Radio astronomers have used a radio telescope network the size of the Earth to zoom in on a unique phenomenon in a distant galaxy: a jet activated by a star being consumed by a supermassive black hole as seen in center of galaxy Messier 106 above. The record-sharp observations reveal a compact and surprisingly slowly moving source of radio waves, with details published in a paper in the journal Monthly Notices of the Royal Astronomical Society.

The artist's impression below shows the remains of a star that came too close to a supermassive black hole. Extremely sharp observations of the event Swift J1644+57 with the radio telescope network EVN (European VLBI Network) have revealed a remarkably compact jet, shown here in yellow. 

The international team, led by Jun Yang (Onsala Space Observatory, Chalmers University of Technology, Sweden), studied the new-born jet in a source known as Swift J1644+57 with the European VLBI Network (EVN), an Earth-size radio telescope array.

When a star moves close to a supermassive black hole it can be disrupted violently. About half of the gas in the star is drawn towards the black hole and forms a disc around it. During this process, large amounts of gravitational energy are converted into electromagnetic radiation, creating a bright source visible at many different wavelengths.
One dramatic consequence is that some of the star's material, stripped from the star and collected around the black hole, can be ejected in extremely narrow beams of particles at speeds approaching the speed of light. These so-called relativistic jets produce strong emission at radio wavelengths.

The first known tidal disruption event that formed a relativistic jet was discovered in 2011 by the NASA satellite Swift. Initially identified by a bright flare in X-rays, the event was given the name Swift J1644+57. The source was traced to a distant galaxy, so far away that its light took around 3.9 billion years to reach Earth.

Jun Yang and his colleagues used the technique of very long baseline interferometry (VLBI), where a network of detectors separated by thousands of kilometres are combined into a single observatory, to make extremely high-precision measurements of the jet from Swift J1644+57.

Three years of extremely precise EVN measurements of the jet from Swift J1644+5734 show a very compact source with no signs of motion. Lower panel: false colour contour image of the jet (the ellipse in the lower left corner shows the size of an unresolved source). Upper panel: position measurement with dates. One microarcsecond is one 3 600 000 000th part of a degree. Image credit: EVN/JIVE/J. Yang. Click for a full size image

"Using the EVN telescope network we were able to measure the jet's position to a precision of 10 microarcseconds. That corresponds to the angular extent of a 2-Euro coin on the Moon as seen from Earth. These are some of the sharpest measurements ever made by radio telescopes", says Jun Yang.

Thanks to the amazing precision possible with the network of radio telescopes, the scientists were able to search for signs of motion in the jet, despite its huge distance.

"We looked for motion close to the light speed in the jet, so-called superluminal motion. Over our three years of observations such movement should have been clearly detectable. But our images reveal instead very compact and steady emission - there is no apparent motion", continues Jun Yang.

The results give important insights into what happens when a star is destroyed by a supermassive black hole, but also how newly launched jets behave in a pristine environment. Zsolt Paragi, Head of User Support at the Joint Institute for VLBI ERIC (JIVE) in Dwingeloo, Netherlands, and member of the team, explains why the jet appears to be so compact and stationary.

"Newly formed relativistic ejecta decelerate quickly as they interact with the interstellar medium in the galaxy. Besides, earlier studies suggest we may be seeing the jet at a very small angle. That could contribute to the apparent compactness", he says.

The record-sharp and extremely sensitive observations would not have been possible without the full power of the many radio telescopes of different sizes which together make up the EVN, explains Tao An from the Shanghai Astronomical Observatory, P.R. China.

"While the largest radio telescopes in the network contribute to the great sensitivity, the larger field of view provided by telescopes like the 25-m radio telescopes in Sheshan and Nanshan (China), and in Onsala (Sweden) played a crucial role in the investigation, allowing us to simultaneously observe Swift J1644+57 and a faint reference source," he says.
Swift J1644+57 is one of the first tidal disruption events to be studied in detail, and it won't be the last.

"Observations with the next generation of radio telescopes will tell us more about what actually happens when a star is eaten by a black hole - and how powerful jets form and evolve right next to black holes", explains Stefanie Komossa, astronomer at the Max Planck Institute for Radio Astronomy in Bonn, Germany.

"In the future, new, giant radio telescopes like FAST (Five hundred meter Aperture Spherical Telescope) and SKA (Square Kilometre Array) will allow us to make even more detailed observations of these extreme and exciting events," concludes Jun Yang.

The Daily Galaxy via Chalmers University

Image credit: ESA/S. Komossa/Beabudai Design

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An open letter a "manifesto" of sorts, framed and singed by many of the great scientists and minds of our century --from Stephen Hawking to Frank Drake, Lord Martin Rees, to Caltech's Kip Thorne shown above-- was published this past April 2016 (and posted below), outlining the philosophical foundations that inspired the Breakthrough Starshot project and the search for the answer to the seminal question of the 21st Century: "Are we alone in the universe?"

As all the world knows by now, Yuri Milner, the Russian billionaire Internet investor, and Stephen Hawking, the famed astrophysicist, have revealed plans for an interstellar mission, $100 million Breakthrough Starshot, that would launch chip-sized robotic probes at more than 25 percent the speed of light for 20-year journeys on the 25-trillion mile trip our nearest star system, Alpha Centauri.

A huge ground-based laser will push the swarms of "laser sails" (up to tens of thousands of probes per year) propelled by light from the sun toward their exotic destination. Light exerts very little pressure, but prior projects have already successfully tested a number of solar sails — spacecraft propelled by light from the sun. As a prelude to the journey, Starshot could launch interplanetary missions to explore unsolved mysteries of our solar system — driving "space-chips" to Mars in roughly 30 minutes, or to the potential life bearing habitats of Enceladus, Titan, and Europa.

Scientists estimate the orange dwarf Alpha Centauri B system is slightly older than our 4.6-billion-year old solar system at anywhere from 4.8 billion to 6.5 billion years old. If life on a planet or moon in the habitable zone of Alpha Centauri B evolved similarly as it did on Earth, then primitive forms of life could already have flourished there when the young Earth collided with a Mars-sized object, forming our moon.

Jonathan McDowell from the Harvard-Smithsonian Center for Astrophysics said that Starshot is humanity's best chance of reaching Alpha Centauri, but has several hurdles to surmount. "The trick is accelerating with the pressure of light to accelerate a big, thin film of plastic that's shiny and catches the laser light so it goes faster," he said. "That's been demonstrated by the Japanese in interplanetary space a couple of years ago, but no one's got it really fast and we're talking about putting something a thousand times faster than any human artifact has ever done." McDowell said that it could take a decade to get a spacecraft to accelerate with a light sail, and longer to adapt the technology for the Starshot nanocraft. "I think 10 years to get to demonstrating something accelerated with a laser light sail, but a generation to be able to do it for real to Alpha Centauri."

Harvard physics professor Abraham Loeb said that the Starshot project is made possible by recent advances in the miniaturization of electronics: "This method we're talking about was conceived as soon as the laser was invented … The problem back then was that people thought that they needed to take humans along," he explained. "The big technological advance over the past decades has been the miniaturization of electronics, smart electronics. It was all driven by the cellphone industry. If you look at an iPhone and strip it from the case and the human interface, you're left with smart electronics that weigh roughly a gram, much lighter than anything else to use."

Loeb said that Starshot will be able to rapidly explore the Solar System. "Just to give you an example, to get to Pluto it would take three days instead of the 9½ years it took New Horizons to get there. If we launch at a fifth of the speed of light, it'll get there the same week," he said.

The seminal "Open Letter,"  the Alpha Centauri Manifesto,  below, lays down the foundational thinking behind the Breakthrough project.

The story of humanity is a story of great leaps out of Africa, across oceans, to the skies and into space. Since Apollo 11's ‘moonshot', we have been sending our machines ahead of us to planets, comets, even interstellar space. A mature civilization, like a mature individual, must ask itself this question. Is humanity defined by its divisions, its problems, its passing needs and trends? Or do we have a shared face, turned outward to the Universe?

In 1990, Voyager 1 swiveled its camera and captured the ‘Pale Blue Dot' - an image of Earth from six billion kilometers away. It was a mirror held up to our planet - home of water, life, and minds. A reminder that we share something precious and rare. But how rare, exactly? The only life? The only minds?

For the last half-century, small groups of scientists have listened valiantly for signs of life in the vast silence. But for government, academia, and industry, cosmic questions are astronomically far down the list of priorities. And that lengthens the odds of finding answers. It is hard enough to comb the Universe from the edge of the Milky Way; harder still from the edge of the public consciousness.

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Yet millions are inspired by these ideas, whether they meet them in science or science fiction. Because the biggest questions of our existence are at stake. Are we the Universe's only child - our thoughts its only thoughts? Or do we have cosmic siblings - an interstellar family of intelligence? As Arthur C. Clarke said, “In either case the idea is quite staggering.”

That means the search for life is the ultimate ‘win-win' endeavor. All we have to do is take part. Today we have search tools far surpassing those of previous generations. Telescopes can pick out planets across thousands of light years. The magic of Moore's law lets our computers sift data orders of magnitude faster than older mainframes - and ever quicker each year.

These tools are now reaping a harvest of discoveries. In the last few years, astronomers and the Kepler Mission have discovered thousands of planets beyond our solar system. It now appears that most stars host a planetary system. Many of them have a planet similar in size to our own, basking in the ‘habitable zone' where the temperature permits liquid water. There are likely billions of earth-like worlds in our galaxy alone. And with instruments now or soon available, we have a chance of finding out if any of these planets are true Pale Blue Dots home to water, life, even minds.

There has never been a better moment for a large-scale international effort to find life in the Universe. As a civilization, we owe it to ourselves to commit time, resources, and passion to this quest.

But as well as a call to action, this is a call to thought. When we find the nearest exo-Earth, should we send a probe? Do we try to make contact with advanced civilizations? Who decides? Individuals, institutions, corporations, or states? Or can we as species - as a planet - think together?

Three years ago, Voyager 1 broke the sun's embrace and entered interstellar space. The 20th century will be remembered for our travels within the solar system. With cooperation and commitment, the present century will be the time when we graduate to the galactic scale, seek other forms of life, and so know more deeply who we are.

But with current rocket propulsion technology, it would take tens or hundreds of millennia to reach our neighboring star system, Alpha Centauri. The stars, it seems, have set strict bounds on human destiny. Until now. In the last decade and a half, rapid technological advances have opened up the possibility of light-powered space travel at a significant fraction of light speed. This involves a ground-based light beamer pushing ultra-light nanocrafts miniature space probes attached to lightsails to speeds of up to 100 million miles an hour. Such a system would allow a flyby mission to reach Alpha Centauri in just over 20 years from launch, and beam home images of possible planets, as well as other scientific data such as analysis of magnetic fields.

Breakthrough Starshot aims to demonstrate proof of concept for ultra-fast light-driven nanocrafts, and lay the foundations for a first launch to Alpha Centauri within the next generation. Along the way, the project could generate important supplementary benefits to astronomy, including solar system exploration and detection of Earth-crossing asteroids.

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January 2016 also saw ‘first light' for Breakthrough Listen, with observations marking the start of the 10-year effort announced in July 2015 at London's Royal Society by Yuri Milner, Stephen Hawking, Lord Martin Rees, Ann Druyan, and Frank Drake. Hundreds of hours of observations have taken place using the Green Bank Radio Telescope in West Virginia and Lick Observatory's Automated Planet Finder in Mt. Hamilton, California.

Breakthrough Listen is the largest ever scientific research program aimed at finding evidence of civilizations beyond Earth. The scope and power of the search are on an unprecedented scale: The program includes a survey of the 1,000,000 closest stars to Earth. It scans the center of our galaxy and the entire galactic plane. Beyond the Milky Way, it listens for messages from the 100 closest galaxies to ours.

The instruments used are among the world's most powerful. They are 50 times more sensitive than existing telescopes dedicated to the search for intelligence.

The radio surveys cover 10 times more of the sky than previous programs. They also cover at least 5 times more of the radio spectrum and do it 100 times faster. They are sensitive enough to hear a common aircraft radar transmitting to us from any of the 1000 nearest stars.

They are also carrying out the deepest and broadest ever search for optical laser transmissions. These spectroscopic searches are 1000 times more effective at finding laser signals than ordinary visible light surveys. They could detect a 100 watt laser (the energy of a normal household bulb) from 25 trillion miles away.

Breakthrough Listen is releasing the first batch of data for public access at the Breakthrough Initiatives website. Data from the Green Bank Telescope is also available to users of UC Berkeley's SETI@home software.

Observations made so far by Breakthrough Listen include most of the stars within 16 light years of Earth (including stars such as 51 Pegasi that are known to host extra-solar planets), and a sample of stars between 16 and 160 light years away. This included nearby sun-like and giant stars as well as numerous binary stars. The search also targeted around 40 of the nearest spiral galaxies, including members of the Maffei Group in the direction of the constellation Cassiopeia. Stars within 16 light years accessible only from the Southern Hemisphere, such as Alpha Centauri, will be observed by the end of the year with the Parkes Telescope.

This year's Observation Plan for all three telescopes has been published and can be found at breakthroughinitiatives.org/OpenDataSearch

The Daily Galaxy via breakthroughinitiatives.org

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"This is just the tip of the iceberg," says Andrew Glikson from The Australian National University (ANU). "We've only found evidence for 17 impacts older than 2.5 billion years, but there could have been hundreds. Asteroid strikes this big result in major tectonic shifts and extensive magma flows. They could have significantly affected the way the Earth evolved."

This May, 2016, scientists have found evidence of a huge asteroid 20 to 30 kilometers across that struck the what is today Australia, creating a 400 kilometer-wide impact zone after breaking in two moments before it slammed into the Earth. The impact crater has long since disappeared. But a team of Aussie geophysicists has found the twin scars of the impacts the largest impact zone ever found on Earth hidden deep in the earth's crust.

Tiny glass beads called spherules, found in north-western Australia were formed from vaporized material from the asteroid impact, said Glikson. “Large impacts like these may have had a far more significant role in the Earth's evolution than previously thought,” Glikson said.

The exact date of the impacts remains unclear. The surrounding rocks are 300 to 600 million years old, but evidence of the type left by other meteorite strikes is lacking. “It's a mystery we can't find an extinction event that matches these collisions. I have a suspicion the impact could be older than 300 million years,” he added.

“There are two huge deep domes in the crust, formed by the Earth's crust rebounding after the huge impacts, and bringing up rock from the mantle below,” Glikson said. The two impact zones total more than 400 kilometres across, in the Warburton Basin in Central Australia. They extend through the Earth's crust, which is about 30 kilometres thick in this area.

"The impact would have triggered earthquakes orders of magnitude greater than terrestrial earthquakes, it would have caused huge tsunamis and would have made cliffs crumble," said Glikson, from the ANU Planetary Institute. "Material from the impact would have spread worldwide. These spherules were found in sea floor sediments that date from 3.46 billion years ago."

About 3.8 to 3.9 billion years ago the moon was struck by numerous asteroids, which formed the craters, called mare, that are still visible from Earth "Exactly where this asteroid struck the earth remains a mystery," Glikson said. "Any craters from this time on Earth's surface have been obliterated by volcanic activity and tectonic movements."

Glikson and Arthur Hickman from Geological Survey of Western Australia found the glass beads in a drill core from Marble Bar, in north-western Australia, in some of the oldest known sediments on Earth. The sediment layer, which was originally on the ocean floor, was preserved between two volcanic layers, which enabled very precise dating of its origin.

Glikson has been searching for evidence of ancient impacts for more than 20 years and immediately suspected the glass beads originated from an asteroid strike. Subsequent testing found the levels of elements such as platinum, nickel and chromium matched those in asteroids. There may have been many more similar impacts, for which the evidence has not been found, said Glikson.

The Daily Galaxy via Australian National University

Image credit: Top of page with thanks to Shutterstock

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Jupiter watchers have long known that the giant planet's ever-present polar auroras thousands of times brighter and many times bigger than Earth are powered by both electrically charged particles from the Sun colliding with Jupiter's magnetic field and a separate interaction between Jupiter and one of its many moons, called Io. But there are also auroral explosions on Jupiter, or periods of dazzling brightening, similar to auroral storms on Earth, that no one could definitively trace back to either of those known causes.

In the aurora-making interaction of Jupiter and Io, volcanoes on the small moon blast clouds of electrically charged atoms (ions) and electrons into a region surrounding Jupiter that's permeated by the planet's powerful magnetic field, thousands of times stronger than Earth's. Rotating along with its rapidly spinning planet, the magnetic field drags the material from Io around with it, causing strong electric fields at Jupiter's poles. The acceleration of the ions and electrons produce intense auroras that shine in almost all parts of the electromagnetic spectrum but most brightly in high-energy bands, like ultraviolet light and X-rays, that are invisible to unaided human eyes.

Io is the only known place in the Solar System with volcanoes erupting extremely hot lava like that seen on Earth. Because of Io's low gravity, large volcanic eruptions produce an umbrella of debris that rises high into space. Such outbursts can send material hundreds of miles above the surface.

The recent eruptions resemble past events that spewed tens of cubic miles of lava over hundreds of square miles in a short period of time. All three events, including the largest, most powerful eruption of the trio on 29 August, 2013, were likely characterized by “curtains of fire," as lava blasted out of fissures perhaps several miles long.

The 29 August, 2013, outburst on Io shown below was among the largest ever observed on the most volcanically active body in the solar system. Infrared image taken by Gemini North telescope. Image credit: Katherine de Kleer, UC Berkeley.

The brightest eruption at a caldera named Rarog Patera, was calculated to have produced a 50 square-mile, 30ft thick lava flow, while another close to a caldera called Heno Patera, produced flows covering 120 square miles. Both were located in Io's southern hemisphere, near its limb, and were nearly gone when imaged five days later.

Now, new observations of the planet's extreme ultraviolet emissions show that bright explosions of Jupiter's aurora likely also get kicked off by the planet-moon interaction, not by solar activity. A new scientific paper about these observations by Tomoki Kimura of the Japan Aerospace Exploration Agency (JAXA), in Sagamihara, Kanagawa, Japan, and his colleagues, was published online today in Geophysical Research Letters, a journal of the American Geophysical Union.

Io produces about 100 times more lava each year than all the volcanoes on Earth. While Earth's volcanoes occur in localized hotspots like the "Ring of Fire" around the Pacific Ocean, Io's volcanoes are distributed all over its surface. A global magma ocean about 30 to 50 kilometers (20 to 30 miles) beneath Io's crust helps explain the moon's activity.

"It has been suggested that both the Earth and its moon may have had similar magma oceans billions of years ago at the time of their formation, but they have long since cooled," said Torrence Johnson, a former Galileo project scientist based at NASA's Jet Propulsion Laboratory in Pasadena, Calif. He was not directly involved in the study. "Io's volcanism informs us how volcanoes work and provides a window in time to styles of volcanic activity that may have occurred on the Earth and moon during their earliest history."

NASA's Voyager spacecraft discovered Io's volcanoes in 1979, making that moon the only body in the solar system other than Earth known to have active magma volcanoes. The energy for the volcanic activity comes from the squeezing and stretching of the moon by Jupiter's gravity as Io orbits the largest planet in the solar system.

Starting in January 2014, a telescope aboard the JAXA's Hisaki satellite, which focused on Jupiter for two months, recorded intermittent brightening of the giant planet's aurora. The telescope detected sudden flare-ups on days when the usual flow of charged particles from the Sun, known as the solar wind, was relatively weak.

Additional space and ground-based telescopes, including the Hubble Space Telescope, also viewed Jupiter during these lulls in the solar wind. Both Hisaki and Hubble witnessed explosions of the planet's aurora despite the solar wind's calm, suggesting that it's the Jupiter-Io interaction driving these explosions, not charged particles from the Sun, according to the new study. The new research does not address exactly what is happening in the Jovian magnetosphere to cause the temporary brightening of auroral explosions.

The Daily Galaxy via NASA/JPL and AGU

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On July 4th, NASA Television aired live coverage of the solar-powered Juno spacecraft's arrival at Jupiter after an almost five-year journey. Juno is the first spacecraft to orbit the poles of our solar system's most massive planet. It will circle the Jovian world 37 times during 20 months, skimming to within 3,100 miles (5,000 kilometers) above the cloud tops, providing new answers to ongoing mysteries about the planet's core, composition and magnetic fields.

After an almost five-year journey to the solar system's largest planet, NASA's Juno spacecraft successfully entered Jupiter's orbit during a 35-minute engine burn. Confirmation that the burn had completed was received on Earth at 8:53 p.m. PDT (11:53 p.m. EDT) Monday, July 4.

“Independence Day always is something to celebrate, but today we can add to America's birthday another reason to cheer -- Juno is at Jupiter,” said NASA administrator Charlie Bolden. “And what is more American than a NASA mission going boldly where no spacecraft has gone before? With Juno, we will investigate the unknowns of Jupiter's massive radiation belts to delve deep into not only the planet's interior, but into how Jupiter was born and how our entire solar system evolved.”

Confirmation of a successful orbit insertion was received from Juno tracking data monitored at the navigation facility at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, as well as at the Lockheed Martin Juno operations center in Littleton, Colorado. The telemetry and tracking data were received by NASA's Deep Space Network antennas in Goldstone, California, and Canberra, Australia.

“This is the one time I don't mind being stuck in a windowless room on the night of the 4th of July,” said Scott Bolton, principal investigator of Juno from Southwest Research Institute in San Antonio. “The mission team did great. The spacecraft did great. We are looking great. It's a great day.”

Preplanned events leading up to the orbital insertion engine burn included changing the spacecraft's attitude to point the main engine in the desired direction and then increasing the spacecraft's rotation rate from 2 to 5 revolutions per minute (RPM) to help stabilize it..

The burn of Juno's 645-Newton Leros-1b main engine began on time at 8:18 p.m. PDT (11:18 p.m. EDT), decreasing the spacecraft's velocity by 1,212 miles per hour (542 meters per second) and allowing Juno to be captured in orbit around Jupiter. Soon after the burn was completed, Juno turned so that the sun's rays could once again reach the 18,698 individual solar cells that give Juno its energy.

“The spacecraft worked perfectly, which is always nice when you're driving a vehicle with 1.7 billion miles on the odometer,” said Rick Nybakken, Juno project manager from JPL. “Jupiter orbit insertion was a big step and the most challenging remaining in our mission plan, but there are others that have to occur before we can give the science team the mission they are looking for.”

Over the next few months, Juno's mission and science teams will perform final testing on the spacecraft's subsystems, final calibration of science instruments and some science collection.

“Our official science collection phase begins in October, but we've figured out a way to collect data a lot earlier than that,” said Bolton. “Which when you're talking about the single biggest planetary body in the solar system is a really good thing. There is a lot to see and do here.”

Juno's principal goal is to understand the origin and evolution of Jupiter. With its suite of nine science instruments, Juno will investigate the existence of a solid planetary core, map Jupiter's intense magnetic field, measure the amount of water and ammonia in the deep atmosphere, and observe the planet's auroras. The mission also will let us take a giant step forward in our understanding of how giant planets form and the role these titans played in putting together the rest of the solar system. As our primary example of a giant planet, Jupiter also can provide critical knowledge for understanding the planetary systems being discovered around other stars.

One of Juno's primary missions is to peer deep inside the gas giant and unravel the mystery of how it generates its powerful magnetic field, the strongest in the solar system. One theory is that about halfway to Jupiter's core, the pressures and temperatures become so intense that the hydrogen that makes up 90 percent of the planet -- molecular gas on Earth -- looses hold of its electrons and begins behaving like a liquid metal. Oceans of liquid metallic hydrogen surrounding Jupiter's core would explain its powerful magnetic field.

The Juno spacecraft launched on Aug. 5, 2011 from Cape Canaveral Air Force Station in Florida. JPL manages the Juno mission for NASA. Juno is part of NASA's New Frontiers Program, managed at NASA's Marshall Space Flight Center in Huntsville, Alabama, for the agency's Science Mission Directorate. Lockheed Martin Space Systems in Denver built the spacecraft. The California Institute of Technology in Pasadena manages JPL for NASA.

The Daily Galaxy via NASA/JPL

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NASA: "The Milky Way and Universe is Awash in Water"

Hundreds of hidden nearby galaxies have been studied for the first time, shedding light on a mysterious gravitational anomaly dubbed the Great Attractor, which appears to be drawing the Milky Way and hundreds of thousands of other galaxies towards it with a gravitational force equivalent to a million billion Suns. Despite being just 250 million light years from Earth--very close in astronomical terms--the new galaxies had been hidden from view until now by the Milky Way.

Using CSIRO's Parkes radio telescope equipped with an innovative receiver, an international team of scientists were able to see through the stars and dust of the Milky Way, into a previously unexplored region of space. Lead author Lister Staveley-Smith, from The University of Western Australia node of the International Centre for Radio Astronomy Research (ICRAR), said the team found 883 galaxies, a third of which had never been seen before. "The Milky Way is very beautiful of course and it's very interesting to study our own galaxy but it completely blocks out the view of the more distant galaxies behind it," he said.

Staveley-Smith said scientists have been trying to get to the bottom of the mysterious Great Attractor since major deviations from universal expansion were first discovered in the 1970s and 1980s. "We don't actually understand what's causing this gravitational acceleration on the Milky Way or where it's coming from," he said.

The Milky Way resides in the outskirts of the Laniakea Supercluster, 500 million light-years in diameter and contains the mass of one hundred million billion Suns spread across 100,000 galaxies.. Within the boundaries of the Laniakea Supercluster, galaxy motions are directed inward, in the same way that water streams follow descending paths toward a valley. The Great Attractor region is a large flat bottom gravitational valley with a sphere of attraction that extends across the Laniakea Supercluster.

"We know that in this region there are a few very large collections of galaxies we call clusters or superclusters, and our whole Milky Way is moving towards them at more than two million kilometers per hour."

"Laniakea," which means "immense heaven" in Hawaiian. This discovery clarifies the boundaries of our galactic neighborhood and establishes previously unrecognized linkages among various galaxy clusters in the local Universe.The Milky Way resides in the outskirts of the supercluster, whose extent has for the first time been carefully mapped using these new techniques. This so-called Laniakea Supercluster is 500 million light-years in diameter and contains the mass of one hundred million billion Suns spread across 100,000 galaxies.

This study also clarifies the role of the Great Attractor, a gravitational focal point in intergalactic space that influences the motion of our Local Group of galaxies and other galaxy clusters. Within the boundaries of the Laniakea Supercluster, galaxy motions are directed inward, in the same way that water streams follow descending paths toward a valley. The Great Attractor region is a large flat bottom gravitational valley with a sphere of attraction that extends across the Laniakea Supercluster.

The Milky Way and its neighboring Andromeda galaxy, along with some 30 smaller ones, form what is known as the Local Group, which lies on the outskirts of a “super cluster”—a grouping of thousands of galaxies—known as Virgo shown in the image above, which is also pulled toward the Great Attractor. Based on the velocities at these scales, the unseen mass inhabiting the voids between the galaxies and clusters of galaxies amounts to perhaps 10 times more than the visible matter.

Even so, adding this invisible material to luminous matter brings the average mass density of the universe still to within only 10-30 percent of the critical density needed to "close" the universe. This phenomena suggests that the universe be "open." Cosmologists continue to debate this question, just as they are also trying to figure out the nature of the missing mass, or "dark matter."

It is believed that this dark matter dictates the structure of the Universe on the grandest of scales. Dark matter gravitationally attracts normal matter, and it is this normal matter that astronomers see forming long thin walls of super-galactic clusters.

Recent measurements with telescopes and space probes of the distribution of mass in M31 -the largest galaxy in the neighborhood of the Milky Way- and other galaxies led to the recognition that galaxies are filled with dark matter and have shown that a mysterious force—a dark energy—fills the vacuum of empty space, accelerating the universe's expansion.

Astronomers now recognize that the eventual fate of the universe is inextricably tied to the presence of dark energy and dark matter.The current standard model for cosmology describes a universe that is 70 percent dark energy, 25 percent dark matter, and only 5 percent normal matter.

We don't know what dark energy is, or why it exists. On the other hand, particle theory tells us that, at the microscopic level, even a perfect vacuum bubbles with quantum particles that are a natural source of dark energy. But a naïve calculation of the dark energy generated from the vacuum yields a value 10120 times larger than the amount we observe. Some unknown physical process is required to eliminate most, but not all, of the vacuum energy, leaving enough left to drive the accelerating expansion of the universe.

A new theory of particle physics is required to explain this physical process. The new "dark attractor" theories skirt the so-called Copernican principle that posits that there is nothing special about us as observers of the universe suggesting that the universe is not homogeneous. These alternative theories explain the observed accelerated expansion of the universe without invoking dark energy, and instead assume we are near the center of a void, beyond which a denser "dark" attractor pulls outwards.

In a paper in Physical Review Letters, Pengjie Zhang at the Shanghai Astronomical Observatory and Albert Stebbins at Fermilab show that a popular void model, and many others aiming to replace dark energy, don't stand up against telescope observation.

Galaxy surveys show the universe is homogeneous, at least on length scales up to a gigaparsec. Zhang and Stebbins argue that if larger scale inhomogeneities exist, they should be detectable as a temperature shift in the cosmic microwave background—relic photons from about 400,000 years after the big bang—that occurs because of electron-photon (inverse Compton) scattering.

Focusing on the “Hubble bubble” void model, they show that in such a scenario, some regions of the universe would expand faster than others, causing this temperature shift to be greater than what is expected. But telescopes that study the microwave background, such as the Atacama telescope in Chile or the South Pole telescope, don't see such a large shift.

Though they can't rule out more subtle violations of the Copernican principle, Zhang and Stebbins' test reinforces Carl Sagan's dictum that "extraordinary claims require extraordinary evidence."

Superclusters are among the largest structures in the known Universe. They are made up of groups, like our own Local Group, that contain dozens of galaxies, and massive clusters that contain hundreds of galaxies, all interconnected in a web of filaments. Though these structures are interconnected, they have poorly defined boundaries.

"We have finally established the contours that define the supercluster of galaxies we can call home," said R. Brent Tully, an astronomer at the University of Hawaii at Manoa. "This is not unlike finding out for the first time that your hometown is actually part of much larger country that borders other nations."

To better refine cosmic mapmaking, the researchers are proposing a new way to evaluate these large-scale galaxy structures by examining their impact on the motions of galaxies. A galaxy between structures will be caught in a gravitational tug-of-war in which the balance of the gravitational forces from the surrounding large-scale structures determines the galaxy's motion.

By using the GBT and other radio telescopes to map the velocities of galaxies throughout our local Universe, the team was able to define the region of space where each supercluster dominates. "Green Bank Telescope observations have played a significant role in the research leading to this new understanding of the limits and relationships among a number of superclusters," said Tully.

The name Laniakea was suggested by Nawa'a Napoleon, an associate professor of Hawaiian Language and chair of the Department of Languages, Linguistics, and Literature at Kapiolani Community College, a part of the University of Hawaii system. The name honors Polynesian navigators who used knowledge of the heavens to voyage across the immensity of the Pacific Ocean.

The GBT is the world's largest fully steerable radio telescope. Its location in the National Radio Quiet Zone and the West Virginia Radio Astronomy Zone protects the incredibly sensitive telescope from unwanted radio interference.

The new CSIRO research identified several new structures that could help to explain the movement of the Milky Way, including three galaxy concentrations (named NW1, NW2 and NW3) and two new clusters (named CW1 and CW2). The study involved researchers from Australia, South Africa, the U.S. and the Netherlands, and was published in the Astronomical Journal.

University of Cape Town astronomer Renée Kraan-Korteweg said astronomers have been trying to map the galaxy distribution hidden behind the Milky Way for decades. "We've used a range of techniques but only radio observations have really succeeded in allowing us to see through the thickest foreground layer of dust and stars," she said. "An average galaxy contains 100 billion stars, so finding hundreds of new galaxies hidden behind the Milky Way points to a lot of mass we didn't know about until now."

The Daily Galaxy via PhysRevLett.107.041301, International Center for Radio Astronomy Research and NRAO

Image credit: Top of page with thanks to artist Adam Dalton