Today’s news includes updates on our understanding of exploding white dwarf stars, observations of a planetary nebula just starting to form, and news about Voyager 2’s ground-based communications systems and OSIRIS-REx continued observations of Bennu.
In a new paper in Astronomy & Astrophysics, a team of Max Planck Institute for Astrophysics researchers led by Maria Bergemann look at how the abundance manganese has changed over the course of history, with generations of supernova adding it into the universe. In their study of chemical abundances, they find that the ratio of manganese to iron stays with time. Since these two elements are created in very different ways, this means that on average, the processes that produce 1 happen as often as the methods that produce the other, like two different factories working on similar production schedules. In looking at all the different ways that manganese can be formed, they realized the only way they could explain their observations is ¾ of all type 1a supernovae – explosions of white dwarf stars – that have occurred in our galaxy of its history were non-standard supernovae.
When we normally talk about Type 1a supernova, we assume a system where a moon-sized white dwarf if orbiting a giant star and slurping off its outer atmosphere with gravity. When the white dwarf star has consumed enough of its neighbor to top 1.4 solar masses, it explodes. This is because the white dwarf can’t support that much matter. But, as we’ve recently pointed out, white dwarfs can find other ways to go boom. They can merge into their companion star, triggering a double detonation as both stars destabilize. They can merge with another white dwarf. Well, the can merge pretty much with whatever they please, and in each of these myriad scenarios they can go supernova and they will often detonate their companion’s core as they go. This new research finds the chemistry of our galaxy is consistent with these double detonations being the donate death explosion of white dwarfs. If this is the case, then our measurements of the expansion of the universe are based solidly on a false assumption about the nature of type 1a supernovae.
Research like this requires replication, and a team at CalTech has already started to see similar results in looking at stars in dwarf galaxies. The next Gaia mission data release should help them identify white dwarf binary systems, and directly determine how common these small dense systems may be. For now, this is one more observational line of evidence indicating we don’t understand our universe as well as we thought we did, and dark energy may someday be the thing our generation of astronomers is laughed at for theorizing… at least one can hope.
From stars dying as supernovae, we now turn to stars dying as planetary nebulae. A team of astronomers using the Atacama Large Millimeter Array has found an aged star not too different from the Sun that is just beginning to exhale its atmosphere. In this image, we can clearly see in blue, high-velocity jets blowing from the star’s poles and interacting with dusty clouds that are shown in orange. This is a system just starting to form a planetary nebula, and in a new paper in the Astrophysical Journal led by Daniel Tafoya, they postulate that the high-speed jets may have only turned on in the past 60 years. This object was part of a large survey being conducted to try and catch planetary nebulae in all stages of formation, and if we’re lucky, ALMA will allow more of these baby systems to be found.
From star deaths we now turn to spacecraft with two quick updates. The first is a bit frustrating. NASA is updating the 70-meter radio antenna in Canberra, Australia that is used to communicate with the Voyager 2 and other missions. While other, closer missions can also chat with smaller dishes, only this great disk is capable of sending the powerful signals needed to send new commands to Voyager 2. It’s estimated that the upgrades will take about 11 months to accomplish, and during that time we’ll be able to receive data from Voyager 2 using other dishes, but while we can listen, we won’t be able to talk back. This shouldn’t have a major impact on this distant mission, but if something goes sideways and it cries out for help, we’re going to not be able to respond.
In more cheerful news, the OSIRIS-REs mission did a 250m flyover of the Nightingale site on Bennu. This is the primary choice of sample site, and this flyover not only got them better data, but it also allowed the mission team to practice the slightly crazy maneuvers that are needed to pass close to the asteroid’s surface. While we haven’t seen these new images, we can tell you they are full of rocks. All joking aside, OSIRIS-REx is designed to collect objects 2cm in size and smaller, and these new images will have sufficient resolution for the mission team to figure out if this kind of debris is present in the sample site. This object is turning out to be rocks on boulders surrounded by rocks with granular material of every size scattered in between.