Sky & Telescope - March 2025 - 10

NEWS NOTES
BLACK HOLES
Black Hole Eats One Star;
Remains Pummel a Second
IN 2019 A SUPERMASSIVE black hole
began to eat a star. Although the resulting
flare of light occurred some 210
million light-years away, it was bright
enough that the Zwicky Transient
Facility in California caught the event,
dubbing it AT2019qiz. But this wasn't
an ordinary stellar feast.
Although the black hole had already
spaghettified the star in 2019, it took
time for that noodle of gas to slip into
the maw - it wasn't until 2023 that
astronomers turned the Chandra X-ray
Observatory to witness the high-energy
emissions from the long-term meal.
That's when they found an unexpected
spike in X-rays.
Follow-up observations with other
space observatories found nine X-ray
bursts, recurring roughly every two
days. Matt Nicholl (Queen's University
Belfast, UK) and colleagues published
the results in the October 24th Nature.
STARS
Astronomers Map Dandelion Supernova
ASTRONOMERS HAVE mapped the 3D
structure of a famous dandelion-shaped
supernova remnant. The map shows
the explosion's debris is still speeding
outward at more than 1,000 kilometers
per second (2 million mph), almost a
millennium after the star at the center
of it all detonated.
In AD 1181, Chinese and Japanese
astronomers recorded the arrival of a
" guest star " in the constellation Cassiopeia.
But it wasn't until 2013 that
amateur astronomer
Dana Patchick found
the explosion's remnant
in archived images
from NASA's Widefield
Infrared Survey
Explorer. Now we know
that the object, named
Pa 30, is the remnant
of a Type Iax supernova,
triggered by the explo10
MARCH 2025 * SKY & TELESCOPE
sion of a white dwarf star. (The " x "
denotes the fact that some of the star
survived the ordeal.)
After a group of astronomers discovered
filaments within Pa 30 in 2023
(S&T: May 2023, p. 10), a team led by
Tim Cunningham (Center for Astrophysics,
Harvard & Smithsonian) and
Ilaria Caiazzo (Institute of Science and
Technology Austria) mapped the structures
in 3D using the Keck Cosmic Web
Imager at the W. M. Keck Observatory
in Hawai'i.
Within the image of
Pa 30, every individual
pixel carries its own
spectrum, from which
the team could calculate
the motions of the gas
at that spot. The analytAn
artist's concept shows
the spindles of the supernova
remnant Pa 30.
other towards the black hole. "
If a single star fell toward a black
hole, the strong gravitational field
would shred the star to pieces. But if a
stellar pair falls in, three-body gravitational
interactions could enable the
black hole to capture one of the stars in
a stable orbit
" These captures are rare, " Nicholl
pIn this artist's illustration, material from a
shredded star that envelopes a supermassive
black hole (at right) also interacts with another
orbiting star (at left).
Such quasi-periodic emissions have
been observed elsewhere, but astronomers
don't know why they happen.
Nicholl's team thinks the bursts come
from something crossing the gaseous
disk that now surrounds the black hole:
another star.
" We don't expect many stars orbiting
this close to a black hole, " admits Nicholl.
" We think that most of the stars
are sitting much farther away, but every
now and again they can deflect each
notes. But once bound to the black hole,
the star's orbit decays only slowly. " At
any given time, a black hole at the center
of an average galaxy will have about
one star in a tight orbit like this. " Then,
if another star by chance falls into the
black hole, its material spreads out into
a disk and begins to interact with the
captured star.
" However, this is just our simple
picture, " Nicholl cautions. " Now that
we think we know what to look for,
we can observe what fraction of tidal
disruption events have quasi-periodic
oscillations, and this will let us actually
measure how common these close orbiting
stars really are, to test this theory. "
¢MONICA YOUNG
sis is published in the November 1st
Astrophysical Journal Letters.
" We find the material in the filaments
is expanding ballistically; this
means that the material has not been
slowed down nor sped up since the
explosion, " says Cunningham. " From
the measured velocities, looking back in
time, you can pinpoint the explosion to
almost exactly the year 1181. "
The analysis reveals an unexpected
asymmetry to the explosion that hints
at an unusal origin. The data also reveal
a large cavity inside the spindles. A
reverse shock wave, traveling more slowly
than the initial blast, may have cleared
out the central space.
Georgios Dimitriadis (Lancaster
University, UK), who was not involved
in the research, says the detailed mapping
of the most extreme supernovae,
such as Pa 30, might shed light on more
typical Type Ia supernovae.
¢COLIN STUART
To see a 3D view of the supernova, visit
https://is.gd/DandelionSN.
TIDAL DISRUPTION EVENT: NASA / CXC / SAO AND SOHEB MANDHAI / THE ASTRO
PHOENIX; DANDELION SUPERNOVA: W. M. KECK OBSERVATORY / ADAM MAKARENKO
https://www.is.gd/DandelionSN
Sky & Telescope - March 2025

Table of Contents for the Digital Edition of Sky & Telescope - March 2025
