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.
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