Astronomy and space news summarized by Don Lynn from NASA and other sources
Neutron Star Found – In 1987, astronomers witnessed the nearest supernova in hundreds of years explode in the nearby dwarf galaxy known as the Large Magellanic Cloud. Being the first observed of the year, the astronomical event was named SN 1987A. Astronomers have been monitoring the aftermath of this explosion ever since, learning much about supernovas. The star that exploded should have left behind a neutron star, but none had ever been found, until now when the ALMA radio telescope array in Chile finally located it. The star was so difficult to find because it is surrounded by thick dust clouds, but the frequencies ALMA was observing were able to penetrate through the dust.
Super Spirals – A new study of the largest known spiral galaxies, known as “super spirals,” has found how they differ from more common spirals like our Milky Way. The stars orbit about twice as fast, indicating they contain substantially more dark matter. They also tend to be about two to four times the diameter and up to 20 times the mass. Surprisingly, though they have more stars, there are not enough stars to be proportional to their masses. Scientists believe that above a certain galaxy mass it becomes more difficult to form stars. Only about 100 super spirals are known.
Star Formation Cause – Astrophysicists have long hypothesized that when galaxies collide, it results in bursts of star formation. There are other theories for what causes high rates of star formation and astronomers wanted to see how much galactic collisions contributed. A new study that looked at 200,000 galaxies concluded that collision is the major factor causing bursts of star formation. Because of the huge number of galaxies studied, the astronomers wrote an algorithm that used sample images of colliding galaxies to learn how to identify collisions among the 200,000 galaxy dataset.
Most Energetic Gamma-ray Burst – A number of telescopes, including the Hubble Space Telescope, followed up observing the source of a gamma-ray burst that occurred last January. The burst was extremely bright and long lived. Some photons of the burst had the highest energy ever observed: One tera electron volt. It is believed these high-energy bursts are caused by material thrown out of a collapsing star at 99.999 percent the speed of light, hitting surrounding gas which causes a shock wave that emits gamma rays. The Hubble observations showed the source was in the center of a galaxy five billion light-years away that is colliding with another galaxy. Astronomers surmise that this unusual environment for a gamma-ray burst contributed to its high energy.
Galaxy Wind – Galaxies are known to have gas surrounding them that, if cool enough, will fall into them and be used in star formation. Further, it is believed that winds emanating from within the galaxy replenish the gas surrounding it. An imaging instrument at the Keck Observatory in Hawaii has for the first time directly observed gas blowing out of a galaxy, replenishing the external gas supply. Images and spectra of it were taken. Previous detections of similar galactic wind had not been able to trace the winds as far out of the galaxy as the gas supply is located. The observing astronomers are calling the galaxy Makani, which means “wind” in Hawaiian.
Pluto Far Side Image – When the New Horizons spacecraft flew by Pluto in 2015, it got a close-up look at only one side of the dwarf planet. It takes six Earth days for Pluto to revolve, so the side opposite of the flyby was visible about three days before encounter, and the speed of the spacecraft was so great that it was millions of miles away at that point, too far to get detailed images. The New Horizons team just released a mosaic of the far side of New Horizons’ encounter, using the best images available of the various areas of Pluto. The quality varies and is nowhere near the resolution of the encounter-side images, but several conclusions can be reached from this new image. Though the far side has nothing like Sputnik Planitia, the distinctive heart-shaped impact crater on the encounter side, there is a feature exactly opposite from it, which may be a shock wave feature caused by the Sputnik impact. It is reminiscent of a similar feature seen on Mercury opposite the largest impact on that planet. The team also made a geological feature map of both of Pluto’s sides, based on the image mosaic. The strange bladed terrain seen near the edge of the encounter side was found to extend across large parts of the far side. The bladed terrain is composed of huge methane ice towers likely caused by uneven sublimation, since they resemble water ice features seen high in the Andes of South America, though Pluto’s are far larger.
Arrokoth Named – More than three years after Pluto, New Horizons flew past a Kuiper Belt object named 2014 MU69. At the time, the New Horizons team nicknamed the object “Ultima Thule,” but the IAU declared that Kuiper Belt objects are to be named with mythological names related to creation. The New Horizons team submitted “Arrokoth,” which was accepted as the official name. Arrokoth is the word for sky in the Algonquian language of the Maryland-area Powhatan people. Maryland is the home of the Space Telescope Institute, which operates the New Horizons spacecraft. Data from the flyby of Arrokoth is still being sent from the spacecraft and the team will likely hold off on submitting the names of Arrokoth’s features until 2021 after all the data is received.
Three Sun Planet – A likely rocky exoplanet has been discovered that has three suns. It is known as LTT1445Ab and is only 22 light-years away. The three stars the planet orbits are all red dwarf stars. The planet is too close to its primary star to be in the habitable zone, that area where temperatures will allow liquid water to exist. Its year is only five and a half Earth days. Because of its proximity and the fact that it passes directly in front of its primary star, astronomers hope that future observations of starlight passing through its possible atmosphere will determine its atmospheric constituents. The planet was discovered by NASA’s Transiting Exoplanet Survey Satellite, or TESS, a planet-finding space telescope.
Exoplanet Mystery – A red giant star has been found to have a planet orbiting closely around it. What astronomers found mysterious is that the star has already gone through its swollen phase, when it expanded to larger than the planet’s orbit. A planet should not be able to survive being engulfed in star material. The state of evolution of the red giant was established by asteroseismology, the study of the vibration in the surface of the star. The asteroseismology observations were made by the TESS spacecraft, which was actually looking for exoplanets, not the surface vibrations of stars. Computer simulations of the orbit of the planet show that it likely had its orbit shrunk by tidal forces, so that it orbited beyond reach when the star was in its swollen state.
Exoplanets and Multiple Stars – A new study examined 1,300 stars known to have orbiting exoplanets in order to determine which of these stars had companion stars orbiting them. Altogether, 200 companion stars were found. They included closely orbiting companion stars (20 AU, where an AU is Earth’s distance from the Sun) out to distant companion stars (over 9000 AU). The masses of the companion stars ranged from 8 percent to 140 percent of the Sun’s mass. Of these, eight white dwarf companion stars were found, meaning those exoplanets survived a nearby stellar collapse. The systems included two dozen triple stars and one quadruple. These findings were less than average (of non-planet-bearing stars) numbers of companion stars and greater than average for distance between companion stars. These differences indicate that the presence of companion stars definitely impacts how planets form.
Microlensed Planet – In October 2017 an amateur astronomer in Japan reported an unexpected brightening of a star. Follow-up professional observations by multiple telescopes showed that the brightening was caused by a planet about the mass of Neptune gravitationally microlensing the star. Microlensing occurs when a massive object passes precisely in front of a star, and the gravity of the front object bends the light from the star behind like a lens. This lensing event is unusual in part because it occurred in an area of the sky not dense in stars, so the odds of something passing in foreground are lower. In addition, it is relatively nearby. The planet orbits its star only 1.1 AU from it, which is a small orbit for a Neptune-sized planet. This is likely because the star is comparatively dim, putting temperatures where Neptune-like planets can form quite close to the star.
Least Massive Black Hole – There is a gap in masses between the largest known neutron star (2.17 solar masses) and the smallest black hole (3.8 solar masses). Both neutron stars and black holes form as a result of stars collapsing at the end of their respective lives. A black hole has been found in that gap, with an estimated mass of 3.3 solar masses. Astronomers found it by sifting through spectra of 100,000 stars, looking for any star whose spectral lines wobbled in the manner expected from orbiting a black hole. It is possible that this is the first of a new class of black holes, formed by a different kind of stellar collapse that does not happen often.
Runaway Star – Another runaway star has been discovered, moving about ten times the speed of most stars in the Milky Way. Dubbed S5-HVS1, it is moving fast enough that it is escaping the gravity of our galaxy. Astronomers who traced its path back to its origin showed that it was ejected during an encounter with the supermassive black hole at the center of the Milky Way. This was predicted to happen when a black hole pulls apart a binary pair of stars, consuming one and throwing the other out of the galaxy. The team that found it, part of the Southern Stellar Stream Spectroscopic Survey, was actually studying stellar streams about our galaxy when it stumbled on this runaway star.
InSight – After the Martian InSight lander successfully resumed hammering its heat probe into the ground, as reported here last month, the probe known as “the mole” unexpectedly started backing out of its excavation hole. This is a significant setback and spacecraft controllers are planning the next steps. The probe must reach two to three yards deep to get meaningful data. The probe is designed to measure the heat escaping from the core of Mars which would tell scientists a great deal about the planet’s interior.
Martian Oxygen – Measurements of the oxygen levels in Martian atmosphere made by the Curiosity rover have shown seasonal changes that scientists haven’t yet been able to explain. No source of oxygen that has been yet investigated could produce the size of changes observed. It appears that some source is releasing oxygen, but only in spring or summer, and then that oxygen is being consumed by some process more quickly than expected. The precise amount of rise varies year to year. Oxygen represents about one-sixth of 1 percent of the Martian atmosphere, but this is well within the capabilities to be accurately measured by the sensitive instrument on Curiosity.
Europan Water – Scientists have for the first time detected water vapor above Jupiter’s icy moon Europa. There is good evidence that a liquid ocean lies beneath the icy surface and some evidence that water is leaking and escaping the moon. Hydrogen and oxygen, presumed to be the result of escaping water breaking down into its constituent elements, had previously been found above the moon, but this is the first time water vapor was found before it broke down. The vapor was found only occasionally during many observations, so the water is likely escaping in episodes, perhaps as geyser activity. The observations were made by the Keck Observatory in Hawaii.
DESI Installed – An instrument known as DESI made its first images after being installed on the 4-meter Mayall Telescope in Arizona. It has 5000 optical fibers that can be positioned by computer in about two seconds, with each feeding a spectrograph. It is designed to take spectra of 5000 different galaxies every 20 minutes. It will start its observational program early in 2020. The goal is to collect data, including redshifts, on 35 million galaxies and 2.4 million quasars. As with any large telescope, seeing more distant objects will see them as they were when the light left them, farther back in time. This observation program will allow scientists to get a picture of how the structure of the Universe changed over time. Analysis of these changes will show what effects dark energy and gravity had over the life of the Universe.
