My first Magazine Sky & Telescope - 01.2019 | Page 15

SUPERNOVAE What Makes Supernovae Superluminous? A TYPICAL EXPLODING STAR gener- ates up to a billion Suns’ worth of light at its peak. But so-called superlumi- nous supernovae are in a rare class of their own, shining hundreds of times brighter than their “ordinary” cousins. Reporting September 10th in Nature Astronomy, Ragnhild Lunnan (Stockholm University) and colleagues describe a detailed analysis of one of the most superluminous super- novae known: iPTF16eh, discovered by the Palomar Transient Factory in December 2015. Most importantly, this supernova shows a signature in its spectrum that astronomers haven’t seen in its ilk before. As this star went supernova, the explosion’s light refl ected off a thick SOLAR SYSTEM New Object Found in Far Outer Solar System THERE’S A NEWLY FOUND body in the extreme backwaters of the solar system. Designated 2015 TG 387 and nicknamed “The Goblin” by its discoverers, this object resides in the inner Oort Cloud, a vast region beyond the Kuiper Belt that’s thought to be a comet reservoir and until now harbored only two other known bodies: the dwarf planet Sedna and the less well-known 2012 VP 113 . This far-fl ung body keeps its distance from the Sun, never coming closer than about 65 astronomical units (a.u.), or just under twice Pluto’s closest approach. However, that’s downright cozy compared to how far out it goes. A highly elongated orbit takes 2015 TG 387 out to a whopping 2,300 a.u., much farther away than its two comrades in the inner Oort Cloud. The International Astronomical Union’s Minor Planet Center announced the discovery on October 2nd. A team led by Scott Sheppard (Carn- egie Institution for Science) discovered 2015 TG 387 in images acquired in mid- sphere of gas surrounding the star, producing an emission line that the astronomers tracked in the year follow- ing the eruption. The gaseous cocoon is expanding so rapidly — 3,300 kilome- ters per second (7.4 million mph) — that it must be the result of an explo- sive ejection, rather than the kind of steady wind that precedes the death of other massive stars. Lunnan and col- leagues argue that this ejection, which occurred roughly 30 years before the star went boom, points to a particular cause of death: a pulsational pair-insta- bility supernova. As stars more massive than about 100 Suns run out of fuel to burn in their cores, things start to go haywire. Rather than fusing elements, the stel- October 2015 at the 8.2-meter Subaru Telescope in Hawai‘i. At the time, the body was about 80 a.u. from the Sun. Since then, the observers have used other telescopes to track the object and refi ne its orbit. They estimate that the tiny world is 300 km wide, roughly the width of Saturn’s moon Hyperion. Extrapolating from the three objects now known to lie in the inner Oort Cloud, the team estimates that this lar core produces pairs of electrons and their antimatter partners, positrons. But pair production takes energy away from the star’s support system, which causes the core to implode, inducing nuclear fusion. In really massive stars (more than about 130 solar masses), that’s enough to cause “rapid unsched- uled disassembly” — in other words, the star obliterates itself. But in stars between roughly 100 and 130 solar masses, explosive results aren’t so immediate. Instead, the star pulsates, alternately imploding and burning, before its core catastrophi- cally collapses anywhere from hours to thousands of years later. The pulsations can eject a huge amount of mass, and the researchers argue that an ejection of up to 10 solar masses from a 115 solar- mass star matches the observations. ■ MONICA YOUNG largely unexplored region of space harbors roughly 2 million bodies wider than 40 km. That puts the projected mass of this ensemble on par with that of the Kuiper Belt. Aligned orbits of bodies in and near the inner Oort Cloud hint at a planet out there. While 2015 TG 387 doesn’t make or break that case, its orbit seems consistent with a planet’s presence. ■ CHRISTOPHER CROCKETT 2012 VP 113 “The Goblin” 2015 TG 387 Kuiper Belt Giant planets Sedna p This diagram shows the orbits of the newly discovered body, 2015 TG 387 , and its fellow inner Oort Cloud objects, 2012 VP 113 and Sedna, compared with the rest of the solar system. sk yandtele scope.com • JA N UA RY 2 019 13