Formation of massive BHs

Supersonic gas streams enhance the formation of massive black holes in the early universe

Science  29 Sep 2017

Thermal evolution of the collapsing cloud. In each run, the cloud became unstable at the points marked by the circles.

The first supermassive Black Holes

Supermassive black holes existed less than a billion years after the Big Bang. Because black holes can grow at a rate that depends on their current mass, it has been difficult to understand how such massive black holes could have formed so quickly. Hirano et al. developed simulations to show that streaming motions—velocity offsets between the gas and dark matter components—could have produced black holes with tens of thousands of solar masses in the early universe. That’s big enough to grow into today’s supermassive black holes.

Science, this issue p. 1375


The origin of super-massive black holes in the early universe remains poorly understood. Gravitational collapse of a massive primordial gas cloud is a promising initial process, but theoretical studies have difficulty growing the black hole fast enough. We report numerical simulations of early black hole formation starting from realistic cosmological conditions. Supersonic gas motions left over from the Big Bang prevent early gas cloud formation until rapid gas condensation is triggered in a protogalactic halo. A protostar is formed in the dense, turbulent gas cloud, and it grows by sporadic mass accretion until it acquires 34,000 solar masses. The massive star ends its life with a catastrophic collapse to leave a black hole—a promising seed for the formation of a monstrous black hole.

Recent discoveries of super-massive black holes (SMBHs) at redshift z ~ 7, when the universe was just 5% of its present age, pose a serious challenge to the theory of black hole (BH) formation and evolution. The physical mechanisms that form the BH seeds and drive their growth are not yet known but must explain how an initial seed BH can reach a mass of 10 billion times that of the Sun within 1 billion years after the Big Bang. It is thought that the mass growth is a self-regulating process, limited by the so-called Eddington rate that is proportional to the BH mass; therefore, starting from a massive BH holds a key to the rapid formation of SMBHs.

Sloshing, supersonic gas may have built the baby universe’s biggest black holes

By Joshua Sokol |

Joshua Sokol is a journalist based in Boston.

A central mystery surrounds the supermassive black holes that haunt the cores of galaxies: How did they get so big so fast? Now, a new, computer simulation–based study suggests that these giants were formed and fed by massive clouds of gas sloshing around in the aftermath of the big bang.

“This really is a new pathway,” says Volker Bromm, an astrophysicist at the University of Texas in Austin who was not part of the research team. “But it’s not … the one and only pathway.”

Astronomers know that, when the universe was just a billion years old, some supermassive black holes were already a billion times heavier than the sun. That’s much too big for them to have been built up through the slow mergers of small black holes formed in the conventional way, from collapsed stars a few dozen times the mass of the sun. Instead, the prevailing idea is that these behemoths had a head start. They could have condensed directly out of seed clouds of hydrogen gas weighing tens of thousands of solar masses, and grown from there by gravitationally swallowing up more gas. But the list of plausible ways for these “direct-collapse” scenarios to happen is short, and each option requires a perfect storm of circumstances.

For theorists tinkering with computer models, the trouble lies in getting a massive amount of gas to pile up long enough to collapse all at once, into a vortex that feeds a nascent black hole like water down a sink drain. If any parts of the gas cloud cool down or clump up early, they will fragment and coalesce into stars instead. Once formed, radiation from the stars would blow away the rest of the gas cloud.

One option, pioneered by Bromm and others, is to bathe a gas cloud in ultraviolet light, perhaps from stars in a next-door galaxy, and keep it warm enough to resist clumping. But having a galaxy close enough to provide that service would be quite the coincidence.

The new study proposes a different origin. Both the early universe and the current one are composed of familiar matter like hydrogen, plus unseen clumps of dark matter. Today, these two components move in sync. But very early on, normal matter may have sloshed back and forth at supersonic speeds across a skeleton provided by colder, more sluggish dark matter. In the study, published today in Science, simulations show that where these surges were strong, and crossed the path of heavy clumps of dark matter, the gas resisted premature collapse into stars and instead flowed into the seed of a supermassive black hole. These scenarios would be rare, but would still roughly match the number of supermassive black holes seen today, says Shingo Hirano, an astrophysicist at the University of Texas and lead author of the study.

Priya Natarajan, an astrophysicist at Yale University, says the new simulation represents important computational progress. But because it would have taken place at a very distant, early moment in the history of the universe, it will be difficult to verify. “I think the mechanism itself in detail is not going to be testable,” she says. “We will never see the gas actually sloshing and falling in.”

But Bromm is more optimistic, especially if such direct-collapse black hole seeds also formed slightly later in the history of the universe. He, Natarajan, and other astronomers have been looking for these kinds baby black holes, hoping to confirm that they do, indeed, exist and then trying to work out their origins from the downstream consequences.

In 2016, they found several candidates, which seem to have formed through direct collapse and are now accreting matter from clouds of gas. And earlier this year, astronomers showed that the early, distant universe is missing the glow of x-ray light that would be expected from a multitude of small black holes—another sign favoring the sudden birth of big seeds that go on to be supermassive black holes. Bromm is hopeful that upcoming observations will provide more definite evidence, along with opportunities to evaluate the different origin theories. “We have these predictions, we have the signatures, and then we see what we find,” he says. “So the game is on.”


Hacker culture

Hacker culture

The hacker culture is a subculture of individuals who enjoy the intellectual challenge of creatively overcoming limitations of software systems to achieve novel and clever outcomes. The act of engaging in activities (such as programming or other media) in a spirit of playfulness and exploration is termed “hacking”. However, the defining characteristic of a hacker is not the activities performed themselves (e.g. programming), but the manner in which it is done and whether it is something exciting and meaningful. Activities of playful cleverness can be said to have “hack value” and therefore the term “hacks” came about, with early examples including pranks at MIT done by students to demonstrate their technical aptitude and cleverness. Therefore, the hacker culture originally emerged in academia in the 1960s around the Massachusetts Institute of Technology (MIT)’s Tech Model Railroad Club (TMRC) and MIT Artificial Intelligence Laboratory.

A solution or feat has “hack value” if it is done in a way that has finesse, cleverness or brilliance, which makes creativity an essential part of the meaning. For example, picking a difficult lock has hack value; smashing it does not. As another example, proving Fermat’s last theorem by linking together most of modern mathematics has hack value; solving a combinatorial problem by exhaustively trying all possibilities does not. Hacking is not using process of elimination to find a solution; it’s the process of finding a clever solution to a problem.

Hackers from this subculture tend to emphatically differentiate themselves from what they pejoratively call “crackers“; those who are generally referred to by media and members of the general public using the term “hacker”, and whose primary focus‍—‌be it to malign or for malevolent purposes‍—‌lies in exploiting weaknesses in computer security.


History of Information

Norbert Wiener Issues “Cybernetics”, the First Widely Distributed Book on Electronic Computing

Jeremy Norman

“Use the word ‘cybernetics’, Norbert, because nobody knows what it means. This will always put you at an advantage in arguments.”

— Widely quoted: attributed to Claude Shannon in a letter to Norbert Wiener in the 1940s

In 1948 mathematician Norbert WienerOffsite Link at MIT published Cybernetics or Control and Communication in the Animal and the MachineOffsite Link, a widely circulated and influential book that applied theories of information and communication to both biological systems and machines. Computer-related words with the “cyber” prefix, including “cyberspace,” originate from Wiener’s book. Cybernetics was also the first conventionally published book to discuss electronic digital computing. Writing as a mathematician rather than an engineer, Wiener’s discussion was theoretical rather than specific. Strangely the first edition of the book was published in English in Paris at the press of Hermann et Cie. The first American edition was printed offset from the French sheets and issued by John Wiley in New York, also in 1948. I have never seen an edition printed or published in England.

Independently of Claude Shannon, Wiener conceived of communications engineering as a brand of statistical physics and applied this viewpoint to the concept of information. Wiener’s chapter on “Time series, information, and communication” contained the first publication of Wiener’s formula describing the probability density of continuous information. This was remarkably close to Shannon’s formula dealing with discrete time published in A Mathematical Theory of Communication (1948). Cybernetics also contained a chapter on “Computing machines and the nervous system.” This was a theoretical discussion, influenced by McCulloch and Pitts, of differences and similarities between information processing in the electronic computer and the human brain. It contained a discussion of the difference between human memory and the different computer memories then available. Tacked on at the end of Cybernetics were speculations by Wiener about building a chess-playing computer, predating Shannon’s first paper on the topic.

Cybernetics is a peculiar, rambling blend of popular and highly technical writing, ranging from history to philosophy, to mathematics, to information and communication theory, to computer science, and to biology. Reflecting the amazingly wide range of the author’s interests, it represented an interdisciplinary approach to information systems both in biology and machines. It influenced a generation of scientists working in a wide range of disciplines. In it were the roots of various elements of computer science, which by the mid-1950s had broken off from cybernetics to form their own specialties. Among these separate disciplines were information theory, computer learning, and artificial intelligence.

It is probable that Wiley had Hermann et Cie supervise the typesetting because they specialized in books on mathematics.  Hermann printed the first edition by letterpress; the American edition was printed offset from the French sheets. Perhaps because the typesetting was done in France Wiener did not have the opportunity to read proofs carefully, as the first edition contained many typographical errors which were repeated in the American edition, and which remained uncorrected through the various printings of the American edition until a second edition was finally published by John Wiley and MIT Press in 1961.

Though the book contained a lot of technical mathematics, and was not written for a popular audience, the first American edition went through at least 5 printings during 1948,  and several later printings, most of which were probably not read in their entirety by purchasers. Sales of Wiener’s book were helped by reviews in wide circulation journals such as the review in TIME Magazine on December 27, 1948, entitled “In Man’s ImageOffsite Link.” The reviewer used the word calculator to describe the machines; at this time the word computer was reserved for humans.

Presumably the commercial success of Cybernetics encouraged Wiley to publish Berkeley’s Giant Brains, or Machines that Think in 1949.


KIC-8462852 News

KIC 8462852 (Tabby’s Star or Boyajian’s Star)

2 May to 28 Sep 2017: g-prime − Bruce Gary

2017 dimming events

On 20 May 2017, Boyajian and her colleagues reported, via The Astronomer’s Telegram, on an ongoing dimming event (named “Elsie”) which possibly began on 14 May 2017. It was detected by the Las Cumbres Observatory Global Telescope Network, specifically by its telescope located in Maui (LCO Maui). This was verified by the Fairborn Observatory (part of the N2K Consortium) in Southern Arizona (and later by LCO Canary Islands). Further optical and infrared spectroscopy and photometry were urgently requested, given the short duration, measured in days or weeks, of these events. Observations from multiple observers globally were coordinated, including polarimetry. Furthermore, the independent SETI projects Breakthrough Listen and Near-InfraRed Optical SETI (NIROSETI), both at Lick Observatory, continue to monitor the star. By the end of the three-day dimming event, a dozen observatories had taken spectra, with some astronomers having dropped their own projects to provide telescope time and resources. More generally the astronomical community was described as having gone “mildly bananas” over the opportunity to collect data in real-time on the unique star, and the 2% dip itself was named “Elsie” (in reference to Las Cumbres and light curve).

Initial spectra with FRODOSpec at the two-meter Liverpool Telescope showed no evidence of any changes visible between a reference spectrum and this dip. Several observatories, however, including the twin Keck telescopes (HIRES) and numerous citizen science observatories, took spectra of the star. This dimming dip had a complex shape, and initially had a pattern similar to the one at 759.75 days from the Kepler event 2, epoch 2 data. Observations were taken across the electromagnetic spectrum.

Evidence of a second dimming event (named “Celeste”) was observed on 13–14 June 2017, and which possibly began 11 June, by amateur astronomer Bruce Gary. While the light curve on 14 and 15 June indicated a possible recovery from the dimming event, the dimming continued to increase afterwards, and on 16 June, Boyajian wrote that the event was approaching a 2% dip in brightness.

A third prominent 1% dimming event (named “Skara Brae”) was detected beginning 2 August 2017, and which recovered by 17 August.

A fourth prominent dimming event (named “Angkor”) began 5 September 2017, and is, as of 16 September 2017, between 2.3% and 3% dimming event, making it the “deepest dip this year”.


JWST Launches Spring 2019

NASA’s James Webb Space Telescope to be Launched Spring 2019

NASA’s James Webb Space Telescope now is planning to launch between March and June 2019 from French Guiana, following a schedule assessment of the remaining integration and test activities. Previously Webb was targeted to launch in October 2018.

“The change in launch timing is not indicative of hardware or technical performance concerns,” said Thomas Zurbuchen, associate administrator for NASA’s Science Mission Directorate at Headquarters in Washington. “Rather, the integration of the various spacecraft elements is taking longer than expected.”

As part of an international agreement with the ESA (European Space Agency) to provide a desired launch window one year prior to launch, NASA recently performed a routine schedule assessment to ensure launch preparedness and determined a launch schedule change was necessary. The careful analysis took into account the remaining tasks that needed to be completed, the lessons learned from unique environmental testing of the telescope and science instruments at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and the current performance rates of integrating the spacecraft element.

Testing of the telescope and science instruments continues to go well and on schedule at NASA’s Johnson Space Center in Houston, Texas. The spacecraft itself, comprised of the spacecraft bus and sunshield, has experienced delays during its integration and testing at Northrop Grumman in Redondo Beach, California.

The additional environmental testing time of the fully assembled observatory–the telescope and the spacecraft–will ensure that Webb will be fully tested before launching into space. All the rigorous tests of the telescope and the spacecraft to date show the mission is meeting its required performance levels.

Existing program budget accommodates the change in launch date, and the change will not affect planned science observations.

“Webb’s spacecraft and sunshield are larger and more complex than most spacecraft. The combination of some integration activities taking longer than initially planned, such as the installation of more than 100 sunshield membrane release devices, factoring in lessons learned from earlier testing, like longer time spans for vibration testing, has meant the integration and testing process is just taking longer,” said Eric Smith, program director for the James Webb Space Telescope at NASA Headquarters in Washington. “Considering the investment NASA has made, and the good performance to date, we want to proceed very systemmatically through these tests to be ready for a Spring 2019 launch.”

The launch window request has been coordinated with ESA, which is providing the Ariane 5 launch of Webb as part of its scientific collaboration with NASA.

The James Webb Space Telescope is NASA’s next great multi-purpose observatory and will be the world’s most powerful space telescope ever built, serving thousands of astronomers worldwide. The 21-foot (6.5-meter) diameter infrared-optimized telescope is designed to study an extremely wide range of astrophysical phenomena: the first stars and galaxies that formed; the atmospheres of nearby planets outside our solar system, known as exoplanets; and objects within our own solar system. Webb is an international project led by NASA with its partners ESA and the Canadian Space Agency.

Last Updated: Sept. 28, 2017
Editor: Brian Dunbar

15 high-energy radio bursts

Distant galaxy sends out 15 high-energy radio bursts

Robert Sanders |

Breakthrough Listen, an initiative to find signs of intelligent life in the universe, has detected 15 brief but powerful radio pulses emanating from a mysterious and repeating source – FRB 121102 – far across the universe.

Fast radio bursts are brief, bright pulses of radio emission from distant but largely unknown sources, and FRB 121102 is the only one known to repeat: more than 150 high-energy bursts have been observed coming from the object, which was identified last year as a dwarf galaxy about 3 billion light years from Earth.

Possible explanations for the repeating bursts range from outbursts from rotating neutron stars with extremely strong magnetic fields – so-called magnetars – to a more speculative idea: They are directed energy sources, powerful laser bursts used by extraterrestrial civilizations to power spacecraft, akin to Breakthrough Starshot’s plan to use powerful laser pulses to propel nano-spacecraft to our solar system’s nearest star, Proxima Centauri.

“Bursts from this source have never been seen at this high a frequency,” said Andrew Siemion, director of the Berkeley SETI Research Center and of the Breakthrough Listen program.

As astronomers around the globe try to understand the mechanism generating fast radio bursts, they have repeatedly turned their radio telescopes on FRB 121102. Siemion and his team alerted the astronomical community to the high-frequency activity via an Astronomer’s Telegram on Monday evening, Aug. 28.

“As well as confirming that the source is in a newly active state, the high resolution of the data obtained by the Listen instrument will allow measurement of the properties of these mysterious bursts at a higher precision than ever possible before,” said Breakthrough Listen postdoctoral researcher Vishal Gajjar, who discovered the increased activity.

First detected with the Parkes Telescope in Australia, fast radio bursts have now been seen by several radio telescopes around the world. FRB 121102 was discovered on Nov. 2, 2012, (hence its name) and in 2015 it was the first fast radio burst seen to repeat, ruling out theories of bursts’ origins that involved the catastrophic destruction of the progenitor, at least in this instance.

Regardless of FRB 121102’s ultimate source, when the recently detected pulses left their host galaxy, our solar system was less than 2 billion years old, noted Steve Croft, a Breakthrough Listen astronomer at UC Berkeley. Life on Earth consisted only of single-celled organisms; it would be another billion years before even the simplest multi-cellular life began to evolve.

As part of Breakthrough Listen’s program to observe nearby stars and galaxies for signatures of extraterrestrial technology, the project science team at UC Berkeley added FRB 121102 to its list of targets. In the early hours of Saturday, Aug. 26, Gajjar observed that area of the sky using the Breakthrough Listen backend instrument at the Green Bank Telescope in West Virginia.

The instrument accumulated 400 terabytes (a million million bytes) of data over a five-hour period, observing across the entire 4 to 8 GHz frequency band. This large dataset was searched for signatures of short pulses from the source over a broad range of frequencies, with a characteristic dispersion, or delay as a function of frequency, caused by the presence of gas in space between Earth and the source. The distinctive shape that the dispersion imposes on the initial pulse is an indicator of the amount of material between us and the source, and hence an indicator of the distance to the host galaxy.

Analysis by Gajjar and the Breakthrough Listen team revealed 15 new pulses from FRB 121102. The observations show for the first time that fast radio bursts emit at higher frequencies than previously observed, with the brightest emission occurring at around 7 GHz.

“The extraordinary capabilities of the backend receiver, which is able to record several gigahertz of bandwidth at a time, split into billions of individual channels, enable a new view of the frequency spectrum of FRBs, and should shed additional light on the processes giving rise to FRB emission.” Gajjar said.

“Whether or not fast radio bursts turn out to be signatures of extraterrestrial technology, Breakthrough Listen is helping to push the frontiers of a new and rapidly growing area of our understanding of the universe around us,” Siemion said.


Crab Pulsar’s Giant Pulses

Mapping the Emission Location of the Crab Pulsar’s Giant Pulses

ABSTRACT: The Crab pulsar has striking radio emission properties, with the two dominant pulse components — the main pulse and the interpulse — consisting entirely of giant pulses. The emission is scattered in both the Crab nebula and the interstellar medium, causing multi-path propagation and thus scintillation. We study the scintillation of the Crab’s giant pulses using phased Westerbork data at 1668 MHz. From correlations of the giant pulse spectra, we find that the main pulse and the interpulse are significantly offset in time and frequency. This suggests that they arise in physically distinct regions, which are, assuming the scattering takes place in the nebular filaments, separated by about a light cylinder radius (as projected on the sky). With further VLBI and multi-frequency data, it should be possible to measure both the distance to the scattering screens and the physical separation between the pulse components.


GW170814: 3-detector observation

GW170814: A three-detector observation of gravitational waves from a binary black hole coalescence


The rapid localization using data from the two LIGO sites is shown in yellow, with the inclusion of data from Virgo shown in green. The full Bayesian localization is shown in purple.

ABSTRACT: On August 14, 2017 at 10:30:43 UTC, the Advanced Virgo detector and the two Advanced LIGO detectors coherently observed a transient gravitational-wave signal produced by the coalescence of two stellar mass black holes, with a false-alarm-rate of ≲ 1 in 27000 years. The signal was observed with a three-detector network matched-filter signal-to-noise ratio of 18. The inferred masses of the initial black holes are 30.5-3.0+5.7 Msun and 25.3-4.2+2.8 Msun (at the 90% credible level). The luminosity distance of the source is 540-210+130 Mpc, corresponding to a redshift of z=0.11-0.04+0.03. A network of three detectors improves the sky localization of the source, reducing the area of the 90% credible region from 1160 deg2 using only the two LIGO detectors to 60 deg2 using all three detectors. For the first time, we can test the nature of gravitational wave polarizations from the antenna response of the LIGO-Virgo network, thus enabling a new class of phenomenological tests of gravity.

Trio of detectors homes in on black hole sources of gravitational waves

By Adrian Cho |

For a fourth time, physicists have spotted gravitational waves—ripples in space itself—set off by the merger of two massive black holes. But this time, they detected the waves not only with two detectors in the United States, but also with a third detector in Europe: the Virgo detector near Pisa, Italy. The three-way detection enabled researchers to home in on the location of the black holes on the sky with 10 times greater precision than before, and to probe the polarization of gravitational waves in new ways. The result also independently confirms the blockbuster discovery of gravitational waves made 2 years ago.

“Virgo is in the game and that’s very important,” says Clifford Will, a gravitational theorist at the University of Florida in Gainesville who was not involved in the work.

Gravitational waves are a spectacular prediction of Albert Einstein’s theory of gravity, general relativity. Einstein explained that gravity arises because massive objects warp space and time. When these objects spin around each other like twirling barbells, he predicted, they should produce ripples in spacetime, or gravitational waves, that spread at light-speed.

That prediction came to fruition in September 2015. Physicists working with the Laser Interferometer Gravitational-Wave Observatory (LIGO), which has twin instruments in Livingston, Louisiana, and Hanford, Washington, spotted a burst of gravitational waves from black holes 29 and 36 times as massive as the sun that spiraled into each other 1.3 billion light-years away. Since then, the 1000-member LIGO team has spotted two other black hole mergers, using its exquisitely sensitive L-shaped optical instruments called interferometers, which use lasers and mirrors to compare the stretching of space in one direction to that in the perpendicular direction. LIGO completed its two interferometers, with 4-kilometer-long arms, in 1999.

But LIGO hasn’t been alone in the hunt for gravitational waves. In 2003, European physicists completed construction of Virgo, a €300 million interferometer with 3-kilometer-long arms, funded by French national research agency CNRS and the Italian National Institute of Nuclear Physics (INFN). In 2007, LIGO and Virgo researchers signed a data-sharing agreement, and on 1 August, after a 5-year, €24 million upgrade, Virgo rejoined LIGO in the search for gravitational waves.

It didn’t take Virgo long to strike scientific gold. On 14 August at 12:30:43 p.m. in Italy, the detector’s automated triggering system sensed a potentially exciting tremor, as did the systems of the two LIGO detectors. “This is really a great surprise, having an event just 2 weeks after the start of the run,” says Benoit Mours, a Virgo team member and a physicist from the Annecy Laboratory of Particle Physics in France. Subsequent analysis showed that the signal came from a black hole merger, Virgo researchers announced at a press briefing today in Turin, Italy.

The observation should reassure the roughly 280 Virgo scientists, who just a few months ago were dealing with technical difficulties with their machine. “For the experimenters it’s tremendous because you have to see the light at the end of the tunnel,” says Ettore Majorana, a physicist and Virgo team member with INFN in Rome, who worked on the specific technical problems. During the observing run, which ended 25 August, Virgo ran with between a quarter to a half the sensitivity of LIGO, Mours says.

The new black hole merger is similar to the first one seen by LIGO. In it, black holes 25 and 31 times as massive as the sun spiraled together in a galaxy 1.8 billion light-years away. By timing the arrivals of the signals at all three detectors, which differ by milliseconds, researchers were able to determine that the black hole merger took place somewhere within a 60-square-degree patch of sky in the Southern Hemisphere. That’s a big chunk of sky—the full moon covers only 0.2 square degrees—but it’s an area 10 times smaller than what could have been determined with the LIGO detectors alone.

Such pointing capability could prove crucial for finding flashes of light that accompany the pulses of gravitational waves. Although no such flash is expected from the merger of black holes, it would be expected in the merger of two neutron stars. Rumors have been swirling that such a case has occurred after astronomers last month trained several different telescopes on a particular galaxy.

The new observation also tests a key property of the gravitational waves themselves, their polarization. Just as light waves can be polarized horizontally or vertically depending on which way the electromagnetic field in them jiggles, gravitational waves can be polarized in two ways, according to general relativity, Will says. In one way, an oncoming gravitational wave can squeeze space vertically and stretch it horizontally, and then vice versa, in a repeating cycle. The second way is for that pattern to be tilted by 45°.

However, if Einstein was wrong and general relativity is incorrect, then, in principle, gravitational waves could come with four other polarization patterns, Will says. “If you see any of the other four it kills general relativity,” he says. With the data from the three detectors, physicists found no evidence for polarization in three of the four unacceptable ways, Will says. So general relativity lives to fight another day.

Perhaps most important, the latest result shows that the infant field of gravitational waves continues to live up to scientists’ sky-high expectation, Will says. “Nature has just blown us away.”

LIGO and Virgo observatories detect gravitational wave signals from black hole collision

September 27, 2017

In August, detectors on two continents recorded gravitational wave signals from a pair of black holes colliding. This discovery, announced today, is the first observation of gravitational waves by three different detectors, marking a new era of greater insights and improved localization of cosmic events now available through globally networked gravitational-wave observatories.

The collision was observed Aug. 14 at 10:30:43 a.m. Coordinated Universal Time (UTC) using the two National Science Foundation (NSF)-funded Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors located in Livingston, Louisiana, and Hanford, Washington, and the Virgo , funded by CNRS and INFN and located near Pisa, Italy.

The detection by the LIGO Scientific Collaboration (LSC) and the Virgo collaboration is the first confirmed gravitational wave signal recorded by the Virgo detector. A paper about the event, a collision designated GW170814, has been accepted for publication in the journal Physical Review Letters.

“Little more than a year and a half ago, NSF announced that its Laser Interferometer Gravitational Wave Observatory had made the first-ever detection of gravitational waves, which resulted from the collision of two in a galaxy a billion light-years away,” said NSF Director France Córdova. “Today, we are delighted to announce the first discovery made in partnership between the Virgo gravitational-wave observatory and the LIGO Scientific Collaboration, the first time a gravitational wave detection was observed by these observatories, located thousands of miles apart. This is an exciting milestone in the growing international scientific effort to unlock the extraordinary mysteries of our universe.”

The detected gravitational waves—ripples in space and time—were emitted during the final moments of the merger of two black holes, one with a mass about 31 times that of our sun, the other about 25 times the mass of the sun. The event, located about 1.8 billion light-years away resulted in a spinning black hole with about 53 times the mass of our sun—that means about three solar masses were converted into gravitational-wave energy during the coalescence.

“This is just the beginning of observations with the network enabled by Virgo and LIGO working together,” says LSC spokesperson David Shoemaker of the Massachusetts Institute of Technology (MIT). “With the next observing run planned for fall 2018, we can expect such detections weekly or even more often.”

LIGO has transitioned into a second-generation gravitational-wave detector, known as Advanced LIGO, that consists of two identical interferometers. Beginning operations in September 2015, Advanced LIGO has conducted two observing runs. The second observing run, “O2,” began Nov. 30, 2016, and ended Aug. 25, 2017.

The Virgo detector, also now a second-generation detector, joined the O2 run Aug. 1, 2017 at 10 a.m. UTC. The real-time detection Aug. 14 was triggered with data from all three LIGO and Virgo instruments.

“It is wonderful to see a first gravitational-wave signal in our brand new Advanced Virgo detector only two weeks after it officially started taking data,” says Jo van den Brand of Nikhef and Vrije Universiteit Amsterdam, spokesperson of the Virgo collaboration. “That’s a great reward after all the work done in the Advanced Virgo project to upgrade the instrument over the past six years.”

When an event is detected by a three-detector network, the area in the sky likely to contain the source shrinks significantly, improving distance accuracy. The sky region for GW170814 has a size of only 60 square degrees, more than 10 times smaller than the size using data available from the two LIGO interferometers alone.

“Being able to identify a smaller search region is important, because many compact object mergers—for example those involving neutron stars—are expected to produce broadband electromagnetic emissions in addition to ,” says Georgia Tech’s Laura Cadonati, deputy spokesperson for the LIGO Scientific Collaboration. “This precision pointing information enabled 25 partner facilities to perform follow-up observations based on the LIGO-Virgo detection, but no counterpart was identified—as expected for black holes.”

“With this first joint detection by the Advanced LIGO and Virgo detectors, we have taken one step further into the gravitational-wave cosmos,” says Caltech’s David H. Reitze, executive director of the LIGO Laboratory. “Virgo brings a powerful new capability to detect and better locate gravitational-wave sources, one that will undoubtedly lead to exciting and unanticipated results in the future.”

Gravitational waves from a binary black hole merger observed by LIGO and Virgo

News Release • September 27, 2017

The LIGO Scientific Collaboration and the Virgo collaboration report the first joint detection of gravitational waves with both the LIGO and Virgo detectors. This is the fourth announced detection of a binary black hole system and the first significant gravitational-wave signal recorded by the Virgo detector, and highlights the scientific potential of a three-detector network of gravitational-wave detectors.

The three-detector observation was made on August 14, 2017 at 10:30:43 UTC. The two Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors, located in Livingston, Louisiana, and Hanford, Washington, and funded by the National Science Foundation (NSF), and the Virgo detector, located near Pisa, Italy, detected a transient gravitational-wave signal produced by the coalescence of two stellar mass black holes.

A paper about the event, known as GW170814, has been accepted for publication in the journal Physical Review Letters.

The detected gravitational waves—ripples in space and time—were emitted during the final moments of the merger of two black holes with masses about 31 and 25 times the mass of the sun and located about 1.8 billion light-years away. The newly produced spinning black hole has about 53 times the mass of our sun, which means that about 3 solar masses were converted into gravitational-wave energy during the coalescence.

“This is just the beginning of observations with the network enabled by Virgo and LIGO working together,” says David Shoemaker of MIT, LSC spokesperson. “With the next observing run planned for Fall 2018 we can expect such detections weekly or even more often.”

“It is wonderful to see a first gravitational-wave signal in our brand new Advanced Virgo detector only two weeks after it officially started taking data,” says Jo van den Brand of Nikhef and VU University Amsterdam, spokesperson of the Virgo collaboration. “That’s a great reward after all the work done in the Advanced Virgo project to upgrade the instrument over the past six years.”

“Little more than a year and a half ago, NSF announced that its Laser Gravitational-Wave Observatory had made the first-ever detection of gravitational waves resulting from the collision of two black holes in a galaxy a billion light-years away,” says France Córdova, NSF director. “Today, we are delighted to announce the first discovery made in partnership between the Virgo Gravitational-Wave Observatory and the LIGO Scientific Collaboration, the first time a gravitational-wave detection was observed by these observatories, located thousands of miles apart. This is an exciting milestone in the growing international scientific effort to unlock the extraordinary mysteries of our Universe.”

Advanced LIGO is a second-generation gravitational-wave detector consisting of the two identical interferometers in Hanford and Livingston, and uses precision laser interferometry to detect gravitational waves. Beginning operating in September 2015, Advanced LIGO has conducted two observing runs. The second “O2” observing run began on November 30, 2016 and ended on August 25, 2017.

Advanced Virgo is the second-generation instrument built and operated by the Virgo collaboration to search for gravitational waves. With the end of observations with the initial Virgo detector in October 2011, the integration of the Advanced Virgo detector began. The new facility was dedicated in February 2017 while its commissioning was ongoing. In April, the control of the detector at its nominal working point was achieved for the first time.

The Virgo detector joined the O2 run on August 1, 2017 at 10:00 UTC. The real-time detection on August 14 was triggered with data from all three LIGO and Virgo instruments. Virgo is, at present, less sensitive than LIGO, but two independent search algorithms based on all the information available from the three detectors demonstrated the evidence of a signal in the Virgo data as well.

Overall, the volume of universe that is likely to contain the source shrinks by more than a factor of 20 when moving from a two-detector network to a three-detector network. The sky region for GW170814 has a size of only 60 square degrees, more than 10 times smaller than with data from the two LIGO interferometers alone; in addition, the accuracy with which the source distance is measured benefits from the addition of Virgo.

“This increased precision will allow the entire astrophysical community to eventually make even more exciting discoveries, including multi-messenger observations,” says Georgia Tech professor Laura Cadonati, the deputy spokesperson of the LSC. “A smaller search area enables follow-up observations with telescopes and satellites for cosmic events that produce gravitational waves and emissions of light, such as the collision of neutron stars.”

“As we increase the number of observatories in the international gravitational wave network, we not only improve the source location, but we also recover improved polarization information that provides better information on the orientation of the orbiting objects as well as enabling new tests of Einstein’s theory,” says Fred Raab, LIGO associate director for observatory operations.

LIGO and VIRGO’s partner electromagnetic facilities around the world didn’t identify a counterpart for GW170814, which was similar to the three prior LIGO observations of black hole mergers. Black holes produce gravitational waves but not light.

“With this first joint detection by the Advanced LIGO and Virgo detectors, we have taken one step further into the gravitational-wave cosmos,” says Caltech’s David H. Reitze, the executive director of the LIGO Laboratory. “Virgo brings a powerful new capability to detect and better locate gravitational-wave sources, one that will undoubtedly lead to exciting and unanticipated results in the future.”

Near-Earth asteroid 1991 VG

Dynamical evolution of near-Earth asteroid 1991 VG

ABSTRACT: The discovery of 1991 VG on 1991 November 6 attracted an unprecedented amount of attention as it was the first near-Earth object (NEO) ever found on an Earth-like orbit. At that time, it was considered by some as the first representative of a new dynamical class of asteroids, while others argued that an artificial (terrestrial or extra-terrestrial) origin was more likely. Over a quarter of a century later, this peculiar NEO has been recently recovered and the new data may help in confirming or ruling out early theories about its origin. Here, we use the latest data to perform an independent assessment of its current dynamical status and short-term orbital evolution. Extensive N-body simulations show that its orbit is chaotic on time-scales longer than a few decades. We confirm that 1991 VG was briefly captured by Earth’s gravity as a minimoon during its previous flyby in 1991-1992; although it has been a recurrent transient co-orbital of the horseshoe type in the past and it will return as such in the future, it is not a present-day co-orbital companion of the Earth. A realistic NEO orbital model predicts that objects like 1991 VG must exist and, consistently, we have found three other NEOs (2001 GP2, 2008 UA202 and 2014 WA366), which are dynamically similar to 1991 VG. All this evidence confirms that there is no compelling reason to believe that 1991 VG is not natural.


Atmospheric tides & rotational dynamics

Atmospheric tides and their consequences on the rotational dynamics of terrestrial planets

ABSTRACT: Atmospheric tides can have a strong impact on the rotational dynamics of planets. They are of most importance for terrestrial planets located in the habitable zone of their host star, where their competition with solid tides is likely to drive the body towards non-synchronized rotation states of equilibrium, as observed in the case of Venus. Contrary to other planetary layers, the atmosphere is sensitive to both gravitational and thermal forcings, through a complex dynamical coupling involving the effects of Coriolis acceleration and characteristics of the atmospheric structure. These key physics are usually not taken into account in modelings used to compute the evolution of planetary systems, where tides are described with parametrised prescriptions. In this work, we present a new ab initio modeling of atmospheric tides adapting the theory of the Earth’s atmospheric tides (Chapman & Lindzen 1970) to other terrestrial planets. We derive analytic expressions of the tidal torque, as a function of the tidal frequency and parameters characterizing the internal structure (e.g. the Brunt-Väisälä frequency, the radiative frequency, the pressure heigh scale). We show that stratification plays a key role, the tidal torque being strong in the case of convective atmospheres (i.e. with a neutral stratification) and weak in case of atmosphere convectively stable. In a second step, the model is used to determine the non-synchronized rotation states of equilibrium of Venus-like planets as functions of the physical parameters of the system. These results are detailed in Auclair-Desrotour et al. (2017a) and Auclair-Desrotour et al. (2017b).