First named Pterosaur from Japan sheds light on ancient flying reptiles – Newly identified Nipponopterus mifunensis highlights international collaboration and Japan’s rich prehistoric heritage
A team of researchers from Japan, China, and Brazil has announced the discovery of a new species of pterosaur from the Late Cretaceous of Japan, marking the first time a pterosaur has been named based on body fossils found in the country.
The species, Nipponopterus mifunensis, was identified from a partial neck vertebra originally discovered in the 1990s in the Mifune Group geological formation in Kumamoto Prefecture, located on Japan’s southern island of Kyushu. After a detailed reassessment using advanced CT scanning provided by Kumamoto University and subsequent phylogenetic analysis, the research team concluded that the specimen represents a new genus and species within the Azhdarchidae family—a group known for containing some of the largest flying animals that ever lived. The fossil is now on public display at the Mifune Dinosaur Museum in Kumamoto Prefecture, offering visitors a rare glimpse into Japan’s ancient skies.
“This is a major step forward for Japanese paleontology,” said Dr. Naoki Ikegami from the Mifune Dinosaur Museum, “Until now, no pterosaur had been formally named from skeletal remains found in Japan. This discovery provides crucial new insight into the diversity and evolution of pterosaurs in East Asia.”
Interestingly, Nipponopterus may have had a wingspan approaching 3 to 3.5 meters and lived during the Turonian–Coniacian stages of the Late Cretaceous, making it one of the earliest known members of its lineage.
The newly identified sixth cervical vertebra (neck bone) of Nipponopterus mifunensis reveals a set of striking features not seen in any previously known species. Most notably, it has a prominent, elevated dorsal keel that runs along the back of the bone—extending not just over the epipophysis but across the entire postexapophyseal peduncle. Additional distinctive traits include a long groove running along the underside (ventral sulcus), a subtriangular-shaped condyle, and unusually positioned postexapophyses that project outward to the sides. These characteristics set Nipponopterus mifunensis apart from all other known azhdarchid pterosaurs. Phylogenetic analysis places it within the Quetzalcoatlinae subfamily, identifying it as a close relative of both the mysterious “Burkhant azhdarchid” from Mongolia and the giant Quetzalcoatlus of North America.
Published in the peer-reviewed journal Cretaceous Research, the study was the result of an international collaboration involving researchers from Shihezi University in China, the Zoology Museum at the University of São Paulo in Brazil, and a team in Japan from the Mifune Dinosaur Museum, Kumamoto University, and Hokkaido University. Researchers worked closely together, combining expertise in fossil analysis, imaging technology, analytical modeling and evolutionary studies.
“It’s a beautiful example of how science transcends borders,”
noted Professor Toshifumi Mukunoki from the Faculty of Advanced Science and Technology, Kumamoto University.
Nipponopterus mifunensis, a newly identified pterosaur known from a single neck vertebra, once soared through the ancient skies of what is now Japan. Picture Credits: Zhao Chuang
Bibliographic information:
Xuanyu Zhou, Naoki Ikegami, Rodrigo V. Pêgas, Toru Yoshinaga, Takahiro Sato, Toshifumi Mukunoki, Jun Otani, Yoshitsugu Kobayashi, Reassessment of an azhdarchid pterosaur specimen from the Mifune Group, Upper Cretaceous of Japan, Cretaceous Research Volume 167, 2025, 106046, ISSN 0195-6671, DOI: https://doi.org/10.1016/j.cretres.2024.106046
Understanding the “eating just one potato chip is impossible” gene
Scientists reveal genetic mechanism associated with high-calorie food-fueled obesity
Understanding the “eating just one potato chip is impossible” gene. Osaka Metropolitan University scientists have revealed that the transcription cofactor gene CRTC1 mediates the obesity-suppressing effects of melanocortin-4 receptor (MC4R) by regulating appetite for fats and oils, high-fat diet metabolism, and blood sugar. Credits: Shigenobu Matsumura, Osaka Metropolitan University
High-calorie foods—high in fat, oil, and sugar—can taste good but often cause overeating, leading to obesity and major health problems. But what stimulates the brain to cause overeating?
Recently, it has become clear that a gene called CREB-Regulated Transcription Coactivator 1 (CRTC1) is associated with obesity in humans. When CRTC1 is deleted in mice, they become obese, indicating that functioning CRTC1 suppresses obesity. However, since CRTC1 is expressed in all neurons in the brain, the specific neurons responsible for suppressing obesity and the mechanism present in those neurons remained unknown.
To elucidate the mechanism by which CRTC1 suppresses obesity, a research group led by Associate Professor Shigenobu Matsumura from the Graduate School of Human Life and Ecology at Osaka Metropolitan University focused on neurons expressing the melanocortin-4 receptor (MC4R). They hypothesized that CRTC1 expression in MC4R-expressing neurons suppressed obesity because mutations in the MC4R gene are known to cause obesity. Consequently, they created a strain of mice that expresses CRTC1 normally except in MC4R-expressing neurons where it is blocked to examine the effect that losing CRTC1 in those neurons had on obesity and diabetes.
When fed a standard diet, the mice without CRTC1 in MC4R-expressing neurons showed no changes in body weight compared to control mice. However, when the CRTC1-deficient mice were raised on a high-fat diet, they overate, then became significantly more obese than the control mice and developed diabetes.
“This study has revealed the role that the CRTC1 gene plays in the brain, and part of the mechanism that stops us from overeating high-calorie, fatty, and sugary foods,” said Professor Matsumura. “We hope this will lead to a better understanding of what causes people to overeat.”
The research results were published in the FASEB Journal on November 9, 2022.
Funding
This study was supported by the Takeda Life Science Foundation, Sugiyama Sangyo-Kagaku General Incorporated Foundation, and JSPS KAKENHI grant numbers 19H02909 and 18K19174.
Massive marimo algae balls at risk from deadly winter sunburn
Reduced lake-ice cover due to climate change may further decline of endangered species
Massive marimo algae balls at risk from deadly winter sunburn. The alga Aegagropila linnaei can live as free-floating filaments, grow on rocks, grow into the signature ball shape and form flattened balls when squished, depending on their environment. Ball growth is slow at about 5 millimeters per year and they can live for centuries. Credits: copyright 2022 Yoichi Oyama
Climate change could overexpose rare underwater “marimo” algae balls to sunlight, killing them off according to a new study at the University of Tokyo. Marimo are living fluffy balls of green algae. The world’s largest marimo can be found in Lake Akan in Hokkaido, Japan’s northern main island. Here they are sheltered from too much winter sunlight by a thick layer of ice and snow, but the ice is thinning due to global warming. Researchers found that the algae could survive bright light for up to four hours and would recover if then placed under a moderate light for 30 minutes. However, the algae died when exposed to bright light for six hours or more. The team hopes this discovery will highlight the threat of climate change to this endangered species and the urgent need to protect their habitat.
Some people have pet cats, others pet rocks, but how about pet algae? Marimo are fluffy, squishy green balls of underwater algae which have become popular with tourists, nature enthusiasts and aquarium owners. They range in size from about a pea to a basketball, and form naturally when floating strands of the algae Aegagropila linnaei are bundled together through the gentle rolling motion of lake water. They are only found in a few countries and the largest marimo, found in Lake Akan, can grow up to 30 centimeters in diameter. In Japan, they are so popular that they have their own annual festival, merchandise and even a mascot. However, marimo are an endangered species and globally their numbers are generally in decline.
Temperatures underwater are kept relatively stable and warm at around 1-4 degrees Celsius, thanks to the blanket of ice and snow. Above ground, however, they vary from minus 18 degrees to 1 degree Celsius. Credits: copyright 2022 Asami Fujita
Marimo rely on nutrients and photosynthesis to survive. Their decline is usually attributed to human intervention altering or polluting the freshwater lakes in which they live. However, there has not been much research into the effect of changing access to sunlight.
“We know that marimo can survive bright sunlight in warm summer waters, but the photosynthetic properties in marimo at low winter temperatures have not been studied, so we were fascinated by this point,” said Project Assistant Professor Masaru Kono from the Graduate School of Science at the University of Tokyo. “We wanted to find out whether Marimo could tolerate it and how they respond to a low-temperature, high light-intensity environment.”
Kono and team visited Lake Akan’s Churui Bay in winter to measure the temperature and light intensity underwater, both with and without ice cover. First, they bored a small hole in the ice 80 meters offshore and then carved a large 2.5 meter-by-2.5 meter square to take readings from. They also carefully collected several marimo balls about the size of a shot put (10-15 cm) by hand. Back in Tokyo, the team recreated the environmental conditions using trays of ice made with an icemaker and white LED lamps. Algae strands were removed from the marimo balls and tested for their normal photosynthetic ability. They were then placed in containers in the ice under the artificial light, which was adjusted to shine at different intensities for different periods of time.
“We demonstrated a new finding that damaged cells in marimo can repair themselves even after exposure to simulated strong daylight for up to four hours at cold temperatures (2-4 degrees Celsius), when followed by moderate light exposure for just 30 minutes. This moderate light had a restorative effect which did not occur in the dark. However, when exposed to strong daylight for six hours or more, certain cells involved in photosynthesis were damaged and the algae died, even after being treated with moderate light,” explained Kono. “These results suggest that photoinhibition (the inability to photosynthesize due to cell damage) would be a serious threat to marimo in Lake Akan, which receives more than 10 hours of sunlight a day in winter, if global warming proceeds and ice cover recedes.”
Massive marimo algae balls at risk from deadly winter sunburn. A researcher takes samples of algae filaments from the marimo ball. The ball is made up of green algae throughout and doesn’t have a different material at its core. Credits: Copyright 2022 Akina Obara
Next, the team want to find out what would happen to whole marimo balls and whether the outcome would be the same as with the smaller threads.
“In the present study, we used dissected filamentous cells, so we did not consider the effects of the structure of the spherical marimo and how it might protect against exposure to bright light. However, if damage to the surface cells increases under longer exposure to the direct sunlight, in an extreme case, this may affect the maintenance of their round bodies and lead to the disappearance of giant marimo. So, we need to constantly monitor the conditions at Lake Akan in the future” said Kono.
Kono hopes this research will help both local and national governments to understand the urgent need to protect Japan’s unique marimo and their habitat.
“We also hope this will be an opportunity for all people to think seriously about the effects of global warming,” he said.
Too much sun in cold temperatures cannot be processed and instead causes harmful, reactive chemicals to form. This damages the marimo’s ability to photosynthesize and repair itself. Credits: Copyright 2022 Akina Obara
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Paper Title:
Akina Obara, Mari Ogawa, Yoichi Oyama, Yoshihiro Suzuki, Masaru Kono. Effects of high irradiance and low water-temperature on photoinhibition and repair of photosystems in Marimo (Aegagropila linnaei) in Lake Akan, Japan. Int. J. Mol. Sci.2023, 24(1), 60; https://doi.org/10.3390/ijms24010060
ALMA finds possible sign of neutron star in supernova 1987A
Two teams of astronomers have made a compelling case in the 33-year-old mystery surrounding Supernova 1987A. Based on observations of the Atacama Large Millimeter/submillimeter Array (ALMA) and a theoretical follow-up study, the scientists provide new insight for the argument that a neutron star is hiding deep inside the remains of the exploded star. This would be the youngest neutron star known to date.
This artist’s illustration of Supernova 1987A shows the dusty inner regions of the exploded star’s remnants (red), in which a neutron star might be hiding. This inner region is contrasted with the outer shell (blue), where the energy from the supernova is colliding (green) with the envelope of gas ejected from the star prior to its powerful detonation. Credits: NRAO/AUI/NSF, B. Saxton
Ever since astronomers witnessed one of the brightest explosions of a star in the night sky, creating Supernova 1987A (SN 1987A), they have been searching for a compact object that should have formed in the leftovers from the blast.
Because particles known as neutrinos were detected on Earth on the day of the explosion (23 February 1987), astronomers expected that a neutron star had formed in the collapsed center of the star. But when scientists could not find any evidence for that star, they started to wonder whether it subsequently collapsed into a black hole instead. For decades the scientific community has been eagerly awaiting a signal from this object that has been hiding behind a very thick cloud of dust.
The “blob”
Extremely high-resolution ALMA images revealed a hot “blob” in the dusty core of Supernova 1987A (inset), which could be the location of the missing neutron star. The red color shows dust and cold gas in the center of the supernova remnant, taken at radio wavelengths with ALMA. The green and blue hues reveal where the expanding shock wave from the exploded star is colliding with a ring of material around the supernova. The green represents the glow of visible light, captured by NASA’s Hubble Space Telescope. The blue color reveals the hottest gas and is based on data from NASA’s Chandra X-ray Observatory. The ring was initially made to glow by the flash of light from the original explosion. Over subsequent years the ring material has brightened considerably as the explosion’s shock wave slams into it. Credits: ALMA (ESO/NAOJ/NRAO), P. Cigan and R. Indebetouw; NRAO/AUI/NSF, B. Saxton; NASA/ESA
Recently, observations from the ALMA radio telescope provided the first indication of the missing neutron star after the explosion. Extremely high-resolution images revealed a hot “blob” in the dusty core of SN 1987A, which is brighter than its surroundings and matches the suspected location of the neutron star.
“We were very surprised to see this warm blob made by a thick cloud of dust in the supernova remnant,” said Mikako Matsuura from Cardiff University and a member of the team that found the blob with ALMA. “There has to be something in the cloud that has heated up the dust and which makes it shine. That’s why we suggested that there is a neutron star hiding inside the dust cloud.”
Even though Matsuura and her team were excited about this result, they wondered about the brightness of the blob. “We thought that the neutron star might be too bright to exist, but then Dany Page and his team published a study that indicated that the neutron star can indeed be this bright because it is so very young,” said Matsuura.
Dany Page is an astrophysicist at the National Autonomous University of Mexico, who has been studying SN 1987A from the start. “I was halfway through my PhD when the supernova happened,” he said, “it was one of the biggest events in my life that made me change the course of my career to try to solve this mystery. It was like a modern holy grail.”
The theoretical study by Page and his team, published today in The Astrophysical Journal, strongly supports the suggestion made by the ALMA team that a neutron star is powering the dust blob. “In spite of the supreme complexity of a supernova explosion and the extreme conditions reigning in the interior of a neutron star, the detection of a warm blob of dust is a confirmation of several predictions,” Page explained.
These predictions were the location and the temperature of the neutron star. According to supernova computer models, the explosion has “kicked away” the neutron star from its birthplace with a speed of hundreds of kilometers per second (tens of times faster than the fastest rocket). The blob is exactly at the place where astronomers think the neutron star would be today. And the temperature of the neutron star, which was predicted to be around 5 million degrees Celsius, provides enough energy to explain the brightness of the blob.
Not a pulsar or a black hole
Contrary to common expectations, the neutron star is likely not a pulsar. “A pulsar’s power depends on how fast it spins and on its magnetic field strength, both of which would need to have very finely tuned values to match the observations,” said Page, “while the thermal energy emitted by the hot surface of the young neutron star naturally fits the data.”
“The neutron star behaves exactly like we expected,” added James Lattimer of Stony Brook University in New York, and a member of Page’s research team. Lattimer has also followed SN 1987A closely, having published prior to SN 1987A predictions of a supernova’s neutrino signal that subsequently matched the observations. “Those neutrinos suggested that a black hole never formed, and moreover it seems difficult for a black hole to explain the observed brightness of the blob. We compared all possibilities and concluded that a hot neutron star is the most likely explanation.”
This neutron star is a 25 km wide, extremely hot ball of ultra-dense matter. A teaspoon of its material would weigh more than all the buildings within New York City combined. Because it can only be 33 years old, it would be the youngest neutron star ever found. The second youngest neutron star that we know of is located in the supernova remnant Cassiopeia A and is 330 years old.
Only a direct picture of the neutron star would give definite proof that it exists, but for that astronomers may need to wait a few more decades until the dust and gas in the supernova remnant become more transparent.
Detailed ALMA images
This colorful, multiwavelength image of the intricate remains of Supernova 1987A is produced with data from three different observatories. The red color shows dust and cold gas in the center of the supernova remnant, taken at radio wavelengths with ALMA. The green and blue hues reveal where the expanding shock wave from the exploded star is colliding with a ring of material around the supernova. The green represents the glow of visible light, captured by NASA’s Hubble Space Telescope. The blue color reveals the hottest gas and is based on data from NASA’s Chandra X-ray Observatory. The ring was initially made to glow by the flash of light from the original explosion. Over subsequent years the ring material has brightened considerably as the explosion’s shock wave slams into it. Credits: ALMA (ESO/NAOJ/NRAO), P. Cigan and R. Indebetouw; NRAO/AUI/NSF, B. Saxton; NASA/ESA
Even though many telescopes have made images of SN 1987A, none of them have been able to observe its core with such high precision as ALMA. Earlier (3-D) observations with ALMA already showed the types of molecules found in the supernova remnant and confirmed that it produced massive amounts of dust.
“This discovery builds upon years of ALMA observations, showing the core of the supernova in more and more detail thanks to the continuing improvements to the telescope and data processing,” said Remy Indebetouw of the National Radio Astronomy Observatory and the University of Virginia, who has been a part of the ALMA imaging team.
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This research is presented in two papers:
ALMA observation of the “blob”: “High Angular Resolution ALMA Images of Dust and Molecules in the SN 1987A Ejecta”, by P. Cigan et al., The Astrophysical Journal. https://doi.org/10.3847/1538-4357/ab4b46
The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.
The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Organisation for Astronomical Research in the Southern Hemisphere (ESO), the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the Ministry of Science and Technology (MOST) and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).
ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.
What started out as a hunt for ice lurking in polar lunar craters turned into an unexpected finding that could help clear some muddy history about the Moon’s formation.
Team members of the Miniature Radio Frequency (Mini-RF) instrument on NASA’s Lunar Reconnaissance Orbiter (LRO) spacecraft found new evidence that the Moon’s subsurface might be richer in metals, like iron and titanium, than researchers thought. That finding, published July 1 in Earth and Planetary Science Letters, could aid in drawing a clearer connection between Earth and the Moon.
“The LRO mission and its radar instrument continue to surprise us with new insights about the origins and complexity of our nearest neighbor,” said Wes Patterson, Mini-RF principal investigator from the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland, and a study coauthor.
This image based on data from NASA’s Lunar Reconnaissance Orbiter spacecraft shows the face of the Moon we see from Earth. The more we learn about our nearest neighbor, the more we begin to understand the Moon as a dynamic place with useful resources that could one day even support human presence. Credits: NASA / GSFC / Arizona State University
Substantial evidence points to the Moon as the product of a collision between a Mars-sized protoplanet and young Earth, forming from the gravitational collapse of the remaining cloud of debris. Consequently, the Moon’s bulk chemical composition closely resembles that of Earth.
Look in detail at the Moon’s chemical composition, however, and that story turns murky. For example, in the bright plains of the Moon’s surface, called the lunar highlands, rocks contain smaller amounts of metal-bearing minerals relative to Earth. That finding might be explained if Earth had fully differentiated into a core, mantle and crust before the impact, leaving the Moon largely metal-poor. But turn to the Moon’s maria — the large, darker plains — and the metal abundance becomes richer than that of many rocks on Earth.
This discrepancy has puzzled scientists, leading to numerous questions and hypotheses regarding how much the impacting protoplanet may have contributed to the differences. The Mini-RF team found a curious pattern that could lead to an answer.
Using Mini-RF, the researchers sought to measure an electrical property within lunar soil piled on crater floors in the Moon’s northern hemisphere. This electrical property is known as the dielectric constant, a number that compares the relative abilities of a material and the vacuum of space to transmit electric fields, and could help locate ice lurking in the crater shadows. The team, however, noticed this property increasing with crater size.
For craters approximately 1 to 3 miles (2 to 5 kilometers) wide, the dielectric constant of the material steadily increased as the craters grew larger, but for craters 3 to 12 miles (5 to 20 kilometers) wide, the property remained constant.
“It was a surprising relationship that we had no reason to believe would exist,” said Essam Heggy, coinvestigator of the Mini-RF experiments from the University of Southern California in Los Angeles and lead author of the published paper.
Discovery of this pattern opened a door to a new possibility. Because meteors that form larger craters also dig deeper into the Moon’s subsurface, the team reasoned that the increasing dielectric constant of the dust in larger craters could be the result of meteors excavating iron and titanium oxides that lie below the surface. Dielectric properties are directly linked to the concentration of these metal minerals.
If their hypothesis were true, it would mean only the first few hundred meters of the Moon’s surface is scant in iron and titanium oxides, but below the surface, there’s a steady increase to a rich and unexpected bonanza.
Comparing crater floor radar images from Mini-RF with metal oxide maps from the LRO Wide-Angle Camera, Japan’s Kaguya mission and NASA’s Lunar Prospector spacecraft, the team found exactly what it had suspected. The larger craters, with their increased dielectric material, were also richer in metals, suggesting that more iron and titanium oxides had been excavated from the depths of 0.3 to 1 mile (0.5 to 2 kilometers) than from the upper 0.1 to 0.3 miles (0.2 to 0.5 kilometers) of the lunar subsurface.
“This exciting result from Mini-RF shows that even after 11 years in operation at the Moon, we are still making new discoveries about the ancient history of our nearest neighbor,” said Noah Petro, the LRO project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “The MINI-RF data is incredibly valuable for telling us about the properties of the lunar surface, but we use that data to infer what was happening over 4.5 billion years ago!”
These results follow recent evidence from NASA’s Gravity Recovery and Interior Laboratory (GRAIL) mission that suggests a significant mass of dense material exists just a few tens to hundreds of kilometers beneath the Moon’s enormous South Pole-Aitken basin, indicating that dense materials aren’t uniformly distributed in the Moon’s subsurface.
The team emphasizes that the new study can’t directly answer the outstanding questions about the Moon’s formation, but it does reduce the uncertainty in the distribution of iron and titanium oxides in the lunar subsurface and provide critical evidence needed to better understand the Moon’s formation and its connection to Earth.
“It really raises the question of what this means for our previous formation hypotheses,” Heggy said.
Anxious to uncover more, the researchers have already started examining crater floors in the Moon’s southern hemisphere to see if the same trends exist there.
LRO is managed by NASA’s Goddard Space Flight Center in Greenbelt, Maryland for the Science Mission Directorate at NASA Headquarters in Washington. Mini-RF was designed, built and tested by a team led by APL, Naval Air Warfare Center, Sandia National Laboratories, Raytheon and Northrop Grumman.
Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) found quasi-periodic flickers in millimeter-waves from the center of the Milky Way, Sagittarius (Sgr) A*. The team interpreted these blinks to be due to the rotation of radio spots circling the supermassive black hole with an orbit radius smaller than that of Mercury. This is an interesting clue to investigate space-time with extreme gravity.
“It has been known that Sgr A* sometimes flares up in millimeter wavelength,” tells Yuhei Iwata, the lead author of the paper published in the Astrophysical Journal Letters and a graduate student at Keio University, Japan. “This time, using ALMA, we obtained high-quality data of radio-wave intensity variation of Sgr A* for 10 days, 70 minutes per day. Then we found two trends: quasi-periodic variations with a typical time scale of 30 minutes and hour-long slow variations.”
The different color dots show the flux at different frequencies (blue: 234.0 GHz, green: 219.5 GHz, red: 217.5 GHz). Variations with about a 30-minute period are seen in the diagram. Credits: Y. Iwata et al./Keio University
Astronomers presume that a supermassive black hole with a mass of 4 million suns is located at the center of Sgr A*. Flares of Sgr A* have been observed not only in millimeter wavelength, but also in infrared light and X-ray. However, the variations detected with ALMA are much smaller than the ones previously detected, and it is possible that these levels of small variations always occur in Sgr A*.
Hot spots circling around the black hole could produce the quasi-periodic millimeter emission detected with ALMA. Credits: Keio University
The black hole itself does not produce any kind of emission. The source of the emission is the scorching gaseous disk around the black hole. The gas around the black hole does not go straight to the gravitational well, but it rotates around the black hole to form an accretion disk.
The team focused on short timescale variations and found that the variation period of 30 minutes is comparable to the orbital period of the innermost edge of the accretion disk with the radius of 0.2 astronomical units (1 astronomical unit corresponds to the distance between the Earth and the Sun: 150 million kilometers). For comparison, Mercury, the solar system’s innermost planet, circles around the Sun at a distance of 0.4 astronomical units. Considering the colossal mass at the center of the black hole, its gravity effect is also extreme in the accretion disk.
“This emission could be related with some exotic phenomena occurring at the very vicinity of the supermassive black hole,” says Tomoharu Oka, a professor at Keio University.
Their scenario is as follows. Hot spots are sporadically formed in the disk and circle around the black hole, emitting strong millimeter waves. According to Einstein’s special relativity theory, the emission is largely amplified when the source is moving toward the observer with a speed comparable to that of light. The rotation speed of the inner edge of the accretion disk is quite large, so this extraordinary effect arises. The astronomers believe that this is the origin of the short-term variation of the millimeter emission from Sgr A*.
The team supposes that the variation might affect the effort to make an image of the supermassive black hole with the Event Horizon Telescope. “In general, the faster the movement is, the more difficult it is to take a photo of the object,” says Oka. “Instead, the variation of the emission itself provides compelling insight for the gas motion. We may witness the very moment of gas absorption by the black hole with a long-term monitoring campaign with ALMA.” The researchers aim to draw out independent information to understand the mystifying environment around the supermassive black hole.
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The research team members are: Yuhei Iwata (Keio University), Tomoharu Oka (Keio University), Masato Tsuboi (Japan Space Exploration Agency/The University of Tokyo), Makoto Miyoshi (National Astronomical Observatory of Japan/SOKENDAI), and Shunya Takekawa (National Astronomical Observatory of Japan)
