White dwarfs have turned out to be more interesting than I had imagined. We know how they form: A star like the Sun exhausts the hydrogen in its core and swells into a red giant, a scenario that is a trope in science fiction, as it posits an Earth of the far-future incinerated by its star. Losing its outer layers near the end of nuclear burning, a red giant ultimately leaves behind an object with much of the mass of the Sun now crammed into a white dwarf that is about the size of the Earth. For years I assumed white dwarfs were dead ends, a terminus for life whose only function seemed to be in binary systems, where they could be the locus, through accretion from the other star, of a stellar explosion in the form of a nova. Lately we've been learning, though, that through analysis of their atmospheres, white dwarfs can yield information about objects that have fallen into them, such as remnants of the original stellar system. Some white dwarfs may have habitable zones lasting several...

Here's a story that's both mind-bending and light-bending. It involves a supernova that, on the one hand, happened 10 billion years ago, and on the other hand, has appeared in our skies not once but three times, with a fourth in the works. In play here is gravitational lensing, in which light from a background galaxy bends around a foreground galactic cluster known as MACS J0138.0-2155. Out of this we get multiple mirror images, and researchers predict another supernova appearance in the year 2037. Three of the appearances of the supernova, labeled AT 2016jka and nicknamed 'Requiem,' are in the image below, a Hubble view from 2016, all three circled for ease of identification. The light of the supernova has been split into different images by the lensing effect. Using archival data, researchers led by Steve Rodney (University of South Carolina) have analyzed differences in brightness and color that reflect different phases of the event as the supernova faded. "This new discovery is...

The brown dwarf WISEA J153429.75-104303.3 -- happily nicknamed ‘The Accident’ -- is peculiar enough that it may point to a rare population of extremely old brown dwarfs. Dan Caselden, a citizen scientist who built an online program to filter data from the NEOWISE spacecraft, is able to highlight brown dwarfs moving through the NEOWISE field with his software, and while looking at one, he caught a glimpse of another. Call that a lucky catch, because the object didn’t match his program’s profile of a conventional brown dwarf. We’ve found about 2,000 brown dwarfs thus far, many using data from WISE -- Wide Field Infrared Survey Explorer -- which was launched in 2009, placed into hibernation in 2011 after its primary mission ended, and then reactivated in 2013 as NEOWISE, a repurposed spacecraft given the new goal of tracking near-Earth objects. WISE 1534?1043 -- the shortened name of the object, used by the authors of a new paper on it -- stands out from all previously known brown...

Anomalies in our models are productive. Often they can be explained by errors in analysis or sometimes systematic issues with equipment. In any case, they force us to examine assumptions and suggest hypotheses to explain them, as in the case of the unusual acceleration of stars that has turned up in two areas. Greg Matloff has written about one of them in these pages, the so-called Parenago’s Discontinuity that flags an unusual fact about stellar motion: Cool stars, including the Sun, revolve around galactic center faster than hotter ones. This shift in star velocities occurs around (B-V) = 0.62, which corresponds to late F- or early G-class stars and extends down to M-dwarfs. In other words, stars with (B-V) greater than 0.61 revolve faster. The (B-V) statement refers to a color index that is used to quantify the colors of stars using two filters. One, the blue (B) filter, lets only a narrow range of wavelengths centered on blue colors through, while the (V) visual filter only...

Infrared imagery drawn from Spitzer Space Telescope data, coupled with the massive Gaia Early third Data Release (EDR3), have just given us a new insight into our galaxy's spiral structure. The Milky Way's Sagittarius Arm is now shown to have a 'spur' of star-forming gas and young stars emerging at a steep angle and stretching some 3,000 light years. The authors of the paper on this work refer to it as "unprecedented in the context of the generally adopted model of the Milky Way spiral structure." The spur was a tricky catch, because from our position within the galactic disk we can only see the full spiral structure in galaxies other than our own. But the authors point out that in these galaxies, spiral arms often show smaller-scale structures including 'spurs,' which are luminous groupings of stars, and 'feathers,' which are dust features. We also find branching in the main arms. Now we've identified a spur structure in the Milky Way. Image: Artist's concept of the Milky Way. The...