Bulge in Venus’ atmosphere likely caused by gravity waves

The massive bow wave is visible in the upper atmosphere of Venus in this infrared image

A massive, bow-shaped wave was spotted for the first time in the highest regions of Venus’ atmosphere, perplexing astronomers.

The structure was captured by the Japan Aerospace Exploration Agency (JAXA) in some of the first images returned by their Akatsuki orbiter following a troubled orbital insertion in late 2015. Using both infrared and UV imaging, researchers spotted the prominent feature in the planet’s upper atmosphere, where winds whip by in excess of 200 miles per hour. Any features spotted in the atmosphere should get carried along by the fierce winds, but this curved wave remained planted firmly in place, lasting for at least four days.

Planet-spanning

The wave extends for more than 6,000 miles, stretching nearly from pole to pole. It is marked by the presence of slightly warmer air in the upper portion of the planet’s thick atmosphere, some 40 miles above the surface. While small aberrations are common in the upper atmosphere, such a large feature, to say nothing of one that refuses to move, is highly uncommon.

Venus’ atmosphere is in a state of super-rotation, meaning it moves much faster than the planet does. Venus rotates very slowly on its axis, completing just one rotation every 243 Earth days — longer than it takes the planet to go around the sun. On Earth, winds move only 10 to 20 percent the speed of the planet at most, but on Venus they far outpace the planet’s stately spin.

Gravity Waves

The researchers believe that the enormous structure might be caused by so-called “gravity waves” in Venus’ atmosphere. Gravity waves (which are entirely different than gravitational waves), are upheavals in a planet’s atmosphere caused by winds colliding with features on the surface. In the case of Venus, mountainous features on the surface may be forcing winds into the upper atmosphere, where they slow down enough to create a lasting bow wave. Indeed, the atmospheric bulge is located above Aphrodite Terra, a continent-sized region of highlands. The researchers discuss their findings in a paper published Monday in Nature Geoscience.

An illustration of how gravity waves likely form on Venus. Surface winds are pushed upwards by topological features such as mountains into the upper atmosphere where they “break” like waves on a shore, slowing down high-altitude winds.

ESA

The bow wave was only spotted for four days near the beginning of Akatsuki’s mission. When researchers looked again a month later, it had disappeared. Scientists have observed the presence of gravity waves in the upper atmosphere of Venus before — the European Space Agency’s Venus Express orbiter found the telltale cloud shapes over the smaller Ishtar Terra region in 2014 — but those gravity waves were not nearly as large as the planet-spanning feature found by JAXA.

Our understanding of gravity waves is currently based on models of Earth’s atmosphere. On Venus, where the air is composed mainly of carbon dioxide and the atmospheric pressure is almost 100 times greater than that on Earth, the atmospheric dynamics are likely different. The waves could give astronomers another way to discern the terrain hidden beneath Venus’ thick layer of opaque clouds.

Signs of Modern Astronomy Seen in Ancient Babylon

Clay tablets, including one at the left, revealed that Babylonian astronomers employed a sort of precalculus to describe Jupiter’s motion across the night sky relative to distant background stars. They did this 15 centuries earlier than Europeans were first credited with making such measurements.CreditLeft to right: Trustees of the British Museum/Mathieu Ossendrijver; NASA

For people living in the ancient city of Babylon, Marduk was their patron god, and thus it is not a surprise that Babylonian astronomers took an interest in tracking the comings and goings of the planet Jupiter, which they regarded as a celestial manifestation of Marduk.

What is perhaps more surprising is the sophistication with which they tracked the planet, judging from inscriptions on a small clay tablet dating to between 350 B.C. and 50 B.C. The tablet, a couple of inches wide and a couple of inches tall, reveals that the Babylonian astronomers employed a sort of precalculus in describing Jupiter’s motion across the night sky relative to the distant background stars. Until now, credit for this kind of mathematical technique had gone to Europeans who lived some 15 centuries later.

“That is a truly astonishing find,” said Mathieu Ossendrijver, a professor at Humboldt University in Berlin, who describes his archaeological astronomy discovery in an article on Thursday in the journal Science.

“It’s a figure that describes a graph of velocity against time,” he said. “That is a highly modern concept.”

Mathematical calculations on four other tablets show that the Babylonians realized that the area under the curve on such a graph represented the distance traveled.

“I think it’s quite a remarkable discovery,” said Alexander Jones, a professor at the Institute for the Study of the Ancient World at New York University, who was not involved with the research. “It’s really quite clear from the text.”

Ancient Babylon, situated in what is now Iraq, south of Baghdad, was a thriving metropolis, a center of trade and science. Early Babylonian mathematicians who lived between 1800 B.C. and 1600 B.C. had figured out, for example, how to calculate the area of a trapezoid, and even how to divide a trapezoid into two smaller trapezoids of equal area.

For the most part, Babylonians used their mathematical skills for mundane calculations, like figuring out the size of a plot of land. But on some tablets from the later Babylonian period, there appear to be some trapezoid calculations related to astronomical observations.

In the 1950s, an Austrian-American mathematician and science historian, Otto E. Neugebauer, described two of them. Dr. Ossendrijver, in his recent research, turned up two more.

But it was not clear what the Babylonian astronomers were calculating.

A year ago, a visitor showed Dr. Ossendrijver a stack of photographs of Babylonian tablets that are now held by the British Museum in London. He saw a tablet he had not seen before. This tablet, with impressions of cuneiform script pressed into clay, did not mention trapezoids, but it recorded the motion of Jupiter, and the numbers matched those on the tablets with the trapezoid calculations.

“I was certain now it was Jupiter,” Dr. Ossendrijver said.

When Jupiter first appears in the night sky, it moves at a certain velocity relative to the background stars. Because Jupiter and Earth both constantly move in their orbits, to observers on Earth, Jupiter appears to slow down, and 120 days after it becomes visible, it comes to a standstill and reverses course.

In September, Dr. Ossendrijver went to the British Museum, where the tablets were taken in the late 19th century after being excavated. A close-up look of the new tablet confirmed it: The Babylonians were calculating the distance Jupiter traveled in the sky from its appearance to its position 60 days later. Using the technique of splitting a trapezoid into two smaller ones of equal area, they then figured out how long it took Jupiter to travel half that distance.

Dr. Ossendrijver said he did not know the astronomical or astrological motivation for these calculations.

It was an abstract concept not known elsewhere at the time. “Ancient Greek astronomers and mathematicians didn’t make plots of something against time,” Dr. Ossendrijver said. He said that until now, such calculations were not known until the 14th century by scholars in England and France. These mathematicians of the Middle Ages perhaps had seen some as yet unknown texts dating to Babylonian times, or they developed the same techniques independently.

“It anticipates integral calculus,” Dr. Ossendrijver said. “This is utterly familiar to any modern physicist or mathematician.”

Supernova observed colliding with its companion star

In this still from a simulation, a Type Ia supernova explodes (dark brown colour). The supernova material is ejected outwards at a velocity of about 10,000 kilometres/second. The ejected material then slams into its companion star (light blue colour). The violent collision produces an ultraviolet pulse that is emitted from the conical hole carved out by the companion star. Image credit: Daniel Kasen.
The origin of type Ia supernovae, the standard candles used to reveal the presence of dark energy in the universe, is one of astronomy’s most beguiling mysteries. Astronomers know they occur when a white dwarf explodes in a binary system with another star, but the properties of that second star — and how it triggers the explosion — have remained elusive for decades.

Now, a team of astronomers from the intermediate Palomar Transient Factory (iPTF), including those associated with UC Santa Barbara, have witnessed a supernova smashing into a nearby star, shocking it, and creating an ultraviolet glow that reveals the size of the companion. The discovery involved the rapid response and coordination of iPTF, NASA’s Swift satellite and the new capabilities of the Las Cumbres Observatory Global Telescope Network (LCOGT).

The supernova, named iPTF14atg, is located 300 million light-years away in the galaxy IC 831. The study, appearing in the May 21st issue of Nature, was led by graduate student Yi Cao of Caltech, but included physics postdoctoral fellows Iair Arcavi and Stefano Valenti, and physics faculty member Andrew Howell of UCSB and LCOGT.

In a type Ia supernova, a white dwarf star explodes after it gains matter from a companion star in the same binary star system. One of the leading theories is that the supernova happens when two white dwarf stars merge. But a competing theory says that the companion could be a normal or giant star that survives the explosion, although not without some damage. The supernova is expected to hit the companion star, creating a shock wave that glows in ultraviolet light. This had been theorised in 2010, but such an effect had never been seen. This and other factors led many to conclude that most type Ia supernovae arise from the mergers of two white dwarf stars.

“As you can imagine, I was fired up when I first saw a bright spot at the location of this supernova in the ultraviolet image,” first author Yi Cao said of seeing the ultraviolet flash. “I knew this was likely what we had been hoping for.”

LCOGT, a global network of robotic telescopes, was influential in obtaining early and regular data, allowing the researchers to determine the type and even the strange subclass of the supernova. Initially, the team was puzzled, said Arcavi.

“Hot, blue supernovae are not supposed to happen in old, dead galaxies,” he said. “And yet, as our robotic telescopes gathered the data, we watched in amazement as the blue supernova morphed into a type Ia supernova.”

Upon hearing about the supernova, the LCOGT team immediately triggered their worldwide fleet of robotic telescopes. As the Earth rotated, data was collected at different sites, depending on where it was nighttime and the observing conditions were ideal. Ultimately they combined data from LCOGT telescopes located in Texas, Hawaii and South Africa with data from Palomar and NASA’s Swift satellite to piece together the story of the supernova.

“As the data came in, I started to notice that this supernova was a weird one,” said Valenti. “It was a type Ia, but one with a slow-moving explosion.”

According to the researchers, the supernova belongs to a subclass of SNe Ia sometimes called SN 2002cx-like. These supernovae may even be partially failed or incomplete explosions. In a normal type Ia the entire white dwarf blows up, but this class may leave a piece behind.

There have been conflicting observations about the progenitors of type Ia supernovae. The new study builds on previous work by Howell and some of the study’s coauthors showing that the type Ia SN 2011fe was likely the result of a merger of two white dwarf stars, while the SN Ia PTF11kx seemed to have a red giant companion star.

Said Howell, “No wonder we’ve been so confused for decades. Apparently you can blow up stars in two different ways and still get nearly identical explosions.”

In fact, the study complements work by another postdoc and member of the supernova team at LCOGT and UCSB, Curtis McCully, who was not involved in the present study. He led a team of astronomers who announced in Nature in 2014 that they had found a progenitor on pre-explosion images from the Hubble Space Telescope for a similar SN 2002cx-like supernova, SN 2012Z. In that case, they think what they saw was the companion star, the star that in the case of iPTF14atg shocked the supernova.

“We are finally beginning to see how differences in the progenitor stars relate to differences in the explosion,” McCully said. “This is exciting because the better we understand the origin of type Ia supernovae, the better we can use them as standard candles for cosmology.”

The iPTF project is a scientific collaboration between Caltech; Los Alamos National Laboratory; the University of Wisconsin-Milwaukee; the Oskar Klein Center in Sweden; the Weizmann Institute of Science in Israel; the TANGO Program of the University System of Taiwan; and the Kavli Institute for the Physics and Mathematics of the Universe in Japan. The Caltech team is funded in part by the National Science Foundation.

LCOGT is a global network of 11 one-meter and two-meter telescopes with headquarters in Santa Barbara, California. It has telescopes in Hawaii, Texas, Australia, South Africa and Chile.

NASA’s WISE spacecraft discovers most luminous galaxy in universe

This artist's concept depicts the current record holder for the most luminous galaxy in the universe.

A remote galaxy shining with the light of more than 300 trillion Suns has been discovered using data from NASA’s Wide-field Infrared Survey Explorer (WISE). The galaxy is the most luminous found to date and belongs to a new class of objects recently discovered by WISE — extremely luminous infrared galaxies (ELIRGs).

“We are looking at a very intense phase of galaxy evolution,” said Chao-Wei Tsai of NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California. “This dazzling light may be from the main growth spurt of the galaxy’s black hole.”

The brilliant galaxy, known as WISE J224607.57-052635.0, may have a behemoth black hole at its belly, gorging itself on gas. Supermassive black holes draw gas and matter into a disk around them, heating the disk to roaring temperatures of millions of degrees and blasting out high-energy, visible, ultraviolet, and X-ray light. The light is blocked by surrounding cocoons of dust. As the dust heats up, it radiates infrared light.

Immense black holes are common at the cores of galaxies, but finding one this big so “far back” in the cosmos is rare. Because light from the galaxy hosting the black hole has traveled 12.5 billion years to reach us, astronomers are seeing the object as it was in the distant past. The black hole was already billions of times the mass of our Sun when our universe was only a tenth of its present age of 13.8 billion years.

The new study outlines three reasons why the black holes in the ELIRGs could have grown so massive. First, they may have been born big. In other words, the “seeds,” or embryonic black holes, might be bigger than thought possible.

“How do you get an elephant?” asked Peter Eisenhardt from JPL. “One way is start with a baby elephant.”

The other two explanations involve either breaking or bending the theoretical limit of black hole feeding called the Eddington limit. When a black hole feeds, gas falls in and heats up, blasting out light. The pressure of the light actually pushes the gas away, creating a limit to how fast the black hole can continuously scarf down matter. If a black hole broke this limit, it could theoretically balloon in size at a breakneck pace. Black holes have previously been observed breaking this limit; however, the black hole in the study would have had to repeatedly break the limit to grow this large.

Alternatively, the black holes might just be bending this limit.

“Another way for a black hole to grow this big is for it to have gone on a sustained binge, consuming food faster than typically thought possible,” said Tsai. “This can happen if the black hole isn’t spinning that fast.”

If a black hole spins slowly enough, it won’t repel its meal as much. In the end, a slow-spinning black hole can gobble up more matter than a fast spinner.

“The massive black holes in ELIRGs could be gorging themselves on more matter for a longer period of time,” said Andrew Blain of the University of Leicester in the United Kingdom. “It’s like winning a hot-dog-eating contest lasting hundreds of millions of years.”

More research is needed to solve this puzzle of these dazzlingly luminous galaxies. The team has plans to better determine the masses of the central black holes. Knowing these objects’ true hefts will help reveal their history, as well as that of other galaxies, in this very crucial and frenzied chapter of our cosmos.

WISE has been finding more of these oddball galaxies in infrared images of the entire sky captured in 2010. By viewing the whole sky with more sensitivity than ever before, WISE has been able to catch rare cosmic specimens that might have been missed otherwise.

The new study reports a total of 20 new ELIRGs, including the most luminous galaxy found to date. These galaxies were not found earlier because of their distance, and because dust converts their powerful visible light into an incredible outpouring of infrared light.

“We found in a related study with WISE that as many as half of the most luminous galaxies only show up well in infrared light,” said Tsai.

Herschel and Planck find missing clue to galaxy cluster formation

The Planck all-sky map at submillimeter wavelengths (545 GHz). The band running through the middle corresponds to dust in our Milky Way Galaxy. The black dots indicate the location of the proto-cluster candidates identified by Planck and subsequently observed by Herschel. The inset images showcase some of the observations made by Herschel’s SPIRE instrument; the contours represent the density of galaxies.

By combining observations of the distant universe made with the European Space Agency’s (ESA) Herschel and Planck space observatories, cosmologists have discovered what could be the precursors of the vast clusters of galaxies that we see today. 

Galaxies like our Milky Way with its 100 billion stars are usually not found in isolation. In the universe today, 13.8 billion years after the Big Bang, many are in dense clusters of tens, hundreds, or even thousands of galaxies. 

However, these clusters have not always existed, and a key question in modern cosmology is how such massive structures assembled in the early universe. 

Pinpointing when and how they formed should provide insight into the process of galaxy cluster evolution, including the role played by dark matter in shaping these cosmic metropolises. 

Now, using the combined strengths of Herschel and Planck, astronomers have found objects in the distant universe seen at a time when it was only 3 billion years old that could be precursors of the clusters seen around us today.

Planck’s main goal was to provide the most precise map of the relic radiation of the Big Bang, the cosmic microwave background. To do so, it surveyed the entire sky in nine different wavelengths from the far-infrared to radio in order to eliminate foreground emission from our galaxy and others in the universe. 

But those foreground sources can be important in other fields of astronomy, and it was in Planck’s short-wavelength data that scientists were able to identify 234 bright sources with characteristics that suggested they were located in the distant early universe. 

Herschel then observed these objects across the far-infrared to submillimeter wavelength range but with much higher sensitivity and angular resolution. 

Herschel revealed that the vast majority of the Planck-detected sources are consistent with dense concentrations of galaxies in the early universe, vigorously forming new stars. 

Each of these young galaxies is seen to be converting gas and dust into stars at a rate of a few hundred to 1,500 times the mass of our Sun per year. By comparison, our Milky Way Galaxy today is producing stars at an average rate of just one solar mass per year. 

While the astronomers have not yet conclusively established the ages and luminosities of many of these newly discovered distant galaxy concentrations, they are the best candidates yet found for “protoclusters” — precursors of the large mature galaxy clusters we see in the universe today. 

“Hints of these kinds of objects had been found earlier in data from Herschel and other telescopes, but the all-sky capability of Planck revealed many more candidates for us to study,” said Hervé Dole of the Institut d’Astrophysique Spatiale, Orsay. 

“We still have a lot to learn about this new population, requiring further follow-up studies with other observatories. But we believe that they are a missing piece of cosmological structure formation.” 

“We are now preparing an extended catalog of possible protoclusters detected by Planck, which should help us identify even more of these objects,” said Ludovic Montier from the Institut de Recherche en Astrophysique et Planétologie, Toulouse. 

“This exciting result was possible thanks to the synergy between Herschel and Planck: rare objects could be identified from the Planck data covering the entire sky, and then Herschel was able to scrutinize them in finer detail,” said Göran Pilbratt from ESA. 

“Both space observatories completed their science observations in 2013, but their rich datasets will be exploited for plentiful new insights about the cosmos for years to come.”