, “the material that gets flung out eventually turns into a kind of radioactive ‘waste,’” he said. “You can see the radioactive glow of that material for a period of days or weeks, from more than a hundred million light years away.” Scientists refer to this observable radioactive glow as a “kilonova.”

The simulations use different sets of calculations to help scientists visualize how matter escapes from these mergers. By modeling the speed, trajectory, amount and type of matter, and even the color of the light it gives off, astrophysicists can learn how to track down actual events.

The size range of neutron stars is set by the ultimate limit on how densely matter can be compacted, and neutron stars are among the most superdense objects we know about in the universe.

Neutron stars have been observed to have masses up to at least two times that of our sun but measure only about 12 miles in diameter, on average, while our own sun has a diameter of about 865,000 miles. At large enough masses, perhaps about three times the mass of the sun, scientists expect that neutron stars must collapse to form black holes.

A cubic inch of matter from a neutron star is estimated to weigh up to 10 billion tons. As their name suggests, neutron stars are thought to be composed largely of the neutrally charged subatomic particles called neutrons, and some models expect them to contain long strands of matter – known as “nuclear pasta” – formed by atomic nuclei that bind together.

Neutron stars are also expected to be almost perfectly spherical, with a rigid and incredibly smooth crust and an ultrapowerful magnetic field. They can spin at a rate of about 43,000 revolutions per minute (RPMs), or about five times faster than a NASCAR race car engine’s RPMs.

The researchers’ simulations showed that the radioactive matter that first escapes the black hole mergers may be traveling at speeds of about 20,000 to 60,000 miles per second, or up to about one-third the speed of light, as it is swung away in a long “tidal tail.”

“This would be strange material that is loaded with neutrons,” Kasen said. “As that expanding material cools and decompresses, the particles may be able to combine to build up into the heaviest elements.” This latest research shows how scientists might find these bright bundles of heavy elements.

“If we can follow up LIGO detections with telescopes and catch a radioactive glow, we may finally witness the birthplace of the heaviest elements in the universe,” he said. “That would answer one of the longest-standing questions in astrophysics.”

Most of the matter in a black hole–neutron star merger is expected to be sucked up by the black hole within a millisecond of the merger, and other matter that is not flung away in the merger is likely to form an extremely dense, thin, donut-shaped halo of matter.

The thin, hot disk of matter that is bound by the black hole is expected to form within about 10 milliseconds of the merger, and to be concentrated within about 15 to 70 miles of it, the simulations showed. This first 10 milliseconds appears to be key in the long-term evolution of these disks.

Over timescales ranging from tens of milliseconds to several seconds, the hot disk spreads out and launches more matter into space. “A number of physical processes – from magnetic fields to particle interactions and nuclear reactions – combine in complex ways to drive the evolution of the disk,” said Rodrigo Fernández, an assistant professor of physics at the University of Alberta in Canada who led one of the studies.

Simulations carried out on NERSC’s Edison supercomputer were crucial in understanding how the disk ejects matter and in providing clues for how to observe this matter, said Fernández, a former UC Berkeley postdoctoral researcher.

Eventually, it may be possible for astronomers scanning the night sky to find the “needle in a haystack” of radioactive kilonovae from neutron star mergers that had been missed in the LIGO data, Kasen said.

“With improved models, we are better able to tell the observers exactly which flashes of light are the signals they are looking for,” he said. Kasen is also working to build increasingly sophisticated models of neutron star mergers and supernovae through his involvement in the DOE Exascale Computing Project.

As the sensitivity of gravitational-wave detectors improves, Foucart said, it may be possible to detect a continuous signal produced by even a tiny bump on the surface of a neutron star, for example, or signals from theorized one-dimensional objects known as cosmic strings.

“This could also allow us to observe events that we have not even imagined,” he said.

Credit: lbl.gov

Hubble Detects Exoplanet with Glowing Water Atmosphere

Hubble Detects Exoplanet with Glowing Water Atmosphere:

An international team of researchers, led by the University of Exeter, made the new discovery by observing glowing water molecules in the atmosphere of the exoplanet WASP-121b with NASA’s Hubble Space Telescope. In order to study the gas giant’s stratosphere - a layer of atmosphere where temperature increases with higher altitudes - scientists used spectroscopy to analyse how the planet’s brightness changed at different wavelengths of light.

Water vapor in the planet's atmosphere, for example, behaves in predictable ways in response to different wavelengths of light, depending on the temperature of the water. At cooler temperatures, water vapor in the planet’s upper atmosphere blocks light of specific wavelengths radiating from deeper layers towards space. But at higher temperatures, the water molecules in the upper atmosphere glow at these wavelengths instead.

The phenomenon is similar to what happens with fireworks, which get their colors from chemicals emitting light. When metallic substances are heated and vaporized, their electrons move into higher energy states. Depending on the material, these electrons will emit light at specific wavelengths as they lose energy: sodium produces orange-yellow and strontium produces red in this process, for example.

The water molecules in the atmosphere of WASP-121b similarly give off radiation as they lose energy, but it is in the form of infrared light, which the human eye is unable to detect.

The research is published in leading scientific journal Nature.

“Theoretical models have suggested that stratospheres may define a special class of ultra-hot exoplanets, with important implications for the atmospheric physics and chemistry,” said Dr Tom Evans, lead author and research fellow at the University of Exeter. “When we pointed Hubble at WASP-121b, we saw glowing water molecules, implying that the planet has a strong stratosphere.”

WASP-121b, located approximately 900 light years from Earth, is a gas giant exoplanet commonly referred to as a ‘hot Jupiter’, although with a greater mass and radius than Jupiter, making it much puffier. The exoplanet orbits its host star every 1.3 days, and is around the closest distance it could be before the star's gravity would start ripping it apart.

This close proximity also means that the top of the atmosphere is heated to a blazing hot 2,500 degrees Celsius – the temperature at which iron exists in gas rather than solid form.

In Earth's stratosphere, ozone traps ultraviolet radiation from the sun, which raises the temperature of this layer of atmosphere. Other solar system bodies have stratospheres, too - methane is responsible for heating in the stratospheres of Jupiter and Saturn's moon Titan, for example. In solar system planets, the change in temperature within a stratosphere is typically less than 100 degrees Celsius. However, on WASP-121b, the temperature in the stratosphere rises by 1000 Celsius.

“We’ve measured a strong rise in the temperature of WASP-121b’s atmosphere at higher altitudes, but we don’t yet know what’s causing this dramatic heating,” says Nikolay Nikolov, co-author and research fellow at the University of Exeter. “We hope to address this mystery with upcoming observations at other wavelengths.”

Vanadium oxide and titanium oxide gases are candidate heat sources, as they strongly absorb starlight at visible wavelengths, similar to ozone absorbing UV radiation. These compounds are expected to be present in only the hottest of hot Jupiters, such as WASP-121b, as high temperatures are required to keep them in the gaseous state. Indeed, vanadium oxide and titanium oxide are commonly seen in brown dwarfs, ‘failed stars’ that have some commonalities with exoplanets.

Previous research spanning the past decade has indicated possible evidence for stratospheres on other exoplanets, but this is the first time that glowing water molecules have been detected, the clearest signal yet for an exoplanet stratosphere. It is one of the first results to come out of a new observing program being carried out by an international team of scientists, led by Associate Professor David Sing at the University of Exeter and Dr. Mercedes Lopez-Mórales at the Smithsonian Institution. The program has been awarded 800 hours to study and compare 20 different exoplanets, representing one of the largest time allocations for a single program in the entire 27 year history of Hubble.

“This new research is the smoking gun evidence scientists have been searching for when studying hot exoplanets. We have discovered this hot Jupiter has a stratosphere, a common feature seen in most of our solar system planets.” says Professor David Sing, co-author and Associate Professor of Astrophysics at the University of Exeter. “It’s a truly exciting find as we’re seeing dramatic differences planet-to-planet which is giving valuable clues in figuring out how planets behave under different conditions, and we’re only just scratching the surface of all the new Hubble data.”

NASA's forthcoming James Webb Space Telescope will be able to follow up on the atmospheres of planets like WASP-121b with higher sensitivity than any telescope currently in space.

"This super-hot exoplanet is going to be a benchmark for our atmospheric models, and will be a great observational target moving into the Webb era," said Hannah Wakeford, co-author and Research Fellow at the University of Exeter.

“A stratosphere in an ultra-hot gas giant exoplanet” is published in Nature on Thursday, August 3, 2017.

Credit: exeter.ac.uk

New Clue to Solving the Mystery of the Sun’s Hot Atmosphere

New Clue to Solving the Mystery of the Sun’s Hot Atmosphere:

The elemental composition of the Sun’s hot atmosphere known as the ‘corona’ is strongly linked to the 11-year solar magnetic activity cycle, a team of scientists from UCL, George Mason University and Naval Research Laboratory has revealed for the first time.

The study, published in Nature Communications and funded by the NASA Hinode program, shows that an increase in magnetic activity goes hand in hand with an increase of certain elements, such as Iron, in the solar corona. It is thought that the results could have significant implications for understanding the process leading to the heating of the Sun’s corona.

“Elemental composition is an important component of the flow of mass and energy into the atmospheres of the Sun and other stars. How that composition changes, if it does indeed change, as material flows from the surface of the Sun to its corona influences ideas we have about the heating and activity in atmospheres of other stars,” said Dr Deborah Baker (UCL Space & Climate Physics).

Through its 11-year cycle, the Sun moves from relatively quiet periods at solar minimum, to intense magnetic activity at solar maximum, when large numbers of sunspots appear and there is an increase in radiation. 

“Previously, many astronomers thought that elemental composition in a star’s atmosphere depended on the properties of the star that don’t change, such as the rotation rate or surface gravity. Our results suggest that it may also be linked with the magnetic activity and heating processes in the atmosphere itself, and they change with time, at least in the Sun,” said the study’s lead author, Dr David H. Brooks (George Mason University). 

The Sun’s surface, the photosphere, has a temperature of around 6000 degrees, but the outer atmosphere, the corona – best seen from Earth during total solar eclipses – is several hundred times hotter. How the corona is heated to millions of degrees is one of the most significant unsolved problems in astrophysics. The solution will help scientists better understand the heating of other stars.

“Why the Sun’s corona is so hot is a long-standing puzzle. It’s as if a flame were coming out of an ice cube. It doesn’t make any sense! Solar astronomers think that the key lies in the magnetic field, but there are still arguments about the details,” added Dr Brooks.

The team of scientists analysed observations from the Solar Dynamics Observatory at a time of low activity (solar minimum) starting in 2010, and through till 2014 when huge magnetic active regions crossing the solar disk were common. 

An unknown mechanism preferentially transports certain elements, such as Iron, into the corona instead of others, giving the corona its own distinctive elemental signature. The team think that the mechanism that separates the elements and supplies material to the corona may also be closely related to the transport of energy, and that understanding it may provide clues to explain the whole coronal heating process.

“Our observations started in 2010, near the last solar minimum, and so observations of the global coronal spectrum for a complete solar cycle have not been possible. The fact that we detected this variation of the Sun in a relatively small period of time really highlights the importance of observing stars over complete stellar cycles, which we hope to do in the future. Currently we tend to just have snapshots of stars, but these are potentially missing some important clues,” said Dr Baker. 

Whilst it would require long-term planning, the scientists expect that observing full stellar cycles would provide new insight into the nature of the atmospheres of stars and how they are heated to million degree temperatures.

Credit: ucl.ac.uk

Standard Model of the Universe Withstands Most Precise Test by Dark Energy Survey

Standard Model of the Universe Withstands Most Precise Test by Dark Energy Survey:

Astrophysicists have a fairly accurate understanding of how the universe ages: That’s the conclusion of new results from the Dark Energy Survey (DES), a large international science collaboration, including researchers from the Department of Energy’s SLAC National Accelerator Laboratory, that put models of cosmic structure formation and evolution to the most precise test yet.

The survey’s researchers analyzed light from 26 million galaxies to study how structures in the universe have changed over the past 7 billion years – half the age of the universe. The data were taken with the DECam, a 570-megapixel camera attached to the 4-meter Victor M. Blanco Telescope at the Cerro Tololo Inter-American Observatory in Chile.

Previously, the most precise test of cosmological models came from measurements with the European Space Agency’s Planck satellite of what is known as the cosmic microwave background (CMB) – a faint glow in the sky emitted 380,000 years after the Big Bang.

“While Planck looked at the structure of the very early universe, DES has measured structures that evolved much later,” said Daniel Gruen, a NASA Einstein postdoctoral fellow at the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC), a joint institute of Stanford University and SLAC. “The growth of these structures from the early ages of the universe until today agrees with what our models predict, showing that we can describe cosmic evolution very well.”

Gruen will present the results, which are based on the first year of data from the 5-year-long survey, today at the 2017 Division of Particles and Fields meeting of the American Physical Society at the DOE’s Fermi National Accelerator Laboratory.

KIPAC faculty member Risa Wechsler, a founding member of DES, said, “For the first time, the precision of key cosmological parameters coming out of a galaxy survey is comparable to the ones derived from measurements of the cosmic microwave background. This allows us to test our models independently and combine both approaches to obtain parameter values with unprecedented precision.” 

The standard model of cosmology, called Lambda-CDM, includes two key ingredients. Cold dark matter (CDM), an invisible form of matter that is five times more prevalent than regular matter, clumps together and is at the heart of the formation of structures such as galaxies and galaxy clusters. Lambda, the cosmological constant, describes the accelerated expansion of the universe, driven by an unknown force referred to as dark energy.

Astrophysicists need precise tests of the model because its ingredients are not completely certain. Dark matter has never been directly detected. Dark energy is even more mysterious, and it’s not known whether it actually is a constant or changes over time.

DES has now succeeded in carrying out such a precision test. The scientists used the fact that images of faraway galaxies get slightly distorted by the gravity of galaxies in the foreground – an effect known as weak gravitational lensing. This analysis led to the largest map ever constructed for the distribution of mass – both regular and dark matter – in the universe, as well as its evolution over time.

“Within an error bar of less than 5 percent, the combined Planck and DES results are consistent with Lambda-CDM,” Wechsler said. “This also means that, so far, we don’t need anything but a constant form of dark energy to describe the expansion history of the universe.” 

In addition to Gruen, who led the weak lensing working group, and Wechsler, whose group provided realistic simulations of the survey critical to testing several aspects of the cosmological analysis, a large number of KIPAC scientists, postdoctoral fellows, graduate students and alumni have made crucial contributions to DES – from building the instrument to developing theory and simulations and analyzing the data.

Postdoctoral fellow Elisabeth Krause, for example, leads the DES theory and combined probes working group. In that role, she led the charge in developing theoretical models that match the experimental precision obtained with the DES data. This involved writing computer codes that calculate what weak gravitational lensing should look like for a given model.

“Different people develop slightly different codes that are meant to do the same thing,” she said. “I helped bring code developers together to cross-check their results and to make sure that we get the most precise theory codes possible.”

Another key to the creation of the mass distribution map was to accurately determine the distances to the observed galaxies – information that is usually derived from independent surveys that analyze the properties of light coming from those objects or from exploding stars.

“We’ve shown that we can use the color of certain red galaxies – red is the color they would have if you were right in front of them – to determine how far they are away,” said SLAC staff scientist Eli Rykoff, who had a leading role in this part of the analysis. “It turns out that if we map where these red galaxies are in the sky, we can use them to calibrate the distances of the lenses and background galaxies used in the study.” 

In the near future, more DES data will allow astrophysicists to test their cosmological models with even more precision. The analysis of data collected during the first three years of the survey will begin soon, and the fifth year of observations will also soon be underway. 

With even better data, the researchers said, we might find out if the relatively simple Lambda-CDM model needs to be modified.

“The methods developed for DES and the experience its researchers are gaining along the way will also benefit the natural flow of ever-evolving experiments,” said KIPAC faculty member David Burke, head of SLAC’s DES group.

Both will prepare scientists for future surveys, including ones with the Large Synoptic Survey Telescope (LSST). With its 3.2-gigapixel camera, which is under construction at SLAC, astrophysicists will be able to explore the depths of our universe like never before.

DES is a collaboration of more than 400 scientists from 26 institutions in seven countries. Part of the funding has been provided by the U.S. Department of Energy Office of Science. A full list of collaborating institutions can be found at:

www.darkenergysurvey.org/collaboration.

Credit: slac.stanford.edu