Sky & Telescope - April 2021 - 10

NEWS NOTES

The Decline of the Youngest
Planetary Nebula
THE YOUNGEST PLANETARY NEBULA

ever found is fading away, shedding
light on its star's unique evolution.
Dying low-mass stars emit harsh
radiation that causes previously ejected
gas to fluoresce in colorful displays
known as planetary nebulae. These typically last a few thousand years as the
central star radiates the last of its heat
into space.
But the Stingray Nebula (Hen 3-1357)
has other ideas. It likely appeared sometime in the 1980s, but it wasn't imaged
until 1993 when Matthew Bobrowsky
(then at Orbital Sciences Corporation)
captured it using the Hubble Space
Telescope. It's the only planetary nebula
caught shortly after it brightened.
Now, my colleagues and I - Martín
Guerrero (Institute of Astrophysics of

60,000 K (100,000°F),
Andalusia, Spain) and
and it began emitting
Gerardo Ramos-Larios
intense UV radiation, ion(University of Guadaizing previously ejected gas
lajara, Mexico) - have
and producing the Stingray
found that the Stingray
Nebula. The nebula and
seems destined to vanthe shrunken star have
ish in the next few years:
1996
been fading in tandem
start to finish in only two
ever since. By 2016, the
human generations!
blue-green light emitted by
Observations of the
doubly ionized oxygen in
central star showed it had
the nebula was 900 times
unexpectedly contracted
fainter than in 1990; the
in the early 1980s, dimreddish light emitted by
ming its visible light. This
ionized hydrogen is fading
likely happened because it
more slowly.
underwent a helium flash,
2016
Now that the helium
in which some unburned
flash has ended, Reindl's
S Stingray Nebula
helium suddenly reignited,
team has predicted that
contracting its core and
the star will resume its previous evoheating its surface, as suggested previlutionary path. The fluorescence of the
ously by Nicole Reindl (University of
nebula may one day resume, and the
Potsdam, Germany) and colleagues.
revived nebula will be " born again. "
Over the next decade, the star's
surface heated up by a factor of five, to
„ BRUCE BALICK

BLACK HOLES

Newborn Black Hole Jets Found in Distant Galaxies
ASTRONOMERS HAVE SPOTTED a

dozen quasars - gargantuan black holes
munching on gas at the centers of
galaxies - that appear to have launched
jets within the last couple of decades.
Kristina Nyland (U.S. Naval
Research Laboratory) and collaborators found them by investigating radio
sources detected in an ongoing sky survey by the Very Large Array (VLA) but

missing from the same telescope's older
FIRST survey, which ran from 1993 to
2011. Out of about 2,000 new sources,
167 appeared in known quasars.
The team followed up on 14 of the
brightest sources with additional VLA
observations. The quasars' radio emissions appear to come from young jets
that turned on in the last 10 to 20
years. It remains unclear, though, if

Full-grown plasma jets ejected
by supermassive black holes,
like the one shown in this illustration, can extend thousands of
light-years. Newborn jets would
be much smaller.

the jets are truly newborn, or if they're
slightly older and larger ones that have
only recently bent toward Earth.
If they are newborns, they've
launched recently from pre-existing
quasars. While a decade or two is probably too short for a wholescale change
to the accretion disk feeding the central
black hole, quasars could have reactivated on that time scale, says accretion
expert Sera Markoff (University of
Amsterdam, The Netherlands).
The result, which appeared in the
December 10th Astrophysical Journal,
adds to an accelerating shift in our
understanding of active galactic nuclei
(AGN). Although AGN constantly
flicker at low levels, astronomers have
nevertheless thought of them as relatively stable on human time scales. Yet
numerous studies have revealed large,
rapid changes in quasars' light (e.g.,
S&T: May 2016, p. 14), and observations
suggest most radio jets never make it
into old age. The data paint a picture in
favor of intermittent snacking behavior
for these gargantuan black holes.
„ CAMILLE M. CARLISLE

Read more at https://is.gd/newbornjets.

10

APRIL 2 021 * SK Y & TELESCOPE

STING R AY NEBUL A (2): N ASA / ESA / B. BA LICK (UNIV ERSIT Y OF WASHINGTON) / M. GUERRERO
(INSTIT U TO DE ASTROFÍSICA DE A NDA LUCÍA) / G. R A M OS-L A RIOS (UNIV ERSIDA D DE
GUA DA L A JA R A); BL ACK HOLE JE T: SOPHIA DAG NELLO / NR AO / AUI / NSF

STARS


https://www.is.gd/newbornjets

Sky & Telescope - April 2021

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