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

Mass Gap Breached – The largest known neutron star is about 2.2 times the mass of the Sun, which aligns with theoretical projections that predict a neutron star should collapse into a black hole at about this mass. The smallest known black hole is about five solar masses, though there are some controversial measurements of ones somewhat smaller. This agrees with the theoretical mechanisms where massive stars at the ends of their lives explode as supernovas, leaving behind a black hole. The discrepancy between the biggest neutron star and the smallest black hole is called the “mass gap.” The LIGO-Virgo teams, which run the three operational gravitational-wave detectors, have announced that an event in August of last year was the merging of a black hole of 23 solar masses with an unidentified object of 2.6 solar masses, right in the mass gap. Though astronomers disagree whether this was a heavy neutron star or a light black hole, many believe a lightweight black hole is more believable. Since a supernova should not have produced this small of a black hole, theories are being proposed for rarer events that might produce black holes with smaller masses, such as a three star interaction. This event set the gravitational-wave record for the biggest disparity in masses merging, an almost nine to one mass ratio. Astronomers were surprised by this mass difference, since most theories of how double stars form and age will never result in such a mass difference. One theory put forth is that young dense star clusters might occasionally result in gravitational interactions that pair extremely different mass stars. Also unusual about this event is that the 23-solar-mass black hole was barely spinning. Many black holes are spinning about 70 percent as fast as relativity allows, particularly if they have ever merged with any massive objects, which speed up the spins of black holes.

Black Hole Merger Seen Optically – When two black holes merge, they don’t normally give off light in any form, the just emit gravitational waves. However, observations soon after a gravitational wave event in May of last year apparently saw a burst of light in the same place, which then faded over the next month. The visible-light observations were found by astronomers from Caltech in archived data from the Zwicky Transient Facility, a project that uses the large Schmidt telescope at Palomar to image large portions of the sky every night. Unfortunately, the observations were found after fading, so no new observations, such as spectra, were possible. The gravitational wave event, seen by LIGO, showed that two stellar-mass black holes merged. Astronomers think that that most likely explanation for this burst of light is the two smaller black holes merged near the accretion disc of a supermassive black hole. When they combined, the newly formed black hole shot off in a new direction and plowed through the accretion disk around the supermassive black hole, creating the observed burst of light. There are a few other possible explanations that have yet to be completely ruled out. But if the likely explanation is true, then the merged black hole should hit the accretion disk again in a few years, and observations of that would go far in confirming it.

Star Disappeared – For about 20 years some astronomers have been observing the Kinman Dwarf Galaxy because it has an unusually low concentration of heavier elements. The spectra of the galaxy as a whole contained the distinctive pattern of a Luminous Blue Variable (LBV) star mixed in with spectra of all its other stars. The LBV star was never resolved in images because the galaxy is too far away at about 75 million light-years distance. But the spectra had showed unmistakably that an LBV was there … until recently. From data taken in 2019, scientists from the University of Dublin announced that the LBV spectral lines are gone. An LBV should end its life as a supernova, but none was seen in Kinman. The most likely explanation seems to be that the LBV collapsed directly to a black hole without bothering to explode. Some theorists have been proposing that such a collapse can happen, but more evidence is needed to firmly conclude that this happened in Kinman.

Black Hole Corona Disappeared – Supermassive black holes are surrounded by a corona, a ring of super-hot particles. Astronomers from MIT have watched such a corona disappear and then rebuild itself, for the first time ever. Their best guess at what caused the disappearance is that a passing star got torn apart by tidal forces and fell in, pulling the corona with it. The brightness of the black hole first flashed brilliantly, then dropped to 1/10,000 of its normal value as the corona disappeared. Over a few months the brightness climbed almost to normal. The event was first seen by an automated survey for supernovas called ASSASN. This prompted monitoring in many wavelengths over the months of the event.

Gas Giant Core – The core of a gas giant planet has been discovered by astronomers at the University of Warwick using data from the TESS planet-finding space telescope. Known as TOI 849 b, it orbits a Sun-like star about 730 light-years away. The TESS observations showed that it is about the diameter of Neptune, while follow-up Doppler observations made at the La Silla observatory in Chile determined that its mass is about two to three times that of Neptune. The resulting high density object could only be explained by a gas giant planet without its gas, just an exposed core. Astronomers have come up with only two explanations. Either when the gas giant formed, something prevented the accumulation of hydrogen and other gas around the core, or a gas giant formed normally but then heat or something else stripped away the planet’s gas. The object orbits quite close to its star, with a surface temperature of 2800 degrees Fahrenheit, so this could be what ripped away its gas. However, calculations show the current heat is not enough to fully explain the gas loss. Very few Neptune-like planets are found orbiting very close to their stars, so finding this one is surprising. Astronomers who want to know what is in the core of a gas giant need to study this object.

Cosmic Magnetic Fields – Twenty years ago astronomers first discovered magnetic fields in galaxy clusters. Last year magnetic fields were detected in a piece of the cosmic web that connects galaxy clusters. Some astronomers now believe that magnetic fields could be everywhere, even in cosmic voids, and recent observations of blazar light passing through voids seem to support this. That would pose the question, how did magnetic fields form everywhere? Some theories propose that various steps in inflation or the Big Bang would have created such fields, while other theories show how the fields could grow later. An interesting aspect of magnetic fields everywhere would be that they would distort the sizes of the blobs seen in the cosmic microwave background (CMB), which in turn would alter the calculations of the expansion rate of the Universe, also known as the Hubble constant. A recent paper led by a researcher at the Universite de Montpellier, suggests that magnetic fields could explain why calculating the Hubble constant from the CMB results in a different number from calculating it from distant supernova brightnesses. A lot more work needs to be done, both in determining the effects of magnetic fields and in measuring magnetic fields.

New Map of the Universe – The Sloan Digital Sky Survey released its latest data, a map and spectral data of a large part of the sky. This included the eBOSS phase of the survey which studied the large-scale structure of the Universe by analyzing the location and spectra of millions of galaxies and quasars. The data contains numerous quasars out to distances from which light took about 11 billion years to reach us. A value of the Hubble constant was calculated from this structure, and the value agreed with the values derived from the CMB. Also, the strength of dark energy at various distances, and therefore look-back times, was calculated, and it appears not to have changed over time. The flatness of the Universe was confirmed to quite close tolerance, meaning that the total mass and energy (including dark energy) is exactly at the critical level so that, ignoring local concentrations of mass, space-time allows parallel light beams to remain parallel forever.

X-ray Map – eRosita is an X-ray telescope on board the SRG (Spektrum-Röntgen-Gamma) German-Russian spacecraft and it has been surveying the entire sky since its launch about a year ago. The eRosita team just released its first all-sky X-ray map. It shows more than a million X-ray sources, roughly doubling the known number of such sources. This is the first updated X-ray map in 30 years because it has been that long since a wide-field X-ray telescope was in service. One goal of the mission is to map galaxy clusters and track the growth of structure of the Universe over much of its life. Galaxy clusters are visible in X-rays because of the hot gas between galaxies in those clusters. More than 20,000 galaxy clusters are already in this map, but scientists expect over 100,000 will be found by the time eRosita completes several more sweeps of the entire sky and stacks the images. Also found in the map are numerous stars with magnetic activity and black holes actively swallowing matter. The SRG is in a halo orbit about the Earth-Sun L2 Lagrange point, about 900,000 miles away from Earth.

Exoplanets Imaged – Astronomers from Leiden University using the Very Large Telescope (VLT) in Chile imaged two exoplanets in orbit around their star. Only about 1 percent of all known exoplanets have been imaged because they are generally too faint and too close to their stars to be resolved. The newly imaged planets are both unusually far from their planet and unusually bright in infrared because of their temperatures. An instrument on the VLT was used to block the star’s light, allowing the individual planets be resolved. This is only the second time two exoplanets in one system have been imaged, and the first time two planets were imaged orbiting a Sun-like star. The star is known as TYC 8998-760-1 and is about 300 light-years away in the constellation Musca. It is estimated to be only 17 million years old. The planets orbit at about five and ten times the distances from their star compared to Neptune’s distance from our Sun. The planets are each several times the mass of Jupiter.

Solar Radio Emission – Observations by scientists at the Tata Institute of Fundamental Research using the LOFAR radiotelescope array have shown faint bursts of radio being emitted all over the Sun. Some astronomers propose that this is from nanoflares, but more work is needed to establish this. LOFAR works at lower radio frequencies than other radiotelescopes, and these faint bursts have not been seen at higher frequencies. Some theorists believe that nanoflares, too small to be observed individually, may be the means by which million-degree heat is carried into the Sun’s corona, or outer atmosphere.

Cosmic Wall – An international team led by astronomers at the Université Paris-Saclay and the University of Hawaiʻi have discovered a wall made of clusters of clusters of galaxies that range from at least from 300 to 500 million light-years away. It has been dubbed the South Pole Wall. It was found by observing its gravitational effects on the velocities of galaxies. It is comparable to the Laniakea structure announced in 2014. The team has spent the past decade mapping this wall and they just released their results.

Venus Volcanoes – A new simulation by scientists at the University of Maryland of how round geologic structures might form on Venus has produced landforms that strongly resemble those seen on the actual planet. Known as coronae, these ring-shaped structures were formed by lava erupting through the planet’s crust. In total, 37 coronae on the planet matched well with the simulated objects that were quite young or even still forming. This led scientists to conclude that those 37 represent still evolving volcanic activity, meaning that Venus appears to have active volcanoes.

Earth Invades Mars – Every 26 months Mars and Earth align in their orbits in a way that allows rockets to more easily reach to the Red Planet. Now is the alignment and three Mars missions have been launched. The first launch was the Hope mission on July 19. Built by the United Arab Emirates, it is the country’s first interplanetary mission, and will study the Martian atmosphere and weather from orbit. Next, launched on July 23 was China’s Tianwen-1 mission that includes an orbiter, lander, and rover. The orbiter has cameras, a spectrometer and a radar to search for ice below the surface. The rover is solar powered and has weather, magnetic-field and radar instruments. Lastly was NASA’s rover Perseverance launched on July 30. It resembles the currently operating Curiosity, but with new and different instruments. The landing area is Jezero Crater, which was once a lake with a geologically interesting river delta. Besides analyzing rocks and soil with onboard instruments, the rover will collect samples to be returned to Earth by a separate mission to be launched in future years. A drone helicopter named Ingenuity is fastened to the rover and will be let loose after landing to take aerial images of the surrounding terrain. It takes a few days of solar battery charging to ready the copter for a flight. The extremely thin Martian air is 140 times thinner than Earth’s, which dictates that the helicopter has to spin its blades particularly fast and can lift little weight, so it is limited to only 1.5 minutes per flight. Unfortunately, the joint European-Russian mission ExoMars lander and rover ran into delays and will launch in 2022 instead of this year. Almost had four invaders go to Mars this time.

Webb Telescope Delayed – NASA announced that the James Webb Space Telescope launch has been delayed seven months to October 2021. About three months of the delay was due to the COVID-19 pandemic. Projections are that it won’t cost more, as the current budget will support work until the new launch date.