Sky and Telescope - February 2018 - 12

NEWS NOTES

A SUPER-LONG SUPERNOVA has

astronomers reaching for new explanations of stellar explosions.
In a typical core-collapse supernova,
the inner collapse occurs so quickly
that infalling layers of stellar material
rebound off the core, driving a shock
wave that sends much of the star ﬂying
outward. The expanding outer shells of
ionized hydrogen glow for roughly 100
days before beginning to fade.
Iair Arcavi (Las Cumbres Observatory) and colleagues thought they were
seeing a typical core-collapse supernova
when the Intermediate Palomar Transient Factory (iPTF) caught the 18thmagnitude explosion dubbed iPTF14hls.
But the supernova kept on going, not
for 100 days but for almost two years, as
reported in the November 9th Nature.
What's more, it exhibited at least ﬁve

SOLAR SYSTEM

An artist's concept shows Haumea and
its dark, dense ring

Dwarf Planet Haumea
Has a Ring
THE DWARF PLANET 136108 Haumea
brieﬂy slipped in front of an 18th-magnitude star in January 2017. Observers
at a network of 10 observatories across
central Europe recorded the cover-up,
discovering something unexpected: A
ring encircles this little world.
Haumea, which orbits in the realm
beyond Neptune, was already a wellknown oddball. It's among the largest
objects in the Kuiper Belt, has a highly

FE B RUA RY 2 018 * SK Y & TELESCOPE

3.5

iPTF14hls
behind the Sun

3.0
2.5
2.0

iPTF14hls

1.5
1.0
Normal supernova

0.5
0
0

100

200

300

400

500

600

Days since discovery
p Instead of fading away, the unusually longlasting supernova iPTF14hls brightened again
four more times over two years.

distinct peaks in luminosity, including the initial burst. A look back at the
Palomar Observatory Sky Survey found
that the star might have had another
outburst back in 1954. There are other
oddities too: The glowing gas maintains
a roughly constant temperature, which
implies that its radius stays the same.
Yet it also maintains its speed - unex-

elongated shape, spins rapidly, and possesses two moons.
Now, as José Luis Ortiz (Institute
of Astrophysics of Andalucía, Spain)
and colleagues detail in October 12th's
Nature, several observing teams have
detected a ring via secondary dips in the
star's light roughly 2 minutes before and
after the main occultation. The ring is
dark, narrow (70 km wide), and dense
enough to block half the star's light.
The ring appears to lie in Haumea's
equatorial plane, which is shared by the
larger, outer moon Hi'iaka. The ring's
orbit has a radius of about 2,287 km
(1,421 miles) - that's too close to Haumea, well inside a gravitational threshold called the Roche limit, to be able to
collect into a single body.
Haumea isn't the only outer-solarsystem body with a ring; occultations
by the Centaur objects 10199 Chariklo
(S&T: July 2014, p. 14) and 2060 Chiron, both in 2013, also turned up rings.
So while the origin of Haumea's ring
isn't yet clear, the feature might be common to the trans-Neptunian region.
■ J. KELLY BEATTY

pected behavior for shells of ionized gas
that ought to expand, thin, and cool.
So Arcavi and colleagues rule out
standard models of stellar explosions
and turn instead to pulsational pairinstability supernovae. If a star is massive
enough (but not too massive), its core
can convert photons into electrons and
their antimatter partners, positrons.
The resulting instability sets off blasts
that carry away tens of solar masses.
A star with an initial mass just above
100 Suns could have caused iPTF14hls's
multiple blasts. Yet this scenario still
can't explain all of the observations.
"As of now," writes Stan Woosley
(University of California, Santa Cruz),
author of an accompanying perspective piece, "no detailed model has been
published that can explain the observed
emission and constant temperature of
iPTF14hls, let alone the possible eruption 60 years before the supernova."
■ MONICA YOUNG

IN BRIEF
Comet Heinze to Fly
by in January
Discovered on October 2, 2017, Comet
Heinze (C/2017 T1) will fly 33 million km from Earth on January 4th
before coming within 87 million km of
the Sun on February 21st. Aren Heinze
(University of Hawai'i) found the object
using the Asteroid Terrestrial-impact
Last Alert System (ATLAS) project,
which employs two telescopes positioned 160 km apart. The two "eyes"
enable distance determination using
parallax, which helps calculate a new
object's orbit. Heinze confirmed the
comet's orbit using additional ATLAS
observations. Despite its intrinsic faintness, both JPL Horizons and Seichi
Yoshida predict the comet will peak at
magnitude 8.8, putting it within range
of small telescopes. For observing
guidance and detailed sky charts go to
https://is.gd/CometHeinze.
■ BOB KING

SUPER NOVA: LE A H TISCIONE, SOURCE: L AS CU MBRES OBSERVATORY / S. WILK INSON; H AU ME A: IA A- CSIC / UHU

The Star That Wouldn't Die

Brightness (in billions of Suns)

STELLAR

https://www.is.gd/CometHeinze

Sky and Telescope - February 2018

Table of Contents for the Digital Edition of Sky and Telescope - February 2018