New Way Supermassive Black Holes Are ‘Fed’

Supermassive black holes weigh millions to billions times more than our sun and lie at the center of most galaxies. A supermassive black hole several million times the mass of the sun is situated in the heart of our very own Milky Way.

Despite how commonplace supermassive black holes are, it remains unclear how they grow to such enormous proportions. Some black holes constantly swallow gas in their surroundings, some suddenly swallow whole stars. But neither theory independently explains how supermassive black holes can “switch on” so unexpectedly and keep growing so fast for a long period.

A new Tel Aviv University-led study published today in Nature Astronomy finds that some supermassive black holes are triggered to grow, suddenly devouring a large amount of gas in their surroundings.

In February 2017, the All Sky Automated Survey for Supernovae discovered an event known as AT 2017bgt. This event was initially believed to be a “star swallowing” event, or a “tidal disruption” event, because the radiation emitted around the black hole grew more than 50 times brighter than what had been observed in 2004.

However, after extensive observations using a multitude of telescopes, a team of researchers led by Dr. Benny Trakhtenbrot and Dr. Iair Arcavi, both of TAU’s Raymond & Beverly Sackler School of Physics and Astronomy, concluded that AT 2017bgt represented a new way of “feeding” black holes.

“The sudden brightening of AT 2017bgt was reminiscent of a tidal disruption event,” says Dr. Trakhtenbrot. “But we quickly realized that this time there was something unusual. The first clue was an additional component of light, which had never been seen in tidal disruption events.”

Dr. Arcavi, who led the data collection, adds, “We followed this event for more than a year with telescopes on Earth and in space, and what we saw did not match anything we had seen before.”

The observations matched the theoretical predictions of another member of the research team, Prof. Hagai Netzer, also of Tel Aviv University.

“We had predicted back in the 1980s that a black hole swallowing gas from its surroundings could produce the elements of light seen here,” says Prof. Netzer. “This new result is the first time the process was seen in practice.”

Astronomers from the U.S., Chile, Poland and the U.K. took part in the observations and analysis effort, which used three different space telescopes, including the new NICER telescope installed on board the International Space Station.

One of the ultraviolet images obtained during the data acquisition frenzy turned out to be the millionth image taken by the Neil Gehrels Swift Observatory — an event celebrated by NASA, which operates this space mission.

The research team identified two additional recently reported events of black holes “switched on,” which share the same emission properties as AT 2017bgt. These three events form a new and tantalizing class of black hole re-activation.

“We are not yet sure about the cause of this dramatic and sudden enhancement in the black holes’ feeding rate,” concludes Dr. Trakhtenbrot. “There are many known ways to speed up the growth of giant black holes, but they typically happen during much longer timescales.”

“We hope to detect many more such events, and to follow them with several telescopes working in tandem,” says Dr. Arcavi. “This is the only way to complete our picture of black hole growth, to understand what speeds it up, and perhaps finally solve the mystery of how these giant monsters form.”

Double Star System Flips Planet-Forming Disk Into Pole Position

New research led by an astronomer at the University of Warwick has found the first confirmed example of a double star system that has flipped its surrounding disc to a position that leaps over the orbital plane of those stars. The international team of astronomers used the Atacama Large Millimeter/sub-millimeter Array (ALMA) to obtain high-resolution images of the Asteroid belt-sized disc.

The overall system presents the unusual sight of a thick hoop of gas and dust circling at right angles to the binary star orbit. Until now this setup only existed in theorists’ minds, but the ALMA observation proves that polar discs of this type exist, and may even be relatively common.

The new research is published today (14 January) by Royal Society University Research Fellow Dr Grant M. Kennedy of the University of Warwick’s Department of Physics and Centre for Exoplanets and Habitability in Nature Astronomy in a paper entitled “A circumbinary protoplanetary disc in a polar configuration.”

Dr Grant M. Kennedy of the University of Warwick said:

“Discs rich in gas and dust are seen around nearly all young stars, and we know that at least a third of the ones orbiting single stars form planets. Some of these planets end up being misaligned with the spin of the star, so we’ve been wondering whether a similar thing might be possible for circumbinary planets. A quirk of the dynamics means that a so-called polar misalignment should be possible, but until now we had no evidence of misaligned discs in which these planets might form.”

Dr Kennedy and his fellow researchers used ALMA to pin down the orientation of the ring of gas and dust in the system. The orbit of the binary was previously known, from observations that quantified how the stars move in relation to each other. By combining these two pieces of information they were able to establish that the dust ring was consistent with a perfectly polar orbit. This means that while the stellar orbits orbit each other in one plane, like two horses going around on a carousel, the disc surrounds these stars at right angles to their orbits, like a giant ferris wheel with the carousel at the centre.

Dr Grant M. Kennedy of the University of Warwick added:

“Perhaps the most exciting thing about this discovery is that the disc shows some of the same signatures that we attribute to dust growth in discs around single stars. We take this to mean planet formation can at least get started in these polar circumbinary discs. If the rest of the planet formation process can happen, there might be a whole population of misaligned circumbinary planets that we have yet to discover, and things like weird seasonal variations to consider.”

If there were a planet or planetoid present at the inner edge of the dust ring, the ring itself would appear from the surface as a broad band rising almost perpendicularly from the horizon. The polar configuration means that the stars would appear to move in and out of the disc plane, giving objects two shadows at times. Seasons on planets in such systems would also be different. On Earth they vary throughout the year as we orbit the Sun. A polar circumbinary planet would have seasons that also vary as different latitudes receive more or less illumination throughout the binary orbit.

Co-author Dr Daniel Price of Monash University’s Centre for Astrophysics (MoCA) and School of Physics and Astronomy added:

“We used to think other solar systems would form just like ours, with the planets all orbiting in the same direction around a single sun. But with the new images we see a swirling disc of gas and dust orbiting around two stars. It was quite surprising to also find that that disc orbits at right angles to the orbit of the two stars.

“Incredibly, two more stars were seen orbiting that disc. So if planets were born here there would be four suns in the sky!

“ALMA is just a fantastic telescope, it is teaching us so much about how planets in other solar systems are born.”

The research is supported by the Monash Warwick Alliance, established by the University of Warwick and Monash University in 2012 as a bold and innovative project to develop an Alliance with a breadth, scale and impact beyond standard practice in the sector.

California Storms Bring Fear Of Devastating Mudslides, Residents Warned To Evacuate

LOS ANGELES — A year after a mudslide swept through a fire-devastated California town, killing 21 people, residents of hundreds of homes in burn areas were told to pack up and leave as a Pacific storm threatened potential catastrophe.

In Riverside County east of Los Angeles, mandatory evacuations were ordered Monday for a dozen areas around the Holy Fire, which swept through an enormous swath of the Cleveland National Forest and surrounding areas last August.

“People in these zones MUST GO NOW. Rainstorms carry the potential for dangerous debris flows that can send mud, boulders and trees crashing down hillsides” with little or no warning, a county statement said.

The evacuation was later downgraded to voluntary, but authorities urged people to stay alert because of continuing rain forecasts.

In Santa Barbara County on the central coast, evacuation orders were set to take effect at 10 a.m. Tuesday for areas hit by the Sherpa, Whittier and Thomas fires.

“Gather family members, pets, and essential items,” a county statement said. A debris flow could also make roads impassable and strand people near the evacuation areas, especially in Montecito, Summerland and Carpinteria, the county warned.

After a devastating fire that burned and destabilized foothills, Montecito was hit by a powerful storm on Jan. 9, 2018, that sent water, mud and boulders sluicing down creeks and canyons. Twenty-three people died and over 100 homes were destroyed.

Weather forecasters have predicted a series of storms that could continue to bring rain and snow into the middle of the week. Flash flood watches were issued by the National Weather Service for burn areas in Los Angeles, Ventura and Santa Barbara counties, which could see as much as an inch of rain per hour from Tuesday afternoon into the evening.

All schools in Malibu were closed Tuesday.

Flooding and debris flows were a threat to hundreds of homes in areas below foothills and canyons that were swept by flames in recent years.

Los Angeles County authorities issued evacuation orders beginning Tuesday morning for some areas of the Woolsey Fire. The blaze that broke out in November destroyed more than 1,500 homes and other buildings from Ventura County to Malibu and killed four people.

On Monday, the first in the series of storms dumped an inch of rain in Los Angeles and snow in the mountains.

Rain closed the Knott’s Berry Farm and Six Flags Magic Mountain amusement parks.

In San Diego County, a 20-foot-long, 20-foot-deep sinkhole on an Interstate 805 off-ramp near Serra Mesa.

A mudslide closed a 4.4-mile section of section of Pacific Coast Highway just north of Malibu on Monday for several hours. In Encino, in the San Fernando Valley of Los Angeles, a guest house was pushed off its foundation by a 250-foot-long debris flow from a hillside. No one was hurt but the Fire Department said up to a dozen other homes were in the slide zone.

Ice and blowing snow shut down the Grapevine, a high pass on Interstate 5, a major route connecting Los Angeles with San Francisco. Dozens of cars and trucks were stranded before the road reopened after nightfall.

The Orderly Chaos Of Black Holes

During the formation of a black hole a bright burst of very energetic light in the form of gamma-rays is produced, these events are called gamma-ray bursts. The physics behind this phenomenon includes many of the least understood fields within physics today: general gravity, extreme temperatures and acceleration of particles far beyond the energy of the most powerful particle accelerators on Earth. In order to analyse these gamma-ray bursts, researchers from the University of Geneva (UNIGE), in collaboration with the Paul Scherrer Institute (PSI) of Villigen, Switzerland, the Institute of High Energy Physics in Beijing and the National Center for Nuclear Research of Swierk in Poland, have built the POLAR instrument, sent in 2016 to the Chinese Tiangong-2 space laboratory, to analyze gamma-ray bursts. Contrary to the theories developed, the first results of POLAR reveal that the high energy photons coming from gamma-ray bursts are neither completely chaotic, nor completely organized, but a mixture of the two: within short time slices, the photons are found to oscillate in the same direction, but the oscillation direction changes with time. These unexpected results are reported in a recent issue of the journal Nature Astronomy.

When two neutron stars collide or a super massive star collapses into itself, a black hole is created. This birth is accompanied by a bright burst of gamma-rays — very energetic light such as that emitted by radioactive sources — called a gamma-ray burst (GRB).

Is black hole birth environment organized or chaotic?

How and where the gamma-rays are produced is still a mystery, two different schools of thought on their origin exist. The first predicts that photons from GRBs are polarized, meaning the majority of them oscillate in the same direction. If this were the case, the source of the photons would likely be a strong and well organized magnetic field formed during the violent aftermath of the black hole production. A second theory suggests that the photons are not polarized, implying a more chaotic emission environment. But how to check this?

“Our international teams have built together the first powerful and dedicated detector, called POLAR, capable of measuring the polarization of gamma-rays from GRBs. This instrument allows us to learn more about their source,” said Xin Wu, professor in the Department of Nuclear and Particle Physics of the Faculty of Sciences of UNIGE. Its operating system is rather simple. It is a square of 50×50 cm2 consisting of 1600 scintillator bars in which the gamma-rays collide with the atoms that make up these bars. When a photon collides in a bar we can measure it, afterwards it can produce a second photon which can cause a second visible collision. “If the photons are polarized, we observe a directional dependency between the impact positions of the photons, continues Nicolas Produit, researcher at the Department of Astronomy of the Faculty of Sciences of UNIGE. On the contrary, if there is no polarization, the second photon resulting from the first collision will leave in a fully random direction.”

Order within chaos

In six months, POLAR has detected 55 gamma-ray bursts and scientist analyzed the polarization of gamma-rays from the 5 brightest ones. The results are surprising to say the least. “When we analyse the polarization of a gamma-ray burst as a whole, we see at most a very weak polarization, which seems to clearly favour several theories,” says Merlin Kole, a researcher at the Department of Nuclear and Particle Physics of the Faculty of Sciences of UNIGE and one of the main authors of the paper. Faced with this first result, the scientists looked in more detail at a very powerful 9 second long gamma-ray burst and cut it into time slices, each of 2 seconds long. “There, we discovered with surprise that, on the contrary, the photons are polarized in each slice, but the oscillation direction is different in each slice!,” Xin Wu enthuses. It is this changing direction which makes the full GRB appear as very chaotic and unpolarized. “The results show that as the explosion takes place, something happens which causes the photons to be emitted with a different polarization direction, what this could be we really don’t know,” continues Merlin Kole.

These first results confront the theorists with new elements and requires them to produce more detailed predictions. “We now want to build POLAR-2, which is bigger and more precise. With that we can dig deeper into these chaotic processes, to finally discover the source of the gamma-rays and unravel the mysteries of these highly energetic physical processes,” explains Nicolas Produit.

Santorini Volcano (Greece): Earthquake Swarm Southwest Off The Island

An earthquake swarm has been occurring near the island since this morning. So far, 16 quakes of magnitudes between 2 and 3.9 and at depths ranging between about 30-6 km have been detected.

The quakes are clustered about half way between Santorini’s SW end and the Christiana Island group.

The strongest shock with magnitude 3.9 occurred at 10:27 local time and might have been felt weakly by residents of the southern part of Santorini.

Although the quakes are near the Kameni line, a tectonic lineament in SW-NE direction which has been the preferred location for magma ascent (i.e. formation of volcanic vents) in the volcano’s past few 100,000 years of history, there is currently no indication that the earthquakes are volcanic in origin. It is much more likely that they represent a normal tectonic event.

However, Santorini being both a popular tourist destination and an active volcano, the situation merits close monitoring.

Cosmic Telescope Zooms In On The Beginning Of Time

Observations from Gemini Observatory identify a key fingerprint of an extremely distant quasar, allowing astronomers to sample light emitted from the dawn of time. Astronomers happened upon this deep glimpse into space and time thanks to an unremarkable foreground galaxy acting as a gravitational lens, which magnified the quasar’s ancient light. The Gemini observations provide critical pieces of the puzzle in confirming this object as the brightest appearing quasar so early in the history of the Universe, raising hopes that more sources like this will be found.

Before the cosmos reached its billionth birthday, some of the very first cosmic light began a long journey through the expanding Universe. One particular beam of light, from an energetic source called a quasar, serendipitously passed near an intervening galaxy, whose gravity bent and magnified the quasar’s light and refocused it in our direction, allowing telescopes like Gemini North to probe the quasar in great detail.

“If it weren’t for this makeshift cosmic telescope, the quasar’s light would appear about 50 times dimmer,” said Xiaohui Fan of the University of Arizona who led the study. “This discovery demonstrates that strongly gravitationally lensed quasars do exist despite the fact that we’ve been looking for over 20 years and not found any others this far back in time.”

The Gemini observations provided key pieces of the puzzle by filling a critical hole in the data. The Gemini North telescope on Maunakea, Hawai’i, utilized the Gemini Near-InfraRed Spectrograph (GNIRS) to dissect a significant swath of the infrared part of the light’s spectrum. The Gemini data contained the tell-tale signature of magnesium which is critical for determining how far back in time we are looking. The Gemini observations also led to a determination of the mass of the black hole powering the quasar. “When we combined the Gemini data with observations from multiple observatories on Maunakea, the Hubble Space Telescope, and other observatories around the world, we were able to paint a complete picture of the quasar and the intervening galaxy,” said Feige Wang of the University of California, Santa Barbara, who is a member of the discovery team.

That picture reveals that the quasar is located extremely far back in time and space — shortly after what is known as the Epoch of Reionization — when the very first light emerged from the Big Bang. “This is one of the first sources to shine as the Universe emerged from the cosmic dark ages,” said Jinyi Yang of the University of Arizona, another member of the discovery team. “Prior to this, no stars, quasars, or galaxies had been formed, until objects like this appeared like candles in the dark.”

The foreground galaxy that enhances our view of the quasar is especially dim, which is extremely fortuitous. “If this galaxy were much brighter, we wouldn’t have been able to differentiate it from the quasar,” explained Fan, adding that this finding will change the way astronomers look for lensed quasars in the future and could significantly increase the number of lensed quasar discoveries. However, as Fan suggested, “We don’t expect to find many quasars brighter than this one in the whole observable Universe.”

The intense brilliance of the quasar, known as J0439+1634 (J0439+1634 for short), also suggests that it is fueled by a supermassive black hole at the heart of a young forming galaxy. The broad appearance of the magnesium fingerprint captured by Gemini also allowed astronomers to measure the mass of the quasar’s supermassive black hole at 700 million times that of the Sun. The supermassive black hole is most likely surrounded by a sizable flattened disk of dust and gas. This torus of matter — known as an accretion disk — most likely continually spirals inward to feed the black hole powerhouse. Observations at submillimeter wavelengths with the James Clerk Maxwell Telescope on Maunakea suggest that the black hole is not only accreting gas but may be triggering star birth at a prodigious rate — which appears to be up to 10,000 stars per year; by comparison, our Milky Way Galaxy makes one star per year. However, because of the boosting effect of gravitational lensing, the actual rate of star formation could be much lower.

Quasars are extremely energetic sources powered by huge black holes thought to have resided in the very first galaxies to form in the Universe. Because of their brightness and distance, quasars provide a unique glimpse into the conditions in the early Universe. This quasar has a redshift of 6.51, which translates to a distance of 12.8 billion light years, and appears to shine with a combined light of about 600 trillion Suns, boosted by the gravitational lensing magnification. The foreground galaxy which bent the quasar’s light is about half that distance away, at a mere 6 billion light years from us.

Fan’s team selected J0439+1634 as a very distant quasar candidate based on optical data from several sources: the Panoramic Survey Telescope and Rapid Response System1 (Pan-STARRS1; operated by the University of Hawai’i’s Institute for Astronomy), the United Kingdom Infra-Red Telescope Hemisphere Survey (conducted on Maunakea, Hawai’i), and NASA’s Wide-field Infrared Survey Explorer (WISE) space telescope archive.

The first follow-up spectroscopic observations, conducted at the Multi-Mirror Telescope in Arizona, confirmed the object as a high-redshift quasar. Subsequent observations with the Gemini North and Keck I telescopes in Hawai’i confirmed the MMT’s finding, and led to Gemini’s detection of the crucial magnesium fingerprint — the key to nailing down the quasar’s fantastic distance. However, the foreground lensing galaxy and the quasar appear so close that it is impossible to separate them with images taken from the ground due to blurring of the Earth’s atmosphere. It took the exquisitely sharp images by the Hubble Space Telescope to reveal that the quasar image is split into three components by a faint lensing galaxy.

The quasar is ripe for future scrutiny. Astronomers also plan to use the Atacama Large Millimeter/submillimeter Array, and eventually NASA’s James Webb Space Telescope, to look within 150 light-years of the black hole and directly detect the influence of the gravity from black hole on gas motion and star formation in its vicinity. Any future discoveries of very distant quasars like J0439+1634 will continue to teach astronomers about the chemical environment and the growth of massive black holes in our early Universe.

Giant Pattern Discovered In The Clouds Of Planet Venus

A Japanese research group has identified a giant streak structure among the clouds covering planet Venus based on observation from the spacecraft Akatsuki. The team also revealed the origins of this structure using large-scale climate simulations. The group was led by Project Assistant Professor Hiroki Kashimura (Kobe University, Graduate School of Science) and these findings were published on January 9 in Nature Communications.

Venus is often called Earth’s twin because of their similar size and gravity, but the climate on Venus is very different. Venus rotates in the opposite direction to Earth, and a lot more slowly (about one rotation for 243 Earth days). Meanwhile, about 60 km above Venus’ surface a speedy east wind circles the planet in about 4 Earth days (at 360 km/h), a phenomenon known as atmospheric superrotation.

The sky of Venus is fully covered by thick clouds of sulfuric acid that are located at a height of 45-70 km, making it hard to observe the planet’s surface from Earth-based telescopes and orbiters circling Venus. Surface temperatures reach a scorching 460 degrees Celsius, a harsh environment for any observations by entry probes. Due to these conditions, there are still many unknowns regarding Venus’ atmospheric phenomena.

To solve the puzzle of Venus’ atmosphere, the Japanese spacecraft Akatsuki began its orbit of Venus in December 2015. One of the observational instruments of Akatsuki is an infrared camera “IR2” that measures wavelengths of 2 ?m (0.002 mm). This camera can capture detailed cloud morphology of the lower cloud levels, about 50 km from the surface. Optical and ultraviolet rays are blocked by the upper cloud layers, but thanks to infrared technology, dynamic structures of the lower clouds are gradually being revealed.

Before the Akatsuki mission began, the research team developed a program called AFES-Venus for calculating simulations of Venus’ atmosphere. On Earth, atmospheric phenomena on every scale are researched and predicted using numerical simulations, from the daily weather forecast and typhoon reports to anticipated climate change arising from global warming. For Venus, the difficulty of observation makes numerical simulations even more important, but this same issue also makes it hard to confirm the accuracy of the simulations.

AFES-Venus had already succeeded in reproducing superrotational winds and polar temperature structures of the Venus atmosphere. Using the Earth Simulator, a supercomputer system provided by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), the research team created numerical simulations at a high spatial resolution. However, because of the low quality of observational data before Akatsuki, it was hard to prove whether these simulations were accurate reconstructions.

This study compared detailed observational data of the lower cloud levels of Venus taken by Akatsuki’s IR2 camera with the high-resolution simulations from the AFES-Venus program. The left part of the image above shows the lower cloud levels of Venus captured by the IR2 camera. Note the almost symmetrical giant streaks across the northern and southern hemispheres. Each streak is hundreds of kilometers wide and stretches diagonally almost 10,000 kilometers across. This pattern was revealed for the first time by the IR2 camera, and the team have named it a planetary-scale streak structure. This scale of streak structure has never been observed on Earth, and could be a phenomenon unique to Venus. Using the AFES-Venus high-resolution simulations, the team reconstructed the pattern (right-hand side of above image). The similarity between this structure and the camera observations prove the accuracy of the AFES-Venus simulations.

Next, through detailed analyses of the AFES-Venus simulation results, the team revealed the origin of this giant streak structure. The key to this structure is a phenomenon closely connected to Earth’s everyday weather: polar jet streams. In mid and high latitudes of Earth, a large-scale dynamics of winds (baroclinic instability) forms extratropical cyclones, migratory high-pressure systems, and polar jet streams. The results of the simulations showed the same mechanism at work in the cloud layers of Venus, suggesting that jet streams may be formed at high latitudes. At lower latitudes, an atmospheric wave due to the distribution of large-scale flows and the planetary rotation effect (Rossby wave) generates large vortexes across the equator to latitudes of 60 degrees in both directions. When jet streams are added to this phenomenon, the vortexes tilt and stretch, and the convergence zone between the north and south winds forms as a streak. The north-south wind that is pushed out by the convergence zone becomes a strong downward flow, resulting in the planetary-scale streak structure. The Rossby wave also combines with a large atmospheric fluctuation located over the equator (equatorial Kelvin wave) in the lower cloud levels, preserving the symmetry between hemispheres.

This study revealed the giant streak structure on the planetary scale in the lower cloud levels of Venus, replicated this structure with simulations, and suggested that this streak structure is formed from two types of atmospheric fluctuations (waves), baroclinic instability and jet streams. The successful simulation of the planetary-scale streak structure formed from multiple atmospheric phenomena is evidence for the accuracy of the simulations for individual phenomena calculated in this process.

Until now, studies of Venus’ climate have mainly focused on average calculations from east to west. This finding has raised the study of Venus’ climate to a new level in which discussion of the detailed three-dimensional structure of Venus is possible. The next step, through collaboration with Akatsuki and AFES-Venus, is to solve the puzzle of the climate of Earth’s twin Venus, veiled in the thick cloud of sulfuric acid.