Milky Way Star Formation History – The sub giant phase of a star’s life occurs when nuclear fusion stopped in its core and it is on the way to becoming a red giant star. A sub giant star’s age can be calculated fairly precisely from measurable properties like its elemental composition. A new study by researchers at the Max-Planck Institute for Astronomy used data from the Gaia spacecraft and the LAMOST telescope in China to find and calculate the ages of about a quarter million sub giant stars in our Milky Way galaxy. Using this data, the researchers determined when star formation occurred in various parts of the Milky Way. The thick disk of the galaxy began forming stars a mere 0.8 billion years after the Big Bang and continued for six billion years until the gas to form stars was depleted. The inner halo of the galaxy saw much of its star formation two billion years after the beginning of the thick disk, apparently when the Milky Way collided with and absorbed a small galaxy. The Milky Way’s thin disk, the vertically center part of the thick disk, began forming stars later than the thick disk. The distribution of elements heavier than helium, which are created within stars, was found to be relatively uniform throughout the thick disk, but with increasing heavy element content with age of the Milky Way at the time individual stars formed, implying that gas was well mixed throughout the disk during the period of star formation, apparently by turbulence in the disk.
Milky Way Ring – Scientists at the Max Planck Institute for Extraterrestrial Physics found an inner ring of heavy-element-rich stars just outside the central bar of our Milky Way galaxy. The stars in the ring formed about seven billion years ago and are younger than the stars in the bar. The find was based on data from APOGEE, a large-scale spectroscopic survey of stars made in infrared. A computer model of the inner Milky Way with APOGEE and other data integrated showed patterns of orbits of stars indicating the central bar and the newly found ring.
Megamaser – Scientists at the University of the Western Cape using the MeerKAT radiotelescope array in South Africa discovered a megamaser, a powerful natural laser operating in radio frequencies. It is the most distant megamaser known, at roughly 5 billion light-years distant. The scientists held a contest to nickname the object, and the winner was “Nkalakatha”, meaning “big boss” in isiZulu. Megamasers occur when galaxies collide, causing extremely dense concentrations of gas. Pockets of hydroxyl gas have the property of amplifying a certain microwave radio frequency, and so can produce masers. The discoverers were initially looking for radio emission by hydrogen, but also picked up the hydroxyl frequency, which is not far different.
Farthest Galaxy – An international team of astronomers discovered what is likely the most distant known galaxy, dubbed HD1. Its light originated there only 0.3 billion years after the Big Bang, which astronomers hope to confirm spectrographically using the James Webb Space Telescope. The record holder before is known as GN-z11, whose light left 0.4 billion years after the Big Bang. The new discovery was made by checking for Lyman spectral line shift of 700,000 objects imaged by the Spitzer Space Telescope and various ground-based telescopes. HD1 had the largest redshift among all these objects. A weak oxygen spectral line seen in radio seems to confirm the redshift of HD1, and therefore its distance. It is thought that the brilliant light of HD1 is caused by very active star-formation in the galaxy or possibly an active black hole. Its observed brightness stretches our concepts of how bright star formation can be, of how big early black holes might get, and how brilliantly material falling into them can shine. One possible explanation is that the first stars to form were much more massive than stars forming today, due to their lack of heavier elements, making star formation much brighter.
Star Expelling Rings – Scientists at the University of California, Los Angeles and NASA’s Jet Propulsion Laboratory studying a red giant star called V Hydrae found that the star has thrown off six expanding rings and also an hourglass-shaped formation perpendicular to the rings. The hourglass is shaped by a fast stellar wind, while the mechanism expelling the rings every few hundred years is not known. These features are in addition to the already-known eruptions of the star about every eight years. All these appear to be part of the death of the star as it runs out of fuel. It has long been known that stars like this blow away a large fraction of their mass, but it had been thought this occurred in a steady wind, not in puffs that create rings. The study used ALMA, a radiotelescope array in Chile, and data from the Hubble Space Telescope.
Micronova – A team of astronomers at Durham University examining data from the TESS planet-finding space telescope found three instances of a star brightening for several hours, and have dubbed the phenomenon a micronova. Though they were found to be powerful hydrogen fusion explosions, they are much smaller and shorter lived than an ordinary nova. In an ordinary nova, hydrogen falling onto the surface of a white dwarf star from a nearby companion star collects until it reaches the temperature and concentration to nuclear fuse to helium in an explosion that occurs over the entire surface of the white dwarf. In a micronova, the same thing happens except a powerful magnetic field concentrates the hydrogen at the magnetic poles, and a smaller explosion takes place just at the poles. The team will continue to look for more micronovas.
Supernova Remnant Collision – The supernova remnant nebula known as Cassiopeia A is left over from an exploding star that should have been seen from Earth about the year 1670. However, the explosion was apparently blocked from view by gas and dust. A new study by astronomers from the University of Amsterdam and Harvard of X-ray images of Cassiopeia A over a period of 19 years shows that it is not expanding evenly, apparently because the expanding remnant has collided with material thrown off the star long before it exploded. Some of the remnant is actually moving back toward the explosion center probably because it bounced off the material it collided with. Much of the remnant is expanding at 2,500 to 3,700 miles per second.
Binary Supermassive Black Holes – A team of scientists from Purdue University announced the discovery of a pair of supermassive black holes orbiting each other in a galaxy so distant that its light took 8.8 billion years to reach us. The black holes likely each have masses of about 100 million times that of the Sun. Only a few candidates to be such binary supermassive black holes are known, with varying degrees of confirmation. This newly announced binary seems well confirmed due to variations in the radio observation signals apparently caused by their orbital motion.
Planetary Bodies Collide – Astronomers at the University of Arizona, monitoring a star 388 light-years away, found that for many months a cloud of dust obscured the star. The young star, designated HD 166191, is roughly the size of our Sun. The probable source of such a cloud is that two forming planets collided and pulverized. To produce the size of dust cloud seen, the colliding objects would have to be roughly the size of Vesta, one of the largest asteroids in our Solar System. The monitoring observations were made in infrared light over a period of four years by the Spitzer Space Telescope and in visible light using ground-based telescopes.
Enceladus Geysers – A new study by researchers at the University of California, Davis used computer simulations of Saturn’s moon Enceladus to better understand the icy moon’s “Tiger Stripes.” They found that its surface cracks are caused by the expansion of ice freezing thicker during long cycles of extra cold temperatures resulting from orbital changes. However, the forcing of liquid water through those cracks into geysers has a different cause, the boiling of the underlying liquid when exposed to the vacuum of space. A liquid ocean is thought to lie beneath about 20 to 30 kilometers (12 to 19 miles) of Enceladus’s icy shell since the observation of geysers erupting from cracks in 2006.
Jupiter Twin – A new study by researchers at the University of Manchester discovered an exoplanet nearly identical to Jupiter, in terms of its mass and distance from its star. It is 17,000 light-years away and is known as K2-2016-BLG-0005Lb. The planet was found in archived data from the Kepler planet-finding space telescope. It is twice as distant as any other exoplanet found in Kepler data. It was found by microlensing, instead of the transit method normally used for Kepler discoveries. In the microlensing technique, a massive planet passes in front of a distant star, bending the starlight, focusing and brightening it, according to General Relativity. The transit method looks instead for the dimming of a star by an orbiting planet as it blocks some of the star’s light as it passes. The chances of a planet passing in front of a distant unrelated star are small, but this event happened while Kepler was pointed toward the center of the Milky Way, where stars are dense, raising the chances of an alignment for microlensing. The event was also seen by a ground-based telescope that was also monitoring the galaxy center.
Ingenuity – The Mars helicopter Ingenuity completed its 21st flight several days after it reached its first Earth year on the Red Planet. NASA then approved continuing flights through September. The original plan was to declare the helicopter mission over after 5 flights, but there is so much potential science and engineering possible that its mission keeps getting extended. As of this writing, 27 flights have been completed, the longest trip traveling more than 2,324 feet. The last few flights have been to reach the base of the delta where an ancient river flowed into the lake in Jezero Crater, the area where the rover Perseverance will next explore. The rover is taking a much longer route to the delta that avoids areas that would be dangerous to roll over. Ingenuity will take pictures of the delta to help rover controllers plan Perseverance’s route to reach the top of the delta. Helicopter controllers have loaded new software into the craft several times to add new capabilities, such as flying over rougher terrain, flying higher, higher precision navigation, and changing speed during flight. The helicopter also recently visited the crash site of part of the rover’s landing system, beaming back images of its backshell and parachute.
Marsquakes – A new study of marsquakes by researchers at the Australian National University found that those occurring in the area called Cerberus Fossae are probably caused by movements of magma below the surface, not by tectonic movement or other causes. This may mean that volcanic activity is still happening in some areas of Mars. The new study used new techniques to find very weak marsquakes among the noise in data from the InSight seismograph.
Possible Shards of the Chicxulub Impactor – Scientists digging for fossils at a site named Tanis in North Dakota believe that they have found material splashed from the Chicxulub crater where a meteor hit the Earth 66 million years ago, the impact that scientists think killed off the dinosaurs. Among the new fossils there are glass spherules, a common product of material splashed out of an impact crater. Most of the unmelted rock bits found have high levels of calcium and strontium, as would be expected from splashed limestone, which is found at Chicxulub. Two spherules found contain high levels of iron, chromium and nickel. These would be shards of the meteorite, indicating that it was an asteroid, in fact a carbonaceous chondrite asteroid, not a comet. What distinguishes this find from other finds of splash from Chicxulub is that some of this material landed in tree resin, sealing it in amber, which protected it from weathering. There are also air bubbles preserved in some spherules, raising the possibility of analyzing what the Earth’s air was like 66 million years ago. The Tanis dig also found the leg of a dinosaur, identified as a Thescelosaurus, raising the possibility that it was killed by the flooding that the Chicxulub impact likely caused.
Largest Comet Nucleus – Observations by researchers at the University of California, Los Angeles, using the Hubble Space Telescope and a radiotelescope have yielded a size for the nucleus of Comet Bernardinelli-Bernstein and found it is the largest known comet nucleus, at about 80 miles across. The comet’s closest approach to the Sun will be near Saturn’s orbit in 2031. The comet nucleus is too far for Hubble to resolve, so the size was calculated from brightness and reflectivity measurements and a computer simulation of comet coma. The reflectivity was found to be very low, about that of charcoal. The comet will take about three million years to orbit once, reaching the far point in its orbit of about a half light-year. The previous record holder for nucleus size was comet C/2002 VQ94, at 60 miles across.
CHIME Outriggers – CHIME, a radiotelescope array in Canada, is detecting more than 10 times as many fast radio bursts (FRBs) as all other radiotelescopes combined. It does this by looking at most of the sky simultaneously and using a supercomputer to sort out where each radio signal comes from. Its precision in locating, however, is only about as good as an area of the sky the size of the full Moon. The CHIME group is now constructing three outrigger antennas scattered across North America to pinpoint the locations of FRBs to a fraction of an arcsecond. This should help astronomers determine the sources of FRBs, which remain a mystery.
Exoplanet Milestone – The first planet orbiting another star, or exoplanet, was discovered in 1992. It took 10 years to find the next 90 exoplanets. Last month the number of confirmed exoplanets exceeded 5,000. Another 3,700 have been detected by just one instrument and await confirmation. Most have been discovered using the transit method, where a star is seen to dim slightly because its planet is passing in front. The transit method is inefficient at finding planets because most planets’ orbits pass above or below their star, not in front, from the point of view on Earth. But astronomers throw sheer numbers of stars at the problem and have great success. The Kepler spacecraft’s primary mission stared at more than 150,000 stars for years (and over 300,000 stars in the extended K2 mission) and discovered more than 2,600 planets. With the TESS spacecraft and other telescopes continuing the search, it probably won’t take long to find the next 5,000 exoplanets.
Eugene Parker – The Parker Solar Probe, launched in 2018, was named after Dr. Eugene Parker, a pioneer in study of the Sun. He was the first person to predict the solar wind, before it had been observed. He did trailblazing work on the solar corona and magnetic field. The Parker Solar Probe was the first instance of a spacecraft named after a living person. Dr. Parker died in March at the age of 94, a great loss for solar astronomy.
