Astronomy and space news summarized by Don Lynn from NASA and other sources

Relativity Test – One of the principles of Einstein’s theory of general relativity is that all different objects will fall at the same rate of acceleration at any given strength of gravity. Physicists at the University of Manchester, using data from the Nançay radiotelescope in France, completed another stringent test of this by studying eight years of radiotelescope data observing the orbits of a triple star system consisting of two white dwarfs and a pulsar, which is a kind of neutron star that emits radio pulses. They found that one of the white dwarfs and the pulsar fell toward the third star at the same acceleration, to the limits of accuracy of the observations, about two parts per million. While other observations, such as lunar laser ranging experiments, have measured this principle of relativity to much greater precision, no other tests have done so with objects experiencing as extreme gravity as pulsars have. This result places stronger constraints on many theories of gravity other than general relativity. The studied pulsar is known as PSR J0337+1715, and is located in Taurus.

FRB Pattern – Fast Radio Bursts (FRBs) last only a fraction of a second and astronomers still don’t know what causes them. Most do not repeat, but a few of them do. Astronomers have been trying to find a pattern to the repeaters, and researchers at the University of Manchester seem to have found one. From eight years of observations of the first known repeater, astronomers observed that its bursts cluster in a 90-day period, then disappear for 67 days and the 157-day pattern repeats again. This is only the second repeating FRB that astronomers have found a pattern in. The other has a 16-day period. The best theories of what would cause a repeating pattern are that the emitter is orbiting another body or that the magnetic field of the emitter is wobbling. Much more work needs to be done to understand FRBs.

New Class of Explosion – Three supernovas seen since 2016 resemble each other but differ from previously observed supernovas and likely represent a new class of explosion. They were quite bright initially and brightened and faded more quickly than other supernovas. Led by astronomers at Caltech and Northwestern University, follow-up observations in radio and X-rays showed further peculiarities common amongst the three. They are being referred to as Fast Blue Optical Transients. The best theory to explain the differences is that these occur when a massive star reaches its end of life (like a core-collapse supernova explosion) but then a rotating disk and jets form. Thus far, it sounds like the best theory explaining how gamma-ray bursts occur. However, in these cases, a gamma-ray burst is not seen, presumably because there is surrounding material that blocks the gamma rays. The shock from the explosion hitting this surrounding material explains the bright flash seen for just a few days and the radio emission. Astronomers think that the surrounding material contains substantial amounts of hydrogen, which explains the hydrogen spectrum seen in these three explosions. There is also a competing theory involving black holes to explain these events, so more work is needed to distinguish between the theories.

Early Solar System Water – It is known that three types of meteorites, including a type called howardites, are very likely pieces of the asteroid Vesta. Meteoroids colliding with Vesta knock material off the surface, some of which escapes Vesta’s gravity and eventually falls on Earth. One particular howardite known as the Kapoeta meteorite was seen to fall to Earth in 1942 and quickly recovered, affording scientists the opportunity to study the surface of Vesta relatively unaltered by the weathering that many howardites suffer. A new study of Kapoeta by researchers at the New Washington University in St. Louis found tiny bits of micrometeoroids that struck Vesta and became lodged in its surface. Scientists believe those micrometeoroids are pristine examples of the primitive material that formed the Solar System bodies. Minerals and textures found within them indicated the matter had interacted with water, but Vesta itself is fairly dry. In the early Solar System water-bearing materials should have formed farther out from the Sun than the orbit of Vesta where temperatures were cooler. The scientists see this as evidence that micrometeoroids in the forming Solar System brought water into the inner Solar System and may help explain how the early Earth acquired its oceans.

Planet-forming Disks – A study by astronomers at the Space Telescope Science Institute using the Hubble Space Telescope observed the crowded young open star cluster Westerlund 2. They found that in areas close to particularly massive stars, smaller stars had fewer planet-forming disks, indicating that massive stars destroy the disks around nearby stars. They think that strong ultraviolet light and stellar winds from the massive stars do the damage. The cluster is fairly dusty, so the astronomers used Hubble’s infrared instrument to see through the dust. The disks were detected by their fluctuating effects on their stars’ light, even if the disks were too small to see. In all, about 1500 disks were found, but within four light-years of the cluster’s crowded center, no disks were found. The same disk-destroying effect may explain why planets are rare in globular clusters.

Planet Formation – A new study by astronomers at the Leiden Observatory using the ALMA and VLA radiotelescope arrays observed the dust content of young planet-forming disks less than half a million years old in the Perseus molecular cloud star-forming region. There, they found sufficient dust to form average exoplanet systems. Previous studies of older disks, between about one and three million years old, failed to find enough dust to form exoplanet systems, which was worrying some astronomers. It seems that planets form and use up the dust in the disk faster than previously thought. Astronomers no longer have to worry about insufficient dust but now have to ponder how planets form so fast.

Earth-like Planet – Astronomers at the Max Planck Institute for Solar System Research have discovered a planet quite like Earth about 3,000 light-years away. Known as KOI-456.04, it is 1.9 times the diameter of Earth, likely a rocky planet and orbits a Sun-like star with a year of 378 Earth days. It was found in data from the planet-finding Kepler space telescope by using a new computer program that better separates planetary transit dips in brightness from noise in the data. Its distance from its star makes its temperature likely several degrees cooler than Earth, but still in the “habitable zone” where liquid water can likely exist. Its star is about 10 percent larger diameter than our Sun and 5 percent cooler. The planet is still technically a “planet candidate” until further verification is completed. There are two previously discovered planets orbiting this star, but they are much larger than Earth and much closer to their star, making them hotter.

Disintegrating Planet – The Dispersed Matter Planet Project, or DMPP, has for the past five years been making high-precision radial velocity observations to find low-mass planets orbiting close to their stars. Their first find of three so far announced, consists of four planets orbiting a star about 200 light-years away. However, follow-up observations with the TESS planet-finding space telescope failed to detect any of the four planets transiting in front of their star, but did find transits of a fifth planet with a shorter orbital period of about 3.3 Earth days. The varying amount of light blocked during its transit, combined with orbiting quite close to its star and its small size indicate it is likely a small rocky planet being destroyed by the heat of its star.

Asteroid Rock Weathering – The OSIRIS-Rex spacecraft has been exploring the asteroid Bennu at close range since December 2018. Comparison of old and new pictures taken of surface rocks show many of those rocks cracking on their surfaces or flaking off. It appears that this is being caused by day and night cycle of heating and cooling. A day on Bennu is only a little over four hours long. Scientists ruled out the other possible causes of rock weathering. It had long been believed that this type of weathering would occur when asteroids are close enough to the Sun, but this is the best observation of it.

InSight Progress – The Mars InSight spacecraft landed on the Red Planet in November 2018, and since February 2019 has been trying to get its “mole” to pound itself into the soil. “Mole” is the nickname for the mission’s heat probe, which at a depth of about fifteen feet under the surface will measure heat flowing out from the planet’s core, telling scientists a lot about the internal structure of the planet. However, months of use of the hammer, which is internal to the mole, haven’t been successful, as the mole kept slipping back out of the ground, never reaching even 15 inches deep. After trying many tricks to get the mole to burrow, these past few months have been spent placing the spacecraft arm with downward pressure on the mole while carefully hammering, frequently checking that the arm was not hitting anything fragile. The spacecraft team reports that the mole has disappeared below the surface with this technique. More hammering will be done with the arm pressing on the soil above it. Then hammering without any help will begin. With luck the mole then will be into soil with enough friction to prevent backsliding.

Titan’s Orbit Drifting – It has been believed that Saturn’s moon Titan is slowly moving farther away from the planet for the same reason our moon is expanding its orbit about us. Tides raised on a planet by a moon drag the moon gravitationally. If the planet rotates faster than the moon revolves about the planet, then the moon’s orbit slowly rises. Calculations show that Titan should be rising about 1/25 inch per year. A paper published in 2016 proposed that gravitational interactions between the moons of Saturn would magnify the expansion of Titan’s orbit. Astronomers at Caltech measured the changes in Titan’s orbit from archived Cassini spacecraft images and radio data. They found the expansion to be about four inches per year, 100 times larger than previously calculated, supporting the 2016 paper. This may change the estimates of the age of Titan and other Saturnian moons, as well as the age of the rings.

Hot Galaxy Halo – Most past observations of our Milky Way galaxy’s halo have found gas up to one million degrees Kelvin. In January of this year, astronomers at the Ohio State University announced that an X-ray measurement in one direction through our galaxy halo showed gas up to 10 times as hot. A new follow-up study shows that this one location was not a fluke, by confirming those hot temperatures in four directions. The new study used observations made with Japan’s orbiting Suzaku X-ray telescope. The same study also measured the temperature of the halo of galaxy NGC 3221, about 200 million light-years distant, and found similar temperatures. This probably indicates that 10-million-degree gas in galaxy halos is not unusual.

Dim Galaxies Found – The Dark Energy Survey (DES) uses the 4-meter Blanco Telescope in Chile, fitted with a very sensitive wide-field camera, to study how the structure of the Universe has changed over billions of years. From this, astronomers hope to learn how dark energy has changed that structure over the life of the Universe. About an eighth of the entire sky is included in the survey. A team led by astronomers at the University of Chicago searched the DES data to find low-surface-brightness galaxies (LSBGs), a class of galaxy whose surface brightness at their centers are dimmer than the glow of the night sky, meaning they often go undetected. The team found nearly 21,000 LSBGs in the data. Theories of galaxy formation that exclude or underrepresent LSBGs may be flawed. The new study aimed to find how common the LSBGs are in the sky, as well as other properties, to correct this problem. The team found LSBGs classified as both blue galaxies, which have substantial star formation going on, and red galaxies, which do not. The two types were found to be similar sizes to each other on average, but the reds appeared to have somewhat dimmer surface brightness. The reds also tended to be more clustered than the blues, and those red clusters tended to be where brighter galaxies existed. This LSBG study will give galaxy formation theorists a lot of data to work with.

Galaxy Magnetic Field – Led by astronomers at NASA’s Jet Propulsion Lab using SOFIA, the agency’s airborne 100-inch infrared telescope, the team has measured the polarization of light from dust near the center of our Milky Way, and from that calculated its magnetic strength. The result is about 100 times weaker than the Earth’s surface magnetic field, but this is still strong enough to mean that magnetic forces on particles in this region could be stronger than gravitational forces. This may require computer simulations of the cores of galaxies to take into account magnetic fields, which has not always happened in the past because magnetic fields are difficult to simulate. Magnetic fields near the center of our galaxy could explain two surprises that have long been known: the star formation rate in this area is surprisingly low, and the consumption of matter by the central black hole is also surprisingly low. 

Nancy Grace Roman Space Telescope – NASA announced that it is naming its next large space telescope after Nancy Grace Roman, the first NASA Chief of Astronomy. She championed the development of space telescopes, particularly the Hubble Space Telescope. This next telescope had been known as the Wide Field Infrared Survey Telescope, or “WFIRST.” Its mirror is the size of the Hubble but has a wide field optical design that observes an area 100 times greater than Hubble. It will have both imaging and spectral capabilities, as well as a coronagraph to block light from any bright, nearby star in order to study closely-spaced dim objects, such as exoplanets. Launch is scheduled in the mid 2020s.