Supermassive Black Holes Feed On Cosmic Jellyfish

An Italian-led team of astronomers used the MUSE (Multi-Unit Spectroscopic Explorer) instrument on the Very Large Telescope (VLT) at ESO’s Paranal Observatory in Chile to study how gas can be stripped from galaxies. They focused on extreme examples of jellyfish galaxies in nearby galaxy clusters, named after the remarkable long “tentacles” of material that extend for tens of thousands of light-years beyond their galactic discs .

The tentacles of jellyfish galaxies are produced in galaxy clusters by a process called ram pressure stripping. Their mutual gravitational attraction causes galaxies to fall at high speed into galaxy clusters, where they encounter a hot, dense gas which acts like a powerful wind, forcing tails of gas out of the galaxy’s disc and triggering starbursts within it.

Six out of the seven jellyfish galaxies in the study were found to host a supermassive black hole at the centre, feeding on the surrounding gas [3]. This fraction is unexpectedly high — among galaxies in general the fraction is less than one in ten.

“This strong link between ram pressure stripping and active black holes was not predicted and has never been reported before,” said team leader Bianca Poggianti from the INAF-Astronomical Observatory of Padova in Italy. “It seems that the central black hole is being fed because some of the gas, rather than being removed, reaches the galaxy centre.” [4]

A long-standing question is why only a small fraction of supermassive black holes at the centres of galaxies are active. Supermassive black holes are present in almost all galaxies, so why are only a few accreting matter and shining brightly? These results reveal a previously unknown mechanism by which the black holes can be fed.

Yara Jaffe, an ESO fellow who contributed to the paper explains the significance: “These MUSE observations suggest a novel mechanism for gas to be funnelled towards the black hole’s neighbourhood. This result is important because it provides a new piece in the puzzle of the poorly understood connections between supermassive black holes and their host galaxies.”

The current observations are part of a much more extensive study of many more jellyfish galaxies that is currently in progress.

“This survey, when completed, will reveal how many, and which, gas-rich galaxies entering clusters go through a period of increased activity at their cores,” concludes Poggianti. “A long-standing puzzle in astronomy has been to understand how galaxies form and change in our expanding and evolving Universe. Jellyfish galaxies are a key to understanding galaxy evolution as they are galaxies caught in the middle of a dramatic transformation.”

Galactic Winds Push Researchers To Probe Galaxies At Unprecedented Scale

When astronomers peer into the universe, what they see often exceeds the limits of human understanding. Such is the case with low-mass galaxies — galaxies a fraction of the size of our own Milky Way.

These small, faint systems made up of millions or billions of stars, dust, and gas constitute the most common type of galaxy observed in the universe. But according to astrophysicists’ most advanced models, low-mass galaxies should contain many more stars than they appear to contain.

A leading theory for this discrepancy hinges on the fountain-like outflows of gas observed exiting some galaxies. These outflows are driven by the life and death of stars, specifically stellar winds and supernova explosions, which collectively give rise to a phenomenon known as “galactic wind.” As star activity expels gas into intergalactic space, galaxies lose precious raw material to make new stars. The physics and forces at play during this process, however, remain something of a mystery.

To better understand how galactic wind affects star formation in galaxies, a two-person team led by the University of California, Santa Cruz, turned to high-performance computing at the Oak Ridge Leadership Computing Facility (OLCF), a US Department of Energy (DOE) Office of Science User Facility located at DOE’s Oak Ridge National Laboratory (ORNL). Specifically, UC Santa Cruz astrophysicist Brant Robertson and University of Arizona graduate student Evan Schneider (now a Hubble Fellow at Princeton University), scaled up their Cholla hydrodynamics code on the OLCF’s Cray XK7 Titan supercomputer to create highly detailed simulations of galactic wind.

“The process of generating galactic winds is something that requires exquisite resolution over a large volume to understand — much better resolution than other cosmological simulations that model populations of galaxies,” Robertson said. “This is something you really need a machine like Titan to do.”

After earning an allocation on Titan through DOE’s INCITE program, Robertson and Schneider started small, simulating a hot, supernova-driven wind colliding with a cool cloud of gas across 300 light years of space. (A light year equals the distance light travels in 1 year.) The results allowed the team to rule out a potential mechanism for galactic wind.

Now the team is setting its sights higher, aiming to generate nearly a trillion-cell simulation of an entire galaxy, which would be the largest simulation of a galaxy ever. Beyond breaking records, Robertson and Schneider are striving to uncover new details about galactic wind and the forces that regulate galaxies, insights that could improve our understanding of low-mass galaxies, dark matter, and the evolution of the universe.

Simulating cold clouds

About 12 million light years from Earth resides one of the Milky Way’s closest neighbors, a disk galaxy called Messier 82 (M82). Smaller than the Milky Way, M82’s cigar shape underscores a volatile personality. The galaxy produces new stars about five times faster than our own galaxy’s rate of star production. This star-making frenzy gives rise to galactic wind that pushes out more gas than the system keeps in, leading astronomers to estimate that M82 will run out of fuel in just 8 million years.

Analyzing images from NASA’s Hubble Space Telescope, scientists can observe this slow-developing exodus of gas and dust. Data gathered from such observations can help Robertson and Schneider gauge if they are on the right track when simulating galactic wind.

“With galaxies like M82, you see a lot of cold material at large radius that’s flowing out very fast. We wanted to see, if you took a realistic cloud of cold gas and hit it with a hot, fast-flowing, supernova-driven outflow, if you could accelerate that cold material to velocities like what are observed,” Robertson said.

Answering this question in high resolution required an efficient code that could solve the problem based on well-known physics, such as the motion of liquids. Robertson and Schneider developed Cholla to carry out hydrodynamics calculations entirely on GPUs, highly parallelized accelerators that excel at simple number crunching, thus achieving high-resolution results.

In Titan, a 27-petaflop system containing more than 18,000 GPUs, Cholla found its match. After testing the code on a GPU cluster at the University of Arizona, Robertson and Schneider benchmarked Cholla under two small OLCF Director’s Discretionary awards before letting the code loose under INCITE. In test runs, the code has maintained scaling across more than 16,000 GPUs.

“We can use all of Titan,” Robertson said, “which is kind of amazing because the vast majority of the power of that system is in GPUs.”

The pairing of code and computer gave Robertson and Schneider the tools needed to produce high-fidelity simulations of gas clouds measuring more than 15 light years in diameter. Furthermore, the team can zoom in on parts of the simulation to study phases and properties of galactic wind in isolation. This capability helped the team to rule out a theory that posited cold clouds close to the galaxy’s center could be pushed out by fast-moving, hot wind from supernovas.

“The answer is it isn’t possible,” Robertson said. “The hot wind actually shreds the clouds and the clouds become sheared and very narrow. They’re like little ribbons that are very difficult to push on.”

Galactic goals

Having proven Cholla’s computing chops, Robertson and Schneider are now planning a full-galaxy simulation about 10 to 20 times larger than their previous effort. Expanding the size of the simulation will allow the team to test an alternate theory for the emergence of galactic wind in disk galaxies like M82. The theory suggests that clouds of cold gas condense out of the hot outflow as they expand and cool.

“That’s something that’s been posited in analytical models but not tested in simulation,” Robertson said. “You have to model the whole galaxy to capture this process because the dynamics of the outflows are such that you need a global simulation of the disk.”

The full-galaxy simulation will likely be composed of hundreds of billions of cells representing more than 30,000 light years of space. To cover this expanse, the team must sacrifice resolution. It can rely on its detailed gas cloud simulations, however, to bridge scales and inform unresolved physics within the larger simulation.

“That’s what’s interesting about doing these simulations at widely different scales,” Robertson said. “We can calibrate after the fact to inform ourselves in how we might be getting the story wrong with the coarser, larger simulation.”

Lunar Dynamo’s Lifetime Extended By At Least 1 Billion Years

New evidence from ancient lunar rocks suggests that an active dynamo once churned within the molten metallic core of the moon, generating a magnetic field that lasted at least 1 billion years longer than previously thought. Dynamos are natural generators of magnetic fields around terrestrial bodies, and are powered by the churning of conducting fluids within many stars and planets. In a paper published today in Science Advances, researchers from MIT and Rutgers University report that a lunar rock collected by NASA’s Apollo 15 mission exhibits signs that it formed 1 to 2.5 billion years ago in the presence of a relatively weak magnetic field of about 5 microtesla. That’s around 10 times weaker than Earth’s current magnetic field but still 1,000 times larger than fields in interplanetary space today.

Several years ago, the same researchers identified 4-billion-year-old lunar rocks that formed under a much stronger field of about 100 microtesla, and they determined that the strength of this field dropped off precipitously around 3 billion years ago. At the time, the researchers were unsure whether the moon’s dynamo — the related magnetic field — died out shortly thereafter or lingered in a weakened state before dissipating completely.

The results reported today support the latter scenario: After the moon’s magnetic field dwindled, it nonetheless persisted for at least another billion years, existing for a total of at least 2 billion years.

Study co-author Benjamin Weiss, professor of planetary sciences in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS), says this new extended lifetime helps to pinpoint the phenomena that powered the moon’s dynamo. Specifically, the results raise the possibility of two different mechanisms — one that may have driven an earlier, much stronger dynamo, and a second that kept the moon’s core simmering at a much slower boil toward the end of its lifetime.

“The concept of a planetary magnetic field produced by moving liquid metal is an idea that is really only a few decades old,” Weiss says. “What powers this motion on Earth and other bodies, particularly on the moon, is not well-understood. We can figure this out by knowing the lifetime of the lunar dynamo.”

Weiss’ co-authors are lead author Sonia Tikoo, a former MIT graduate student who is now an assistant professor at Rutgers; David Shuster of the University of California at Berkeley; Clément Suavet and Huapei Wang of EAPS; and Timothy Grove, the R.R. Schrock Professor of Geology and associate head of EAPS.

Apollo’s glassy recorders

Since NASA’s Apollo astronauts brought back samples from the lunar surface, scientists have found some of these rocks to be accurate “recorders” of the moon’s ancient magnetic field. Such rocks contain thousands of tiny grains that, like compass needles, aligned in the direction of ancient fields when the rocks crystallized eons ago. Such grains can give scientists a measure of the moon’s ancient field strength.

Until recently, Weiss and others had been unable to find samples much younger than 3.2 billion years old that could accurately record magnetic fields. As a result, they had only been able to gauge the strength of the moon’s magnetic field between 3.2 and 4.2 billion years ago.

“The problem is, there are very few lunar rocks that are younger than about 3 billion years old, because right around then, the moon cooled off, volcanism largely ceased and, along with it, formation of new igneous rocks on the lunar surface,” Weiss explains. “So there were no young samples we could measure to see if there was a field after 3 billion years.”

There is, however, a small class of rocks brought back from the Apollo missions that formed not from ancient lunar eruptions but from asteroid impacts later in the moon’s history. These rocks melted from the heat of such impacts and recrystallized in orientations determined by the moon’s magnetic field.

Weiss and his colleagues analyzed one such rock, known as Apollo 15 sample 15498, which was originally collected on Aug. 1, 1971, from the southern rim of the moon’s Dune Crater. The sample is a mix of minerals and rock fragments, welded together by a glassy matrix, the grains of which preserve records of the moon’s magnetic field at the time the rock was assembled.

“We found that this glassy material that welds things together has excellent magnetic recording properties,” Weiss says.

Baking rocks

The team determined that the rock sample was about 1 to 2.5 billion years old — much younger than the samples they previously analyzed. They developed a technique to decipher the ancient magnetic field recorded in the rock’s glassy matrix by first measuring the rock’s natural magnetic properties using a very sensitive magnetometer.

They then exposed the rock to a known magnetic field in the lab, and heated the rock to close to the extreme temperatures in which it originally formed. They measured how the rock’s magnetization changed as they increased the surrounding temperature.

“You see how magnetized it gets from getting heated in that known magnetic field, then you compare that field to the natural magnetic field you measured beforehand, and from that you can figure out what the ancient field strength was,” Weiss explains.

The researchers did have to make one significant adjustment to the experiment to better simulate the original lunar environment, and in particular, its atmosphere. While the Earth’s atmosphere contains around 20 percent oxygen, the moon has only imperceptible traces of the gas. In collaboration with Grove, Suavet built a customized, oxygen-deprived oven in which to heat the rocks, preventing them from rusting while at the same time simulating the oxygen-free environment in which the rocks were originally magnetized.

“In this way, we finally have gotten an accurate measurement of the lunar field,” Weiss says.

From ice cream makers to lava lamps

From their experiments, the researchers determined that, around 1 to 2.5 billion years ago, the moon harbored a relatively weak magnetic field, with a strength of about 5 microtesla — two orders of magnitude weaker than the moon’s field around 3 to 4 billion years ago. Such a dramatic dip suggests to Weiss and his colleagues that the moon’s dynamo may have been driven by two distinct mechanisms.

Scientists have proposed that the moon’s dynamo may have been powered by the Earth’s gravitational pull. Early in its history, the moon orbited much closer to the Earth, and the Earth’s gravity, in such close proximity, may have been strong enough to pull on and rotate the rocky exterior of the moon. The moon’s liquid center may have been dragged along with the moon’s outer shell, generating a very strong magnetic field in the process.

It’s thought that the moon may have moved sufficiently far away from the Earth by about 3 billion years ago, such that the power available for the dynamo by this mechanism became insufficient. This happens to be right around the time the moon’s magnetic field strength dropped. A different mechanism may have then kicked in to sustain this weakened field. As the moon moved away from the Earth, its core likely sustained a low boil via a slow process of cooling over at least 1 billion years.

“As the moon cools, its core acts like a lava lamp — low-density stuff rises because it’s hot or because its composition is different from that of the surrounding fluid,” Weiss says. “That’s how we think the Earth’s dynamo works, and that’s what we suggest the late lunar dynamo was doing as well.”

The researchers are planning to analyze even younger lunar rocks to determine when the dynamo died off completely.

“Today the moon’s field is essentially zero,” Weiss says. “And we now know it turned off somewhere between the formation of this rock and today.”

This research was supported, in part, by NASA.

Possible Explanation For The Dominance Of Matter Over Antimatter In The Universe

Neutrinos and antineutrinos, sometimes called ghost particles because difficult to detect, can transform from one type to another. The international T2K Collaboration announces a first indication that the dominance of matter over antimatter may originate from the fact that neutrinos and antineutrinos behave differently during those oscillations. This is an important milestone towards the understanding of our Universe. A team of particle physicists from the University of Bern provided important contributions to the experiment.

The Universe is primarily made of matter and the apparent lack of antimatter is one of the most intriguing questions of today’s science. The T2K collaboration, with participation of the group of the University of Bern, announced today in a colloquium held at the High Energy Accelerator Research Organization (KEK) in Tsukuba, Japan, that it found indication that the symmetry between matter and antimatter (so called “CP-Symmetry”) is violated for neutrinos with 95% probability.

Different Transformation of Neutrinos and Antineutrinos

Neutrinos are elementary particles which travel through matter almost without interaction. They appear in three different types: electron- muon- and tau-neutrinos and their respective antiparticle (antineutrinos). In 2013 T2K discovered a new type of transformation among neutrinos, showing that muon-neutrinos transform (oscillate) into electron-neutrinos while travelling in space and time. The outcome of the latest T2K study rejects with 95% probability the hypothesis that the analogous transformation from muon-antineutrinos to electron-antineutrinos takes place with identical chance. This is a first indication that the symmetry between matter and antimatter is violated in neutrino oscillations and therefore neutrinos also play a role in the creation of the matter-antimatter asymmetry in the universe.

“This result is among the most important findings in neutrino physics over the last years,” said Prof. Antonio Ereditato, director of the Laboratory of High Energy Physics of the University of Bern and leader of the Bern T2K group, “and it is opening the way to even more exciting achievements, pointing to the existence of a tiny but measurable effect.” Ereditato added: “Nature seems to indicate that neutrinos can be responsible for the observed supremacy of matter over antimatter in the Universe. What we measured justifies our current efforts in preparing the next scientific enterprise, DUNE, the ultimate neutrino detector in USA, which should allow reaching a definitive discovery.”

In the T2K experiment a muon-neutrino beam is produced at the Proton Accelerator Research Complex (J-PARC) in Tokai on the east coast of Japan and is detected 295 kilometres away by the gigantic Super-Kamiokande underground detector (“T2K” stands for “Tokai to Kamiokande”). The neutrino beam needs to be fully characterized immediately after production, that means before neutrinos start to oscillate. For this purpose, the ND280 detector was built and installed close to the neutrino departing point.

Researchers from the University of Bern, together with colleagues from Geneva and ETH Zurich, and other international institutions, contributed to the design, realization and operation of ND280. The group of Bern, in particular, took care of the large magnet surrounding the detector and built and operated the so-called muon monitor, a device needed to measure the intensity and the energy spectrum of the muon particles produced together with neutrinos. The Bern group is currently very active in determining the probability of interaction of neutrinos with the ND280 apparatus: an important ingredient to reach high-precision measurements such as the one reported here.

Primordial Black Holes May Have Helped To Forge Heavy Elements

Astronomers like to say we are the byproducts of stars, stellar furnaces that long ago fused hydrogen and helium into the elements needed for life through the process of stellar nucleosynthesis.

As the late Carl Sagan once put it: “The nitrogen in our DNA, the calcium in our teeth, the iron in our blood, the carbon in our apple pies were made in the interiors of collapsing stars. We are made of star stuff.”

But what about the heavier elements in the periodic chart, elements such as gold, platinum and uranium?

Astronomers believe most of these “r-process elements” — elements much heavier than iron — were created, either in the aftermath of the collapse of massive stars and the associated supernova explosions, or in the merging of binary neutron star systems.

“A different kind of furnace was needed to forge gold, platinum, uranium and most other elements heavier than iron,” explained George Fuller, a theoretical astrophysicist and professor of physics who directs UC San Diego’s Center for Astrophysics and Space Sciences. “These elements most likely formed in an environment rich with neutrons.”

In a paper published August 7 in the journal Physical Review Letters, he and two other theoretical astrophysicists at UCLA — Alex Kusenko and Volodymyr Takhistov — offer another means by which stars could have produced these heavy elements: tiny black holes that came into contact with and are captured by neutron stars, and then destroy them.

Neutron stars are the smallest and densest stars known to exist, so dense that a spoonful of their surface has an equivalent mass of three billion tons.

Tiny black holes are more speculative, but many astronomers believe they could be a byproduct of the Big Bang and that they could now make up some fraction of the “dark matter” — the unseen, nearly non-interacting stuff that observations reveal exists in the universe.

If these tiny black holes follow the distribution of dark matter in space and co-exist with neutron stars, Fuller and his colleagues contend in their paper that some interesting physics would occur.

They calculate that, in rare instances, a neutron star will capture such a black hole and then devoured from the inside out by it. This violent process can lead to the ejection of some of the dense neutron star matter into space.

“Small black holes produced in the Big Bang can invade a neutron star and eat it from the inside,” Fuller explained. “In the last milliseconds of the neutron star’s demise, the amount of ejected neutron-rich material is sufficient to explain the observed abundances of heavy elements.”

“As the neutron stars are devoured,” he added, “they spin up and eject cold neutron matter, which decompresses, heats up and make these elements.”

This process of creating the periodic table’s heaviest elements would also provide explanations for a number of other unresolved puzzles in the universe and within our own Milky Way galaxy.

“Since these events happen rarely, one can understand why only one in ten dwarf galaxies is enriched with heavy elements,” said Fuller. “The systematic destruction of neutron stars by primordial black holes is consistent with the paucity of neutron stars in the galactic center and in dwarf galaxies, where the density of black holes should be very high.”

In addition, the scientists calculated that ejection of nuclear matter from the tiny black holes devouring neutron stars would produce three other unexplained phenomenon observed by astronomers.

“They are a distinctive display of infrared light (sometimes termed a “kilonova”), a radio emission that may explain the mysterious Fast Radio Bursts from unknown sources deep in the cosmos, and the positrons detected in the galactic center by X-ray observations,” said Fuller. “Each of these represent long-standing mysteries. It is indeed surprising that the solutions of these seemingly unrelated phenomena may be connected with the violent end of neutron stars at the hands of tiny black holes.”

Funding for this project was provided by the National Science Foundation (PHY-1614864) at UC San Diego and by the U.S. Department of Energy (DE-SC0009937) at UCLA. Alex Kusenko was also supported, in part, by the World Premier International Research Center Initiative (WPI), MEXT, Japan.

Primordial Asteroids Discovered

Southwest Research Institute (SwRI) was part of an international team that recently discovered a relatively unpopulated region of the main asteroid belt, where the few asteroids present are likely pristine relics from early in solar system history. The team used a new search technique that also identified the oldest known asteroid family, which extends throughout the inner region of the main asteroid belt.

The main belt contains vast numbers of irregularly shaped asteroids, also known as planetesimals, orbiting the Sun between Mars and Jupiter. As improved telescope technology finds smaller and more distant asteroids, astronomers have identified clusters of similar-looking bodies clumped in analogous orbits. These familial objects are likely fragments of catastrophic collisions between larger asteroids eons ago. Finding and studying asteroid families allows scientists to better understand the history of main belt asteroids.

“By identifying all the families in the main belt, we can figure out which asteroids have been formed by collisions and which might be some of the original members of the asteroid belt,” said SwRI Astronomer Dr. Kevin Walsh, a coauthor of the online Science paper detailing the findings. “We identified all known families and their members and discovered a gigantic void in the main belt, populated by only a handful of asteroids. These relics must be part of the original asteroid belt. That is the real prize, to know what the main belt looked like just after it formed.”

Identifying the very oldest asteroid families, those billions of years old, is challenging, because over time, a family spreads out. As asteroids rotate in orbit around the Sun, their surfaces heat up during the day and cool down at night. This creates radiation that can act as a sort of mini-thruster, causing asteroids to drift widely over time. After billions of years, family members would be almost impossible to identify, until now. The team used a novel technique, searching asteroid data from the inner region of the belt for old, dispersed families. They looked for the “edges” of families, those fragments that have drifted the furthest.

“Each family member drifts away from the center of the family in a way that depends on its size, with small guys drifting faster and further than the larger guys,” said team leader Marco Delbo, an astronomer from the Observatory of Cote d’Azur in Nice, France. “If you look for correlations of size and distance, you can see the shapes of old families.”

“The family we identified has no name, because it is not clear which asteroid is the parent,” Walsh said. “This family is so old that it appears to have formed over 4 billion years ago, before the gas giants in the outer solar system moved into their current orbits. The giant planet migration shook up the asteroid belt, removing many bodies, possibly including the parent of this family.”

The team plans to apply this new technique to the entire asteroid belt to reveal more about the history of the solar system by identifying the primordial asteroids versus fragments of collisions. This research was supported by the French National Program of Planetology and the National Science Foundation. The resulting paper, “Identification of a primordial asteroid family constrains the original planetesimal population,” appears in the August 3, 2017, online edition of Science.

Twilight Observations Reveal Huge Storm On Neptune

Spectacular sunsets and sunrises are enough to dazzle most of us, but to astronomers, dusk and dawn are a waste of good observing time. They want a truly dark sky.

Not Ned Molter, a UC Berkeley astronomy graduate student. He set out to show that some bright objects can be studied just as well during twilight, when other astronomers are twiddling their thumbs, and quickly discovered a new feature on Neptune: A storm system nearly the size of Earth.

“Seeing a storm this bright at such a low latitude is extremely surprising,” said Molter, who spotted the storm complex near Neptune’s equator during a dawn test run of twilight observing at W. M. Keck Observatory on Maunakea, Hawaii. “Normally, this area is really quiet and we only see bright clouds in the mid-latitude bands, so to have such an enormous cloud sitting right at the equator is spectacular.”

This massive storm system, which was found in a region where no bright cloud has ever been seen before, is about 9,000 kilometers in length, or one-third the size of Neptune’s radius, spanning at least 30 degrees in both latitude and longitude. Molter observed it getting much brighter between June 26 and July 2.

“Historically, very bright clouds have occasionally been seen on Neptune, but usually at latitudes closer to the poles, around 15 to 60 degrees north or south,” said Imke de Pater, a UC Berkeley professor of astronomy and Molter’s adviser. “Never before has a cloud been seen at or so close to the equator, nor has one ever been this bright.”

At first, de Pater thought it was the same Northern Cloud Complex seen by the Hubble Space Telescope in 1994, after the iconic Great Dark Spot, imaged by Voyager 2 in 1989, had disappeared. But de Pater says measurements of its locale do not match, signaling that this cloud complex is different from the one Hubble first saw more than two decades ago.

A huge, high-pressure, dark vortex system anchored deep in Neptune’s atmosphere may be what’s causing the colossal cloud cover, said de Pater. As gases rise up in a vortex, they cool down. When its temperature drops below the condensation temperature of a condensable gas, that gas condenses out and forms clouds, just like water on Earth. On Neptune, however, methane clouds form.

As with every planet, winds in Neptune’s atmosphere vary drastically with latitude, so if there is a big bright cloud system that spans many latitudes, something must hold it together, such as a dark vortex. Otherwise, the clouds would shear apart.

“This big vortex is sitting in a region where the air, overall, is subsiding rather than rising,” said de Pater. “Moreover, a long-lasting vortex right at the equator would be hard to explain physically.”

If it is not tied to a vortex, the system may be a huge convective cloud, similar to those seen occasionally on other planets, like the huge storm on Saturn that was detected in 2010. However, such a cloud would be expected to smear out considerably over a week’s time.

“This shows that there are extremely drastic changes in the dynamics of Neptune’s atmosphere, and perhaps this is a seasonal weather event that may happen every few decades or so,” said de Pater.

A windy planet

Neptune is the windiest planet in our solar system, with the fastest observed wind speeds at the equator reaching up to a violent 1,000 mph. To put this into perspective, a Category 5 hurricane has wind speeds of 156 mph. Neptune orbits the sun every 160 years, and one season is about 40 years.

The discovery of Neptune’s mysterious equatorial cloud complex was made possible by the new Keck Visiting Scholars Program, launched this summer, which gives graduate students and post-doctoral researchers experience working at the telescope, while contributing to Keck Observatory and its scientific community.

“This result by Imke and her first-year graduate student, Ned, is a perfect example of what we’re trying to accomplish with the Keck Visiting Scholars Program,” said Anne Kinney, chief scientist at Keck Observatory. “Ned is our first visiting scholar, and his incredible work is a testament to the value of this program. It’s just been an outrageous success.”

Molter is one of eight scholars accepted into the program this year. His assignment during his six-week stay at the Observatory was to develop a more efficient method for twilight observing, making use of time that otherwise might not be used. Most observers in the Keck Observatory community peer deep into the night sky and cannot observe their targets during twilight.

“Ned had never observed before, and he’s very bright, so when Anne told me about the program, I knew he would be the perfect student for it,” said de Pater. “Now that we’ve discovered this interesting cloud complex in Neptune, Ned has a running start on a nice paper for his Ph.D. thesis.”

“I loved being at Keck. Everyone was extremely friendly and I had a ton of personal interaction with the support astronomers and observing assistants,” Molter said. “Being able to go behind the scenes to see how they run the telescopes and instruments every day, getting 10 nights of observing and engineering time on the telescopes and going up to the summit twice to see the incredible engineering behind this gigantic machine has turned me from a student into an actual observer. It was an incredible opportunity.”

The Keck Visiting Scholars Program is sponsored by Roy and Frances Simperman, with major contributions from the M.R. and Evelyn Hudson Foundation, W.M. Keck Foundation, Edge of Space, Inc., Thomas McIntyre, and Jeff and Rebecca Steele.

Molter and De Pater will continue to analyze their data and propose for more twilight observing time at Keck Observatory this fall so they can learn more about the nature of this storm and get an idea of what it will be doing over time.

Having a better understanding of Neptune’s atmosphere will help give astronomers a clearer picture of this icy giant’s global circulation. This has become increasingly more important in the exoplanet realm, as a majority of exoplanets found so far are nearly the size of Neptune. While scientists can calculate their size and mass, not much is currently known about exoplanets’ atmosphere.