Sky & Telescope - November 2020 - 10

NEWS NOTES

SUPERNOVA

Astronomers Find SN 1987A's Neutron Star
SUPERNOVA 1987A WAS one of the
most-observed supernovae in history
after it exploded in the Large Magellanic Cloud just 168,000 light-years
away. Telescopes around the globe and
in space captured the blast wave, which
illuminated three overlapping rings of
material that had likely blown off in the
star's ﬁnal years.
But in the 33 years since, a puzzle

has plagued astronomers. Neutrinos
received at Earth right after the supernova indicated that the collapsed object
ought to be a neutron star. But astronomers couldn't ﬁnd it. Dust obscures the
center of the blast, and some even wondered if the core had collapsed further
into a black hole.
Closer study showed the gaseous
remains of the star's outer layers to be

GALAXY

Astronomical Society. They found that
over a billion-year period, roughly 80%
of bulge stars would experience close
encounters, passing within 1,000 astronomical units (a.u.) of another star.
Half of bulge stars would have such an
encounter not just once but more than
35 times over the course of a billion
years. About a third of bulge stars could
have company swing by within 100 a.u.,
and less than 1 in 5,000 stars entertain
a visitor within 10 a.u.
The new study takes into account
both the crowded environs at the galactic center and the unusual paths some
stars there take.

Close Encounters in the
Milky Way's Bulge
NEW RESEARCH SHOWS that stellar ﬂybys are common in our galaxy's
crowded center. Visits from interlopers
could affect how young worlds grow in
the Milky Way's bulge.
Moiya McTier (Columbia University) and colleagues conducted simulations of interactions between bulge
stars over time, reporting the results in
the June Monthly Notices of the Royal
q An artist's impression of the Milky Way's disk
and crowded central bulge.

slightly off-kilter, hinting that whatever compact object had formed in the
blast had received a kick away from the
explosion's center.
Last year, observations from the Atacama Large Millimeter/submillimeter
Array (ALMA) hinted that the search
might be at an end. Phil Cigan (Cardiff
University, UK) and colleagues reported
in the November 20, 2019 Astrophysical Journal that they had zeroed in on a
blob of dust heated to 33K (−400°F).
Now, in a separate study that will
appear in the August 1st Astrophysical
Journal, Dany Page (National Autonomous University of Mexico) and colleagues demonstrate that - out of a
smorgasbord of possible alternatives
- the most plausible scenario is one
in which an enshrouded neutron star
warms the dust. What's more, they
showed that the dust blob overlaps the
predicted location of the kicked-out
stellar core.
If all pans out, NS 1987A will be the
youngest neutron star ever observed.
■ MONICA YOUNG

"Some bulge stars move on elliptical
orbits, but some of them also move on
box- or X-shaped orbits," McTier says.
"Many of them move on rosette orbits
that look like what you might draw with
a spirograph."
While McTier's work didn't directly
measure how strongly stellar visitors
affect growing planets, the research
provides a foundation for future studies. Close encounters could destabilize
planetary orbits, strip planets from
their host stars, or even interrupt formation before it can begin. But according to Maxwell Cai (Leiden University,
The Netherlands), who was not involved
in the study, intruder stars could also
help growing planets. A stellar visitor's
tidal gravitational forces could cause
small gravitational changes in the disk
of dust and gas circling a newborn star,
helping material clump together to
make planets.
■ NOLA TAYLOR REDD

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

NOVEMBER 2 02 0 * SK Y & TELESCOPE

SUPER NOVA 1987A: A LM A / ESO / N AOJ / NR AO / P. CIG A N / R. INDEBE TOU W /
NR AO / AUI / NSF / B. SA X TON / N ASA / ESA; MILK Y WAY BULG E: ESO / N ASA / JPLCA LTECH / M. KOR NMESSER / R. HURT

A warm, dusty
"blob" (inset)
offset from the
center of Supernova 1987A is
the likely location
of the remnant
neutron star.

https://is.gd/milkywayencounters https://is.gd/milkywayencounters

Sky & Telescope - November 2020

Table of Contents for the Digital Edition of Sky & Telescope - November 2020